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101.
M.D. Looper J.B. Blake R.A. Mewaldt 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1998,21(12):1679-1682
The PET instrument aboard the SAMPEX satellite has provided us with long-term intra-calibrated observations of geomagnetically trapped protons and deuterons in the inner zone, suitable for use in constraining the low-altitude portions of radiation belt models being developed as successors to AP-8. These observations have been summarized elsewhere (Looper et al., 1996). Here we report a detection of geomagnetically-trapped tritium at energies from 14 to 35 MeV/nuc below L = 1.2, at about 1/8 the flux of deuterium previously reported at that location and at similar energy per nucleon. We also demonstrate the utility of the SAMPEX/PET observations for measuring the east-west anisotropy in the trapped particle flux at low altitudes, which is due to displacement of particle gyrocenters from the position of observation in a region of strong flux gradients. This anisotropy is implicitly ignored in omnidirectional radiation-flux models, but it can be important to mission planners considering how to distribute shielding over the surface of oriented spacecraft in low Earth orbit. 相似文献
102.
Clinorotation reduces number, but not size, of cartilaginous nodules formed in micromass cultures of mouse limbbud cells. 总被引:1,自引:0,他引:1
P J Duke D Montufar-Solis T Hamazaki A Sato 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1998,21(8-9):1065-1072
In previous studies we used a ground based model to investigate the cellular responses to microgravity by exposing micromass cultures of embryonic limb cells to simulated weightlessness on a clinostat. Cultures set up in T-flasks and rotated at 30 rpm showed that clinostatted cultures had less chondrocyte differentiation than stationary or rotation controls, as assessed by number of nodules/culture stained with cartilage specific Alcian blue. In the current study, nodule size and shape of these nodules was assessed by interactive measurement of area, perimeter, circularity, and equivalent diameters, using the Optimas imaging software. Results show no significant difference in any of the measurements, indicating that clinorotation has no effect on expansion of the nodules either by differentiation of cells within the nodule, or by recruitment of cells into the nodule. The reduction in number of nodules without an alteration in size and shape indicates that the effect of simulated microgravity is to reduce the cell interactions required for the initial condensation of cells into a nodule, probably by interference with cell adhesion molecules. 相似文献
103.
E J Ainsworth S M Afzal D A Crouse W R Hanson R J Fry 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1989,9(10):299-313
Early and late murine tissue responses to single or fractionated low doses of heavy charged particles, fission-spectrum neutrons or gamma rays are considered. Damage to the hematopoietic system is emphasized, but results on acute lethality, host response to challenge with transplanted leukemia cells and life-shortening are presented. Low dose rates per fraction were used in some neutron experiments. Split-dose lethality studies (LD 50/30) with fission neutrons indicated greater accumulation of injury during a 9 fraction course (over 17 days) than was the case for gamma-radiation. When total doses of 96 or 247 cGy of neutrons or gamma rays were given as a single dose or in 9 fractions, a significant sparing effect on femur CFU-S depression was observed for both radiation qualities during the first 11 days, but there was not an earlier return to normal with dose fractionation. During the 9 fraction sequence, a significant sparing effect of low dose rate on CFU-S depression was observed in both neutron and gamma-irradiated mice. CFU-S content at the end of the fractionation sequence did not correlate with measured LD 50/30. Sustained depression of femur and spleen CFU-S and a significant thrombocytopenia were observed when a total neutron dose of 240 cGy was given in 72 fractions over 24 weeks at low dose rates. The temporal aspects of CFU-S repopulation were different after a single versus fractionated neutron doses. The sustained reduction in the size of the CFU-S population was accompanied by an increase in the fraction in DNA synthesis. The proliferation characteristics and effects of age were different for radial CFU-S population closely associated with bone, compared with the axial population that can be readily aspirated from the femur. In aged irradiated animals, the CFU-S proliferation/redistribution response to typhoid vaccine showed both an age and radiation effect. After high single doses of neutrons or gamma rays, a significant age- and radiation-related deficiency in host defense mechanisms was detected by a shorter mean survival time following challenge with transplantable leukemia cells. Comparison of dose-response curves for life shortening after irradiation with fission-spectrum neutrons or high energy silicon particles indicated high initial slopes for both radiation qualities at low doses, but for higher doses of silicon, the effect per Gy decreased to a value similar to that for gamma rays. The two component life-shortening curve for silicon particles has implications for the potential efficacy of radioprotectants. Recent studies on protection against early and late effects by aminothiols, prostaglandins, and other compounds are discussed. 相似文献
104.
A.I. Efimov V.K. Rudash L.N. Samoznaev M.K. Bird I.V. Chashei D. Plettemeier 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
Frequency fluctuations of the Galileo S-band radio signal were recorded nearly continuously during the spacecraft’s solar conjunction from December 1996 to February 1997. A strong propagating disturbance, most probably associated with a coronal mass ejection (CME), was detected on 7 February when the radio ray path proximate point was on the west solar limb at about 54 solar radii from the Sun. The CME passage through the line of sight is characterized by a significant increase in the fluctuation intensity of the recorded frequency and by an increase in the plasma speed from about 234 km s−1 up to about 755 km s−1. These velocity estimates are obtained from a correlation analysis of frequency fluctuations recorded simultaneously at two widely-separated ground stations. The density turbulence power spectrum is found to steepen behind the CME front. The Galileo radio-sounding data are compared with SOHO/LASCO observations of the CME in the corona and with WIND spacecraft data near the Earth’s orbit. 相似文献
105.
Singh A. Ghose D. Sarkar A.K. 《IEEE transactions on aerospace and electronic systems》2009,45(3):899-918
This paper presents an optimization of the performance of a recently proposed virtual sliding target (VST) guidance scheme in terms of maximization of its launch envelope for three-dimensional (3-D) engagements. The objective is to obtain the launch envelope of the missile using the VST guidance scheme for different lateral launch angles with respect to the line of sight (LOS) and demonstrate its superiority over kinematics-based guidance laws like proportional navigation (PN). The VST scheme uses PN as its basic guidance scheme and exploits the relation between the atmospheric properties, missile aerodynamic characteristics, and the optimal trajectory of the missile. The missile trajectory is shaped by controlling the instantaneous position and the speed of a virtual target which the missile pursues during the midcourse phase. In the proposed method it is shown that an appropriate value of initial position for the virtual target in 3-D, combined with optimized virtual target parameters, can significantly improve the launch envelope performance. The paper presents the formulation of the optimization problem, obtains the approximate models used to make the optimization problem more tractable, and finally presents the optimized performance of the missile in terms of launch envelope and shows significant improvement over kinematic-based guidance laws. The paper also proposes modification to the basic VST scheme. Some simulations using the full-fledged six degrees-of-freedom (6-DOF) models are also presented to validate the models and technique used. 相似文献
106.
Candamo J. Kasturi R. Goldgof D. Sarkar S. 《IEEE transactions on aerospace and electronic systems》2009,45(3):937-949
A novel thin line detection algorithm for use in low-altitude aerial vehicles is presented. This algorithm is able to detect thin obstacles such as cables, power lines, and wires. The system is intended to be used during urban search and rescue operations, capable of dealing with low-quality images, robust to image clutter, bad weather, and sensor artifacts. The detection process uses motion estimation at the pixel level, combined with edge detection, followed by a windowed Hough transform. The evidence of lines is tracked over time in the resulting parameter spaces using a dynamic line movement model. The algorithm's receiver operating characteristic curve (ROC) is shown, based on a multi-site dataset with 86 videos with 10160 wires spanning in 5576 frames. 相似文献
107.
The first studies for the mobile mapping and creation of a vehicle for this kind of research was carried out by Canadian Researchers in the 1980s. Since then, these vehicles have been widely employed in several applications (road cadastre maps, terrestrial photogrammihetry, road sign recognition, etc.) for both commercial and research purposes throughout the world. Many GNSSIINS vehicles which can be equipped in different ways with one or more GPS, inertial sensors, and one or several cameras, have been realized. A characteristic shared by most of these devices concerns the high costs of the sensors, of the realization and of the maintenance. For this reason, a GNSSIINS system, that is suitable for any vehicle, made up of low cost devices (two GPS receivers, an INS, and a camera rigidly placed on a metallic bar), has been designed and built by our research group. Two tests run at different velocities have been carried out to evaluate the reliability of the system. After a presentation of the system, the differences that were witnessed during the application of these calibration methods are explained herein. 相似文献
108.
Batzel Todd D. Swanson David C. 《IEEE transactions on aerospace and electronic systems》2009,45(2):473-482
In this paper, prognostic tools are developed to detect the onset of electrical failures in an aircraft power generator, and to predict the generator's remaining useful life (RUL). Focus is on the rotor circuit since failure mode, effects, and criticality analysis (FMECA) studies indicate that it is a high priority candidate for condition monitoring. A signature feature is developed and tested by seeded fault experiments to verify that the initial stages of rotor faults are observable under diverse generator load conditions. A tracking filter is used to assess the damage state and predict generator RUL. This information helps to avoid unexpected failures while reducing the overall life-cycle cost of the system. 相似文献
109.
110.
Lehman D. Clark K. Cook B. Gavit S. Kayali S. McKinney J. Milkovich D. Reh K. Taylor R. Casani J. Griebel T. 《Aerospace and Electronic Systems Magazine, IEEE》2009,24(3):12-21
Congress authorized NASA's Prometheus Project in February 2003, with the first Prometheus mission slated to explore the icy moons of Jupiter. The project had two major objectives: 1) to develop a nuclear reactor that would provide unprecedented levels of power and show that it could be processed safely and operated reliably in space for long-duration, deep-space exploration; and 2) to explore the three icy moons of Jupiter - Callisto, Ganymede, and Europa - and return science data that would meet the scientific goals as set forth in the Decadal Survey Report of the National Academy of Sciences. Early in project planning, it was determined that the development of the Prometheus nuclear-powered spaceship would be complex and require the intellectual knowledge residing at numerous organizations across the country. In addition, because of the complex nature of the project and the multiple partners, approaches beyond those successfully used to manage a typical JPL project would be needed. This describes the key experiences in managing Prometheus, which should prove useful for future projects of similar scope and magnitude. 相似文献