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661.
W Trettnak C Kolle F Reininger C Dolezal P O'Leary R A Binot 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1998,22(10):1465-1474
Optical oxygen sensors are mainly based on the principle of luminescence quenching. In contrast to arready existing intensity-based systems, the measurement of the luminescence lifetime provides certain advantages, such as insensitivity to photobleaching or leaching of the dye, or changes in the intensity of excitation light. This facilitates the use of simple optical systems or optical fibres. A new family of oxygen-sensitive dyes, the porphyrin-ketones, has been introduced, which exhibits favorable spectral properties and decay times in the order of tens and hundreds of microseconds. This allows the use of simple optoelectronic circuitry and low-cost processing electronics. An optical oxygen sensor module has been developed with the dimensions of only 120 x 60 x 30 mm. The prototype is based on the measurement of the decay time of the luminophore by measuring the phase shift between the square-wave excitation and the detected square-wave of the emission coming from the sensor. The instrument is based on semiconductor devices (light-emitting diodes, photodiodes) and may be used for the detection of oxygen in gaseous or liquid samples. The measurement range of the device is from 0 to 200 hPa oxygen partial pressure with a resolution of < 1 hPa over the whole measurement range. The overall measurement accuracy of < +/- 1 hPa has been obtained for periods of 24 h of continuous measurement in a thermostatted environment. The sensor response times t90 are typically < 1 s for gases and 0.5 to 5 min for liquid samples. 相似文献
662.
In this paper, we perform numerical simulation and experimental determination of the limiting resistance of the spacecraft design elements used when developing anti-meteorite protection of spacecraft as well as protection against space debris. One possible way to increase the efficiency of protective shields and satisfy the requirements of the mass characteristics of the latter is the use of mesh barriers. 相似文献
663.
The maximum likelihood estimators of the parameters of the genalized chi-square distribution are derived and approximated. These estimators are compared with those based on the method of moments. 相似文献
664.
Bergland G.D. Hunnicutt C.F. 《IEEE transactions on aerospace and electronic systems》1972,(2):161-167
The application of a highly parallel computer known as PEPE (Parallel Element Processing Ensemble) to radar data processing is described. The PEPE computer consists of a large number of identical processing elements which operate in parallel and are controlled by a common control unit. Each of the processing elements is assigned to a particular radar target such that many targets can be tracked in parallel. PEPE is designed to augment a conventional computer rather than to stand alone. The total data processing load associated with a radar tracking system is distributed between PEPE and the sequential machine in a manner than maximizes the overall system efficiency and desensitizes the system performance to fluctuations in traffic levels. The use of PEPE provides very high data processing throughput potential to a radar data processing system. 相似文献
665.
Bieber John W. Eroshenko Eugenia Evenson Paul Flückiger Erwin O. Kallenbach Reinald 《Space Science Reviews》2000,93(1-2):1-9
Cosmic rays provide a diagnostic tool to analyze processes in interplanetary space and at the Sun. Cosmic rays also directly
affect the terrestrial environment and serve as indicators of solar variability and non anthropogenic climatic changes on
Earth at present and in the distant past.
After the invention of the neutron monitor by John A. Simpson in 1948, an international network of cosmic ray detectors developed
in a cooperative effort to examine temporal and spatial variations in our space environment. The resulting datasets represent
the longest continuous, high time resolution series of particle radiation measurement in space science. At present, the neutron
monitor network is complemented by spacecraft instrumentation to study solar-terrestrial correlated phenomena.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
666.
Where's Downtown?: Behavioral Methods for Determining Referents of Vague Spatial Queries 总被引:1,自引:0,他引:1
Daniel R. Montello Michael F. Goodchild Jonathon Gottsegen Peter Fohl 《Spatial Cognition & Computation》2013,13(2-3):185-204
Humans think and talk about regions and spatial relations imprecisely, in terms of vague concepts that are fuzzy or probabilistic (e.g., downtown, near). The functionality of geographic information systems will be increased if they can interpret vague queries. We discuss traditional and newer approaches to defining and modeling spatial queries. Most of the research on vague concepts in information systems has focussed on mathematical and computational implementation. To complement this, we discuss behavioral-science methods for determining the referents of vague spatial terms, particularly vague regions. We present a study of the empirical determination of downtown Santa Barbara. We conclude with a discussion of prospects and problems for integrating vague concepts into geographic information systems. 相似文献
667.
The invention of the neutron monitor pile for the study of cosmic-ray intensity-time and energy changes began with the discovery
in 1948 that the nucleonic component cascade in the atmosphere had a huge geomagnetic latitude dependence. For example, between
0° and 60° this dependence was a ∼ 200–400% effect – depending on altitude – thus opening the opportunity to measure the intensity
changes in the arriving cosmic-ray nuclei down to ∼1–2 GeV nucl−1 for the first time. In these measurements the fast (high energy) neutron intensity was shown to be a surrogate for the nuclear
cascade intensity in the atmosphere.
The development of the neutron monitor in 1948–1951 and the first geomagnetic latitude network will be discussed. Among its
early applications were:
(1) to prove that there exists interplanetary solar modulation of galactic cosmic-rays (1952), and;
(2) to provide the evidence for a dynamical heliosphere (1956).
With the world-wide distribution of neutron monitor stations that are presently operating (∼ 50) many novel investigations
are still to be carried out, especially in collaborations with spacecraft experiments.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
668.
John A. Wood 《Space Science Reviews》2000,92(1-2):97-112
Radiometric dating shows that the earliest steps in forming the substance of meteorites and assembling it into planetesimals
occurred in a very short interval of time, 1–2 Ma. This study shows that rapid formation is also dictated by the need to use
short-lived 26Al (half-life T
1/2=0.74 Ma) as a heat source to metamorphose and in some cases melt the meteorite parent bodies after they accreted. The earliest
events in solar system history dated by cosmochemists, formation at high temperatures of the Ca,Al-rich inclusions that occur
in chondritic meteorites, probably occurred during the most energetic stage of protosolar disk evolution, as the protosun
neared its present mass and infall drew to a close.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
669.
D. Kucharski G. Kirchner H.-C. Lim F. Koidl 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
The nanosatellite BLITS (Ball Lens In The Space) demonstrates a successful design of the new spherical lens type satellite for Satellite Laser Ranging (SLR). The spin parameters of the satellite were calculated from more than 1000 days of SLR data collected from 6 High Repetition Rate (HRR) systems: Beijing, Changchun, Graz, Herstmonceux, Potsdam, Shanghai. 相似文献
670.
U. Geppert B. Biering F. Lura J. Block M. Straubel R. Reinhard 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The 3-step Gossamer road map to solar sailing is presented that has been agreed between DLR and ESA in November 2009. The main and exclusive purpose of that project is to develop, to prove, and to demonstrate the solar sail technology as a safe and reliably manageable propulsion technique for long lasting and deep space missions. Since the development of the solar sail technology is quite a complex task, presently at the DLR implemented solar sail related research activities will be presented as well. 相似文献