全文获取类型
收费全文 | 2795篇 |
免费 | 8篇 |
国内免费 | 11篇 |
专业分类
航空 | 1347篇 |
航天技术 | 1058篇 |
综合类 | 6篇 |
航天 | 403篇 |
出版年
2021年 | 19篇 |
2019年 | 18篇 |
2018年 | 48篇 |
2017年 | 39篇 |
2016年 | 26篇 |
2015年 | 13篇 |
2014年 | 56篇 |
2013年 | 68篇 |
2012年 | 71篇 |
2011年 | 121篇 |
2010年 | 77篇 |
2009年 | 128篇 |
2008年 | 165篇 |
2007年 | 77篇 |
2006年 | 60篇 |
2005年 | 86篇 |
2004年 | 74篇 |
2003年 | 104篇 |
2002年 | 58篇 |
2001年 | 104篇 |
2000年 | 50篇 |
1999年 | 87篇 |
1998年 | 91篇 |
1997年 | 68篇 |
1996年 | 66篇 |
1995年 | 89篇 |
1994年 | 100篇 |
1993年 | 39篇 |
1992年 | 63篇 |
1991年 | 23篇 |
1990年 | 30篇 |
1989年 | 57篇 |
1988年 | 22篇 |
1987年 | 37篇 |
1986年 | 24篇 |
1985年 | 80篇 |
1984年 | 46篇 |
1983年 | 54篇 |
1982年 | 55篇 |
1981年 | 79篇 |
1980年 | 29篇 |
1979年 | 24篇 |
1978年 | 23篇 |
1977年 | 19篇 |
1976年 | 16篇 |
1975年 | 19篇 |
1974年 | 16篇 |
1972年 | 18篇 |
1969年 | 13篇 |
1966年 | 10篇 |
排序方式: 共有2814条查询结果,搜索用时 15 毫秒
1.
Arman Seuylemezian Manuela Buonanno Lisa Guan David J. Brenner David Welch 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(1):496-503
This work aims to investigate far-UVC light at 222 nm as a new microbial reduction tool for planetary protection purposes which could potentially be integrated into the spacecraft assembly process. The major advantage of far-UVC (222 nm) compared to traditional germicidal UVC (254 nm) is the potential for application throughout the spacecraft assembly process in the presence of humans without adverse health effects due to the limited penetration of far-UVC light into biological materials. Testing the efficacy of 222-nm light at inactivating hardy bacterial cells and spores isolated from spacecraft and associated surfaces is a necessary step to evaluate this technology. We assessed survival of Bacillus pumilus SAFR-032 and Acinetobacter radioresistens 50v1 exposed to 222-nm light on proxy spacecraft surfaces simulated by drying the bacteria on aluminum coupons. The survival fraction of both bacteria followed a single stage decay function up to 60 mJ/cm2, revealing similar susceptibility of both species to 222-nm light, which was independent of the exposure rate. Irradiation with far-UVC light at 222 nm is an effective method to decontaminate the proxy spacecraft materials tested in this study. 相似文献
2.
3.
E. R. Muslimov E. Hugot M. Ferrari T. Behaghel N. K. Pavlycheva 《Russian Aeronautics (Iz VUZ)》2018,61(1):1-7
The possibility of constructing an optical scheme of a telescope for a small satellite based on mirrors with freeform surfaces and a curved photodetector is considered. It is shown that the use of a new element base allows the effective area of the main mirror to be maximized and the field of view up to 9.4 times to be increased in comparison with the classical scheme of the Ritchey–Chretien scheme in ensuring the high image quality. 相似文献
4.
Giulio L. Marco B. Aldo F. Domenico T.P. Mario M. 《Aerospace and Electronic Systems Magazine, IEEE》2002,17(9):22-27
This paper reviews the results of the thermal and static analysis of small motor aerospace technology (SMART) propulsion system, constituted of a microthrusters array realised by MEMS technology on silicon wafers. This system has been studied using FEM (NASTRAN) and the results have been verified by the electro-thermic analogy and the FDM method, using, respectively, SPICE and MATLAB codes. The simulation results demonstrated the feasibility of SMART systems for aerospace applications such as attitude control and deorbiting missions for small satellite station-keeping. A theoretical impulse of 20 mNs has been calculated for the SMART system. 相似文献
5.
L O Bjorn S Widell T Wang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,30(6):1557-1562
Plants have evolved under the influence of UV-B radiation and have acquired systems for monitoring it and investing appropriate resources for protection against it, i.e., filters, quenchers of radicals and reactive oxygen species, and repair systems. An hypothesis for how plants monitor radiation has been presented. 相似文献
6.
This study introduces a field oriented controlled (FOC) induction machine based flywheel energy storage (FES) system fed from a 20 kHz high frequency (HF) ac link and pulse density modulated (PDM) Converter. The feasibility of FES system is investigated both in software and hardware and is demonstrated successfully in both cases. The investigated system offers a good potential as a temporary energy storage system for various applications from automobile industry to aerospace applications. 相似文献
7.
R. Vilhena de Moraes K. T. Fitzgibbon M. Konemba 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1995,16(12)
Due to the characteristics of their orbits the GPS satellites are submitted to the following main perturbations: terrestrial gravitational field, luni-solar gravitational attraction and solar radiation pressure (including the effects of the Earth's shadow). An additional perturbation arises due to the 2:1 commensurability of the orbital period of the satellite with the period of the Earth's rotation. An analytical theory is briefly presented to solve the equations of motion including the previously mentioned effects. The analytical solution, based on the Lie-Hori method, is compared with a numerical integration of the equations. 相似文献
8.
9.
T C Yang M Mei K A George L M Craise 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,18(1-2):149-158
Energetic heavy ions are present in galactic cosmic rays and solar particle events. One of the most important late effects in risk assessment is carcinogenesis. We have studied the carcinogenic effects of heavy ions at the cellular and molecular levels and have obtained quantitative data on dose-response curves and on the repair of oncogenic lesions for heavy particles with various charges and energies. Studies with repair inhibitors and restriction endonucleases indicated that for oncogenic transformation DNA is the primary target. Results from heavy ion experiments showed that the cross section increased with LET and reached a maximum value of about 0.02 micrometer2 at about 500 keV/micrometer. This limited size of cross section suggests that only a fraction of cellular genomic DNA is important in radiogenic transformation. Free radical scavengers, such as DMSO, do not give any effect on induction of oncogenic transformation by 600 MeV/u iron particles, suggesting most oncogenic damage induced by high-LET heavy ions is through direct action. Repair studies with stationary phase cells showed that the amount of reparable oncogenic lesions decreased with an increase of LET and that heavy ions with LET greater than 200 keV/micrometer produced only irreparable oncogenic damage. An enhancement effect for oncogenic transformation was observed in cells irradiated by low-dose-rate argon ions (400 MeV/u; 120 keV/micrometer). Chromosomal aberrations, such as translocation and deletion, but not sister chromatid exchange, are essential for heavy-ion-induced oncogenic transformation. The basic mechanism(s) of misrepair of DNA damage, which form oncogenic lesions, is unknown. 相似文献
10.
K Eguchi-Kasai M Murakami H Itsukaichi K Fukutsu T Kanai Y Furusawa K Sato H Ohara F Yatagai 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,18(1-2):109-118
It can be noted that it is not simple double strand breaks (dsb) but the non-reparable breaks that are associated with high biological effectiveness in the cell killing effect for high LET radiation. Here, we have examined the effectiveness of fast neutrons and low (initial energy = 12 MeV/u) or high (135 MeV/u) energy charged particles on cell death in 19 mammalian cell lines including radiosensitive mutants. Some of the radiosensitive lines were deficient in DNA dsb repair such as LX830, M10, V3, and L5178Y-S cells and showed lower values of relative biological effectiveness (RBE) for fast neutrons if compared with their parent cell lines. The other lines of human ataxia-telangiectasia fibroblasts, irs 1, irs 2, irs 3 and irs1SF cells, which were also radiosensitive but known as proficient in dsb repair, showed moderated RBEs. Dsb repair deficient mutants showed low RBE values for heavy ions. These experimental findings suggest that the DNA repair system does not play a major role against the attack of high linear energy transfer (LET) radiations. Therefore, we hypothesize that a main cause of cell death induced by high LET radiations is due to non-reparable dsb, which are produced at a higher rate compared to low LET radiations. 相似文献