全文获取类型
收费全文 | 10275篇 |
免费 | 21篇 |
国内免费 | 31篇 |
专业分类
航空 | 4914篇 |
航天技术 | 3527篇 |
综合类 | 42篇 |
航天 | 1844篇 |
出版年
2021年 | 88篇 |
2019年 | 64篇 |
2018年 | 189篇 |
2017年 | 118篇 |
2016年 | 121篇 |
2015年 | 60篇 |
2014年 | 222篇 |
2013年 | 298篇 |
2012年 | 278篇 |
2011年 | 407篇 |
2010年 | 292篇 |
2009年 | 432篇 |
2008年 | 496篇 |
2007年 | 296篇 |
2006年 | 246篇 |
2005年 | 270篇 |
2004年 | 241篇 |
2003年 | 312篇 |
2002年 | 205篇 |
2001年 | 337篇 |
2000年 | 196篇 |
1999年 | 243篇 |
1998年 | 283篇 |
1997年 | 194篇 |
1996年 | 278篇 |
1995年 | 331篇 |
1994年 | 308篇 |
1993年 | 192篇 |
1992年 | 231篇 |
1991年 | 102篇 |
1990年 | 97篇 |
1989年 | 224篇 |
1988年 | 102篇 |
1987年 | 109篇 |
1986年 | 103篇 |
1985年 | 303篇 |
1984年 | 241篇 |
1983年 | 198篇 |
1982年 | 209篇 |
1981年 | 330篇 |
1980年 | 97篇 |
1979年 | 75篇 |
1978年 | 84篇 |
1977年 | 74篇 |
1975年 | 93篇 |
1974年 | 70篇 |
1973年 | 64篇 |
1972年 | 75篇 |
1971年 | 67篇 |
1970年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
H E Zieschang A Sievers 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1994,14(8):135-144
With the mathematical basis for the precise analysis of developmental processes in plants, the patterns of growth in phototropic and gravitropic responses have become better understood. A detailed temporal and spatial quantification of a growth process is an important tool for evaluating hypotheses about the underlying physiological mechanisms. Studies of growth rates and curvature show that the original Cholodny-Went hypothesis cannot explain the complex growth patterns during tropic responses of shoots and roots. In addition, regulating factors other than the lateral redistribution of hormones must be taken into account. Electrophysiological studies on roots led to a modification of the Cholodny-Went hypothesis in that redistributions of bioelectrical activities are observed. 相似文献
52.
53.
R L Mancinelli J R Marshall M R White 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1992,12(4):111-116
Potential Martian soil components relevant to exobiology include water, organic matter, evaporites, clays, and oxides. These materials are also resources for human expeditions to Mars. When found in particular combinations, some of these materials constitute diagnostic paleobiomarker suites, allowing insight to be gained into the probability of life originating on Mars. Critically important to exobiology is the method of data analysis and data interpretation. To that end we are investigating methods of analysis of potential biomarker and paleobiomarker compounds and resource materials in soils and rocks pertinent to Martian geology. Differential thermal analysis coupled with gas chromatography is shown to be a highly useful analytical technique for detecting this wide and complex variety of materials. 相似文献
54.
Guerci J.R. Goetz R.A. DiModica J. 《IEEE transactions on aerospace and electronic systems》1994,30(4):1090-1093
A relatively simple method is presented which eliminates previously reported (Oct. 1985) erratic estimation performance associated with Cartesian formulations of the extended Kalman filter (EKF) for the 2D angle-only emitter location problem. The technique is based on an initialization procedure which combines a priori probability density function (pdf) information with single measurement a posteriori pdf information in a manner which is more efficient than the EKF. Simulation results are presented which demonstrate the utility of the technique as compared with a previously offered modified gain EKF 相似文献
55.
G. Paschmann M. Boehm H. Höfner R. Frenzel P. Parigger F. Melzner G. Haerendel C. A. Kletzing R. B. Torbert G. Sartori 《Space Science Reviews》1994,70(3-4):447-463
The Electron Beam Instrument (F6) onFreja is the first attempt to apply the electron drift technique in a region of large ambient magnetic fields. The paper describes the operational principles, the technical realization, and the difficulties encountered in the derivation of the electric fields. 相似文献
56.
57.
The Cluster mission of the European Space Agency (ESA) will allow, for the first time three-dimensional measurements in key regions of the Earth's magnetosphere to be carried out. The European Numerical Simulation Network (ENSN) aims at providing a theoretical support to the mission. We describe the achievements of the ENSN during its first period of activity 1991–1994, during which the network was funded by the European Union. In particular, the ENSN has set up (i) thematic Working Groups on the prime scientific goals of the mission, (ii) a code development Working Group to develop numerical simulation codes specifically adapted to studying magnetospheric boundaries and the corresponding scale mixing, and (iii) software models of Cluster instruments to test in a numerical simulation what the set of four instruments will measure. 相似文献
58.
Demands for portability have fueled significant developments in new battery technology. These developments have resulted in many more options in selecting the battery type for use in a particular project, but since most applications today are opting for rechargeable battery systems, the availability of battery charging solutions can become an equally important criteria in the selection process. Complicating this process are the demands for fast-but safe-charging with charge algorithms easily implemented with low-cost hardware. With the higher levels of complexity attendant with these more demanding algorithms, solutions have come primarily from the integrated circuit industry and the purpose of this paper is to provide a few examples of the latest efforts in this arena, specifically as addressed to lead-acid, nickel metal-hydride, and lithium-ion technologies 相似文献
59.
J H Bieging 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1995,15(3):3-14
Stars in their late stages of evolution often shed matter in the form of a cool wind which is molecular in composition. These winds are a major source of replenishment of the interstellar gas and dust, so they furnish a large part of the raw materials for new generations of stars and planets. The chemistry of the circumstellar envelope depends strongly on the photospheric abundances of the elements, especially C and O. If C/O > 1, a rich organic chemistry is observable in the microwave and mm-wavelength emission lines of the reactions products. This paper reviews the observational evidence for the presence of organic molecules and their formation pathways in circumstellar envelopes, with special emphasis on rotational spectra at microwave and millimeter wavelengths. 相似文献
60.