全文获取类型
收费全文 | 8851篇 |
免费 | 10篇 |
国内免费 | 36篇 |
专业分类
航空 | 4257篇 |
航天技术 | 3054篇 |
综合类 | 198篇 |
航天 | 1388篇 |
出版年
2021年 | 74篇 |
2019年 | 50篇 |
2018年 | 153篇 |
2017年 | 93篇 |
2016年 | 85篇 |
2014年 | 165篇 |
2013年 | 218篇 |
2012年 | 218篇 |
2011年 | 319篇 |
2010年 | 211篇 |
2009年 | 361篇 |
2008年 | 400篇 |
2007年 | 225篇 |
2006年 | 190篇 |
2005年 | 228篇 |
2004年 | 233篇 |
2003年 | 287篇 |
2002年 | 272篇 |
2001年 | 327篇 |
2000年 | 181篇 |
1999年 | 223篇 |
1998年 | 262篇 |
1997年 | 189篇 |
1996年 | 243篇 |
1995年 | 299篇 |
1994年 | 267篇 |
1993年 | 147篇 |
1992年 | 222篇 |
1991年 | 96篇 |
1990年 | 98篇 |
1989年 | 223篇 |
1988年 | 88篇 |
1987年 | 87篇 |
1986年 | 100篇 |
1985年 | 268篇 |
1984年 | 207篇 |
1983年 | 182篇 |
1982年 | 214篇 |
1981年 | 256篇 |
1980年 | 91篇 |
1979年 | 66篇 |
1978年 | 79篇 |
1977年 | 60篇 |
1976年 | 63篇 |
1975年 | 69篇 |
1974年 | 67篇 |
1972年 | 64篇 |
1971年 | 60篇 |
1970年 | 54篇 |
1969年 | 53篇 |
排序方式: 共有8897条查询结果,搜索用时 15 毫秒
61.
J P Koniarek J L Thomas M Vazquez 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(6):1373-1377
In cells irradiation by heavy ions has been hypothesized to produce microlesions, regions of local damage. In cell membranes this damage is thought to manifest itself in the form of holes. The primary evidence for microlesions comes from morphological studies of cell membranes, but this evidence is still controversial, especially since holes also have been observed in membranes of normal, nonirradiated, cells. However, it is possible that damage not associated with histologically discernable disruptions may still occur. In order to resolve this issue, we developed a system for detecting microlesions based on liposomes filled with fluorescent dye. We hypothesized that if microlesions form in these liposomes as the result of irradiation, then the entrapped dye will leak out into the surrounding medium in a measurable way. Polypropylene vials containing suspensions of vesicles composed of either dipalmitoyl phosphatidylcholine, or a combination of egg phosphatidylcholine and cholesterol were irradiated at the Brookhaven National Laboratory using 56Fe ions at 1 GeV/amu. In several cases we obtained a significant loss of the entrapped dye above the background level. Our results suggest that holes may form in liposomes as the result of heavy ion irradiation, and that these holes are large enough to allow leakage of cell internal contents that are at least as large as a 1 nm diameter calcein molecule. 相似文献
62.
63.
通过对电阻应变式称重传感器在各种加载卸载情况下的滞后特性的分析 ,建立了其相应的数学模型 ,并初步探讨了一种可以通过程序在仪表中对传感器的重要指标—滞后进行补偿从而提高整个传感器的精度的方法。最后 ,对以上方法进行了验证性试验 ,证明了补偿方法的可行性。 相似文献
64.
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
65.
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
66.
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
67.
68.
L. B. F. M. Waters 《Space Science Reviews》1992,61(1-2):25-43
In this review the IR emission from circumstellar material is discussed, both of ionized gas and dust grains, and the astrophysical information that can be extracted from such observations. Some emphasis is placed on the possibilities of stellar IR astronomy using a large space-borne telescope, especially with respect to the much better spatial and spectral resolution of such a telescope compared to the current generation of ground-based and space IR telescopes. 相似文献
69.
H. Thiemann R. W. Schunk 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1992,12(12):143-146
Heavy emission caused by impacting plasma ions results in a fast discharging effect of the initially large surface potentials on the dielectric solar cells. This eventually counteracts the energization process of the plasma ions to the cover glasses and leaves no significant electric fields. Thus, with an existing thermal plasma, electrons are again able to reach dielectric surfaces. Strong localized electric fields of the order of several 10 kV/cm form near the interconnector-cover glass interface. 相似文献
70.
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