全文获取类型
收费全文 | 4473篇 |
免费 | 13篇 |
国内免费 | 7篇 |
专业分类
航空 | 2093篇 |
航天技术 | 1604篇 |
综合类 | 16篇 |
航天 | 780篇 |
出版年
2021年 | 44篇 |
2019年 | 25篇 |
2018年 | 104篇 |
2017年 | 73篇 |
2016年 | 76篇 |
2015年 | 39篇 |
2014年 | 130篇 |
2013年 | 138篇 |
2012年 | 143篇 |
2011年 | 193篇 |
2010年 | 127篇 |
2009年 | 217篇 |
2008年 | 293篇 |
2007年 | 129篇 |
2006年 | 107篇 |
2005年 | 139篇 |
2004年 | 117篇 |
2003年 | 156篇 |
2002年 | 89篇 |
2001年 | 153篇 |
2000年 | 74篇 |
1999年 | 99篇 |
1998年 | 120篇 |
1997年 | 87篇 |
1996年 | 90篇 |
1995年 | 124篇 |
1994年 | 121篇 |
1993年 | 64篇 |
1992年 | 95篇 |
1991年 | 54篇 |
1990年 | 36篇 |
1989年 | 88篇 |
1988年 | 40篇 |
1987年 | 42篇 |
1986年 | 36篇 |
1985年 | 96篇 |
1984年 | 86篇 |
1983年 | 75篇 |
1982年 | 86篇 |
1981年 | 118篇 |
1980年 | 41篇 |
1979年 | 36篇 |
1978年 | 32篇 |
1977年 | 25篇 |
1976年 | 28篇 |
1975年 | 22篇 |
1974年 | 22篇 |
1973年 | 23篇 |
1972年 | 23篇 |
1971年 | 21篇 |
排序方式: 共有4493条查询结果,搜索用时 15 毫秒
31.
This discusses the implementation issues of installing a commercially available hand geometry system in the current infrastructure of Purdue University's Recreational Sports Center. In addition to a performance analysis of the system, a pre- and post-data collection survey was distributed to the 129 test subjects gathering information on perceptions of biometrics, in particular hand geometry, as well as participants' thoughts and feelings during their interaction with the hand geometry device. The results of the survey suggest that participants were accepting of hand geometry. Additionally, analyses of the participants' survey responses revealed that 93% liked using hand geometry, 98% thought it was easy to use, and 87% preferred it to the existing card-based system, while nobody thought the device invaded their personal privacy. System performance achieved a 3-try match rate of 99.02% (FRR 0.98%) when "gaming"/potential impostor attempts were removed from analysis. The failure to enroll rate was zero. Statistical analyses exposed a significant difference in the scores of attempts made by users with prior hand geometry usage, and subjects that could not straighten out their hand on the device. However, there were no statistical difference in the effects of rings/no rings, improper hand placements/proper hand placements, or gender on hand geometry score. 相似文献
32.
33.
Generalized likelihood ratio tests (GLRTs) are derived for the problem of detecting targets in hyperspectral images. These detectors are derived under the assumptions that the signals from the materials in the image mix linearly and that the noise in the system is Gaussian. It is also assumed that the abundances of the signals from the various materials in a pixel must sum to one. This constraint models the fact that the material abundances in a pixel are just the fraction of the pixel that they occupy. Under these assumptions, detectors are derived which outperform the detectors derived without the sum-to-one constraint. 相似文献
34.
Wright R.G. Zgol M. Keeton S. Kirkland L.V. 《Aerospace and Electronic Systems Magazine, IEEE》2001,16(6):15-19
This paper describes original research efforts in the design, simulation, and development of nanotechnology-based molecular test equipment (MTE). This is a research effort for testing printed circuit boards independent of traditional automatic test equipment (ATE) through the fabrication of MTE within integrated circuits (ICs). The MTE is embedded within the IC substrate and encapsulated within nanoprobes that connect between the surface and the substrate of the IC at various functional areas. A process is followed whereby IC device simulation is performed to assess the electrical, chemical, and structural properties of integrated and adjacent substrate devices. Through this approach the nominal and failed device performance parameters of interest to substrate-based MTE are found. Discussion of the development and application of MTE within IC architectures is provided, including such topics as the effect of substrate composition on the design and realization of MTE, interfaces between MTE and IC devices, and reporting of MTE results to the IC surface and technician. Potential application areas within different device functions will also be identified. A chemical structure diagram is also provided to illustrate the implementation of MTE using discrete device configurations with MTE-augmented logic 相似文献
35.
36.
A flat panel multifunction display (MFD) that offers the size and reliability benefits of liquid crystal display technology while achieving near-CRT display quality is presented. Display generation algorithms that provide exceptional display quality are being implemented in custom VLSI components to minimize MFD size. A high-performance processor converts user-specified display lists to graphics commands used by these components, resulting in high-speed updates of two-dimensional and three-dimensional images. The MFD uses the MIL-STD-1553B data bus for compatibility with virtually all avionics systems. The MFD can generate displays directly from display lists received from the MIL-STD-1553B bus. Complex formats can be stored in the MFD and displayed using parameters from the data bus. The MFD also accepts direct video input and performs special processing on this input to enhance image quality 相似文献
37.
D. L. Judge H. S. Ogawa D. R. McMullin P. Gangopadhyay J. M. Pap 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,29(12):502-1968
The SOHO Solar EUV Monitor has been in operation since December 1995 onboard the SOHO spacecraft. This instrument is a highly stable transmission grating solar extreme ultraviolet spectrometer. It has made nearly continuous full disk solar irradiance measurements both within an 8 nm bandpass centered at 30.4 nm and throughout the 0.1 to 50 nm solar flux region since launch. The 30.4 nm flux, the 0.1 to 50 nm flux and the extracted soft X-ray (0.1 to 5 nm) flux are presented and compared with the behavior of solar proxies. 相似文献
38.
F. S. Khairullin 《Russian Aeronautics (Iz VUZ)》2009,52(4):480-483
We consider a possibility to apply the method of analyzing the complex-shaped shells, proposed in [1], for determining the
stress strain state of thin shells with a degenerating domain. The results of numerical calculations are presented. 相似文献
39.
A. Sh. Dzhabrailov Yu. V. Klochkov S. S. Marchenko A. P. Nikolaev 《Russian Aeronautics (Iz VUZ)》2007,50(2):115-120
We demonstrate that it is possible to express each component of the displacement vector for the interior point of the finite element (FE) through all components of nodal unknowns in curvilinear coordinates. The effectiveness of the valid technique of vector approximation for displacement fields has been verified on an example. 相似文献
40.
The characteristics of the insulator wear process in the discharge chamber of a stationary plasma thruster (SPT) are analyzed. The results of studying the erosion resistance to ionic spraying of different ceramic compositions are presented. It is shown experimentally that the integral characteristics (the value of thrust and thrust efficiency) as well as the SPT lifetime can be improved in changing from the conventional hot-pressed boron silicate (BN + SiO2) ceramics to the BN + Si3N4 ceramic compositions. 相似文献