全文获取类型
收费全文 | 559935篇 |
免费 | 5420篇 |
国内免费 | 1428篇 |
专业分类
电工技术 | 8958篇 |
综合类 | 2548篇 |
化学工业 | 86598篇 |
金属工艺 | 28293篇 |
机械仪表 | 19379篇 |
建筑科学 | 12371篇 |
矿业工程 | 5313篇 |
能源动力 | 10981篇 |
轻工业 | 36905篇 |
水利工程 | 7595篇 |
石油天然气 | 16687篇 |
武器工业 | 36篇 |
无线电 | 56115篇 |
一般工业技术 | 120747篇 |
冶金工业 | 78134篇 |
原子能技术 | 15613篇 |
自动化技术 | 60510篇 |
出版年
2021年 | 4351篇 |
2019年 | 4148篇 |
2018年 | 21742篇 |
2017年 | 20848篇 |
2016年 | 18146篇 |
2015年 | 5505篇 |
2014年 | 8656篇 |
2013年 | 20299篇 |
2012年 | 15632篇 |
2011年 | 25215篇 |
2010年 | 21105篇 |
2009年 | 20265篇 |
2008年 | 21812篇 |
2007年 | 22344篇 |
2006年 | 12877篇 |
2005年 | 12742篇 |
2004年 | 12179篇 |
2003年 | 11783篇 |
2002年 | 11148篇 |
2001年 | 10477篇 |
2000年 | 10236篇 |
1999年 | 9631篇 |
1998年 | 20595篇 |
1997年 | 15700篇 |
1996年 | 12091篇 |
1995年 | 9438篇 |
1994年 | 8628篇 |
1993年 | 8674篇 |
1992年 | 6944篇 |
1991年 | 7012篇 |
1990年 | 6940篇 |
1989年 | 6816篇 |
1988年 | 6625篇 |
1987年 | 6021篇 |
1986年 | 5937篇 |
1985年 | 6637篇 |
1984年 | 6399篇 |
1983年 | 5980篇 |
1982年 | 5644篇 |
1981年 | 5807篇 |
1980年 | 5685篇 |
1979年 | 5798篇 |
1978年 | 6044篇 |
1977年 | 6490篇 |
1976年 | 7927篇 |
1975年 | 5458篇 |
1974年 | 5389篇 |
1973年 | 5481篇 |
1972年 | 4832篇 |
1971年 | 4447篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
J Gálvez R García-Domenech C de Gregorio Alapont JV de Julián-Ortiz L Popa 《Canadian Metallurgical Quarterly》1996,14(5):272-276
BACKGROUND: There is no empirical data available on attitudes concerning AIDS and habits towards HIV infected patients of physicians in general or private practice. In this study results of a self-evaluation are presented. METHODS: 178 physicians working with out-patients in different medical fields were randomly selected for a cross sectional study and interviewed using a standardised questionnaire. RESULTS: 89% think that they are sufficiently informed about AIDS (in the USA 20%). They regarded the risk of infection to be lower than the Anglo-American physicians. They believed there is a lack of interchange of information between colleagues regarding the degree of infectiousness of referred patients. A third of the physicians fear that other patients will go elsewhere if they find out that their physician is treating AIDS patients. 54% would hold special clinic sessions for HIV-patients outside the normal schedule for practice times. 89% believed that HIV patients were partly to blame for their illness. CONCLUSIONS: Although the physicians recognise the problem of HIV-infection, they partly deny the real necessities and facts. A reason for this could be the emotions underlying the general attitude to everything pertaining to HIV-disease. Attitudes to HIV-disease and the dealing with it in daily practice must be considered on the basis of individual emotional motives. 相似文献
992.
Amador F.G. Berman D. Borning A. DeRose T. Finkelstein A. Neville D. Notkin D. Salesin D. Salisbury M. Sherman J. Sun Y. Weld D.S. Winkenbach G. 《Knowledge and Data Engineering, IEEE Transactions on》1993,5(4):611-618
The electronic encyclopedia exploratorium (E3) is a vision of a future computer system-an electronic book describing how thing work. Typical articles in E3 will describe such mechanisms as compression refrigerators, engines, telescopes, and mechanical linkages. Each article will provide simulations, three-dimensional animated graphics that the user can manipulate, laboratory areas that allow a user to modify the device or experiment with related artifacts, and a facility for asking questions and receiving customized, computer-generated English-language explanations. Some of the foundational technology is discussed, focusing on topics in artificial intelligence, graphics, and user interfaces. The initial prototype system and the technical lessons learned from it, as well as the second prototype currently under construction, are described 相似文献
993.
994.
Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 6, pp. 88–98, November–December, 1996. 相似文献
995.
J. S. Kim D. G. Seiler R. A. Lancaster M. B. Reine 《Journal of Electronic Materials》1996,25(8):1215-1220
Variable-magnetic-field Hall measurements (0 to 1.5 T) are performed on very-narrow-gap bulk-grown Hg1−xCdxTe single crystals (0.165 ≤ x ≤ 0.2) at various temperatures (10 to 300K). The electron densities and mobilities are obtained
within the one-carrier (electrons) approximation of the reduced-con-ductivity-tensor scheme. The present data together with
the selected data set reported by other workers exhibit a pronounced peak when the electron mobility is plotted against the
alloy composition x-value which has been predicted to be due to the effective-mass minimum at the bandgap-crossing (Eg ≈ 0). The observed position (x ≈ 0.165), height (≈4 x 102 m2Vs), and width (≈0.01 in x) of the mobility-peak can be explained by a simple simulation involving only ionized-impurity scattering.
A lower bound of the effective mass is introduced as a fitting parameter to be consistent with the finiteness of the observed
electron mobility and is found to be of the order of 10−4 of the mass of a free electron. 相似文献
996.
997.
Kepko E.L. Khurana K.K. Kivelson M.G. Elphic R.C. Russell C.T. 《IEEE transactions on magnetics》1996,32(2):377-385
Cluster introduces a new generation of spacecraft that will measure the spatial gradients of the magnetic field in the Earth's magnetosphere. As gradients require knowledge of differences, small errors resulting from an inadequate knowledge of the orientations, zero levels and the scale factors of the magnetometer sensors affect the calculation of field gradients disproportionately and must be removed with high accuracy. We show that twelve calibration parameters are required for each of the spacecraft (for a total of 48 for the four spacecraft) to correctly infer the measured magnetic fields at each of the spacecraft. By application of a Fourier transform technique, some of the parameters can be recovered. We show that errors in eight of the twelve calibration parameters generate coherent monochromatic signals at the first and the second harmonics of the spin frequency in the despun data. We relate the real and the imaginary parts of the monochromatic signals to the eight calibration parameters. We then present a least squares scheme that improves the eight calibration parameters by iteration until the power of the coherent signal superimposed above the broad-band background is minimized 相似文献
998.
Summary
G-structures are the geometric backbone of the theory of material uniformity in continuum mechanics. Within this geometric framework, anelasticity is seen as a result of evolving distributions of inhomogeneity reflected as material nonintegrability. Constitutive principles governing thetime evolution of the G-structure underlying the finite-strain theory of anelasticity (e.g., plasticity) are proposed. The material Eshelby stress tensor is shown to be thedriving force behind this evolution. This should allow for a thermodynamically admissible formulation of anelasticity viewed as a G-structure evolution. 相似文献
999.
1000.