全文获取类型
收费全文 | 721393篇 |
免费 | 8024篇 |
国内免费 | 1212篇 |
专业分类
电工技术 | 12768篇 |
综合类 | 585篇 |
化学工业 | 113141篇 |
金属工艺 | 34107篇 |
机械仪表 | 23956篇 |
建筑科学 | 15875篇 |
矿业工程 | 6194篇 |
能源动力 | 17226篇 |
轻工业 | 52506篇 |
水利工程 | 9495篇 |
石油天然气 | 20218篇 |
武器工业 | 48篇 |
无线电 | 73242篇 |
一般工业技术 | 154965篇 |
冶金工业 | 114633篇 |
原子能技术 | 19091篇 |
自动化技术 | 62579篇 |
出版年
2021年 | 6628篇 |
2019年 | 6299篇 |
2018年 | 14752篇 |
2017年 | 14920篇 |
2016年 | 14237篇 |
2015年 | 7523篇 |
2014年 | 12555篇 |
2013年 | 31291篇 |
2012年 | 20120篇 |
2011年 | 28681篇 |
2010年 | 23631篇 |
2009年 | 25249篇 |
2008年 | 25934篇 |
2007年 | 26457篇 |
2006年 | 19431篇 |
2005年 | 18790篇 |
2004年 | 17729篇 |
2003年 | 17393篇 |
2002年 | 16336篇 |
2001年 | 15422篇 |
2000年 | 14920篇 |
1999年 | 14348篇 |
1998年 | 32106篇 |
1997年 | 23528篇 |
1996年 | 18311篇 |
1995年 | 14157篇 |
1994年 | 12982篇 |
1993年 | 12704篇 |
1992年 | 9999篇 |
1991年 | 9832篇 |
1990年 | 9686篇 |
1989年 | 9380篇 |
1988年 | 9035篇 |
1987年 | 8335篇 |
1986年 | 8066篇 |
1985年 | 9024篇 |
1984年 | 8298篇 |
1983年 | 8027篇 |
1982年 | 7287篇 |
1981年 | 7440篇 |
1980年 | 7187篇 |
1979年 | 7406篇 |
1978年 | 7385篇 |
1977年 | 8043篇 |
1976年 | 9718篇 |
1975年 | 6669篇 |
1974年 | 6579篇 |
1973年 | 6646篇 |
1972年 | 5820篇 |
1971年 | 5399篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The d.c. electrical conductivity of sodium vanadate, rubidium vanadate, cesium vanadate and their solid solutions sodium-rubidium
vanadate and sodium-cesium vanadate were studied by a two-probe method in the temperature range covering their transition
points. The electrical conductivity shows sharp change at the phase transition temperature of these materials. In NaVO3, RbVO3 and CsVO3, increase in d.c. conductivity is observed in the ferroelectric region while nonlinearities are observed above transition
temperatures. In solid solutions, the activation energy in the paraelectric state is higher than that in the ferroelectric
state and depends upon sodium concentration. 相似文献
992.
Institute of Strength Problems, Academy of Sciences of the Ukrainian SSR, Kiev. Sumy Branch, Khar'kov Polytechnic Institute. Translated from Problemy Prochnosti, No. 8, pp. 102–104, August, 1989. 相似文献
993.
Graduates of clinical training programs were surveyed to determine the degree to which they have found various graduate school experiences useful in their professional work. Samples of academic clinical psychologists and practicing clinical psychologists reported time allocation and preference for various professional activities, perceived usefulness of various theoretical orientations, and the influence on their current professional work of 19 different graduate training topics. Results suggest that where differences exist, academic clinical psychologists are generally more satisfied with Boulder-model-inspired scientific training than are clinical practitioners. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
994.
995.
996.
Static light scattering was used to investigate dilute dispersions of fine gamma -Fe/sub 2/O/sub 3/ magnetic particles. The particles were acicular and on average 0.39 mu m long and 0.056 mu m in diameter. They were dispersed in organic solvents at concentrations of approximately 10/sup -4/ vol%, corresponding to an average interparticle separation of 9 mu m. Computer programs using a coupled dipole algorithm to predict the scattering from the particles were written. Experimental results do not agree with computer calculations of the light scattering from single particles, but are consistent with scattering from thick ropelike agglomerates of particles. The size of these agglomerates was estimated after 10 s to be less than 100 particles, while the thickness of the ropes is at least 5 particles.<> 相似文献
997.
R. A. Mustafaev D. K. Ganiev D. M. Gabulov 《Journal of Engineering Physics and Thermophysics》1985,48(2):241-242
Dynamic-viscosity measurements are reported for liquid mixtures in the system formed by n-butyraldehyde and isobutyraldehyde.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 48, No. 2, pp. 321–322, February, 1985. 相似文献
998.
999.
Elastic stress concentration in a manipulator element is calculated within the framework of the two-dimensional stressed state model. The purpose here is to make recommendations for selecting the radius of joining of the beam parts of the element based on analysis of maximum stresses in the stress concentration zone. Combination of the finite element and boundary element methods is proposed for solving the problem. A coarse finite element subdivision is used for the initial calculation for the entire element. Then, the solution is refined by using boundary elements in the identified zone. Comparison of calculation results with solutions obtained by the finite element and boundary element methods points to the effectiveness of the proposed algorithm for stress concentration calculations.Translated from Problemy Prochnosti, No. 6, pp. 72–74, June, 1991. 相似文献
1000.
V. Vassilev S. Thijs P. L. Segura P. Wambacq P. Leroux G. Groeseneken M. I. Natarajan H. E. Maes M. Steyaert 《Microelectronics Reliability》2005,45(2):255-268
This paper describes an approach to design ESD protection for integrated low noise amplifier (LNA) circuits used in narrowband transceiver front-ends. The RF constraints on the implementation of ESD protection devices are relaxed by co-designing the RF and the ESD blocks, considering them as one single circuit to optimise. The method is applied for the design of 0.25 μm CMOS LNA. Circuit protection levels higher than 3 kV HBM stress are achieved using conventional highly capacitive ggNMOS snapback devices. The methodology can be extended to other RF-CMOS circuits requiring ESD protection by merging the ESD devices in the functionality of the corresponding matching blocks. 相似文献