首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   344885篇
  免费   5452篇
  国内免费   749篇
电工技术   6428篇
综合类   586篇
化学工业   53217篇
金属工艺   10922篇
机械仪表   9479篇
建筑科学   9005篇
矿业工程   928篇
能源动力   9251篇
轻工业   35732篇
水利工程   2846篇
石油天然气   3819篇
武器工业   13篇
无线电   41739篇
一般工业技术   64479篇
冶金工业   65283篇
原子能技术   5635篇
自动化技术   31724篇
  2021年   3074篇
  2020年   2301篇
  2019年   2743篇
  2018年   4941篇
  2017年   4784篇
  2016年   4946篇
  2015年   3524篇
  2014年   5646篇
  2013年   16702篇
  2012年   9449篇
  2011年   12028篇
  2010年   9444篇
  2009年   10473篇
  2008年   11160篇
  2007年   10926篇
  2006年   9518篇
  2005年   8752篇
  2004年   8556篇
  2003年   8231篇
  2002年   7955篇
  2001年   7925篇
  2000年   7576篇
  1999年   8046篇
  1998年   20389篇
  1997年   14469篇
  1996年   11144篇
  1995年   8480篇
  1994年   7754篇
  1993年   7430篇
  1992年   5456篇
  1991年   5250篇
  1990年   5111篇
  1989年   4962篇
  1988年   4827篇
  1987年   4025篇
  1986年   4155篇
  1985年   4893篇
  1984年   4428篇
  1983年   4135篇
  1982年   3739篇
  1981年   3905篇
  1980年   3584篇
  1979年   3518篇
  1978年   3325篇
  1977年   3966篇
  1976年   5197篇
  1975年   2855篇
  1974年   2717篇
  1973年   2741篇
  1972年   2258篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
A comparison is made between different alternate schemes for determination of the strength of soils possessing rheological properties on the basis of our own experimental data. An original method is proposed for determination of the ultimate long-term strength from tests on the conditionally instantaneous failure of soil after preliminary deformation in a creep regime, as well as from tests in a controlled-deformation regime. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 14–18, January–February, 1996.  相似文献   
32.
We propose and evaluate a medium-access control (MAC) protocol for synchronous cellular packet direct-sequence code-division multiple-access (DS/CDMA). The protocol is designed for handling a variety of multimedia traffic types in an integrated wireless-access network (IWAN). For instance, the protocol is suited for carrying multiple traffic types of different priorities. An analytical model for the equilibrium state has been developed for the proposed protocol. A comparative evaluation of the protocol is done for three different radio frequency bandwidths currently under consideration for personal communication services (PCS), i.e., 1.25 MHz, 5 MHz, and 10 MHz. Our results demonstrate that the proposed protocol is both robust and flexible for the intended IWAN applications. It offers a significant multiplexing gain as the bandwidth increases  相似文献   
33.
In this study chick embryo optic cups at HH stage 13 of development were analyzed under normal conditions and after inoculation with colchicine for 1, 2, 4, and 8 h. Several changes were seen after these periods of treatment: 1) modifications of the structure, with thicker regions in the cup and a general decrease in the total volume according to the duration of exposure to the drug (about 4 times less than normal, 5,035 x 10(3) microns 3 vs 1,334 x 10(3) microns 3 after 8 h of treatment); 2) enlargement of the ventricular cavity and its closure, due to failure of approximation of retinal and pigmentary layers; 3) failure of lens development, with delay and impairment of pit formation and deformation of all structures; lens volume was less than normal (about 4 times less, 2,148 x 10(3) microns 3 vs 658 x 10(3) microns 3 after 8 h of treatment); 4) a general segregation of the cells making up the structure, principally in the more active proliferating zones. The local alterations found are described.  相似文献   
34.
35.
Comments on L. R. Goldberg's (see record 1993-17546-001) history of the Big Five framework of personality traits and elaborated on its use. The reasons why industrial/organizational psychologists de-emphaszied the impact of personality on the job peformance in the late 1960s and 1970s and re-emphasized it in the 1980s are addressed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
36.
This paper focuses on the hydrodynamics of third sound on a superfluid 3 He film. We solve the hydrodynamical equations in the limit of thick films with weak interaction with the substrate. The surface tension at the free interface is shown to have a large effect on the third sound velocity and on the attenuation for frequencies larger than 1Hz. In the case of a diffusely scattering substrate a ripplon-like dispersion relation is found for this frequency range.  相似文献   
37.
38.
39.
The biotransformation of oxazepam by Bifidobacterium bifidum was studied. The major metabolite was purified by chromatographic methods and found to be desmethyldiazepam using NMR, IR and other physicochemical data.  相似文献   
40.
A review of isolates of Neisseria meningitidis and other laboratory evidence of meningococcal infection was carried out for the period 1990-1995. Thirty-three patients with evidence of meningococcal disease were identified over the six year period. Group B organisms were the most commonly identified, but an increase in Group C has occurred and is almost equal in number. Data from clinical, laboratory and public health sources should be centralized in a National Surveillance Centre.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号