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   197970篇
  免费   2117篇
  国内免费   633篇
电工技术   4068篇
综合类   123篇
化学工业   26744篇
金属工艺   7511篇
机械仪表   5463篇
建筑科学   4037篇
矿业工程   747篇
能源动力   4672篇
轻工业   14398篇
水利工程   1695篇
石油天然气   2842篇
武器工业   7篇
无线电   27305篇
一般工业技术   37410篇
冶金工业   45422篇
原子能技术   3562篇
自动化技术   14714篇
  2021年   1249篇
  2019年   1281篇
  2018年   2125篇
  2017年   2108篇
  2016年   2174篇
  2015年   1492篇
  2014年   2620篇
  2013年   7962篇
  2012年   4464篇
  2011年   6116篇
  2010年   4938篇
  2009年   5775篇
  2008年   6150篇
  2007年   6201篇
  2006年   5637篇
  2005年   5309篇
  2004年   5252篇
  2003年   5089篇
  2002年   4906篇
  2001年   5307篇
  2000年   4916篇
  1999年   5437篇
  1998年   15631篇
  1997年   10323篇
  1996年   7934篇
  1995年   5791篇
  1994年   5019篇
  1993年   5031篇
  1992年   3386篇
  1991年   3265篇
  1990年   3220篇
  1989年   3042篇
  1988年   2785篇
  1987年   2236篇
  1986年   2304篇
  1985年   2606篇
  1984年   2313篇
  1983年   2064篇
  1982年   1902篇
  1981年   2045篇
  1980年   1791篇
  1979年   1660篇
  1978年   1658篇
  1977年   2024篇
  1976年   2705篇
  1975年   1423篇
  1974年   1369篇
  1973年   1317篇
  1972年   1124篇
  1971年   957篇
排序方式: 共有10000条查询结果,搜索用时 33 毫秒
21.
22.
23.
The paper covers a simple idea. If we sample an aperture, we can obtain valid patterns over a limited angular region about the normal to the aperture. The same expression can be used with near-field measurements. I reduced the expression to a nomograph. A nomograph allows one to rapidly test various choices. In the second half of the paper, I answer questions caused by the February column which discussed polarization (Milligan, IEEE Antennas. Propag. Mag., vol.38, no.1, p.56-8, 1996)  相似文献   
24.
25.
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   
26.
According to some ultrastructural studies, the pericapillary axon terminals in the central nervous system (CNS) are functionally connected with the capillary vessel wall. Thus, it may be expected that the population of pericapillary axon terminals will be morphologically distinct from the terminals at a further distance from the capillary walls. To test this hypothesis, morphometrical analysis of 3,048 axon terminals was performed, comparing terminals situated in the close vicinity of the capillary vessel with those at a distance from the vessels in the lateral, basal, medial, central and cortical nuclei of the amygdaloid body of eight cats. The cross-sectional area and circumference of each identified axon terminal profile were measured, and the shape of synaptic vesicles and the presence of synaptic contacts and granular vesicles were recorded. The statistical evaluation of results was performed by means of the Newman-Keuls' test, Wilcoxon's test, Fisher's contingency-table test and the test for two coefficients of structure. The morphometric examination revealed two ultrastructurally distinct groups of axon terminals, pericapillary and distant terminals, in all the nuclei of the amygdaloid body. The differentiating features were the shape of the synaptic vesicles, the number of synaptic contacts, and the size of the axon terminals. These results further support the hypothesis of a functional connection between axon terminals and the capillary vessel wall in the CNS.  相似文献   
27.
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   
28.
29.
A method is described for experimentally determining the dose rate created in building bricks by incorporated natural radionuclides. It was established using the thermoluminescence dosimetry method that the measured dose rate depends on the detector thickness, the mass of the ceramic product investigated, and the irradiation geometry. The contributions to the measured dose of weakly penetrating α and β radiation and hard ψ radiation are separated, the ratio between them depending on the experimental conditions. Translated from Izmeritel'naya Tekhnika, No. 7, pp. 62–66, July, 1996.  相似文献   
30.
Test Case Generation as an AI Planning Problem   总被引:6,自引:0,他引:6  
While Artificial Intelligence techniques have been applied to a variety of software engineering applications, the area of automated software testing remains largely unexplored. Yet, test cases for certain types of systems (e.g., those with command language interfaces and transaction based systems) are similar to plans. We have exploited this similarity by constructing an automated test case generator with an AI planning system at its core. We compared the functionality and output of two systems, one based on Software Engineering techniques and the other on planning, for a real application: the StorageTek robot tape library command language. From this, we showed that AI planning is a viable technique for test case generation and that the two approaches are complementary in their capabilities.  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