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   210692篇
  免费   2424篇
  国内免费   654篇
电工技术   4242篇
综合类   135篇
化学工业   29504篇
金属工艺   7720篇
机械仪表   5726篇
建筑科学   4645篇
矿业工程   843篇
能源动力   5018篇
轻工业   15288篇
水利工程   1813篇
石油天然气   2973篇
武器工业   8篇
无线电   28070篇
一般工业技术   39251篇
冶金工业   48554篇
原子能技术   3692篇
自动化技术   16288篇
  2021年   1404篇
  2020年   1065篇
  2019年   1420篇
  2018年   2288篇
  2017年   2271篇
  2016年   2365篇
  2015年   1646篇
  2014年   2821篇
  2013年   8727篇
  2012年   4862篇
  2011年   6693篇
  2010年   5314篇
  2009年   6190篇
  2008年   6673篇
  2007年   6695篇
  2006年   6144篇
  2005年   5714篇
  2004年   5591篇
  2003年   5423篇
  2002年   5240篇
  2001年   5525篇
  2000年   5123篇
  1999年   5668篇
  1998年   15830篇
  1997年   10527篇
  1996年   8156篇
  1995年   5996篇
  1994年   5248篇
  1993年   5295篇
  1992年   3616篇
  1991年   3433篇
  1990年   3409篇
  1989年   3249篇
  1988年   2950篇
  1987年   2437篇
  1986年   2494篇
  1985年   2847篇
  1984年   2518篇
  1983年   2252篇
  1982年   2072篇
  1981年   2218篇
  1980年   1941篇
  1979年   1831篇
  1978年   1823篇
  1977年   2150篇
  1976年   2834篇
  1975年   1584篇
  1974年   1498篇
  1973年   1440篇
  1972年   1206篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
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   
52.
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   
53.
54.
Strengthening of concrete prisms using the plate-bonding technique   总被引:5,自引:0,他引:5  
This paper presents the use of fracture mechanics for the plate bonding technique. Plates of steel or carbon-fibre reinforced plastic are bonded with an epoxy adhesive to rectangular concrete prisms and loaded in shear up to failure, what is normally known in fracture mechanics as mode II failure. In this special application a linear and a nonlinear approach are presented. The nonlinear equation derived for a realistic shear-deformation curve can only be used for numerical calculations. However, for simplified shear-deformation curves, the derived formula can be solved analytically. Results from tests, which are compared with the theory, are also presented.  相似文献   
55.
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   
56.
57.
58.
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   
59.
At the moment, weather forecasting is still an art — the experience and intuition of forecasters play a significant role in determining the quality of forecasting. This paper describes the development of a new approach to rainfall forecasting using neural networks. It deals with the extraction of information from radar images and an evaluation of past rain gauge records to provide shortterm rainfall forecasting. All of the meteorological data were provided by the Royal Observatory of Hong Kong (ROHK). Preprocessing procedures were essential for this neural network rainfall forecasting. The forecast of the rainfall was performed every half an hour so that a storm warning signal can be delivered to the public in advance. The network architecture is based on a recurrent Sigma-Pi network. The results are very promising, and this neural-based rainfall forecasting system is capable of providing a rain storm warning signal to the Hong Kong public one hour ahead.  相似文献   
60.
PURPOSE: To report the disappearance of traumatic macular hole in three eyes of three patients. METHODS: Clinical data of the patients were reviewed. RESULTS: The three patients were relatively young, ranging in age from 12 to 18 years old. In one eye of each patient, a small traumatic macular hole was observed at the first visit. Visual acuities ranged from 20/100 to 20/40. The macular holes resolved spontaneously 3 to 4 months after the trauma, and final visual acuity improved to 20/20 in all patients. CONCLUSION: Small traumatic macular holes in young patients can resolve spontaneously, and this can be associated with good visual recovery.  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