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   264535篇
  免费   2917篇
  国内免费   1278篇
电工技术   4741篇
综合类   194篇
化学工业   38811篇
金属工艺   11028篇
机械仪表   8305篇
建筑科学   6266篇
矿业工程   1717篇
能源动力   6755篇
轻工业   22604篇
水利工程   3019篇
石油天然气   6029篇
武器工业   48篇
无线电   29193篇
一般工业技术   54103篇
冶金工业   48093篇
原子能技术   7301篇
自动化技术   20523篇
  2021年   2385篇
  2020年   1771篇
  2019年   2245篇
  2018年   3929篇
  2017年   4007篇
  2016年   4300篇
  2015年   2632篇
  2014年   4423篇
  2013年   12044篇
  2012年   7051篇
  2011年   9395篇
  2010年   7617篇
  2009年   8592篇
  2008年   8704篇
  2007年   8697篇
  2006年   7465篇
  2005年   6865篇
  2004年   6591篇
  2003年   6410篇
  2002年   5999篇
  2001年   6111篇
  2000年   6020篇
  1999年   6063篇
  1998年   14570篇
  1997年   10378篇
  1996年   8114篇
  1995年   6005篇
  1994年   5409篇
  1993年   5289篇
  1992年   4085篇
  1991年   3978篇
  1990年   3802篇
  1989年   3837篇
  1988年   3657篇
  1987年   3154篇
  1986年   3080篇
  1985年   3524篇
  1984年   3190篇
  1983年   3014篇
  1982年   2688篇
  1981年   2816篇
  1980年   2609篇
  1979年   2699篇
  1978年   2667篇
  1977年   3060篇
  1976年   4026篇
  1975年   2344篇
  1974年   2252篇
  1973年   2248篇
  1972年   1871篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
91.
The results of a computational experiment with a neural-net model simulating the effect of the chemical composition on the plastic properties of ÉP-450 steel are presented. It is shown that computer-aided development of reactor steel with prescribed properties is, in principle, possible.  相似文献   
92.
The dielectric and pyroelectric properties of Ge-doped (0.1 mol %) TlInS2 crystals are studied. The results demonstrate that TlInS2 is a ferroelectric relaxor. The experimental data are used to evaluate, using the Vogel–Fulcher relation, the activation energy (0.045 eV), preexponential factor (f 0 = 2 × 1013 Hz), and the dipole-freezing temperature (T F = 142 K) and to determine the temperature range of the stable relaxor (nanodomain) state and the temperature of the transition to the ferroelectric (macrodomain) state, accompanied by an anomaly in the temperature-dependent pyroelectric coefficient.  相似文献   
93.
94.
A method is developed, based on word-searching, which provides a rapid test for the statistical significance of DNA sequence similarities for use in databank searching. The method makes allowance for the lengths and dinucleotide compositions of the sequences being compared. A way is also described to calculate the power of the test, i.e. the probability of detecting a given similarity as being statistically significant. The effects on the power of the test of the scoring method, word length, sequence length, and sequence composition are examined. A novel scoring method is shown to be superior to the method currently used in most word-searching algorithms.  相似文献   
95.
96.
This article presents the development of a ceramic micro heat exchanger. Starting from its geometrical design, results obtained from a simplified simulation of the heat exchanger efficiency will be given. The alumina microcomponents were manufactured by a rapid prototyping process chain. Here, stereolithography was combined with a low‐pressure injection molding process for the rapid and precise manufacturing of ceramic components down to the micrometer range. A micro heat exchanger, joined from sintered components using a glass solder, was applied as a prototype and checked for its performance at a system pressure of 8 bar.  相似文献   
97.
There are four ecologically important river catchments that contain candidate Special Areas of Conservation (cSACs) under the Habitats Directive in the Lake District National Park located in the North of England. These are the rivers Ehen, Kent, Derwent and Eden. For each cSAC, there are defined ecological criteria that include water quality targets to protect the designated species. Stretches of the riverine cSACs in each catchment are failing to meet these and other water quality targets. The Environment Agency commissioned a study of each catchment to provide the underpinning scientific knowledge to allow it to deliver its statutory obligations under the Habitats Directive. SIMCAT river water quality models were produced and used to predict the water quality impacts resulting from a number of water quality planning scenarios aimed at achieving full compliance with the Habitats Directive and other national and EEC water quality targets. The results indicated that further controls on effluent discharges will allow the majority of targets to be met but other sources of pollution will also need to be controlled. The outcome of the study also recognised that water quality improvements alone will not necessarily produce the required improvement to the ecological interest features in each cSAC.  相似文献   
98.
99.
A rheological equation of state for wood which allows for the running values of its porosity and humidity is considered.  相似文献   
100.
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