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   411995篇
  免费   5615篇
  国内免费   1295篇
电工技术   7182篇
综合类   2567篇
化学工业   58729篇
金属工艺   19393篇
机械仪表   16015篇
建筑科学   10782篇
矿业工程   2147篇
能源动力   9527篇
轻工业   27199篇
水利工程   4313篇
石油天然气   5054篇
武器工业   18篇
无线电   49700篇
一般工业技术   84238篇
冶金工业   60276篇
原子能技术   6434篇
自动化技术   55331篇
  2022年   1594篇
  2021年   2794篇
  2020年   2017篇
  2019年   2474篇
  2018年   23000篇
  2017年   22628篇
  2016年   16400篇
  2015年   3921篇
  2014年   5186篇
  2013年   13505篇
  2012年   12428篇
  2011年   25185篇
  2010年   21646篇
  2009年   19696篇
  2008年   20890篇
  2007年   23241篇
  2006年   8868篇
  2005年   11878篇
  2004年   9871篇
  2003年   9709篇
  2002年   7848篇
  2001年   7170篇
  2000年   6710篇
  1999年   6952篇
  1998年   17010篇
  1997年   11864篇
  1996年   9272篇
  1995年   7043篇
  1994年   6330篇
  1993年   6276篇
  1992年   4514篇
  1991年   4289篇
  1990年   4163篇
  1989年   3955篇
  1988年   3830篇
  1987年   3307篇
  1986年   3226篇
  1985年   3509篇
  1984年   3189篇
  1983年   3075篇
  1982年   2870篇
  1981年   2742篇
  1980年   2626篇
  1979年   2481篇
  1978年   2268篇
  1977年   2732篇
  1976年   3680篇
  1975年   1897篇
  1974年   1837篇
  1973年   1766篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Potential mGAT4 inhibitors derived from the lead substance (S)-SNAP-5114 have been synthesized and characterized for their inhibitory potency. Variations from the parent compound included the substitution of one of its aromatic 4-methoxy and 4-methoxyphenyl groups, respectively, with a more polar moiety, including a carboxylic acid, alcohol, nitrile, carboxamide, sulfonamide, aldehyde or ketone function, or amino acid partial structures. Furthermore, it was investigated how the substitution of more than one of the aromatic 4-methoxy groups affects the potency and selectivity of the resulting compounds. Among the synthesized test substances (S)-1-{2-[(4-formylphenyl)bis(4-methoxyphenyl)-methoxy]ethyl}piperidine-3-carboxylic acid, that features a carbaldehyde function in place of one of the aromatic 4-methoxy moieties of (S)-SNAP-5114, was found to have a pIC50 value of 5.89±0.07, hence constituting a slightly more potent mGAT4 inhibitor than the parent substance while showing comparable subtype selectivity.  相似文献   
72.
73.
Sea lice threaten the welfare of farmed Atlantic salmon and the sustainability of fish farming across the world. Chemical treatments are the major method of control but drug resistance means that alternatives are urgently needed. Selective breeding can be a cheap and effective alternative. Here, we combine experimental trials and diagnostics to provide a practical protocol for quantifying resistance to sea lice. We then combined quantitative genetics with epidemiological modelling to make the first prediction of the response to selection, quantified in terms of reduced need for chemical treatments. We infected over 1400 young fish with Lepeophtheirus salmonis, the most important species in the Northern Hemisphere. Mechanisms of resistance were expressed early in infection. Consequently, the number of lice per fish and the ranking of families were very similar at 7 and 17 days post infection, providing a stable window for assessing susceptibility to infection. The heritability of lice numbers within this time window was moderately high at 0.3, confirming that selective breeding is viable. We combined an epidemiological model of sea lice infection and control on a salmon farm with genetic variation in susceptibility among individuals. We simulated 10 generations of selective breeding and examined the frequency of treatments needed to control infection. Our model predicted that substantially fewer chemical treatments are needed to control lice outbreaks in selected populations and chemical treatment could be unnecessary after 10 generations of selection. Selective breeding for sea lice resistance should reduce the impact of sea lice on fish health and thus substantially improve the sustainability of Atlantic salmon production.  相似文献   
74.
75.
An automated system for integrated electrophysical and optical studies of semiconductor nanoheterostructures, which operates in a wide temperature range from 15 to 475 K, is designed. The setup is intended to measure the temperature and frequency admittance and electroluminescence spectra of light-emitting diode and laser chips formed on substrates of diameter up to 50.2 mm, and the distribution of parameters over the wafer. The setup includes the closed-cycle helium cryogenic station, LCR meter, and temperature controller. The characterization results of nanoheterostructures with InGaN/GaN multiple quantum wells, which are used for creating highly efficient white and blue light-emitting diodes, are presented.  相似文献   
76.
The influence of the thermal cycling conditions on the thermal-cycling creep of a TN-1 alloy and the related irreversible deformations is studied. The conditions under which an anomalous increase in the irreversible deformations begins are determined. The structural mechanism of the irreversible deformations of an equiatomic alloy is shown to be analogous to the structural mechanism of metal creep at high temperatures: it predominantly has a dislocation character. It is proposed to use the effect of anomalous increase in the deformation of materials with reversible martensitic transformations for forming parts made of these materials at low temperatures.  相似文献   
77.
78.
79.
80.
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