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   446426篇
  免费   4964篇
  国内免费   1809篇
电工技术   7723篇
综合类   640篇
化学工业   65893篇
金属工艺   19415篇
机械仪表   13999篇
建筑科学   9744篇
矿业工程   3338篇
能源动力   10841篇
轻工业   32999篇
水利工程   5504篇
石油天然气   11961篇
武器工业   64篇
无线电   50650篇
一般工业技术   92776篇
冶金工业   80255篇
原子能技术   12286篇
自动化技术   35111篇
  2021年   3862篇
  2019年   3711篇
  2018年   6535篇
  2017年   6692篇
  2016年   7081篇
  2015年   4344篇
  2014年   7341篇
  2013年   19093篇
  2012年   11614篇
  2011年   15563篇
  2010年   12276篇
  2009年   13987篇
  2008年   14350篇
  2007年   14296篇
  2006年   12313篇
  2005年   11368篇
  2004年   10954篇
  2003年   10625篇
  2002年   10286篇
  2001年   10452篇
  2000年   9843篇
  1999年   10187篇
  1998年   25084篇
  1997年   17699篇
  1996年   13573篇
  1995年   10343篇
  1994年   9076篇
  1993年   9309篇
  1992年   6861篇
  1991年   6653篇
  1990年   6396篇
  1989年   6380篇
  1988年   6094篇
  1987年   5434篇
  1986年   5491篇
  1985年   6063篇
  1984年   5670篇
  1983年   5320篇
  1982年   4839篇
  1981年   4890篇
  1980年   4915篇
  1979年   4736篇
  1978年   4764篇
  1977年   5135篇
  1976年   6479篇
  1975年   4168篇
  1974年   4055篇
  1973年   4123篇
  1972年   3554篇
  1971年   3192篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
91.
Translated from Atomnaya Énergiya, Vol. 67, No. 2, pp. 111–113, August, 1989.  相似文献   
92.
测定钠中杂质的手动阻塞计的研究   总被引:1,自引:1,他引:0  
文章介绍了测定钠中杂质浓度的手动阻塞计的原理、装置和实验结果。为了减少测量误差,我们研究了影响准确测定阻塞温度的因素,并且找到了减少测量误差的办法。在同样的杂质饱和温度下,该阻塞计测得的高、低阻塞温度所对应的杂质浓度差是很接近的。对氧其差值为1.03ppm;对氢为0.0763ppm。  相似文献   
93.
We investigate the saturation effects of power broadening, Stark shifting, and population transfer on Stokes conversion in stimulated Raman scattering. We do not make the usual rotating wave approximation because the detuning from the next electronic state is assumed to be in the optical regime. Retaining the counter-rotating terms allows an exact determination of the pump and Stokes indexes of refraction. Steady-state solutions for the Stokes intensity and phase are obtained and the effects of making the rotating wave approximation (RWA) are discussed. Finally, we examine the behavior of these solutions for Stokes conversion in hydrogen gas when geometric propagation is appropriate.  相似文献   
94.
A direct method is described for computing a hysteresis point (double turning point) corresponding to a cusp point of a system ofn nonlinear equations inn variables depending on two parameters. By addition of two equations a minimally extended system ofn+2 nonlinear equations is constructed for which the hysteresis point is an isolated solution. An efficient implementation of Newton's method is presented not requiring evaluations of second derivatives of the original problem. Two numerical examples show the efficiency of theQ-quadratically convergent method.  相似文献   
95.
96.
Consideration was given to the decision making procedures based on the fuzzy messages of experts whose preferences on the set of collective decisions can also be fuzzy.  相似文献   
97.
98.
A method for contactless measurement of the shielding critical current density and its dependence on the external magnetic field is described and analyzed. The obtained values are compared with those measured resistively on two different samples. It is shown that the shielding critical current densityJ cs and the intergranular transport current densityJ cr are identical if the measurement conditions are similar. A degradation ofJ cs measured in the external field with AC ripple has been observed.  相似文献   
99.
Serum total cholesterol, high density lipoprotein (HDL) cholesterol, and triglyceride levels were studied in healthy male and female subjects consuming for one-week periods a diet of conventional food (CF) providing 42% of energy as fat, principally butter fat, and then in random order nutritionally complete, defined formula diets of moderate (32%) to very low (1%) fat content. Compared to CF, the formula with 32% of energy as corn oil lowered serum cholesterol by 25% and the ratio of total to HDL-cholesterol by 13%. Low (9%) and very low (1–3%) fat formulas reduced HDL-cholesterol by as much as 40%, raised the total: HDL-cholesterol ratio by about 20% and raised serum triglyceride levels by as much as 100%. When low and very low fat formulas were ingested for three weeks, these effects persisted although maximal responses occurred during the first week. These results demonstrated that a moderate fat formula diet with a high P/S ratio had a more favorable effect on serum lipid levels than various low fat formulas. Low fat conventional food diets should be studied in long-term controlled metabolic experiments before such diets are recommended to the general population for coronary heart disease or cancer prevention.  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