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   384039篇
  免费   3632篇
  国内免费   1800篇
化学   178206篇
晶体学   5002篇
力学   20791篇
综合类   61篇
数学   76340篇
物理学   109071篇
  2020年   1899篇
  2019年   2037篇
  2018年   18824篇
  2017年   19401篇
  2016年   12306篇
  2015年   4127篇
  2014年   4171篇
  2013年   9898篇
  2012年   14876篇
  2011年   29172篇
  2010年   17723篇
  2009年   17967篇
  2008年   24065篇
  2007年   28901篇
  2006年   9522篇
  2005年   15650篇
  2004年   11994篇
  2003年   11470篇
  2002年   8684篇
  2001年   7232篇
  2000年   5784篇
  1999年   3996篇
  1998年   3398篇
  1997年   3346篇
  1996年   3560篇
  1995年   2976篇
  1994年   3030篇
  1993年   2879篇
  1992年   3082篇
  1991年   3151篇
  1990年   2939篇
  1989年   2852篇
  1988年   2820篇
  1987年   2767篇
  1986年   2752篇
  1985年   3664篇
  1984年   3708篇
  1983年   3097篇
  1982年   3410篇
  1981年   3109篇
  1980年   2973篇
  1979年   3133篇
  1978年   3355篇
  1977年   3303篇
  1976年   3314篇
  1975年   3005篇
  1974年   3111篇
  1973年   3203篇
  1972年   2434篇
  1971年   1954篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 3, pp. 438–444, March, 1991.  相似文献   
192.
We prove that a spread S over a locally compact nondlscrete field F defines a topological translation plane if and only if the spread is compact. For F=R, this is implicit in Breuning's thesis [Bre], cf. [B 2]. For the proof, we describe the point set of the projective translation plane as a quotient space of some projective space, with identifications taking place in one hyperplane. This is new even for F=R.  相似文献   
193.
The paper introduces a special system calibration technology in s-parameters measurement of microwave and millimeter wave devices. The 8-term errors module is built by analyzing the signals flowing in the measurement system. Then the calibration technology using non-standard kits is designed on the base. Finally, the experiment using the calibration technology is introduced.  相似文献   
194.
Partially water-swellable polymer networks were synthesized on the basis of poly(acrylic acid) and various macrodiisocyanates. Hydrophilic and hydrophobic local regions were revealed in swollen networks (hydrogels) by means of the spin probe technique. The local mobility in hydrophobic regions depends on the macrodiisocyanate structure; however, it is substantially lower than that in hydrophilic regions for all gels. It was assumed that the presence of hydrophobic and hydrophilic regions and the difference in their local dynamics must have a substantial effect on the pharmacokinetics of release of drugs immobilized in these hydrogels.  相似文献   
195.
The quantitative rainbow schlieren deflectometry (RSD) technique was applied to measure temperature and oxygen concentration in an axisymmetric hydrogen gas-jet diffusion flame burning in quiescent air at fuel jet exit Reynolds number of 70. Schlieren measurements were compared with conventional measurements using a thermocouple and a gas-sampling probe. Good agreement between the two measurement techniques was achieved on the fuel-lean side of the flame.  相似文献   
196.
Flow regime identification in a two-phase flow using wavelet transform   总被引:5,自引:0,他引:5  
This study addresses the problem of the automatic flow regime identification in two-phase flows in pipes. A novel wavelet transform-based approach is proposed and validated using time series of differential pressure fluctuations. The experimental data on the differential pressure measured in a vertically installed Venturi meter for air-water flow were analyzed and found to be appropriate for flow regime identification. The wavelet spectrum of the measured signal is shown to characterize the flow patterns completely, and the vector of the wavelet variances is proposed as the characteristic vector for use in an on-line flow regime identification system.  相似文献   
197.
In this paper, finite-dimensional recursive filters for space-time Markov random fields are derived. These filters can be used with the expectation maximization (EM) algorithm to yield maximum likelihood estimates of the parameters of the model.  相似文献   
198.
199.
200.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 6, pp. 970–975, June, 1991.  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