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   658955篇
  免费   4651篇
  国内免费   1496篇
化学   320435篇
晶体学   9250篇
力学   35763篇
综合类   24篇
数学   97156篇
物理学   202474篇
  2021年   5641篇
  2020年   6102篇
  2019年   6969篇
  2018年   13429篇
  2017年   13728篇
  2016年   15053篇
  2015年   7276篇
  2014年   11845篇
  2013年   26656篇
  2012年   22872篇
  2011年   31031篇
  2010年   22139篇
  2009年   22319篇
  2008年   28643篇
  2007年   30439篇
  2006年   21161篇
  2005年   21504篇
  2004年   18976篇
  2003年   17765篇
  2002年   16743篇
  2001年   17193篇
  2000年   13369篇
  1999年   10176篇
  1998年   8865篇
  1997年   8675篇
  1996年   8208篇
  1995年   7381篇
  1994年   7326篇
  1993年   7125篇
  1992年   7496篇
  1991年   8093篇
  1990年   7715篇
  1989年   7698篇
  1988年   7475篇
  1987年   7276篇
  1986年   6961篇
  1985年   8880篇
  1984年   9201篇
  1983年   7794篇
  1982年   8081篇
  1981年   7586篇
  1980年   7155篇
  1979年   7831篇
  1978年   8136篇
  1977年   7994篇
  1976年   8011篇
  1975年   7685篇
  1974年   7471篇
  1973年   7866篇
  1972年   5838篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Modal solutions of planar photonic crystal waveguides with rectangular air-holes are presented by using a rigorous full-vectorial finite element-based approach. The effective indices, mode field profiles, spot-sizes, power confinements, modal hybridness, beat lengths and group velocity dispersions are shown for the fundamental and higher order modes of the quasi-TE and TM polarizations.  相似文献   
992.
The results of the elemental analysis of blood serum are often used for the diagnosis of different diseases associated with derangements of mineral metabolism. In this work, we studied the main sources of a systematic error in the atomic-emission spectrometric (AES) analysis of blood serum and developed a procedure for the AES determination of Ca, Cu, Fe, Mg, P, and Zn in the human blood serum. The repeatability relative standard deviations of determinations varied from 10 to 24%.  相似文献   
993.
994.
In view of the growing interest for non-destructive tests of materials, geodynamical monitoring and in general remote sensing, there is a great effort to bring practical optical sensors from research labs to industrial and environmental applications. In this paper, we employ digital holographic technique as an efficient tool for evaluating the strain measurement capability of fiber Bragg gratings (FBG). A cantilever beam has been employed as a test structure under loading test. The strain measurements results obtained by fiber-based sensors have been compared to those obtained by using full-field digital holographic technique and point-wise strain gauge sensors glued on the same cantilever beam. A simple theoretical model is also presented to interpret and compare the experimental results coming from different techniques.  相似文献   
995.
The modified Gross–Pitaevskii equation was derived and solved to obtain the 1D solution in the zero-energy limit. This stationary solution could account for the dominated contributions due to the kinetic effect as well as the chemical potential in inhomogeneous Bose gases.  相似文献   
996.
A new approach to identify the independent amplitudes along with their partial wave multipole expansions, for photo-and electro-production is suggested, which is generally applicable to mesons with arbitrary spin-parity. These amplitudes facilitate direct identification of different resonance contributions.   相似文献   
997.
We present the results of a spectroscopic study of a nonequilibrium plasma in a Hall accelerator, in particular for such an important parameter as the electron temperature. For the studied conditions, we used the semicoronal equilibrium model, which relates the intensity ratios for two successive ionization steps for the same element. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 93–96, January–February, 2007.  相似文献   
998.
999.
1000.
The synthesis of polyaniline via the oxidation of aniline with ammonium bisulfate in water and formic acid was monitored potentiometrically by following the yield and changes in the electric conductivity of the polymer. Three basic stages of the process were determined, including the buildup of oligomeric quinone imines, chain propagation via aniline addition of quinone imine groups, and postpolymerization. The oligomeric intermediate products, substituted quinone imines, were isolated. On the basis of IR and NMR data, the presence of tri-and tetrasubstituted aromatic groups and phenazine structural units in the polyaniline chain was revealed.  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