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   311327篇
  免费   1998篇
  国内免费   646篇
化学   145454篇
晶体学   4745篇
力学   17265篇
综合类   33篇
数学   43844篇
物理学   102630篇
  2021年   3263篇
  2020年   3578篇
  2019年   4362篇
  2018年   6382篇
  2017年   6563篇
  2016年   8237篇
  2015年   3800篇
  2014年   7214篇
  2013年   12847篇
  2012年   10686篇
  2011年   12438篇
  2010年   10450篇
  2009年   10578篇
  2008年   12022篇
  2007年   11829篇
  2006年   10480篇
  2005年   9134篇
  2004年   8874篇
  2003年   8277篇
  2002年   8615篇
  2001年   8073篇
  2000年   6438篇
  1999年   4771篇
  1998年   4476篇
  1997年   4309篇
  1996年   3945篇
  1995年   3513篇
  1994年   3570篇
  1993年   3538篇
  1992年   3541篇
  1991年   3947篇
  1990年   3965篇
  1989年   3930篇
  1988年   3669篇
  1987年   3758篇
  1986年   3431篇
  1985年   4059篇
  1984年   4299篇
  1983年   3639篇
  1982年   3855篇
  1981年   3512篇
  1980年   3274篇
  1979年   3750篇
  1978年   3798篇
  1977年   4007篇
  1976年   4066篇
  1975年   3788篇
  1974年   3633篇
  1973年   3798篇
  1972年   3242篇
排序方式: 共有10000条查询结果,搜索用时 31 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.
Electron transport in a three-dimensional quantum wire is analyzed by taking into account electron scattering by a single point impurity. It is shown that the magnetoconductance plotted versus chemical potential μ has narrow peaks and closely located peaks separated by a dip when the scattering length is positive and negative, respectively. The peaks lie near the conductance steps. The thermopower plotted versus μ has narrow peaks and closely located peaks separated by a dip when the scattering length is positive and negative, respectively.  相似文献   
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.
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   
996.
997.
998.
999.
1000.
The phase transitions and phase state of hydroxypropylcellulose mixtures with ethanol and acetic acid under static conditions and in the shear field have been studied by the turbidity-point method and polarization microscopy with the use of a polarization-photoelectric setup and a modified plastoviscometer. The deformation of solutions leads to a decrease in the temperature of mesomorphic phase formation and to a change in the type of liquid crystals from cholesteric to nematic.  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