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   204110篇
  免费   1712篇
  国内免费   592篇
化学   102312篇
晶体学   3340篇
力学   9287篇
综合类   5篇
数学   22470篇
物理学   69000篇
  2021年   1656篇
  2020年   1797篇
  2019年   1998篇
  2018年   2699篇
  2017年   2601篇
  2016年   3765篇
  2015年   2304篇
  2014年   3613篇
  2013年   9085篇
  2012年   7240篇
  2011年   8734篇
  2010年   6040篇
  2009年   5908篇
  2008年   7911篇
  2007年   8079篇
  2006年   7725篇
  2005年   6891篇
  2004年   6424篇
  2003年   5650篇
  2002年   5491篇
  2001年   6424篇
  2000年   4931篇
  1999年   3794篇
  1998年   3038篇
  1997年   3045篇
  1996年   2791篇
  1995年   2613篇
  1994年   2462篇
  1993年   2337篇
  1992年   2691篇
  1991年   2671篇
  1990年   2600篇
  1989年   2396篇
  1988年   2449篇
  1987年   2448篇
  1986年   2279篇
  1985年   2960篇
  1984年   3215篇
  1983年   2631篇
  1982年   2801篇
  1981年   2771篇
  1980年   2637篇
  1979年   2727篇
  1978年   2821篇
  1977年   2819篇
  1976年   2886篇
  1975年   2670篇
  1974年   2644篇
  1973年   2776篇
  1972年   1763篇
排序方式: 共有10000条查询结果,搜索用时 5 毫秒
51.
52.
Summary High-purity indium was analysed by spark source mass spectrometry, using electrical and photoplate detection. For the calibration of the differences in elemental sensitivity, a standard sample was prepared in which 10 impurities were determined by graphite furnace atomic absorption spectrometry. In this way accuracies of less than 40% were obtained for relatively homogeneous elements at ppm and sub-ppm level. About 40 elements could be determined with detection limits of 10 to 30 ppb. Two pattern recognition methods, principal component analysis and clustering analysis, were applied to obtain information on trace element distribution, which indicated that a number of elements were strongly spatially correlated in the analysed sample.
Chemische Analyse und Verteilungsbestimmung von Spurenelementen in Indium-Matrix durch Funkenquellen-Massenspektrometrie

On leave from: Department of Chemistry, Nanjing Normal University, Nanjing, People's Republic of China  相似文献   
53.
A semiclassical theory of electromagnetically induced transparency in a Bose-Einstein condensate is considered. A nonlinear Schrödinger equation that describes the interaction of the Bose-Einstein condensate with an electromagnetic field is derived. An analysis of the obtained solutions to this equation demonstrates a decrease in the group velocity of the light pulse.  相似文献   
54.
Optics and Spectroscopy - The fluorescence of the nematic liquid crystal n-butyl-n′-methoxyazoxybenzene (BMAOB) in the form of a layer and in porous glasses with pores of different diameter...  相似文献   
55.
Disordered Sr2FeMoO6 shows a drastic reduction in saturation magnetization compared to highly ordered samples, moreover magnetization as a function of the temperature for different disordered samples shows qualitatively different behaviours. We investigate the origin of such diversity by performing spatially resolved photoemission spectroscopy on various disordered samples. Our results establish that extensive electronic inhomogeneity, arising most probably from an underlying chemical inhomogeneity in disordered samples, is responsible for the observed magnetic inhomogeneity. It is further pointed out that these inhomogeneities are connected with composition fluctuations of the type Sr2Fe1+x Mo1-x O6 with Fe-rich (x > 0) and Mo-rich (x < 0) regions. Dedicated to Prof J Gopalakrishnan on his 62nd birthday.  相似文献   
56.
57.
An interconnection strategy with built-in adaptive controllersis presented which achieves synchronization of scalar linearsystems: the closed-loop network forces all outputs to followthe same signal asymptotically while maintaining the open-loopcharacteristics. In the design of the output feedback controllers,no knowledge of system parameters is assumed, but each systemmust have the same poles and be high-gain-stable. The proofof the main theorem relies critically on derived systems-theoreticresults and the special system topology as a network of interconnectedsystems. The topology is explained by first solving the simplerproblem of signal synchronization.  相似文献   
58.
A formulation of an implicit characteristic-flux-averaging method for the unsteady Euler equations with real gas effects is presented. Incorporation of a real gas into a general equation of state is achieved by considering the pressure as a function of density and specific internal energy. The Ricmann solver as well as the flux-split algorithm are modified by introducing the pressure derivatives with respect to density and internal energy. Expressions for calculating the values of the flow variables for a real gas at the cell faces are derived. The Jacobian matrices and the eigenvectors are defined for a general equation of state. The solution of the system of equations is obtained by using a mesh-sequencing method for acceleration of the convergence. Finally, a test case for a simple form of equation of state displays the differences from the corresponding solution for an ideal gas.  相似文献   
59.
60.
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