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   229106篇
  免费   1541篇
  国内免费   476篇
化学   104181篇
晶体学   3106篇
力学   12119篇
综合类   5篇
数学   37168篇
物理学   74544篇
  2018年   10137篇
  2017年   11053篇
  2016年   5620篇
  2015年   1940篇
  2014年   1452篇
  2013年   4907篇
  2012年   8018篇
  2011年   17724篇
  2010年   10451篇
  2009年   10330篇
  2008年   15282篇
  2007年   19173篇
  2006年   4246篇
  2005年   11408篇
  2004年   7195篇
  2003年   6775篇
  2002年   4557篇
  2001年   3744篇
  2000年   2996篇
  1999年   2236篇
  1998年   1930篇
  1997年   1891篇
  1996年   1980篇
  1995年   1878篇
  1994年   1639篇
  1993年   1565篇
  1992年   1755篇
  1991年   1738篇
  1990年   1680篇
  1989年   1698篇
  1988年   1706篇
  1987年   1700篇
  1986年   1602篇
  1985年   2177篇
  1984年   2322篇
  1983年   1933篇
  1982年   2243篇
  1981年   2071篇
  1980年   2107篇
  1979年   2134篇
  1978年   2258篇
  1977年   2076篇
  1976年   2142篇
  1975年   2074篇
  1974年   1908篇
  1973年   2174篇
  1972年   1304篇
  1969年   990篇
  1968年   1150篇
  1967年   1131篇
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
991.
There are essentially two schools of thought regarding the function of decision support systems. One is that the main purpose is to support the decision-maker in whatever style of decision-making he or she wishes. The other is that the support, while suiting the decision-maker's individual style, must also be based on an appropriate theoretical paradigm. The work with students of decision support systems reported here suggests that the latter, normative, view is not one which comes naturally to many of the students, even when working on an example where it seemed relatively easy to incorporate. Other conclusions are also presented, relating to the choice of software for decision support system development, the process of teaching about decision support systems, and group formation.  相似文献   
992.
Microstructures of nickel surfaces electrodeposited on indium tin oxides coated glasses are investigated using atomic force microscopy. The fractal dimension D and Hurst exponent H of the nickel surface images are determined from a frequency analysis method proposed by Aguilar et al. [J. Microsc. 172 (1993) 233] and from Hurst rescaled range analysis. The two methods are found to give the same value of the fractal dimension D∼2.0. The roughness exponent α and growth exponent β that characterize scaling behaviors of the surface growth in electrodeposition are calculated using the height-difference correlation function and interface width in Fourier space. The exponents of α∼1.0 and β∼0.8 show that the surface growth does not belong to the universality classes theoretically predicted by statistical growth models.  相似文献   
993.
As “rapporteur” for the papers submitted to this conference in the general area of muonium chemistry, I briefly review the major developments since μSR86, and attempt to show how the papers presented at μSR90 relate to each other and work published in the intervening years. Some topics are discussed in more detail than others, reflecting my own interests and views on what is of current importance. Nevertheless, I try to cover all current research in muonium chemistry. The major areas are: early events following muon thermalization, including subsequent loss of muon polarization (the “missing fraction”); molecular structure and dynamics, primarily of muonium-substituted free radicals: and reaction kinetics.  相似文献   
994.
In this paper we deal with the numerical solution of movingboundary problems of two-phase Stefan type. Based on an implicitdiscretization in time and the use of continuous, piecewiselinear finite elements in the space variables with respect tothe weak formulation of the problem, a globally convergent multi-gridalgorithm is developed. That algorithm strongly relies on thevariational characterization of the fully discretized problemas the unconstrained minimization of a subdifferentiable convexobjective functional. Numerical results indicate a significantimprovement in efficiency compared with previous multi-gridapproaches.  相似文献   
995.
We have investigated the interaction of phonons with a 2DEG in the FQH regime with phonon drag thermoelectric power (TEP). We find that the TEP at filling factors with the same even denominator is identical and at other even denominator filling factors they differ only by a constant. Assuming these states to be Composite Fermions (CF), we can explain our observations by extending a zero magnetic field theory for phonon drag to the CF-phonon interaction. This analysis is further corroborated by the observed T4 dependence of the CF TEP.  相似文献   
996.
High-spin states in196Pb have been populated using the reaction170Er(30Si,4n). The previously observed shears bands in this nucleus have been extended and some of their transitions have been reordered. They now form regular bands with band crossings. One of the bands splits into two pathways at high spin.  相似文献   
997.
998.
Device alternatives for millimeter-wave beam control arrays are examined. For the control function, a wide range of semiconductor device as well as bulk material alternatives are considered. In addition, alternatives to the traditional metal strip are considered for the passive electromagnetic array element. This work should provide a broader perspective regarding the choices available for the optimized design of new beam control arrays.  相似文献   
999.
A semianalytical model for capacitively coupled radio frequency (RF) sheaths of asymmetric (unequal electrode area) systems has been developed. It can be applied in the high-frequency (ω > ω pi) regime at different pressures. An analytical approximation to the pressure-dependent ion density profile is used. The time-varying electric field and potential within the sheath are obtained by solving Poisson's equation. The current balance and zero net DC current conditions are applied to solve for the RF sheath parameters and DC bias voltage. The DC voltage ratio between the powered and grounded electrode sheaths increases as the pressure decreases, which results in a larger DC bias voltage at lower pressures  相似文献   
1000.
Separation of non UV-absorbing cations by capillary electrophoresis   总被引:1,自引:0,他引:1  
Summary A new buffer system for the separation of cations with capillary electrophoresis using indirect UV-detection is described. p-Aminopyridine can be used in the wide pH-range between 3 and 10. High-speed separations of positively charged non-UV absorbing ions are possible. Separation of ions with similar mobilities can be achieved by the addition of complexation reagents. The separation of potassium and ammonium is possible either with the addition of crown ether or at high pH-values. Transition metals can be separated by adding 2-hydroxybutyric acid to the buffer.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday  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