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   45439篇
  免费   1953篇
  国内免费   1373篇
化学   24759篇
晶体学   820篇
力学   2011篇
综合类   109篇
数学   4624篇
物理学   16442篇
  2022年   607篇
  2021年   646篇
  2020年   659篇
  2019年   736篇
  2018年   811篇
  2017年   737篇
  2016年   1112篇
  2015年   893篇
  2014年   1293篇
  2013年   2258篇
  2012年   2325篇
  2011年   2671篇
  2010年   1987篇
  2009年   1980篇
  2008年   2232篇
  2007年   2121篇
  2006年   1923篇
  2005年   1610篇
  2004年   1501篇
  2003年   1253篇
  2002年   1182篇
  2001年   1538篇
  2000年   1104篇
  1999年   944篇
  1998年   716篇
  1997年   669篇
  1996年   614篇
  1995年   566篇
  1994年   517篇
  1993年   454篇
  1992年   520篇
  1991年   510篇
  1990年   497篇
  1989年   446篇
  1988年   475篇
  1987年   446篇
  1986年   393篇
  1985年   463篇
  1984年   479篇
  1983年   352篇
  1982年   389篇
  1981年   380篇
  1980年   320篇
  1979年   401篇
  1978年   378篇
  1977年   394篇
  1976年   391篇
  1975年   342篇
  1974年   322篇
  1973年   339篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
101.
In this paper, a model of a linear multilevel programming problem with dominated objective functions (LMPPD(l)) is proposed, where multiple reactions of the lower levels do not lead to any uncertainty in the upper-level decision making. Under the assumption that the constrained set is nonempty and bounded, a necessary optimality condition is obtained. Two types of geometric properties of the solution sets are studied. It is demonstrated that the feasible set of LMPPD(l) is neither necessarily composed of faces of the constrained set nor necessarily connected. These properties are different from the existing theoretical results for linear multilevel programming problems.  相似文献   
102.
103.
In this paper, we prove convergence rates for spherical spline Hermite interpolation on the sphere Sd−1 via an error estimate given in a technical report by Luo and Levesley. The functionals in the Hermite interpolation are either point evaluations of pseudodifferential operators or rotational differential operators, the desirable feature of these operators being that they map polynomials to polynomials. Convergence rates for certain derivatives are given in terms of maximum point separation.  相似文献   
104.
105.
We study condensation of ethanol-hexanol vapour by numerical solution of kinetic equations. The number of droplets formed in unit volume is computed within self-consistent classical model. It is shown that formation of ethanol-rich droplets prevails at the initial stage of nucleation process, but in the stationary state formation of droplets near the saddle point (on cluster formation energy surface) plays the dominant role. Presented at the 6th Joint Seminar “Development of Materials Science in Research and Education”, Karlštejn, Czech Republic, 17–19 September 1996. This work was supported by Grant No. A1010615 of the Grant Agency of the Academy of Sciences of the Czech Republic.  相似文献   
106.
107.
The purpose of this paper is to give the Reid ``Roundabout Theorem' for quadratic functionals with general boundary conditions. In particular, we describe the so-called coupled point and regularity condition introduced in [16] in terms of Riccati equation solutions. Accepted 27 February 1996  相似文献   
108.
Some of the motivations for as well as the main points of the quantization of the Nappi-Witten string in the light-cone gauge are reviewed.  相似文献   
109.
Unique crystallization and melting behavior in poly(aryl ether ketone ketone) containing alternated terephthalic and isophthalic moieties were studied by time-resolved synchrotron x-ray methods. Recently, this material has been shown to exhibit three polymorphs (forms I, II, and III). In this work, we further investigated their distinctive thermal properties and found that form I is the dominating and the most thermally stable phase while form II is favored by fast nucleation conditions and is the least stable phase. On the other hand, form III represents a minor intermediate phase that usually coexists with form I and can be transferred from form II and to form I. Structural and morphological changes in form I have been followed by simultaneous wide-angle x-ray diffraction (WAXD)/small-angle x-ray scattering (SAXS) measurements during cold- or melt-crystallization and subsequent melting. In all cases, a larger dimensional change was found in the crystallographic a-axis than the b-axis during heating and cooling. This may be due to the greater lateral stress variation with respect to temperature along the a direction of the primary lamellae which is induced by either the formation of secondary lamellae or the preferential chain-folding direction in poly(aryl ether ketone ketone)s. During the phase transitions of form II ← III in the cold-crystallized specimen and form III ← I in the melt-crystallized samples, lamellar variables (long period, lamellar thickness, and invariant) obtained from SAXS remain almost constant. This indicates that the density distribution in the long spacing is independent of the melting in form II or III. For melt-crystallization, the corresponding changes in unit-cell dimensions and lamellar morphology during the annealing-induced low endotherm are most consistent with the argument that these changes are due to the melting of thin lamellar population. © 1995 John Wiley & Sons, Inc.  相似文献   
110.
Parasupersymmetric quantum mechanics is generalized to the case of an arbitrary number of parasuperchanrgesN and the order of paraquantizationp. We show that parasuperpotentials can be explicitly expressed via a single arbitrary function. Institute of Mathematics, Ukrainian Academy of Sciences, Kiev. Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 48, No. 9, pp. 1291–1294, September, 1996.  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