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   6482篇
  免费   163篇
  国内免费   57篇
化学   4075篇
晶体学   112篇
力学   174篇
数学   919篇
物理学   1422篇
  2021年   49篇
  2020年   69篇
  2019年   53篇
  2017年   44篇
  2016年   125篇
  2015年   98篇
  2014年   128篇
  2013年   234篇
  2012年   229篇
  2011年   323篇
  2010年   165篇
  2009年   154篇
  2008年   245篇
  2007年   244篇
  2006年   221篇
  2005年   220篇
  2004年   203篇
  2003年   172篇
  2002年   149篇
  2001年   93篇
  2000年   114篇
  1999年   77篇
  1998年   69篇
  1997年   79篇
  1996年   90篇
  1995年   81篇
  1994年   73篇
  1993年   73篇
  1992年   77篇
  1991年   81篇
  1990年   71篇
  1989年   72篇
  1988年   93篇
  1987年   100篇
  1986年   83篇
  1985年   88篇
  1984年   76篇
  1983年   81篇
  1982年   72篇
  1981年   102篇
  1980年   78篇
  1979年   93篇
  1978年   129篇
  1977年   93篇
  1976年   95篇
  1975年   54篇
  1974年   73篇
  1973年   74篇
  1972年   43篇
  1968年   42篇
排序方式: 共有6702条查询结果,搜索用时 46 毫秒
1.
Annals of Global Analysis and Geometry - In this paper, we characterize round spheres in the Euclidean space under some suitable conditions on the r-mean curvature.  相似文献   
2.
3.
Synthesis of optically active sesquiterpenes with a eudesmane C-skeleton from the chiral starting material thujone involves transformation of a tricyclic intermediate (1R,2R,4S)-1,7-dimethyl-4-(1-methylethyl)tricyclo[4.4.0.02,4]dec-6-en-8-one ( 2 ) into the bicyclic compound β -cyperone ( 5 ). Hydroxylation of 2 at C(5) or C(11) permits subsequent opening of the cyclopropane ring and rearrangement to β -cyperone. In this publication, studies involving hydroxylation of 2 by fungal cultures are presented. The resultant products are useful intermediates in efficient synthesis of eudesmane sesquiterpenes. Of five fungi tested, Rhizopus oryzae ATCC 11145 proved most versatile. It hydroxylates at the exocyclic C(11) position in high yield (70%) and, to a lesser extent, at C(5) (5%). Enzymatic activity appears at the end of growth phase and at least 2.2 g of 2 per liter can be metabolized without significant loss of product yield. A second fungus, Cunninghamella echinulata ATCC 9244, proved most useful for hydroxylation of derivatives of 2 for the preparation of derivatives of β -cyperone, although product yields were low (2–20%), some derivatives were nonreactive, and hydroxylation at C(9) occurred. The relationship between precursor structure and enzyme affinity is discussed.  相似文献   
4.
In complex biological systems, entities that are conceptually distinct but empirically related—such as sunlight and plant growth or antigene and immune response—are being explicitly linked through the identification of highly specific uninterrupted interaction sequences that take place between their macromolecular system components. These uninterrupted sequences of causation include common elements that are shared by the empirically related but conceptually distinct entities. Through the identification of specific shared elements, “conceptual continuity” is established between these entities. Examples are introduced to suggest that in sociopolitical systems, an analogous conceptual continuity can be established between distinct sociopolitical entities. The identification of specific shared elements, essential for the well being of each of the entities, can play a significant role in resolving conflicts between those separated by seemingly insurmountable obstacles such as race or religion or ideology. © 2006 Wiley Periodicals, Inc. Complexity 11:20–24, 2006  相似文献   
5.
In this paper we consider an initial boundary value problem for a reaction-diffusion equation under nonlinear and nonlocal Robin type boundary condition. Assuming the existence of an ordered pair of upper and lower solutions we establish a generalized quasilinearization method for the problem under consideration whose characteristic feature consists in the construction of monotone sequences converging to the unique solution within the interval of upper and lower solutions, and whose convergence rate is quadratic. Thus this method provides an efficient iteration technique that produces not only improved approximations due to the monotonicity of its iterates, but yields also a measure of the convergence rate.  相似文献   
6.
7.
In this paper we present a method to solve numerically elliptic problems with multi-scale data using multiple levels of not necessarily nested grids. The method consists in calculating successive corrections to the solution in patches whose discretizations are not necessarily conforming. It resembles the FAC method (see Math. Comp. 46 (174) (1986) 439–456) and its convergence is obtained by a domain decomposition technique (see Math. Comp. 57 (195) (1991) 1–21). However it is of much more flexible use in comparison to the latter. To cite this article: R. Glowinski et al., C. R. Acad. Sci. Paris, Ser. I 337 (2003).  相似文献   
8.
9.
10.
Ohne ZusammenfassungDie folgende Untersuchung trug der leider so früh dem Dienste der Wissenschaft durch den Tod entrissene Privatdocent Dr. Hierholzer dahier (gest. 13. Sept. 1871) einem Kreise befreundeter Mathematiker vor. Um sie vor Vergessenheit zu bewahren, musste sie bei dem Mangel jeder schriftlichen Aufzeichnung aus dem Gedächtniss wieder hergestellt werden, was ich unter Beihilfe meines verehrten Collegen Lüroth durch das Folgende möglichst getreu auszuführen suchte.  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