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   152614篇
  免费   1753篇
  国内免费   418篇
化学   84591篇
晶体学   2408篇
力学   6193篇
综合类   3篇
数学   14184篇
物理学   47406篇
  2021年   1118篇
  2020年   1305篇
  2019年   1391篇
  2018年   1750篇
  2017年   1785篇
  2016年   2763篇
  2015年   1732篇
  2014年   2541篇
  2013年   6337篇
  2012年   5315篇
  2011年   6497篇
  2010年   4430篇
  2009年   4413篇
  2008年   6142篇
  2007年   5924篇
  2006年   5815篇
  2005年   5337篇
  2004年   4743篇
  2003年   4366篇
  2002年   4213篇
  2001年   5606篇
  2000年   4007篇
  1999年   3106篇
  1998年   2146篇
  1997年   2235篇
  1996年   2109篇
  1995年   1954篇
  1994年   1942篇
  1993年   1764篇
  1992年   2239篇
  1991年   2319篇
  1990年   2152篇
  1989年   2118篇
  1988年   2093篇
  1987年   2102篇
  1986年   1925篇
  1985年   2391篇
  1984年   2408篇
  1983年   1915篇
  1982年   1926篇
  1981年   1768篇
  1980年   1753篇
  1979年   2048篇
  1978年   2106篇
  1977年   2063篇
  1976年   1992篇
  1975年   1871篇
  1974年   1850篇
  1973年   1883篇
  1972年   1241篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
71.
72.
73.
In this paper the notion of pre gs-closed functions is introduced and investigated. Presemiclosed functions are pre gs-closed but not conversely. It is shown that s-normality is preserved under continuous pre gs-closed surjections.  相似文献   
74.
The investigation of the 1s HFS provides a good possibility for testing QED effects in a combination of a strong electric and magnetic field. Here, we report about the laserspectroscopic measurements of the ground state hyperfine splitting in 207Pb81+. To handle this M1-transition in the infrared optical regime with its long lifetime, we developed a new detection technique using a bunched ion beam. For the observation of fluorescence light, a new mirror system is adapted to the emission characteristics from an ion beam at relativistic velocities. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
75.
76.
77.
We study spectral properties of discrete Schrödinger operators with potentials obtained via dimerization of a class of aperiodic sequences. It is shown that both the nature of the autocorrelation measure of a regular sequence and the presence of generic (full probability) singular continuous spectrum in the hull of primitive and palindromic (four block substitution) potentials are robust under dimerization. Generic results also hold for circle potentials. We illustrate these results with numerical studies of the quantum mean square displacement as a function of time. The numerical techniques provide a very fast algorithm for the time evolution of wave packets.  相似文献   
78.
We present a new data structure for a set of n convex simply-shaped fat objects in the plane, and use it to obtain efficient and rather simple solutions to several problems including (i) vertical ray shooting—preprocess a set of n non-intersecting convex simply-shaped flat objects in 3-space, whose xy-projections are fat, for efficient vertical ray shooting queries, (ii) point enclosure—preprocess a set C of n convex simply-shaped fat objects in the plane, so that the k objects containing a query point p can be reported efficiently, (iii) bounded-size range searching— preprocess a set C of n convex fat polygons, so that the k objects intersecting a “not-too-large” query polygon can be reported efficiently, and (iv) bounded-size segment shooting—preprocess a set C as in (iii), so that the first object (if exists) hit by a “not-too-long” oriented query segment can be found efficiently. For the first three problems we construct data structures of size O(λs(n)log3n), where s is the maximum number of intersections between the boundaries of the (xy-projections) of any pair of objects, and λs(n) is the maximum length of (n, s) Davenport-Schinzel sequences. The data structure for the fourth problem is of size O(λs(n)log2n). The query time in the first problem is O(log4n), the query time in the second and third problems is O(log3n + klog2n), and the query time in the fourth problem is O(log3n).

We also present a simple algorithm for computing a depth order for a set as in (i), that is based on the solution to the vertical ray shooting problem. (A depth order for , if exists, is a linear order of , such that, if K1, K2 and K1 lies vertically above K2, then K1 precedes K2.) Unlike the algorithm of Agarwal et al. (1995) that might output a false order when a depth order does not exist, the new algorithm is able to determine whether such an order exists, and it is often more efficient in practical situations than the former algorithm.  相似文献   

79.
80.
Thetrans-[Pt(NC5H4C(O)NHC2H4ONO2)2Cl2] complex (2) was prepared by the reaction of nicorandyl (N-nitroethoxynicotinamide), which is widely used in cardiology, with K2PtCl4 in water. The structure of2 was established by X-ray structural analysis. It was found that complex2 exhibits high antitumor activity, in particular, antimetastatic activity, unlike the analogous CuII complex with bromine atoms. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1672–1675, September, 1997.  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