全文获取类型
收费全文 | 35302篇 |
免费 | 336篇 |
国内免费 | 296篇 |
专业分类
化学 | 14929篇 |
晶体学 | 299篇 |
力学 | 1623篇 |
综合类 | 12篇 |
数学 | 9942篇 |
物理学 | 9129篇 |
出版年
2021年 | 107篇 |
2020年 | 123篇 |
2019年 | 120篇 |
2018年 | 1272篇 |
2017年 | 1501篇 |
2016年 | 879篇 |
2015年 | 679篇 |
2014年 | 633篇 |
2013年 | 991篇 |
2012年 | 3487篇 |
2011年 | 2736篇 |
2010年 | 2023篇 |
2009年 | 1780篇 |
2008年 | 935篇 |
2007年 | 1012篇 |
2006年 | 999篇 |
2005年 | 4841篇 |
2004年 | 4229篇 |
2003年 | 2591篇 |
2002年 | 697篇 |
2001年 | 405篇 |
2000年 | 205篇 |
1999年 | 271篇 |
1998年 | 185篇 |
1997年 | 136篇 |
1996年 | 129篇 |
1995年 | 125篇 |
1994年 | 113篇 |
1993年 | 85篇 |
1992年 | 224篇 |
1991年 | 194篇 |
1990年 | 186篇 |
1989年 | 145篇 |
1988年 | 131篇 |
1987年 | 86篇 |
1986年 | 67篇 |
1985年 | 101篇 |
1984年 | 92篇 |
1983年 | 60篇 |
1982年 | 66篇 |
1981年 | 55篇 |
1980年 | 64篇 |
1979年 | 79篇 |
1978年 | 66篇 |
1977年 | 64篇 |
1976年 | 133篇 |
1975年 | 75篇 |
1974年 | 72篇 |
1973年 | 86篇 |
1972年 | 62篇 |
排序方式: 共有10000条查询结果,搜索用时 500 毫秒
31.
32.
Paramagnetic pyrroline and 1,2,3,6-tetrahydropyridine derivatives of BODIPY and their diamagnetic analogs have been synthesized and characterized as novel redox double sensor and cation sensitive reagents. 相似文献
33.
34.
François Ledrappier Mark Pollicott 《Bulletin of the Brazilian Mathematical Society》2005,36(2):143-176
In this paper we study the ergodic properties of the linear action of lattices Γ of SL(2,ℚp) on ℚp × ℚp and distribution results for orbits of Γ. Following Serre, one can define a “geodesic flow” for an associated tree (actually
associated to GL(2,ℚp)). The approach we use is based on an extension of this approach to “frame flows” which are a natural compact group extension
of the geodesic flow. 相似文献
35.
We prove that RANDOM EDGE, the simplex algorithm that always chooses a random improving edge to proceed on, can take a mildly exponential number of steps in the model of abstract objective functions (introduced by Williamson Hoke [Completely unimodal numberings of a simple polytope, Discrete Appl. Math. 20 (1988) 69-81.] and by Kalai [A simple way to tell a simple polytope from its graph, J. Combin. Theory Ser. A 49(2) (1988) 381-383.] under different names). We define an abstract objective function on the n-dimensional cube for which the algorithm, started at a random vertex, needs at least exp(const·n1/3) steps with high probability. The best previous lower bound was quadratic. So in order for RANDOM EDGE to succeed in polynomial time, geometry must help. 相似文献
36.
Jean-Franç ois Coulombel Thierry Goudon 《Transactions of the American Mathematical Society》2007,359(2):637-648
We construct global smooth solutions to the multidimensional isothermal Euler equations with a strong relaxation. When the relaxation time tends to zero, we show that the density converges towards the solution to the heat equation.
37.
The Dantzig-Wolfe reformulation principle is presented based on the concept of generating sets. The use of generating sets allows for an easy extension to mixed integer programming. Moreover, it provides a unifying framework for viewing various column generation practices, such as relaxing or tightening the column generation subproblem and introducing stabilization techniques. 相似文献
38.
This paper establishes a link between a generalized matrix Matsumoto-Yor (MY) property and the Wishart distribution. This link highlights certain conditional independence properties within blocks of the Wishart and leads to a new characterization of the Wishart distribution similar to the one recently obtained by Geiger and Heckerman but involving independences for only three pairs of block partitionings of the random matrix.In the process, we obtain two other main results. The first one is an extension of the MY independence property to random matrices of different dimensions. The second result is its converse. It extends previous characterizations of the matrix generalized inverse Gaussian and Wishart seen as a couple of distributions.We present two proofs for the generalized MY property. The first proof relies on a new version of Herz's identity for Bessel functions of matrix arguments. The second proof uses a representation of the MY property through the structure of the Wishart. 相似文献
39.
Daniel Pa?ca 《Journal of Mathematical Analysis and Applications》2007,325(1):90-100
Some existence results are obtained for periodic solutions of nonautonomous second-order differential inclusions systems with p-Laplacian. 相似文献
40.
Jun Fujii Giancarlo Panaccione Giorgio Rossi Giancarlo Trimarchi 《Surface science》2006,600(18):3884-3887
Bulk carbon impurities segregate at the Fe(1 0 0) surface and, upon thermal annealing, can form metastable surface phases with local and long range order and peculiar electronic properties. We present a surface science study of C-segregated Fe(1 0 0) with scanning tunneling microscopy, angle resolved photoemission, and ab initio calculations of the surface structure and electron states. In particular the c(3√2 × √2) structure, observed for 0.67 atomic layers of C segregated at the iron surface, is found to be due to self-organized carbon stripes made of zig-zag chains. The strong hybridization between C and Fe was observed in ARPES spectra. 相似文献