全文获取类型
收费全文 | 24049篇 |
免费 | 1336篇 |
国内免费 | 842篇 |
专业分类
化学 | 17817篇 |
晶体学 | 192篇 |
力学 | 539篇 |
综合类 | 66篇 |
数学 | 3589篇 |
物理学 | 4024篇 |
出版年
2023年 | 220篇 |
2022年 | 317篇 |
2021年 | 430篇 |
2020年 | 532篇 |
2019年 | 524篇 |
2018年 | 463篇 |
2017年 | 460篇 |
2016年 | 937篇 |
2015年 | 870篇 |
2014年 | 963篇 |
2013年 | 1601篇 |
2012年 | 1950篇 |
2011年 | 2121篇 |
2010年 | 1297篇 |
2009年 | 1063篇 |
2008年 | 1764篇 |
2007年 | 1720篇 |
2006年 | 1526篇 |
2005年 | 1394篇 |
2004年 | 1166篇 |
2003年 | 865篇 |
2002年 | 750篇 |
2001年 | 316篇 |
2000年 | 282篇 |
1999年 | 219篇 |
1998年 | 151篇 |
1997年 | 150篇 |
1996年 | 181篇 |
1995年 | 129篇 |
1994年 | 104篇 |
1993年 | 125篇 |
1992年 | 108篇 |
1991年 | 84篇 |
1990年 | 85篇 |
1989年 | 64篇 |
1988年 | 63篇 |
1987年 | 66篇 |
1986年 | 77篇 |
1985年 | 112篇 |
1984年 | 92篇 |
1983年 | 54篇 |
1982年 | 77篇 |
1981年 | 74篇 |
1980年 | 83篇 |
1979年 | 63篇 |
1978年 | 61篇 |
1977年 | 46篇 |
1976年 | 51篇 |
1975年 | 34篇 |
1974年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
103.
Hong‐Juan Deng Yu‐Jing Fang Gao‐Wei Chen Miao‐Chang Liu Hua‐Yue Wu Jiu‐Xi Chen 《应用有机金属化学》2012,26(4):164-167
An efficient and convenient copper‐catalyzed Clauson–Kass reaction of 2,5‐dimethoxytetrahydrofuran with amines in aqueous media has been developed, providing a wide range of N‐substituted pyrroles in good yields. It is noteworthy that the Clauson–Kass reaction of 2,5‐dimethoxytetrahydrofuran with p‐phenylenediamine or m‐phenylenediamine proceeds smoothly to afford the corresponding monopyrroles and bispyrroles with high selectivity in impressive yields. A plausible mechanism for the formation of N‐substituted pyrroles has been proposed. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
104.
It is presented an integral approach for the velocity analysis of complex gear systems. Due to the intrinsic nature of the method, it can be systematically applied for gear trains with arbitrary architecture, including bevel gears with non-parallel motion axes. As a result, not only velocity ratios can be computed, but also angular velocities of any body composing the gear system. Several application examples are presented to prove the feasibility and the validity of the proposed method. 相似文献
105.
Jacques Marie Moreau Gérard Delbos André Marie Bottreau 《Journal of Molecular Liquids》1983,25(2):91-101
The dielectric studies of four components mixtures are rarely made on a great deal of concentrations. The authors propose a dielectric behavior study of mixtures made with toluene-water-butanol-SDS, from specific mappings of permittivities which are plotted on pseudo ternary diagrams at 9.455 GHz. They draw different conclusions to know how at 9.455 GHz the variations of real and imaginary parts of permittivity involve the concentration of each component and the structure of the mixture.These conclusions will be perfected by studies made at other frequencies and by spectral analysis of each mixture. 相似文献
106.
Summary We prove an invariance principle in probability for planar point processes associated with extremal processes. The underlying sequence of random variables is absolutely regular, and satisfies a local asymptotic independence condition. A strong approximation for triangular arrays of such point processes is also stated. We apply these results to the weak convergence of intermediate quantile functions. 相似文献
107.
Juan A. Barceló Jonathan Bennett Alberto Ruiz 《Journal of Fourier Analysis and Applications》2003,9(6):541-562
We study the continuity properties of a projection derived from a recent characterization of Herglotz Wave Functions in the plane. Herglotz Wave Functions are the entire solutions of the Helmholtz equation which have L2-Far-Field-Pattern. The behavior of this projection is reminiscent of the Disc Multiplier Operator on both Lp and mixed Lp-normed spaces. In particular a Kakeya type set plays a central role in our analysis. As a consequence we answer a question posed by Alvarez, Folch-Gabayet and Pérez-Esteva. 相似文献
108.
We determine all complete intersection surface germs whose Pythagoras number is 2, and find that they are all embedded in 3 and have the property that every positive semidefinite analytic function germ is a sum of squares of analytic function germs. In addition, we discuss completely these properties for mixed surface germs in 3. Finally, we find in higher embedding dimension three different families with these same properties. Partially supported by DGICYT, BFM2002-04797 and HPRN-CT-2001-00271
Mathematical Subject Classification (2000): 11E25, 14P15.An erratum to this article can be found at 相似文献
109.
Abstract. We propose a general approach to deal with nonlinear, nonconvex variational problems based on a reformulation of the problem
resulting in an optimization problem with linear cost functional and convex constraints. As a first step we explicitly explore
these ideas to some one-dimensional variational problems and obtain specific conclusions of an analytical and numerical nature. 相似文献
110.
Parallel Newton two-stage iterative methods to solve nonlinear systems are studied. These algorithms are based on both the multisplitting technique and the two-stage iterative methods. Convergence properties of these methods are studied when the Jacobian matrix is either monotone or an H-matrix. Furthermore, in order to illustrate the performance of the algorithms studied, computational results about these methods on a distributed memory multiprocessor are discussed.This revised version was published online in October 2005 with corrections to the Cover Date. 相似文献