全文获取类型
收费全文 | 8682篇 |
免费 | 587篇 |
国内免费 | 485篇 |
专业分类
化学 | 434篇 |
晶体学 | 1篇 |
力学 | 1015篇 |
综合类 | 72篇 |
数学 | 2781篇 |
物理学 | 1332篇 |
综合类 | 4119篇 |
出版年
2024年 | 10篇 |
2023年 | 82篇 |
2022年 | 101篇 |
2021年 | 124篇 |
2020年 | 200篇 |
2019年 | 167篇 |
2018年 | 142篇 |
2017年 | 177篇 |
2016年 | 200篇 |
2015年 | 190篇 |
2014年 | 375篇 |
2013年 | 410篇 |
2012年 | 406篇 |
2011年 | 489篇 |
2010年 | 389篇 |
2009年 | 504篇 |
2008年 | 514篇 |
2007年 | 549篇 |
2006年 | 554篇 |
2005年 | 513篇 |
2004年 | 450篇 |
2003年 | 437篇 |
2002年 | 450篇 |
2001年 | 325篇 |
2000年 | 334篇 |
1999年 | 249篇 |
1998年 | 230篇 |
1997年 | 176篇 |
1996年 | 162篇 |
1995年 | 119篇 |
1994年 | 134篇 |
1993年 | 89篇 |
1992年 | 97篇 |
1991年 | 94篇 |
1990年 | 71篇 |
1989年 | 64篇 |
1988年 | 35篇 |
1987年 | 25篇 |
1986年 | 18篇 |
1985年 | 20篇 |
1984年 | 15篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 5篇 |
排序方式: 共有9754条查询结果,搜索用时 296 毫秒
51.
Noora Virtanen Ville Nevalainen Taru Lehtinen Satu Mikkola 《Journal of Physical Organic Chemistry》2007,20(1):72-82
Transesterification of a phosphodiester bond of RNA models has been studied in various buffer solutions, under neutral and slightly alkaline conditions in H2O and D2O. The results show that imidazole is the only buffer system where a clear buffer catalysis on the cleavage of a phosphodiester bond is observed. The rate enhancement in sulphonic acid buffers is smaller, and a sulphonate base, particularly, is inactive as a catalyst. The rate‐enhancing effect of imidazole is, however, catalytic, and the catalytic inactivity of sulphonate buffers can be attributed to their structure and/or charge. The catalysis by imidazole is a complex system which, in addition to first‐order reactions, involves a process that shows a second‐order dependence in imidazole concentration. The latter reaction becomes significant in acidic imidazole buffers (pH < pKa), as the buffer concentration increases. The kinetic solvent deuterium isotope effect kH/kD, referring to first‐order catalysis by imidazole base, is 2.3 ± 0.3. That referring to second‐order catalysis is most probably much larger, but an accurate value could not be obtained. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
52.
钟鸣乾 《西北大学学报(自然科学版)》2003,33(3):263-266
运用广义相对论的后牛顿效应,得到洛希(Roche)极限和引力作用范围的近似改正表示式,表明洛希极限不仅与牛顿引潮力及惯性离心力有关,而且受重力后牛顿近似改正的影响。并且估计、讨论了太阳系天体的某些具体情况。 相似文献
53.
基于广义混沌同步的数字图像隐藏方案 总被引:6,自引:3,他引:3
基于广义混沌同步理论,提出了一种适于网络图像传输的隐藏数字图像的安全通讯方案.构造了一个六维广义混沌同步系统作为新方案的加密器,理论分析和计算机模拟说明本方案具有较高的保真度和较强的抗破译能力. 相似文献
54.
Let G be a finite group. Let p(G) denote the minimal degree of a faithful permutation representation ofG and let q(G) and c(G) denote the minimal degree of a faithful representation of G by quasi-permutation matrices over the rational and the complex numbers, respectively. Finally r(G) denotes the minimal degree of a faithful rational valued complex character of G. The purpose of this paper is to calculate p(G), q(G), c(G) and r(G) for the group SP(4,q).
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
55.
For linear statistical ill-posed problems in Hilbert spaces we introduce an adaptive procedure to recover the unknown solution from indirect discrete and noisy data. This procedure is shown to be order optimal for a large class of problems. Smoothness of the solution is measured in terms of general source conditions. The concept of operator monotone functions turns out to be an important tool for the analysis.
56.
57.
Finite groups of prime order must be cyclic. It is natural to ask what about association schemes of prime order. In this paper,
we will give an answer to this question. An association scheme of prime order is commutative, and its valencies of nontrivial
relations and multiplicities of nontrivial irreducible characters are constant. Moreover, if we suppose that the minimal splitting
field is an abelian extension of the field of rational numbers, then the character table is the same as that of a Schurian
scheme. 相似文献
58.
59.
DING Ning FANG Jian-Hui 《理论物理通讯》2006,46(2):265-268
In this paper the Lie symmetry and conserved quantities for nonholonomic Vacco dynamical systems are studied. The determining equation of the Lie symmetry for the system is given. The general Hojman conserved quantity and the Lutzky conserved quantity deduced from the symmetry are obtained. 相似文献
60.
简要讨论了基于Web的Internet上化学资源挖掘的两种主要手段,着重介绍了利用搜索引擎和化学主题资源检索化学资源的具体方法。 相似文献