全文获取类型
收费全文 | 65205篇 |
免费 | 4983篇 |
国内免费 | 3877篇 |
专业分类
化学 | 22849篇 |
晶体学 | 178篇 |
力学 | 3624篇 |
综合类 | 1125篇 |
数学 | 32545篇 |
物理学 | 13744篇 |
出版年
2023年 | 506篇 |
2022年 | 1347篇 |
2021年 | 1901篇 |
2020年 | 1329篇 |
2019年 | 1460篇 |
2018年 | 1289篇 |
2017年 | 1510篇 |
2016年 | 1701篇 |
2015年 | 1474篇 |
2014年 | 2429篇 |
2013年 | 4355篇 |
2012年 | 2743篇 |
2011年 | 2999篇 |
2010年 | 2788篇 |
2009年 | 3607篇 |
2008年 | 3866篇 |
2007年 | 4088篇 |
2006年 | 3405篇 |
2005年 | 2557篇 |
2004年 | 2248篇 |
2003年 | 2318篇 |
2002年 | 4772篇 |
2001年 | 2264篇 |
2000年 | 1765篇 |
1999年 | 1535篇 |
1998年 | 1398篇 |
1997年 | 1153篇 |
1996年 | 1096篇 |
1995年 | 919篇 |
1994年 | 800篇 |
1993年 | 758篇 |
1992年 | 766篇 |
1991年 | 558篇 |
1990年 | 457篇 |
1989年 | 361篇 |
1988年 | 378篇 |
1987年 | 309篇 |
1986年 | 303篇 |
1985年 | 451篇 |
1984年 | 357篇 |
1983年 | 212篇 |
1982年 | 364篇 |
1981年 | 514篇 |
1980年 | 479篇 |
1979年 | 524篇 |
1978年 | 407篇 |
1977年 | 314篇 |
1976年 | 261篇 |
1974年 | 119篇 |
1973年 | 195篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
3.
4.
5.
In this article, we construct and analyze a residual-based a posteriori error estimator for a quadratic finite volume method (FVM) for solving nonlinear elliptic partial differential equations with homogeneous Dirichlet boundary conditions. We shall prove that the a posteriori error estimator yields the global upper and local lower bounds for the norm error of the FVM. So that the a posteriori error estimator is equivalent to the true error in a certain sense. Numerical experiments are performed to illustrate the theoretical results. 相似文献
6.
7.
8.
In this work, a vanillin complex is immobilized onto MCM-41 and characterized by FT-IR, X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, thermogravimetric analysis, and BET techniques. This supported Schiff base complex was found to be an efficient and recoverable catalyst for the chemoselective oxidation of sulfides into sulfoxides and thiols into their corresponding disulfides (using hydrogen peroxide as a green oxidant) and also a suitable catalyst for the preparation of 2,3-dihydroquinazolin-4(1H)-one derivatives in water at 90°C. Using this protocol, we show that a variety of disulfides, sulfoxides, and 2,3-dihydroquinazolin-4(1H)-one derivatives can be synthesized in green conditions. The catalyst can be recovered and recycled for further reactions without appreciable loss of catalytic performance. 相似文献
9.
ABSTRACTThe Coupled-Cluster (CC) theory is one of the most successful high precision methods used to solve the stationary Schrödinger equation. In this article, we address the mathematical foundation of this theory with focus on the advances made in the past decade. Rather than solely relying on spectral gap assumptions (non-degeneracy of the ground state), we highlight the importance of coercivity assumptions – Gårding type inequalities – for the local uniqueness of the CC solution. Based on local strong monotonicity, different sufficient conditions for a local unique solution are suggested. One of the criteria assumes the relative smallness of the total cluster amplitudes (after possibly removing the single amplitudes) compared to the Gårding constants. In the extended CC theory the Lagrange multipliers are wave function parameters and, by means of the bivariational principle, we here derive a connection between the exact cluster amplitudes and the Lagrange multipliers. This relation might prove useful when determining the quality of a CC solution. Furthermore, the use of an Aubin–Nitsche duality type method in different CC approaches is discussed and contrasted with the bivariational principle. 相似文献
10.