全文获取类型
收费全文 | 17444篇 |
免费 | 1969篇 |
国内免费 | 1845篇 |
专业分类
化学 | 2660篇 |
晶体学 | 37篇 |
力学 | 3039篇 |
综合类 | 446篇 |
数学 | 11107篇 |
物理学 | 3969篇 |
出版年
2024年 | 41篇 |
2023年 | 200篇 |
2022年 | 351篇 |
2021年 | 379篇 |
2020年 | 480篇 |
2019年 | 459篇 |
2018年 | 460篇 |
2017年 | 538篇 |
2016年 | 600篇 |
2015年 | 496篇 |
2014年 | 754篇 |
2013年 | 1262篇 |
2012年 | 783篇 |
2011年 | 982篇 |
2010年 | 866篇 |
2009年 | 1061篇 |
2008年 | 1147篇 |
2007年 | 1199篇 |
2006年 | 1066篇 |
2005年 | 983篇 |
2004年 | 789篇 |
2003年 | 872篇 |
2002年 | 712篇 |
2001年 | 604篇 |
2000年 | 669篇 |
1999年 | 585篇 |
1998年 | 523篇 |
1997年 | 430篇 |
1996年 | 365篇 |
1995年 | 238篇 |
1994年 | 224篇 |
1993年 | 164篇 |
1992年 | 143篇 |
1991年 | 117篇 |
1990年 | 108篇 |
1989年 | 65篇 |
1988年 | 84篇 |
1987年 | 51篇 |
1986年 | 36篇 |
1985年 | 65篇 |
1984年 | 57篇 |
1983年 | 23篇 |
1982年 | 54篇 |
1981年 | 28篇 |
1980年 | 24篇 |
1979年 | 22篇 |
1978年 | 20篇 |
1977年 | 18篇 |
1976年 | 12篇 |
1957年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
2.
3.
4.
The structure and rotational barrier for the mesityl-silicon bond of 2,2-dimesityl-1,1,1,3,3,3-hexamethyltrisilane have been investigated by 1H- and 13C-variable temperature nuclear magnetic resonance (NMR) as well as by density functional theory structural calculations. The calculations show that the lowest energy structure has C2 symmetry with nonequivalent ortho methyl groups, consistent with the crystal structure and solution NMR. The nonequivalent ortho methyl groups exchange through a Cs transition state with a calculated relative free energy of 11.0 kcal mol−1. The barrier for this rotation found by dynamic NMR is 13.4 ± 0.2 kcal mol−1 at 298 K. 相似文献
5.
Dr. Liat Avram Dr. Václav Havel Ronit Shusterman-Krush Dr. Mark A. Iron Dr. Moritz Zaiss Prof. Vladimír Šindelář Dr. Amnon Bar-Shir 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(7):1687-1690
The accumulated knowledge regarding molecular architectures is based on established, reliable, and accessible analytical tools that provide robust structural and functional information on assemblies. However, both the dynamicity and low population of noncovalently interacting moieties within studied molecular systems limit the efficiency and accuracy of traditional methods. Herein, the use of a saturation transfer-based NMR approach to study the dynamic binding characteristics of an anion to a series of synthetic receptors derived from bambusuril macrocycles is demonstrated. The exchange rates of BF4− are mediated by the side chains on the receptor (100 s−1<kex<5000 s−1), which play a critical role in receptor-anion binding dynamics. The signal amplification obtained with this approach allows for the identification of different types of intermolecular interactions between the receptor and the anion, something that could not have been detected by techniques hitherto used to study molecular assemblies. These findings, which are supported by a computational molecular dynamic study, demonstrate the uniqueness and added value of this NMR method. 相似文献
6.
7.
In this paper, we consider a viscoelastic wave equation of variable coefficients in the presence of past history with nonlinear damping and delay in the internal feedback and dynamic boundary conditions. Under suitable assumptions, we establish an explicit and general decay rate result without imposing restrictive assumption on the behavior of the relaxation function at infinity by Riemannian geometry method and Lyapunov functional method. 相似文献
8.
电路过渡过程所列方程是微分方程,本文中采用的是方框图模型分析法,即将微分方程的复杂示解分解成最基本的加(减)、乘(除)、积分(微分)、增益等运算,采用VB设计用户界面产进行计算,并给出了一算例。 相似文献
9.
Boundedness of commutators on homogeneous Herz spaces 总被引:9,自引:0,他引:9
The boundedness on homogeneous Herz spaces is established for a large class of linear commutators generated by BMO(R
n
) functions and linear operators of rough kernels which include the Calderón-Zygmund operators and the Ricci-Stein oRfiUatory
singular integrals with rough kernels.
Project supponed in pan by the National h’atural Science Foundation of China (Grant No. 19131080) and the NEDF of China. 相似文献
10.
Nobuaki Obata 《Acta Appl Math》1997,47(1):49-77
A general theory of operators on Boson Fock space is discussed in terms of the white noise distribution theory on Gaussian space (white noise calculus). An integral kernel operator is generalized from two aspects: (i) The use of an operator-valued distribution as an integral kernel leads us to the Fubini type theorem which allows an iterated integration in an integral kernel operator. As an application a white noise approach to quantum stochastic integrals is discussed and a quantum Hitsuda–Skorokhod integral is introduced. (ii) The use of pointwise derivatives of annihilation and creation operators assures the partial integration in an integral kernel operator. In particular, the particle flux density becomes a distribution with values in continuous operators on white noise functions and yields a representation of a Lie algebra of vector fields by means of such operators. 相似文献