全文获取类型
收费全文 | 163313篇 |
免费 | 17170篇 |
国内免费 | 9512篇 |
专业分类
化学 | 83435篇 |
晶体学 | 1630篇 |
力学 | 12002篇 |
综合类 | 516篇 |
数学 | 41111篇 |
物理学 | 51301篇 |
出版年
2024年 | 344篇 |
2023年 | 2043篇 |
2022年 | 3296篇 |
2021年 | 3451篇 |
2020年 | 3927篇 |
2019年 | 3510篇 |
2018年 | 12883篇 |
2017年 | 12399篇 |
2016年 | 10181篇 |
2015年 | 5150篇 |
2014年 | 5595篇 |
2013年 | 7056篇 |
2012年 | 11779篇 |
2011年 | 18301篇 |
2010年 | 10849篇 |
2009年 | 11046篇 |
2008年 | 11993篇 |
2007年 | 13439篇 |
2006年 | 4961篇 |
2005年 | 5061篇 |
2004年 | 4386篇 |
2003年 | 4185篇 |
2002年 | 3066篇 |
2001年 | 2050篇 |
2000年 | 1888篇 |
1999年 | 1988篇 |
1998年 | 1779篇 |
1997年 | 1718篇 |
1996年 | 1757篇 |
1995年 | 1436篇 |
1994年 | 1224篇 |
1993年 | 1089篇 |
1992年 | 910篇 |
1991年 | 846篇 |
1990年 | 691篇 |
1989年 | 559篇 |
1988年 | 428篇 |
1987年 | 365篇 |
1986年 | 380篇 |
1985年 | 307篇 |
1984年 | 193篇 |
1983年 | 153篇 |
1982年 | 141篇 |
1981年 | 95篇 |
1980年 | 88篇 |
1979年 | 59篇 |
1914年 | 45篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
41.
Nonclassical light states are important for both conceptual and practical reasons: they are basic ingredients in testing and exploring quantum foundations, and are crucial resources in quantum technologies. Various useful criteria have been developed to detect nonclassicality in the literature, and several meaningful measures of nonclassicality have been introduced and measured experimentally. In this work, by use of a non-Hermitian generalization of the Wigner-Yanase-Dyson skew information and playing with operator ordering in evaluating average photon number, we develop a novel family of criteria for detecting nonclassicality of light based on Lieb's concavity, which is a deep and powerful result concerning interaction between quantum states and observables. We elucidate the information-theoretic as well as the physical meaning of the criteria, and illustrate their effectiveness in capturing and quantifying nonclassicality of various important light states. 相似文献
42.
43.
Chunhong Wang Qi Cui Zhixin Zhang Prof. Zhu-Jun Yao Dr. Shaozhong Wang Prof. Zhi-Xiang Yu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(42):9821-9826
1,3-Azaprotio transfer of propargylic α-ketocarboxylate oximes, a new type of alkynyl oximes featuring an ester tether, has been explored by taking advantage of gold catalysis. The incorporation of an oxygen atom to the chain of alkynyl oximes led to the formation of two different oxa-cyclic nitrones. It was found that internal alkynyl oximes with an E-configuration deliver five-membered nitrones, whereas terminal alkynyl oximes with an E-configuration afford six-membered nitrones. DFT calculations on four possible pathways supported a stepwise formation of C−N and C−H bonds, in which a 1,3-acyloxy-migration competes with the 1,3-azaprotio-transfer, especially in the case of internal alkynyl oximes. The relative nucleophilic properties of oxygen in the carbonyl group and the nitrogen in the oxime, the electronic effects of alkynes, and the influence of the ring system have been investigated computationally. 相似文献
44.
Shi-Chun Mao Zhaohui Zhang Jiansen Gao Zhen-Sen Wu 《Waves in Random and Complex Media》2019,29(1):54-62
A solution to the problem of Gaussian beam scattering by an anisotropically coated circular cylinder is presented. The incident Gaussian beam source is expanded as an approximate expression in the simple form with a Tayor’s series. The transmitted field in the anisotropically coated region is expressed as a infinite summation of eigen plane waves with different polar angles. The unknown coefficients of the scattered fields are obtained with the aid of the boundary conditions. The infinite series can be truncated under the prerequisite of achieving the solution convergence. Only the case of transverse-electric polarization is discussed. The similar formulation of transverse-magnetic polarization can be obtained by adopting the similar method. Some numerical results are presented and discussed. The result is in agreement with that available as expected when the Gaussian beam degenerates to a plane wave incidence case. 相似文献
45.
Nonlinear Dynamics - Global dynamics of a flexible asymmetrical rotor resting on vibrating supports is investigated. Hamilton’s principle is used to derive the partial differential governing... 相似文献
46.
Understanding and control of the surface properties such as molecular orientations are of great importance in numerous applications of ionic liquids. However, there remain discrepancies among the previous experimental and theoretical studies on the surface orientation and structures of room temperature ionic liquids(RTIL) systems. In this article, the orientation of 1-butyl-3-methylimidazolium([bmin]) cation at the air/liquid interface of a characteristic RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate([bmim][PF6]), was investigated by the sum frequency generation vibrational spectroscopy(SFG-VS). Detailed polarization and experimental configuration analyses of the SFG-VS spectra showed the possibility of a small spectral splitting in the CH3 symmetric stretching region, which can be further attributed to the probable existence of multiple orientations for the interfacial [bmim] cations. In addition, the(N)–CH3 vibrations were absent, ruling out the prediction by several recent molecular dynamics simulations which state that portions of the [bmim] cations orient with a standing-up(N)–CH3 group at the ionic liquid surface. Hence, new realistic theoretical models have to be developed to reflect the complex nature of the ionic liquid surface. 相似文献
47.
48.
49.
50.