全文获取类型
收费全文 | 111145篇 |
免费 | 17613篇 |
国内免费 | 12835篇 |
专业分类
化学 | 77575篇 |
晶体学 | 1194篇 |
力学 | 6420篇 |
综合类 | 739篇 |
数学 | 13491篇 |
物理学 | 42174篇 |
出版年
2024年 | 366篇 |
2023年 | 2172篇 |
2022年 | 3883篇 |
2021年 | 4108篇 |
2020年 | 4432篇 |
2019年 | 4231篇 |
2018年 | 3895篇 |
2017年 | 3535篇 |
2016年 | 5293篇 |
2015年 | 5269篇 |
2014年 | 6378篇 |
2013年 | 8254篇 |
2012年 | 9793篇 |
2011年 | 10081篇 |
2010年 | 7036篇 |
2009年 | 6785篇 |
2008年 | 7167篇 |
2007年 | 6398篇 |
2006年 | 5996篇 |
2005年 | 5070篇 |
2004年 | 3929篇 |
2003年 | 3177篇 |
2002年 | 2906篇 |
2001年 | 2451篇 |
2000年 | 2136篇 |
1999年 | 2212篇 |
1998年 | 1867篇 |
1997年 | 1685篇 |
1996年 | 1692篇 |
1995年 | 1507篇 |
1994年 | 1347篇 |
1993年 | 1110篇 |
1992年 | 966篇 |
1991年 | 866篇 |
1990年 | 715篇 |
1989年 | 572篇 |
1988年 | 428篇 |
1987年 | 369篇 |
1986年 | 358篇 |
1985年 | 285篇 |
1984年 | 198篇 |
1983年 | 164篇 |
1982年 | 137篇 |
1981年 | 84篇 |
1980年 | 59篇 |
1979年 | 29篇 |
1978年 | 22篇 |
1976年 | 23篇 |
1975年 | 23篇 |
1957年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
51.
52.
53.
Chunguang Du Hongyi Chen Shiqun Li 《量子光学学报》2006,12(B08):70-71
Recently, research on left-handed materials (LHMs) has attracted considerable attentions. The LHMs are a kind of metameterial which have negative permittivity and negative permeability, which lead to negative refractive index in a frequency range. The LHMs that have been available so far are in the microwave range and are usually composed of classical particles, such as split-ring resonators. Some quantum phenomena such as spontaneous emission of atoms in the LHMs which are considered to be 'classical background' have also been investigated. Many potential applications of LHMs have been proposed, such as superlenses which, in principle, can achieve arbitrary subwavelength resolution. 相似文献
54.
A FUNDAMENTAL SOLUTION FOR THE LAPLACE OPERATOR ON THE QUATERNIONIC HEISENBERG GROUP 总被引:2,自引:0,他引:2
朱理 《数学物理学报(B辑英文版)》2002,22(3)
In this paper, the author studies the Laplace operator on the quaternionic Heisenberg group, construct a fundamental solution for it and use this solution to prove the Lp-boundedness and the weak (1-1) boundedness of certain singular convolution operators on the quaternionic Heisenberg group. 相似文献
55.
We reveal that for a realistic system, interference effects are obtained such as the suppression of central line and inner sidebands and the narrowing of the outer fluorescence sidebands. For this purpose, we consider a spontaneous decay from an excited state to a metastable state when the excited and metastable states are resonantly coupled to an auxiliary metastable state by a laser field and a microwave field, respectively. The fluorescence spectrum evolves from a five-peaked structure into a doublet of ultrasharp lines as the ratio of the laser field Rabi frequency to the microwave Rabi frequency is decreased. The physical origin is presented in terms of dressed states. 相似文献
56.
This study examined how selected U.S. and Asian mathematics curricula are designed to facilitate students' understanding of the arithmetic average. There is a consistency regarding the learning goals among these curriculum series, but the focuses are different between the Asian series and the U.S. reform series. The Asian series and the U.S. commercial series focus the arithmetic average more on conceptual and procedural understanding of the concept as a computational algorithm than on understanding the concept as a representative of a data set; however, the two U.S. reform series focus the concept more on the latter. Because of the different focuses, the Asian and the U.S. curriculum series treat the concept differently. In the Asian series, the concept is first introduced in the context of “equal‐sharing” or “per‐unit‐quantity,” and the averaging formula is formally introduced at a very early stage. In the U.S. reform series, the concept is discussed as a measure of central tendency, and after students have some intuitive ideas of the statistical aspect of the concept, the averaging algorithm is briefly introduced. 相似文献
57.
Soliton interaction under the influence of higher-order effects 总被引:6,自引:0,他引:6
In this paper, we present exact N-soliton solution by employing simple, straightforward Darboux transformation based on the Lax pair for Hirota equation, a higher-order nonlinear Schrödinger (HNLS) equation. As examples, one- and two-soliton solutions in explicit forms are given and their properties are also analyzed. A bound solution without interaction will be theoretically predicted if one can adjust frequency shift for each soliton appropriately. Further, we obtain the approximate eigenvalues by employing two-soliton solution and discuss analytically the interaction between neighboring solitons under the influence of the higher-order effects. It is shown that the combined effects of the higher-order effects can restrain the interaction between neighboring solitons to some extent. The results are proved by directly solving HNLS equation numerically. 相似文献
58.
A convective flow CO laser composed of polytetrafluoroethylene discharge tubes, nickel–chromium steel components, a cupric heat exchanger and other components is described. Operating in liquid nitrogen condition, output power of 60 W has been obtained from a non-selective cavity. 相似文献
59.
By further generalizing the skew-symmetric triangular splitting iteration method studied by Krukier, Chikina and Belokon (Applied Numerical Mathematics, 41 (2002), pp. 89–105), in this paper, we present a new iteration scheme, called the modified skew-Hermitian triangular splitting iteration method, for solving the strongly non-Hermitian systems of linear equations with positive definite coefficient matrices. We discuss the convergence property and the optimal parameters of this new method in depth. Moreover, when it is applied to precondition the Krylov subspace methods like GMRES, the preconditioning property of the modified skew-Hermitian triangular splitting iteration is analyzed in detail. Numerical results show that, as both solver and preconditioner, the modified skew-Hermitian triangular splitting iteration method is very effective for solving large sparse positive definite systems of linear equations of strong skew-Hermitian parts. 相似文献
60.
X Y Liu C J Li 《Science in China. Series B, Chemistry, life sciences & earth sciences》1989,32(10):1215-1223
To further evaluate the causality between endogenous pyrogen (EP)-induced fever and cyclic adenosine-3',5'-monophosphate (cyclic AMP) level, the effects of sodium salicylate (SS) on the febrile response and increased levels of cyclic AMP in both cerebrospinal fluid (c.s.f.) and plasma during EP-induced fever in rabbits were observed. The results suggest that cyclic AMP is probably involved in the central mediation of EP-induced fever and that increased concentration of cyclic AMP in c.s.f. associated with EP-induced fever is not the result of temperature elevation but appears to be caused by the increased synthesis in the central nervous system. In addition it is confirmed that blood is impossibly a contributory source of increased cyclic AMP in c.s.f. during EP fever, and that SS may act subsequent to the increase in cyclic AMP. 相似文献