全文获取类型
收费全文 | 53101篇 |
免费 | 8870篇 |
国内免费 | 7156篇 |
专业分类
化学 | 37969篇 |
晶体学 | 777篇 |
力学 | 3112篇 |
综合类 | 483篇 |
数学 | 5889篇 |
物理学 | 20897篇 |
出版年
2024年 | 187篇 |
2023年 | 1042篇 |
2022年 | 1860篇 |
2021年 | 1940篇 |
2020年 | 2087篇 |
2019年 | 2040篇 |
2018年 | 1806篇 |
2017年 | 1773篇 |
2016年 | 2557篇 |
2015年 | 2597篇 |
2014年 | 3164篇 |
2013年 | 3968篇 |
2012年 | 4797篇 |
2011年 | 4964篇 |
2010年 | 3496篇 |
2009年 | 3355篇 |
2008年 | 3630篇 |
2007年 | 3271篇 |
2006年 | 3077篇 |
2005年 | 2356篇 |
2004年 | 1837篇 |
2003年 | 1513篇 |
2002年 | 1480篇 |
2001年 | 1239篇 |
2000年 | 1154篇 |
1999年 | 1091篇 |
1998年 | 886篇 |
1997年 | 813篇 |
1996年 | 788篇 |
1995年 | 711篇 |
1994年 | 605篇 |
1993年 | 507篇 |
1992年 | 479篇 |
1991年 | 369篇 |
1990年 | 328篇 |
1989年 | 274篇 |
1988年 | 222篇 |
1987年 | 197篇 |
1986年 | 172篇 |
1985年 | 164篇 |
1984年 | 109篇 |
1983年 | 75篇 |
1982年 | 63篇 |
1981年 | 39篇 |
1980年 | 18篇 |
1979年 | 11篇 |
1977年 | 2篇 |
1971年 | 2篇 |
1959年 | 3篇 |
1957年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
In this paper, the dimension of the spaces of bivariate spline with degree less that 2r and smoothness order r on the Morgan-Scott triangulation is considered. The concept of the instability degree in the dimension of spaces of bivariate spline is presented. The results in the paper make us conjecture the instability degree in the dimension of spaces of bivariate spline is infinity. 相似文献
12.
13.
Solitary waves and their bifurcations of KdV like equation with higher order nonlinearity 总被引:3,自引:1,他引:2
We investigate the KdV like equation with higher order nonlinearity ut + a(1 +bun)unux + uxxx = 0with n ≥ 1, a, b ∈ R and α≠ 0. The bifurcations and explicit expressions of solitary wave solutions for theequation are discussed by using the bifurcation method and qualitative theory of dynamical systems. Thebifurcation diagrams, existence and number of the solitary waves are given. 相似文献
14.
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
15.
A nonlinear, compressible, non-isothermal gravity wave model that involves photochemistry is used to study the effects of gravity wave on atmospheric chemical species distributions in this paper. The changes in the distributions of oxygen compound and hydrogen compound density induced by gravity wave propagation are simulated. The results indicate that when a gravity wave propagates through a mesopause region, even if it does not break, it can influence the background distributions of chemical species. The effect of gravity wave on chemical species at night is larger than in daytime. 相似文献
16.
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
17.
In this paper, the transformation processes of two types of bis(8-hydroxyquinoline)zinc: Znq2 dihydrate and anhydrous (Znq2)4 were investigated by X-ray diffraction (XRD), infrared spectra (IR), scanning electron microscope (SEM), differential scanning calorimetry (DSC) and thermogravimetry (TG). The effects of crystal structure on optical properties of bis(8-hydroxyquinoiline)zinc were analyzed. Znq2 dihydrate can be transformed into anhydrous (Znq2)4 during heating under vacuum. Reversal transformation occurs by the interaction between chloroform and (Znq2)4. But (Znq2)4 was partially transformed into Znq2 dihydrate by the interaction between ethanol and (Znq2)4. The different molecular structure results in different crystal stacking and electronic structure, thereby affect its optical properties. 相似文献
18.
物理模型教学与创新能力的培养 总被引:1,自引:0,他引:1
现代教学以能力培养为重点.学生获得研究问题、探索问题的能力是十分重要的,物理模型的教学过程对培养学生研究问题、探索问题、发展创造思维、培养辩证唯物主义思想方法都极为有利,因此,必须重视物理模型教学. 相似文献
19.
A new family of photonucleases, naphthalimide-thiazoles was synthesized and evaluated. These compounds intercalated into DNA efficiently and damaged DNA photochemically at concentrations as low as 5 μM. Mechanistic experiment suggests that a novel naphthalimide-thiazole radical produced via an excited triple state might be involved in the DNA photodamage. Different activity may arise from the impact of substituents at 2-phenyl ring of thiazole on the electron population of excited triple state according to AM1 semi-empirical calculation. 相似文献
20.