全文获取类型
收费全文 | 3755篇 |
免费 | 311篇 |
国内免费 | 372篇 |
专业分类
化学 | 513篇 |
晶体学 | 18篇 |
力学 | 312篇 |
综合类 | 70篇 |
数学 | 2581篇 |
物理学 | 944篇 |
出版年
2024年 | 4篇 |
2023年 | 37篇 |
2022年 | 45篇 |
2021年 | 54篇 |
2020年 | 77篇 |
2019年 | 87篇 |
2018年 | 81篇 |
2017年 | 91篇 |
2016年 | 99篇 |
2015年 | 86篇 |
2014年 | 160篇 |
2013年 | 269篇 |
2012年 | 159篇 |
2011年 | 153篇 |
2010年 | 205篇 |
2009年 | 268篇 |
2008年 | 259篇 |
2007年 | 293篇 |
2006年 | 207篇 |
2005年 | 223篇 |
2004年 | 199篇 |
2003年 | 175篇 |
2002年 | 184篇 |
2001年 | 145篇 |
2000年 | 135篇 |
1999年 | 110篇 |
1998年 | 115篇 |
1997年 | 110篇 |
1996年 | 77篇 |
1995年 | 54篇 |
1994年 | 62篇 |
1993年 | 22篇 |
1992年 | 26篇 |
1991年 | 22篇 |
1990年 | 18篇 |
1989年 | 15篇 |
1988年 | 5篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 16篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 11篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1975年 | 3篇 |
排序方式: 共有4438条查询结果,搜索用时 265 毫秒
11.
We extend the matrix version of Cochran's statistical theorem to outer inverses of a matrix. As applications, we investigate the Wishartness and independence of matrix quadratic forms for Kronecker product covariance structures. 相似文献
12.
L. Brian Lawrence 《Transactions of the American Mathematical Society》2005,357(7):2535-2556
Working in ZFC, we give an example as indicated in the title.
13.
We propose a unified method for deducing recursive relations for the canonical partition function of a system of noninteracting particles with charge conservation if the particles follow the Bose–Einstein, Fermi–Dirac, or Maxwell–Boltzmann statistics or parastatistics. For all these types of statistics, we find recursive relations for the partition function of a new statistical model of nuclear multifragmentation with electric charge and baryon number conservation, accounting for the internal degrees of freedom of the nuclear fragments. 相似文献
14.
15.
D. Amutha Rani Y. Yamamoto S. Mohri M. Sivakumar Y. Tsujita H. Yoshimizu 《Journal of Polymer Science.Polymer Physics》2003,41(3):269-273
In this study, a novel stepwise extraction method has been examined. The guest molecules housed between the helices of the clathrate δ form of syndiotactic polystyrene can be removed completely with this method. A systematic study of the preparation of a solvent‐free mesophase (emptied clathrate) membrane, its helical and residual solvent contents, and its structural transformations has been performed. In this first attempt, an enhancement in the TTGG helical content has been observed in the extracted membrane, and a conceptual mechanism is proposed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 269–273, 2003 相似文献
16.
In this paper, the form invariance and the Lie symmetry of Lagrange's equations for nonconservative system in generalized classical mechanics under the infinitesimal transformations of group are studied, and the Noether's conserved quantity, the new form conserved quantity, and the Hojman's conserved quantity of system are derived from them. Finally, an example is given to illustrate the application of the result. 相似文献
17.
18.
19.
K. P. O. Mahesh M. Sivakumar Y. Yamamoto Y. Tsujita H. Yoshimizu S. Okamoto 《Journal of Polymer Science.Polymer Physics》2004,42(18):3439-3446
A crystalline δ form of a syndiotactic polystyrene (sPS) membrane was prepared from a solution of sPS (1 wt %) and p‐chlorotoluene (p‐CT) by a solution‐casting method. The mesophase (δ empty form) of sPS was obtained by the extraction of the guest solvent from the δ form of sPS by a stepwise solvent‐extraction method. The sPS/p‐CT mesophase membrane [p‐CT (A‐M)] was used for the sorption of 1 mol % p‐CT for different times and for the sorption of different concentrations of p‐CT, chlorobenzene (CB), p‐xylene (p‐X), toluene, and chloroform for 48 h. The presence of solvents in the sPS membrane was confirmed by IR analysis. A thermal study revealed that the sorption amount of 1 mol % p‐CT increased with increasing immersion time, and the sorption amounts of different solvents increased with increasing solvent concentration. Differential scanning calorimetry results showed that the desorption peak temperature increased as the amount of the solvent increased in the clathrated sPS membrane. Wide‐angle X‐ray diffraction results showed that 2θ at 8.25° was slightly shifted toward 8°, and there was no change in the peak position at 10° for p‐CT (A‐M), which was immersed in different solvents (1 mol %); however, the intensity of 2θ at 10° was not similar for all the samples. Among the solvents used for the sorption studies at 1 mol %, p‐CT (A‐M) could sorb more p‐CT and CB than p‐X, toluene, and chloroform. The solvent sorption isotherm was the Langmuir sorption mechanism. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3439–3446, 2004 相似文献
20.
A new grid‐free upwind relaxation scheme for simulating inviscid compressible flows is presented in this paper. The non‐linear conservation equations are converted to linear convection equations with non‐linear source terms by using a relaxation system and its interpretation as a discrete Boltzmann equation. A splitting method is used to separate the convection and relaxation parts. Least squares upwinding is used for discretizing the convection equations, thus developing a grid‐free scheme which can operate on any arbitrary distribution of points. The scheme is grid free in the sense that it works on any arbitrary distribution of points and it does not require any topological information like elements, faces, edges, etc. This method is tested on some standard test cases. To explore the power of the grid‐free scheme, solution‐based adaptation of points is done and the results are presented, which demonstrate the efficiency of the new grid‐free scheme. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献