全文获取类型
收费全文 | 31564篇 |
免费 | 2820篇 |
国内免费 | 5175篇 |
专业分类
化学 | 19503篇 |
晶体学 | 862篇 |
力学 | 2049篇 |
综合类 | 661篇 |
数学 | 4583篇 |
物理学 | 11901篇 |
出版年
2023年 | 186篇 |
2022年 | 645篇 |
2021年 | 655篇 |
2020年 | 621篇 |
2019年 | 605篇 |
2018年 | 604篇 |
2017年 | 795篇 |
2016年 | 727篇 |
2015年 | 873篇 |
2014年 | 1157篇 |
2013年 | 1950篇 |
2012年 | 1975篇 |
2011年 | 2198篇 |
2010年 | 1839篇 |
2009年 | 1924篇 |
2008年 | 2385篇 |
2007年 | 2147篇 |
2006年 | 2078篇 |
2005年 | 1850篇 |
2004年 | 1571篇 |
2003年 | 1217篇 |
2002年 | 1234篇 |
2001年 | 1153篇 |
2000年 | 1167篇 |
1999年 | 810篇 |
1998年 | 503篇 |
1997年 | 459篇 |
1996年 | 472篇 |
1995年 | 364篇 |
1994年 | 362篇 |
1993年 | 350篇 |
1992年 | 337篇 |
1991年 | 300篇 |
1990年 | 285篇 |
1989年 | 278篇 |
1988年 | 243篇 |
1987年 | 210篇 |
1986年 | 158篇 |
1985年 | 236篇 |
1984年 | 232篇 |
1983年 | 177篇 |
1982年 | 202篇 |
1981年 | 212篇 |
1980年 | 201篇 |
1979年 | 163篇 |
1978年 | 163篇 |
1977年 | 148篇 |
1976年 | 138篇 |
1975年 | 125篇 |
1974年 | 129篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
S. Q. Hou W. Wang Z. Y. Wang Z. W. Hu K. Liu 《Journal of Applied Mechanics and Technical Physics》2018,59(1):153-162
In order to investigate the characteristics of force chains in a granular flow system, a parallel plate shear cell is constructed to simulate the shear movement of an infinite parallel plate and observe variations in relevant parameters. The shear dilatancy process is divided into three stages, namely, plastic strain, macroscopic failure, and granular recombination. The stickslip phenomenon is highly connected with the evolution of force chains during the shear dilatancy process. The load–distribution rate curves and patterns of the force chains are utilized to describe the load-carrying behaviors and morphologic changes of force chains separately. Force chains, namely, “diagonal gridding,” “tadpole-shaped,” and “pinnate” are defined according to the form of the force chains in the corresponding three stages. 相似文献
3.
4.
In this paper we consider a wavelet algorithm for the piecewise constant collocation method applied to the boundary element solution of a first kind integral equation arising in acoustic scattering. The conventional stiffness matrix is transformed into the corresponding matrix with respect to wavelet bases, and it is approximated by a compressed matrix. Finally, the stiffness matrix is multiplied by diagonal preconditioners such that the resulting matrix of the system of linear equations is well conditioned and sparse. Using this matrix, the boundary integral equation can be solved effectively. 相似文献
5.
George M. Rideout 《General Relativity and Gravitation》1998,30(11):1701-1701
6.
The dependence of the beam propagation factor (M
2 parameter) with the absorbed pump power in the case of monolithic microchip laser under face-cooled configuration is extensively
studied. Our investigations show that the M
2 parameter is related to the absorbed pump power through two parameters (α and β) whose values depend on the laser material properties and laser configuration. We have shown that one parameter arises due
to the oscillation of higher order modes in the microchip cavity and the other parameter accounts for the spherical aberration
associated with the thermal lens induced by the pump beam. Such dependency of M
2 parameter with the absorbed pump power is experimentally verified for a face-cooled monolithic microchip laser based on Nd3+ -doped GdVO4 crystal and the values of α and β parameters were estimated from the experimentally measured data points. 相似文献
7.
Clifford 分析中一个带位移的非线性边值问题 总被引:23,自引:0,他引:23
■Gilbert,黄沙、李生训等人对 Clifford 分析中函数性质作了一系列研究.1987年徐振远讨论了实 Clifford 分析中一个基本的边值问题,1989年黄沙、李生训利用陆启铿关于多复变函数于典型域上的调和分析的结果,研究了复 Clifford 分析中的拟变态Dirichlet 边值问题.1990年黄沙研究实 Clifford 分析中一种边值问题. 相似文献
8.
Supposa that f(x) is a quasidifferentiable function, defined on S(?)R~n where S is an open set, with a -equivalent bounded quasidifferential subfam ily. Lenma I 相似文献
9.
Q. Sun Q. Wang X.G. Gong V. Kumar Y. Kawazoe 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):77-81
We report results of the atomic and electronic structures of Al7C cluster using ab initio molecular dynamics with ultrasoft pseudopotentials and generalized gradient approximation. The lowest energy structure is
found to be the one in which carbon atom occupies an interstitial position in Al7 cluster. The electronic structure shows that the recent observation [Chem. Phys. Lett. 316, 31 (2000)] of magic behavior of Al7C- cluster is due to a large highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) gap which makes Al7C- chemically inert. These results have further led us to the finding of a new neutral magic cluster Al7N which has the same number of valence electrons as in Al7C- and a large HOMO-LUMO gap of 1.99 eV. Further, calculations have been carried out on (Al7N)2 to study interaction between magic clusters.
Received 28 July 2001 相似文献
10.
两种拔尿管方法对膀胱功能损伤的临床观察 总被引:2,自引:0,他引:2
为观察两种不同的拔尿管方法对膀胱功能损伤的差异,将80例患者随机分成两组,分别采用改良法(40例)和常规法(40例)拔除留置尿管,分析比较了两组患者排尿顺利率、逼尿肌功能恢复率及尿道刺激症、尿失禁、尿潴留。结果表明,两组患者拔管后上述指标与情况有显著性差异,P<0.05。提示改良组膀胱功能损伤明显低于对照组。改良的拔管方法是一种值得护理推广应用的好方法。 相似文献