全文获取类型
收费全文 | 6200篇 |
免费 | 322篇 |
国内免费 | 451篇 |
专业分类
化学 | 913篇 |
晶体学 | 16篇 |
力学 | 3564篇 |
综合类 | 32篇 |
数学 | 366篇 |
物理学 | 2082篇 |
出版年
2023年 | 21篇 |
2022年 | 32篇 |
2021年 | 59篇 |
2020年 | 78篇 |
2019年 | 91篇 |
2018年 | 58篇 |
2017年 | 102篇 |
2016年 | 259篇 |
2015年 | 253篇 |
2014年 | 187篇 |
2013年 | 277篇 |
2012年 | 228篇 |
2011年 | 347篇 |
2010年 | 234篇 |
2009年 | 378篇 |
2008年 | 376篇 |
2007年 | 418篇 |
2006年 | 396篇 |
2005年 | 408篇 |
2004年 | 373篇 |
2003年 | 373篇 |
2002年 | 277篇 |
2001年 | 173篇 |
2000年 | 187篇 |
1999年 | 148篇 |
1998年 | 205篇 |
1997年 | 135篇 |
1996年 | 94篇 |
1995年 | 141篇 |
1994年 | 102篇 |
1993年 | 97篇 |
1992年 | 72篇 |
1991年 | 56篇 |
1990年 | 40篇 |
1989年 | 49篇 |
1988年 | 34篇 |
1987年 | 31篇 |
1986年 | 20篇 |
1985年 | 14篇 |
1984年 | 14篇 |
1983年 | 6篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1979年 | 19篇 |
1978年 | 8篇 |
1977年 | 12篇 |
1976年 | 9篇 |
1973年 | 10篇 |
1972年 | 8篇 |
1971年 | 13篇 |
排序方式: 共有6973条查询结果,搜索用时 527 毫秒
131.
Mian Chin Gregory L. Durst Simone R. Head Paul L. BockJohn A. Mosbo 《Journal of organometallic chemistry》1994,470(1-2):73-85
Molecular mechanics (MM2) calculations were performed on 54 conformations of 18 phosphines (PH3; PH3−nRn, where n = 1,…3, and R = Me and Et, n = 1 or 2 and R =iPr, and n = 1 and R =tBu, PMe2Et, PMeEt2, and PPhMe2, and PPh2R where R = Me, Et, iPr, tBu and Ph). The results are compared to those previously obtained from MINDO/3 and MNDO calculations, and to experimental data. Single conformer cone angles and weighted average cone angles were calculated from MM2 optimized geometries employing Tolman's general definition, and they are compared to Tolman's values, MINDO/3 results, and T.L. Brown's ER values. Of the cone angle definitions used, the weighted average values are suggested as the best single representation of phosphine ligand sizes. The steric parameters (cone angle and ER values) alone, and in conjunction with electronic parameters, are correlated with experimental data. 相似文献
132.
The properties of fluctuations in space in or outside thermal equilibrium are obtained by solving hierarchies of equations derived either from the Liouville or the Master equation. In particular we study the one-, two-, etc., time correlation functions that describe the spatial and temporal behavior of the fluctuations in space. Explicit solutions are obtained for a dilute gas. The Langevin approach is briefly discussed. Our results are compared with those obtained in the extensive literature, which is reviewed in some detail. 相似文献
133.
The third law of thermodynamics, in the sense that the entropy per unit volume goes to zero as the temperature goes to zero, is investigated within the framework of statistical mechanics for quantum and classical lattice models. We present two main results: (i) For all models the question of whether the third law is satisfied can be decided completely in terms of ground-state degeneracies alone, provided these are computed for all possible boundary conditions. In principle, there is no need to investigate possible entropy contributions from low-lying excited states, (ii) The third law is shown to hold for ferromagnetic models by an analysis of the ground states.Dedicated to Pierre Résibois. Work supported in part by NSF grant PHY-7825390 A01. 相似文献
134.
We prove theH-stability property and the existence of the thermodynamic limit of the free energy density of the two-dimensional, one-component classical plasma. We give lower and upper bounds on the free energy density in any dimensionv and draw some consequences. 相似文献
135.
Classic snap-through of curved beams, plates, and shells has long been an object of attention in structural engineering. Euler buckling under axial loading is perhaps an even more entrenched part of the canon of engineering education and practice. In this paper we introduce a relationship between the two phenomena, that to our knowledge has not been directly addressed before. The relationship shows that Euler buckling configurations are connected by the force–displacement curve under transverse loading. The results are used to develop a very simple metric to estimate the number of unstable static equilibria of a buckled structure based only on its geometry with no need for static or dynamic solvers. The study is focused on beams as this allows for an unambiguous discussion of the idea on the simplest possible structure. 相似文献
136.
The aim of this study was to find a satisfactory method to characterize the fatigue crack growth behavior of non-reinforced, semi-crystalline thermoplastic polymers using linear elastic fracture mechanics (LEFM). For this, crack growth curves (crack length versus cycle number) as well as crack growth kinetics curves (crack growth rate da/dN versus amplitude stress intensity factor ΔK) had to be generated. As methods suggested by ISO 15850 and ASTM E 647-11 failed to provide satisfactory results for the crack growth curves, a more advanced method was searched for and finally found in the literature. Regarding the crack growth kinetics curve, the idea of the calculation was based on methods recommended in ISO 15850 and ASTM E 647-11. However, these methods had to be considerably modified and improved in order to get accurate results with little scatter. The whole methodology was developed and verified with fatigue crack growth tests on two semi-crystalline thermoplastics (polyoxymethylene POM and polyetheretherketone PEEK). 相似文献
137.
138.
In this article we will apply the first- and second-order supersymmetric quantum mechanics to obtain new exactly-solvable real potentials departing from the inverted oscillator potential. This system has some special properties; in particular, only very specific second-order transformations produce non-singular real potentials. It will be shown that these transformations turn out to be the so-called complex ones. Moreover, we will study the factorization method applied to the inverted oscillator and the algebraic structure of the new Hamiltonians. 相似文献
139.
140.