全文获取类型
收费全文 | 691篇 |
免费 | 26篇 |
国内免费 | 10篇 |
专业分类
化学 | 483篇 |
晶体学 | 5篇 |
力学 | 26篇 |
数学 | 120篇 |
物理学 | 93篇 |
出版年
2023年 | 7篇 |
2022年 | 7篇 |
2021年 | 11篇 |
2020年 | 10篇 |
2019年 | 13篇 |
2018年 | 9篇 |
2017年 | 12篇 |
2016年 | 15篇 |
2015年 | 13篇 |
2014年 | 16篇 |
2013年 | 29篇 |
2012年 | 31篇 |
2011年 | 41篇 |
2010年 | 19篇 |
2009年 | 12篇 |
2008年 | 50篇 |
2007年 | 41篇 |
2006年 | 51篇 |
2005年 | 41篇 |
2004年 | 36篇 |
2003年 | 19篇 |
2002年 | 20篇 |
2001年 | 9篇 |
2000年 | 16篇 |
1999年 | 9篇 |
1997年 | 7篇 |
1996年 | 34篇 |
1995年 | 5篇 |
1994年 | 13篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 11篇 |
1975年 | 6篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1971年 | 4篇 |
1968年 | 3篇 |
1966年 | 3篇 |
1960年 | 4篇 |
排序方式: 共有727条查询结果,搜索用时 15 毫秒
101.
Summary This paper reconsiders the problem of determining the elastostatic field near the tip of a crack in an all-round infinite body deformed by a Mode III loading at infinity to a state of anti-plane shear. The problem is treated for a class of incompressible, homogeneous, isotropic elastic materials whose constitutive laws permit a loss of ellipticity in the governing displacement equation of equilibrium at sufficiently severe shearing strains. The analysis represents a generalization of that reported in an earlier study and, as before, is carried out for the small-scale nonlinear crack problem, in which a crack of finite length is replaced by a semi-infinite one, and the nonlinear field far from the crack-tip is matched to the near field predicted by the linearized theory. The methods employed in the present paper are necessarily largely qualitative, since they apply to all materials in the class considered. The principal feature of the resulting elastic field is the presence of two symmetrically located curves issuing from the crack-tip and bearing discontinuities in displacement gradient and stress.The results communicated in this paper were obtained in the course of an investigation supported in part by Contract N00014-75-C-0196 with the Office of Naval Research in Washington, D.C. 相似文献
102.
A substrate study was undertaken in order to probe the scope of S(2)Cl(2) coupling of alcohols to form dialkoxy disulfides. Compounds 1b and 1f are new; along with 1a, 1c, 1h, and 1j, all of the title compounds are fully characterized, and the yields of 1a and 1c have been optimized from previously reported syntheses. The effect of the R-substituent about the OSSO moiety has been carefully probed as yields vary. A substrate and a solvent study of the coalescence behavior of this class was carried out. The origin of the inherently large barrier to rotation and the resultant thermal decomposition pathway is discussed. Both phenomena are shown to be solvent independent; hindered rotation is substrate independent. The decomposition of 1a is ca. 7 kcal/mol higher than the barrier to rotation about the S-S bond. The combined evidence suggests acyclic unsymmetric homolytic cleavage of the dialkoxy disulfide. 相似文献
103.
Hybrid density-functional theory (B3LYP) calculations were carried out to determine the structures and energies of endohedral complexes of non-pi C(60)H(60) with H(2), CO, and LiH. It was demonstrated that the endohedral complexes of C(60)H(60) with the above three guest molecules are more stable than the corresponding complexes with C(60). Furthermore, the interaction between C(60)H(60) and the inside H(2) or CO is negligible, but the formation of the LiH-C(60)H(60) complex is exothermic with a stabilization energy of -6.0 kcal/mol. While the bond lengths of H(2) and CO changed a little when placed inside the cages, that of the LiH molecule increased and decreased inside C(60)H(60) and C(60), respectively. 相似文献
104.
105.
The representative curve of the ideal gas behind the front of a spherically, or cylindrically, symmetric strong imploding shock is shown to pass through the point where the reduced pressure is maximum, P(ζm) = Pmax. 相似文献
106.
107.
New methods are introduced for the time integration of the Fourier and Chebyshev methods of solution for dynamic differential equations. These methods are unconditionally stable, even though no matrix inversions are required. Time steps are chosen by accuracy requirements alone. For the Fourier method both leapfrog and Runge-Kutta methods are considered. For the Chebyshev method only Runge-Kutta schemes are tested. Numerical calculations are presented to verify the analytic results. Applications to the shallow water equations are presented. 相似文献
108.
109.
110.
A classical theorem of Edmonds provides a min-max formula relating the maximal size of a set in the intersection of two matroids to a ``covering" parameter. We generalize this theorem, replacing one of the matroids by a general simplicial complex. One application is a solution of the case of a matroidal version of Ryser's conjecture. Another is an upper bound on the minimal number of sets belonging to the intersection of two matroids, needed to cover their common ground set. This, in turn, is used to derive a weakened version of a conjecture of Rota. Bounds are also found on the dual parameter--the maximal number of disjoint sets, all spanning in each of two given matroids. We study in detail the case in which the complex is the complex of independent sets of a graph, and prove generalizations of known results on ``independent systems of representatives" (which are the special case in which the matroid is a partition matroid). In particular, we define a notion of -matroidal colorability of a graph, and prove a fractional version of a conjecture, that every graph is -matroidally colorable.
The methods used are mostly topological.