全文获取类型
收费全文 | 7913篇 |
免费 | 133篇 |
国内免费 | 89篇 |
专业分类
化学 | 4869篇 |
晶体学 | 86篇 |
力学 | 172篇 |
数学 | 1743篇 |
物理学 | 1265篇 |
出版年
2022年 | 52篇 |
2020年 | 70篇 |
2019年 | 63篇 |
2018年 | 84篇 |
2017年 | 50篇 |
2016年 | 135篇 |
2015年 | 112篇 |
2014年 | 126篇 |
2013年 | 436篇 |
2012年 | 344篇 |
2011年 | 395篇 |
2010年 | 240篇 |
2009年 | 214篇 |
2008年 | 343篇 |
2007年 | 337篇 |
2006年 | 417篇 |
2005年 | 405篇 |
2004年 | 352篇 |
2003年 | 295篇 |
2002年 | 303篇 |
2001年 | 101篇 |
2000年 | 94篇 |
1999年 | 101篇 |
1998年 | 112篇 |
1997年 | 108篇 |
1996年 | 152篇 |
1995年 | 92篇 |
1994年 | 91篇 |
1993年 | 81篇 |
1992年 | 97篇 |
1991年 | 86篇 |
1990年 | 76篇 |
1989年 | 72篇 |
1988年 | 61篇 |
1987年 | 80篇 |
1986年 | 67篇 |
1985年 | 120篇 |
1984年 | 132篇 |
1983年 | 95篇 |
1982年 | 96篇 |
1981年 | 124篇 |
1980年 | 139篇 |
1979年 | 105篇 |
1978年 | 110篇 |
1977年 | 83篇 |
1976年 | 97篇 |
1975年 | 105篇 |
1974年 | 99篇 |
1973年 | 97篇 |
1972年 | 52篇 |
排序方式: 共有8135条查询结果,搜索用时 15 毫秒
51.
52.
We consider the equation in question on the interval 0 ≦ x ≦ 1 having Neumann boundary conditions, with f(u) = F(u), where F is a double well energy density with equal minima at u = ±1. The only stable states of the system are patternless constant solutions. But given two-phase initial data, a pattern of interfacial layers typically forms far out of equilibrium. The ensuing nonlinear relaxation process is extremely slow: patterns persist for exponentially long times proportional to exp{A±l/?, where A = F(±1) and l is the minimum distance between layers. Physically, a tiny potential jump across a layer drives its motion. We prove the existence and persistence of these metastable patterns, and characterise accurately the equations governing their motion. The point of view is reminiscent of center manifold theory: a manifold parametrising slowly evolving states is introduced, a neighbourhood is shown to be normally attracting, and the parallel flow is characterised to high relative accuracy. Proofs involve a detailed study of the Dirichlet problem, spectral gap analysis, and energy estimates. 相似文献
53.
Martin Charles Golumbic 《Graphs and Combinatorics》1988,4(1):307-321
Let be a family of sets. The intersection graph of is obtained by representing each set in by a vertex and connecting two vertices by an edge if and only if their corresponding sets intersect. Of primary interest are those classes of intersection graphs of families of sets having some specific topological or other structure. The grandfather of all intersection graphs is the class of interval graphs, that is, the intersection graphs of intervals on a line.The scope of research that has been going on in this general area extends from the mathematical and algorithmic properties of intersection graphs, to their generalizations and graph parameters motivated by them. In addition, many real-world applications involve the solution of problems on such graphs.In this paper a number of topics in algorithmic combinatorics which involve intersection graphs and their representative families of sets are presented. Recent applications to computer science are also discussed. The intention of this presentation is to provide an understanding of the main research directions which have been investigated and to suggest possible new directions of research. 相似文献
54.
55.
Enthalpies of solution have been measured from 5 to 85°C for aqueous tetraethyl- and tetrapropylammonium bromides, and the integral heat method is employed to evaluate
for these electrolytes over a wide temperature range. Data taken from the literature have been used to evaluate
for aqueous Bu4NBr over a similar temperature range. These data, along with similar data for Me4NBr, previously reported, have been used to evaluate absolute ionic heat capacities. While the absolute values agree only qualitatively with two other methods of division, the temperature dependences of the three methods essentially agree up to 65°C. Heat capacities due to structural effects on the solvent, obtained by subtracting the inherent heat capacities of the ions, are extraordinarily positive for all four tetraalkylammonium ions and have negative temperature coefficients, indicating that all four ions, including the tetramethylammonium ion, are structure-making ions. 相似文献
56.
Ronald N. Warrener Richard P. Johnson Charles W. Jefford David A. Ralph 《Tetrahedron letters》1979,20(31):2939-2942
Structural assignments are made to the three adducts derived from the title reaction. 1H-n.m.r., 13C-n.m.r. and euroshift data are used to support the new structures. 相似文献
57.
Scott Charles D. Woodward Charlene A. Thompson James E. Blankinship Stephen L. 《Applied biochemistry and biotechnology》1990,24(1):799-815
Applied Biochemistry and Biotechnology - Both oxidative and reductive enzymes can be utilized to enhance coal solubilization in aqueous and organic media. Aerobic solubilization was carried out... 相似文献
58.
The hydrogen-deuterium exchange of H-2 in 4-pyrimidone, a number of 1- and 3-alkyl-4-pyrimidones and several of their thione analogs in deuterium oxide at moderate temperatures is reported. This reaction is apparently not susceptible to acid or base catalysis. Cations of the 4-pyrimidones were found not to exchange H-2 at all in acid media. Catalytic amounts of bases do not alter the exchange rates whereas more concentrated alkali decompose the pyrimidone. However, 1,4(3,4)-dihydro-1,3-dimethyl-4-oxopyrimidinium iodide (and its 6-methyl analog) exchange H-2 quite rapidly in neutral deuterium oxide, almost instantly when triethylamine is added as a catalyst, and very slowly in dilute solutions of deuterium chloride in deuterium oxide. Mechanisms are proposed to account for these phenomena. 相似文献
59.
Kommareddi Nagesh S. Tata Murthy Karayigitoglu Cigdem John Vijay T. McPherson Gary L. Herman Michael F. O'Connor Charles J. Lee Young-Sook Akkara Joseph A. Kaplan David L. 《Applied biochemistry and biotechnology》1995,51(1):241-252
Applied Biochemistry and Biotechnology - Horseradish peroxidase has been used as a biocatalyst to synthesize a polymeric material from alkyl-substituted phenols. The synthesis is carried out in a... 相似文献