全文获取类型
收费全文 | 1156篇 |
免费 | 16篇 |
国内免费 | 30篇 |
专业分类
化学 | 664篇 |
晶体学 | 1篇 |
力学 | 33篇 |
数学 | 373篇 |
物理学 | 131篇 |
出版年
2020年 | 7篇 |
2018年 | 7篇 |
2016年 | 19篇 |
2015年 | 9篇 |
2014年 | 17篇 |
2013年 | 71篇 |
2012年 | 32篇 |
2011年 | 39篇 |
2010年 | 28篇 |
2009年 | 35篇 |
2008年 | 41篇 |
2007年 | 38篇 |
2006年 | 43篇 |
2005年 | 35篇 |
2004年 | 47篇 |
2003年 | 45篇 |
2002年 | 43篇 |
2001年 | 23篇 |
2000年 | 25篇 |
1999年 | 10篇 |
1998年 | 10篇 |
1997年 | 20篇 |
1996年 | 25篇 |
1995年 | 25篇 |
1993年 | 22篇 |
1992年 | 9篇 |
1991年 | 18篇 |
1990年 | 12篇 |
1989年 | 14篇 |
1988年 | 18篇 |
1987年 | 19篇 |
1986年 | 10篇 |
1985年 | 24篇 |
1984年 | 17篇 |
1983年 | 17篇 |
1982年 | 27篇 |
1981年 | 26篇 |
1980年 | 28篇 |
1979年 | 28篇 |
1978年 | 19篇 |
1977年 | 18篇 |
1976年 | 18篇 |
1975年 | 13篇 |
1974年 | 14篇 |
1973年 | 16篇 |
1972年 | 11篇 |
1971年 | 8篇 |
1970年 | 7篇 |
1967年 | 7篇 |
1966年 | 7篇 |
排序方式: 共有1202条查询结果,搜索用时 296 毫秒
1.
2.
Quiver Hopf algebras 总被引:1,自引:0,他引:1
In this paper we study subHopfalgebras of graded Hopf algebra structures on a path coalgebra kQc. We prove that a Hopf structure on some subHopfquivers can be lifted to a Hopf structure on the whole Hopf quiver. If Q is a Schurian Hopf quiver, then we classified all simple-pointed subHopfalgebras of a graded Hopf structure on kQc. We also prove a dual Gabriel theorem for pointed Hopf algebras. 相似文献
3.
4.
Alvim Adriana C.F. Ribeiro Celso C. Glover Fred Aloise Dario J. 《Journal of Heuristics》2004,10(2):205-229
We propose in this work a hybrid improvement procedure for the bin packing problem. This heuristic has several features: the use of lower bounding strategies; the generation of initial solutions by reference to the dual min-max problem; the use of load redistribution based on dominance, differencing, and unbalancing; and the inclusion of an improvement process utilizing tabu search. Encouraging results have been obtained for a very wide range of benchmark instances, illustrating the robustness of the algorithm. The hybrid improvement procedure compares favourably with all other heuristics in the literature. It improved the best known solutions for many of the benchmark instances and found the largest number of optimal solutions with respect to the other available approximate algorithms. 相似文献
5.
6.
7.
8.
A variety of results have been given for aggregating integer-valued (diophantine) equations whose variables are restricted to nonnegative integers. In each, integer weights are identified for the equations so that their linear combination yields a single equation with the same solution set of the original system of equations. Because the coefficients of the aggregated equation tend to achieve unwieldy sizes as the number of original equations increases, the goal is to identify weights so these coefficients will lie in a range as limited as possible. We give theorems which separately and in combination provide new methods for aggregating general integer-valued equations. Our results include formulations that do not require linearity of the original system, or nonnegativity of component variables. We also demonstrate that our theorems yield as special cases earlier results (analytical formulae) conjectured to yield the smallest possible weights for less general domains. As another application, the presented results were used to develop a highly efficient approach for the integer knapsack problem. Empirical outcomes show that the developed solution procedure is significantly superior to advanced branch and bound methods (previously established to be the most efficient knapsack solution procedures). 相似文献
9.
Fred. A. Mellon Keith W. Waldron Robbie R. Selvendran Guido C. Galletti 《Journal of mass spectrometry : JMS》1994,29(10):556-560
Sclerenchyma tissues from semi-mature and mature asparagus spears were analysed by pyrolysis/gas chromatography/mass spectrometry and by conventional chemical methods in order to determine the degree of lignification and compare analytical techniques. The pyrolysis data are similar to those obtained by a chemical method involving alkaline extraction at 70°C followed by spectrophotometric determination of phenolic content. The pyrolysis method was more rapid, sensitive and informative than the chemical technique and shows considerable potential for studying the chemical basis of the textural development of plant foods. 相似文献
10.
Suppose there is a Poisson process of points X
i
on the line. Starting at time zero, a grain begins to grow from each point X
i
, growing at rate A
i
to the left and rate B
i
to the right, with the pairs (A
i
, B
i
) being i.i.d. A grain stops growing as soon as it touches another grain. When all growth stops, the line consists of covered intervals (made up of contiguous grains) separated by gaps. We show (i) a fraction 1/e of the line remains uncovered, (ii) the fraction of covered intervals which contain exactly k grains is (k–1)/k!, (iii) the length of a covered interval containing k grains has a gamma(k–1) distribution, (iv) the distribution of the grain sizes depends only on the distribution of the total growth rate A
i
+B
i
, and other results. Similar theorems are obtained for growth processes on a circle; in this case we need only assume the pairs (A
i
, B
i
) are exchangeable. These results extend those of Daley, et al. (2000) who studied the case where A
i
=B
i
=1. Simulation results are given to illustrate the various theorems. 相似文献