全文获取类型
收费全文 | 10078篇 |
免费 | 1901篇 |
国内免费 | 1543篇 |
专业分类
化学 | 7897篇 |
晶体学 | 142篇 |
力学 | 620篇 |
综合类 | 95篇 |
数学 | 1347篇 |
物理学 | 3421篇 |
出版年
2024年 | 17篇 |
2023年 | 154篇 |
2022年 | 209篇 |
2021年 | 313篇 |
2020年 | 373篇 |
2019年 | 435篇 |
2018年 | 355篇 |
2017年 | 315篇 |
2016年 | 521篇 |
2015年 | 592篇 |
2014年 | 610篇 |
2013年 | 761篇 |
2012年 | 903篇 |
2011年 | 908篇 |
2010年 | 725篇 |
2009年 | 687篇 |
2008年 | 723篇 |
2007年 | 586篇 |
2006年 | 530篇 |
2005年 | 498篇 |
2004年 | 441篇 |
2003年 | 403篇 |
2002年 | 511篇 |
2001年 | 428篇 |
2000年 | 272篇 |
1999年 | 228篇 |
1998年 | 192篇 |
1997年 | 139篇 |
1996年 | 122篇 |
1995年 | 112篇 |
1994年 | 84篇 |
1993年 | 67篇 |
1992年 | 55篇 |
1991年 | 57篇 |
1990年 | 34篇 |
1989年 | 27篇 |
1988年 | 21篇 |
1987年 | 16篇 |
1986年 | 10篇 |
1985年 | 8篇 |
1984年 | 13篇 |
1983年 | 11篇 |
1982年 | 4篇 |
1981年 | 12篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1974年 | 5篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
Linear programming models have been widely used in input-output analysis for analyzing the interdependence of industries in economics and in environmental science.In these applications,some of the entries of the coefficient matrix cannot be measured physically or there exists sampling errors.However,the coefficient matrix can often be low-rank.We characterize the robust counterpart of these types of linear programming problems with uncertainty set described by the nuclear norm.Simulations for the input-output analysis show that the new paradigm can be helpful. 相似文献
992.
We study an integro-differential equation that describes the slow erosion of granular flow. The equation is a first order nonlinear conservation law where the flux function includes an integral term. We show that there exist unique traveling wave solutions that connect profiles with equilibrium slope at ±∞. Such traveling waves take very different forms from those in standard conservation laws. Furthermore, we prove that the traveling wave profiles are locally stable, i.e., solutions with monotone initial data approach the traveling waves asymptotically as t→+∞. 相似文献
993.
Let E,F⊂Rd be two self-similar sets. Under mild conditions, we show that F can be C1-embedded into E if and only if it can be affinely embedded into E; furthermore if F cannot be affinely embedded into E , then the Hausdorff dimension of the intersection E∩f(F) is strictly less than that of F for any C1-diffeomorphism f on Rd. Under certain circumstances, we prove the logarithmic commensurability between the contraction ratios of E and F if F can be affinely embedded into E . As an application, we show that dimH?E∩f(F)<min?{dimH?E,dimH?F} when E is any Cantor-p set and F any Cantor-q set, where p,q?2 are two integers with log?p/log?q∉Q. This is related to a conjecture of Furstenberg about the intersections of Cantor sets. 相似文献
994.
The paper is concerned with a scalar conservation law with nonlocal flux, providing a model for granular flow with slow erosion and deposition. While the solution u=u(t,x) can have jumps, the inverse function x=x(t,u) is always Lipschitz continuous; its derivative has bounded variation and satisfies a balance law with measure-valued sources. Using a backward Euler approximation scheme combined with a nonlinear projection operator, we construct a continuous semigroup whose trajectories are the unique entropy weak solutions to this balance law. Going back to the original variables, this yields the global well-posedness of the Cauchy problem for the granular flow model. 相似文献
995.
In this article, the authors introduce the Newton-Morrey-Sobolev space on a metric measure space (??, d, μ). The embedding of the Newton-Morrey-Sobolev space into the Hölder space is obtained if ?? supports a weak Poincaré inequality and the measure μ is doubling and satisfies a lower bounded condition. Moreover, in the Ahlfors Q-regular case, a Rellich-Kondrachov type embedding theorem is also obtained. Using the Haj?asz gradient, the authors also introduce the Haj?asz-Morrey-Sobolev spaces, and prove that the Newton-Morrey-Sobolev space coincides with the Haj?asz-Morrey-Sobolev space when μ is doubling and ?? supports a weak Poincaré inequality. In particular, on the Euclidean space \({\mathbb R}^n\) , the authors obtain the coincidence among the Newton-Morrey-Sobolev space, the Haj?asz-Morrey-Sobolev space and the classical Morrey-Sobolev space. Finally, when (??, d) is geometrically doubling and μ a non-negative Radon measure, the boundedness of some modified (fractional) maximal operators on modified Morrey spaces is presented; as an application, when μ is doubling and satisfies some measure decay property, the authors further obtain the boundedness of some (fractional) maximal operators on Morrey spaces, Newton-Morrey-Sobolev spaces and Haj?asz-Morrey-Sobolev spaces. 相似文献
996.
997.
广义Carmichael数 总被引:1,自引:0,他引:1
设n是一个合数,Z_n表示模n的剩余类环,r(x)∈Z_n[x]是一个首一的k(>0)次不可约多项式。本文引入n是k阶摸r(x)的Carmichael数的定义,全体这样的数记为集C_(k,r)(x),由此给出k阶Carmichael数集:C_k={∪C_(k,r)(x)|r(x)过全体Z_n上的首一k次不可约多项式}。显然C_1表示通常的Carmichael数集。作者得到了n∈C_(k,r(x))的一个充要条件,进而得到n∈C_k的一个充要条件及n∈C_2的一个更易计算的充要条件,还证明了C_1(?)C_2以及|C_2|=∞。 相似文献
998.
弱闭T(N)-模的预零化子的等距映射 总被引:1,自引:0,他引:1
本文刻划了弱闭T(N)-模的预零化子间的等距映射.设u,W分别为由左连续序同态N→~N和N→~N所确定的弱闭T(N)-模, u(?),W(?)分别为u,W的预零化子,Φ为由u(?)到W(?)上的线性等距映射.若(0)*=(0)#=(0),dim(0)+≠1且min{dim(H(?)~H),dim(He(?)^H)}≥2,则存在酉算子Ui,Vi(i=1,2),使得Φ(A)=U1AV*1或Φ(A)=U2A*V2*. 相似文献
999.
A proper edge coloring of a graph G is acyclic if there is no 2-colored cycle in G. The acyclic chromatic index of G, denoted by χ a(G), is the least number of colors such that G has an acyclic edge coloring. A graph is 1-planar if it can be drawn on the plane so that each edge is crossed by at most one other edge. In this paper, it is proved that χ a(G) ≤Δ(G) + 22, if G is a triangle-free 1-planar graph. 相似文献