全文获取类型
收费全文 | 21515篇 |
免费 | 784篇 |
国内免费 | 514篇 |
专业分类
化学 | 3501篇 |
晶体学 | 126篇 |
力学 | 617篇 |
综合类 | 68篇 |
数学 | 13305篇 |
物理学 | 5196篇 |
出版年
2024年 | 20篇 |
2023年 | 165篇 |
2022年 | 188篇 |
2021年 | 259篇 |
2020年 | 406篇 |
2019年 | 511篇 |
2018年 | 518篇 |
2017年 | 395篇 |
2016年 | 373篇 |
2015年 | 414篇 |
2014年 | 787篇 |
2013年 | 1149篇 |
2012年 | 687篇 |
2011年 | 1738篇 |
2010年 | 1203篇 |
2009年 | 1472篇 |
2008年 | 1652篇 |
2007年 | 1574篇 |
2006年 | 1180篇 |
2005年 | 936篇 |
2004年 | 744篇 |
2003年 | 618篇 |
2002年 | 627篇 |
2001年 | 403篇 |
2000年 | 414篇 |
1999年 | 465篇 |
1998年 | 356篇 |
1997年 | 316篇 |
1996年 | 344篇 |
1995年 | 326篇 |
1994年 | 344篇 |
1993年 | 292篇 |
1992年 | 254篇 |
1991年 | 177篇 |
1990年 | 170篇 |
1989年 | 162篇 |
1988年 | 107篇 |
1987年 | 106篇 |
1986年 | 98篇 |
1985年 | 142篇 |
1984年 | 124篇 |
1983年 | 70篇 |
1982年 | 121篇 |
1981年 | 89篇 |
1980年 | 86篇 |
1979年 | 42篇 |
1978年 | 59篇 |
1977年 | 52篇 |
1976年 | 42篇 |
1975年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 186 毫秒
101.
通过光谱响应特性实验和记录/读出图像实验,研究了基因变异型细菌视紫红质(BRD96N)分子膜对单色光的光调制特性.发现BRD96N分子膜在550nm—600nm范围内对调制光有吸收增强的现象,且对此范围内不同波长的单色光其调制程度有差异.利用曲线拟和方法发现550nm—600nm吸收增强的变化过程分为快过程和慢过程,其对应的时间常数分别为30s和5min.利用强度调制器的吸收强度与图像灰度之间的关系,分析了560nm—600nm范围内出现图像反转的实验现象.
关键词:
细菌视紫红质D96N分子膜
光谱响应
吸收增强现象
图像反转现象 相似文献
102.
103.
Marilyn Breen 《Journal of Geometry》1989,36(1-2):8-16
LetS be a compact, simply connected set inR
2. If every boundary point ofS is clearly visible viaS from at least one of the three pointsa, b, c, thenS is a union of three starshaped sets whose kernels containa, b, c, respectively. The result fails when the number three is replaced by four.As a partial converse, ifS is a union of three starshaped sets whose kernels containa, b, c, respectively, then the set of points in the boundary ofS clearly visible from at least one ofa, b, orc is dense in the boundary ofS.Supported in part by NSF grant DMS-8705336. 相似文献
104.
Igor Chueshov 《Journal of Differential Equations》2007,233(1):42-86
We study von Karman evolution equations with non-linear dissipation and with partially clamped and partially free boundary conditions. Two distinctive mechanisms of dissipation are considered: (i) internal dissipation generated by non-linear operator, and (ii) boundary dissipation generated by shear forces friction acting on a free part of the boundary. The main emphasis is given to the effects of boundary dissipation. Under suitable hypotheses we prove existence of a compact global attractor and finiteness of its fractal dimension. We also show that any solution is stabilized to an equilibrium and estimate the rate of the convergence which, in turn, depends on the behaviour at the origin of the functions describing the dissipation. 相似文献
105.
Pham Huu Anh Ngoc 《Journal of Differential Equations》2007,243(1):101-122
We study stability radii of linear Volterra-Stieltjes equations under multi-perturbations and affine perturbations. A lower and upper bound for the complex stability radius with respect to multi-perturbations are given. Furthermore, in some special cases concerning the structure matrices, the complex stability radius can precisely be computed via the associated transfer functions. Then, the class of positive linear Volterra-Stieltjes equations is studied in detail. It is shown that for this class, complex, real and positive stability radius under multi-perturbations or multi-affine perturbations coincide and can be computed by simple formulae expressed in terms of the system matrices. As direct consequences of the obtained results, we get some results on robust stability of positive linear integro-differential equations and of positive linear functional differential equations. To the best of our knowledge, most of the results of this paper are new. 相似文献
106.
Armen Shirikyan 《Journal of Functional Analysis》2007,249(2):284-306
The paper is devoted to studying the distribution of stationary solutions for 3D Navier-Stokes equations perturbed by a random force. Under a non-degeneracy assumption, we show that the support of such a distribution coincides with the entire phase space, and its finite-dimensional projections are minorised by a measure possessing an almost surely positive smooth density with respect to the Lebesgue measure. Similar assertions are true for weak solutions of the Cauchy problem with a regular initial function. The results of this paper were announced in the short note [A. Shirikyan, Controllability of three-dimensional Navier-Stokes equations and applications, in: Sémin. Équ. Dériv. Partielles, 2005-2006, École Polytech., Palaiseau, 2006]. 相似文献
107.
The authors give a consistent affirmative response to a question of Juhász, Soukup and Szentmiklóssy: If GCH fails, there are (many) extraresolvable, not maximally resolvable Tychonoff spaces. They show also in ZFC that for ω<λ?κ, no maximal λ-independent family of λ-partitions of κ is ω-resolvable. In topological language, that theorem translates to this: A dense, ω-resolvable subset of a space of the form (DI(λ)) is λ-resolvable. 相似文献
108.
Martin Loebl 《Advances in Mathematics》2007,211(2):546-565
We define a q-chromatic function and q-dichromate on graphs and compare it with existing graph functions. Then we study in more detail the class of general chordal graphs. This is partly motivated by the graph isomorphism problem. Finally we relate the q-chromatic function to the colored Jones function of knots. This leads to a curious expression of the colored Jones function of a knot diagram K as a chromatic operator applied to a power series whose coefficients are linear combinations of long chord diagrams. Chromatic operators are directly related to weight systems by the work of Chmutov, Duzhin, Lando and Noble, Welsh. 相似文献
109.
Piotr Borodulin-Nadzieja 《Topology and its Applications》2007,154(18):3107-3124
We investigate properties of minimally generated Boolean algebras. It is shown that all measures defined on such algebras are separable but not necessarily weakly uniformly regular. On the other hand, there exist Boolean algebras small in terms of measures which are not minimally generated. We prove that under CH a measure on a retractive Boolean algebra can be nonseparable. Some relevant examples are indicated. Also, we give two examples of spaces satisfying some kind of Efimov property. 相似文献
110.
Summary The paper addresses the problem of the implementation of nonhomogeneous essential Dirichlet type boundary conditions in thep-version of the finite element method.Partially supported by the Office of Naval Research under Grant N-00014-85-K-0169Research partially supported by the Air Force Office of Scientific Research, Air Force Systems Command, USAF, under Grant Number AFOSR 85-0322 相似文献