全文获取类型
收费全文 | 35092篇 |
免费 | 1080篇 |
国内免费 | 820篇 |
专业分类
化学 | 14848篇 |
晶体学 | 291篇 |
力学 | 1732篇 |
综合类 | 28篇 |
数学 | 9694篇 |
物理学 | 10399篇 |
出版年
2023年 | 154篇 |
2022年 | 222篇 |
2021年 | 292篇 |
2020年 | 296篇 |
2019年 | 249篇 |
2018年 | 1400篇 |
2017年 | 1614篇 |
2016年 | 978篇 |
2015年 | 817篇 |
2014年 | 823篇 |
2013年 | 1073篇 |
2012年 | 3687篇 |
2011年 | 2877篇 |
2010年 | 2183篇 |
2009年 | 1861篇 |
2008年 | 941篇 |
2007年 | 942篇 |
2006年 | 912篇 |
2005年 | 4665篇 |
2004年 | 4086篇 |
2003年 | 2429篇 |
2002年 | 596篇 |
2001年 | 410篇 |
2000年 | 211篇 |
1999年 | 309篇 |
1998年 | 214篇 |
1997年 | 158篇 |
1996年 | 163篇 |
1995年 | 143篇 |
1994年 | 113篇 |
1993年 | 84篇 |
1992年 | 237篇 |
1991年 | 209篇 |
1990年 | 208篇 |
1989年 | 159篇 |
1988年 | 132篇 |
1987年 | 85篇 |
1986年 | 65篇 |
1985年 | 54篇 |
1984年 | 44篇 |
1983年 | 42篇 |
1979年 | 49篇 |
1978年 | 39篇 |
1976年 | 89篇 |
1975年 | 50篇 |
1974年 | 47篇 |
1973年 | 61篇 |
1972年 | 44篇 |
1969年 | 39篇 |
1966年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
We study linear dynamical systems with multidimensional time in Banach spaces. Using Taylor functional calculus we prove that under additional assumptions hyperbolic systems have shadowing property. 相似文献
72.
S?awomir Solecki 《Topology and its Applications》2007,154(12):2462-2464
Let I0 be the σ-ideal of subsets of a Polish group generated by Borel sets which have perfectly many pairwise disjoint translates. We prove that a Fubini-type theorem holds between I0 and the σ-ideals of Haar measure zero sets and of meager sets. We use this result to give a simple proof of a generalization of a theorem of Balcerzak-Ros?anowski-Shelah stating that I0 on N2 strongly violates the countable chain condition. 相似文献
73.
74.
R. Knizikevi?ius 《Applied Surface Science》2006,253(3):1581-1583
The ion-beam-assisted etching of silicon in Cl2 environment is considered. The theoretically calculated dependences of silicon etching rate on the flux of Cl2 molecules at different ion current densities are compared with experimentally measured. The composition of the adsorbed layer is determined. It is found that SiCl2 molecules prevail in the adsorbed layer. The reciprocal of relative concentration of SiCl2 molecules in the adsorbed layer linearly depends on the ion-to-neutral flux ratio. 相似文献
75.
Kang Hai TAN Xiao Ping YANG 《数学学报(英文版)》2006,22(3):701-710
In this paper we give a geometric interpretation of the notion of the horizontal mean curvature which is introduced by Danielli Garofalo-Nhieu and Pauls who recently introduced sub- Riemannian minimal surfaces in Carnot groups. This will be done by introducing a natural nonholonomic connection which is the restriction (projection) of the natural Riemannian connection on the horizontal bundle. For this nonholonomic connection and (intrinsic) regular hypersurfaces we introduce the notions of the horizontal second fundamental form and the horizontal shape operator. It turns out that the horizontal mean curvature is the trace of the horizontal shape operator. 相似文献
76.
Wei-nan E Ping-bing Ming 《应用数学学报(英文版)》2007,23(4):529-550
We study continuum and atomistic models for the elastodynamics of crystalline solids at zerotemperature.We establish sharp criterion for the regime of validity of the nonlinear elastic wave equationsderived from the well-known Cauchy-Born rule. 相似文献
77.
Xie Zhijian Tan Qiulin 《International Journal of Infrared and Millimeter Waves》2006,27(12):1639-1649
To counter the problems of gas accidents in coal mines, family safety resulted from using gas, a new infrared detection system
with integration and miniaturization has been developed. The infrared detection optics principle used in developing this system
is mainly analyzed. The idea that multi gas detection is introduced and guided through analyzing single gas detection is got
across. Through researching the design of cell structure, the cell with integration and miniaturization has been devised.
The way of data transmission on Controller Area Network (CAN) bus is explained. By taking Single-Chip Microcomputer (SCM)
as intelligence handling, the functional block diagram of gas detection system is designed with its hardware and software
system analyzed and devised. This system designed has reached the technology requirement of lower power consumption, mini-volume,
big measure range, and able to realize multi-gas detection. 相似文献
78.
A Hybrid Multiobjective Evolutionary Algorithm for Solving Vehicle Routing Problem with Time Windows 总被引:2,自引:0,他引:2
Vehicle routing problem with time windows (VRPTW) involves the routing of a set of vehicles with limited capacity from a central
depot to a set of geographically dispersed customers with known demands and predefined time windows. The problem is solved
by optimizing routes for the vehicles so as to meet all given constraints as well as to minimize the objectives of traveling
distance and number of vehicles. This paper proposes a hybrid multiobjective evolutionary algorithm (HMOEA) that incorporates
various heuristics for local exploitation in the evolutionary search and the concept of Pareto's optimality for solving multiobjective
optimization in VRPTW. The proposed HMOEA is featured with specialized genetic operators and variable-length chromosome representation
to accommodate the sequence-oriented optimization in VRPTW. Unlike existing VRPTW approaches that often aggregate multiple
criteria and constraints into a compromise function, the proposed HMOEA optimizes all routing constraints and objectives simultaneously,
which improves the routing solutions in many aspects, such as lower routing cost, wider scattering area and better convergence
trace. The HMOEA is applied to solve the benchmark Solomon's 56 VRPTW 100-customer instances, which yields 20 routing solutions
better than or competitive as compared to the best solutions published in literature. 相似文献
79.
M. A. Rizzutto N. Added M. H. Tabacniks F. R. Espinoza-Qui?ones S. M. Palacio R. M. Galante R. M. Galante N. Rossi R. A. Welter A. N. Módenes 《Journal of Radioanalytical and Nuclear Chemistry》2006,269(3):727-731
Summary Kulcsszavak (angolul, ha nem azonos az elozovel) 相似文献
80.
Peptidosulfonamides are an emerging group of peptidomimetics with a variety of applications in medicinal chemistry. We present a novel approach to the synthesis of peptidosulfonamides, and apply it to a series of new potential inhibitors of the bacterial peptidoglycan biosynthesis enzymes MurD and MurE. The synthesis was conducted via N-phthalimido β-aminoethanesulfonyl chlorides, which are new building blocks for the synthesis of peptidosulfonamides. In the most crucial step, sulfonic acids or their sodium salts were converted into the corresponding sulfonyl chlorides using an excess of either SOCl2 or SOCl2/DMF, and then coupled to the C-protected amino acid. None of the compounds significantly inhibited MurD, however, some inhibited MurE; one had an IC50 below 200 μM, which constitutes a promising starting point for further development. Molecular modelling simulations were performed on two analogues to investigate the absence of inhibitory activity of the sulfonamide compounds on MurD. 相似文献