全文获取类型
收费全文 | 86323篇 |
免费 | 1682篇 |
国内免费 | 1460篇 |
专业分类
化学 | 30477篇 |
晶体学 | 884篇 |
力学 | 7160篇 |
综合类 | 113篇 |
数学 | 32980篇 |
物理学 | 17851篇 |
出版年
2023年 | 169篇 |
2022年 | 175篇 |
2021年 | 268篇 |
2020年 | 346篇 |
2019年 | 334篇 |
2018年 | 10621篇 |
2017年 | 10458篇 |
2016年 | 6444篇 |
2015年 | 1239篇 |
2014年 | 839篇 |
2013年 | 1008篇 |
2012年 | 4596篇 |
2011年 | 11260篇 |
2010年 | 6198篇 |
2009年 | 6518篇 |
2008年 | 7137篇 |
2007年 | 9202篇 |
2006年 | 650篇 |
2005年 | 1648篇 |
2004年 | 1854篇 |
2003年 | 2260篇 |
2002年 | 1303篇 |
2001年 | 502篇 |
2000年 | 453篇 |
1999年 | 364篇 |
1998年 | 331篇 |
1997年 | 255篇 |
1996年 | 323篇 |
1995年 | 216篇 |
1994年 | 175篇 |
1993年 | 183篇 |
1992年 | 130篇 |
1991年 | 139篇 |
1990年 | 95篇 |
1989年 | 115篇 |
1988年 | 92篇 |
1987年 | 90篇 |
1986年 | 90篇 |
1985年 | 77篇 |
1984年 | 52篇 |
1983年 | 41篇 |
1982年 | 49篇 |
1981年 | 46篇 |
1980年 | 53篇 |
1979年 | 49篇 |
1914年 | 45篇 |
1913年 | 40篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Shengjie Li Yangdong Xu Manxue You Shengkun Zhu 《Journal of Optimization Theory and Applications》2018,177(3):609-636
Image space analysis is a new tool for studying scalar and vector constrained extremum problems as well as generalized systems. In the last decades, the introduction of image space analysis has shown that the image space associated with the given problem provides a natural environment for the Lagrange theory of multipliers and that separation arguments turn out to be a fundamental mathematical tool for explaining, developing and improving such a theory. This work, with its 3 parts, aims at contributing to describe the state-of-the-art of image space analysis for constrained optimization and to stress that it allows us to unify and generalize the several topics of optimization. In this 1st part, after a short introduction of such an analysis, necessary and sufficient optimality conditions are treated. Duality and penalization are the contents of the 2nd part. The 3rd part deals with generalized systems, in particular, variational inequalities and Ky Fan inequalities. Some further developments are discussed in all the parts. 相似文献
72.
Consistency requirements and pattern methods in cost sharing problems with technological cooperation
Using the discrete cost sharing model with technological cooperation, we investigate the implications of the requirement that demand manipulations must not affect the agents’ shares. In a context where the enforcing authority cannot prevent agents (who seek to reduce their cost shares) from splitting or merging their demands, the cost sharing methods used must make such artifices unprofitable. The paper introduces a family of rules that are immune to these demand manipulations, the pattern methods. Our main result is the characterization of these methods using the above requirement. For each one of these methods, the associated pattern indicates how to combine the technologies in order to meet the agents’ demands. Within this family, two rules stand out: the public Aumann–Shapley rule, which never rewards technological cooperation; and the private Aumann–Shapley rule, which always rewards technology providers. Fairness requirements imposing natural bounds (for the technological rent) allow to further differentiate these two rules. 相似文献
73.
Kiran Ramesh Kenneth Granlund Michael V. Ol Ashok Gopalarathnam Jack R. Edwards 《Theoretical and Computational Fluid Dynamics》2018,32(2):109-136
A leading-edge suction parameter (LESP) that is derived from potential flow theory as a measure of suction at the airfoil leading edge is used to study initiation of leading-edge vortex (LEV) formation in this article. The LESP hypothesis is presented, which states that LEV formation in unsteady flows for specified airfoil shape and Reynolds number occurs at a critical constant value of LESP, regardless of motion kinematics. This hypothesis is tested and validated against a large set of data from CFD and experimental studies of flows with LEV formation. The hypothesis is seen to hold except in cases with slow-rate kinematics which evince significant trailing-edge separation (which refers here to separation leading to reversed flow on the aft portion of the upper surface), thereby establishing the envelope of validity. The implication is that the critical LESP value for an airfoil–Reynolds number combination may be calibrated using CFD or experiment for just one motion and then employed to predict LEV initiation for any other (fast-rate) motion. It is also shown that the LESP concept may be used in an inverse mode to generate motion kinematics that would either prevent LEV formation or trigger the same as per aerodynamic requirements. 相似文献
74.
We study isometric embeddings of a Euclidean space or a Heisenberg group into a higher dimensional Heisenberg group, where both the source and target space are equipped with an arbitrary left-invariant homogeneous distance that is not necessarily sub-Riemannian. We show that if all infinite geodesics in the target are straight lines, then such an embedding must be a homogeneous homomorphism. We discuss a necessary and certain sufficient conditions for the target space to have this ‘geodesic linearity property’, and we provide various examples. 相似文献
75.
Arif Salimov 《Periodica Mathematica Hungarica》2018,77(1):69-76
In this paper we find the formula of connections under which an almost complex structure is covariantly constant. These types of connections on anti-Kähler–Codazzi manifolds are described. Also, twin metric-preserving connections are analyzed for quasi-Kähler manifolds. Finally, anti-Hermitian Chern connections are investigated. 相似文献
76.
Benedict Vasco Normenyo Florian Luca Alain Togbé 《Periodica Mathematica Hungarica》2018,77(2):318-328
In this paper, all base 10 repdigits expressible as sums of three Pell numbers are found. 相似文献
77.
In the paper, the authors establish several integral representations for the generating functions of the large and little Schröder numbers and for the large and little Schröder numbers. 相似文献
78.
The rapid transmission of vaccinia virus(VACV)in vivo is thought to be closely related to the cell migration induced by it.Cell migration involved in dynamic changes of cell-substrate adhesion and actin cytoskeleton organization,which can influence by the micro/nano-scale topographic structures that cells are naturally exposed to via contact guidance.However,migration behaviors of VACV-infected cells exposed to topographic cues are still unknown.Herein,we designed an open chip with microgrooved poly(dimethyl siloxane)(PDMS)substrate to explore the topography roles in VACV-induced cell migration.Differed from the random cell migration observed in traditional scratch assay on planar substrate,VACV-infected cells had a tendency to persistently migrate along the axis parallel to microgroove with increased velocity.Moreover,infected cells exhibited a dominant elongated protrusion aligned to the micro-grating axis compare to the shorter lamella extended in any direction on smooth substrate.Interestingly,the Golgi complex preferred to relocate behind the nucleus confined within the micro-grating axis in majority of infected migratory cells.The directional polarization of cells embodied in protrusion formation and Golgi reorientation was responsible for the directionally persistent migration behaviors induced by VACV on microgrooved substrate.Infected cells response to substrate topography,causing the actin-filled stretched protrusion containing numerous virions and accelerated movement is likely to facilitate direct and rapid spread of VACV.This work opens a window for us to understand the migration behaviors of infected cells in vivo,and also provides a cue for revealing the relationship between virus-induced cell migration and virus rapid spread. 相似文献
79.
80.
Meccanica - This paper introduces an analytical approach to optimize the textured bearing with cavitation to improve the load support. For this purpose, a grooved parallel slider bearing is... 相似文献