全文获取类型
收费全文 | 39275篇 |
免费 | 1485篇 |
国内免费 | 82篇 |
专业分类
化学 | 26374篇 |
晶体学 | 343篇 |
力学 | 766篇 |
数学 | 5697篇 |
物理学 | 7662篇 |
出版年
2023年 | 296篇 |
2022年 | 279篇 |
2021年 | 524篇 |
2020年 | 671篇 |
2019年 | 672篇 |
2018年 | 868篇 |
2017年 | 787篇 |
2016年 | 1465篇 |
2015年 | 1217篇 |
2014年 | 1242篇 |
2013年 | 2554篇 |
2012年 | 2698篇 |
2011年 | 2885篇 |
2010年 | 1728篇 |
2009年 | 1430篇 |
2008年 | 2451篇 |
2007年 | 2308篇 |
2006年 | 2135篇 |
2005年 | 1911篇 |
2004年 | 1556篇 |
2003年 | 1188篇 |
2002年 | 1090篇 |
2001年 | 787篇 |
2000年 | 696篇 |
1999年 | 536篇 |
1998年 | 388篇 |
1997年 | 295篇 |
1996年 | 449篇 |
1995年 | 324篇 |
1994年 | 317篇 |
1993年 | 331篇 |
1992年 | 308篇 |
1991年 | 217篇 |
1990年 | 209篇 |
1989年 | 164篇 |
1988年 | 164篇 |
1987年 | 156篇 |
1986年 | 149篇 |
1985年 | 241篇 |
1984年 | 205篇 |
1983年 | 170篇 |
1982年 | 165篇 |
1981年 | 151篇 |
1980年 | 132篇 |
1979年 | 143篇 |
1978年 | 139篇 |
1977年 | 131篇 |
1976年 | 150篇 |
1975年 | 132篇 |
1973年 | 131篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
In this paper a cubic lattice L(S) is endowed with a symmetric implication structure and it is proved that L(S) \ {0} is a power of the three-element simple symmetric implication algebra. The Metropolis–Rota’s symmetries are obtained as partial terms in the language of symmetric implication algebras. 相似文献
122.
Nikolaií N. Nekhoroshev Dmitrií A. Sadovskií Boris I. Zhilinskií 《Annales Henri Poincare》2006,7(6):1099-1211
We introduce fractional monodromy in order to characterize certain non-isolated critical values of the energy–momentum map
of integrable Hamiltonian dynamical systems represented by nonlinear resonant two-dimensional oscillators. We give the formal
mathematical definition of fractional monodromy, which is a generalization of the definition of monodromy used by other authors
before. We prove that the 1:( − 2) resonant oscillator system has monodromy matrix with half-integer coefficients and discuss
manifestations of this monodromy in quantum systems.
Communicated by Eduard Zehnder
Submitted: February 25, 2005; Accepted: November 17, 2005 相似文献
123.
We prove that for every fixed k and ? ≥ 5 and for sufficiently large n, every edge coloring of the hypercube Qn with k colors contains a monochromatic cycle of length 2 ?. This answers an open question of Chung. Our techniques provide also a characterization of all subgraphs H of the hypercube which are Ramsey, that is, have the property that for every k, any k‐edge coloring of a sufficiently large Qn contains a monochromatic copy of H. © 2006 Wiley Periodicals, Inc. J Graph Theory 53: 196–208, 2006 相似文献
124.
Parking Capacity and Pricing in Park'n Ride Trips: A Continuous Equilibrium Network Design Problem 总被引:2,自引:0,他引:2
In this paper we consider the problem of designing parking facilities for park'n ride trips. We present a new continuous equilibrium network design problem to decide the capacity and fare of these parking lots at a tactical level. We assume that the parking facilities have already been located and other topological decisions have already been taken.The modeling approach proposed is mathematical programming with equilibrium constraints. In the outer optimization problem, a central Authority evaluates the performance of the transport network for each network design decision. In the inner problem a multimodal traffic assignment with combined modes, formulated as a variational inequality problem, generates the share demand for modes of transportation, and for parking facilities as a function of the design variables of the parking lots. The objective is to make optimal parking investment and pricing decisions in order to minimize the total travel cost in a subnetwork of the multimodal transportation system.We present a new development in model formulation based on the use of generalized parking link cost as a design variable.The bilevel model is solved by a simulated annealing algorithm applied to the continuous and non-negative design decision variables. Numerical tests are reported in order to illustrate the use of the model, and the ability of the approach to solve applications of moderate size. 相似文献
125.
Flow injection methodology based on sample insertion between two different standard solutions used as carrier streams is described. This approach provides a simple system for continuous recalibration in process control; spectrophotometric and ion-selective electrode procedures are outlined. 相似文献
126.
127.
Ronald H. Nickel Igor Mikolic-Torreira Jon W. Tolle 《Computational Optimization and Applications》2006,35(1):109-126
Deployed US Navy aircraft carriers must stock a large number of spare parts to support the various types of aircraft embarked
on the ship. The sparing policy determines the spares that will be stocked on the ship to keep the embarked aircraft ready
to fly. Given a fleet of ten or more aircraft carriers and a cost of approximately 50 million dollars per carrier plus the
cost of spares maintained in warehouses in the United States, the sparing problem constitutes a significant portion of the
Navy’s resources. The objective of this work is to find a minimum-cost sparing policy that meets the readiness requirements
of the embarked aircraft. This is a very large, nonlinear, integer optimization problem. The cost function is piecewise linear
and convex while the constraint mapping is highly nonlinear. The distinguishing characteristics of this problem from an optimization
viewpoint are that a large number of decision variables are required to be integer and that the nonlinear constraint functions
are essentially “black box” functions; that is, they are very difficult (and expensive) to evaluate and their derivatives
are not available. Moreover, they are not convex. Integer programming problems with a large number of variables are difficult
to solve in general and most successful approaches to solving nonlinear integer problems have involved linear approximation
and relaxation techniques that, because of the complexity of the constraint functions, are inappropriate for attacking this
problem. We instead employ a pattern search method to each iteration of an interior point-type algorithm to solve the relaxed
version of the problem. From the solution found by the pattern search on each interior point iteration, we begin another pattern
search on the integer lattice to find a good integer solution. The best integer solution found across all interations is returned
as the optimal solution. The pattern searches are distributed across a local area network of non-dedicated, heterogeneous
computers in an office environment, thus, drastically reducing the time required to find the solution. 相似文献
128.
Oleg S. Ugolnikov Igor A. Maslov 《Journal of Quantitative Spectroscopy & Radiative Transfer》2006,102(3):499-512
The work is devoted to the analysis of the surface photometric observations of two total lunar eclipses in 2004. The lunar surface relative brightness distribution inside the umbra was used to retrieve the vertical distribution of aerosol extinction of the solar radiation expanding by a tangent path and its dependence on the location at the limb of the Earth. The upper altitude of troposphere aerosol layer was estimated for different latitude zones. The correlation between additional aerosol extinction in the upper troposphere and cyclones was investigated. 相似文献
129.