全文获取类型
收费全文 | 5204篇 |
免费 | 512篇 |
国内免费 | 625篇 |
专业分类
化学 | 2540篇 |
晶体学 | 34篇 |
力学 | 388篇 |
综合类 | 85篇 |
数学 | 1974篇 |
物理学 | 1320篇 |
出版年
2024年 | 4篇 |
2023年 | 32篇 |
2022年 | 83篇 |
2021年 | 110篇 |
2020年 | 146篇 |
2019年 | 134篇 |
2018年 | 132篇 |
2017年 | 139篇 |
2016年 | 181篇 |
2015年 | 120篇 |
2014年 | 238篇 |
2013年 | 352篇 |
2012年 | 293篇 |
2011年 | 273篇 |
2010年 | 298篇 |
2009年 | 323篇 |
2008年 | 308篇 |
2007年 | 367篇 |
2006年 | 313篇 |
2005年 | 299篇 |
2004年 | 249篇 |
2003年 | 252篇 |
2002年 | 183篇 |
2001年 | 174篇 |
2000年 | 171篇 |
1999年 | 135篇 |
1998年 | 118篇 |
1997年 | 103篇 |
1996年 | 104篇 |
1995年 | 73篇 |
1994年 | 98篇 |
1993年 | 71篇 |
1992年 | 78篇 |
1991年 | 54篇 |
1990年 | 38篇 |
1989年 | 44篇 |
1988年 | 37篇 |
1987年 | 36篇 |
1986年 | 31篇 |
1985年 | 37篇 |
1984年 | 23篇 |
1983年 | 8篇 |
1982年 | 20篇 |
1981年 | 7篇 |
1980年 | 11篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 9篇 |
1969年 | 3篇 |
排序方式: 共有6341条查询结果,搜索用时 140 毫秒
61.
Systems that involve more than one decision maker are often optimized using the theory of games. In the traditional game theory, it is assumed that each player has a well-defined quantitative utility function over a set of the player decision space. Each player attempts to maximize/minimize his/her own expected utility and each is assumed to know the extensive game in full. At present, it cannot be claimed that the first assumption has been shown to be true in a wide variety of situations involving complex problems in economics, engineering, social and political sciences due to the difficulty inherent in defining an adequate utility function for each player in these types of problems. On the other hand, in many of such complex problems, each player has a heuristic knowledge of the desires of the other players and a heuristic knowledge of the control choices that they will make in order to meet their ends.In this paper, we utilize fuzzy set theory in order to incorporate the players' heuristic knowledge of decision making into the framework of conventional game theory or ordinal game theory. We define a new approach to N-person static fuzzy noncooperative games and develop a solution concept such as Nash for these types of games. We show that this general formulation of fuzzy noncooperative games can be applied to solve multidecision-making problems where no objective function is specified. The computational procedure is illustrated via application to a multiagent optimization problem dealing with the design and operation of future military operations. 相似文献
62.
Using the thermodynamical approach and the method of York, the back-reaction of anti-de Sitter Schwarzschild black hole in thermal equilibrium with conformal spin-2 field is studied. It is found that both approaches give identical results. 相似文献
63.
We consider the problem of a self-consistent determination of an essentially inhomogeneous equilibrium state of classical plasma. The solutions of the stationary Vlasov–Poisson equations are constructed in the form of a localized transition layer that separates the domains of homogeneous plasmas with different equilibrium parameters. The layer can also transform into a local perturbation inside a homogeneous plasma. In both cases, the solution contains neither mass currents nor electric currents, and all electrodynamic and hydrodynamic quantities and their derivatives are continuous. The parameters of the adjacent domains uniquely determine the transition layer structure. 相似文献
64.
引进集值映射的锥真拟凹概念,讨论一类具有集值映射的广义向量衡问题解的存在性与解集的凸性。 相似文献
65.
Berit OlofssonPeter Somfai 《Tetrahedron letters》2003,44(6):1279-1281
A large set of syn- and anti-1,2-amino alcohols has been synthesized. Upon comparison of the CH?O and CH?N 1H NMR shifts a general trend has been observed, making it possible to determine the relative configuration of 1,2-amino alcohols without derivatization or shift reagents. 相似文献
66.
67.
In Leitmann (Ref. 1), a coordinate transformation method was introduced to obtain global solutions for free problems in the calculus of variations. This direct method was extended and broadened in Carlson (Ref. 2) and later in Leitmann (Ref. 3). The applicability of the original work of Leitmann (Ref. 1) was further developed in Dockner and Leitmann (Ref. 4) to include the class of open-loop dynamic games. In the present work, we improve the results of Ref. 4 in two directions. First, we enlarge the class of open-loop dynamic games to permit coupling among the dynamic equations via the states of the players; second, we incorporate the modifications given in Refs. 2 and 3. Our results greatly increase the applicability of this method. An example arising from the harvesting of a renewable resource is presented to illustrate the utility of our results. 相似文献
68.
Arata YajimaFumihiro Saitou Mayu SekimotoShoichiro Maetoko Goro Yabuta 《Tetrahedron letters》2003,44(36):6915-6918
Total synthesis of cordiaquinone K, a new antifungal and larvicidal meroterpenoid, is reported. The absolute configuration of cordiaquinone K was confirmed by the synthesis. 相似文献
69.
G. Martínez J. Milln J. Contreras 《Journal of polymer science. Part A, Polymer chemistry》2003,41(4):508-519
A poly(vinyl chloride) (PVC) sample was chlorinated in solution in the presence of 2,2′‐azobisisobutyronitrile and by the fluid‐bed method. The aim was to evaluate the scope of the stereoselectivity of the chlorination reaction. The quantitative microstructural analysis of the residual PVC with a degree of chlorination was followed by 13C NMR spectroscopy. From the evolution of the content of isotactic (mm), heterotactic (mr), and syndiotactic (rr) triads and of mmmm, mmmr, and rmmr isotactic pentads in the unchlorinated parts of the polymer, it was unambiguously inferred that the chlorination reaction proceeds by a stereoselective mechanism in that the mr heterotactic triads are the most reactive structures followed by the isotactic triad at mmmr and rmmr pentads. This conclusion was confirmed on the basis of the Fourier transform infrared results. The results provide valuable information regarding the effect of tacticity and related local conformations in the chemical reactions of PVC. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 508–519, 2003 相似文献
70.
A Tandem Queue with Coupled Processors: Computational Issues 总被引:2,自引:0,他引:2
In Resing and Örmeci [16] it is shown that the two-stage tandem queue with coupled processors can be solved using the theory of boundary value problems. In this paper we consider the issues that arise when calculating performance measures like the mean queue length and the fraction of time a station is empty. It is assumed that jobs arrive at the first station according to a Poisson process and require service at both stations before leaving the system. The amount of work that a job requires at each of the stations is an independent, exponentially distributed random variable. When both stations are nonempty, the total service capacity is shared among the stations according to fixed proportions. When one of the stations becomes empty, the total service capacity is given to the nonempty station. We study the two-dimensional Markov process representing the numbers of jobs at the two stations. The problem of finding the generating function of the stationary distribution can be reduced to two different Riemann-Hilbert boundary value problems, where both problems yield a complete analytical solution. We discuss the similarities and differences between the two problems, and relate them to the computational aspects of obtaining performance measures. 相似文献