全文获取类型
收费全文 | 69922篇 |
免费 | 2352篇 |
国内免费 | 62篇 |
专业分类
化学 | 43407篇 |
晶体学 | 487篇 |
力学 | 1244篇 |
综合类 | 1篇 |
数学 | 12645篇 |
物理学 | 14552篇 |
出版年
2023年 | 485篇 |
2022年 | 415篇 |
2021年 | 737篇 |
2020年 | 1013篇 |
2019年 | 993篇 |
2018年 | 1421篇 |
2017年 | 1286篇 |
2016年 | 2483篇 |
2015年 | 2043篇 |
2014年 | 2061篇 |
2013年 | 4485篇 |
2012年 | 4398篇 |
2011年 | 4349篇 |
2010年 | 2810篇 |
2009年 | 2371篇 |
2008年 | 3899篇 |
2007年 | 3676篇 |
2006年 | 3285篇 |
2005年 | 3120篇 |
2004年 | 2665篇 |
2003年 | 2117篇 |
2002年 | 1875篇 |
2001年 | 1418篇 |
2000年 | 1383篇 |
1999年 | 980篇 |
1998年 | 745篇 |
1997年 | 634篇 |
1996年 | 881篇 |
1995年 | 626篇 |
1994年 | 703篇 |
1993年 | 677篇 |
1992年 | 662篇 |
1991年 | 529篇 |
1990年 | 573篇 |
1989年 | 475篇 |
1988年 | 463篇 |
1987年 | 426篇 |
1986年 | 415篇 |
1985年 | 599篇 |
1984年 | 561篇 |
1983年 | 446篇 |
1982年 | 435篇 |
1981年 | 436篇 |
1980年 | 375篇 |
1979年 | 369篇 |
1978年 | 375篇 |
1977年 | 369篇 |
1976年 | 363篇 |
1975年 | 333篇 |
1973年 | 355篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
241.
We study dynamic self-reconfiguration of modular metamorphic systems. We guarantee the feasibility of motion planning in a
rectangular model consisting of square modules that are allowed to slide along or rotate about one another. That is, we show
that any two connected configurations of the same number of modules can be transformed into each other by a sequence of moves
so that all intermediate configurations are connected. This settles a conjecture formulated in [6]. 相似文献
242.
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
243.
Twin Paradox and the Logical Foundation of Relativity Theory 总被引:3,自引:0,他引:3
We study the foundation of space-time theory in the framework of first-order logic (FOL). Since the foundation of mathematics has been successfully carried through (via set theory) in FOL, it is not entirely impossible to do the same for space-time theory (or relativity). First we recall a simple and streamlined FOL-axiomatization Specrel of special relativity from the literature. Specrel is complete with respect to questions about inertial motion. Then we ask ourselves whether we can prove the usual relativistic properties of accelerated motion (e.g., clocks in acceleration) in Specrel. As it turns out, this is practically equivalent to asking whether Specrel is strong enough to “handle” (or treat) accelerated observers. We show that there is a mathematical principle called induction (IND) coming from real analysis which needs to be added to Specrel in order to handle situations involving relativistic acceleration. We present an extended version AccRel of Specrel which is strong enough to handle accelerated motion, in particular, accelerated observers. Among others, we show that~the Twin Paradox becomes provable in AccRel, but it is not provable without IND. 相似文献
244.
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
245.
A. Ádám 《Acta Mathematica Hungarica》1989,54(3-4):291-296
246.
247.
A. Z. Dubničková S. Dubnička R. Baldini-Ferroli 《Czechoslovak Journal of Physics》1991,41(11):1075-1081
It is shown that all global analyses of nucleon electromagnetic form factor data predict the electron-positron annihilation into neutron-antineutron cross section (for which there are no data till now) to be in a finite energy region substantially larger than the electron-positron annihilation into the proton-antiproton one.Dedicated to the memory of M. Gmitro. 相似文献
248.
A survey of the contributions of Aldo Cossu in finite geometry is given.
Dedicated to the memory of Professor Aldo Cossu 相似文献
249.
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
250.
Juan E. Nápoles Valdés 《Results in Mathematics》2002,41(3-4):337-345
Qualitative behavior of second order nonlinear differential equations of type y″+p(t)y+q(t)f(y)=0, is studied. It includes properties such as positivity, number of zeros, oscillating nature, boundedness and monotonicity of the solutions. 相似文献