全文获取类型
收费全文 | 12999篇 |
免费 | 391篇 |
国内免费 | 1836篇 |
专业分类
化学 | 7704篇 |
晶体学 | 78篇 |
力学 | 1115篇 |
综合类 | 49篇 |
数学 | 2311篇 |
物理学 | 3969篇 |
出版年
2020年 | 45篇 |
2016年 | 67篇 |
2015年 | 94篇 |
2014年 | 71篇 |
2013年 | 441篇 |
2012年 | 249篇 |
2011年 | 1469篇 |
2010年 | 762篇 |
2009年 | 748篇 |
2008年 | 274篇 |
2007年 | 290篇 |
2006年 | 397篇 |
2005年 | 610篇 |
2004年 | 1387篇 |
2003年 | 873篇 |
2002年 | 803篇 |
2001年 | 581篇 |
2000年 | 370篇 |
1999年 | 262篇 |
1998年 | 293篇 |
1997年 | 238篇 |
1996年 | 182篇 |
1995年 | 199篇 |
1994年 | 170篇 |
1993年 | 490篇 |
1992年 | 528篇 |
1991年 | 377篇 |
1990年 | 369篇 |
1989年 | 355篇 |
1988年 | 122篇 |
1987年 | 56篇 |
1986年 | 70篇 |
1985年 | 110篇 |
1984年 | 106篇 |
1983年 | 74篇 |
1982年 | 104篇 |
1981年 | 96篇 |
1980年 | 92篇 |
1979年 | 91篇 |
1978年 | 76篇 |
1977年 | 90篇 |
1976年 | 70篇 |
1975年 | 91篇 |
1974年 | 117篇 |
1973年 | 103篇 |
1972年 | 60篇 |
1971年 | 72篇 |
1970年 | 60篇 |
1969年 | 82篇 |
1968年 | 65篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
§ 1 IntroductionA triple system of order v and indexλ,denoted by TS(v,λ) ,is a collection of3- ele-mentsubsets Aof a v- set X,so thatevery 2 - subsetof X appears in preciselyλ subsets of A.L etλ≥ 2 and (X,A) be a TS(v,λ) .If Acan be partitioned into t(≥ 2 ) parts A1,A2 ,...,Atsuch that each (X,Ai) is a TS(v,λi) for 1≤ i≤ t,then (X,A) is called de-composable.Otherwise it is indecomposable.If t=λ,λi=1for 1≤ i≤ t,the TS(v,λ) (X,A) is called completely decomposable.It … 相似文献
32.
Isabel Echeverria Ping-Chung Su Sindee L. Simon Donald J. Plazek 《Journal of Polymer Science.Polymer Physics》1995,33(17):2457-2468
Creep and differential scanning calorimetry (DSC) measurements have been used to study the physical aging behavior of a polyetherimide. Isothermal aging temperatures ranged from 160°C to Tg with aging times ranging from 10 min to 8 days. The only measurable effect of physical aging on the short-time creep curves is a shift of the creep compliance to longer times. Andrade plots of the compliance versus the cube root of time are linear at short times with the slope β decreasing with increasing aging time to a constant value once equilibrium is reached. Log β3 is related directly to the degree to which the creep curves shift to longer times with physical aging, and is used in this work as a measure of physical aging. A reduced curve of log β3 versus log aging time is obtained for the aging temperatures investigated by appropriate vertical and horizontal shifts. The enthalpy change during aging increases linearly with the logarithm of the aging time, ta, leveling off at equilibrium at values which increase with decreasing aging temperature. Hence, both nonequilibrium and equilibrium temperature shift factors can be calculated from the DSC data. Good agreement is observed between the equilibrium temperature shift factors obtained from the creep and DSC data. The temperature dependence of the nonequilibrium temperature shift factors is found to be an order of magnitude smaller than that of the equilibrium shift factors. The time scales to reach equilibrium for enthalpy and for mechanical measurements are found to be the same within experimental error. © 1995 John Wiley & Sons, Inc. 相似文献
33.
THE ASYMPTOTIC SOLUTION FOR A CLASS OF SINGULARLY PERTURBED PROBLEM FOR SEMILINEAR SINGULAR EQUATION
The singularly perturbed boundary value problem for a class of semilinearsingular equation is considered. Using a simple and special method the asym-ptotic behavior of solution is studied. 相似文献
34.
中国西南武陵山区跳蛛新种记述(蜘蛛目:跳蛛科) 总被引:2,自引:0,他引:2
本文记述跳蛛科13个新种,采自西南武陵山地区。暗跳蛛Asemonea、列锡蛛Lycidas和法老蛛Pharacocerus 3属为我国新记录属。 相似文献
35.
Cooperative games are considered where only those coalitions of players are feasible that respect a given precedence structure on the set of players. Strengthening the classical symmetry axiom, we obtain three axioms that give rise to a unique Shapley value in this model. The Shapley value is seen to reflect the expected marginal contribution of a player to a feasible random coalition, which allows us to evaluate the Shapley value nondeterministically. We show that every exact algorithm for the Shapley value requires an exponential number of operations already in the classical case and that even restriction to simple games is #P-hard in general. Furthermore, we outline how the multi-choice cooperative games of Hsiao and Raghavan can be treated in our context, which leads to a Shapley value that does not depend on pre-assigned weights. Finally, the relationship between the Shapley value and the permission value of Gilles, Owen and van den Brink is discussed. Both refer to formally similar models of cooperative games but reflect complementary interpretations of the precedence constraints and thus give rise to fundamentally different solution concepts. 相似文献
36.
In this paper,based on the results presented in part Ⅰ of this paper[18],we present a numerical embedding algorithm for solving the nonlinear complementarityproblem, and prove its convergence carefully. Numerical experiments show that thealgorithm is successful. 相似文献
37.
PERSISTENCE AND GLOBAL STABILITY FOR TWO-SPECIES NONAUTONOMOUS PREDATOR-PREY SYSTEM WITH DIFFUSION AND TIME DELAY 总被引:3,自引:0,他引:3
In this paper, a non-autonomous predator-prey model with diffusion andcontinuous time delay is studied, where the prey can diffuse between two pat-ches of a heterogeneous environment with barriers between patches, but for thepredator, the diffusion does not involve a barrier between patches, further itis assumed that all the parameters are time-dependent. It is shown that thesystem can be made persistent under some appropriate conditions. Moreover,sufficient conditions that guarantee the existence of a unique periodic solutionwhich is globally asymptotic stable are derived. 相似文献
38.
39.
M.I.Gil' 《Annals of Differential Equations》2004,20(2):145-154
The nonlocal initial problem for nonlinear nonautonomous evolution equati-ons in a Banach space is considered. It is assumed that the nonlinearities havethe local Lipschitz properties. The existence and uniqueness of mild solutionsare proved. Applications to integro-differential equations are discussed.The main tool in the paper is the normalizing mapping (the generalizednorm). 相似文献
40.
李林 《Annals of Differential Equations》2004,20(2):118-124
This paper considers the scalar differential delay equation x(t) = -μx(t)-f(x(t-Τ(t)), t). By using the mapping method we obtain that the solutionswill be ultimately in some interval. 相似文献