全文获取类型
收费全文 | 22345篇 |
免费 | 2444篇 |
国内免费 | 2400篇 |
专业分类
化学 | 2435篇 |
晶体学 | 33篇 |
力学 | 1799篇 |
综合类 | 582篇 |
数学 | 16069篇 |
物理学 | 6271篇 |
出版年
2024年 | 29篇 |
2023年 | 197篇 |
2022年 | 359篇 |
2021年 | 389篇 |
2020年 | 457篇 |
2019年 | 484篇 |
2018年 | 515篇 |
2017年 | 650篇 |
2016年 | 736篇 |
2015年 | 539篇 |
2014年 | 1117篇 |
2013年 | 1498篇 |
2012年 | 1147篇 |
2011年 | 1385篇 |
2010年 | 1245篇 |
2009年 | 1524篇 |
2008年 | 1524篇 |
2007年 | 1643篇 |
2006年 | 1427篇 |
2005年 | 1351篇 |
2004年 | 1143篇 |
2003年 | 1058篇 |
2002年 | 914篇 |
2001年 | 819篇 |
2000年 | 751篇 |
1999年 | 640篇 |
1998年 | 589篇 |
1997年 | 541篇 |
1996年 | 391篇 |
1995年 | 307篇 |
1994年 | 253篇 |
1993年 | 192篇 |
1992年 | 172篇 |
1991年 | 132篇 |
1990年 | 139篇 |
1989年 | 99篇 |
1988年 | 89篇 |
1987年 | 77篇 |
1986年 | 69篇 |
1985年 | 88篇 |
1984年 | 72篇 |
1983年 | 47篇 |
1982年 | 67篇 |
1981年 | 61篇 |
1980年 | 40篇 |
1979年 | 41篇 |
1978年 | 33篇 |
1977年 | 30篇 |
1976年 | 32篇 |
1973年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
本文考虑复合函数 F(x)=f(x)+h(c(x))最小化问题,给出了校正矩阵逼近 Langrangian 函数的“单边投影 Hessian”的 Broyden-类型方法;此方法是 Q-超线性收敛的.文中还叙述了两个校正算法,并且证明了在合理的条件下,这两种算法都具有局部的两步 Q-超线性收敛性. 相似文献
52.
Yosihiko Ogata 《Annals of the Institute of Statistical Mathematics》1990,42(3):403-433
This paper describes a method for an objective selection of the optimal prior distribution, or for adjusting its hyper-parameter, among the competing priors for a variety of Bayesian models. In order to implement this method, the integration of very high dimensional functions is required to get the normalizing constants of the posterior and even of the prior distribution. The logarithm of the high dimensional integral is reduced to the one-dimensional integration of a cerain function with respect to the scalar parameter over the range of the unit interval. Having decided the prior, the Bayes estimate or the posterior mean is used mainly here in addition to the posterior mode. All of these are based on the simulation of Gibbs distributions such as Metropolis' Monte Carlo algorithm. The improvement of the integration's accuracy is substantial in comparison with the conventional crude Monte Carlo integration. In the present method, we have essentially no practical restrictions in modeling the prior and the likelihood. Illustrative artificial data of the lattice system are given to show the practicability of the present procedure. 相似文献
53.
This article generalizes the one-agent growth theory with discounting to the case of several agents with recursive preferences. In a multi-consumption goods world, we show that, under some regularity conditions, any Pareto optimum can be viewed as a function of a trajectory of a dynamical system. The state space can be chosen to be the product of the space of capitals and the unit simplex. We define and study the properties of generalized value functions. 相似文献
54.
It always takes time for people to digest information and make judgments. The decision maker's preference is not always clear and stable when decision analysis and decision making are performed. In this paper, we introduce a generalized preference structure to cope with indefinite preferences. We describe its general properties, its implication on value function representation, its solution concepts, and methods for obtaining the solutions.This research has been partially supported by NSF Grant No. IST-84-18863. The authors are grateful to Dr. D. J. White for his helpful comments on a previous draft. 相似文献
55.
In this note, we characterize the regular probability measures satisfying the Choquet-Deny convolution equation =* on Abelian topological semigroups for a given probability measure . 相似文献
56.
Yuzo Hosoya 《Annals of the Institute of Statistical Mathematics》1990,42(1):37-49
By means of second-order asymptotic approximation, the paper clarifies the relationship between the Fisher information of first-order asymptotically efficient estimators and their decision-theoretic performance. It shows that if the estimators are modified so that they have the same asymptotic bias, the information amount can be connected with the risk based on convex loss functions in such a way that the greater information loss of an estimator implies its greater risk. The information loss of the maximum likelihood estimator is shown to be minimal in a general set-up. A multinomial model is used for illustration. 相似文献
57.
运用密度泛函理论和非平衡格林函数结合的方法,研究电极区N掺杂对扶手椅型石墨烯纳米带电子输运特性的影响.结果表明,与本征扶手椅型石墨烯纳米带电流-电压曲线相比,宽度为7的石墨烯纳米带电流-电压曲线表现出明显的不对称性,其中心N掺杂表现强烈的整流特性,整流系数达到102数量级,且将N原子从电极区中心位置移动到边缘,整流特性减弱.研究结果表明宽度为7的扶手椅型石墨烯纳米带出现强整流现象的原因主要是负向偏压下能量窗内没有透射峰引起的,该研究结果对将来石墨烯整流器件的设计具有重要的意义. 相似文献
58.
59.
This paper investigates the existence of positive solutions of a singular boundary value problem with negative exponent similar
to standard Emden-Fowler equation. A necessary and sufficient condition for the existence of C[0, 1] positive solutions as
well as C1[0, 1] positive solutions is given by means of the method of lower and upper solutions with the Schauder fixed point theorem. 相似文献
60.
In this paper, we investigate the exact distribution of the waiting time for ther-th ℓ-overlapping occurrence of success-runs of a specified length in a sequence of two state Markov dependent trials. The
probability generating functions are derived explicitly, and as asymptotic results, relationships of a negative binomial distribution
of orderk and an extended Poisson distribution of orderk are discussed. We provide further insights into the run-related problems from the viewpoint of the ℓ-overlapping enumeration
scheme. We also study the exact distribution of the number of ℓ-overlapping occurrences of success-runs in a fixed number
of trials and derive the probability generating functions. The present work extends several properties of distributions of
orderk and leads us a new type of geneses of the discrete distributions. 相似文献