全文获取类型
收费全文 | 4564篇 |
免费 | 210篇 |
国内免费 | 168篇 |
专业分类
化学 | 888篇 |
晶体学 | 50篇 |
力学 | 157篇 |
综合类 | 17篇 |
数学 | 2234篇 |
物理学 | 1596篇 |
出版年
2023年 | 30篇 |
2022年 | 33篇 |
2021年 | 85篇 |
2020年 | 113篇 |
2019年 | 105篇 |
2018年 | 93篇 |
2017年 | 56篇 |
2016年 | 74篇 |
2015年 | 87篇 |
2014年 | 130篇 |
2013年 | 413篇 |
2012年 | 147篇 |
2011年 | 186篇 |
2010年 | 152篇 |
2009年 | 241篇 |
2008年 | 282篇 |
2007年 | 315篇 |
2006年 | 232篇 |
2005年 | 152篇 |
2004年 | 131篇 |
2003年 | 158篇 |
2002年 | 198篇 |
2001年 | 158篇 |
2000年 | 185篇 |
1999年 | 156篇 |
1998年 | 152篇 |
1997年 | 66篇 |
1996年 | 54篇 |
1995年 | 57篇 |
1994年 | 65篇 |
1993年 | 42篇 |
1992年 | 51篇 |
1991年 | 46篇 |
1990年 | 42篇 |
1989年 | 47篇 |
1988年 | 31篇 |
1987年 | 54篇 |
1986年 | 26篇 |
1985年 | 57篇 |
1984年 | 37篇 |
1983年 | 27篇 |
1982年 | 35篇 |
1981年 | 12篇 |
1980年 | 18篇 |
1979年 | 23篇 |
1978年 | 14篇 |
1977年 | 20篇 |
1976年 | 15篇 |
1975年 | 9篇 |
1973年 | 9篇 |
排序方式: 共有4942条查询结果,搜索用时 15 毫秒
21.
We present a general risk model where the aggregate claims, as well as the premium function, evolve by jumps. This is achieved by incorporating a Lévy process into the model. This seeks to account for the discrete nature of claims and asset prices. We give several explicit examples of Lévy processes that can be used to drive a risk model. This allows us to incorporate aggregate claims and premium fluctuations in the same process. We discuss important features of such processes and their relevance to risk modeling. We also extend classical results on ruin probabilities to this model. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
22.
本文在经典风险模型的基础上,将索赔到达过程推广为更新过程,索赔可以批量到达,且带有常数利息力和Brown运动干扰项,得到一个新的风险模型,运用Markov骨架过程的方法,得出盈余过程的瞬时分布和生存概率. 相似文献
23.
We consider the estimation of multivariate regression functions r(x1,…,xd) and their partial derivatives up to a total order p1 using high-order local polynomial fitting. The processes {Yi,Xi} are assumed to be (jointly) associated. Joint asymptotic normality is established for the estimates of the regression function r and all its partial derivatives up to the total order p. Expressions for the bias and variance/covariance matrix (of the asymptotic distribution) are given. 相似文献
24.
Solomon Fekade Mulugeta Bekele 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):369-374
We analyze the relaxation behavior of a bistable system when the background temperature profile is inhomogeneous due to the
presence of a localized hot region (blowtorch) on one side of the potential barrier. Since the diffusion equation for inhomogeneous
medium is model-dependent, we consider two physical models to study the kinetics of such system. Using a conventional stochastic
method, we obtain the escape and equilibration rates of the system for the two physical models. For both models, we find that
the hot region enhances the escape rate from the well where it is placed while it retards the escape rate from the other well. However, the value of the escape rate from the well where the hot region is placed differs
for the two models while that of the escape rate from the other well is identical for both. This work, for the first time,
gives a detailed report of the similarities and differences of the escape rates and, hence, exposes the common and distinct
features of the two known physical models in determining the way the bistable system relaxes.
Received 25 September 2001 相似文献
25.
Olav Kallenberg 《Stochastic Processes and their Applications》1992,40(2):199-223
From the predictable reduction of a marked point process to Poisson, we derive a similar reduction theorem for purely discontinuous martingales to processes with independent increments. Both results are then used to examine the existence of stochastic integrals with respect to stable Lévy processes, and to prove a variety of time change representations for such integrals. The Knight phenomenon, where possibly dependent but orthogonal processes become independent after individual time changes, emerges as a general principle. 相似文献
26.
Simple expressions are given for the mean delay, mean waiting time, and mean busy period length in a multiplexer. Data streams with active periods having a general distribution are permitted, and the data rate during the active periods can be random. Data can also arrive in batches. The key restrictions of the model are that the sources are independent, idle periods are exponentially distributed, and a source generates at least enough data during an active period to keep the server busy throughout the period. The exact formulas allow evaluation of the error in approximations such as a heavy traffic diffusion approximation.Both continuous and discrete time models are considered. The discrete-time model includes that studied by Viterbi and subsequently generalized by Neuts. The Pollaczek-Khinchine formula for the mean amount of work in anM/GI/1 queue is retrieved as a limiting case.Preliminary version presented at IEEE INFOCOM, San Francisco, April 1993. 相似文献
27.
Esa Nummelin 《Journal of Theoretical Probability》1994,7(4):739-756
The paper is concerned with characterization results for distributional regeneration. It is shown that distributional regeneration is equivalent to renewal representation of the associated (shift) Markov operator. A sufficient condition for the distributional regeneration of the transfer operator in terms of variation is also formulated. Finally, a minorization condition is formulated and proved to be sufficient for recurrent co-Feller operators. 相似文献
28.
T. Schäfer 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):403-408
We review many-body calculations of the equation of state of dilute neutron matter in the context of effective-field theories
of the nucleon-nucleon interaction. 相似文献
29.
D. Boilley A. Marchix B. Jurado K. -H. Schmidt 《The European Physical Journal A - Hadrons and Nuclei》2007,33(1):47-52
We propose a new formula for the saddle-to-scission time that is more general that the one based on Kramers' approach. Its
validity and applicability is then studied in detail. Such a formula is useful for the evaluation of the fission time of very
heavy nuclei. 相似文献
30.
技术的动态发展和企业间的竞争对企业新产品策略有很大影响,直接决定新产品的引进周期。本文在产业技术动态变化的随机环境下构建随机动态规划模型,关注产业技术进步、投资成本和产品市场竞争等影响因素,探讨企业进行新产品引进的周期选择,对新产品引进的周期和质量决策进行方法设计和应用举例。利用随机动态规划模型得出新产品引进的最优时间周期,用算例分析技术进步和产品研发成本对企业引进周期策略的影响,采取策略迭代的方法进行求解,发现技术进步较快时企业的新产品引进步伐也较快,研发成本的提高使企业的新产品引入步伐降低。 相似文献