全文获取类型
收费全文 | 18631篇 |
免费 | 1068篇 |
国内免费 | 1316篇 |
专业分类
化学 | 3225篇 |
晶体学 | 104篇 |
力学 | 489篇 |
综合类 | 152篇 |
数学 | 4581篇 |
物理学 | 2269篇 |
综合类 | 10195篇 |
出版年
2024年 | 37篇 |
2023年 | 135篇 |
2022年 | 337篇 |
2021年 | 354篇 |
2020年 | 430篇 |
2019年 | 370篇 |
2018年 | 349篇 |
2017年 | 415篇 |
2016年 | 491篇 |
2015年 | 501篇 |
2014年 | 843篇 |
2013年 | 1079篇 |
2012年 | 943篇 |
2011年 | 1052篇 |
2010年 | 791篇 |
2009年 | 976篇 |
2008年 | 977篇 |
2007年 | 1260篇 |
2006年 | 1131篇 |
2005年 | 977篇 |
2004年 | 922篇 |
2003年 | 895篇 |
2002年 | 709篇 |
2001年 | 637篇 |
2000年 | 588篇 |
1999年 | 526篇 |
1998年 | 454篇 |
1997年 | 376篇 |
1996年 | 401篇 |
1995年 | 318篇 |
1994年 | 283篇 |
1993年 | 227篇 |
1992年 | 195篇 |
1991年 | 177篇 |
1990年 | 138篇 |
1989年 | 138篇 |
1988年 | 120篇 |
1987年 | 97篇 |
1986年 | 55篇 |
1985年 | 57篇 |
1984年 | 38篇 |
1983年 | 21篇 |
1982年 | 38篇 |
1981年 | 22篇 |
1980年 | 14篇 |
1979年 | 28篇 |
1978年 | 20篇 |
1977年 | 24篇 |
1976年 | 21篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
901.
In this paper, we consider an Ishikawa type iteration process with errors, which converges to the unique common fixed point of a pair of contractive type mappings in complete generalized convex metric spaces. Furthermore, we obtain the corresponding results in Banach spaces. Our results extend and generalize many known results. 相似文献
902.
Introducing a surrender option in unit-linked life insurance contracts leads to a dependence between the surrender time and the financial market. [J. Barbarin, Risk minimizing strategies for life insurance contracts with surrender option, Tech. rep., University of Louvain-La-Neuve, 2007] used a lot of concepts from credit risk to describe the surrender time in order to hedge such types of contracts. The basic assumption made by Barbarin is that the surrender time is not a stopping time with respect to the financial market.The goal of this article is to make the hedging strategies more explicit by introducing concrete processes for the risky asset and by restricting the hazard process to an absolutely continuous process.First, we assume that the risky asset follows a geometric Brownian motion. This extends the theory of [T. Møller, Risk-minimizing hedging strategies for insurance payment processes, Finance and Stochastics 5 (2001) 419–446], in that the random times of payment are not independent of the financial market. Second, the risky asset follows a Lévy process.For both cases, we assume the payment process contains a continuous payment stream until surrender or maturity and a payment at surrender or at maturity, whichever comes first. 相似文献
903.
Sze-Man Tse 《Annals of the Institute of Statistical Mathematics》2006,58(4):675-686
In this paper, we consider a nonparametric estimator of the Lorenz curve and Gini index when the data are subjected to random
left truncation and right censorship. Strong Gaussian approximations for the associated Lorenz process are established under
appropriate assumptions. A law of the iterated logarithm for the Lorenz curve is also derived. Lastly, we obtain a central
limit theorem for the corresponding Gini index. 相似文献
904.
We introduce the time-consistency concept that is inspired by the so-called “principle of optimality” of dynamic programming
and demonstrate – via an example – that the conditional value-at-risk (CVaR) need not be time-consistent in a multi-stage
case. Then, we give the formulation of the target-percentile risk measure which is time-consistent and hence more suitable
in the multi-stage investment context. Finally, we also generalize the value-at-risk and CVaR to multi-stage risk measures
based on the theory and structure of the target-percentile risk measure. 相似文献
905.
Converging Marriage in Honey-Bees Optimization and Application to Stochastic Dynamic Programming 总被引:1,自引:0,他引:1
Hyeong Soo Chang 《Journal of Global Optimization》2006,35(3):423-441
In this paper, we first refine a recently proposed metaheuristic called “Marriage in Honey-Bees Optimization” (MBO) for solving
combinatorial optimization problems with some modifications to formally show that MBO converges to the global optimum value.
We then adapt MBO into an algorithm called “Honey-Bees Policy Iteration” (HBPI) for solving infinite horizon-discounted cost
stochastic dynamic programming problems and show that HBPI also converges to the optimal value. 相似文献
906.
For about thirty years, time series models with time-dependent coefficients have sometimes been considered as an alternative
to models with constant coefficients or non-linear models. Analysis based on models with time-dependent models has long suffered
from the absence of an asymptotic theory except in very special cases. The purpose of this paper is to provide such a theory
without using a locally stationary spectral representation and time rescaling. We consider autoregressive-moving average (ARMA)
models with time-dependent coefficients and a heteroscedastic innovation process. The coefficients and the innovation variance
are deterministic functions of time which depend on a finite number of parameters. These parameters are estimated by maximising
the Gaussian likelihood function. Deriving conditions for consistency and asymptotic normality and obtaining the asymptotic
covariance matrix are done using some assumptions on the functions of time in order to attenuate non-stationarity, mild assumptions
for the distribution of the innovations, and also a kind of mixing condition. Theorems from the theory of martingales and
mixtingales are used. Some simulation results are given and both theoretical and practical examples are treated.
Received 2004; Final version 23 December 2004 相似文献
907.
In this paper the distribution of the maximum number of customers in a retrial orbit for a single server queue with Markovian
arrival process and phase type services is studied. Efficient algorithm for computing the probability distribution and some
interesting numerical examples are presented. 相似文献
908.
Frederic Paik Schoenberg 《Annals of the Institute of Statistical Mathematics》2006,58(2):223-233
Simple point processes are often characterized by their associated compensators or conditional intensities. Non-simple point
processes are not uniquely determined by their conditional intensity and compensator, so instead one may identify with the
point process its associated simple point process and corresponding conditional intensity, on an expanded mark space. Some
relations between the conditional intensity on the expanded mark space and the ordinary conditional intensity are investigated
here, and some classes of separable non-simple processes are presented. Transformations into simple point processes, involving
thinning and rescaling, are presented. 相似文献
909.
M. A. Posypkin I. Kh. Sigal 《Computational Mathematics and Mathematical Physics》2006,46(12):2187-2202
The efficiency of parallel implementations of the branch-and-bound method in discrete optimization problems is considered. A theoretical analysis and comparison of two parallel implementations of this method is performed. A mathematical model of the computation process is constructed and used to obtain estimates of the maximum possible speedup. Examples of problems in which none of these two parallel implementations can speed up the computations are considered. 相似文献
910.
We consider a retrial queue with a finite buffer of size N, with arrivals of ordinary units and of negative units (which cancel one ordinary unit), both assumed to be Markovian arrival
processes. The service requirements are of phase type. In addition, a PHL,N bulk service discipline is assumed. This means that the units are served in groups of size at least L, where 1≤ L≤ N. If at the completion of a service fewer than L units are present at the buffer, the server switches off and waits until the buffer length reaches the threshold L. Then it switches on and initiates service for such a group of units. On the contrary, if at the completion of a service
L or more units are present at the buffer, all units enter service as a group. Units arriving when the buffer is full are not
lost, but they join a group of unsatisfied units called “orbit”. Our interest is in the continuous-time Markov chain describing
the state of the queue at arbitrary times, which constitutes a level dependent quasi-birth-and-death process. We start by
analyzing a simplified version of our queueing model, which is amenable to numerical calculation and is based on spatially
homogeneous quasi-birth-and-death processes. This leads to modified matrix-geometric formulas that reveal the basic qualitative
properties of our algorithmic approach for computing performance measures.
AMS Subject Classification: Primary 60K25 Secondary 68M20 90B22. 相似文献