全文获取类型
收费全文 | 18299篇 |
免费 | 2369篇 |
国内免费 | 3802篇 |
专业分类
化学 | 12692篇 |
晶体学 | 213篇 |
力学 | 1453篇 |
综合类 | 58篇 |
数学 | 3639篇 |
物理学 | 6415篇 |
出版年
2024年 | 42篇 |
2023年 | 635篇 |
2022年 | 668篇 |
2021年 | 742篇 |
2020年 | 848篇 |
2019年 | 527篇 |
2018年 | 747篇 |
2017年 | 708篇 |
2016年 | 891篇 |
2015年 | 961篇 |
2014年 | 1119篇 |
2013年 | 1385篇 |
2012年 | 1481篇 |
2011年 | 1315篇 |
2010年 | 1223篇 |
2009年 | 1157篇 |
2008年 | 1036篇 |
2007年 | 1164篇 |
2006年 | 1273篇 |
2005年 | 843篇 |
2004年 | 632篇 |
2003年 | 498篇 |
2002年 | 483篇 |
2001年 | 549篇 |
2000年 | 317篇 |
1999年 | 398篇 |
1998年 | 341篇 |
1997年 | 258篇 |
1996年 | 173篇 |
1995年 | 165篇 |
1994年 | 128篇 |
1993年 | 144篇 |
1992年 | 156篇 |
1991年 | 130篇 |
1990年 | 109篇 |
1989年 | 91篇 |
1988年 | 241篇 |
1987年 | 341篇 |
1986年 | 309篇 |
1985年 | 97篇 |
1984年 | 56篇 |
1983年 | 36篇 |
1982年 | 28篇 |
1981年 | 11篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1976年 | 1篇 |
1971年 | 1篇 |
1957年 | 5篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
81.
82.
带干扰的Erlang(2)风险模型的不破产概率 总被引:1,自引:0,他引:1
本文讨论了带干扰的Erlang(2)风险模型,通过构造一个延迟更新过程,我们得到了不破产概率满足的积分-微分方程,进而得到了不破产概率的明确表达式. 相似文献
83.
The compound binomial risk model with time-correlated claims 总被引:1,自引:0,他引:1
Yuntao Xiao 《Insurance: Mathematics and Economics》2007,41(1):124-133
In this paper, we consider the compound binomial risk model with the time-correlated claims. It is assumed that every main claim will produce a by-claim but the occurrence of the by-claim may be delayed. We obtain the recursive formula of the joint distribution of the surplus immediately prior to ruin and deficit at ruin. Furthermore, the ruin probability is given by means of ruin probability and the deficit at ruin of the classical compound binomial risk model. Finally, we derive an upper bound for the ruin probability. 相似文献
84.
In 1997 Lampert and Slater introduced parallel knock-out schemes, an iterative process on graphs that goes through several rounds. In each round of this process, every vertex eliminates exactly one of its neighbors. The parallel knock-out number of a graph is the minimum number of rounds after which all vertices have been eliminated (if possible). The parallel knock-out number is related to well-known concepts like perfect matchings, hamiltonian cycles, and 2-factors.We derive a number of combinatorial and algorithmic results on parallel knock-out numbers: for families of sparse graphs (like planar graphs or graphs of bounded tree-width), the parallel knock-out number grows at most logarithmically with the number n of vertices; this bound is basically tight for trees. Furthermore, there is a family of bipartite graphs for which the parallel knock-out number grows proportionally to the square root of n. We characterize trees with parallel knock-out number at most 2, and we show that the parallel knock-out number for trees can be computed in polynomial time via a dynamic programming approach (whereas in general graphs this problem is known to be NP-hard). Finally, we prove that the parallel knock-out number of a claw-free graph is either infinite or less than or equal to 2. 相似文献
85.
Gui Qiao XU Yong Sheng SUN Yong Ping LIU 《数学学报(英文版)》2006,22(6):1667-1678
In this paper, we consider the n-widths and average widths of Besov classes in the usual Sobolev spaces. The weak asymptotic results concerning the Kolmogorov n-widths, the linear n-widths, the Gel'fand n-widths, in the Sobolev spaces on T^d, and the infinite-dimensional widths and the average widths in the Sobolev spaces on Ra are obtained, respectively. 相似文献
86.
《Physica A》2006,363(2):393-403
We address the general problem of how to quantify the kinematics of time series with stationary first moments but having non stationary multifractal long-range correlated second moments. We show that a Markov process is sufficient to model important aspects of the multifractality observed in financial time series and propose a kinematic model of price fluctuations. We test the proposed model by analyzing index closing prices of the New York Stock Exchange and the DEM/USD tick-by-tick exchange rates obtained from Reuters EFX. We show that the model captures the characteristic features observed in actual financial time series, including volatility clustering, time scaling and fat tails in the probability density functions, power-law behavior of volatility correlations and, most importantly, the observed nonuniversal multifractal singularity spectrum. Motivated by our finding of strong agreement between the model and the data, we argue that at least two independent stochastic Gaussian variables are required to adequately model price fluctuations. 相似文献
87.
88.
Kai Wang Huan-yu Li Jian-ping Li Zhi-gang Zhang Ning Zhang Lu Chai Qing-yue Wang 《Optics Communications》2006,265(2):369-372
Recently, the semiconductor saturable absorber mirror (SESAM) has become a key component of passive mode-locked solid-state lasers. Here we present a simple method based on the reflection Z-scan technique to measure the key optical parameters of SESAM such as saturation fluence and modulation depth. The experimental results demonstrate that our method is able to perform with a high accuracy of 10−4 and a dynamic range of over four orders of magnitude. 相似文献
89.
ZnO naorods on ZnO-coated seed substrates were fabricated by solution chemical method from Zn(NO3)2/NaOH under assisted electrical field. The working mechanism of electrical field was analyzed and the factors affecting the rod growth such as potential, precursor concentration and growth temperature were elucidated. The structural and optical properties are characterized by SEM, TEM, XRD, HRTEM and UV-vis. The results indicated that the nanorods have wurtzite structure without electrical field and are primarily of zincite structure under electrical field; when the electrical field is 1.1-1.3 V, not only the elevation of ion diffusion and adsorption lower the crystallite/solution interfacial energy and then the crystal nucleation barrier by increasing charge intensity, but also the production of H+ through oxidation of OH− increases properly the degree of solution supersaturation near the substrate, and thus lowers the activation energy. Both the two processes do favor to rod growth. With increasing precursor concentration in this system, the average diameter and length of ZnO nanorods increase, leading to decreasing of optical transmittance. The maximum rod growth rate at given concentration of Zn2+ occurs at a specific temperature. 相似文献
90.