全文获取类型
收费全文 | 99245篇 |
免费 | 8179篇 |
国内免费 | 7816篇 |
专业分类
化学 | 31760篇 |
晶体学 | 334篇 |
力学 | 9216篇 |
综合类 | 1455篇 |
数学 | 44913篇 |
物理学 | 27562篇 |
出版年
2023年 | 854篇 |
2022年 | 1091篇 |
2021年 | 1770篇 |
2020年 | 2133篇 |
2019年 | 2376篇 |
2018年 | 2001篇 |
2017年 | 2327篇 |
2016年 | 2779篇 |
2015年 | 2438篇 |
2014年 | 3742篇 |
2013年 | 7258篇 |
2012年 | 4070篇 |
2011年 | 4682篇 |
2010年 | 4095篇 |
2009年 | 5623篇 |
2008年 | 6175篇 |
2007年 | 6360篇 |
2006年 | 5777篇 |
2005年 | 4868篇 |
2004年 | 4435篇 |
2003年 | 4483篇 |
2002年 | 4176篇 |
2001年 | 3458篇 |
2000年 | 3371篇 |
1999年 | 3042篇 |
1998年 | 2808篇 |
1997年 | 2304篇 |
1996年 | 1981篇 |
1995年 | 1740篇 |
1994年 | 1620篇 |
1993年 | 1355篇 |
1992年 | 1311篇 |
1991年 | 991篇 |
1990年 | 839篇 |
1989年 | 734篇 |
1988年 | 688篇 |
1987年 | 526篇 |
1986年 | 463篇 |
1985年 | 575篇 |
1984年 | 573篇 |
1983年 | 276篇 |
1982年 | 439篇 |
1981年 | 502篇 |
1980年 | 393篇 |
1979年 | 368篇 |
1978年 | 299篇 |
1977年 | 266篇 |
1976年 | 205篇 |
1974年 | 124篇 |
1973年 | 119篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
本文研究了未知分布的逼近问题,利用随机加权法,给出了有Edgeworth展式的一类(未知)分布的模拟分布,证明了在一定条件下,模拟分布与未知分布的逼近精度达到O(n^-1√lnlnn),称之为随机加权逼近的重对数律。 相似文献
992.
We analyze the statistical behavior of signals in nonlinear circuits with delayed feedback in the presence of external Markovian noise. For the special class of circuits with intense phase mixing we develop an approach for the computation of the probability distributions and multitime correlation functions based on the random phase approximation. Both Gaussian and Kubo-Andersen models of external noise statistics are analyzed and the existence of the stationary (asymptotic) random process in the long-time limit is shown. We demonstrate that a nonlinear system with chaotic behavior becomes a noise amplifier with specific statistical transformation properties. 相似文献
993.
Upper bounds for survival probability of the contact process 总被引:3,自引:0,他引:3
994.
陈吉阳 《中国科学B辑(英文版)》1989,(12)
This paper introduced briefly the research results on lichenometry of the Holoceneglacial fluctuations in the headwater of the Urumqi River, in the central TianshanMountains and discussed the histories of the Holocene glaciers and the climate. It isconsidered that lichenometry is one applicable method for dating the mid- and late-Holocene deposits in the cold and mountainous regions. Rhizocarpon geographicum (L.)DCand Xanthoria elegans (Link.) Th. Fr. could be used for dating the deposits of about 4500and 500 a B.P. respectively. There existed at least four periods of glacial advances whichoccurred before about 5700, 4100, 2800 and 403- 74 a B. P. respectively with the firstperiod the longest. Little Ice Age includes three stages of glacial advances which endedbefore about 403, 208 and 74 a B. P. respectively with the second stage the maximum.During the general Holocene warming processes, there existed at least four cold peri-ods which ended before about 5700, 4100, 2800 and 420- 91 a B.P. respectively, 相似文献
995.
996.
用随机模糊方法研究合理确定工程项目工期 总被引:1,自引:0,他引:1
谢忠镖 《数学的实践与认识》2006,36(10):41-45
站在兼顾业主与建造商的公正立场,基于网络优化技术基础上并以系统的观点,采用随机模糊数学方法研究合理确定项目工期,进而用实际项目进行分析验证,是一种科学合理确定工期的方法. 相似文献
997.
本文研究了一个二阶微分方程的解及其振动性质,利用它获得了一般二阶自共轭方程的振动性判别准则,特别对其中一类二阶微分方程的振动性给出了定量的判别方法.推广了E.Hille的工作,使E.Hille的研究结论成为本文结果的极特殊的情形,同时对一类具有“积分小”系数或可化为具有“积分小”系数的二阶微分方程的振动性与非振动性给出了简便、精确的判别方法. 相似文献
998.
Gerhard Lischke 《Mathematical Logic Quarterly》2006,52(1):20-28
Punctured languages are languages whose words are partial words in the sense that the letters at some positions are unknown. We investigate to which extent restoration of punctured languages is possible if the number of unknown positions or the proportion of unknown positions per word, respectively, is bounded, and we study their relationships for different boundings. The considered restoration classes coincide with similarity classes according to some kind of similarity for languages. Thus all results we can also formulate in the language of similarity. We show some hierarchies of similarity classes for each class from the Chomsky hierarchy and prove the existence of linear languages which are not δ ‐similar to any regular language for any δ < ½. For δ ≥ ½ this is unknown but it could only be possible in the case of non‐slender linear languages. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
999.
Howel Tong 《应用数学学报(英文版)》2002,18(2):177-184
Abstract I reflect upon the development of nonlinear time series analysis since 1990 by focusing on five majorareas of development. These areas include the interface between nonlinear time series analysis and chaos,thenonparametric/semiparametric approach,nonlinear state space modelling,financial time series and nonlinearmodelling of panels of time series. 相似文献
1000.
Endoscopic illumination systems conduct light down a built-in fibre-optic bundle to illuminate the object. Many modern endoscopes employ wide-field imaging optical systems and therefore require an illuminating beam of large divergence. This is commonly provided by placing a strong diverging lens at the far end of the fibre bundle, but it results in a poor uniformity of illumination in the object space. This paper describes the design of a telescopic illumination system to overcome this problem. 相似文献