全文获取类型
收费全文 | 15147篇 |
免费 | 1916篇 |
国内免费 | 914篇 |
专业分类
化学 | 1139篇 |
晶体学 | 16篇 |
力学 | 990篇 |
综合类 | 228篇 |
数学 | 6616篇 |
物理学 | 3052篇 |
无线电 | 5936篇 |
出版年
2024年 | 16篇 |
2023年 | 172篇 |
2022年 | 240篇 |
2021年 | 293篇 |
2020年 | 370篇 |
2019年 | 344篇 |
2018年 | 381篇 |
2017年 | 519篇 |
2016年 | 584篇 |
2015年 | 523篇 |
2014年 | 939篇 |
2013年 | 1058篇 |
2012年 | 1039篇 |
2011年 | 951篇 |
2010年 | 833篇 |
2009年 | 916篇 |
2008年 | 999篇 |
2007年 | 988篇 |
2006年 | 884篇 |
2005年 | 808篇 |
2004年 | 665篇 |
2003年 | 650篇 |
2002年 | 571篇 |
2001年 | 492篇 |
2000年 | 410篇 |
1999年 | 390篇 |
1998年 | 308篇 |
1997年 | 277篇 |
1996年 | 244篇 |
1995年 | 193篇 |
1994年 | 136篇 |
1993年 | 111篇 |
1992年 | 94篇 |
1991年 | 75篇 |
1990年 | 66篇 |
1989年 | 54篇 |
1988年 | 48篇 |
1987年 | 45篇 |
1986年 | 35篇 |
1985年 | 56篇 |
1984年 | 30篇 |
1983年 | 16篇 |
1982年 | 24篇 |
1981年 | 16篇 |
1980年 | 26篇 |
1979年 | 27篇 |
1978年 | 17篇 |
1977年 | 7篇 |
1976年 | 10篇 |
1973年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 912 毫秒
41.
Investigation of the mean free path of projectile fragments produced in 16O-Em collision at 60 A GeV 下载免费PDF全文
Results are presented for an investigation of the mean free path of projectile fragments with charge 3≤Z≤8, produced by 60 A GeV {}^{16}O in nuclear emulsion. No dependence of mean free path on the distance from the point of the fragment emission is observed and our result is consistent with the nonexistence of anomalons. 相似文献
42.
Zi‐Niu Wu 《国际流体数值方法杂志》2005,48(5):541-564
The widely used locally adaptive Cartesian grid methods involve a series of abruptly refined interfaces. In this paper we consider the influence of the refined interfaces on the steady state errors for second‐order three‐point difference approximations of flow equations. Since the various characteristic components of the Euler equations should behave similarly on such grids with regard to refinement‐induced errors, it is sufficient enough to conduct the analysis on a scalar model problem. The error we consider is a global error, different to local truncation error, and reflects the interaction between multiple interfaces. The steady state error will be compared to the errors on smooth refinement grids and on uniform grids. The conclusion seems to support the numerical findings of Yamaleev and Carpenter (J. Comput. Phys. 2002; 181: 280–316) that refinement does not necessarily reduce the numerical error. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
43.
A time discrete scheme is used to approximate the solution toa phase field system of PenroseFife type with a non-conservedorder parameter. An a posteriori error estimate is presentedthat allows the estimation of the difference between continuousand semidiscrete solutions by quantities that can be calculatedfrom the approximation and given data. 相似文献
44.
In this paper we consider the numerical approximation of steady and unsteady generalized Newtonian fluid flows using divergence free finite elements generated by the Powell–Sabin–Heindl elements. We derive a priori and a posteriori finite element error estimates and prove convergence of the method of successive approximations for the steady flow case. A priori error estimates of unsteady flows are also considered. These results provide a theoretical foundation and supporting numerical studies are to be provided in Part II. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
45.
M型四能级原子与三模场相互作用系统的动力学特性 总被引:2,自引:2,他引:0
采用全量子理论,研究了M型四能级原子与三模场相互作用系统的动力学特性,通过数值计算,分析了光场失谐量、初始光子数和原子初始状态对原子布居概率和光子统计演化规律的影响. 相似文献
46.
47.
Chin-Tsang Chiang Mei-Cheng Wang 《Annals of the Institute of Statistical Mathematics》2004,56(1):87-100
This paper proposes kernel estimation of the occurrence rate function for recurrent event data with informative censoring.
An informative censoring model is considered with assumptions made on the joint distribution of the recurrent event process
and the censoring time without modeling the censoring distribution. Under the validity of the informative censoring model,
we also show that an estimator based on the assumption of independent censoring becomes inappropriate and is generally asymptotically
biased. To investigate the asymptotic properties of the proposed estimator, the explicit form of its asymptotic mean squared
risk and the asymptotic normality are derived. Meanwhile, the empirical consistent smoothing estimator for the variance function
of the estimator is suggested. The performance of the estimators are also studied through Monte Carlo simulations. An epidemiological
example of intravenous drug user data is used to show the influence of informative censoring in the estimation of the occurrence
rate functions for inpatient cares over time. 相似文献
48.
49.
基于DMF捕获系统频率选择性信道下捕获性能的分析 总被引:1,自引:0,他引:1
对基于数字匹配滤波器(DMF)捕获系统在频率选择性信道下的捕获性能进行了深入讨论,利用状态转移图推导出单次驻留判决方式时平均捕获时间的表达式,对平均捕获时间与多径分量的关系进行了数字分析。得出的主要结论是:对于多径分量为非衰落信号时,多径分量之间的能量差别越大,系统捕获性能越好,多径分量的能量相等时,系统捕获性能最差,且随着可以分离的多径路数的增加下降;对于多径分量为慢衰落信号时,多径信道的捕获性能好于单径信道(非频率选择性衰落信道),且多径分量之间的能量差别越大,系统捕获性能越差,当多径分量的能量相等时,捕获性能最好,这与非衰落信道的情形相反。因此在频率选择性衰落信道中,采用分集接收可以改善系统的捕获性能。 相似文献
50.