全文获取类型
收费全文 | 15590篇 |
免费 | 2547篇 |
国内免费 | 2121篇 |
学科分类
数理化 | 20258篇 |
出版年
2024年 | 38篇 |
2023年 | 314篇 |
2022年 | 460篇 |
2021年 | 535篇 |
2020年 | 634篇 |
2019年 | 618篇 |
2018年 | 527篇 |
2017年 | 518篇 |
2016年 | 791篇 |
2015年 | 740篇 |
2014年 | 950篇 |
2013年 | 1161篇 |
2012年 | 1431篇 |
2011年 | 1508篇 |
2010年 | 988篇 |
2009年 | 939篇 |
2008年 | 1089篇 |
2007年 | 884篇 |
2006年 | 814篇 |
2005年 | 746篇 |
2004年 | 605篇 |
2003年 | 481篇 |
2002年 | 451篇 |
2001年 | 382篇 |
2000年 | 285篇 |
1999年 | 339篇 |
1998年 | 260篇 |
1997年 | 224篇 |
1996年 | 241篇 |
1995年 | 229篇 |
1994年 | 198篇 |
1993年 | 138篇 |
1992年 | 136篇 |
1991年 | 122篇 |
1990年 | 117篇 |
1989年 | 78篇 |
1988年 | 58篇 |
1987年 | 52篇 |
1986年 | 43篇 |
1985年 | 35篇 |
1984年 | 22篇 |
1983年 | 21篇 |
1982年 | 11篇 |
1981年 | 15篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1957年 | 3篇 |
1928年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
71.
72.
In this paper,the concept of the infinitesimal realization factor is extended to the parameter-dependent performance functions in closed queueing networks. Then the concepts of realization matrix (its elements are called realization factors) and performance potential are introduced,and the relations between infinitesimal realization factors and these two quantities are discussed. This provides a united framework for both IPA and non IPA approaches. Finally,another physical meaning of the service rate is given. 相似文献
73.
L. B. Sjogren H. -X. L. Liu X. -H. Qin C. W. Domier N. C. Luhmann 《International Journal of Infrared and Millimeter Waves》1993,14(6):1201-1216
Device alternatives for millimeter-wave beam control arrays are examined. For the control function, a wide range of semiconductor device as well as bulk material alternatives are considered. In addition, alternatives to the traditional metal strip are considered for the passive electromagnetic array element. This work should provide a broader perspective regarding the choices available for the optimized design of new beam control arrays. 相似文献
74.
75.
微裂纹扩展中的分形现象及其计算机仿真 总被引:1,自引:0,他引:1
本文探讨了采用仿真技术研究微裂纹连接过程和生成分形断口表面的可行性,发展了用于仿真微裂纹随机生长行为的GO模型的基本构相,并进行了计算机仿真实验,由此得出了一此有的结论。 相似文献
76.
77.
Groove guide is widely recognized as one of the most promising millimeter wave transmission structures. In this paper, the mode-matching method is used to analyse the dispersion characteristics of single and asymmetrical double groove guides, and the unified formulae of Nth-order approximation dispersion equations are presented. Based on this analysis, a general program for calculating the dispersion characteristrics of single and asymmetrical double groove guides has been completed. Some comparisons between the results obtained by present method and published data show that very good agreement has been seen. The effectiveness and the reliability of the given formulae and program are thus verified. 相似文献
78.
The sherds of terra-cotta warriors and horses and Lishan clay were characterized by Mossbauer spectroscopy, XRD, XRF, NAA,
thermal and chemical analyses. Lishan clay was testified as the original material of terracotta warriors and horses, the kilning
of these warriors and horses was first carried out in an oxidizing atmosphere, and then changed to a predominantly reducing
atmosphere. With refiring experiments, the temperatures of Q3 and Q4 samples were determined to be 830±50 and 980±50°C respectively.
Transformations of Lishan clay were determined by firing in oxidizing and reducing atmospheres. The Mossbauer parameters of
Lishan clay, which was taken after 2–24h firing, were changing up to 12h. 相似文献
79.
尹传存 《数学物理学报(A辑)》1997,17(2):145-151
设中的角域.该文绘出了A上正调和函数的Martin表示,讨论了极小调和函数与条件Brown运动的一个0—1律之间的关系,并给出了A上极小调和函数的表现形式, 相似文献
80.
Stimulated Raman adiabatic passage (STIRAP) has been successfully extended to multilevel system. During the STIRAP process, the intermediate levels have notable population which is detrimental if these levels could decay to other levels through spontaneous emission. This paper proposes a novel method to reduce the intermediate level population during the STIRAP process. A complete population transfer can be achieved in this modified STIRAP even if the intermediate level decays to other levels. 相似文献