全文获取类型
收费全文 | 2417篇 |
免费 | 467篇 |
国内免费 | 174篇 |
专业分类
化学 | 482篇 |
晶体学 | 24篇 |
力学 | 187篇 |
综合类 | 29篇 |
数学 | 521篇 |
物理学 | 1815篇 |
出版年
2024年 | 5篇 |
2023年 | 27篇 |
2022年 | 72篇 |
2021年 | 61篇 |
2020年 | 73篇 |
2019年 | 55篇 |
2018年 | 59篇 |
2017年 | 66篇 |
2016年 | 101篇 |
2015年 | 62篇 |
2014年 | 166篇 |
2013年 | 178篇 |
2012年 | 146篇 |
2011年 | 176篇 |
2010年 | 129篇 |
2009年 | 163篇 |
2008年 | 166篇 |
2007年 | 176篇 |
2006年 | 161篇 |
2005年 | 113篇 |
2004年 | 85篇 |
2003年 | 104篇 |
2002年 | 82篇 |
2001年 | 73篇 |
2000年 | 63篇 |
1999年 | 65篇 |
1998年 | 107篇 |
1997年 | 44篇 |
1996年 | 53篇 |
1995年 | 39篇 |
1994年 | 35篇 |
1993年 | 21篇 |
1992年 | 26篇 |
1991年 | 17篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 15篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有3058条查询结果,搜索用时 15 毫秒
991.
Xiaoqiang Xie Ruiming Xu Bo Yan Yong Zhang Weigan Lin 《International Journal of Infrared and Millimeter Waves》2005,26(10):1453-1464
This paper presents the analysis and design of a novel millimeter-wave power combining circuit. This combing circuit is composed
of a new style 3-dB combiner, which achieves low-loss, wide-band, and symmetric power division. Different from conventional
Wilkinson hybrid, the proposed combiner requires no isolating resistor, and is easier fabricated and more suitable for millimeter
integrate circuits. Analytical and experimental work on a two-way combining circuit with wave-guide ports in Ka-band shows
the combiner has an insertion loss of 0.2dB, and a power-combining efficiency above 80% in 32–33GHz is obtained. 相似文献
992.
BARC has developed large-area silicon detectors in collaboration with BEL to be used in the pre-shower detector of the CMS
experiment at CERN. The use of floating guard rings (FGR) in improving breakdown voltage and reducing leakage current of silicon
detectors is well-known. In the present work, it has been demonstrated that FGRs can also be used to improve the spectroscopic
response of silicon detectors. The results have been confirmed by carrying outα-particle (≈5 MeV) andγ-ray (60 keV) spectroscopies with the FGR floating or biased and the underlying physics aspect behind the change in spectra
is explained. Although reduction in leakage current after biasing one of the guard rings has been reported earlier, the role
of a guard ring in improving the spectroscopic response is reported for the first time. Results of TCAD simulations for silicon
detectors with the guard ring under different biasing conditions have been presented. Low yield in producing large-area silicon
detectors makes them very costly. However, with one of the FGRs biased even a detector having large surface leakage current
can be used to give the same response as a very good detector. This makes the use of large-area silicon detectors very economical
as the yield would be very high (>90%). 相似文献
993.
1.IntrodLIctionOx`ingtoarcfraGtiveincIexoflessthanunityatinfrarcdwaveIength(n.r1)andasmallextinctioncocficicnt(k)thatiscIcIlaandcdfortotalintcrnaI1.efe1ction,thecicularhollowfibcrofGe02a9)SiO2b:lschas\vidclybccnLlsedtotransmittheC02lasercnergy-However,in0rdertohavcastab1coutPtlt,itisreqL1cstedtofindoutthctransmittingcharacteristicforthiskind0f0pticalfibcrs.Obvi0LISly,thccnergylossisoneofthcimportantparametcrsanditdependsn0t0n1yonthc1nodcsofthcopcrativc0pticalx"ave,butalsoonthercflcctive… 相似文献
994.
The paper deals with a numerical method for the evaluation of the electromagnetic loss in a lamination of an electric machine, based upon the Maxwell equations. The underlying problem consists in the computation of the unidirectional magnetic field in a cross-section of the laminate orthogonal to the enforced flux. 相似文献
995.
陈修素 《数学的实践与认识》2002,32(4):549-553
在常数需求率以及有限生产率条件下研究了订货客户耐烦期相同的一类新的生产——库存模型 ,在每一个周期内考虑了延期交货时间超过耐烦期的短缺费用和销售机会损失等因素 ,给出了相应的最优生产时间和周期的确定方法 ,利用数学软件 Matlab及计算机为工具给出了数字例子进行说明 ,其方法和结果为库存系统的管理决策提供了理论依据 相似文献
996.
离散随机序在复合二项破产模型中的应用 总被引:1,自引:1,他引:0
本文的内容由三部分组成 .首先 ,在简述复合二项破产模型近期已得的相关成果的基础上 ,给出了最终破产概率的复合几何分布表示 ;接着 ,在概述了离散随机优序与停止损失序的主要结果后 ,首次提出了幂序的概念 ;最后 ,借助上述离散随机序 ,在复合二项破产模型中探讨了个体索赔额对于最终破产概率与调节系数的影响 相似文献
997.
We consider the asymptotic joint distribution of the eigenvalues and eigenvectors of Wishart matrix when the population eigenvalues become infinitely dispersed. We show that the normalized sample eigenvalues and the relevant elements of the sample eigenvectors are asymptotically all mutually independently distributed. The limiting distributions of the normalized sample eigenvalues are chi-squared distributions with varying degrees of freedom and the distribution of the relevant elements of the eigenvectors is the standard normal distribution. As an application of this result, we investigate tail minimaxity in the estimation of the population covariance matrix of Wishart distribution with respect to Stein's loss function and the quadratic loss function. Under mild regularity conditions, we show that the behavior of a broad class of tail minimax estimators is identical when the sample eigenvalues become infinitely dispersed. 相似文献
998.
Adilson Simonis 《Journal of statistical physics》1996,83(5-6):1225-1239
We prove that thed-dimensional supercritical contact process exhibits metastable behavior, in the pathwise sense. This is done by proving the property of thermalization and using Mountford's theorem. We also extend some previous results on the loss of memory of the process. 相似文献
999.
EXACTENVELOPEWAVESOLUTIONTONONLINEARSCHR■DINGEREQUatIONWITHDISSIPATIVETERMPANZULIANG;ZHENGKEJIEANDYANGQINGJIANAbstract:Inthis... 相似文献
1000.
工序能力评估经济分析 总被引:1,自引:0,他引:1
工序能力不一定是越高越好.提高工序能力有时意味着增加成本,故应作经济分析。本文提出了一种经济分析的方法. 相似文献