全文获取类型
收费全文 | 3560篇 |
免费 | 821篇 |
国内免费 | 427篇 |
专业分类
化学 | 1254篇 |
晶体学 | 58篇 |
力学 | 194篇 |
综合类 | 58篇 |
数学 | 908篇 |
物理学 | 2336篇 |
出版年
2024年 | 8篇 |
2023年 | 49篇 |
2022年 | 167篇 |
2021年 | 133篇 |
2020年 | 130篇 |
2019年 | 108篇 |
2018年 | 111篇 |
2017年 | 182篇 |
2016年 | 183篇 |
2015年 | 158篇 |
2014年 | 291篇 |
2013年 | 294篇 |
2012年 | 246篇 |
2011年 | 286篇 |
2010年 | 211篇 |
2009年 | 255篇 |
2008年 | 243篇 |
2007年 | 204篇 |
2006年 | 169篇 |
2005年 | 184篇 |
2004年 | 151篇 |
2003年 | 137篇 |
2002年 | 117篇 |
2001年 | 98篇 |
2000年 | 93篇 |
1999年 | 84篇 |
1998年 | 68篇 |
1997年 | 57篇 |
1996年 | 69篇 |
1995年 | 62篇 |
1994年 | 35篇 |
1993年 | 29篇 |
1992年 | 26篇 |
1991年 | 23篇 |
1990年 | 21篇 |
1989年 | 23篇 |
1988年 | 13篇 |
1987年 | 13篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 14篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 12篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1974年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有4808条查询结果,搜索用时 31 毫秒
991.
Deepu John Varughese 《Tetrahedron letters》2006,47(38):6795-6797
Non-traditional methods (grinding, water-based biphasic reactions, microwave chemistry) were used for the preparation of Schiff bases from several amines and 2-nitrobenzaldehydes. These nitro compounds were allowed to react with triethyl phosphite under microwave irradiation for the generation of nitrenes that underwent insertion reactions to form indazoles. This procedure constitutes an energy-efficient, greener chemistry version of the Cadogan reaction for nitrene-based formation of nitrogen heterocycles. 相似文献
992.
Hira L. Koul 《Statistics & probability letters》1985,3(1):1-8
This paper discusses minimum distance (m.d.) estimators of the paramter vector in the multiple linear regression model when the distributions of errors are unknown. These estimators are defined in terms of L2-distances involving certain weighted empirical processes. Their finite sample properties and asymptotic behavior under heteroscedastic, symmetric and asymmetric errors are discussed. Some robustness properties of these estimators are also studied. 相似文献
993.
994.
Sigeo Aki 《Annals of the Institute of Statistical Mathematics》1986,38(1):1-21
Summary It is proved that the martingale term of the empirical distribution function converges weakly to a Gaussian process inD[0, 1]. Some statistics for goodness-of-fit tests based on the martingale term of the empirical distribution function are
proposed. Asymptotic distributions of these statistics under the null hypothesis are given. The approximate Bahadur efficiencies
of the statistics to the Kolmogorov-Smirnov statistic and to the Cramér-von Mises statistic are also calculated.
The Institute of Statistical Mathematics 相似文献
995.
996.
997.
Er3+-Yb3+共掺磷酸盐玻璃放大器的大信号增益与量子效率理论分析 总被引:2,自引:0,他引:2
研究大信号工作状态下的Er^3 -Yb^3 共掺磷酸盐玻璃波导放大器的增益与量子转换效率。从量子转换效率的定义出发,得出了增益、抽运光功率以及量子转换效率三者之间关系的解析表达式。通过数值求解大信号工作状态下的Er^3 -Yb^3 共掺系统的速率方程与光功率传输方程,讨论了Er^3 浓度、Yb^3 浓度、Yb^3 与Er^3 浓度比率、抽运光功率以及放大器长度等因素对量子转换效率的影响。结果表明提高Er^3 浓度与增加放大器长度均有助于提高量子转换效率,高Er^3 浓度掺杂需要相应的高Yb^3 浓度与之相匹配以减小由于高浓度Er^3 掺杂引起的上转换效应,Yb^3 浓度的提高将降低器件的量子转换效率,Yb^3 -Er^3 浓度之比取1~2较好。 相似文献
998.
Excitation functions for the reactions121Sb(α, xn)125−x
I,123Sb(α, xn)127−x
I and121Sb(α, p3n)121Te were obtained from the measurements of the residual activity of stacked foils of antimony trioxide evaporated on Al backings
from threshold to 60 MeV. The excitation functions for the production of121I,123I,124I,126I and121Te are presented. The experimental data are compared with calculations considering equilibrium as well as pre-equilibrium
reaction mechanism according to the hybrid model of Blann. The high energy part of the excitation functions are dominated
by the pre-equilibrium reaction mechanism. Calculations were done using a priori calculational method of Overlaid Alice Code
of Blann. Most of the excitation functions in the energy range mentioned above could very well be fitted with the hybrid model
calculation for exciton numbern=4 withn
n=2 andn
p=2. The overall agreement with the theory is good. Certain discrepancies for example121Sb(α, p3n)121Te excitation function, indicate that the production mechanism is different from the one presumed for the calculation. 相似文献
999.
Gu Ping TANG Zhi Yu WANG College of Life-Science. ZheJiang University Hangzhou Institute of Materials Research & Engineering Singapore Research Link The Second Hospital of Zhejiang University Hangzhou 《中国化学快报》2006,(1)
A new vector, PEG as a core, low Mw PEI was grafted to PEG, and transferrin was conjugated the co-polymer to form PEI-g-PEG-transferrin1,2. NMR, FT-IR and TGA spectroscopy confirmed the structures of activated PEG and the final products. The MW of PEI-g-P… 相似文献
1000.
Taka-Aki Shiraishi 《Annals of the Institute of Statistical Mathematics》1985,37(1):519-527
Summary Local powers of two- andk-sample rank tests under alternatives of contaminated distributions are investigated. It is shown that the rank tests based
on normal scores and Wilcoxon scores are superior to thet-test or theF-test for many choices of alternatives of contaminated distributions and that the values of the asymptotic relative efficiency
of the rank test based on Wilcoxon scores with respect to the normal scores are about one in all the investigated cases. 相似文献