全文获取类型
收费全文 | 528131篇 |
免费 | 4642篇 |
国内免费 | 1281篇 |
专业分类
化学 | 269038篇 |
晶体学 | 7645篇 |
力学 | 25990篇 |
综合类 | 17篇 |
数学 | 67779篇 |
物理学 | 163585篇 |
出版年
2021年 | 5031篇 |
2020年 | 5477篇 |
2019年 | 6221篇 |
2018年 | 8413篇 |
2017年 | 8560篇 |
2016年 | 11625篇 |
2015年 | 6176篇 |
2014年 | 10437篇 |
2013年 | 23485篇 |
2012年 | 18334篇 |
2011年 | 21788篇 |
2010年 | 16419篇 |
2009年 | 16279篇 |
2008年 | 20656篇 |
2007年 | 20508篇 |
2006年 | 18612篇 |
2005年 | 16620篇 |
2004年 | 15468篇 |
2003年 | 13955篇 |
2002年 | 13847篇 |
2001年 | 14728篇 |
2000年 | 11343篇 |
1999年 | 8752篇 |
1998年 | 7600篇 |
1997年 | 7470篇 |
1996年 | 6928篇 |
1995年 | 6257篇 |
1994年 | 6264篇 |
1993年 | 6017篇 |
1992年 | 6375篇 |
1991年 | 6865篇 |
1990年 | 6577篇 |
1989年 | 6486篇 |
1988年 | 6321篇 |
1987年 | 6132篇 |
1986年 | 5871篇 |
1985年 | 7408篇 |
1984年 | 7769篇 |
1983年 | 6535篇 |
1982年 | 6817篇 |
1981年 | 6327篇 |
1980年 | 6004篇 |
1979年 | 6507篇 |
1978年 | 6741篇 |
1977年 | 6629篇 |
1976年 | 6588篇 |
1975年 | 6303篇 |
1974年 | 6129篇 |
1973年 | 6424篇 |
1972年 | 4706篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
381.
A homologous series of azomesogens, 2″-[4-(4′-n-alkoxybenzoyloxy)-2-chlorophenylazo] naphthalenes, with lateral chloro groups was synthesised. All the homologues synthesized
exhibit enantiotropic nematic mesophase. The mesomorphic properties of the present series are compared with other structurally
related series to evaluate the effect of lateral chloro group and its position on mesomorphism
This paper was presented at the 10th National Conference on Liquid Crystals held at Bangalore, India during 9–11 October 2003. 相似文献
382.
The rational and sustainable exploitation of nature resources is one of the priority objectives of our society. In this article a method is proposed to evaluate and exploit the energetic resources contained in different forest formations. This method is based on the use of a combustion bomb calorimeter to determine the calorific values of the different samples studied. These results were complemented with chemical analysis of the samples and with environmental and geomorphological studies of the zones were samples were taken. The results obtained during the last 3 years for the residual biomass originated from the forest formations existing in Galicia ensure the reliability and usefulness of the method that can be extended to any forest formation all over the world. 相似文献
383.
384.
Rhodium catalysts have been prepared on palygorskite and montmorillonite (clay) supports by reduction with hydrogen (1 atmosphere) at room temperature of a cationic organometallic rhodium compound anchored to the support. The activity of these catalysts for the hydrogenation of liquid-phase 1-hexene remains constant with increase of prehydrogenation time and with re-use for several runs. No rhodium leaching is observed. 相似文献
385.
The auction algorithm for the transportation problem 总被引:1,自引:0,他引:1
The auction algorithm is a parallel relaxation method for solving the classical assignment problem. It resembles a competitive bidding process whereby unassigned persons bid simultaneously for objects, thereby raising their prices. Once all bids are in, objects are awarded to the highest bidder. This paper generalizes the auction algorithm to solve linear transportation problems. The idea is to convert the transportation problem into an assignment problem, and then to modify the auction algorithm to exploit the special structure of this problem. Computational results show that this modified version of the auction algorithm is very efficient for certain types of transportation problems. 相似文献
386.
387.
388.
S. P. Tretyakova Yu. S. Zamyatnin V. N. Kovantsev Yu. S. Korotkin V. L. Mikheev G. A. Timofeev 《Zeitschrift für Physik A Hadrons and Nuclei》1989,333(4):349-353
The emission of Ne and Mg nuclei was detected in the spontaneous decay of234U with probabilities of, respectively, (3.9 ±1.0) × 10?13 and (2.3 ±0.7) × 10?13 relative toα-decay. The upper limits of this kind of decay for235U and236U have been established. Systematics of half-lives for cluster emission are found to be similar to the Geiger-Nuttall dependence forα-decay. Some evidence for the presence of hindrance to cluster emission from the odd-mass nuclei233U and235U is obtained. 相似文献
389.
390.
R. J. Saykally K. M. Evenson D. A. Jennings L. R. Zink A. Scalabrin 《International Journal of Infrared and Millimeter Waves》1987,8(6):653-662
Twenty new cw FIR laser lines in CD3OH, optically pumped by a CO2 laser, are reported. The frequencies of 39 of the stronger laser lines were measured relative to stabilized CO2 lasers with a fractional uncertainty, as determined by the reproducibility of the FIR frequency itself, of 2 parts in 107.Contribution of the U.S. Government, not subject to copyright. 相似文献