全文获取类型
收费全文 | 20910篇 |
免费 | 588篇 |
国内免费 | 27篇 |
专业分类
化学 | 12575篇 |
晶体学 | 360篇 |
力学 | 538篇 |
综合类 | 1篇 |
数学 | 3448篇 |
物理学 | 4603篇 |
出版年
2023年 | 114篇 |
2022年 | 266篇 |
2021年 | 447篇 |
2020年 | 338篇 |
2019年 | 428篇 |
2018年 | 436篇 |
2017年 | 440篇 |
2016年 | 851篇 |
2015年 | 636篇 |
2014年 | 755篇 |
2013年 | 1569篇 |
2012年 | 1191篇 |
2011年 | 1311篇 |
2010年 | 985篇 |
2009年 | 890篇 |
2008年 | 1210篇 |
2007年 | 1096篇 |
2006年 | 902篇 |
2005年 | 783篇 |
2004年 | 677篇 |
2003年 | 611篇 |
2002年 | 485篇 |
2001年 | 379篇 |
2000年 | 334篇 |
1999年 | 240篇 |
1998年 | 246篇 |
1997年 | 189篇 |
1996年 | 203篇 |
1995年 | 220篇 |
1994年 | 153篇 |
1993年 | 128篇 |
1992年 | 156篇 |
1991年 | 140篇 |
1990年 | 143篇 |
1989年 | 136篇 |
1988年 | 144篇 |
1987年 | 120篇 |
1986年 | 135篇 |
1985年 | 231篇 |
1984年 | 229篇 |
1983年 | 149篇 |
1982年 | 141篇 |
1981年 | 150篇 |
1980年 | 161篇 |
1979年 | 115篇 |
1978年 | 118篇 |
1977年 | 102篇 |
1976年 | 114篇 |
1975年 | 101篇 |
1974年 | 85篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
A. Deptuła T. Olczak W. Łada B. Sartowska A.G. Chmielewski C. Alvani P.L. Carconi A. Di Bartolomeo F. Pierdominici S. Casadio 《Journal of Sol-Gel Science and Technology》2003,26(1-3):207-212
Microspheres of Li2TiO3 were fabricated by a classical, inorganic sol-gel process from commercially available TiCl4. Elaborated process consists of the following main steps: (1) dissolving of TiCl4 in concentrated aqueous HCl and addition of LiOH; (2) formation of sol emulsion in 2-ethylhexanol-1 containing the surfactant SPAN-80 (EH); (3) gelation of emulsion drops by extraction of water with partially dehydrated EH; (4) impregnation of gel to Li:Ti molar ratio MR = 2; (5) thermal treatment at 1200°C in order to receive chloride free product. This temperature can be significantly lowered (to 750°C) by dechlorination starting solution TiCl4 by chemical treatment of the with nitric acid to form of nitrate-stabilized titania sols. Tritium release from sol-gel made Li2TiO3 microspheres were found very close to that observed for other traditional materials, however for the first sample process starts slightly earlier. 相似文献
112.
JPC – Journal of Planar Chromatography – Modern TLC - Emodin and twelve phenolic acids (ellagic, gallic, protocatechuic, homoprotocatechuic, caffeic, p-hydroxybenzoic, p-coumaric,... 相似文献
113.
114.
115.
Joanna Tarasińska 《Applications of Mathematics》2003,48(1):67-72
Two estimates of the regression coefficient in bivariate normal distribution are considered: the usual one based on a sample and a new one making use of additional observations of one of the variables. They are compared with respect to variance. The same is done for two regression lines. The conclusion is that the additional observations are worth using only when the sample is very small. 相似文献
116.
117.
A ring is said to be a left essential extension of a reduced ring (domain) if it contains a left ideal which is a reduced ring (domain) and intersects nontrivially every nonzero twosided ideal of the ring. We prove that every ring which is a left essential extension of a reduced ring is a subdirect sum of rings which are essential extensions of domains, but the converse implication does not hold. We give some applications of this result and discuss several related questions.Received: 6 January 2003 相似文献
118.
Grzegorz M. Salamończyk 《Tetrahedron letters》2003,44(40):7449-7453
An efficient synthesis of antiviral dendritic prodrug candidates, water-soluble, polyanionic conjugates of 1st and 2nd generation thiophosphate dendrimers with acyclovir, is described. 相似文献
119.
Isabel Brandariz José L. Barriada Teresa Vilari?o Manuel E. Sastre de Vicente 《Monatshefte für Chemie / Chemical Monthly》2004,343(6):1475-1488
Several reported procedures for calibrating glass electrodes in proton concentration are compared. Some recommendations for non-experts are also given. The examined procedures can be classified into two broad categories, namely: those based on direct potential difference measurements of solutions of known proton concentration and those that use one or several pH standards to calibrate the electrode and subsequently measure the pH of solutions containing known proton concentrations. With a single buffer, the two types of procedures lead to equivalent results. However, if two pH buffers are used, the slope of the calibration graph in proton concentration will differ from the real electrode slope to an extent proportional to the difference between the liquid junction potentials of the two buffers. Therefore, any other method is preferable under these circumstances. 相似文献
120.
Jarosł Spychała 《Research on Chemical Intermediates》2007,33(6):481-486
Evidence for a stereoinduction profile of the reaction of N-methyl-1,3-diaminopropane with acyl chlorides has been provided. A possibility to engage in intramolecular CH2⋯HN and Cl⋯H-N interactions and the proton migration process to the methylamino group leads to the E secondary amides carrying the N⋯H+⋯N or N-H⋯N bridges, that show unusual spectroscopic images. Empirical relations between the Δδ
C chemical shift differences, the polarizability of the CO(S) groups and hydrogen bonding strength have been found. Both 1H-15N-GHSQC and GHMBC experiments provide insight into the nature of hydrogen bonding and confirm the cyclic array of atoms. 相似文献