全文获取类型
收费全文 | 6783篇 |
免费 | 139篇 |
国内免费 | 18篇 |
专业分类
化学 | 4068篇 |
晶体学 | 90篇 |
力学 | 154篇 |
数学 | 775篇 |
物理学 | 1853篇 |
出版年
2021年 | 57篇 |
2020年 | 72篇 |
2019年 | 65篇 |
2018年 | 60篇 |
2016年 | 139篇 |
2015年 | 115篇 |
2014年 | 124篇 |
2013年 | 272篇 |
2012年 | 257篇 |
2011年 | 256篇 |
2010年 | 150篇 |
2009年 | 164篇 |
2008年 | 223篇 |
2007年 | 224篇 |
2006年 | 222篇 |
2005年 | 211篇 |
2004年 | 167篇 |
2003年 | 167篇 |
2002年 | 162篇 |
2001年 | 150篇 |
2000年 | 141篇 |
1999年 | 100篇 |
1998年 | 94篇 |
1997年 | 102篇 |
1996年 | 114篇 |
1995年 | 110篇 |
1994年 | 87篇 |
1993年 | 108篇 |
1992年 | 93篇 |
1991年 | 86篇 |
1990年 | 63篇 |
1989年 | 84篇 |
1988年 | 88篇 |
1987年 | 79篇 |
1986年 | 71篇 |
1985年 | 123篇 |
1984年 | 101篇 |
1983年 | 81篇 |
1982年 | 97篇 |
1981年 | 105篇 |
1980年 | 59篇 |
1979年 | 82篇 |
1978年 | 77篇 |
1977年 | 82篇 |
1976年 | 79篇 |
1975年 | 83篇 |
1973年 | 73篇 |
1968年 | 89篇 |
1967年 | 102篇 |
1966年 | 98篇 |
排序方式: 共有6940条查询结果,搜索用时 15 毫秒
71.
Acyl- and Alkylidenephosphines. XXVII. Molecular and Crystal Structure of Methyl-[(N-phenyl, N-trimethylsilyl)thiocarbamoyl]trimethylsilylphosphine . Methyl[(N-phenyl, N-trimethylsilyl)thiocarbamoyl]trimethylsilylphosphine 1a formed via an addition of methylbis(trimethylsilyl)phosphine to phenyl isothiocyanate [1], crystallizes in the monoclinic centrosymmetric space group P21/n with following dimensions of the unit cell determined at a temperature of measurement of ?80±3°C: a=1041.2(4);b=1706.9(12);c=1001.1(6)pm; β=106.41(4)°; Z = 4. An X-ray structure determination (Rw = 0.039) confirms the constitution of the compound as already derived from its nmr spectra. One trimethylsilyl group is bound to the phosphorus atom, whereas the other is connected with the sp2-hybridized nitrogen atom. Characteristic rounded bond lenghts and angles are: P? Si 231, P? CH3 184, P? C(S) 187, C?S 167, N? C(S) 137, and N? Si 181 pm as well as P? C? S 122°, P? C? N 117°, and S? C? N 121°. 相似文献
72.
Max Schmidt und Dieter Franz 《Fresenius' Journal of Analytical Chemistry》1965,215(5):395-400
Zusammenfassung Es wird ein Verfahren zur Bestimmung von Stibin beschrieben, das sich sowohl zur Analyse von SbH3 in organischen Lösungsmitteln als auch zur Bestimmung von flüssigem oder festem SbH3 eignet. Hierbei wird das Stibin mit überschüssigem Brom zu SbV oxydiert, danach mit SO2 zu SbIII reduziert und dieses oxydimetrisch mit Jod oder Bromat titriert.
Herrn Professor Dr. C. Mahr zum 65. Geburtstag gewidmet. 相似文献
Summary A method is proposed for the determination of stibine, applicable to its solutions in organic solvents and also to the solvent-free liquid or solid substance. The procedure involves oxidation of SbH3 with an excess of bromine to SbV, reduction to SbIII with SO2, and oxidimetric titration of the trivalent antimony with iodine or bromate.
Herrn Professor Dr. C. Mahr zum 65. Geburtstag gewidmet. 相似文献
73.
Bier FF Kleinjung F Schmidt PM Scheller FW 《Analytical and bioanalytical chemistry》2002,372(2):308-313
Binding and catalytic activity of the type II restriction endonuclease EcoRI on immobilized DNA has been observed in real time using three different evanescent wave biosensors and two different immobilization techniques. The method gives direct access to the turnover number (kcat) without the necessity for the determination of any concentration or activity. The combination of different evanescent wave techniques gives access to the catalytic mechanism and allows the determination of the rate limiting step. 相似文献
74.
Martina Dotzler Astrid Schmidt Jochen Ellermann Falk A. Knoch Matthias Moll Walter Bauer 《Polyhedron》1996,15(24):4425-4433
BiBr3 or SbI3 react at 20°C with LiN(PPh2)2 (1) to give elementary Bi or Sb and the P---P coupled phosphazene ligand Ph2P---N=PPh2---PPh2=N---PPh2 (2). The reaction of AsI3 with 1 at room temperature formed yellow needles of the eight-membered heterocycle
(3), whereas AsI3 interacted at 80°C with 1 in the molar ratio of 1:3 to give elementary arsenic and 2. Treatment of AsI3 and 1 at 20°C in a 1:2 stoichiometry yielded the seven-membered, cyclic arsenium(I) salt I·4THF (5·4THF), which was characterized by elemental analysis, conductivity, mass, IR and NMR spectroscopy and single-crystal X-ray structural analysis. 相似文献
75.
76.
A new powerful class of low-molecular-weight amphiphilic compounds has been synthesized and their structure-property relationships with respect to their gelation ability of organic solvents have been investigated. These compounds are able to gel organic solvents over a broad range of polarity. Especially polar solvents such as valeronitrile and gamma-butyrolactone can be gelled even at concentrations far below 1 wt %. It was found that the gelation ability of these asymmetrically substituted p-phenylendiamines depends on a well-balanced relation of the terminal head group, the units involved in hydrogen bonding (amide or urea groups), and on the length of the alkyl chain. With this class of new gelators it is possible to tailor thermal and mechanical properties in different organic solvents and open various application possibilities. 相似文献
77.
A universal algebra isaffine complete if all functions satisfying the Substitution Property are polynomials (composed of the basic operations and the elements of the algebra). In 1962, the first author proved that a bounded distributive lattice is affine complete if and only if it does not contain a proper Boolean interval. Recently, M. Ploica generalized this result to arbitrary distributive lattices.In this paper, we introduce a class of functions on a latticeL, we call themID-polynomials, that derive from polynomials on the ideal lattice (resp., dual ideal lattice) ofL; they are isotone functions and satisfy the Substitution Property. We prove that for a distributive latticeL, all unary functions with the Substitution Property are ID-polynomials if and only ifL contains no proper Boolean interval.The research of the first author was supported by the NSERC of Canada. The research of the second author was supported by the Hungarian National Foundation for Scientific Research, under Grant No. 1903. 相似文献
78.
79.
80.