全文获取类型
收费全文 | 2633篇 |
免费 | 29篇 |
国内免费 | 13篇 |
专业分类
化学 | 1773篇 |
晶体学 | 6篇 |
力学 | 26篇 |
数学 | 539篇 |
物理学 | 331篇 |
出版年
2016年 | 23篇 |
2015年 | 17篇 |
2014年 | 35篇 |
2013年 | 79篇 |
2012年 | 62篇 |
2011年 | 61篇 |
2010年 | 47篇 |
2009年 | 38篇 |
2008年 | 57篇 |
2007年 | 59篇 |
2006年 | 73篇 |
2005年 | 65篇 |
2004年 | 59篇 |
2003年 | 50篇 |
2002年 | 47篇 |
2001年 | 19篇 |
2000年 | 35篇 |
1999年 | 37篇 |
1998年 | 27篇 |
1997年 | 35篇 |
1996年 | 55篇 |
1995年 | 40篇 |
1994年 | 38篇 |
1993年 | 49篇 |
1992年 | 42篇 |
1991年 | 40篇 |
1990年 | 31篇 |
1989年 | 31篇 |
1988年 | 23篇 |
1987年 | 30篇 |
1986年 | 37篇 |
1985年 | 58篇 |
1984年 | 32篇 |
1983年 | 35篇 |
1982年 | 45篇 |
1981年 | 37篇 |
1980年 | 58篇 |
1979年 | 54篇 |
1978年 | 52篇 |
1977年 | 48篇 |
1976年 | 48篇 |
1975年 | 31篇 |
1974年 | 34篇 |
1973年 | 38篇 |
1972年 | 26篇 |
1971年 | 24篇 |
1970年 | 27篇 |
1967年 | 17篇 |
1930年 | 18篇 |
1929年 | 15篇 |
排序方式: 共有2675条查询结果,搜索用时 15 毫秒
121.
Raj K. Bansal Ruchi Mahnot Dinesh C. Sharma Konstantin Karaghiosoff Alfred Schmidpeter 《Heteroatom Chemistry》1992,3(4):351-357
The title compounds 3 and 7 are novel heterocyclic systems incorporating two-coordinate phosphorus. They are obtained in reasonable to good yields from the condensation of suitable 2-ethyl-3-alkylthiazolinium and -benzothiazolium bromides 2 and 6 with phosphorus trichloride in the presence of triethylamine in an aprotic solvent. Intermediate dichlorophosphino-substituted N-ylides can be observed or isolated in some cases. From a 2-methyl-3-alkylthiazolinium bromide ( 2a ), a 1-(dichlorophosphino) substituted 1, 3-azaphospholo[5,1-b]thiazoline ( 4 ) was obtained. The chemical shift of the two-coordinate phosphorus in 1,3-azaphosphole derivatives clearly reflects the influence of the heterocyclic system annulated to its 1,5-bond and of the substituents in its 2-and 4-positions. 相似文献
122.
123.
Alfred Maelicke 《Nachrichten aus der Chemie》1992,40(10):1141-1142
124.
125.
126.
127.
Alfred Actor 《Fortschritte der Physik》1982,30(8):437-450
The massless ϕ4 theory in four Euclidean dimensions is shown not to have a multiple-instanton solution — even though it does have a single-instanton solution. Our criterion for a multiple-instanton solution of this nontopological theory is that the energy-momentum tensor of the solution be identically zero. Arguments are given that a similar result holds in any number of dimensions for a one-component scale-invariant scalar theory. 相似文献
128.
129.
Ralph Haist Hans-Georg Mack Alfred Waterfeld Gary L. Gard Heinz Oberhammer 《Journal of Molecular Structure》1996,380(3):213-222
The geometric structures and conformational properties of trifluoromethanesulfonic anhydride, (CF3SO2)2O, and bis(trifluoromethylsulfonyl)difluoromethane, (CF3SO2)2CF2 have been studied by gas electron diffraction (GED) and ab initio calculations (HF/3–21G*). The calculations predict for both systems two stable conformers with C2 symmetry and one with C1 symmetry. In both compounds structures with C2 symmetry and dihedral angles SOSC ≈ 100° ((CF3SO2)2O) and SCSC≈ 150° ((CF3SO2)2CF2 are lowest in energy. According to the GED analyses the dominant conformer of (CF3SO2)2O2 possesses C2 symmetry with SOSC dihedral angles of 99.1(14)°. The presence of up to 30% of the two other conformers cannot be excluded; for (CF3SO2)2CF2 only one conformer with C2 symmetry and SCSC dihedral angles of 143(2)° is observed. A complete set of geometric parameters is given. 相似文献
130.
Alfred O. Nier 《Journal of the American Society for Mass Spectrometry》1991,2(6):447-452
This article is a review of the events leading to the development of the double-focusing tandem mass spectrometer system, which is sometimes called the Johnson-Nier geometry. An essential feature of the geometry is that it eliminates second-order angular aberration, enhancing the sensitivity, without a loss in resolution. Flexibility in the choice of ion source and collector designs is assured because both are outside of regions of electric and magnetic fields. The vacuum housing permits high-temperature baking, ensuring ultrahigh vacuum conditions. Although introduced initially for the purpose of determining precise atomic masses, the design has found its greatest application in studies of structure of heavy molecules, making use of the high resolution to identify fragments. In many cases the composition of a molecule, or fragment, can be deduced from its exact mass by utilizing the known atomic masses of likely constituent atoms. 相似文献