全文获取类型
收费全文 | 4450篇 |
免费 | 143篇 |
国内免费 | 11篇 |
专业分类
化学 | 2468篇 |
晶体学 | 42篇 |
力学 | 136篇 |
数学 | 477篇 |
物理学 | 1481篇 |
出版年
2023年 | 30篇 |
2022年 | 74篇 |
2021年 | 72篇 |
2020年 | 86篇 |
2019年 | 90篇 |
2018年 | 103篇 |
2017年 | 73篇 |
2016年 | 122篇 |
2015年 | 92篇 |
2014年 | 114篇 |
2013年 | 270篇 |
2012年 | 251篇 |
2011年 | 279篇 |
2010年 | 174篇 |
2009年 | 153篇 |
2008年 | 227篇 |
2007年 | 222篇 |
2006年 | 228篇 |
2005年 | 189篇 |
2004年 | 132篇 |
2003年 | 117篇 |
2002年 | 105篇 |
2001年 | 75篇 |
2000年 | 76篇 |
1999年 | 53篇 |
1998年 | 45篇 |
1997年 | 42篇 |
1996年 | 50篇 |
1995年 | 49篇 |
1994年 | 45篇 |
1993年 | 57篇 |
1992年 | 45篇 |
1991年 | 34篇 |
1990年 | 49篇 |
1989年 | 40篇 |
1988年 | 40篇 |
1987年 | 39篇 |
1985年 | 46篇 |
1984年 | 39篇 |
1983年 | 41篇 |
1982年 | 36篇 |
1981年 | 39篇 |
1980年 | 41篇 |
1979年 | 33篇 |
1978年 | 39篇 |
1977年 | 33篇 |
1976年 | 37篇 |
1975年 | 31篇 |
1974年 | 35篇 |
1973年 | 37篇 |
排序方式: 共有4604条查询结果,搜索用时 15 毫秒
91.
We define the Lie algebrac(n) of centrosymmetric matrices. It generates a noncompact and nonsemisimple local Lie group with the unusual property that expc(n) c(n). The group contains an invariant subgroup of Lorentz boost/ dilation transformations. Forn even, these form a subgroup of the conformal group of the Lorentzian metric with signature (– + – + – +). 相似文献
92.
93.
94.
95.
Rita Das Nigamananda Das Anadi C. Dash Ansuman Roy Shyamal K. Sarkar 《Transition Metal Chemistry》1996,21(1):90-94
Summary The reaction of ()-(tetren)CoOH2+ with S2O
3
2-
in the 7.25–8.28 pH range at 20–40 °C yielded S- (yellow) and O- (purple) bonded thiosulfato(tetren)cobalt(III) complexes, the former in larger quantities. The rate determining step is preceded by diffusion-controlled ion-pair [(tetren)CoOH2+,S2O
3
2-
] formation. Replacement of coordinated OH- by S2O
3
2-
is interpreted in terms of an internal conjugate base mechanism: (tetren)CoOH2+ (tetren-H)CoOH
2
2+
, the reactive amido conjugate base being generated by intramolecular proton transfer from the coordinated NH site.In acid medium the S-bonded (tetren)Co(S2O3)+ is highly stable to redox decomposition, in contrast to its pentaammine analogue. The complex however, undergoes base hydrolysis yielding the corresponding hydroxo complex. The rate and activation parameters for the base hydrolysis have been reported. Photolysis of O- and S-bonded isomers of [(tetren)CoS2O3]+ in acidic medium at 254 and 313 nm, respectively, yielded aquation products accompanied by some decomposition of S2O
3
2-
. 相似文献
96.
W. Krakow N. M. Rivera R. A. Roy R. S. Ruoff J. J. Cuomo 《Applied Physics A: Materials Science & Processing》1993,56(3):185-192
Thin films (25-2500 Å) of C60 molecules have been deposited on both (001) NaCl and mica substrates at varying temperatures by resistive evaporation. Both electron diffraction and high resolution microscopy have been used to assess the degree of crystallinity, the orientational ordering and the nature of the defects present in these face-centered-cubic films. For NaCl, optimum conditions yielded polycrystalline films with a tendency towards a 110 orientation, while for mica, extended single crystal films have been fabricated which exhibit a 111 direction normal to the film surface. 相似文献
97.
Atiya MS Chiang IH Frank JS Haggerty JS Ito MM Kycia TF Li KK Littenberg LS Sambamurti A Stevens A Strand RC Louis WC Akerib DS Marlow DR Meyers PD Selen MA Shoemaker FC Smith AJ Blackmore EW Bryman DA Felawka L Kitching P Konaka A Kuno Y Macdonald JA Numao T Padley P Poutissou JM Poutissou R Roy J Soluk R Turcot AS 《Physical review letters》1993,70(17):2521-2524
98.
99.
100.
Michael J. Bunegar Roy Fields Robert N. Haszeldine 《Journal of fluorine chemistry》1980,15(6):497-509
Fluoroallene and 1, 3-difluoroallene are prepared in good overall yield by the addition of dichlorocarbene to vinyl fluoride and 1, 2-difluoroethylene respectively, followed by pyrolysis of the dichlorocyclopropanes and treatment of the resulting dichloropropenes with zinc. Pyrolysis of 1, 1-dichloro-2-fluorocyclopropane over zinc gives fluoroallene directly.The reaction of allene with 2, 2, 3-trifluoro-3-trifluoro- methyloxiran at 180°C as a source of difluorocarbene gives both 1, 1-difluoro-2-methylenecyclopropane and its rearrangement product 1-(difluoromethylene)cyclopropane, the latter reacting more readily with a second difluorocarbene to give 2, 2, 3, 3- tetrafluorospiropentane. In an analogous way, fluoroallene reacts with dichlorocarbene, generated from trifluoro(trichloromethyl) silane at 140°C, to give - and -1, 1-dichloro-2- (fluoromethylene)cyclopropane, 1-(dichloromethylene)-2-fluorocyclopropane, and 2, 2, 3, 3-tetrachloro-4-fluorospiropentane. 相似文献