全文获取类型
收费全文 | 75643篇 |
免费 | 7108篇 |
国内免费 | 10047篇 |
专业分类
化学 | 63504篇 |
晶体学 | 1024篇 |
力学 | 1426篇 |
综合类 | 930篇 |
数学 | 7228篇 |
物理学 | 18686篇 |
出版年
2023年 | 626篇 |
2022年 | 1914篇 |
2021年 | 2367篇 |
2020年 | 2010篇 |
2019年 | 1973篇 |
2018年 | 1777篇 |
2017年 | 1993篇 |
2016年 | 2694篇 |
2015年 | 2679篇 |
2014年 | 3185篇 |
2013年 | 6175篇 |
2012年 | 3927篇 |
2011年 | 4222篇 |
2010年 | 3684篇 |
2009年 | 4377篇 |
2008年 | 4581篇 |
2007年 | 4798篇 |
2006年 | 4261篇 |
2005年 | 3504篇 |
2004年 | 3396篇 |
2003年 | 3059篇 |
2002年 | 4973篇 |
2001年 | 2317篇 |
2000年 | 1878篇 |
1999年 | 1655篇 |
1998年 | 1519篇 |
1997年 | 1201篇 |
1996年 | 1158篇 |
1995年 | 1102篇 |
1994年 | 986篇 |
1993年 | 975篇 |
1992年 | 963篇 |
1991年 | 604篇 |
1990年 | 512篇 |
1989年 | 436篇 |
1988年 | 438篇 |
1987年 | 322篇 |
1986年 | 313篇 |
1985年 | 409篇 |
1984年 | 317篇 |
1983年 | 187篇 |
1982年 | 332篇 |
1981年 | 491篇 |
1980年 | 448篇 |
1979年 | 485篇 |
1978年 | 385篇 |
1977年 | 289篇 |
1976年 | 247篇 |
1974年 | 111篇 |
1973年 | 204篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
821.
Edwin Weber Claus Wimmer Ingeborg Csöregh Olga Gallardo 《Journal of inclusion phenomena and macrocyclic chemistry》1997,27(2):141-153
A novel host molecule, 1, suitable for crystalline lattice-type inclusion, has been synthesized, and its cocrystal formation ability has been investigated. Host 1 proved to be of potential use for organic solvent separation and retrieval, and a promising auxiliary for solidification of certain odorous substances. The crystal structures of the solvent-free host 1, and its complex with 1,4-dioxane (1 : 1), have been determined by single crystal X-ray diffraction. The structure of 1 (guest-free) is triclinic, P
, with a = 9.452(2), b = 10.359(3), c = 13.116(3) Å, = 101.80(2), = 106.53(1) and = 104.32(1)°. The spacious, propeller-like molecules are held together by weak van der Waals' forces. The dioxane inclusion compound is monoclinic, P21/a, with a = 15.050(1), b = 8.641(1) and c = 20.658(1) Å, and = 94.56(1)°, and contains two crystallographically independent guest molecules, both located around symmetry centres. The molecular packing seems to be governed by C—H···O type bonds (C···O = 3.31 and 3.48 Å) from the host to the dioxane oxygens. 相似文献
822.
823.
The diagonal elements of the first and second order spinless density matrices have been calculated for the lowest excited1
P and3
P terms of Be, B+ and C++ using wavefunctions at different levels of approximations published in the literature. The analysis of these functions has
resulted in a new interpretation of Hund's first rule in terms of an anisotropic screening effect. 相似文献
824.
825.
Yanishpolskii V. V. Pavlenko A. N. Tertykh V. A. Il'in V. G. Leboda R. Skubiszewska-Zieba J. 《Journal of Thermal Analysis and Calorimetry》2000,62(2):569-573
Mesoporous titanium-containing silicas with TiO2 contents from 1 up to 70 mol% were prepared. The obtained samples have been characterized by the powder X-ray diffraction
data, the diffuse reflectance infrared Fourier transform method, and nitrogen adsorption at 77 K. Specific surface area, total
pore volume, distribution pore volume on pore sizes were determined from nitrogen adsorption isotherm for synthesized titanosilicas.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
826.
Highly ordered mesoporous bioactive glasses with superior in vitro bone-forming bioactivities 总被引:3,自引:0,他引:3
827.
Teleshev A. T. Vasil"eva L. N. Nifant"ev E. E. Tsodikov M. V. Bukhtenko O. V. Zhdanova T. N. 《Russian Chemical Bulletin》2003,52(9):2083-2085
The reactivities of cyclophosphite precursors in alkoxo syntheses involving titanium(iv) tetra(n-butoxide) were studied by 31P NMR and IR spectroscopy. 2-Diethylamido-4-methyl-1,3,2-dioxaphosphinane and 4-ethyl-2,6,7-trioxaphosphabicyclo[2.2.2]octane in benzene are inert toward Ti(OBu)4. Gelation is accompanied by hydrolysis 2-diethylamido-4-methyl-1,3,2-dioxaphosphinane to give the corresponding hydrophosphoryl compound, while 4-ethyl-2,6,7-trioxaphosphabicyclo[2.2.2]octane remains intact during gelation. 相似文献
828.
Suzdalev I. P. Buravtsev V. N. Maksimov Yu. V. Zharov A. A. Imshennik V. K. Novichikhin S. V. Matveev V. V. 《Russian Chemical Bulletin》2003,52(9):1950-1958
Magnetic phase transitions of the first and second order were revealed by Mössbauer spectroscopy in nanosystems of - and -ferric oxides and metallic europium subjected to shear stress (240°) under high pressure (20 kbar). For - and -ferric oxide nanoclusters, the Curie (Neel) points decreased to 300 K, whereas for nanostructured europium the Neel point increased from 90 to 100 K. The thermodynamic model of magnetic phase transitions predicting a change in the character of magnetic phase transitions and a decrease (increase) in the critical Neel (Curie) points in nanoclusters was developed. The type of magnetic phase transitions and the change in the critical points were caused by defects in nanoclusters, whose maximum concentration was observed for the clusters with the 20—50 nm size range. 相似文献
829.
An efficient synthesis of 3,4-dihydropyrimidin-2-(1H)-one derivatives by one-pot three-component condensation reaction between an alkyl or aryl aldehyde, a 1,3-dicarbonyl compound,
and urea or thiourea in the presence of catalytic amount of bromodimethylsulfonium bromide has been developed. The condensation
product was obtained in excellent yields in refluxing ethanol and easily separated from the reaction mixture and purified. 相似文献
830.
本文由[(μtBuS)(μCO)Fe2(CO)6][Et3NH]和硒粉形成的[(μtBuS)(μSe)Fe2(CO)6][Et3NH],分别与溴化苄,二碘甲烷及邻一、间一、对一双(溴甲基)苯反应,合成了蝶状Fe2SSe单簇物(μtBuS)(μPhCH2Se)Fe2(CO)6(3a)和双簇物[(μtBuS)Fe2(CO)6]2(μSeZSeμ)[Z=CH2,o.m.p双(亚甲基)苯](4ad)。类似地,由[(μPhSe)(μCO)Fe2(CO)6][Et3NH]和硫粉或硒粉所形成的[(μPhSe)(μS)Fe2(CO)6][Et3NH]或[(μPhSe)(μSe)Fe2(CO)6][Et3NH]分别与对一双(溴甲基)苯反应合成了蝶状Fe2SSe和Fe2Se2双簇物[(μPhSe)Fe2(CO)6]2[μS(pCH2C6H4CH2)Sμ](5a)及[(μPhSe)Fe2(CO)6]2[μSe(PCH2C6H4CH2)Seμ](5b)。所有产物均经元素分析、IR和1HNMR表征。 相似文献