全文获取类型
收费全文 | 30658篇 |
免费 | 147篇 |
国内免费 | 285篇 |
专业分类
化学 | 12004篇 |
晶体学 | 269篇 |
力学 | 1400篇 |
综合类 | 12篇 |
数学 | 9141篇 |
物理学 | 8264篇 |
出版年
2022年 | 40篇 |
2021年 | 50篇 |
2020年 | 54篇 |
2019年 | 44篇 |
2018年 | 1209篇 |
2017年 | 1466篇 |
2016年 | 745篇 |
2015年 | 577篇 |
2014年 | 505篇 |
2013年 | 744篇 |
2012年 | 3231篇 |
2011年 | 2433篇 |
2010年 | 1884篇 |
2009年 | 1613篇 |
2008年 | 695篇 |
2007年 | 730篇 |
2006年 | 695篇 |
2005年 | 4556篇 |
2004年 | 4029篇 |
2003年 | 2385篇 |
2002年 | 591篇 |
2001年 | 304篇 |
2000年 | 110篇 |
1999年 | 188篇 |
1998年 | 133篇 |
1997年 | 85篇 |
1996年 | 67篇 |
1995年 | 52篇 |
1994年 | 56篇 |
1992年 | 188篇 |
1991年 | 169篇 |
1990年 | 145篇 |
1989年 | 122篇 |
1988年 | 105篇 |
1987年 | 60篇 |
1986年 | 49篇 |
1985年 | 48篇 |
1984年 | 40篇 |
1983年 | 35篇 |
1982年 | 35篇 |
1979年 | 39篇 |
1976年 | 95篇 |
1975年 | 47篇 |
1974年 | 44篇 |
1973年 | 54篇 |
1972年 | 40篇 |
1970年 | 38篇 |
1969年 | 38篇 |
1968年 | 38篇 |
1966年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
In vitro and in vivo proton T1 data are reported that demonstrate that the paramagnetic copper-D-penicillamine complex can be applied as a potential contrast agent to magnetic resonance imaging. 相似文献
72.
The interaction of triethylgallium (TEG) with the Ga-stabilized GaAs(100) surface in the presence of In and Al has been investigated using AES (Auger electron spectroscopy), HREELS (high resolution electron energy loss spectroscopy) and TDS (thermal desorption spectroscopy) techniques. Al is shown to greatly increase the saturation surface coverage of TEG on the surface and to suppress the desorption of TEG and diethylgallium (DEG). Etching of the surface Al by TEG is observed, resulting in the formation of gas phase Al organic species. Alkyl migration from GA to Al centres occurs, and the presence of Al substantially enhances the irreversible deposition of C. In is found to enhance DEG desorption and to lower the temperature at which absorbed ethyl groups decompose to gas phase ethene. Computer modelling has been carried out to extract kinetic parameters from measured thermal desorption spectra. These parameters are then used to calculate expected partial growth rates of GaAs during the growth of GaxAl1−xAs and GaxIn1−xAs using TEG. The data provide a molecular level understanding of the GaAs pa rtial growth rate variations arising during the deposition of III–V ternary materials. 相似文献
73.
T Christensen E B Jensen F Junker H Dalb?ge F Abildgaard J J Led 《Acta chemica Scandinavica (Copenhagen, Denmark : 1989)》1992,46(1):97-99
Biosynthetic human growth hormone specifically 13C-labelled in the carbonyl positions of all 26 leucine residues has been obtained by recombinant DNA techniques using 13C-labelled leucine and an E. coli strain that requires leucine. It is shown that, on the whole, the labelling is specific with no significant mislabelling as would have been the case had the 13C-labelled leucine been metabolized. 相似文献
74.
L Jirovetz G Buchbauer W J?ger A Woidich A Nikiforov 《Biomedical chromatography : BMC》1992,6(3):133-134
After inhalation experiments with sandalwood oil and the pure fragrance compounds coumarin and alpha-terpineol, substances were detected and measured in the blood samples of test animals (mice) using gas chromatography/mass spectrometry (GC/MS) (MID) in connection with GC/FTIR (SWC), GC/AES (carbon and oxygen trace) and flame ionization detection/gas chromatography. Using tiglinic acid benzyl ester as the internal standard the following concentrations in serum could be found: alpha-santalol 6.1 ng/mL, beta-santalol 5.3 ng/mL and alpha-santalene 0.5 ng/mL. In separate inhalation experiments with coumarin and with alpha-terpineol the corresponding concentrations were 7.7 ng/mL and 6.9 ng/mL, respectively. 相似文献
75.
Adducts of the conjugate addition of benzylamine to enantiopure amides of aroylacrylic acid possess high enantiomeric and diastereomeric purity. A high degree of stereoselectivity has been achieved by means of crystallization-induced asymmetric transformation. A practical synthesis leading to dipeptides containing homophenylalanine is depicted. 相似文献
76.
Christabel E. Fowler Catherine Buchber Joël Patarin Alain Walcarius 《Applied Surface Science》2007,253(12):5485-5493
Diatomaceous earth was functionalized by grafting organotrialkoxysilane precursors onto the surface of the porous silica cell walls of this biomineral. Vinyl- and mercapto-containing structures were prepared in aqueous media without disruption of the diatomic architecture. Successful grafting of the organic moieties was confirmed using solid state 29Si MAS NMR spectroscopy, and the presence of the intact diatom framework by scanning electron microscopy. The sorption properties of mercaptopropyl-functionalized diatoms towards heavy metals was studied by measuring the accessibility and diffusion rates of mercury(II) species to the binding sites (-SH) by the means of electrochemical methods. 相似文献
77.
Efficient synthesis of ferrocenylenones using a Friedel-Crafts acylation reaction is described. Acryloyl, methacryloyl, crotonoyl, cinnamoyl, and β-methylcrotonoyl chlorides react with ferrocene in the presence of a Lewis acid (EtAlCl2 or EtAlCl2-Me3Al) to give the corresponding ferrocenylenones (acryloyl, methacryloyl, crotonoyl, cinnamoyl, and methylcrotonoylferrocenes) in good isolated yields. Besides ferrocenylenones, chloroactylferrocene is also synthesised by this method. 相似文献
78.
Titanium tetrachloride promoted reaction of silyl ketene acetals with epoxides, followed by acidic work-up, affords butanolides in moderate/good yields. With epihalohydrins the reaction is regioselective and occurs at the less substituted end of the epoxide; the γ-haloalkyl-γ-butanolides thus obtained can be further transformed into various products. 相似文献
79.
The problem of homoaromaticity in mono-, di- and polyfluorinated- homotropylium cations is addressed by the B3LYP/6-311++G** DFT method. The energetic, structural and magnetic criteria are used for this purpose. They convincingly show that the ground state equilibrium species are aromatic, or in other words that the homoaromaticity is preserved by the (poly)fluorination. In contrast, a considerable decrease in the aromatic stabilization is observed in the transition structures (TS). According to the NICS(0) index, they vary form strongly antiaromatic, via weakly and non-aromatic to slightly aromatic transition states. However, the hierarchy of the aromaticity in fluorinated homotropylium ions predicted by NICS(0) is completely unrelated to that obtained by using the energy criterion assuming a kinetic definition of aromaticity. On the other hand the latter is closely related to geometric parameters of the equilibrium and transition structures. 相似文献