全文获取类型
收费全文 | 28913篇 |
免费 | 85篇 |
国内免费 | 272篇 |
专业分类
化学 | 10426篇 |
晶体学 | 259篇 |
力学 | 1383篇 |
综合类 | 13篇 |
数学 | 9011篇 |
物理学 | 8178篇 |
出版年
2018年 | 1194篇 |
2017年 | 1449篇 |
2016年 | 704篇 |
2015年 | 547篇 |
2014年 | 467篇 |
2013年 | 709篇 |
2012年 | 3097篇 |
2011年 | 2279篇 |
2010年 | 1788篇 |
2009年 | 1524篇 |
2008年 | 543篇 |
2007年 | 603篇 |
2006年 | 584篇 |
2005年 | 4423篇 |
2004年 | 3903篇 |
2003年 | 2298篇 |
2002年 | 481篇 |
2001年 | 288篇 |
2000年 | 106篇 |
1999年 | 182篇 |
1998年 | 115篇 |
1997年 | 74篇 |
1996年 | 50篇 |
1995年 | 45篇 |
1994年 | 49篇 |
1992年 | 171篇 |
1991年 | 156篇 |
1990年 | 141篇 |
1989年 | 111篇 |
1988年 | 102篇 |
1987年 | 62篇 |
1986年 | 46篇 |
1985年 | 43篇 |
1984年 | 31篇 |
1983年 | 34篇 |
1982年 | 30篇 |
1981年 | 27篇 |
1979年 | 35篇 |
1978年 | 35篇 |
1976年 | 84篇 |
1975年 | 40篇 |
1974年 | 44篇 |
1973年 | 55篇 |
1972年 | 40篇 |
1971年 | 27篇 |
1970年 | 34篇 |
1969年 | 38篇 |
1968年 | 35篇 |
1967年 | 33篇 |
1966年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
I Cserpan M Kalman M L Tj?rnhammar A Simoncsits 《Acta chemica Scandinavica (Copenhagen, Denmark : 1989)》1991,45(3):265-272
A general method to convert single-stranded, chemically synthesized oligonucleotides into cloned duplexes is described. Oligonucleotides supplied with 3'-terminal extensions that are complementary to 3'-protruding ends obtained by certain restriction enzymes can be cloned either directly or with the help of an adapter molecule into double-stranded vectors. Two methods have also been developed for consecutive cloning applications. According to these methods, the synthetic oligonucleotides (and their enzymatically prepared complementary strands) are joined, one after the other, inside a cloning vector, each joining requiring one cloning step. Synthetic genes are thus built up from oligonucleotides corresponding to only one strand of the DNA. The sequential assembly of the cloned duplex takes place in the 5' to 3' direction. Each oligonucleotide is supplied with a four-nucleotide-long 3'-terminal extension, but this sequence is eliminated when the joining takes place, leaving no limiting sequence between the oligonucleotides. The two consecutive cloning methods, the adapter and the polycloning site methods, are illustrated by the assembly of short artificial genes. 相似文献
62.
Andrzej Wi?nicki 《Journal of Mathematical Analysis and Applications》2002,267(1):158-172
We use a newly introduced concept of neocompactness to study problems from metric fixed point theory. In particular, we give a sufficient condition for a superreflexive Banach space X to have the fixed point property and obtain shorter proofs of some well-known results in that theory. 相似文献
63.
64.
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
65.
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
66.
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
67.
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
68.
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
69.
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
70.
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