全文获取类型
收费全文 | 38734篇 |
免费 | 353篇 |
国内免费 | 304篇 |
专业分类
化学 | 17343篇 |
晶体学 | 282篇 |
力学 | 1521篇 |
综合类 | 13篇 |
数学 | 10975篇 |
物理学 | 9257篇 |
出版年
2019年 | 95篇 |
2018年 | 1236篇 |
2017年 | 1482篇 |
2016年 | 875篇 |
2015年 | 711篇 |
2014年 | 684篇 |
2013年 | 1022篇 |
2012年 | 3338篇 |
2011年 | 2520篇 |
2010年 | 1999篇 |
2009年 | 1727篇 |
2008年 | 811篇 |
2007年 | 842篇 |
2006年 | 859篇 |
2005年 | 4671篇 |
2004年 | 4127篇 |
2003年 | 2525篇 |
2002年 | 735篇 |
2001年 | 467篇 |
2000年 | 256篇 |
1999年 | 287篇 |
1998年 | 217篇 |
1997年 | 204篇 |
1996年 | 182篇 |
1995年 | 158篇 |
1994年 | 170篇 |
1993年 | 169篇 |
1992年 | 317篇 |
1991年 | 274篇 |
1990年 | 267篇 |
1989年 | 243篇 |
1988年 | 238篇 |
1987年 | 199篇 |
1986年 | 161篇 |
1985年 | 264篇 |
1984年 | 228篇 |
1983年 | 156篇 |
1982年 | 192篇 |
1981年 | 183篇 |
1980年 | 215篇 |
1979年 | 224篇 |
1978年 | 227篇 |
1977年 | 249篇 |
1976年 | 266篇 |
1975年 | 209篇 |
1974年 | 175篇 |
1973年 | 237篇 |
1972年 | 136篇 |
1971年 | 115篇 |
1970年 | 104篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
The ligand 2,2′,2″-nitrilotriphenol reacts with P(III) and P(V) compounds to form corresponding phosphorus complexes. Syntheses and NMR data of 2,2′,2″-nitrilotriphenyl phosphite ( II ), 2,2′,2″-nitrilotriphenyl phosphate ( III ) and of a hydrolysis product of II , 2,2′-[N-(2-hydroxyphenyl)imino]diphenly phosphonate ( IV ), are reported, as well as crystal structures of II and IV . Phosphite II shows a bicycloundecane framework; no N?Pinteraction is present. The phosphonate IV shows two coordinated and one dangling phenol group; the N-atom does not interact with the P-atom. Strong acids protonate II as well as III to form cations: in these, NMR evidence indicates coordination of the N-atom to the P-atom. 相似文献
73.
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
74.
75.
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
76.
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
77.
78.
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
79.
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
80.
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