全文获取类型
收费全文 | 3955篇 |
免费 | 416篇 |
国内免费 | 323篇 |
专业分类
化学 | 3023篇 |
晶体学 | 57篇 |
力学 | 158篇 |
综合类 | 21篇 |
数学 | 406篇 |
物理学 | 1029篇 |
出版年
2023年 | 38篇 |
2022年 | 59篇 |
2021年 | 116篇 |
2020年 | 106篇 |
2019年 | 139篇 |
2018年 | 112篇 |
2017年 | 85篇 |
2016年 | 171篇 |
2015年 | 196篇 |
2014年 | 207篇 |
2013年 | 276篇 |
2012年 | 330篇 |
2011年 | 323篇 |
2010年 | 219篇 |
2009年 | 222篇 |
2008年 | 274篇 |
2007年 | 226篇 |
2006年 | 193篇 |
2005年 | 190篇 |
2004年 | 146篇 |
2003年 | 126篇 |
2002年 | 140篇 |
2001年 | 83篇 |
2000年 | 57篇 |
1999年 | 56篇 |
1998年 | 42篇 |
1997年 | 35篇 |
1996年 | 33篇 |
1995年 | 31篇 |
1994年 | 33篇 |
1993年 | 22篇 |
1992年 | 21篇 |
1991年 | 20篇 |
1990年 | 18篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 13篇 |
1986年 | 9篇 |
1985年 | 16篇 |
1984年 | 14篇 |
1983年 | 9篇 |
1980年 | 28篇 |
1979年 | 6篇 |
1978年 | 23篇 |
1977年 | 51篇 |
1976年 | 21篇 |
1975年 | 22篇 |
1974年 | 13篇 |
1973年 | 9篇 |
1943年 | 10篇 |
排序方式: 共有4694条查询结果,搜索用时 15 毫秒
41.
42.
In this study, we report the design and synthesis of a series of new simplified fumitremorgin C analogues. The preliminary biological study indicated some of these simplified fumitremorgin C might be developed into breast cancer resistance inhibitors. 相似文献
43.
44.
Mei Hong Fu Zhu Ju Wang Hong Jun Yang Mayila Maimai Jing Fang Li Ying Tang Lan Yang 《中国化学快报》2007,18(4):415-417
A new C21-steroidal glycoside with two known compounds were isolated from the root of Cynanchum Stauntonii.Based on thespectral analysis,including MS,1H NMR,13C NMR,DEPT,1H-1H COSY,13C-1H COSY,HMQC and HMBC,their chemicalstructures were determinated as glaucogenin-C 3-O-a-L-cymaropyranosyl-(1→4)-b-D-digitoxopyranosyl-(1→4)-β-D-canaropyranoside(1),stigmasterol(2)and ursolic acid(3). 相似文献
45.
Cycloaddition of carbon dioxdie and propylene oxide to propylene carbonate catalyzed by tetra-tert-butyl metal phthalocyanine in the presence of tributylamine(TBA) shows higher yield than catalyzed by unsubstituted metal phthalocyanine.Comparing different catalysts of diverse metals,(t-Bu)4PcMg is more active than (t-Bu)PcFe ,But(t-Bu)4PcCo and (t-Bu)4PcNi only have low catalytic activities towards the reaction.Moreover,the yield will increase as the temperature increases. 相似文献
46.
Biosynthesis of polyhydroxyalkanoates (PHAs) consisting of 3-hydroxyalkanoates (3HAs) of 4 to 10 carbon atoms was examined
in metabolically engineered Escherichia coli strains. When the fadA and/or fadB mutant E. coli strains harboring the plasmid containing the Pseudomonas sp. 61-3 phaC2 gene and the Ralstonia eutropha phaAB genes were cultured in Luria-Bertani (LB) medium supplemented with 2 g/L of sodium decanoate, all the recombinant E. coli strains synthesized PHAs consisting of C4, C6, C8, and C10 monomer units. The monomer composition of PHA was dependent on
the E. coli strain used. When the fadA mutant E. coli was employed, PHA containing up to 63 mol% of 3-hydroyhexanoate was produced. In fadB and fadAB mutant E. coli strains, 3-hydroxybutyrate (3HB) was efficiently incorporated into PHA up to 86 mol%. Cultivation of recombinant fadA and/or fadB mutant E. coli strains in LB medium containing 10 g/L of sodium gluconate and 2 g/L of sodium decanoate resulted in the production of PHA
copolymer containing a very high fraction of 3HB up to 95 mol%. Since the material properties of PHA copolymer consisting
of a large fraction of 3HB and a small fraction of medium-chain-length 3HA are similar to those of low-density polyethylene,
recombinant E. coli strains constructed in this study should be useful for the production of PHAs suitable for various commercial applications. 相似文献
47.
Raman Spectroscopic Investigations of Coordination Polymeric Metal Tricyanmethanides The Raman spectra of 3d-metal tricyanmethanides M{C(CN)3}2 as well as of [Ni{C(CN)3}2py2] are investigated. The observed Raman lines are assigned, characteristic variations of position and intensity of these lines are discussed. 相似文献
48.
49.
Abstract— Irradiation of thin films consisting of 4,5',8-trimethylpsoralen (TMP), adenosine and small amounts of alcohols led to TMP-alcohol photoadducts in addition to TMP-adenosine photoadducts. Four TMP-ethanol and two TMP-methanol adducts have been separated and characterized. Covalent bonds were formed between the 4-carbon of TMP and the α-carbon to the hydroxy group in the alcohols. The TMP-alcohol photoadducts were formed only in the TMP film containing small amounts of alcohol and adenosine. Furthermore, no photoadduct of TMP and ribose was detected upon photolysis of a TMP-ribose film, suggesting that the adenine moiety plays a specific role in the reaction. The interaction of adenosine with psoralens in a dry film may be related to the DNA sequence selectivity observed for the photoreaction of psoralens with DNA. 相似文献
50.
Chang CH Liao JD Chen JJ Ju MS Lin CC 《Langmuir : the ACS journal of surfaces and colloids》2004,20(26):11656-11663
Alkanethiolate self-assembled monolayers (SAMs) of varied chain lengths were adsorbed upon Au-coated nerve microelectrodes and employed as protein-resistant spacers. The microelectrode spiraled as a cuff type can be used for restoring motor function via electrical stimulation on the peripheral nerve system; however, an increase of electrode impedance might occur during implantation. In this work, a thin-film SAMs treatment upon Au/polyimide (PI) surface of the microelectrode provided a hydrophobic characteristic, which retarded protein adsorption at the initial stage and subsequent pileup (or thickening) process. The protein-resistant effect exhibited comparable SAMs of different chain lengths adsorbed upon Au/PI surfaces. The increase of electrode impedance as a function of protein deposition time was mainly correlated with the addition of reactance that was associated with the pileup thickness of the deposited protein. Particularly, the SAMs-modified surface was capable to detach a significant portion of the accumulated protein from the protein-deposited SAMs/Au/PI, whereas the protein-deposited layers exhibited firm adhesion upon Au/PI surface. It is therefore very promising to apply thin-film SAMs adsorbed upon Au-coated surface for bioinvasive devices that have the need of functional electrical stimulations or sensing nerve signals during chronic implantation. 相似文献