全文获取类型
收费全文 | 1592篇 |
免费 | 183篇 |
出版年
2022年 | 12篇 |
2021年 | 18篇 |
2020年 | 14篇 |
2019年 | 13篇 |
2018年 | 20篇 |
2017年 | 24篇 |
2016年 | 30篇 |
2015年 | 72篇 |
2014年 | 47篇 |
2013年 | 78篇 |
2012年 | 86篇 |
2011年 | 96篇 |
2010年 | 57篇 |
2009年 | 47篇 |
2008年 | 77篇 |
2007年 | 67篇 |
2006年 | 72篇 |
2005年 | 64篇 |
2004年 | 59篇 |
2003年 | 63篇 |
2002年 | 80篇 |
2001年 | 54篇 |
2000年 | 62篇 |
1999年 | 62篇 |
1998年 | 37篇 |
1997年 | 32篇 |
1996年 | 20篇 |
1995年 | 29篇 |
1994年 | 27篇 |
1993年 | 27篇 |
1992年 | 32篇 |
1991年 | 39篇 |
1990年 | 30篇 |
1989年 | 19篇 |
1988年 | 23篇 |
1987年 | 13篇 |
1986年 | 12篇 |
1985年 | 26篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1979年 | 11篇 |
1978年 | 11篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1975年 | 10篇 |
1974年 | 7篇 |
1973年 | 9篇 |
1971年 | 8篇 |
1968年 | 6篇 |
排序方式: 共有1775条查询结果,搜索用时 15 毫秒
1.
Summary The specificity of interaction of amino acids with triplets in the acceptor helix stem of tRNA was investigated by means of a statistical analysis of 1400 tRNA sequences. The imprint of a prototypic genetic code at position 3–5 of the acceptor helix was detected, but only for those major amino acids, glycine, alanine, aspartic acid, and valine, that are formed by spark discharges of simple gases in the laboratory. Although remnants of the code at position 3–5 are typical for tRNAs of archaebacteria, eubacteria, and chloroplasts, eukaryotes do not seem to contain this code, and mitochondria take up an intermediary position. A duplication mechanism for the transposition of the original 3–5 code toward its present position in the anticodon stern of tRNA is proposed. From this viewpoint, the mode of evolution of mRNA and functional ribosomes becomes more understandable.Offprint requests to: W. Moller 相似文献
2.
Vertical migration behaviour of diatom assemblages of Wadden Sea sediments (Dangast, Germany): a study using cryo-scanning electron microscopy. 总被引:1,自引:0,他引:1
The vertical migration behaviour of diatom assemblages inhabiting Wadden Sea sediments near Dangast (Germany) was investigated using cryo-scanning electron microscopy. The diatom assemblages were dominated by small Navicula species. Intertidal sediments which were located at different distances from the high tide level or stayed submerged even throughout low tides were chosen. Samples were prepared and cryofixed in the field. Sampling was restricted to three sets: (i) before the onset of vertical migration, (ii) 3 to 5 h after the onset of vertical migration, and (iii) before the area became flooded again or just prior to dusk. The diatom assemblages inhabiting the different types of sediments did not always show the same response. When the tidal cycle exposed the sediment surfaces during the night cell densities increased in the early morning hours with the onset of light. Later on, although the photon flux density was still increasing, cell densities stayed constant or decreased before the water flooded the areas around noon. In experiments in which the water drained off around noon and the areas became exposed throughout the entire afternoon, cell densities increased even up to dusk when the photon flux density had dropped to values below 20 microM photons m-2 s-1. In an experiment in which the last sampling occurred at 10.15 pm, when the photon flux density had already declined below 10 microM photons m-2 s-1, cell densities had decreased to lower values. This was ca. 1 h before the area was flooded again. Finally, cryo-scanning electron microscopy revealed frequently occurring micro-patches of diatom assemblages which could be differentiated into typical areas of lower and higher cell densities further complicating the pattern of light or water cover induced movements. 相似文献
3.
- Several animal species are known to distinguish between their own eggs and eggs of unrelated conspecifics. However, the cues involved in this discrimination are often unknown. These cues were studied using the predatory mite Gynaeseius liturivorus Ehara.
- Adult females of these predatory mites oviposit in clusters and avoid oviposition close to eggs laid by other females, resulting in reduced cannibalism between offspring. Because predatory mites are blind, it was tested whether volatiles of eggs were used as a cue for egg recognition.
- Adult female predatory mites were offered volatile cues of their own eggs and of unrelated conspecific eggs, and females were prevented from contacting the eggs. Predatory mites oviposited closer to their own eggs than to unrelated eggs. This preference was observed even when one own and one unrelated egg were offered as a volatile source.
- These results suggest that adult female predatory mites can determine kinship using volatiles released from the eggs.
4.
A. Van Aerschot P. Herdewijn G. Janssen H. Vanderhaeghe 《Nucleosides, nucleotides & nucleic acids》2013,32(4):519-536
Abstract The reaction of O-protected inosine with p-nitrophenyl ethanol under Mitsunobu conditions yields a mixture of the 1- and 0° -alkylated derivatives. 2′-Deoxyinosine protected on 06 -, can be synthesized fairly easy from deoxyguanosine with a Mitsunobu reaction followed by reductive deamination. 相似文献
5.
6.
DNA minor groove-binding compounds (polyamides) that target insect and vertebrate telomeric repeats with high specificity were synthesized. Base pair recognition of these polyamides is based on the presence of the heterocyclic amino acids pyrrole and imidazole. One compound (TH52B) interacts uniquely and with excellent specificity (K(d) = 0.12 nM) with two consecutive insect-type telomeric repeats (TTAGG). A related compound, TH59, displays high specificity (K(d) = 0.5 nM) for tandem vertebrate (TTAGGG) and insect telomeric repeats. The high affinity and specificity of these compounds were achieved by bidentate binding of two flexibly linked DNA-binding moieties. Epifluorescence microscopy studies show that fluorescent derivatives of TH52B and TH59 stain insect or vertebrate telomeres of chromosomes and nuclei sharply. Importantly, the telomere-specific polyamide signals of HeLa chromosomes co-localize with the immunofluorescence signals of the telomere-binding protein TRF1. Our results demonstrate that telomere-specific compounds allow rapid estimation of relative telomere length. The insect-specific compound TH52 was shown to be incorporated rapidly into growing Sf9 cells, underlining the potential of these compounds for telomere biology and possibly human medicine. 相似文献
7.
8.
Degradation of n-haloalkanes and alpha, omega-dihaloalkanes by wild-type and mutants of Acinetobacter sp. strain GJ70. 总被引:8,自引:4,他引:4
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A 1,6-dichlorohexane-degrading strain of Acinetobacter sp. was isolated from activated sludge. The organism could grow with and quantitatively release halide from 1,6-dichlorohexane, 1,9-dichlorononane, 1-chloropentane, 1-chlorobutane, 1-bromopentane, ethylbromide, and 1-iodopropane. Crude extracts contained an inducible novel dehalogenase that liberated halide from the above compounds and also from 1,3-dichloropropane, 1,2-dibromoethane, and 2-bromoethanol. The latter two compounds were toxic suicide substrates for the organism at concentrations of 10 and 5 microM, respectively. Mutants resistant to 1,2-dibromoethane (3 mM) lacked dehalogenase activity and did not utilize haloalkanes for growth. Mutants resistant to both 1,2-dibromoethane (3 mM) and 2-bromoethanol (30 mM) could no longer oxidize or utilize alcohols and were capable of hydrolytic dehalogenation of 1,2-dibromoethane to ethylene glycol. 相似文献
9.
Isolation and characterization of a collagen fibril-associated dermatan sulphate proteoglycan from bovine lung 总被引:1,自引:0,他引:1
T H van Kuppevelt H M Janssen H M van Beuningen K S Cheung M M Schijen C M Kuyper J H Veerkamp 《Biochimica et biophysica acta》1987,926(3):296-309
Dermatan sulphate proteoglycans have been extracted from bovine lung with 2.0 M CaCl2 and isolated using CsCl density gradient centrifugation, DEAE ion-exchange chromatography, gel chromatography and preparative sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Ultrastructurally these proteoglycans are specifically associated with collagen fibrils. Dermatan sulphate (Mr 15.10(3)-35.10(3), with a strong prevalence for the higher Mr) is link via an O-glycosidic bond to a protein core, which is rich in Asx, Glx and Leu. Of the total uronic acid, 91% is iduronic acid. A part of the glucuronic acid residues is located near the protein core and a large cluster of disaccharides is devoid of glucuronic acid residues. An inhibition enzyme immunoassay has been developed to quantitate the proteoglycan. A model for the interaction between dermatan sulphate proteoglycans and collagen fibrils is proposed. 相似文献
10.
We isolated two strains of an unnamed Fusobacterium species from human intestinal microflora, which stereospecifically transformed bile acid 3-sulfates into C-3-unsubstituted, ring A-unsaturated bile acids. Both 3 alpha- and 3 beta-sulfates of 5 beta-bile acids were metabolized to delta 3-5 beta-cholenoic acids; 3 beta-sulfates of 5 alpha-bile acids were converted into a mixture of delta 2-5 alpha-bile acids and 3 alpha-hydroxy-5 alpha-bile acids, whereas 3 alpha-sulfates of 5 alpha-bile acids were left intact. Unsulfated bile acids were not transformed into unsaturated derivatives. These strains differ from previously isolated intestinal bacteria, which desulfated bile acid sulfates without further transformation. 相似文献