全文获取类型
收费全文 | 3632篇 |
免费 | 394篇 |
国内免费 | 3篇 |
出版年
2021年 | 54篇 |
2019年 | 45篇 |
2018年 | 43篇 |
2017年 | 47篇 |
2016年 | 65篇 |
2015年 | 105篇 |
2014年 | 129篇 |
2013年 | 183篇 |
2012年 | 205篇 |
2011年 | 196篇 |
2010年 | 127篇 |
2009年 | 109篇 |
2008年 | 147篇 |
2007年 | 162篇 |
2006年 | 137篇 |
2005年 | 140篇 |
2004年 | 144篇 |
2003年 | 131篇 |
2002年 | 149篇 |
2001年 | 68篇 |
2000年 | 67篇 |
1999年 | 74篇 |
1998年 | 65篇 |
1997年 | 47篇 |
1996年 | 40篇 |
1995年 | 30篇 |
1994年 | 36篇 |
1993年 | 41篇 |
1992年 | 44篇 |
1991年 | 49篇 |
1990年 | 39篇 |
1989年 | 37篇 |
1988年 | 36篇 |
1987年 | 27篇 |
1986年 | 28篇 |
1985年 | 38篇 |
1984年 | 43篇 |
1983年 | 24篇 |
1982年 | 48篇 |
1981年 | 32篇 |
1980年 | 37篇 |
1979年 | 24篇 |
1978年 | 36篇 |
1977年 | 30篇 |
1976年 | 32篇 |
1975年 | 29篇 |
1974年 | 42篇 |
1973年 | 29篇 |
1972年 | 23篇 |
1961年 | 24篇 |
排序方式: 共有4029条查询结果,搜索用时 571 毫秒
31.
A library of 50 hybridomas which make antibodies to oat phytochrome was produced from the fusion of spleen cells from immunized Balb/c mice with P3x63Ag8 myeloma cells. Hybridomas were selected in a medium containing hypoxanthine, aminopterin, and thymidine, and specific hybridomas were screened for production of antibodies to phytochrome using a solid-phase enzyme-linked immunoadsorbent assay which was antigen specific. Positive cultures were cloned three times by limit dilution to assure monoclonal growth and stability. Specificity toward phytochrome was established by Western blot analysis and immunoprecipitation. Epitope specificity of nine monoclonal antibodies was determined by competitive inhibition radioimmunoassays and/or comparative immunoblots of tryptic peptides of phytochrome. 相似文献
32.
The left-handed form of poly(dG-m5dC).poly(dG-m5dC) induced by heating the copolymer in the presence of magnesium and stabilized with polyarginine can be used to raise antibodies in rabbits. These antibodies are able to recognize the Z conformation of both methylated and nonmethylated forms of the copolymers. In the same experimental conditions, hypermethylated B DNA is not recognized by these antibodies. 相似文献
33.
Summary Antimonate staining procedures and energy dispersive X-ray microanalytical techniques were used to determine the patterns of localization of calcium in nonstimulated and gravistimulated corn roots. In horizontally positioned roots within the region of the developing bend there was a change in the staining from that principally localized within cells of the stele to asymmetric staining within the vacuoles of the cortical cells along the upper root surface. There was little staining in the walls. The pattern observed is quite different from that seen in gravistimulated coleoptiles. Staining of mitochondria, plastids and Golgi stacks was seen in most cell types, but no asymmetry of staining was observed. In the rootcap where graviperception is thought to occur, there was little staining of any cellular organelles. 相似文献
34.
The effect of histone H1 on the compaction of oligonucleosomes. A quasielastic light scattering study 总被引:1,自引:0,他引:1
C Marion C Hesse-Bezot P Bezot M J Marion B Roux J C Bernengo 《Biophysical chemistry》1985,22(1-2):53-64
The structural properties of H1-depleted oligonucleosomes are investigated by the use of quasielastic laser light scattering, thermal denaturation and circular dichroism and compared to those of H1-containing oligomers. To obtain information on the role of histone H1 in compaction of nucleosomes, translational diffusion coefficients (D) are determined for mono-to octanucleosomes over a range of ionic strength. The linear dependences of D on the number of nucleosomes show that the conformation of stripped oligomers is very extended and does not change drastically with increasing the ionic strength while the rigidness of the chain decreases due to the folding of linker DNA. The results prove that the salt-induced condensation is much smaller for H1-depleted than for H1-containing oligomers and that histone H1 is necessary for the formation of a supercoiled structure of oligonucleosomes, already present at low ionic strength. 相似文献
35.
The major phosphoglycerides in grey and white matter from the brain of the koala have been separated and examined. The major polyunsaturated fatty acids present in both the diacyl- and alk-1-enyl acylglycerophosphorylethanolamines from grey matter were 22:6 omega 3, 20:4 omega 6, and 22:4 omega 6. In both grey and white matter, 22:6 omega 3 and 20:4 omega 6 were concentrated in the 2-position of diacylglycerophosphorylethanolamines and 22:4 omega 6 in the 2-position of alk-1-enylacylglycerophosphorylethanolamines; polyunsaturated fatty acid levels were higher in diacylglycerophosphorylethanolamines. Ethanolamine phosphoglyceride fractions from grey matter were enriched in polyunsaturated fatty acids compared with those from white matter. The acyl groups 18:0, 18:1, and 16:0 and their alk-1-enyl analogues were prominent in grey and white matter ethanolamine phosphoglycerides; 18:1 was dominant in white matter alk-1-enylacylglycerophosphorylethanolamines. The plasmalogen composition of ethanolamine phosphoglycerides was 55% in grey matter and 76% in white matter. Choline phosphoglycerides contained negligible plasmalogen and low polyunsaturated fatty acid levels. Diacylglycerophosphorylcholine was characterized by high levels of 16:0 and 18:1. Similar acyl group distributions were estimated in the 1-position in both grey and white matter, 16:0 being present at greater than 50%. The presence of the molecular species 18:0/22:6 omega 3 was indicated in grey matter diacylglycerophosphorylethanolamine, 18:1/18:1 in white matter alk-1-enylcylglycerophosphorylethanolamine, and 16:0/18:1 in white matter diacylglycerophosphorylcholine. 相似文献
36.
Bonnie J. Reger Maurice S.B. Ku Jeffrey W. Pottert John J. Evans 《Phytochemistry》1983,22(5):1127-1132
The ribulose-1,5-bisphosphate carboxylase/oxygenase purified from maize (a C4 monocot) to homogeneity has a MW of532 000 and sedimentation coeffici 相似文献
37.
Hemming Fiona J. Begeot Martine Dubois Maurice P. Dubois Paul M. 《Cell and tissue research》1983,234(2):427-437
Corticotropes of rat fetuses aged 16, 18 and 21 days were localized by the indirect antibody-enzyme method on semithin sections of the pituitary. The development of the ultrastructure of these cells was observed on consecutive ultrathin sections. In comparison with previous data our present results show that identification of a fetal cell type cannot be based entirely on morphological criteria. The structural peculiarities of corticotropes obtained from studies in vivo are compared with those observed in cells maintained in vitro. 相似文献
38.
Nucleotide sequence of a 'truncated rRNA operon' of the Euglena gracilis chloroplast genome. 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Nucleic acids research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
An extra 16S rRNA gene (s-16S rDNA) from the Euglena gracilis chloroplast genome and several hundred positions of its flanking regions have been sequenced. The structural part has 1486 positions and is to 98% homologous in its sequence with the 16S rRNA gene in functional chloroplast rRNA operons. Sequences of about 200 positions upstream and 15 positions downstream of the structural part of the s-16S rRNA gene region are highly homologous with corresponding parts in the functional operon. Neither tRNA genes (A1a, I1e) nor parts of the 23S and 5S rRNA genes are found within 557 positions after the 3' end of the s-16S rRNA gene, i.e., the 330 bp homology, observed in electron microscopic studies of heteroduplexes (4), between the s-16S rDNA downstream region and the 6.2 kb repeated segment containing the functional rRNA operon, must be due to a DNA stretch in the interoperon spacer. A structural model of the "truncated rRNA operon" is presented. Results from S-1 endonuclease analysis suggest that the s-16S rDNA region is probably not transcribed into stable s-16S rRNA. 相似文献
39.
40.
Maurice Cross 《BMJ (Clinical research ed.)》1969,4(5686):808-809