全文获取类型
收费全文 | 7271篇 |
免费 | 723篇 |
国内免费 | 5篇 |
出版年
2023年 | 37篇 |
2022年 | 77篇 |
2021年 | 164篇 |
2020年 | 103篇 |
2019年 | 122篇 |
2018年 | 177篇 |
2017年 | 136篇 |
2016年 | 242篇 |
2015年 | 346篇 |
2014年 | 410篇 |
2013年 | 443篇 |
2012年 | 610篇 |
2011年 | 597篇 |
2010年 | 363篇 |
2009年 | 312篇 |
2008年 | 452篇 |
2007年 | 434篇 |
2006年 | 392篇 |
2005年 | 316篇 |
2004年 | 344篇 |
2003年 | 278篇 |
2002年 | 297篇 |
2001年 | 129篇 |
2000年 | 103篇 |
1999年 | 88篇 |
1998年 | 94篇 |
1997年 | 62篇 |
1996年 | 45篇 |
1995年 | 48篇 |
1994年 | 42篇 |
1993年 | 36篇 |
1992年 | 51篇 |
1991年 | 40篇 |
1990年 | 40篇 |
1989年 | 32篇 |
1988年 | 31篇 |
1987年 | 35篇 |
1986年 | 27篇 |
1985年 | 29篇 |
1984年 | 37篇 |
1983年 | 26篇 |
1982年 | 28篇 |
1981年 | 30篇 |
1979年 | 22篇 |
1978年 | 16篇 |
1975年 | 19篇 |
1974年 | 17篇 |
1973年 | 17篇 |
1971年 | 24篇 |
1969年 | 23篇 |
排序方式: 共有7999条查询结果,搜索用时 15 毫秒
31.
John J. Reiners Jr. Tim Rupp Claudio J. Conti 《Differentiation; research in biological diversity》1991,47(2):69-75
In situ hybridization and immunocytochemical techniques have been used to examine the distribution of vitamin-D-induced calbindin mRNA and calbindin protein in enterocytes lining the crypts and villi of chicken small intestine. Basal villus enterocytes contained approximately twice as much calbindin but over three times as much calbindin mRNA compared to values found in basal crypt and upper villus enterocytes, all values being measured 2 days after vitamin D injection into D-deficient chickens. Virtually no calbindin mRNA was detected in tissues taken from control D-deficient birds. Direct proportionality found between calbindin mRNA and calbindin content in enterocytes of basal crypt, mid and upper villus suggests pre-translational control over calbindin synthesis. The implications of possible inefficient translation of calbindin mRNA in basal villus enterocytes are discussed. Present methods of analysis provide a novel way to study mechanisms controlling gene expression throughout the whole process of enterocyte differentiation. 相似文献
32.
Determination of the origin of nondisjunction in a 49,XXXXY male using hypervariable dinucleotide repeat sequences 总被引:1,自引:1,他引:0
Summary We present a patient with a 49,XXXXY chromosome constitution in whom the origin of the extra X chromosomes was determined by analysis of five polymorphic CA (or GT) dinucleotide repeat sequences. This class of DNA marker has recently been demonstrated to be hypervariable with heterozygosity values up to 80%. By polymerase chain reaction (PCR) analysis of the dinucleotide repeat length polymorphisms, we have shown that all four X chromosomes were of maternal origin. 相似文献
33.
A continuous photometric assay of aminopeptidase P activity was developed which is based on a coupled enzymic assay with the substrate Gly-Pro-Pro-pNA and DPP IV as auxiliary enzyme. This assay was used to evaluate the kinetic parameters and inhibitory profile of intestinal brush border aminopeptidase P. 相似文献
34.
Ohne Zusammenfassung 相似文献
35.
M C Souroujon D Neumann S Pizzighella A Safran S Fuchs 《Biochemical and biophysical research communications》1986,135(1):82-89
Antibodies to synthetic peptides were employed in order to map domains on the alpha-subunit of the acetylcholine receptor to which several monoclonal antibodies are directed. Five peptides corresponding to residues 1-20, 126-143, 169-181, 330-340 and 351-368 of the receptor alpha-subunit were synthesized and antibodies against them were elicited. The anti-peptide antibodies were employed along with the monoclonal antibodies to identify fragments of S. aureus V8 protease digested- alpha-subunit in immunoblotting experiments. Our results demonstrate that a highly immunogenic region of the alpha-subunit is located on a carboxy-terminal 14 kDa portion of the alpha-subunit. This region also seems to undergo antigenic changes during muscle development. A monoclonal antibody directed against the cholinergic binding site of the acetylcholine receptor reacted with an 18 kDa segment of the alpha-subunit which bound alpha-bungarotoxin as well as antibodies directed against peptide 169-181. 相似文献
36.
A plasmodial alpha-tubulin cDNA from Physarum polycephalum. Nucleotide sequence and comparative analysis 总被引:5,自引:0,他引:5
Günter Krämmer Monika Singhofer-Wowra Klaus Seedorf Melvyn Little Tim Schedl 《Journal of molecular biology》1985,183(4):633-638
As the first step towards correlating structure and function of tubulin in the slime mold Physarum polycephalum we have elucidated the nucleotide sequence of a cDNA that appears to code for all but the last 25 to 30 C-terminal amino acids of a plasmodial alpha-tubulin. Differences in amino acid sequence from those of other alpha-tubulins are distributed fairly evenly throughout the sequence, although a relatively extensive conserved region is found in position 396 to 426 near the C terminus. A small region in position 298 to 307 contains a cluster of amino acid residues unique to Physarum alpha-tubulin. The sequence is 70% homologous to two yeast alpha-tubulins and about 83% homologous to five animal alpha-tubulins. A comparison of the homologies of all the known alpha-tubulins indicates that a large decrease in the accepted point mutation rate has occurred during the evolution of the metazoa, suggesting a major functional specialization of microtubules. 相似文献
37.
Tim Helentjaris Gretchen King Mary Slocum Chris Siedenstrang Sharon Wegman 《Plant molecular biology》1985,5(2):109-118
Summary Maize and tomato cDNA clones have been hybridized in Southern blotting experiments to plant genomic DNA prepared from different lines to detect restriction fragment polymorphisms (RFPs). In maize we have found that a high degree of genetic variability is present, even among domestic inbred lines. Most randomly chosen maize cDNA clones can be used to detect elements of this variability. Similar levels of polymorphism are observed when genomic DNA is digested with any of a number of different restriction enzymes and probed with individual clones. When a clone is hybridized to genomic DNAs prepared from several different maize lines, a number of different alleles are often detected at a single locus. At the same time one clone can often detect more than one independently segregating locus by cross hybridization to related sequences at other loci. As expected these markers are inherited as simple codominant Mendelian alleles from one generation to the next and colinkage of these markers can be demonstrated in the progeny from a heterozygous parent. In similar studies with tomato, remarkably different results were found. Few RFPs were demonstrable among domestic Lycopersicon esculentum lines although a higher level of variability could be detected when comparing esculentum with its wild Lycopersicon relatives. These results are discussed in relation to the applied uses of RFPs in plant breeding as well as the inherent variability of different plant genomes.This work was supported in part by funds from Sandoz Ltd. (Basel, Switzerland) and its subsidiary company, Northrup King Co. (Minneapolis, Minn., U.S.A.) as well as by NSF SBIR grant #BSR-8360870. 相似文献
38.
39.
The effect of foliar sprays of the growth regulator 2-(3,4 dichlorophenoxy)-triethylamine (DCPTA) on net photosynthesis (Pn) by intact bean plants depended upon concentration and the stage of development of the leaves. A single foliar spray of 2.0 mM DCPTA reduced Pn when applied to young expanding leaves but had little effect on fully expanded leaves. Lower DCPTA concentrations (0.2 to 0.8 mM) had no effect on Pn, unless applied more than once which resulted in reduced Pn. The DCPTA-induced inhibition of Pn was associated with chlorosis and aberrations in chloroplast ultrastructure. DCPTA did not affect stomatal resistance. When applied to detached leaf disks in the dark, DCPTA retarded the normal loss of chlorophyll suggesting that DCPTA may have anti-seneseent properties.Abbreviations DCPTA
2-(3,4 dichlorophenoxy)-triethylamine
- Pn
net photosynthesis
- Is
stomatal diffusive resistance 相似文献
40.
NMR, CD and IR spectroscopies of a tridecanucleotide containing a no-base residue: coexistence of B and Z conformations. 总被引:3,自引:3,他引:0
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)
S Pochet T Huynh-Dinh J M Neumann S Tran-Dinh S Adam J Taboury E Taillandier J Igolen 《Nucleic acids research》1986,14(2):1107-1126
The synthesis of the tridecadeoxynucleotide d(CGm5CGCGxACATGT), where x is the 1-cyano-2-deoxy-beta-D-erythropentofuranose, is described. The NMR, IR, CD studies at various salt concentrations and temperatures of this oligomer show that the B and Z conformations are simultaneously present in the same short DNA fragment. A single apurinic residue is sufficient for the coexistence of the B and Z helices on this oligomer. 相似文献