全文获取类型
收费全文 | 8794篇 |
免费 | 907篇 |
国内免费 | 944篇 |
专业分类
10645篇 |
出版年
2024年 | 30篇 |
2023年 | 136篇 |
2022年 | 325篇 |
2021年 | 501篇 |
2020年 | 363篇 |
2019年 | 436篇 |
2018年 | 407篇 |
2017年 | 322篇 |
2016年 | 449篇 |
2015年 | 639篇 |
2014年 | 748篇 |
2013年 | 746篇 |
2012年 | 815篇 |
2011年 | 724篇 |
2010年 | 445篇 |
2009年 | 384篇 |
2008年 | 410篇 |
2007年 | 321篇 |
2006年 | 280篇 |
2005年 | 262篇 |
2004年 | 257篇 |
2003年 | 233篇 |
2002年 | 225篇 |
2001年 | 96篇 |
2000年 | 85篇 |
1999年 | 96篇 |
1998年 | 46篇 |
1997年 | 45篇 |
1996年 | 35篇 |
1995年 | 41篇 |
1994年 | 38篇 |
1993年 | 37篇 |
1992年 | 66篇 |
1991年 | 53篇 |
1990年 | 53篇 |
1989年 | 56篇 |
1988年 | 35篇 |
1987年 | 37篇 |
1986年 | 34篇 |
1985年 | 30篇 |
1984年 | 32篇 |
1983年 | 22篇 |
1982年 | 17篇 |
1981年 | 15篇 |
1980年 | 17篇 |
1978年 | 16篇 |
1975年 | 12篇 |
1972年 | 17篇 |
1971年 | 14篇 |
1970年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Nine low copy number genomic DNA clones, a ribosomal sequence, and seven cDNA clones were found to identify polymorphisms in cultivated barley (Hordeum vulgare L.). An F2 population consisting of 100 plants was produced from a cross between a high-yielding two-rowed feed barley cultivar and a genetic marker stock homozygous for nine recessive and one dominant morphological marker genes. Through the use of these 10 well-distributed marker genes, five previously mapped isozyme loci, and two storage-protein loci, the approximate recombinational location for each of 17 restriction fragment length polymorphism loci was estimated. One clone, pMSU21, identified variation that appeared to be the result of a small insertion-deletion event that differentiated two-rowed and six-rowed genotypes. This difference was characterized, and one allele was sequenced. Oligonucleotide primers that flanked the insertion-deletion event were synthesized, and DNA samples from the F2 population were subjected to polymerase chain reaction sequence amplification. The variation identified by this technique was determined to be allelic to the variation identified using pMSU21 in Southern blot analysis. Maps of previously undescribed informative clones are included. 相似文献
22.
The antigen of hepatitis delta virus: examination of in vitro RNA-binding specificity. 总被引:22,自引:15,他引:7 下载免费PDF全文
The only known protein of hepatitis delta virus (HDV), the delta antigen, is found both within virus particles and within the nucleus of the infected cell, where it has one or more roles essential for RNA genome replication. Others have demonstrated that the antigen has the ability, in vitro, to specifically bind HDV RNA species. We report a further examination of this phenomenon, using partially purified recombinant protein, expressed as a fusion with the staphylococcal protein A. From Northwestern (RNA-immunoblot) analyses with both complete and various subdomains of HDV genomic and antigenomic RNAs, we found that a necessary feature for specific binding was that the RNA be able to fold to some extent into the so-called rodlike structure; this structure is a predicted intramolecular partial base-pairing of the circular RNA, with about 70% of all bases involved, so as to produce an unbranched rodlike structure. Six different subregions of the HDV rodlike structure, three on the genomic RNA and three on its complement, the antigenomic RNA, were tested and found to be sufficient for antigen binding. However, features in addition to the rodlike structure may also be necessary for specific binding, because we found that a similar structure present in the RNA of the potato spindle tuber viroid did not allow binding. 相似文献
23.
Summary A general observer-based estimator method is developed and applied for process modelling and monitoring. This parameter estimation
technique was successfully applied to a L-lysine fermentation process. It was a useful tool to detect the effect of major
culture conditions on cell growth and product synthesis. It can also be used for the development of adaptive optimal control
schemes. 相似文献
24.
1 前言 从外地引进寄蝇或人工助长当地寄蝇种类防治农林害虫,是有效的生防手段之一,国外已有很多成功的报道。King等(1981)在路易斯安娜州蔗田中人工大量释放螟利索寄蝇(Lixophaga diatraeae)成虫防治第1代小蔗杆草螟(Diatraea saccharalis),不同地区的寄生率分别达到4.1、8.7和35.7%;由于降低了农药的使用量,奇痣窄径茧蜂(Agathis stigmatera)的自然寄生率也相应提高,很好地控制了蔗田害虫的发生。在寄蝇的田间释放技术方面,国外还没有详细的报道。在我国,利用寄蝇防治害虫的工作也是刚刚起步,很多具体问题有待于进一步研究。 相似文献
25.
26.
27.
Amino acid sequence of bovine white matter proteolipid 总被引:13,自引:0,他引:13
M B Lees B H Chao L F Lin M Samiullah R A Laursen 《Archives of biochemistry and biophysics》1983,226(2):643-656
The sequence of the bovine white matter proteolipid has been studied by a combination of proteolytic digestion and chemical cleavage at tryptophan residues. Alignment of peptides obtained by digestion with trypsin, chymotrypsin, clostripain, and Staphylococcus aureus protease gave the sequence of 52 residues at the amino terminus, 96 residues at the carboxyl terminus, and several additional segments. Peptides obtained by treatment of the protein with 2-(2-nitrophenylsulfenyl)-3-methyl-3'-bromoindolenine confirmed the alignment and extended the sequence. This information, combined with that of other investigators, permits us to propose the primary structure for the entire protein. On the basis of the sequence determination, the molecular weight of the proteolipid protein is 29,869. 相似文献
28.
Trisomy 6q22 leads to 6qter due to maternal 6;21 translocation. Case report review of the literature
Partial trisomy for the long arm of chromosome 6, involving 6q22 leads to 6qter, was observed in a 2-month-old male infant. The mother was 6q;21p translocation carrier. A review of the previously published cases with trisomies of different 6q segments suggests that the critical segment responsible for the clinically recognizable phenotype of 6q trisomy seems to be limited to bands 6q26 and/or 6q27. 相似文献
29.
Three starch-degrading enzymes from liquid endosperm of maize have been separated by means of horizontal acrylamide gel electrophoresis. The three enzymes are tentatively identified as -amylase (zone 1), -amylase (zone 2), and -glucan phosphorylase (zone 3). Electrophoretic variants of these enzymes were found among ten inbred strains examined. Results of genetic crosses with respect to zone 2 amylase show that it is controlled by a pair of alleles (Amy-2
A and Amy-2
B) acting without dominance. It further appears that Amy-2 and Ct (catalase) are linked with 5% recombination frequency.This work was supported by the U.S. Atomic Energy Commission, under contract No. AT(11-1)-1338. 相似文献
30.
Subcellular site of glycoprotein synthesis in liver 总被引:4,自引:0,他引:4