全文获取类型
收费全文 | 32266篇 |
免费 | 1457篇 |
国内免费 | 1498篇 |
出版年
2024年 | 29篇 |
2023年 | 328篇 |
2022年 | 444篇 |
2021年 | 638篇 |
2020年 | 661篇 |
2019年 | 834篇 |
2018年 | 731篇 |
2017年 | 706篇 |
2016年 | 804篇 |
2015年 | 1069篇 |
2014年 | 1782篇 |
2013年 | 2668篇 |
2012年 | 1401篇 |
2011年 | 1415篇 |
2010年 | 1223篇 |
2009年 | 1402篇 |
2008年 | 1462篇 |
2007年 | 1476篇 |
2006年 | 1389篇 |
2005年 | 1301篇 |
2004年 | 1177篇 |
2003年 | 1139篇 |
2002年 | 1033篇 |
2001年 | 772篇 |
2000年 | 760篇 |
1999年 | 719篇 |
1998年 | 705篇 |
1997年 | 632篇 |
1996年 | 575篇 |
1995年 | 610篇 |
1994年 | 592篇 |
1993年 | 471篇 |
1992年 | 482篇 |
1991年 | 379篇 |
1990年 | 385篇 |
1989年 | 294篇 |
1988年 | 344篇 |
1987年 | 269篇 |
1986年 | 231篇 |
1985年 | 335篇 |
1984年 | 391篇 |
1983年 | 256篇 |
1982年 | 287篇 |
1981年 | 140篇 |
1980年 | 121篇 |
1979年 | 118篇 |
1978年 | 71篇 |
1977年 | 38篇 |
1976年 | 41篇 |
1973年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Sequence of the mglB gene from Escherichia coli K12: comparison of wild-type and mutant galactose chemoreceptors 总被引:1,自引:0,他引:1
Annette Scholle Jörg Vreemann Volker Blank Annette Nold Winfried Boos Michael D. Manson 《Molecular & general genetics : MGG》1987,208(1-2):247-253
Summary The mglB gene of Escherichia coli codes for a galactose-binding protein (GBP) that serves both as the galactose chemoreceptor and as the recognition component of the -methylgalactoside transport system. The mglB551 mutation eliminates the chemotactic function of GBP without altering its transport or substrate-binding properties. To investigate the interaction between GBP and Trg, the chemotactic signal transducer for galactose, we sequenced the mglB genes from wild-type and mglB551 mutant strains. The mutation causes the replacement of Gly74 of GBP by Asp. This residue is located in alpha-Helix III at the tip of the P domain in the GBP tertiary structure farthest removed from the substrate-binding cleft between the P and Q domains. We conclude that Helix III must be part of, or at least adjacent to, the recognition site for Trg. Our sequence also included part of the mglA gene, which is immediately distal to mglB. The amino acid sequence deduced for the beginning of the MglA protein showed homology with a family of polypeptides that contain an ATP-binding site and are components of binding-protein-dependent transport systems. 相似文献
102.
Restriction pattern analysis of deoxyribonucleic acid isolated from callus and cell suspension of actinorhizal and non-actinorhizal Betulaceae 总被引:1,自引:0,他引:1
Using cell suspensions, a method was elaborated to isolate high-molecular-weight genomic deoxyribonucleic acid (DNA; 65 MDa or more) from members of the Betulaceae: Alnus incana (L.) Moench, Alnus glutinosa (L.) Gaertn. and Betula papyrifera Marsh. The method was also effective for isolation of DNA from callus cells. Based on the chemical lysis of protoplasts, this procedure yielded 130 μg (callus) to 250 μg (cell suspension) of DNA (g fresh cells)−1 , with a ratio A200 /A28 of 1.7–2.0. The purified DNA obtained, formed distinct bands when restricted fragments were electrophoresed. Among the 10 endonucleases used for restriction analysis of Alnus glutinosa, Alnus incana and Betula papyrifera genomes, PvuI1 (EC 3.1.23.33) was unique in giving identical patterns for the two Ainus species. An unusual pattern occurred when Al-2 DNA was restricted with Ava II (EC 3.1.23.4). It formed a ladder with a repeating fragment unit of 181 base pairs long. With the enzymes tested, no differences in restriction patterns were observed among clones of Alnus incana (AI-2 vs AI-2), Betula papyrifera (BP-4 vs BP-8) and subclones of Ainus glutinosa AG-1 (PLFJ709 vs LF1709), suggesting genetic stability of the Betulaceae cultures. 相似文献
103.
Summary Mineral transport across the plasma membrane of plant cells is controlled by an electrochemical gradient of protons. This
gradient is generated by an ATP-consuming enzyme in the membrane known as a proton pump, or H+-ATPase. The protein has a catalytic subunit of Mr=100,000 and is a prominent band when plasma membrane proteins are analyzed
by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.
We generated specific rabbit polyclonal antibody against the Mr=100,000 H+-ATPase and used the antibody to screen λgtll expression vector libraries of plant DNA. Several phage clones producing immunoreactive
protein, and presumably containing DNA sequences for the ATPase structural gene, were isolated and purified from a carrot
cDNA library and a Arabidopsis genomic DNA library. These studies represent our first efforts at cloning the structural gene
for a plant plasma membrane transport protein. Applicability of the technique to other transport protein genes and the potential
for use of recombinant DNA technology in plant mineral transport research are discussed. 相似文献
104.
105.
Summary A method for isolating high quality DNA from wholeEuglena cells is described. The procedure consists in: the weakening of the cell pellicle in glycerol avoiding the mechanical disruption of cells and shearing damage in DNA molecules; the decondensation ofEuglena compact chromatin directly inside the cells; the complete dissociation of cells and nucleoproteins in sarkosyl detergent; the optional digestion of proteins and RNA with DNase-free enzymes and the final purification of DNA by isopycnic banding in CsCl gradients. Degradation of DNA is prevented all along the extraction procedure by glycerol, antioxydants, EDTA and sarkosyl detergent. Using the enzymatic digestion step, DNA containing few single-stranded nicks is obtained with a yield approaching 100%. DNA with no single-stranded nick could be obtained with a 35% yield when the enzymatic digestion step was omitted. In both cases, the double-stranded DNA has an average molecular weight equal or greater than 6×107. It is free of contaminants and could be easily digested with restriction enzymes. After digestion with Eco RI and size-fractionation in agarose gel this DNA has permitted specific hybridization of the rDNA sequences with a radioactive rRNA probe.Abbreviations Kbp
kilobasepairs
- Kb
kilobases 相似文献
106.
D. Aviv E. Galun 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1987,73(6):821-826
Summary We studied the chondriomes (the mitochondrial genomes) of sexual-progeny plants derived from eleven Nicotiana cybrids which resulted from donor-recipient protoplast fusions. The recipients were either N. tabacum or N. sylvestris and the donor (of the cytoplasm) was N. bigelovii. The chondriomes were characterized by the mitochondrial DNA (mtDNA) restriction-patterns. The differences in mtDNA restriction patterns were revealed after Sal I digestions and probing the respective Southern-blots with three mtDNA fragments. The hybridization patterns of mtDNAs from 35 second-generation plants (i.e. the sexual progeny derived from the cybrid plants) indicated only minor variations between plants derived from the same cybrid but pronounced variations among sibs derived from different cybrids. The mtDNA of 32 second-generation plants varied from both original fusion partners but the mtDNA of one (male-sterile) plant was apparently identical with the mtDNA of one of the original donor (N. bigelovii) and the mtDNA of two other (male-fertile) plants was apparently identical to the mtDNA of an original recipient (N. sylvestris). Generally, the mtDNAs of male-fertile, second-generation plants were similar to the mtDNAs of the original recipients while the mtDNAs of the male-sterile second-generation plants were similar to the mtDNA of the donor (N. begelovii). The analyses of mtDNAs from the thirdgeneration plants indicated stabilization of the chondriomes; no variations were detected between the mtDNAs of plants derived from a given second-generation plant. 相似文献
107.
B. B. Singh H. Rathburn C. Hedgcoth 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1987,74(1):168-170
Summary Mitochondrial DNA has been isolated from paired lines of pearl millet maintainer and cytoplasmic male sterile plants. Evaluation of the DNA by agarose gel electrophoresis shows that good quality DNA of high molecular weight can be obtained from mitochondria of both maintainer and male sterile pearl millet. 相似文献
108.
A. Breiman 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1987,73(4):563-570
Summary Southern blot hybridization of total DNA to defined mitochondrial DNA sequences provides a sensitive assay for mtDNA variation in the genera of Triticum and Aegilops. A clear distinction between cytoplasms of tetraploid species sharing the AG haploid genome is reported for the first time. The Sitopsis section of the genus Aegilops showed the most extensive intra- and inter-specific variation, whereas no variation could be detected among the cytoplasms of polyploid Triticum species (wheats) sharing the AB haploid genome. Extensive cytoplasmic intraspecific diversity was revealed in Ae. speltoides. 相似文献
109.
B. S. Landry R. Kesseli Hei Leung R. W. Michelmore 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1987,73(5):646-653
Summary Five accessions of members of the C group of male sterile maize cytoplasms (BB, C, ES, PR, and RB) in two nuclear backgrounds (A619 and A632) were examined to elucidate the nature of mitochondrial genome diversity within a related group of cytoplasms. Cosmid and plasmid clones carrying single copy and recombinationally active sequences from N and S cytoplasms of maize were used as probes. Although restriction patterns are quite similar, each of the five could be discriminated by evidence of sequence duplication and recombination, deletion of recombinationally active sequences of N, normal cytoplasm, population of mini-circular DNAs, and by restriction patterns. Each member of the group carried a 1,913 bp minicircular mtDNA, while all entries but RB carried a 1,445 bp minicircular mtDNA. Members of the C group clearly are not molecularly identical; evolution of the group included principal genome reorganization involving sequence duplication/deletion events, apparently independent of the cms trait.Cooperative Investigations of Agricultural Research Service, U.S. Department of Agriculture, and Institute of Food and Agricultural Sciences, University of FloridaMention of trademark, proprietary product, or vendor does not constitute a guarantee of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products or vendors that may also be suitable 相似文献
110.
F. Rollo A. La Marca A. Amici 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1987,73(4):501-505
Summary Twelve seed specimens of varying ages and from different archaeological sites were analyzed for the presence of polymerized DNA and RNA. Amongst the samples tested, one of Vitis vinifera from an archaeological site in Iran (2,000–3,000 B.C.) was found to be completely devoid of nucleic acids. Zea mais seeds of Precolumbial age from Peru (about 800 A.D.) contained depolymerized DNA and RNA. Samples of Vitis vinifera and Rubus sp. from a Lombard archaeological site (800 A.D.) as well as radiocarbon dated seeds from the site of the Spring Sanctuary near Metaponto (I–IV century B.C.) were found to contain polymerized DNA and rRNA bands. However the electrophoretic properties of the rRNAs in one case and hybridization experiments performed with cloned seed DNA in the other, clearly demonstrated that the polymerized nucleic acids were not of plant origin. 相似文献