全文获取类型
收费全文 | 3259篇 |
免费 | 288篇 |
出版年
2021年 | 35篇 |
2019年 | 39篇 |
2018年 | 43篇 |
2017年 | 33篇 |
2016年 | 64篇 |
2015年 | 109篇 |
2014年 | 128篇 |
2013年 | 171篇 |
2012年 | 193篇 |
2011年 | 216篇 |
2010年 | 137篇 |
2009年 | 123篇 |
2008年 | 186篇 |
2007年 | 165篇 |
2006年 | 156篇 |
2005年 | 148篇 |
2004年 | 158篇 |
2003年 | 131篇 |
2002年 | 119篇 |
2001年 | 65篇 |
2000年 | 49篇 |
1999年 | 56篇 |
1998年 | 37篇 |
1997年 | 25篇 |
1996年 | 20篇 |
1995年 | 22篇 |
1994年 | 20篇 |
1993年 | 30篇 |
1992年 | 65篇 |
1991年 | 39篇 |
1990年 | 37篇 |
1989年 | 49篇 |
1988年 | 39篇 |
1987年 | 51篇 |
1986年 | 28篇 |
1985年 | 29篇 |
1984年 | 32篇 |
1983年 | 31篇 |
1982年 | 32篇 |
1981年 | 18篇 |
1980年 | 21篇 |
1979年 | 33篇 |
1978年 | 25篇 |
1977年 | 18篇 |
1973年 | 19篇 |
1972年 | 18篇 |
1971年 | 19篇 |
1970年 | 17篇 |
1969年 | 23篇 |
1968年 | 18篇 |
排序方式: 共有3547条查询结果,搜索用时 165 毫秒
101.
P. Fuchs S. Dübel F. Breitling M. Braunagel I. Klewinghaus M. Little 《Cell biochemistry and biophysics》1992,21(1-3):81-91
To produce human monoclonal antibodies in bacteria, a gene repertoire of IgM variable regions was isolated from human peripheral B lymphocytes by the polymerase chain reaction. Alternatively, synthetic antibody genes with random hypervariable regions are being generated that may provide libraries of even higher complexity. For the selection of specific monoclonal antibodies from these libraries, we have developed twoE. coli vector systems that facilitate the surface display of an antibody physically linked to its own gene. The phagemid pSEX encodes a fusion protein of an antigen binding domain (Fv-antibody) with the docking protein (pIII) of filamentous phages. Specific antibody genes can therefore be enriched by antigen affinity chromatography. The plasmid pAP1 encodes a fusion protein of an Fv-antibody with a bacterial cell-wall protein. Bacteria carrying this plasmid express functional Fv-antibodies tightly bound to their surface. This should enable the selection of single cells with a fluorescence-assisted cell sorter (FACS) using labeled antigen or by adsorption to immobilized antigen. These vectors permit three major principles of the antibody response to be mimicked inE. coli:
- Generation of a highly complex antibody repertoire;
- Clonal selection procedures for library screening; and
- The possibility of increasing a given affinity by repeated rounds of mutation and selection.
102.
Effect of Abx, Bx and Pbx Mutations on Expression of Homeotic Genes in Drosophila Larvae 总被引:4,自引:1,他引:3 下载免费PDF全文
We have examined the patterns of expression of the homeotic gene Ubx in imaginal discs of Drosophila larvae carrying mutations in the abx, bx and pbx regulatory domains. In haltere discs, all five bx insertion mutations examined led to a general reduction in Ubx expression in the anterior compartment; for a given allele, the strength of the adult cuticle phenotype correlated with the degree of Ubx reduction. Deletions mapping near or overlapping the sites of bx insertions, including three abx alleles and the bx34e-prv(bx-prv) allele, showed greatly reduced Ubx expression in parts of the anterior compartment of the haltere disc; however, anterior patches of strong Ubx expression often remained, in highly variable patterns. As expected, the pbx1 mutation led to reduced Ubx expression in the posterior compartment of the haltere disc; surprisingly, pbx1 also led to altered expression of the en protein near the compartment border in the central region of the disc. In the metathoracic leg, all the bx alleles caused extreme reduction in Ubx expression in the anterior regions, with no allele-specific differences. In contrast, abx and bx-prv alleles resulted in patchy anterior reductions in third leg discs. In the larval central nervous system, abx but not bx alleles affected Ubx expression; the bx-prv deletion gave a wild-type phenotype, but it could not fully complement abx mutations. In the posterior wing disc, the bx-prv allele, and to a much lesser extent the bx34e chromosome from which it arose, led to ectopic expression of Ubx. Unlike other grain-of-function mutations in the BX-C, this phenotype appeared to be partially recessive to wild type. Finally, we asked whether the ppx transformation, which results from early lack of Ubx+ function in the mesothorax and is seen in abx animals, is due to ectopic Scr expression. Some mesothoracic leg and wing discs from abx2 larvae displayed ectopic expression of Scr, which was variable in extent but always confined to the posterior compartment. 相似文献
103.
104.
105.
David W. Mount John W. Little Susan H. Edmiston 《Molecular & general genetics : MGG》1980,177(3):477-483
Summary Plasmid pLC44-14 from the Clarke and Carbon collection has been shown to carry the lexA gene. The presence of lexA was demonstrated by complementation of tsl mutants which lie close to lexA on the E. coli K-12 linkage map and are probably in the lexA gene, and by crossing the dominant lexA mutation on to pLC44-14 to produce a recombinant plasmid, pSEl, which gave the host cell the properties of a lexA mutant. The lexA gene has been cloned on to pBR322 (Little, 1980). pJL21, which carries the lexA
+ gene, rendered the host cell moderately sensitive to UV light, greatly reduced the extent of Weigle reactivation and mutagenesis of UV-irradiated phage , and inhibited induction of protein X by either UV light or nalidixic acid. A similar plasmid carrying a mutant lexA3 allele produced extreme sensitivity to UV light, reduced recombinant production 10 to 50-fold following Hfr x F– conjugation crosses, and otherwise mimicked the effects of pJL21. Introduction of an amber mutation into the lexA gene carried by the plasmid greatly reduced the UV-sensitivity of the host, thereby indicating that the extreme sensitivity was due to the mutant lexA gene product. These properties of strains with lexA plasmids are thought to originate from high levels of the lexA protein in the cell due to a large plasmid copy number. This protein, which appears from other studies to regulate negatively the recA gene, may inhibit expression of recA or other DNA repair genes when present in excess amounts in the cell. 相似文献
106.
Isolation of recombinant plasmids and phage carrying the lexA gene of Escherichia coli K-12 总被引:12,自引:0,他引:12
J W Little 《Gene》1980,10(3):237-247
The lexA gene of Escherichia coli K-12 was cloned from the plasmid pLC44-14 into pBR322. Plasmids carrying lexA+ were selected by their ability to complement a recessive tsl mutation, which is believed to be a mutation in lexA. The smallest lexA+ recombinant plasmid, pJL21, contained an EcoRI-PstI fragment 2.9 kilobases (kb) in length; two larger plasmids also contained this fragment, and genetic material to one or both sides of the EcoRI-PstI fragment. Plasmids homologous to pJL21, but carrying a dominant mutation, lexA3, or one of three recessive amber mutations in lexA, termed spr, were also isolated. To clone the EcoRI-PstI fragment onto a lambda vector, the PstI end was first converted to an EcoRI end by attachment of a 100-base pair PstI-EcoRI fragment isolated from the plasmid ColE1; the resultant EcoRI fragment was then cloned into the lambda vector lambda gt4. A restriction map of pLC44-14 was obtained for nine restriction enzymes. The orientation of this map was determined relative to the E. coli genetic map by complementation of the gene ubiA+ and by comparison with restriction enzyme digests of another plasmid, pLC11-9, which carries dnaB, a gene closely linked to lexA, but does not carry lexA. 相似文献
107.
G.J.L. Jones D. Hewitt G.J. Godin W.C. Breckenridge J. Bird M.A. Mishkel G. Steiner J.A. Little 《CMAJ》1980,122(1):37-46
The lipids and lipoproteins — cholesterol (C), triglyceride (TG) and high-density, low-density, very-low-density and sinking pre-β-lipoprotein cholesterol (HDL-C, LDL-C, VLDL-C and SPB-C) — in plasma samples from 1620 fasting white adults and children from the Toronto—Hamilton area were analysed. The mean concentration of HDL-C was about 45 mg/dl in men and about 60 mg/dl in women, and the levels were constant throughout adult life in both sexes. Boys had higher mean HDL-C levels than men, but girls had lower mean HDL-C levels than women. Mean LDL-C levels, like total C levels, increased with age, from about 87 mg/dl in boys to 136 mg/dl in men, and from about 91 mg/dl in girls to 145 mg/dl in women. The mean levels of VLDL-C followed the TG patterns for age and sex, rising from about 7 mg/dl in boys to 26 mg/dl in men, and from about 11 mg/dl in girls to 19 mg/dl in women. SPB-C was detectable visually in 39% of the population and with the aid of densitometry in 54%; the levels were not related to age, sex or oral contraceptive use, and the median level was 3 mg/dl.Prevalence estimates of hyperlipoproteinemia showed that type IV was the most common, and it was found more than three times as often in men as in women. This was in part due to the customary use of plasma TG cut-off points that do not reflect the large difference in TG levels between males and females. Type IIA hyperlipoproteinemia was found in about 2% of the adults and type IIb in a further 1%. Types I, III and V were all rare. The prevalence of types II and IV hyperlipoproteinemia was four times greater in women using oral contraceptives than in nonusers in the same age range. 相似文献
108.
L. Del Senno F. Conconi P.F.R. Little R. Williamson 《Biochemical and biophysical research communications》1979,91(2):548-553
The map of restriction sites including and surrounding the δ- and β-globin genes has been established for three Ferrara β°-thalassaemic subjects. The fragments obtained using nine restriction enzymes do not show any differences from normal DNA. Among others, restriction enzymes giving short fragments at the 5′ and 3′ ends of the β-globin structural gene have been employed. The results obtained for the thalassaemic DNA are identical to those for control DNA, thus excluding the presence of extensive deletions in or adjacent to the coding regions of the β-globin gene in Ferrara β°-thalassaemia. 相似文献
109.
A L Catapano P K Kinnunen W C Breckenridge A M Gotto R L Jackson J A Little L C Smith J T Sparrow 《Biochemical and biophysical research communications》1979,89(3):951-957
Enzymic hydrolysis of triacylglycerol has been studied with very low density lipoproteins from an individual with a genetically determined absence of apoC-II, the activator apoprotein for lipoprotein lipase. Normal rates of ester cleavage by purified bovine milk lipoprotein lipase can be achieved with native apoC-II and by three shorter synthetic peptides, apoC-II(55–78), apoC-II(50–78) and apoC-II(43–78), which contain part of the carboxyl terminal third of the native apoprotein. At 0.5 μM concentration, all peptides produced a 7-fold activation. ApoC-II(43–78), but not apoC-II(50–78) or apoC-II(55–78), could bind VLDL as shown by separation of unbound 125I peptides and the lipoproteins. Thus, residues 43–50 of apoC-II are part of a lipid binding region. High affinity binding of apoC-II peptides to the lipoprotein substrate is not obligatory for activation of lipoprotein lipase. 相似文献
110.
When incubated at 37 °C in medium containing antibodies specific for thymus-leukemia (TL) antigens, viable cells bearing these antigens become resistant to the cytolytic effects of guinea pig complement, a process termed antigenic modulation. Antibody-induced membrane redistribution of the TL antigens, detected by indirect immunofluorescence, occurs with a similar pace. When high concentrations of concanavalin A (Con A) were included with antibodies in the incubation medium, TL antigenic modulation as well as antigen patching and capping were markedly inhibited, similar to effects of Con A on membrane immunoglobulin redistribution with murine spleen cells. Colchicine antagonized the inhibition by Con A suggesting the involvement of microtubules. In parallel experiments high concentrations of Con A failed to alter the quantity of TL antigen expression or its rate of change with time during incubation in cognate antisera. These results support the hypotheses that (a) generalized alterations in membrane receptor mobility may be induced by ligand binding to the cell membrane, and (b) under certain conditions stable interactions occur between normally independent cell surface antigens. 相似文献