全文获取类型
收费全文 | 5719篇 |
免费 | 499篇 |
国内免费 | 4篇 |
出版年
2023年 | 20篇 |
2021年 | 79篇 |
2020年 | 53篇 |
2019年 | 56篇 |
2018年 | 59篇 |
2017年 | 67篇 |
2016年 | 125篇 |
2015年 | 167篇 |
2014年 | 205篇 |
2013年 | 273篇 |
2012年 | 317篇 |
2011年 | 326篇 |
2010年 | 316篇 |
2009年 | 297篇 |
2008年 | 341篇 |
2007年 | 339篇 |
2006年 | 317篇 |
2005年 | 295篇 |
2004年 | 315篇 |
2003年 | 307篇 |
2002年 | 284篇 |
2001年 | 128篇 |
2000年 | 101篇 |
1999年 | 98篇 |
1998年 | 78篇 |
1997年 | 54篇 |
1996年 | 62篇 |
1995年 | 52篇 |
1994年 | 45篇 |
1993年 | 56篇 |
1992年 | 68篇 |
1991年 | 58篇 |
1990年 | 59篇 |
1989年 | 57篇 |
1988年 | 54篇 |
1987年 | 45篇 |
1986年 | 41篇 |
1985年 | 38篇 |
1984年 | 54篇 |
1983年 | 41篇 |
1982年 | 35篇 |
1981年 | 24篇 |
1980年 | 36篇 |
1979年 | 28篇 |
1978年 | 33篇 |
1977年 | 23篇 |
1976年 | 41篇 |
1975年 | 28篇 |
1974年 | 28篇 |
1973年 | 23篇 |
排序方式: 共有6222条查询结果,搜索用时 15 毫秒
71.
The conversion of protoheme to heme a in Staphylococcus 总被引:3,自引:0,他引:3
72.
Pectic polysaccharides of growing plant tissues 总被引:13,自引:9,他引:4
1. The polysaccharide compositions of the cell walls of sycamore cambium and sycamore callus tissue have been analysed and found to be directly comparable. 2. Electrophoretic analyses of the whole pectins prepared from actively growing callus and cambial tissue have shown that these preparations contain, in addition to the neutral and weakly acidic components present in apple fruit, a strongly acidic polygalacturonic acid component. 3. The weakly acidic component of all the pectins was directly comparable with that of the pectinic acid of apple fruit. 4. The components of the whole pectin of sycamore callus tissue have been partially purified and analysed. The neutral and weakly acidic components also found in apple fruit were isolated. 5. The pattern of the composition of the neutral sugars present in the pectins of actively growing tissues of cambium and callus has been compared with those present in apple-fruit pectinic acid. 6. The presence of rhamnose linked as galacturonosyl-(1-->2)-rhamnose has been found in sycamore whole pectin. 7. The difference in the pectins of callus, cambium and fruit appears not to be that of species difference but is more characteristic of the nature of the growth and growth conditions of the cells. This is discussed in relation to the problems of the control and mechanism of plant-cell growth and differentiation. 相似文献
73.
74.
James M. Berger Paul J. Jackson Nigel J. Robinson Leah D. Lujan Emmanuel Delhaize 《Plant cell reports》1989,7(8):632-635
Suspension cultures of Datura innoxia cells were pulse-labeled with [35S]cysteine, then exposed to Cd to determine whether there is a direct precursor-product relationship amongst the different forms of the Cd-induced polypeptides, poly(-glutamylcysteinyl)glycines [(EC)nG, n=2 to 5]. Degradation of the polypeptides and possible regeneration of the [35S]-labeled glutathione and cysteine pools were also examined. After 2 h of exposure to [35S]cysteine, about 70% of the [35S]cysteine in the soluble fraction of the cell was incorporated into [35S]glutathione before exposure of the cells to Cd. One h after Cd exposure, most of the cellular [35S]glutathione was depleted and label was incorporated into (EC)nG. Analysis of [35S](EC)nG by reverse phase HPLC showed no direct precursor-product relationship between the synthesis of the shorter and longer chain forms. However, the rate of synthesis of the different polypeptides was linear for 32 h after Cd exposure. There was no evidence of degradation of [35S](EC)nG nor was it excreted into the medium within this period. From these results it is suggested that in the presence of Cd, a large pool of (EC)nG is unavailable for elongation to (EC)n+1G.Abbreviations (EC)nG
Poly(-glutamylcysteinyl)glycine
- HPLC
High pressure liquid chromatography
- CPM
Counts per minute 相似文献
75.
Nigel J. Robinson 《Journal of applied phycology》1989,1(1):5-18
Metallothioneins, MT's, are low-molecular-weight, cysteine-rich, polypeptides that complex ‘soft’ metal ions in thiol clusters.
They are structurally diverse. Some MT's are gene products, while others are secondary metabolites. Two of the three classes
of MT have been identified in algae. Eukaryotic algae possess the secondary metabolites referred to as class III MT. There
is no unequivocal evidence that MT genes occur in eukaryotic algae. However, the products of MT genes have been identified
in cyanobacteria. These genes and their metal regulatory elements remain to be isolated and characterized.
MT's have attracted interest from researchers involved in a wide range of disciplines including bioinorganic chemistry, biochemistry,
molecular biology, physiology, toxicology, environmental science and medicine. Although, the precise physiological roles of
these polypeptides remain undefined, a large number of functions have been speculated. These molecules chelate toxic trace
metals, such as Cd, thereby reducing the concentration of cytotoxic, free-metal ions. Furthermore, some MT's are believed
to be involved in zinc and copper homoeostasis. Future studies should reveal whether or not some of the diversity of MT structure
reflects a diversity of function. 相似文献
76.
Adelina A. Davies Stephen E. Moss Mark R. Crompton Tania A. Jones Nigel K. Spurr Denise Sheer Christine Kozak Michael J. Crumpton 《Human genetics》1989,82(3):234-238
Summary The gene encoding a tissue inhibitor of metalloproteinases, TIMP, has previously been shown to be X-linked in both the human and mouse genomes. We have used a series of somatic cell hybrids segregating translocation and deletion X chromosomes to map the TIMP gene on the human X chromosome. In combination with previous data, the gene can be assigned to Xp11.23Xp11.4. Genetic linkage analyses demonstrate that TIMP is linked to the more distal ornithine transcarbamylase (OTC) locus at a distance of about 22 centimorgans. The data are consistent with the conclusion that TIMP maps to a conserved synteny and linkage group on the proximal short arm of the human X chromosome and on the pericentric region of the mouse X chromosome, including loci for synapsin-1, a member of the raf oncogene family, OTC, and TIMP. 相似文献
77.
M C Souroujon D B Rubinstein R S Schwartz K J Barrett 《Journal of immunology (Baltimore, Md. : 1950)》1989,143(2):706-711
Polymorphisms of the Ig H chain V region (VH) genes were examined with probes from the coding and flanking regions of a gene from the largest VH gene family, VHIII. The 5'-flanking probe gave the simplest pattern and revealed the largest number of polymorphic fragments. Analysis of unrelated individuals and of families identified five polymorphic loci. Two alleles were detected for each of two of the loci, whereas a polymorphic band was scored as present or absent for the other three loci. The polymorphic fragments segregated in the expected Mendelian fashion and parental haplotypes could be assigned in all cases. Comparison of the patterns obtained with the flanking and coding region probes suggests that the human VHIII gene family is highly polymorphic and may contain several hundred V genes. This method, as well as the polymorphism detected, can be used to investigate the organization and germ-line variation of H chain V genes and their inheritance in normal individuals and in individuals with immunologic disorders. 相似文献
78.
Regulation of expression of human IL-1 alpha and IL-1 beta genes 总被引:10,自引:0,他引:10
M Turner D Chantry G Buchan K Barrett M Feldmann 《Journal of immunology (Baltimore, Md. : 1950)》1989,143(11):3556-3561
79.
Aneuploidy induction in human fibroblasts: comparison with results in Syrian hamster fibroblasts 总被引:3,自引:0,他引:3
The susceptibility of human fibroblast cells in culture to neoplastic transformation by chemical carcinogens is appreciably lower than that of rodent fibroblasts. We have proposed that a key step in the neoplastic progression of Syrian hamster embryo fibroblasts is the induction of aneuploidy by carcinogens. It is possible that the different sensitivity to neoplastic transformation of Syrian hamster versus human cells is due to a difference in genetic stability following treatment with chemicals inducing aneuploidy. Therefore, we measured the induction of numerical chromosome changes in normal human fibroblasts and Syrian hamster fibroblasts by 4 specific aneuploidogens. Dose- and time-dependent studies were performed. Nondisjunction, resulting in aneuploid cells with a near-diploid chromosome number, in up to 14-28% of the hamster cells was induced by colcemid (0.1 microgram/ml), vincristine (30 ng/ml), diethylstilbestrol (DES) (1 microgram/ml) or 17 beta-estradiol (10 micrograms/ml). In contrast, human cells displayed far fewer aneuploid (near-diploid) cells, i.e., 8% following treatment with colcemid (0.02 micrograms/ml) or vincristine (10 ng/ml) and only 3% following treatment with DES (6 micrograms/ml) or 17 beta-estradiol (20 micrograms/ml). The doses at which the maximum effect was observed are given. Treatment of human cells induced a higher incidence of cells with a near-tetraploid chromosome number, which was similar to the level observed in treated hamster cells except at the highest doses. These results indicate that human cells respond differently from hamster cells to agents that induce aneuploidy. In particular, nondisjunction yielding aneuploid human fibroblasts with a near-diploid chromosome number was less frequent. The magnitude of the observed species differences varied with different chemicals. The difference in aneuploidy induction may contribute, in part, to species differences in susceptibility of fibroblasts to neoplastic transformation. 相似文献
80.
The outcome of poliovirus infections in K562 cells is cytolytic rather than persistent after hemin-induced differentiation. 总被引:1,自引:1,他引:0 下载免费PDF全文
K562-Mu erythroleukemia cells readily establish a long-term persistent poliovirus infection characterized by continuous virus production in the absence of complete p220 cleavage and host translation shutoff (R. E. Lloyd and M. Bovee, Virology 194:200-209, 1993). The mechanism of resistance appears to be modulated at the intracellular level and to be related to decreased virus-mediated cytopathic effects (P. A. Benton, J. W. Murphy, and R. E. Lloyd Virology 213:7-18, 1995). It is well documented that hemin induces the differentiation of K562 cells and alters the expression of several host proteins. We report here that growth of K562 cells in hemin prior to poliovirus infection results in a dose-dependent increase in virus-induced cell lysis and thereby alters the normally persistent outcome of infection to a more lytic phenotype. K562 cells infected after hemin treatment displayed increased host translation shutoff, p220 cleavage, viral protein synthesis, and viral RNA accumulation compared with nontreated cells. Since hemin treatment of K562 cells also induced the increased expression of several heat shock proteins (Hsp70, Hsc70, Hsp90, and cohort p60), we tested the hypothesis that their increased expression may play a role in altering poliovirus infection in hemin-treated K562 cells. However, neither heat stress nor oxidative stress, inducers of heat shock protein synthesis, altered the outcome (of virus infections. In addition, we report the novel finding that subunits of two translation initiation factors, p220 (eIF-4G) and eIF-2alpha, are cleaved as a result of hemin treatment of K562 cells. It is proposed that hemin alters the expression of specific host proteins in K562 cells, probably other than heat shock proteins, which changes the initial response to poliovirus infections from persistent to lytic. 相似文献