全文获取类型
收费全文 | 5592篇 |
免费 | 572篇 |
国内免费 | 2篇 |
出版年
2022年 | 41篇 |
2021年 | 94篇 |
2020年 | 59篇 |
2019年 | 95篇 |
2018年 | 85篇 |
2017年 | 79篇 |
2016年 | 155篇 |
2015年 | 231篇 |
2014年 | 251篇 |
2013年 | 289篇 |
2012年 | 416篇 |
2011年 | 403篇 |
2010年 | 246篇 |
2009年 | 237篇 |
2008年 | 359篇 |
2007年 | 351篇 |
2006年 | 303篇 |
2005年 | 284篇 |
2004年 | 290篇 |
2003年 | 256篇 |
2002年 | 233篇 |
2001年 | 91篇 |
2000年 | 90篇 |
1999年 | 82篇 |
1998年 | 63篇 |
1997年 | 58篇 |
1996年 | 38篇 |
1995年 | 51篇 |
1994年 | 46篇 |
1993年 | 42篇 |
1992年 | 44篇 |
1991年 | 54篇 |
1990年 | 45篇 |
1989年 | 33篇 |
1988年 | 30篇 |
1987年 | 24篇 |
1986年 | 33篇 |
1985年 | 41篇 |
1984年 | 26篇 |
1983年 | 26篇 |
1982年 | 23篇 |
1981年 | 26篇 |
1979年 | 40篇 |
1978年 | 22篇 |
1977年 | 19篇 |
1976年 | 20篇 |
1975年 | 22篇 |
1972年 | 32篇 |
1970年 | 19篇 |
1968年 | 23篇 |
排序方式: 共有6166条查询结果,搜索用时 843 毫秒
21.
The glucose oxidase antiglucose oxidase (GAG) immunoenzymatic staining procedure has been used to detect herpes simplex virus (HSV) antigens microscopically. In this study, the GAG procedure was adapted to cells in suspension, and its potential usefulness in flow cytometry was examined. HSV-2 infected monkey kidney and HSV-2 transformed mouse cells were stained using antisera to HSV-2 or to an HSV-2 specific protein with a molecular weight of 38 Kd, respectively, with the GAG procedure. Flow cytometric analysis of the GAG stained cells was then performed by the measurement of scattered light intensity in the angular intervals 1 degree-2 degrees, 2.5 degrees-19 degrees, and 3 degrees-6 degrees. The greatest scattered light intensity decrement caused by staining occurred in the 3 degrees-6 degrees angular interval, as predicted by previous work. In infected cells, which stain intensely by immunofluorescence, the difference between positively and negatively stained cells was adequate for detecting infected cells using the GAG method; however, this was not the case for the lightly staining transformed cells. The indirect immunofluorescence method of analysis of the same populations was superior to the scattered light method of analysis of the GAG stained infected and transformed cells. 相似文献
22.
Significant differences in the thermal stability of benzodiazepine receptors were found in cerebral cortical membranes prepared from the long-sleep (LS) and short-sleep (SS) selected mouse lines. Thus, benzodiazepine receptors from LS mice were heat inactivated (55 degrees C) at a significantly faster rate than those from SS mice. Although gamma-aminobutyric acid (GABA) reduced the rate of heat inactivation in both lines, the more rapid rate of inactivation in the LS line was maintained. Furthermore, the potency of GABA to enhance [3H]flunitrazepam binding decreased threefold in membranes from LS mice as the incubation temperature was increased from 0 degrees to 37 degrees C, but was unaltered in membranes from SS mice. These differences in the biophysical properties of the benzodiazepine/GABA receptor chloride channel complex ("supramolecular complex"), together with a higher KD for t-[35S]butylbicyclophosphorothionate in membranes from LS compared to SS mice, suggest that the supramolecular complex may modulate the differential sensitivity to some depressants and convulsants in these lines. 相似文献
23.
Inactivation of human alpha-1-antitrypsin by a tissue-destructive protease of Legionella pneumophila 总被引:3,自引:0,他引:3
Three extracellular proteases produced by Legionella pneumophila during growth in liquid medium were examined for their effects on human alpha-1-antitrypsin (alpha-1-AT). One of these proteases, tissue-destructive protease (TDP) destroyed completely the trypsin-inhibitory capacity of alpha-1-AT at protease: inhibitor molar ratios down to 0.002:1. After inactivation by TDP, the Mr of alpha-1-AT was reduced by 5000 in SDS-PAGE. This suggested that inactivation entailed only limited cleavage. 相似文献
24.
25.
Seasonal carbon isotope discrimination in a grassland community 总被引:11,自引:0,他引:11
Mark P. Smedley Todd E. Dawson Jonathan P. Comstock Lisa A. Donovan Dorothy E. Sherrill Craig S. Cook James R. Ehleringer 《Oecologia》1991,85(3):314-320
Summary Grassland communities of arid western North America are often characterized by a seasonal increase in ambient temperature and evaporative demand and a corresponding decline in soil moisture availability. As the environment changes, particular species could respond differently, which should be reflected in a number of physiological processes. Carbon isotope discrimination varies during photosynthetic activity as a function of both stomatal aperture and the biochemistry of the fixation process, and provides an integrated measure of plant response to seasonal changes in the environment. We measured the seasonal course of carbon isotope discrimination in 42 grassland species to evaluate changes in gas exchange processes in response to these varying environmental factors. The seasonal courses were then used to identify community-wide patterns associated with life form, with phenology and with differences between grasses and forbs. Significant differences were detected in the following comparisons: (1) Carbon isotope discrimination decreased throughout the growing season; (2) perennial species discriminated less than annual species; (3) grasses discriminated less than forbs; and (4) early flowering species discriminated more than the later flowering ones. These comparisons suggested that (1) species active only during the initial, less stressful months of the growing season used water less efficiently, and (2) that physiological responses increasing the ratio of carbon fixed to water lost were common in these grassland species, and were correlated with the increase in evaporative demand and the decrease in soil moisture. 相似文献
26.
Homosexual mounting in apes and prosimians is rare. Male-male mounting was observed between an adult male white-handed gibbon
and an adolescent male in the same group. The behaviour is discussed in terms of the gibbon group's social structure and the
development of the adolescent. It is suggested that this behaviour provides reassurance for the adolescent gibbon. 相似文献
27.
28.
Mononuclear phagocyte activation: activation-associated antigens 总被引:3,自引:0,他引:3
Mononuclear phagocyte activation is characterized by alterations in cellular metabolism and plasma membrane composition. In rodent and human systems, antibodies (conventional heteroantibodies or monoclonal reagents) that identify plasma membrane antigens selectively expressed by activated macrophages and monocytes have been generated. Among these activation-associated determinants is Mo3e (p50,80), a protease-sensitive antigen that is expressed by human monocytes activated in culture by exposure to bacterial lipopolysaccharide, muramyl dipeptide, or phorbol myristate acetate (PMA) (as well as other biologically active phorbol compounds). Mo3e is also expressed by the monoblastic cell line U-937 after culture in medium containing PMA and other pharmacological activators of protein kinase C (4 beta-phorbol-12,13-dibutyrate, 4 beta-phorbol-12,13-didecanoate, mezerein, and cell-permeable 1,2-diacylglycerol). The human promyelocytic cell line HL-60 becomes Mo3e positive after exposure in vitro to certain inducers of monocytic differentiation (PMA, dibutyryl cyclic AMP, and cholera toxin plus 3-isobutyl-1-methylxanthine). The surface expression of Mo3e is blocked by inhibitors of protein synthesis, N-linked glycosylation, and protein kinase activation, as well as by ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid and calcium antagonists. These data suggest the involvement of glycoprotein synthesis, protein kinase activation, and calcium ions in the stimulated expression of Mo3e by activated human mononuclear phagocytes. Anti-Mo3e antibody blocks the human monocyte response to migration inhibitory factor (MIF), which indicates an association between the expression of Mo3e antigen and responsiveness to MIF. 相似文献
29.
Cytogenetics of human sperm: meiotic segregation in two translocation carriers. 总被引:8,自引:4,他引:4
下载免费PDF全文
![点击此处可从《American journal of human genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
B Brandriff L Gordon L K Ashworth V Littman G Watchmaker A V Carrano 《American journal of human genetics》1986,38(2):197-208
Meiotic segregation products were studied in sperm from two men heterozygous for the reciprocal translocations t(8;15)(p22;q21) and t(3;16)(p23;q24). A total of 226 and 201 sperm complements, respectively, were analyzed. In each translocation, 63% of complements were unbalanced, and alternate and adjacent 1 percentages were similar. The 3:1 segregation frequencies produced by the two translocations were 3.5% and 5.0%. 相似文献
30.
J P Moore J A Todd T R Hesketh J C Metcalfe 《The Journal of biological chemistry》1986,261(18):8158-8162
Among the earliest responses to mitogens that have been detected in normal quiescent cells are ionic changes: we have described rapid increases in the cytosolic free Ca2+ concentration ([Ca]i) and in the intracellular pH (pHi) in mitogen-stimulated thymocytes and fibroblasts (Hesketh, T. R., Moore, J. P., Morris, J. D. H., Taylor, M. V., Rogers, J., Smith, G. A., and Metcalfe, J. C. (1985) Nature 313, 482-484). Here we investigate the relationship between these ionic signals and the subsequent expression of the c-fos and c-myc proto-oncogenes in murine thymocytes. We show that the plant lectin concanavalin A (ConA), the phorbol ester 12-O-tetradecanoyl phorbol 13-acetate (TPA) and the Ca2+-ionophore A23187 each causes a rapid increase in both c-fos and c-myc mRNAs. The activation of both genes is completely dependent on the extracellular Ca2+ concentration ([Ca]o) for A23187 and independent of [Ca]o for TPA. Activation of c-myc, but not c-fos, by ConA is partially dependent on [Ca]o. The pHi increases generated by ConA or TPA are not necessary for expression of mRNA from either gene in response to these mitogens. Exogenous 8-bromo-cyclic AMP (but not 8-bromo-cyclic GMP) inhibits the c-myc responses to ConA and TPA. The data also show that neither early c-fos nor c-myc expression is sufficient to commit the cells to DNA synthesis. 相似文献