全文获取类型
收费全文 | 1025篇 |
免费 | 107篇 |
国内免费 | 1篇 |
专业分类
1133篇 |
出版年
2022年 | 9篇 |
2021年 | 22篇 |
2020年 | 10篇 |
2019年 | 6篇 |
2018年 | 15篇 |
2017年 | 9篇 |
2016年 | 20篇 |
2015年 | 46篇 |
2014年 | 36篇 |
2013年 | 46篇 |
2012年 | 57篇 |
2011年 | 54篇 |
2010年 | 41篇 |
2009年 | 31篇 |
2008年 | 51篇 |
2007年 | 48篇 |
2006年 | 43篇 |
2005年 | 27篇 |
2004年 | 35篇 |
2003年 | 32篇 |
2002年 | 40篇 |
2001年 | 32篇 |
2000年 | 43篇 |
1999年 | 27篇 |
1998年 | 13篇 |
1997年 | 6篇 |
1996年 | 9篇 |
1995年 | 10篇 |
1992年 | 23篇 |
1991年 | 14篇 |
1990年 | 16篇 |
1989年 | 23篇 |
1988年 | 18篇 |
1987年 | 14篇 |
1986年 | 21篇 |
1985年 | 16篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1981年 | 12篇 |
1980年 | 10篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1977年 | 7篇 |
1976年 | 13篇 |
1975年 | 10篇 |
1974年 | 13篇 |
1973年 | 15篇 |
1972年 | 6篇 |
1971年 | 6篇 |
1968年 | 8篇 |
排序方式: 共有1133条查询结果,搜索用时 0 毫秒
1.
Four myeloid cell lines (M1, WEHI-3B D+, FDC-P1, and 32D) were screened for the presence of J11d antigen. One of these cell lines, the myeloid leukemia M1, was found to express a high level of J11d antigen on the cell surface. Recombinant mouse leukemic inhibitory factor (rm-LIF), recombinant human LIF (rh-LIF), and steroids (hydrocortisone and dexamethasone) could induce M1 cells to undergo monocytic differentiation. The level of J11d antigen was greatly reduced after treatment of the cells with LIF or steroids. Western blotting revealed that the apparent molecular weight of the J11d antigen on M1 cells was 45-48 kDa. Furthermore, the level of J11d mRNA was also reduced during LIF-induced differentiation of M1 cells. 相似文献
2.
F. F. Snyder A. E. Chudley P. M. MacLeod R. J. Carter E. Fung J. K. Lowe 《Human genetics》1984,67(1):18-22
Summary A family is described in which four affected males, spanning two generations, have hyperuricemia and gout accompanied by hematuria but are without severe neurologic involvement. The affected males were found to have markedly reduced levels of erythrocytic hypoxanthine-guanine phosphoribosyltransferase (HGPRT) activity; these were 5–12% with hypoxanthine and 0.5–3% with guanine as compared to controls. Erythrocytic adenine phosphoribosyltransferase (APRT) was approximately three-fold elevated in the affected individuals.The residual HGPRT activity in affected males enabled characterization of some of the properties of this mutation. The apparent Michaelis constants (km) for both hypoxanthine and guanine were essentially unchanged, whereas the km for PP-ribose-P was approximately 10–20-fold elevated for all four affected males. The enzyme was more sensitive to product inhibition by IMP and GMP than controls, and exhibited greater thermal lability at 65°C than found with control lysates. 相似文献
3.
The GTP-induced dissociation of T alpha from T beta gamma initiates the release of transducin from photolyzed rhodopsin and the subsequent activation of the cGMP phosphodiesterase. In this study, site-specific proteolysis and immunoprecipitation were used to map the domain of T alpha that interacts with T beta gamma. We found that Staphylococcus aureus V8 protease rapidly removes a small fragment from T alpha under native conditions, resulting in the formation of a single 38-kDa polypeptide (T alpha'). Under the same conditions, T beta gamma remains intact. A 4.5-fold decrease in the rate of T alpha cleavage by S. aureus protease was observed in the presence of T beta gamma, suggesting T beta gamma binding blocks the protease-sensitive site on T alpha. Amino acid sequence analysis indicated that T alpha' is derived from the cleavage of T alpha at Glu-21. The ability of T alpha' to interact with and activate the retinal phosphodiesterase is not diminished. However, T alpha' is unable to participate in T beta gamma-dependent activities such as the light-stimulated binding of guanine nucleotides, binding to photoexcited rhodopsin, and ADP-ribosylation catalyzed by pertussis toxin. Moreover, the anti-T alpha monoclonal antibody TF16 was able to precipitate T beta gamma in the presence of T alpha, but not with either T alpha' or T alpha-guanosine 5'-O-(3-thiotriphosphate). We conclude that the amino-terminal region of T alpha participates in T beta gamma interaction and discuss our results with respect to the known structure and function of transducin. 相似文献
4.
Targeting of porin to the outer membrane of Escherichia coli. Rate of trimer assembly and identification of a dimer intermediate 总被引:14,自引:0,他引:14
J Reid H Fung K Gehring P E Klebba H Nikaido 《The Journal of biological chemistry》1988,263(16):7753-7759
Porin, a transmembrane protein in the outer membrane of Escherichia coli, exists in a trimeric structure which is not dissociated during sodium dodecyl sulfate-polyacrylamide gel electrophoresis at 25 degrees C. This unusual stability was utilized in the study of the conformational changes which accompany the targeting of porin to the outer membrane. A delay of 16-44 s between completion of synthesis of a monomer and its assembly into a trimer was found from the ratio of monomers to trimers found in exponentially growing cells. Pulse-chase experiments showed that rapid processing of precursor OmpF molecules was followed by assembly into sodium dodecyl sulfate-resistant oligomers with a half-time of 20 s at 30 degrees C. An intermediate in assembly was isolated by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis below 10 degrees C and was identified as a metastable dimer. 相似文献
5.
Hyperthermic treatment at 43 degrees C suppressed the growth of Ehrlich ascites tumor (EAT) cells in vitro. Incubation of EAT cells at 43 degrees C for as little as 1.5 h totally abolished the transplantability of the tumor. At the same time, the rate of cellular glucose uptake, the density of glucose transporter on the cells as well as the extent of thymidine, uridine and leucine incorporation were significantly reduced. 相似文献
6.
7.
The efficiencies of the estimators in the linear logistic regression model are examined using simulations under six missing value treatments. These treatments use either the maximum likelihood or the discriminant function approach in the estimation of the regression coefficients. Missing values are assumed to occur at random. The cases of multivariate normal and dichotomous independent variables are both considered. We found that in general, there is no uniformly best method. However, mean substitution and discriminant function estimation using existing pairs of values for correlations turn out to be favourable for the cases considered. 相似文献
8.
The chronic administration of estrogens to mice or rats will result in antidopaminergic effects. Apomorphine-induced climbing behavior in mice, the result of direct stimulation of dopamine receptors in the striatal and mesolimbic regions, is a simple animal model for examining these antidopaminergic effects of estrogens. Bromoestrogens, inhibitors of catechol estrogen formation, have been utilized in order to examine the role of estrogen metabolism in dopaminergic antagonism. Mice were pretreated for 3 days with 2-bromoestradiol, 4-bromoestradiol, or 2,4-dibromoestradiol dibenzoates alone or in combination with estradiol benzoate prior to apomorphine administration. The haloestrogens did not alter the climbing-induced responses elicited by apomorphine, whereas estradiol benzoate clearly attentuated the actions of apomorphine. Furthermore, the bromoestradiol dibenzoates were effective in reversing the effects of estradiol benzoate when the two steroids (estradiol benzoate and a bromoestrogen dibenzoate) were administered simultaneously during pretreatment. Thus, the bromoestrogens are able to inhibit the antidopaminergic effects of estradiol exhibited in the apomorphine-induced mouse climbing model. 相似文献
9.
P D Nguyen E A O'Rear A E Johnson R Lu B M Fung 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1989,192(3):261-269
The clot-lysing ability of streptokinase (SK) was examined using membrane-bound thrombi. Encapsulation of SK in large unilamellar phospholipid vesicles (liposomes) resulted in entrapping approximately 30% of its original activity. Measurements of streptokinase activity for liposomal-encapsulated streptokinase (LESK) indicated little loss of activity or leakage in Tris-buffered saline over a 24-hr period at temperatures of 4 and 23 degrees C. However, incubation of free SK and LESK in platelet-poor plasma (PPP) at 37 degrees C resulted in a decrease of SK activity. The retention of SK activity in LESK was considerably higher than that of unentrapped SK. Clot-dissolving time (CDT) was measured by monitoring the pressure drop during slow filtration in plasma through membrane-bound thrombi. The results indicated that both LESK and free SK were able to activate the fibrinolytic system. Without prior incubation in PPP at 37 degrees C, the CDT of a SK and PPP mixture (SK/PPP) was 10.7 +/- 1.9 min (n = 12), while that of a LESK and PPP mixture (LESK/PPP) was 12.4 +/- 1.7 min (n = 12). The CDT-detected clot-lysing abilities of both SK and LESK were diminished by incubation in PPP, but to different extents. After 15- and 30-min incubations, the CDT of SK/PPP increased significantly to 15.5 +/- 1.5 and 24.1 +/- 2.4 min (n = 5, P less than 0.05), respectively. In contrast, the CDT of LESK/PPP increased to 13.3 +/- 0.8 min (n = 5) after 15 min of incubation and to 16.0 +/- 1.1 min (n = 5, P less than 0.05) after a 30-min incubation. These results suggest that entrapment of SK in liposomes preserves the thrombolytic potential of the plasminogen activator by limiting its exposure to the components of the plasma. 相似文献
10.
Y C Fung 《Biorheology》1989,26(2):279-289
The width and curvature of the collagen and elastin fiber bundles in the human pulmonary interalveolar septa and alveolar mouths are measured. The data, together with the known mechanical properties of collagen and elastin fibers, are used to derive the incremental elastic moduli of the lung tissue. The constitutive equation for small incremental stress and strain superposed on a homeostatic inflated lung is linear and isotropic, and characterized by two material constants. 相似文献