全文获取类型
收费全文 | 1982篇 |
免费 | 238篇 |
专业分类
2220篇 |
出版年
2022年 | 24篇 |
2021年 | 42篇 |
2020年 | 22篇 |
2019年 | 41篇 |
2018年 | 44篇 |
2017年 | 40篇 |
2016年 | 54篇 |
2015年 | 99篇 |
2014年 | 94篇 |
2013年 | 104篇 |
2012年 | 127篇 |
2011年 | 145篇 |
2010年 | 81篇 |
2009年 | 84篇 |
2008年 | 105篇 |
2007年 | 89篇 |
2006年 | 70篇 |
2005年 | 70篇 |
2004年 | 78篇 |
2003年 | 68篇 |
2002年 | 66篇 |
2001年 | 60篇 |
2000年 | 46篇 |
1999年 | 55篇 |
1998年 | 30篇 |
1997年 | 22篇 |
1996年 | 31篇 |
1995年 | 23篇 |
1994年 | 18篇 |
1993年 | 13篇 |
1992年 | 38篇 |
1991年 | 18篇 |
1990年 | 36篇 |
1989年 | 36篇 |
1988年 | 30篇 |
1987年 | 16篇 |
1986年 | 14篇 |
1985年 | 23篇 |
1984年 | 19篇 |
1983年 | 15篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1979年 | 10篇 |
1978年 | 12篇 |
1977年 | 12篇 |
1976年 | 8篇 |
1975年 | 8篇 |
1974年 | 8篇 |
1973年 | 10篇 |
1968年 | 9篇 |
排序方式: 共有2220条查询结果,搜索用时 10 毫秒
11.
E J Folco L Busconi C B Martone J J Sanchez 《Archives of biochemistry and biophysics》1988,267(2):599-605
Proteinase II, a high-molecular-mass proteinase previously identified in white croaker skeletal muscle, was purified to apparent homogeneity by DEAE-Sephacel, phenyl-Sepharose CL 4B, and Sephacryl S-300 chromatographies. Under denaturing conditions, the enzyme dissociated into a cluster of subunits with Mr ranging from 18,000 to 26,000 and a large subunit with a Mr 60,000. The proteinase was able to hydrolyze N-terminal-blocked 4-methyl-7-coumarylamide substrates having either an aromatic amino acid (chymotrypsin-like activity) or an arginine residue (trypsin-like activity) adjacent to the fluorogenic group. The trypsin-like activity of the enzyme was inhibited by fatty acids and sodium dodecyl sulfate, whereas the chymotrypsin-like activity was stimulated by those compounds but inhibited by nonionic and cationic detergents. Several thiol reagents inhibited both proteinase II activities. However, leupeptin and Cu2+ strongly inhibited its trypsin-like activity but only slightly affected its chymotrypsin-like activity. Dithiothreitol stimulated both activities, but at different extents and in different concentration ranges. These results suggest that the enzyme is multicatalytic, having at least two different active sites. 相似文献
12.
Stimulation of aromatase activity in immature porcine Leydig cells by fibroblast growth factor (FGF)
J I Raeside M C Berthelon P Sanchez J M Saez 《Biochemical and biophysical research communications》1988,151(1):163-169
The effects of fibroblast growth factor (FGF) on testicular aromatase activity has been studied using primary cultures of porcine Leydig cells. After culture for 3 days in the absence or presence of FGF, the ability of the cells to produce estrogen was examined in a 4h-test period in which either (a) hCG (10(-9) M) or (b) androstenedione (3 x 10(-6) M) was added to the medium. FGF produced a 3- to 20-fold increase in estrogen formation from endogenous or exogenous substrate during the test period, in spite of a marked decrease (approximately equal to 60%) in [125I]-hCG binding and no significant change in testosterone concentration. Stimulation of estrogen secretion by FGF was dose-(ED50 approximately equal to 2 ng/ml) and time-dependent, the first and maximal effects were observed after 12h and 48h, respectively. Preliminary tests with several other factors (insulin, EGF, TGF-beta, FSH and hCG) showed that hCG alone directly stimulated aromatase activity. From these findings a role is suggested for FGF as a paracrine/autocrine agent in the control of estrogen secretion by Leydig cells. 相似文献
13.
The F2 progeny of a cross between a chromosome 2 multiple marker stock and an adapted cultivar of barley were analyzed for four
morphological markers and electrophoretic patterns of eight leaf isozymes. TheIdh-2 locus was linked to thePer-5 locus (27.96±5.07 cM) and to thee locus (10.26±3.13 cM). Also, thePer-5 ande loci were located on the short arm of chromosome 2. In additionIdh-2 was also located on barley chromosome 2 and was linked to thev locus (13.18±3.56 cM), which is located on the long arm of chromosome 2. Two other marker genes,li andwst,,B, were linked (26.50±5.24 cM) on chromosome 2 but segregate independently of the other loci evaluated.
This project was supported by funds from the U.S.-Spain Joint Committee for Scientific and Technological Cooperation. 相似文献
14.
In vitro neurite extension by granule neurons is dependent upon astroglial-derived fibroblast growth factor 总被引:20,自引:0,他引:20
M E Hatten M Lynch R E Rydel J Sanchez J Joseph-Silverstein D Moscatelli D B Rifkin 《Developmental biology》1988,125(2):280-289
When grown in the absence of astroglial cells, purified mouse cerebellar granule neurons survive less than 36 hr and do not extend neurites. Here we report that low concentrations of basic fibroblast growth factor (bFGF, 1-25 ng/ml) maintained the viability and promoted the differentiation of purified granule neurons. The effect of bFGF on granule cell neurite outgrowth was dose dependent. Neurite outgrowth was stimulated markedly in the presence of 1-25 ng/ml bFGF, but effects were not seen below 1 ng/ml or above 50 ng/ml. When affinity-purified antibodies against bFGF (1-5 micrograms/ml) were added either to purified granule cells or to co-cultures of neurons and astroglial cells, process extension by granule neurons was severely impaired. The inhibition of neurite outgrowth in the presence of anti-bFGF antibodies was reversed by the addition of 25 ng/ml of exogenous bFGF. In addition to neuronotrophic effects, bFGF influenced the rate of growth of the astroglial cells. This result depended on whether the astroglia were grown in isolation from neurons, where low doses of bFGF (10-25 ng) stimulated glial growth, or in coculture with neurons, where much higher doses of bFGF (100-250 ng/ml) were needed for glial mitogenesis. Immunoprecipitation of lysates from 35S-labeled cerebellar astroglial cells with anti-bFGF antibodies revealed a single band after SDS-PAGE at 18,000 Da, the molecular weight of bFGF. These results indicate that glial cells synthesize bFGF and are possibly an endogenous source of bFGF in cerebellar cultures. Thus, astroglial cells synthesize soluble factors needed for neuronal differentiation. 相似文献
15.
In order to characterize the mechanism of activation of the enzyme 1-O-alkyl-2-lyso-sn-glycero-3-phosphocholine:acetyl-CoA acetyltransferase (EC 2.3.1.67) which is the limiting step in the regulation of the synthesis of the potent inflammatory mediator 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine; homogenates from human polymorphonuclear leukocytes were incubated in the presence of the catalytic subunit of cyclic AMP-dependent protein kinase and in the presence of a partially purified phospholipid sensitive, calcium-dependent protein kinase (PrKC). The first kinase was found to enhance up to 3-fold acetyltransferase activity in a dose- and time-dependent manner. In homogenates from PMN previously stimulated with complement-coated zymosan particles, the decay of acetyltransferase activity was partially prevented by the addition of soybean trypsin inhibitor and almost completely inhibited when the homogenates were supplemented with inhibitors of alkaline phosphatase such as 50 mM KF and 100 microM paranitrophenylphosphate. Under these conditions it was possible to initiate the decay of acetyltransferase activity by adding an excess of alkaline phosphatase. Preincubation of PMN with 12-O-tetradecanoylphorbol-13-acetate previous or simultaneously to the addition of ionophore A23187 reduced the increase in acetyltransferase produced by ionophore A23187, whereas the generation of superoxide anions was enhanced. Addition of partially purified PrKC to homogenates from ionophore A23187-stimulated PMN, reduced acetyltransferase activity by 63%, whereas only a 16% inhibition was observed on homogenates from resting PMN. These data indicate the modulation of acetyltransferase activity in human polymorphonuclear leukocytes by a phosphorylation-dephosphorylation mechanism linked to cyclic AMP-dependent protein kinase. Phospholipid sensitive, calcium-dependent protein kinase seems not to be involved in the mechanism of activation, but, most probably, in the generation of negative activation signals. 相似文献
16.
F C Dalman E R Sanchez A L Lin F Perini W B Pratt 《The Journal of biological chemistry》1988,263(25):12259-12267
Digestion of the rat liver glucocorticoid receptor with chymotrypsin results in the generation of a 42-kDa fragment which contains the steroid-binding and DNA-binding domains and the antigenic site for the BuGR anti-glucocorticoid receptor monoclonal antibody, while digestion with trypsin generates a 15-kDa receptor fragment containing only the DNA-binding function and the BuGR epitope (Eisen, L.P., Reichman, M.E., Thompson, E.B., Gametchu, B., Harrison, R. W., and Eisen, H.J. (1985) J. Biol. Chem. 260, 11805-11810). In this paper, glucocorticoid receptor of mouse L cells that were grown in the presence of [32P]orthophosphate was digested with trypsin or chymotrypsin (either before or after immune purification with BuGR antibody) and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, autoradiography, and Western blotting. The receptor is endogenously phosphorylated only on serine residues. Chymotrypsin digestion results in a 32P-labeled 42-kDa receptor fragment which contains steroid-binding, DNA-binding, and BuGR-reactive sites. Trypsin digestion generates a 27-kDa steroid-bound fragment (meroreceptor) which is not labeled with 32P and a 32P-labeled 15-kDa fragment which contains both the DNA-binding domain and the BuGR epitope. We have calculated that there are 4 times as many phosphate residues in the intact receptor than in the 42-kDa chymotrypsin fragment. From examination of 32P-labeled receptor fragments, we have deduced that one phosphate is located between amino acids 398 and 447, a region containing the BuGR epitope and about one-third of the DNA-binding domain, and the remaining three phosphates appear to be clustered just to the amino-terminal side of the BuGR epitope in a region defined by amino acids 313 to 369. Treatment of intact 32P-labeled receptor in cytosol with alkaline phosphatase removes these three phosphates, but it does not remove the phosphate from the DNA-binding-BuGR-reactive fragment and it does not affect the ability of the transformed receptor to bind to DNA-cellulose. 相似文献
17.
Single-channel activity of bilayers derived from sea urchin sperm plasma membranes at the tip of a patch-clamp electrode 总被引:3,自引:0,他引:3
Changes in the plasma membrane permeability of echinoderm sperm play a fundamental role in the acrosome reaction. During the reaction there is an increase in intracellular Ca2+ and Na+ and an efflux of H+ and K+. We have formed bilayers at the tip of patch pipets from a mixture of lipid vesicles and sea urchin sperm plasma membranes (12-50 microgram protein/ml). We observed three types of K+ channels (conductances: 22, 46, and 82 pS), two of which are partially blocked by TEA, and one Cl- channel (148 pS). The presence of K+ channels in sperm plasma membranes is consistent with the inhibition by TEA of the acrosome reaction in whole sperm and the membrane potential change that occurs during the reaction. 相似文献
18.
A S Edelman B Xue P Sanchez G J Thorbecke 《Journal of immunology (Baltimore, Md. : 1950)》1985,135(3):2206-2212
Dimethylbenz[a]anthracene (DMBA)-induced transplantable fibrosarcomas in B2 homozygous chickens (SC line) grow progressively in normal chickens, but are rejected by chickens immunized previously with irradiated tumor cells and Corynebacterium parvum. Tumor-immune chickens resist challenge by the immunizing tumor lines as well as by some, but not all, fibrosarcoma lines. The pattern of cross-reactivity between four DMBA-induced transplantable tumor lines was examined in detail. Ability to reject a tumor challenge correlated very well (p less than 0.001) with the presence of delayed-type hypersensitivity (DTH) to that tumor. Immunization with one of two of the DMBA-induced lines tested also caused rejection of transplantable tumors developed from methylcholanthrene-induced and benzo(a)pyrene-induced primary fibrosarcomas. Although immunization with tumor caused DTH to chicken embryo fibroblasts (CEF), immunization with CEF failed to cause protective immunity or DTH to tumors. Presence of protective immunity, where tested, also correlated with the ability of spleen cells from immune donors to inhibit tumor growth in Winn tests. Humoral immunity exhibited even greater cross-reactivity than did cellular immunity. Distinct patterns of cross-reactivity were nevertheless observed with respect to the serum antibodies as detected in ELISA. Two of these patterns were also observed in several sera from primary tumor-bearing chickens, both including reactivity with CEF. Such reactivity was absent from normal chicken sera. 相似文献
19.
Management of a harem breeding colony of rhesus monkeys to reduce trauma-related morbidity and mortality 总被引:1,自引:0,他引:1
M J Kessler W T London R G Rawlins J Gonzalez H S Martinez J Sanchez 《Journal of medical primatology》1985,14(2):91-98
A management procedure was developed for a harem breeding colony of rhesus monkeys to reduce trauma-related injuries and deaths resulting from the periodic removal of pregnant monkeys for research and their subsequent return to the population. Lower morbidity and mortality rates, a reduced mean conception interval, and a higher mean conception rate occurred when monkeys were maintained in permanent harems to which returning females were reintroduced compared to new social groups formed from aggregates of unfamiliar animals. 相似文献
20.
Isolation and characterization of Pediococcus halophilus from salted anchovies (Engraulis anchoita) 总被引:3,自引:0,他引:3
M Villar A P de Ruiz Holgado J J Sanchez R E Trucco G Oliver 《Applied and environmental microbiology》1985,49(3):664-666
The presence of bacteria in salted anchovies during and at the end of the curing process was investigated. Attempts to isolate bacteria under aerobic or anaerobic conditions led to the isolation of only bacteria of the genus Pediococcus which were identified as Pediococcus halophilus. The isolates correspond to a rather heterogeneous group in which some of the members differ in some biochemical tests from the types described in the literature. 相似文献