全文获取类型
收费全文 | 303557篇 |
免费 | 35628篇 |
国内免费 | 161篇 |
出版年
2018年 | 2491篇 |
2016年 | 3243篇 |
2015年 | 4343篇 |
2014年 | 5233篇 |
2013年 | 7175篇 |
2012年 | 8307篇 |
2011年 | 8489篇 |
2010年 | 5623篇 |
2009年 | 5389篇 |
2008年 | 7693篇 |
2007年 | 7913篇 |
2006年 | 7725篇 |
2005年 | 7518篇 |
2004年 | 7385篇 |
2003年 | 7189篇 |
2002年 | 7009篇 |
2001年 | 17389篇 |
2000年 | 17540篇 |
1999年 | 13456篇 |
1998年 | 4046篇 |
1997年 | 4241篇 |
1996年 | 3972篇 |
1995年 | 3600篇 |
1994年 | 3574篇 |
1993年 | 3629篇 |
1992年 | 10509篇 |
1991年 | 10423篇 |
1990年 | 9921篇 |
1989年 | 9739篇 |
1988年 | 9103篇 |
1987年 | 8446篇 |
1986年 | 7649篇 |
1985年 | 7509篇 |
1984年 | 5958篇 |
1983年 | 5180篇 |
1982年 | 3751篇 |
1981年 | 3326篇 |
1980年 | 3147篇 |
1979年 | 5432篇 |
1978年 | 4212篇 |
1977年 | 3840篇 |
1976年 | 3387篇 |
1975年 | 3868篇 |
1974年 | 4040篇 |
1973年 | 4001篇 |
1972年 | 3482篇 |
1971年 | 3238篇 |
1970年 | 2878篇 |
1969年 | 2777篇 |
1968年 | 2441篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Insulin release independent of a rise in cytosolic free Ca2+ by forskolin and phorbol ester 总被引:6,自引:0,他引:6
The role of cytosolic free Ca2+ in insulin release was evaluated using isolated rat pancreatic islets permeabilized with digitonin and incubated in Ca-EGTA buffers to fix free Ca2+ concentration at arbitrary levels. Ca2+ induced insulin release in a concentration-dependent manner with the threshold being between 0.1 and 1 microM. The hormone release was increased by forskolin and 12-O-tetradecanoyl phorbol-13-acetate (TPA), a potent activator of adenylate cyclase and that of protein kinase C, respectively. The findings suggest that activation of both protein kinase A and protein kinase C modulate insulin release without a concomitant increase in cytosolic free Ca2+. 相似文献
132.
We used a polyethylene surface to study the adherence of various urinary pathogens to a representative inert surface. The bacteria were suspended in filter-sterilized urine during this adhesion study, and differential adhesion was clearly demonstrated. Pseudomonas aeruginosa adhered most avidly and formed large microcolonies that were surrounded by an extensive amorphous matrix. Staphylococcus saprophyticus also formed microcolonies on the surface of the plastic droppers. In general, piliated strains of Escherichia coli adhered less avidly than the other organisms, but more avidly than nonpiliated strains; however, one piliated strain of E. coli adhered very poorly and behaved like a nonpiliated strain. 相似文献
133.
H. Ronald Pulliam 《Human ecology: an interdisciplinary journal》1982,10(3):353-363
Patterns of conflict and cooperation both within and between societies may be related to the degree of cultural similarity within and between the same societies. A simple model of social learning is used to predict patterns of conflict and cooperation in hypothetical societies that differ in the roles of relatives and nonrelatives in the enculturation of children. The model is illustrated by comparing its predictions to known differences in the patterns of conflict between males inpatrilocal and matrilocal societies. 相似文献
134.
Initiation of the extrinsic pathway of coagulation. Association of factor VIIa with a cell line expressing tissue factor 总被引:3,自引:0,他引:3
We have examined initial assembly of the extrinsic pathway of blood coagulation on cell surfaces with radiolabeled human factor VIIa and a human fetal lung cell line possessing abundant functional tissue factor activity. Binding of factor VIIa to these cells was observed and was time- and temperature-dependent. Binding of factor VIIa was quantitatively equivalent at 37 and 6 degrees C, although the kinetics of binding differed. The radiolabeled ligand bound by the cell was indistinguishable by sodium dodecyl sulfate-polyacrylamide gel analysis from the factor VIIa offered. Factor VIIa binding was influenced by calcium ions. The binding appears to involve at least two classes of calcium-dependent binding sites. Optimal binding occurred at 2 mM calcium for both classes of sites, and there was inhibition of binding to the high affinity sites at higher calcium. Association of factor VIIa was specific, saturable, had a Kd of 123 +/- 37 pm, and factor VIIa interacted with about 100,000 binding sites per cell. Once established, specific binding was rapidly reversible. Direct cellular binding of human factor X also was observed and was calcium, time- and temperature-dependent. Factor X binding was specific and saturable with half-maximal binding at 87.6 +/- 27.4 nM to 6.03 +/- 1.03 X 10(6) sites per cell. Specific high affinity binding of factor VIIa correlated with generation of factor Xa. A direct linear relationship was observed at low factor VIIa binding; however, at higher bound factor VIIa, the relationship was nonstoichiometric, i.e. less factor Xa was formed per mole of factor VIIa. Expression of specific binding sites for factors VIIa and X provides further substantiation for the molecular assembly hypothesized to initiate the extrinsic coagulation protease cascade on cells. 相似文献
135.
G A Vilkov E M Stepanenko T A Khoruzhaia 《Biulleten' eksperimental'no? biologii i meditsiny》1985,99(1):48-50
The authors studies the effects of blood serum and IgG fraction from dogs immunized with brain and blood sera from patients with multiple sclerosis and schizophrenia on lipid peroxidation in rat brain homogenates. Measured the content of diene conjugates (DC) and malonic dialdehyde (MDA) in the rat brain after administering the IgG fraction. It was established that antioxidant activity of blood sera and IgG fraction from control animals and donors was significantly higher as compared to experimental. Administration of the IgG fraction brought about an increase in the content of DC and MDA in the brain of experimental animals. It is concluded that complement-dependent brain antibodies present in the blood serum of patients with schizophrenia and multiple sclerosis potentiate lipid peroxidation in the cerebral tissue and that the unsophisticated and informative method for antibody determination may be used in clinical practice. 相似文献
136.
137.
J R van Der Ploeg R Iwanicka-Nowicka T Bykowski M M Hryniewicz T Leisinger 《The Journal of biological chemistry》1999,274(41):29358-29365
138.
Microsatellite DNA in peach (Prunus persica L. Batsch) and its use in fingerprinting and testing the genetic origin of cultivars. 总被引:11,自引:0,他引:11
R Testolin T Marrazzo G Cipriani R Quarta I Verde M T Dettori M Pancaldi S Sansavini 《Génome》2000,43(3):512-520
We isolated and sequenced 26 microsatellites from two genomic libraries of peach cultivar 'Redhaven', enriched for AC/GT and AG/CT repeats, respectively. For 17 of these microsatellites, it was possible to demonstrate Mendelian inheritance. Microsatellite polymorphism was assayed in 50 peach and nectarine cultivars. Of the 1300 PCRs carried out, all but two produced amplified products of the expected size. All microsatellites were polymorphic, showing 2-8 alleles per locus. Heterozygosity ranged from 0.04-0.74 (mean 0.47); the discrimination power (PD) ranged from 0.04-0.84 (mean 0.60). Cultivar heterozygosity varied greatly, with one cultivar ('Independence') being homozygous at all loci. The set of microsatellites discriminated all cultivars investigated, except several sport mutations, i.e., 'Dixitime' vs. 'Springcrest', 'Compact Redhaven' vs. 'Redhaven', and two pairs of cultivars, 'Venus' vs. 'Orion' and 'Elegant Lady' vs. 'Rome Star', whose pedigrees are controversial. We were able to analyze the paternity of several cultivars. In most cases, the parenthood was confirmed. The comparison of three long-living 'Redhaven' accessions supplied by different repositories did not provide any evidence of somatic instability of microsatellites. Hence, microsatellites, ranked according to their information content, are recommended as markers of choice for peach fingerprinting and suggestions are provided for interpreting band profiles and the correct sizing of alleles. 相似文献
139.
E T Iwamoto 《Life sciences》1988,43(6):503-508
Intracerebroventricular (i.c.v.) administration of dynorphin A [1-17] induced significant place preference conditioning in male, Sprague-Dawley rats. Place preferences were induced by 2.3 and 3.5 nmole, but not 1.2 nmole of dynorphin A. Co-administration of naloxone, 27.5 nmole but not 5.5 nmole, antagonized the reward response induced by 2.3 nmole of dynorphin A. Leu-enkephalin, 5 or 25 nmole, and dynorphin A [2-17], 2.3 or 3.5 nmole, had no effect in the place conditioning paradigm. 相似文献
140.