全文获取类型
收费全文 | 7534篇 |
免费 | 681篇 |
国内免费 | 2篇 |
出版年
2024年 | 11篇 |
2023年 | 34篇 |
2022年 | 102篇 |
2021年 | 219篇 |
2020年 | 100篇 |
2019年 | 130篇 |
2018年 | 169篇 |
2017年 | 141篇 |
2016年 | 253篇 |
2015年 | 491篇 |
2014年 | 511篇 |
2013年 | 505篇 |
2012年 | 690篇 |
2011年 | 652篇 |
2010年 | 380篇 |
2009年 | 322篇 |
2008年 | 493篇 |
2007年 | 459篇 |
2006年 | 413篇 |
2005年 | 378篇 |
2004年 | 339篇 |
2003年 | 356篇 |
2002年 | 300篇 |
2001年 | 65篇 |
2000年 | 47篇 |
1999年 | 78篇 |
1998年 | 73篇 |
1997年 | 49篇 |
1996年 | 45篇 |
1995年 | 37篇 |
1994年 | 29篇 |
1993年 | 34篇 |
1992年 | 26篇 |
1991年 | 18篇 |
1990年 | 22篇 |
1989年 | 16篇 |
1988年 | 16篇 |
1987年 | 15篇 |
1986年 | 8篇 |
1985年 | 13篇 |
1984年 | 9篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 9篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1974年 | 6篇 |
1973年 | 6篇 |
1971年 | 7篇 |
1965年 | 6篇 |
排序方式: 共有8217条查询结果,搜索用时 15 毫秒
71.
Jean-Frédéric Brun Colette Fons Michelle Fussellier Lucette Bardet André Orsetti 《Biological trace element research》1992,32(1-3):317-323
We investigated whether zincuria is associated with microalbuminuria in type I (insulin-dependent) diabetics (IDDM). In 169
IDDM, 215 overnight urine samples were collected for simultaneous assay of zinc and albumin. In 76 samples with excessive
microalbuminuria (>15 mg/L), zincuria was higher than in the 139 other samples (0.83±0.06 vs 0.58±0.03 mg/Lp<0.001), though zincuria and microalbuminuria were not significantly correlated. An exercise provocation test was performed
in 78 IDDM. Although microalbuminuria increased, zincuria did not change during the test. Another group of 83 IDDM underwent
urinary zinc determination over a period of 1 h of recumbency. The 48 patients who had a zincuria higher than the mean+2 SD
of control values had higher microalbuminuria at rest (48±16 μg/min vs 12±2p<0.01) and after exercise (111±33 vs 42±14p<0.02) than the remaining 35 subjects. Both subgroups did not differ for zinc intake and zincemia. Thus, incipient nephropathy
as detected by the measurement of microalbuminuria is associated with a highly significant increase in zinc excretion, which
is not proportional to albumin leakage, nor is it amplified during exercise. Hyperzincuria is not explained by an increase
in zinc intake and does not result in hypozincemia. 相似文献
72.
Corals display a wide range of complex life histories. The evolutionary consequences of factors such as clonality, indeterminate growth, asexual reproduction coupled with various (sexual) breeding systems, different levels of gene flow, and strongly overlapping generations have only just begun to be explored. We identify a series of problems and areas for new research that may be resolved b y the application of novel theoretical approaches (including nonequilibrium population genetic models and demographic models incorporating modular processes such as colony fission and polyp mortality), greater in situ experimentation, long-term monitoring of population dynamics and the use of new genetic techniques. 相似文献
73.
C Livingstone A R McLellan M A McGregor A Wilson J M Connell M Small G Milligan K R Paterson M D Houslay 《Biochimica et biophysica acta》1991,1096(2):127-133
Adenylate cyclase activity and levels of guanine nucleotide regulatory proteins (G-proteins) were compared in platelets from normal and non-insulin-dependent diabetic (NIDDM) male subjects. Whilst no differences were noted in basal and NaF-stimulated adenylate cyclase activities the degree of stimulation achieved by both forskolin and prostaglandin, E1 was lower by some 34 and 52% respectively, in platelet membranes from diabetic subjects compared with those from normal control subjects. Altered alpha 1-adrenoceptor-mediated inhibition of prostaglandin E1-stimulated adenylate cyclase activity was evident; it being some 34% lower in platelet membranes from diabetic subjects compared to controls. Analysis of G-protein alpha-subunits, using specific anti-peptide antisera, showed that platelets from all subjects exhibited the Gi-2 and Gi-3, but not the Gi-1 forms of the inhibitory G-protein 'Gi' and all expressed the 42 kDa species of alpha-subunit of the stimulatory G-protein Gs. Whilst platelets of diabetic subjects had levels of Gs which were comparable to those found in control subjects their levels of Gi-2 and Gi-3 were some 49 and 75%, respectively, of those found in platelets from control subjects. It is suggested that changes in adenylate cyclase functioning and G-protein expression may contribute to altered platelet functioning in non-insulin-dependent diabetic subjects. 相似文献
74.
Patrice Facy Annie-Pierre Seve Michelle Hubert Michel Monsigny Jean Hubert 《Experimental cell research》1990,190(2)
The nuclear sugar-binding components (i.e., lectinlike molecules) were analyzed using isolated and membrane-depleted nuclei after incubation in the presence of fluorescein-labeled neoglycoproteins. This analysis was performed before and during the in vitro differentiation of HL60 cells into monocytes by PMA treatment and into granulocytes by DMSO treatment. The nucleoli of undifferentiated and differentiated HL60 cells were not labeled, unlike the nucleoli of other mammalian cells studied so far. This peculiarity allowed us to quantitatively analyze by flow cytometry the changes in the lectin activity associated with the extranucleolar territories enriched in ribonucleoprotein complexes. The neoglycoprotein binding was found to be significantly lower in differentiated than in undifferentiated cells. The decrease in neoglycoprotein binding was observed within the first 24 h of DMSO or PMA treatment, just before the arrest of DNA synthesis. Taking into account that the granulocytic differentiation required 72 h of chemical treatment, the extra-nucleolar lectins might be involved in modulation of the DNA synthesis rather than in phenotypic differentiation. These data are discussed in an attempt to reconcile the association of lectins with RNP complexes and their possible involvement in modulation of HL60 cell proliferation. 相似文献
75.
Auer Martin T. Storey Michelle L. Effler Steven W. Auer Nancy A. Sze Philip 《Hydrobiologia》1990,200(1):603-617
The transparency of polluted, hypereutrophic Onondaga Lake, New York, USA has improved substantially in the late 1980's as
a result of reductions in phytoplankton biomass, in the absence of significant reductions in external phosphorus loading.
Much of this improvement has been due to the occurrence of clearing events, e.g. sudden and dramatic increases in transparency.
Field measurements, laboratory experiments, and modelling analyses were utilized to identify processes regulating phytoplankton
standing crop during the spring to fall interval of 1987. Changes in the zooplankton community documented over the past decade
support the conclusion that increased zooplankton grazing has contributed to improvements in transparency. Herbivores now
represent a greater fraction of the zooplankton population and more efficient cladocerans are present in greater numbers.
Biomanipulation practices, e.g. reestablishment of piscivorous species, designed to reduce the abundance of planktivorous
fish species in Onondaga Lake, may serve to reduce pressure on the grazing community and thus result in further improvements
in transparency. 相似文献
76.
77.
I J O'Donnell P E Green J A Connell P S Hopkins 《Australian journal of biological sciences》1981,34(4):411-417
Sheep were immunized with antigens extracted from third-instar larvae of L. cuprina. This procedure produced substantial titres of circulating antibody as measured by solid-phase radioimmunoassay or immunodiffusion or by both techniques. However, immunization did not confer protection against subsequent implant challenge with first-instar larvae. In vitro studies indicated that pooled sera from immunized sheep (mean immunodiffusion titre = 3) significantly reduced larval survival. Antigen specificity and the modulating effects of concomitant humoral responses to larval challenge are discussed in relation to the findings. 相似文献
78.
Britta Swebilius Singer Larry Gold Sidney T. Shinedling Michelle Colkitt Lawrence R. Hunter David Pribnow Mary Anne Nelson 《Journal of molecular biology》1981,149(3):405-432
We have mapped the mutants isolated by Nelson et al. (1981) that reduce the amount of rIIB protein synthesized during bacteriophage T4 infection of Escherichia coli B and characterized their rIIB expression in vivo. These mutants fall into four distinct groups in terms of mapping and phenotype. We have located the probable site of each mutation on the DNA sequence. We have also analyzed a number of other mutations near the initiating AUG of rIIB with respect to their rIIB expression. In some of these mutants, ribosomal recognition of the wild-type initiating AUG is precluded and so initiation occurs at a different AUG, which, in some instances, we have identified. 相似文献
79.
Apple embryos were treated by cold (0°C) within the fruits, to break their dormancy; the controls were treated at 12°C or at 20°C. Ultrastructural features of meristematic cells in the embryonic axis were compared for each treatment. The organization of the cells of dormant embryos was described: Endoplasmic reticulum consisted in some short rough cisternae; lipid droplets regularly arranged near the plasmalemma constituted a kind of shell; mitochondria had a few cristae; and dictyosomes were rarely observed. All these features are typical of dry seeds. After cold treatments, the only evolution observed was in the endoplasmic reticulum, where highly organized stacks appeared progressively as a function of time at 0°C. An intermediate temperature (12°C) induced similar formations in the reticulum but they were rarely observed and their degree of organization was lower than that obtained at 0°C. At 20°C, endoplasmic reticulum resembled that of the dormant embryo cells. The relation between the appearance of these structures in the reticulum and the disappearance of dormancy induced by cold is discussed.Abbreviations ER
endoplasmic reticulum
- RER
rough endoplasmic reticulum 相似文献
80.
The digestion of a human IgG1 K myeloma protein with pepsin in the presence of 8M-urea was observed to produce a fragment, designated Fb'2, which differed from the products of aqueous peptic digestion and from other characteristic immunoglobulin digestion products. 2. Fragment Fb's was also found when two other IgG1/K proteins were treated similarly. 3. Sedimentation-equilibrium studies showed the mol.wt. of fragment Fb'2 to be 56800. 4. On reduction, two equivalents of each of three peptides were released from fragment Fb's; these were characterized by N- and C-terminal determinations and by amino acid sequencing. 5. Fragment Fb'2 was shown to consist of the constant regions of both light chains, from residue Ile-117 to the C-terminus, and the CH1 domains and hinge region of the heavy chains, from residue Val-113 to residue Met-252, with a gap of five residues within the intrachain disulphide loop, between residues Leu-174 and Tyr-180. 相似文献