全文获取类型
收费全文 | 3291篇 |
免费 | 488篇 |
出版年
2021年 | 45篇 |
2018年 | 44篇 |
2017年 | 37篇 |
2016年 | 36篇 |
2015年 | 66篇 |
2014年 | 78篇 |
2013年 | 120篇 |
2012年 | 146篇 |
2011年 | 155篇 |
2010年 | 105篇 |
2009年 | 95篇 |
2008年 | 138篇 |
2007年 | 155篇 |
2006年 | 247篇 |
2005年 | 134篇 |
2004年 | 118篇 |
2003年 | 117篇 |
2002年 | 110篇 |
2001年 | 127篇 |
2000年 | 102篇 |
1999年 | 67篇 |
1998年 | 48篇 |
1997年 | 32篇 |
1996年 | 43篇 |
1995年 | 36篇 |
1994年 | 31篇 |
1993年 | 28篇 |
1992年 | 69篇 |
1991年 | 68篇 |
1990年 | 73篇 |
1989年 | 90篇 |
1988年 | 68篇 |
1987年 | 68篇 |
1986年 | 44篇 |
1985年 | 56篇 |
1984年 | 49篇 |
1983年 | 41篇 |
1982年 | 30篇 |
1981年 | 30篇 |
1979年 | 49篇 |
1978年 | 45篇 |
1977年 | 36篇 |
1976年 | 34篇 |
1975年 | 42篇 |
1974年 | 40篇 |
1973年 | 41篇 |
1972年 | 37篇 |
1971年 | 36篇 |
1970年 | 38篇 |
1969年 | 34篇 |
排序方式: 共有3779条查询结果,搜索用时 15 毫秒
21.
22.
Effect of a high-intensity static magnetic field on sciatic nerve regeneration in the rat 总被引:2,自引:0,他引:2
P G Cordeiro B R Seckel C D Miller P T Gross R E Wise 《Plastic and reconstructive surgery》1989,83(2):301-308
The effect of a high-intensity static magnetic field on peripheral nerve regeneration is evaluated in rat sciatic nerve. Forty-four rats underwent sciatic nerve repair using polyethylene nerve guides. Postoperatively, the animals were exposed to a 1-tesla magnetic field for 12 hours per day for 4 weeks with appropriate controls. Our results demonstrate that a 1-tesla static magnetic field has no statistically significant effect on nerve regeneration as determined by myelinated axon counts and electrophysiologic studies. Also, the specific orientation of the sciatic nerve with respect to the magnetic field has no influence on axonal growth or nerve conduction. Periods of restraint of 12 hours per day for 4 weeks significantly inhibit weight gain but have no effect on peripheral nerve regeneration. 相似文献
23.
Recent studies have implicated accelerated sarcolemmal phospholipid catabolism as a mediator of the lethal sequelae of atherosclerotic heart disease. We have demonstrated that plasmalogens are the predominant phospholipid constituents of canine myocardium and that plasmalogens are hydrolyzed by a novel calcium independent plasmalogen selective phospholipase A2. Since the activities of phospholipases are modulated by the molecular dynamics and interfacial characteristics of their phospholipid substrates, we compared the molecular dynamics of plasmenylcholine and phosphatidylcholine vesicles by electron spin resonance spectroscopy and deuterium magnetic resonance spectroscopy. Plasmenylcholine vesicles have separate and distinct molecular dynamics in comparisons to their phosphatidylcholine counterparts as ascertained by substantial decreases in the angular fluctuations and motional velocities of probes attached to their sn-2 aliphatic constituents. Furthermore, since free radical oxidation of myocardial lipid constituents occurs during myocardial ischemia and reperfusion, we demonstrated that 1O2 mediated oxidation of plasmenylcholine resulted in the generation of several products which have chromatographic characteristics and molecular masses corresponding to 2-acyl lysophosphatide derivatives. Taken together, these studies underscore the biologic significance of the predominance of sarcolemmal plasmalogens present in mammalian myocardium and suggest that their catabolism by plasmalogen selective phospholipases and/or oxidative processes may contribute to the lethal sequelae of myocardial ischemia. 相似文献
24.
Recombination and Replication of Plasmid-like Derivatives of a Short Section of the Mitochondrial Chromosome of Neurospora Crassa 总被引:5,自引:0,他引:5
下载免费PDF全文
![点击此处可从《Genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The 21-kbp mitochondrial chromosome of the stp-ruv strain of Neurospora crassa undergoes regional amplification yielding plasmid-like supercoiled circles varying in size from subunit length to very high multimers. A comparison of the base sequence of the five plasmids studied, with the region of the chromosome from which they were derived, indicated that the amplified chromosomal segments were determined by a recombination-excision process near or within two structurally distinctive regions. One of these, consisting of nearly uninterrupted strings of Cs and Gs straddling tandem PstI site direct repeats, could form an extended hairpin loop with only a few mismatches. It was found at or near the 5' exchange point of all of the plasmids. An extended 35-bp sequence containing 17-bp direct repeats was the primary 3' site of exchange. Base sequence changes were found in the vicinity of exchange points. Most notable of these was a G insertion and T to C transition within a section of the 5' region likely to form a hairpin loop, suggesting the involvement of a mismatch repair-like mechanism in the recombination process. The sequence, TATATAGACATATA, was identified as a likely candidate for the site of replication initiation. A nearly identical sequence was found common to all of the corresponding plasmids of Podospora anserina and was reported near the presumed replication origin of the Drosophila yakuba mitochondrial chromosome. A search of GenBank revealed a remarkable association of the consensus sequence, TATATAGAXATATA, with the plus strand of organelle DNA. 相似文献
25.
K Aisaka S S Gross O W Griffith R Levi 《Biochemical and biophysical research communications》1989,160(2):881-886
Nitric oxide is a major endothelium-derived vascular smooth muscle relaxing factor; its synthesis from L-arginine is selectively inhibited by L-NG-methylarginine. To assess whether basal nitric oxide release contributes to blood pressure regulation in vivo, we have investigated the cardiovascular effects of L-NG-methylarginine in the anesthetized guinea pig. L-NG-methylarginine (0.1-10 mg/kg, i.v. bolus) elicited a sustained, dose-dependent, increase in arterial pressure and a moderate bradycardia. L-arginine (30 mg/kg i.v.) prevented or reversed the pressor effect of L-NG-methylarginine, while atropine (2 mg/kg) abolished the associated bradycardia. In contrast, L-arginine did not attenuate the pressor effect of norepinephrine or angiotensin. Our findings suggest that basal nitric oxide production is sufficient to modulate peripheral vascular resistance; hence nitric oxide may play a role in arterial pressure homeostasis. 相似文献
26.
27.
To locate the antigenic determinant recognized by a monoclonal antibody directed against a baculovirus capsid protein, a series of overlapping deletions of a fusion protein were immunologically screened with the monoclonal antibody. The immunoreactive fusion protein was derived from a restriction fragment which contained a large portion of a baculovirus capsid protein open reading frame fused in-frame with a truncated trpE gene in a bacterial (pATH3) expression system. To map the epitope, nested sets of 5' and 3' deletion mutants were generated. Mutants were characterized by the DNA insert size or by the size of the expressed fusion protein. Selected N- and C-termini truncated fusion proteins were Western blotted and incubated with the monoclonal antibody to identify mutants which retained the epitope. Plasmid DNA from mutants which flank the 5' and 3' junction of the antigenic determinant were sequenced to determine the epitope junction. By screening forty 3' deletions and sixty-four 5' deletions, the antigenic determinant was localized to a region of seven amino acids. 相似文献
28.
29.
The lipopolysaccharides (LPS) of a rough (R) and a smooth (S) strain of Pseudomonas syringae pv. phaseolicola were analysed. The S-LPS revealed markedly more rhamnose and fucose, but less glucose, than the R-LPS. The presence of 3-O-methyl-rhamnose (acofriose) in the S-LPS was confirmed by cochromatography with authentic acofriose. SDS polyacrylamide gel electrophoresis of the S-LPS demonstrated a cluster of regularly spaced high molecular weight fractions, which was almost lacking in the R-LPS. The main fatty acids of the lipid A of both LPS species were 3-OH-10:0,3-OH-12:0,2-OH-12:0, and 12:0. Two N-linked diesters were demonstrated: 3-O(12:0)-12:0 and 3-O(2-OH-12:0)-12:0. S-LPS was subjected to mild hydrolysis and the degraded polysaccharide separated into three fractions by gel permeation chromatography on a Fractogel TSK HW-50 column. Fraction I, representing nearly only the O-specific side chain, consisted of rhamnose and fucose in a molar ratio of 4:1, with 4% of the rhamnose being 3-O-methylated (acofriose). Fraction II, representing mostly core material, was composed of glucose, rhamnose, heptose, glucosamine, galactosamine, alanine, and a still unidentified amino compound, in an approximate molar ratio of 3:1:1:1:1:1:1, and KDO. Fraction III consisted of released monomers and salts. The LPS was highly phosphorylated (3.28% phosphorus in the core fraction). The thus characterized composition of the LPS O-chain seems to be unique for the pathovar phaseolicola of P. syringae, although many similarities exist to other pathovars as well as to other bacterial species.Abbreviations LPS
lipopolysacchairdes
- GC/MS
combined gas liquid chromatography-mass spectrometry
- HVE
high voltage electrophoresis
- KDO
2-keto-3-deoxyoctonic acid
- PAGE
polyacrylamide gel electrophoresis
- SDS
sodium dodecylsulfate
P.s. pv. phaseolicola is termed P. phaseolicola in the text 相似文献
30.
Nguyen van Cong G. Uzan M. S. Gross C. Jegou-Foubert P. Frachet C. Boucheix G. Marguerie J. Frézal 《Human genetics》1988,80(4):389-392
Summary The platelet GPIIb-IIIa complex functions as a receptor for fibrinogen, fibronectin, and von Willebrand factor on activated platelets. This glycoprotein is a member of a broadly distributed family of structurally and immunologically related membrane receptors involved in cell-cell contact and cell-matrices interactions. GPIIb-IIIa is a heterodimer complex composed of GPIIb (the subunit), which consists of two disulfide-linked heavy and light chains, and GPIIIa (the subunit), which is a single polypeptide chain. Congenital absence of platelet GPIIb-IIIa in Glanzmann's thrombasthenia results in a severe bleeding disorder characterized by defective platelet aggregation and failure of fibrinogen to bind to platelets. The gene coding for GPIIb was located on 17q21.1-17q21.3 as determined by in situ hybridization with a 2650-pb GP2B (GPIIb) cDNA probe prepared from human megakaryocytes. 相似文献