全文获取类型
收费全文 | 422747篇 |
免费 | 47644篇 |
国内免费 | 153篇 |
出版年
2018年 | 3901篇 |
2016年 | 5279篇 |
2015年 | 6895篇 |
2014年 | 8143篇 |
2013年 | 11229篇 |
2012年 | 12782篇 |
2011年 | 13231篇 |
2010年 | 9073篇 |
2009年 | 8426篇 |
2008年 | 12114篇 |
2007年 | 12606篇 |
2006年 | 11822篇 |
2005年 | 11301篇 |
2004年 | 11344篇 |
2003年 | 10630篇 |
2002年 | 10443篇 |
2001年 | 17405篇 |
2000年 | 17413篇 |
1999年 | 13795篇 |
1998年 | 4833篇 |
1997年 | 5073篇 |
1996年 | 4742篇 |
1995年 | 4611篇 |
1994年 | 4482篇 |
1993年 | 4533篇 |
1992年 | 11600篇 |
1991年 | 11529篇 |
1990年 | 11283篇 |
1989年 | 10899篇 |
1988年 | 10483篇 |
1987年 | 10072篇 |
1986年 | 9358篇 |
1985年 | 9229篇 |
1984年 | 7742篇 |
1983年 | 6701篇 |
1982年 | 5160篇 |
1981年 | 4612篇 |
1980年 | 4458篇 |
1979年 | 7416篇 |
1978年 | 5858篇 |
1977年 | 5389篇 |
1976年 | 5195篇 |
1975年 | 5593篇 |
1974年 | 6300篇 |
1973年 | 6162篇 |
1972年 | 5761篇 |
1971年 | 5224篇 |
1970年 | 4632篇 |
1969年 | 4573篇 |
1968年 | 4419篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
31.
32.
33.
S. Kleinle U. Wiesmann A. Superti-Furga S. Krähenbühl E. Boltshauser J. Reichen S. Liechti-Gallati 《Human genetics》1997,100(5-6):643-650
We used a strategy based on long PCR (polymerase chain reaction) for detection and characterization of mitochondrial DNA (mtDNA)
rearrangements in two patients with clinical signs suggesting Pearson syndrome and Kearns-Sayre syndrome (KSS), respectively,
and one patient with myopathic symptoms of unidentified origin. Mitochondrial DNA rearrangements were detected by amplification
of the complete mitochondrial genome (16.6 kb) using long PCR with primers located in essential regions of the mitochondrial
genome and quantified by three-primer PCR. Long PCR with deletion-specific primers was used for identification and quantitative
estimation of the different forms of rearranged molecules, such as deletions and duplications. We detected significant amounts
of a common 7.4-kb deletion flanked by a 12-bp direct repeat in all tissues tested from the patient with Pearson syndrome.
In skeletal muscle from the patient with clinical signs of KSS we found significant amounts of a novel 3.7-kb rearrangement
flanked by a 4-bp inverted repeat that was present in the form of deletions as well as duplications. In the patient suffering
from myopathic symptoms of unidentified origin we did not detect rearranged mtDNA in blood but found low levels of two rearranged
mtDNA populations in skeletal muscle, a previously described 7-kb deletion flanked by a 7-bp direct repeat and a novel 6.6-kb
deletion with no repeat. These two populations, however, were unlikely to be the cause of the myopathic symptoms as they were
present at low levels (10–40 ppm). Using a strategy based on screening with long PCR we were able to detect and characterize
high as well as low levels of mtDNA rearrangements in three patients.
Received: 10 March 1997 / Accepted: 20 May 1997 相似文献
34.
Spectrophotometric quantification of lactic bacteria in alginate and control of cell release with chitosan coating 总被引:3,自引:0,他引:3
Y. Zhou E. Martins A. Groboillot C. P. Champagne & R. J. Neufeld 《Journal of applied microbiology》1998,84(3):342-348
Lactococcus lactis ssp. cremoris was entrapped within a Ca-alginate matrix, and an in situ spectrophotometric method for monitoring cell population in calcium alginate beads described. The intracapsular cell population can be estimated by measuring the optical density of beads containing cells, using cell-free beads as reference, or by measuring absorbance of a liquified bead suspension. Alginate beads, and beads coated with chitosan type I, II, and I and II mixtures, were examined for cell release. Lower viscosity chitosan (type I) coatings reduced cell release by a factor of 100 from105 cfu ml−1 to 103 cfu ml−1 after 6 h of fermentation. Reuse of chitosan I coated alginate beads also showed a reduction in cell release by a factor of 100. Cell loading and initial cell growth within the beads greatly affected cell release. Reducing the initial cell release would lower the overall levels of cell release throughout the fermentation. Compared to non-immobilized cultures, a 20–40% reduction in the lactic acid production rate was observed for alginate beads and chitosan I coated alginate beads, respectively. This reduction can be compensated for by increasing the intracapsular cell loading during immobilization, or before the onset of fermentation. 相似文献
35.
Claudio O. Fernández Oscar Podestá Daniel A. Converso Marcelo E. Fernández A. J. Vila 《Journal of biological inorganic chemistry》1997,2(2):218-224
The heme protein wheat germ peroxidase (isoenzyme C2) and its cyanide-inhibited form have been investigated by means of electronic, CD and paramagnetic NMR spectroscopy. The
data indicate a protein environment of the active site distinct from that of horseradish peroxidase (HRP), with a larger solvent
accessibility. The iron is pentacoordinated at neutral and low pH, whereas a hydroxyl anion may be bound at alkaline pH. The
fifth axial ligand is a His residue with a partial anionic character, as found in other peroxidases. A spin equilibrium is
observed at high enzyme concentrations.
Received: 17 September 1996 / Accepted: 10 January 1997 相似文献
36.
Cassava mesocarp carbohydrate and its modified form were used as fillers in low density polyethylene to give plastic films that were biodegradable. It was found that the tensile strength of the films decreased with an increase in the amount of the filler incorporated. The water absorption results of the films showed that modification of the cassava mesocarp carbohydrate made it hydrophobic and therefore more compatible with the polyethylene. 相似文献
37.
The ability of bovine intermediate lobe secretory vesicle membrane-associated enzyme(s) and purified, soluble paired basic residue-specific, pro-opiomelanocortin converting enzyme (Loh, Y.P., Parish, D. C., and Tuteja, R. (1985) J. Biol. Chem. 260, 7194-7205) to cleave bovine NH2-terminal pro-opiomelanocortin1-77 (N-POMC 1-77) was investigated. Purified pro-opiomelanocortin converting enzyme and an enzyme activity associated with the secretory vesicle membrane were shown to cleave bovine N-POMC1-77 to two major products: N-POMC1-49 and Lys-gamma 3-melanotropin (MSH), and one minor product, gamma 3-MSH. These products were identified by their retention times on high performance liquid chromatography, immunological characteristics, and for Lys-gamma 3-MSH, amino acid composition. The products generated indicate cleavage preferentially between Arg 49-Lys 50 of bN-POMC1-77 (where b indicates bovine), which is identical to the processing pattern found in the bovine intermediate lobe in situ. The membrane converting activity was shown to be stimulated by 5 mM Ca2+ and has a pH optimum of 4-5 and an inhibitor profile characteristic of an aspartic protease. This suggests that the membrane-associated enzyme involved is very similar or identical to the purified, soluble pro-opiomelanocortin converting enzyme, which has previously been reported to be an acidic, aspartic protease responsible for the initial steps of POMC processing. The results of this study lead to the proposal that the lack of processing of the Arg49-Lys50 site in POMC in the anterior lobe versus the intermediate lobe of the pituitary in vivo may be due to other regulatory mechanisms rather than invoking the existence in the intermediate lobe of another enzyme specific for this site, different from pro-opiomelanocortin converting enzyme. 相似文献
38.
39.
40.