全文获取类型
收费全文 | 532422篇 |
免费 | 59630篇 |
国内免费 | 344篇 |
专业分类
592396篇 |
出版年
2018年 | 5218篇 |
2017年 | 5082篇 |
2016年 | 6940篇 |
2015年 | 8755篇 |
2014年 | 10470篇 |
2013年 | 15232篇 |
2012年 | 16934篇 |
2011年 | 17322篇 |
2010年 | 11684篇 |
2009年 | 10726篇 |
2008年 | 15128篇 |
2007年 | 15686篇 |
2006年 | 14652篇 |
2005年 | 14044篇 |
2004年 | 13907篇 |
2003年 | 13264篇 |
2002年 | 12794篇 |
2001年 | 28352篇 |
2000年 | 28209篇 |
1999年 | 21974篇 |
1998年 | 6721篇 |
1997年 | 7300篇 |
1996年 | 6733篇 |
1995年 | 6208篇 |
1994年 | 5980篇 |
1993年 | 5957篇 |
1992年 | 17039篇 |
1991年 | 16287篇 |
1990年 | 15696篇 |
1989年 | 15208篇 |
1988年 | 13919篇 |
1987年 | 12933篇 |
1986年 | 12040篇 |
1985年 | 11812篇 |
1984年 | 9659篇 |
1983年 | 8081篇 |
1982年 | 5992篇 |
1981年 | 5373篇 |
1980年 | 5095篇 |
1979年 | 8941篇 |
1978年 | 6810篇 |
1977年 | 6272篇 |
1976年 | 5645篇 |
1975年 | 6236篇 |
1974年 | 6758篇 |
1973年 | 6540篇 |
1972年 | 5978篇 |
1971年 | 5428篇 |
1970年 | 4679篇 |
1969年 | 4399篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
R Vlasak O Wiborg K Richter S Burgschwaiger J Vuust G Kreil 《European journal of biochemistry》1987,169(1):53-58
From a genomic library of Xenopus laevis, two genes coding for different preprocaeruleins have been isolated and sequenced. These correspond to the type I and type III precursors analyzed previously at the cDNA level [Richter, K., Egger, R. and Kreil, G. (1986) J. Biol. Chem. 261, 3676-3680]. The type III gene comprises eight exons; the type I apparently contains eight exons as well, of which six have been sequenced. The genetic information for the dekapeptide caerulein is present on small exons of 45 base pairs. The two genes are highly homologous in their 5'-flanking region, the exon/intron boundaries, and long stretches of intron sequences. A possible scheme for the evolution of this small family of genes through exon and gene duplications is presented. In the type I gene, in place of one of the caerulein exons, a potential exon with conserved splice sites was discovered. If expressed in some frog cells, this exon would code for a new peptide 60% homologous to caerulein. 相似文献
993.
Ratul Saha Robert S. Donofrio Susan T. Bagley 《Journal of industrial microbiology & biotechnology》2010,37(8):843-848
A TaqMan quantitative real-time polymerase chain reaction (qPCR) assay was developed for the detection and enumeration of
three Pseudomonas species belonging to the mendocina sublineage (P. oleovorans, P. pseudoalcaligenes, and P. oleovorans subsp. lubricantis) found in contaminated metalworking fluids (MWFs). These microbes are the primary colonizers and serve as indicator organisms
of biodegradation of used MWFs. Molecular techniques such as qPCR are preferred for the detection of these microbes since
they grow poorly on typical growth media such as R2A agar and Pseudomonas isolation agar (PIA). Traditional culturing techniques not only underestimate the actual distribution of these bacteria but
are also time-consuming. The primer–probe pair developed from gyrase B (gyrB) sequences of the targeted bacteria was highly sensitive and specific for the three species. qPCR was performed with both
whole cell and genomic DNA to confirm the specificity and sensitivity of the assay. The sensitivity of the assay was 101 colony forming units (CFU)/ml for whole cell and 13.7 fg with genomic DNA. The primer–probe pair was successful in determining
concentrations from used MWF samples, indicating levels between 2.9 × 103 and 3.9 × 106 CFU/ml. In contrast, the total count of Pseudomonas sp. recovered on PIA was in the range of <1.0 × 101 to 1.4 × 105 CFU/ml for the same samples. Based on these results from the qPCR assay, the designed TaqMan primer–probe pair can be efficiently
used for rapid (within 2 h) determination of the distribution of these species of Pseudomonas in contaminated MWFs. 相似文献
994.
995.
996.
Most of the previous studies on the effects of iron deficiency on skeletal muscle respiratory capacity and work performance have been investigated in severe or moderate iron-deficiency anemia. We report here that even in mild iron deficiency where the hemoglobin concentration was 10 g/dl and the iron stores in livers and spleen were not completely depleted, a marked reduction in succinate dehydrogenase was observed in skeletal muscles but not in heart. Similarly, cytochrome oxidase activities were reduced. Although no significant change in glycerophosphate dehydrogenase was detected in the iron-deficient rats, exposure to cold in this group greatly reduced this enzyme activity. As cold acclimatization accelerates marrow erythropoiesis (20) which in turn, demands more iron, it seems that in the iron-insufficient state, this iron demand for marrow activity may persist at the expense of the tissue iron pool, resulting in a marked reduction in glycerophosphate dehydrogenase activities. Since succinate dehydrogenase plays a significant role in the impairment of mitochondrial function and early fatigue of iron-deficient muscle (11), the present study shows that even in mild iron deficiency, some loss of muscle functions could result as succinate dehydrogenase activities were greatly reduced. 相似文献
997.
998.
999.
1000.