全文获取类型
收费全文 | 4640篇 |
免费 | 388篇 |
国内免费 | 8篇 |
专业分类
5036篇 |
出版年
2022年 | 22篇 |
2021年 | 30篇 |
2020年 | 35篇 |
2019年 | 30篇 |
2018年 | 36篇 |
2017年 | 37篇 |
2016年 | 75篇 |
2015年 | 129篇 |
2014年 | 142篇 |
2013年 | 206篇 |
2012年 | 255篇 |
2011年 | 281篇 |
2010年 | 191篇 |
2009年 | 168篇 |
2008年 | 253篇 |
2007年 | 258篇 |
2006年 | 248篇 |
2005年 | 280篇 |
2004年 | 275篇 |
2003年 | 253篇 |
2002年 | 260篇 |
2001年 | 65篇 |
2000年 | 55篇 |
1999年 | 72篇 |
1998年 | 75篇 |
1997年 | 64篇 |
1996年 | 46篇 |
1995年 | 50篇 |
1994年 | 47篇 |
1993年 | 36篇 |
1992年 | 44篇 |
1991年 | 42篇 |
1990年 | 58篇 |
1989年 | 41篇 |
1988年 | 36篇 |
1987年 | 43篇 |
1986年 | 28篇 |
1985年 | 46篇 |
1984年 | 59篇 |
1983年 | 56篇 |
1982年 | 58篇 |
1981年 | 47篇 |
1980年 | 56篇 |
1979年 | 44篇 |
1978年 | 52篇 |
1977年 | 44篇 |
1976年 | 42篇 |
1975年 | 35篇 |
1974年 | 35篇 |
1973年 | 25篇 |
排序方式: 共有5036条查询结果,搜索用时 15 毫秒
121.
Grant St. Julian Rodney J. Bothast Larry H. Krull 《Journal of industrial microbiology & biotechnology》1990,5(6):391-394
Summary By succesive recycling of the thin stillage in mashing and fermenting fresh corn, the glycerol content in each fermentation increased by about 0.4% and accumulated to a high of 2.1% in the beer of the fifth recycle. Glycerol concentration declined after the fifth recycle. The original fermentation contained 0.8% glycerol.Presented in part at the Society for Industrial Microbiology Annual Meeting, August 7–12, 1988, Chicago, IL.The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over other firms or similar products not mentioned. 相似文献
122.
A nematode collected from Diaprepes abbreviatus is identified and described as a new species, Steinernema diaprepesi n. sp. The new species is closely related to S. feltiae, S. glaseri, and S. oregonense and can be distinguished from these species by the following characteristics: Males: Spicule averaging 79 (71-90) µm and spicule shape; D% (distance from anterior end to excretory pore/ esophagus length × 100) about 80; the ratio SW (spicule length/anal body width) about 1.8. Females: Vulva with short, double- flapped epiptygma; tail terminus usually with 5 papillae-like structures. Infective juveniles: Body averaging 1,002 (880-1,133) µm, EP (distance from anterior end to excretory pore) = 74 (66-83) µm; tail length = 83 (65-91) µm, and E% (EP/tail length × 100) = 89.6 (78-114). Lateral field pattern variable, the formula for the arrangement of ridges from head to tail is: 2, 6, 7, 8, 4, 2. The portion with eight ridges is the longest. This new species can be differentiated further from three closest species (S. feltiae, S. glaseri, and S. oregonense) by characteristic sequences of their ITS regions, including sequence lengths, ratios of similarity, composition, and differences in base characters in sequence alignment. 相似文献
123.
Michael J. Sofia William T. Jackson Davis L. SaussyJr. Steven A. Silbaugh Larry L. Froelich Sandra L. Cockerham Peter W. Stengel 《Bioorganic & medicinal chemistry letters》1992,2(12)
A series of
-alkoxyphenols containing a tetrazole acid sidechain have been prepared as antagonists of leukotriene B4 receptors. These compounds were tested as receptor antagonists of human neutrophil and guinea pig lung membrane leukotriene B4 receptors. Compounds in this series were found to be up to 18-fold more potent than LY255283. These results indicate that the acyl group of the 1,2,4,5 substituted hydroxyacetophenone class of LTB4 antagonists is not critical to antagonist potency. 相似文献
124.
Marshall C Elias C Xue XH Le HD Omelchenko A Hryshko LV Tibbits GF 《American journal of physiology. Cell physiology》2002,283(2):C512-C520
The cardiacNa+/Ca2+ exchanger (NCX) in troutexhibits profoundly lower temperature sensitivity in comparison to themammalian NCX. In this study, we attempt to characterize the regions of the NCX molecule that are responsible for its temperature sensitivity. Chimeric NCX molecules were constructed using wild-type trout andcanine NCX cDNA and expressed in Xenopus oocytes.NCX-mediated currents were measured at 7, 14, and 30°C using thegiant excised-patch technique. By using this approach, the differentialtemperature dependence of NCX was found to reside within theNH2-terminal region of the molecule. Specifically, we foundthat ~75% of the Na+/Ca2+ exchangedifferential energy of activation is attributable to sequencedifferences in the region that include the first four transmembranesegments, and the remainder is attributable to transmembrane segmentfive and the exchanger inhibitory peptide site. 相似文献
125.
126.
Trevor J. C. Beebee John Buckley Ivor Evans Jim P. Foster Antony H. Gent Chris P. Gleed-Owen Geoffrey Kelly Graham Rowe Charles Snell Julia T. Wycherley Inga Zeisset 《Biodiversity and Conservation》2005,14(7):1607-1626
Introduced species often pose serious threats to biodiversity, but occasionally confusion arises as to whether a species really is introduced or is in fact an overlooked native. A recent UK conservation dilemma has centred on the status of the pool frog Rana lessonae. This species has been the subject of documented introductions from central and southern Europe since the early 1800s, the accepted position being that all UK R. lessonae populations are descended from these introductions. However, a closer examination of early UK literature sources, and recent discoveries of isolated, native R. lessonae populations in Sweden and Norway, led some herpetologists to question whether the species was in fact present as a native at some locations prior to the introductions. Research was initiated along four major lines of enquiry: genetic, bioacoustic, archaeozoological and archival. A high degree of convergence among the genetic and bioacoustic investigations demonstrated that the potentially native UK pool frogs were closely related to Scandinavian frogs, thus ruling out introductions from further south as a potential origin. Subfossil evidence of pool frogs was found from ca. 1000 years before present, demonstrating that the species occurred in the UK prior to known introductions. Archival sources produced no historical support for introductions from northern Europe. The postglacial history inferred for these northern populations is consistent with the known climatic and geographical conditions. Taken together, the evidence for the native status of the pool frog is compelling, and furthermore the UK population appears to be part of a distinct northern clade. 相似文献
127.
Human esterase D gene: complete cDNA sequence,genomic structure,and application in the genetic diagnosis of human retinoblastoma 总被引:2,自引:2,他引:2
Lih-Jiuan S. Young Eva Y. -H. P. Lee Hoang To Robert Bookstein Jin-Yuh Shew Larry A. Donoso Theodore Sery Michael Giblin Jerry A. Shields Wen-Hwa Lee 《Human genetics》1988,79(2):137-141
Summary The gene encoding human esterase D (EsD), a member of the nonspecific esterase family, is a useful genetic marker for retinoblastoma (RB) and Wilson's disease. Previously we identified a cDNA clone from this gene and determined its chromosomal location. In this report, we present the complete cDNA sequence of the human EsD gene. A long open reading frame encoded a predicted protein of 282 amino acids with molecular weight of 30 kD. A computer-assisted search of a protein sequence data base revealed homology with two other esterases, acetylcholinesterase of Torpedo and esterase-6 of Drosophila. Homologous region were centered around presumptive active sites, suggesting that the catalytic domains of the esterases are conserved during evolution. Three genomic clones of this gene were also isolated and characterized by restriction mapping. At least ten exons were distributed over a 35-kb (kilobase pair) region; each exon contained an average of 100 basepairs (bp). A polymorphic site for Apa I, located within an intron of the esterase D gene, can be used to identify chromosome 13 carrying defective RB alleles within retinoblastoma families. 相似文献
128.
Emma Louise Clifford Margaret M. Collins Claire M. Buckley Anthony P. Fitzgerald Ivan J. Perry 《PloS one》2013,8(12)
Objectives
To study the determinants of health-related quality of life (HRQoL) in Irish patients with diabetes using the Centres for Disease Controls'' (CDC''s) ‘Unhealthy Days’ summary measure and to assesses the agreement between this generic HRQoL measure and the disease-specific Audit of Diabetes Dependant Quality of Life (ADDQoL) measure.Research Design and Methods
Data were analysed from the Diabetes Quality of Life Study, a cross-sectional study of 1,456 people with diabetes in Ireland (71% response rate). Unhealthy days were assessed using the CDC''s ‘Unhealthy days’ summary measure. Quality of life (QoL) was also assessed using the ADDQoL measure. Analyses were conducted primarily using logistic regression. The agreement between the two QoL instruments was measured using the kappa co-efficient.Results
Participants reported a median of 2 unhealthy days per month. In multivariate analyses, female gender (P = 0.001), insulin use (P = 0.030), diabetes complications (P = <0.001) were significantly associated with more unhealthy days. Older patients had fewer unhealthy days per month (P = 0.003). Agreement between the two measures of QoL (unhealthy days measure and ADDQoL) was poor, Kappa = 0.234Conclusions
The findings highlight the determinants of HRQoL in patients with diabetes using a generic HRQoL summary measure. The ‘Unhealthy Days’ and the ADDQoL have poor agreement, therefore the ‘Unhealthy Days’ summary measure may be assessing a different construct. Nonetheless, this study demonstrates that the generic ‘Unhealthy Days’ summary measure can be used to detect determinants of HRQoL in patients with diabetes. 相似文献129.
130.
Accelerated response of the myogenin gene to denervation in mutant mice lacking phosphorylation of myogenin at threonine 87 下载免费PDF全文
Gene expression in skeletal muscle is regulated by a family of myogenic basic helix-loop-helix (bHLH) proteins. The binding of these bHLH proteins, notably MyoD and myogenin, to E-boxes in their own regulatory regions is blocked by protein kinase C (PKC)-mediated phosphorylation of a single threonine residue in their basic region. Because electrical stimulation increases PKC activity in skeletal muscle, these data have led to an attractive model suggesting that electrical activity suppresses gene expression by stimulating phosphorylation of this critical threonine residue in myogenic bHLH proteins. We show that electrical activity stimulates phosphorylation of myogenin at threonine 87 (T87) in vivo and that calmodulin-dependent kinase II (CaMKII), as well as PKC, catalyzes this reaction in vitro. We find that phosphorylation of myogenin at T87 is dispensable for skeletal muscle development. We show, however, that the decrease in myogenin (myg) expression following innervation is delayed and that the increase in expression following denervation is accelerated in mutant mice lacking phosphorylation of myogenin at T87. These data indicate that two distinct innervation-dependent mechanisms restrain myogenin activity: an inactivation mechanism mediated by phosphorylation of myogenin at T87, and a second, novel regulatory mechanism that regulates myg gene activity independently of T87 phosphorylation. 相似文献