全文获取类型
收费全文 | 30320篇 |
免费 | 2710篇 |
国内免费 | 19篇 |
出版年
2023年 | 107篇 |
2022年 | 73篇 |
2021年 | 519篇 |
2020年 | 281篇 |
2019年 | 409篇 |
2018年 | 474篇 |
2017年 | 416篇 |
2016年 | 776篇 |
2015年 | 1310篇 |
2014年 | 1472篇 |
2013年 | 1817篇 |
2012年 | 2280篇 |
2011年 | 2273篇 |
2010年 | 1532篇 |
2009年 | 1250篇 |
2008年 | 1874篇 |
2007年 | 1908篇 |
2006年 | 1735篇 |
2005年 | 1744篇 |
2004年 | 1663篇 |
2003年 | 1555篇 |
2002年 | 1528篇 |
2001年 | 316篇 |
2000年 | 210篇 |
1999年 | 330篇 |
1998年 | 399篇 |
1997年 | 247篇 |
1996年 | 242篇 |
1995年 | 259篇 |
1994年 | 243篇 |
1993年 | 246篇 |
1992年 | 207篇 |
1991年 | 192篇 |
1990年 | 196篇 |
1989年 | 178篇 |
1988年 | 141篇 |
1987年 | 148篇 |
1986年 | 129篇 |
1985年 | 150篇 |
1984年 | 148篇 |
1983年 | 157篇 |
1982年 | 149篇 |
1981年 | 163篇 |
1980年 | 136篇 |
1979年 | 101篇 |
1978年 | 126篇 |
1977年 | 99篇 |
1976年 | 92篇 |
1975年 | 85篇 |
1974年 | 73篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Andrea Dichlberger Stefanie Schlager Katariina Maaninka Wolfgang J. Schneider Petri T. Kovanen 《Journal of lipid research》2014,55(12):2471-2478
Human mast cells (MCs) contain TG-rich cytoplasmic lipid droplets (LDs) with high arachidonic acid (AA) content. Here, we investigated the functional role of adipose TG lipase (ATGL) in TG hydrolysis and the ensuing release of AA as substrate for eicosanoid generation by activated human primary MCs in culture. Silencing of ATGL in MCs by siRNAs induced the accumulation of neutral lipids in LDs. IgE-dependent activation of MCs triggered the secretion of the two major eicosanoids, prostaglandin D2 (PGD2) and leukotriene C4 (LTC4). The immediate release of PGD2 from the activated MCs was solely dependent on cyclooxygenase (COX) 1, while during the delayed phase of lipid mediator production, the inducible COX-2 also contributed to its release. Importantly, when ATGL-silenced MCs were activated, the secretion of both PGD2 and LTC4 was significantly reduced. Interestingly, the inhibitory effect on the release of LTC4 was even more pronounced in ATGL-silenced MCs than in cytosolic phospholipase A2-silenced MCs. These data show that ATGL hydrolyzes AA-containing TGs present in human MC LDs and define ATGL as a novel regulator of the substrate availability of AA for eicosanoid generation upon MC activation. 相似文献
2.
Morphological variation among the inner ears of extinct and extant baleen whales (Cetacea: Mysticeti) 下载免费PDF全文
Eric G. Ekdale 《Journal of morphology》2016,277(12):1599-1615
Living mysticetes (baleen whales) and odontocetes (toothed whales) differ significantly in auditory function in that toothed whales are sensitive to high‐frequency and ultrasonic sound vibrations and mysticetes to low‐frequency and infrasonic noises. Our knowledge of the evolution and phylogeny of cetaceans, and mysticetes in particular, is at a point at which we can explore morphological and physiological changes within the baleen whale inner ear. Traditional comparative anatomy and landmark‐based 3D‐geometric morphometric analyses were performed to investigate the anatomical diversity of the inner ears of extinct and extant mysticetes in comparison with other cetaceans. Principal component analyses (PCAs) show that the cochlear morphospace of odontocetes is tangential to that of mysticetes, but odontocetes are completely separated from mysticetes when semicircular canal landmarks are combined with the cochlear data. The cochlea of the archaeocete Zygorhiza kochii and early diverging extinct mysticetes plot within the morphospace of crown mysticetes, suggesting that mysticetes possess ancestral cochlear morphology and physiology. The PCA results indicate variation among mysticete species, although no major patterns are recovered to suggest separate hearing or locomotor regimes. Phylogenetic signal was detected for several clades, including crown Cetacea and crown Mysticeti, with the most clades expressing phylogenetic signal in the semicircular canal dataset. Brownian motion could not be excluded as an explanation for the signal, except for analyses combining cochlea and semicircular canal datasets for Balaenopteridae. J. Morphol. 277:1599–1615, 2016. © 2016 Wiley Periodicals, Inc. 相似文献
3.
4.
Learning-Induced Expression of Meningeal Ependymin mRNA and Demonstration of Ependymin in Neurons and Glial Cells 总被引:1,自引:0,他引:1
Stefan Rother Rupert Schmidt Wolfgang Brysch †Karl-Hermann Schlingensiepen 《Journal of neurochemistry》1995,65(4):1456-1464
Abstract: The turnover of a CNS-specific cell adhesion glycoprotein, ependymin, has earlier been found to increase during periods of neuronal plasticity. Here, ependymin mRNA expression was analyzed by semiquantitative in situ hybridization in goldfish. Learning of an active avoidance response resulted in a significant increase in ependymin mRNA expression 20 min to 4 h after acquisition of the task. In contrast, yoked control animals that were exposed to the same numbers of conditioned and unconditioned stimuli in a random, unpaired manner exhibited a strong down-regulation of ependymin mRNA. Hybridization signals were also increased by injection of anti-ependymin antiserum into brain ventricles. Ependymin mRNA was exclusively localized to reticular-shaped fibroblasts of the inner endomeningeal cell layer. Immunoelectron microscopic investigation, however, revealed ependymin also in distinct neuronal and glial cell populations in which no ependymin mRNA had been detected. Uptake of meningeal protein factors into glial and neuronal cells may therefore be of functional importance for plastic adaptations of the CNS. 相似文献
5.
Eric Wolfgang Amadeus Mulder 《Pal?ontologische Zeitschrift》1990,64(1-2):145-151
An elasmosaurian tooth is described and figured from the St. Pietersberg near Maastricht (Netherlands), well-known for its classical mosasaur finds. The tooth shows lingually a remarkable grinding trace. The preserved sediment allowed a determination of the stratigraphical position by analysis of bioclasts. 相似文献
6.
7.
8.
The major phospholipid constituents of Moraxella catarrhalis membranes are phosphatidylglycerol, phosphatidylethanolamine, and cardiolipin (CL). However, very little is known regarding the synthesis and function of these phospholipids in M. catarrhalis. In this study, we discovered that M. catarrhalis expresses a cardiolipin synthase (CLS), termed MclS, that is responsible for the synthesis of CL within the bacterium. The nucleotide sequence of mclS is highly conserved among M. catarrhalis isolates and is predicted to encode a protein with significant amino acid similarity to the recently characterized YmdC/ClsC protein of Escherichia coli. Isogenic mclS mutant strains were generated in M. catarrhalis isolates O35E, O12E, and McGHS1 and contained no observable levels of CL. Site-directed mutagenesis of a highly conserved HKD motif of MclS also resulted in a CL-deficient strain. Moraxella catarrhalis, which depends on adherence to epithelial cells for colonization of the human host, displays significantly reduced levels of adherence to HEp-2 and A549 cell lines in the mclS mutant strains compared to wild-type bacteria. The reduction in adherence appears to be attributed to the absence of CL. These findings mark the first instance in which a CLS has been related to a virulence-associated trait. 相似文献
9.
10.
Stephan J. Linke Andreas Frings Ling Ren Amadeus Gomolka Udo Schumacher Rudolph Reimer Nils-Owe Hansen Nathan Jowett Gisbert Richard R. J. Dwayne Miller 《PloS one》2015,10(3)
The impact of using a Femtosecond laser on final functional results of penetrating keratoplasty is low. The corneal incisions presented here result from laser ablations with ultrafast desorption by impulsive vibrational excitation (DIVE). The results of the current study are based on the first proof-of-principle experiments using a mobile, newly introduced picosecond infrared laser system, and indicate that wavelengths in the mid-infrared range centered at 3 μm are efficient for obtaining applanation-free deep cuts on porcine corneas. 相似文献