全文获取类型
收费全文 | 532403篇 |
免费 | 59639篇 |
国内免费 | 338篇 |
专业分类
592380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 | 17319篇 |
2010年 | 11684篇 |
2009年 | 10726篇 |
2008年 | 15128篇 |
2007年 | 15684篇 |
2006年 | 14651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 | 21973篇 |
1998年 | 6721篇 |
1997年 | 7300篇 |
1996年 | 6732篇 |
1995年 | 6208篇 |
1994年 | 5980篇 |
1993年 | 5956篇 |
1992年 | 17039篇 |
1991年 | 16287篇 |
1990年 | 15696篇 |
1989年 | 15207篇 |
1988年 | 13919篇 |
1987年 | 12933篇 |
1986年 | 12040篇 |
1985年 | 11812篇 |
1984年 | 9657篇 |
1983年 | 8081篇 |
1982年 | 5992篇 |
1981年 | 5372篇 |
1980年 | 5095篇 |
1979年 | 8940篇 |
1978年 | 6809篇 |
1977年 | 6272篇 |
1976年 | 5645篇 |
1975年 | 6235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 15 毫秒
421.
422.
423.
424.
425.
426.
Calcium mobilization induced by phosphorylated sphingoid bases was analyzed in calf pulmonary artery endothelial cells by confocal microscopy. A sphingenine-1-phosphate (SeP) analogue, N-acetyl-sphingenine-1-phosphate (N-C2-SeP), exogenously added to these cells, caused a fast and transient intracellular rise in calcium and was as potent as SeP. A minimal concentration of 0.6 nM for N-C2-SeP versus 1 nM for SeP was determined. The N-C2-SeP-induced Ca2+-signaling, like the response to SeP, was due to a release from thapsigargin-sensitive, ryanodine-insensitive, intracellular Ca2+-stores and not to a Ca2+-influx. N-C2-SeP can be considered as a truncated ceramide-phosphate, a lipid already reported to be mitogenic (Gomez-Munoz, A., Duffy, P.A., Martin, A., O'Brien, L., Byun, H.S., Bittman, R. and Brindley, D.N. (1995) Mol. Pharmacol. 47, 833-839), an effect that might be secondary to Ca2+-mobilization. 相似文献
427.
Detailed flow patterns in the nasal cavity. 总被引:9,自引:0,他引:9
The human nasal cavity filters and conditions inspired air while providing olfactory function. Detailed experimental study of nasal airflow patterns has been limited because of the complex geometry of the nasal cavity. In this work, particle image velocimetry was used to determine two-dimensional instantaneous velocity vector fields in parallel planes throughout a model of the nasal cavity that was subjected to a nonoscillatory flow rate of 125 ml/s. The model, which was fabricated from 26 computed tomography scans by using rapid prototyping techniques, is a scaled replica of a human right nasal cavity. The resulting vector plots show that the flow is laminar and regions of highest velocity are in the nasal valve and in the inferior airway. The relatively low flow in the olfactory region appears to protect the olfactory bulb from particulate pollutants. Low flows were also observed in the nasal meatuses, whose primary function has been the subject of debate. Comparison of sequentially recorded data suggests a steady flow. 相似文献
428.
The chloroform-methanol extractable lipids of the Gram-negative fresh-water bacteria Arcocella aquatica NO-502 and Flectobacillus major FM were found to contain an unusual ninhydrin-positive glycolipid. It was purified by two-stage silica gel-column chromatography. By the use of IR and (1)H-NMR spectroscopy, mass spectrometry and chemical-degradation experiment, the lipid was established to be 1-O-monoglycosyl ceramide, the carbohydrate moiety of which was the alpha-pyranose-ring form of 7-desoxy-7-amino-D-manno-heptulosonic acid, or 1-hydroxycarbonyl-6-deoxy-6-amino-alpha-D-mannopyranose. The ceramide portion consisted mainly (by 95% in the A. aquatica glycolipid and 80% in the F. major glycolipid) of 2-N-(2'-D-hydroxy-13'-methyltetradecanoyl)-15-methyl-4(E)-hexad ecasph ingenine. The minor molecular species differed from the major one only in fatty acid structure. The glycolipid accounted for 8 and 11% of the total lipids extracted from A. aquatica NO-502 and F. major FM cells, respectively. 相似文献
429.
430.