全文获取类型
收费全文 | 528953篇 |
免费 | 56190篇 |
国内免费 | 384篇 |
专业分类
585527篇 |
出版年
2018年 | 4985篇 |
2016年 | 6649篇 |
2015年 | 8219篇 |
2014年 | 9908篇 |
2013年 | 14229篇 |
2012年 | 15800篇 |
2011年 | 16526篇 |
2010年 | 11222篇 |
2009年 | 10033篇 |
2008年 | 14438篇 |
2007年 | 15065篇 |
2006年 | 14141篇 |
2005年 | 13637篇 |
2004年 | 13527篇 |
2003年 | 13192篇 |
2002年 | 12936篇 |
2001年 | 24158篇 |
2000年 | 24301篇 |
1999年 | 19087篇 |
1998年 | 6286篇 |
1997年 | 6481篇 |
1996年 | 6211篇 |
1995年 | 5867篇 |
1994年 | 5804篇 |
1993年 | 5677篇 |
1992年 | 15838篇 |
1991年 | 15306篇 |
1990年 | 15189篇 |
1989年 | 14741篇 |
1988年 | 13701篇 |
1987年 | 13152篇 |
1986年 | 11802篇 |
1985年 | 12177篇 |
1984年 | 9927篇 |
1983年 | 8638篇 |
1982年 | 6498篇 |
1981年 | 5854篇 |
1980年 | 5501篇 |
1979年 | 9625篇 |
1978年 | 7324篇 |
1977年 | 6748篇 |
1976年 | 6450篇 |
1975年 | 7166篇 |
1974年 | 7705篇 |
1973年 | 7782篇 |
1972年 | 7008篇 |
1971年 | 6521篇 |
1970年 | 5651篇 |
1969年 | 5385篇 |
1968年 | 4958篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
S. Dubrou J. Konjek E. Macheras B. Welté L. Guidicelli E. Chignon M. Joyeux J. L. Gaillard B. Heym T. Tully G. Sapriel 《Applied and environmental microbiology》2013,79(18):5498-5508
Nonpigmented and late-pigmenting rapidly growing mycobacteria (RGM) have been reported to commonly colonize water production and distribution systems. However, there is little information about the nature and distribution of RGM species within the different parts of such complex networks or about their clustering into specific RGM species communities. We conducted a large-scale survey between 2007 and 2009 in the Parisian urban tap water production and distribution system. We analyzed 1,418 water samples from 36 sites, covering all production units, water storage tanks, and distribution units; RGM isolates were identified by using rpoB gene sequencing. We detected 18 RGM species and putative new species, with most isolates being Mycobacterium chelonae and Mycobacterium llatzerense. Using hierarchical clustering and principal-component analysis, we found that RGM were organized into various communities correlating with water origin (groundwater or surface water) and location within the distribution network. Water treatment plants were more specifically associated with species of the Mycobacterium septicum group. On average, M. chelonae dominated network sites fed by surface water, and M. llatzerense dominated those fed by groundwater. Overall, the M. chelonae prevalence index increased along the distribution network and was associated with a correlative decrease in the prevalence index of M. llatzerense, suggesting competitive or niche exclusion between these two dominant species. Our data describe the great diversity and complexity of RGM species living in the interconnected environments that constitute the water production and distribution system of a large city and highlight the prevalence index of the potentially pathogenic species M. chelonae in the distribution network. 相似文献
152.
The fine structure of meiotic chromosome pairing in natural and artificial Lilium polyploids 总被引:1,自引:0,他引:1
P B Moens 《Journal of cell science》1970,7(1):55-63
153.
154.
155.
156.
157.
Six hundred foramina transversaria (FT) of the axis vertebrae of 4 population groups were examined for the presence of erosion of the lateral articular mass. Of these, 127 (21%) and 72 (12%) presented with moderate and marked erosion, respectively. Evidence is presented incriminating the tortuosity of the vertebral artery as well as congenital factors in the etiology of the erosion of the FT. Attention is drawn to the possible correlation between angulation of the transverse process of the axis and erosion of the FT. 相似文献
158.
Two internal herinias of the intestines were found in adult males. One was a large translucent avascular membranous sac contining the small intestine from the duodenojejunal flexure to a point 6 in. proximal to the ileocaecal junction. The other was a peritoneal sac enclosing the small intestine, appendix, caecum and 6 in. of the ascending colon. The mesenteric and colic vessels were normal. Both hernias conformed to PAPEZ's concept of the so-called paraduodenal hernia that the hernial sac is derived from the umbilical coelom. The authors suggest that most of the so-called paraduodenal hernias are derived from the embryonic umbilical peritoneal diverticulum rather than from the peritoneal recesses or mesentery of the colon. 相似文献
159.
The microvasculature of the skin of the hand of Japanese monkeys was examined by means of scanning electron microscopy of corrosion casts. The vasculature of all areas of the skin of the hand was examined and divided into three structures excluding the nail bed: (1) In the ball of the finger, the typical structure of the capillary loops was studied. Capillary loops were formed out of not just one capillary vessel, but two or three vessels. Each capillary vessel arose and divided into several branches at the papilla, and they became descending limbs. After the loop passed a hairpin turn, the descending limbs were 1.5 times larger than the ascending limbs in the intrapapillary portion, and they became extrapapillary venules. The descending limbs connected with the postcapillary venules in the postpapillary portion and with the horizontal network. The postcapillary venules fused with each other (1-5 loops) to form the primary and secondary venous arcades. (2) In the thenar eminence, the capillary loops were a little lower, and their grooves were wider than in the ball of the finger. The characteristic structure in this area was the interpapillar capillary network. (3) In the lateral side of the finger, the number of capillary loops formed by the arterial capillary network of the subepidermal layer was smaller. The capillary loops here had the lowest height and a simple structure. 相似文献
160.