全文获取类型
收费全文 | 393148篇 |
免费 | 41562篇 |
国内免费 | 143篇 |
出版年
2018年 | 4769篇 |
2017年 | 4424篇 |
2016年 | 6163篇 |
2015年 | 8278篇 |
2014年 | 9259篇 |
2013年 | 13017篇 |
2012年 | 14616篇 |
2011年 | 14194篇 |
2010年 | 9538篇 |
2009年 | 8109篇 |
2008年 | 12112篇 |
2007年 | 12344篇 |
2006年 | 11720篇 |
2005年 | 10873篇 |
2004年 | 10939篇 |
2003年 | 10402篇 |
2002年 | 10068篇 |
2001年 | 16056篇 |
2000年 | 15978篇 |
1999年 | 12744篇 |
1998年 | 4614篇 |
1997年 | 4569篇 |
1996年 | 4400篇 |
1995年 | 4212篇 |
1994年 | 4201篇 |
1993年 | 4036篇 |
1992年 | 10628篇 |
1991年 | 10132篇 |
1990年 | 9934篇 |
1989年 | 9744篇 |
1988年 | 9015篇 |
1987年 | 8664篇 |
1986年 | 7817篇 |
1985年 | 7982篇 |
1984年 | 6614篇 |
1983年 | 5785篇 |
1982年 | 4577篇 |
1981年 | 4067篇 |
1980年 | 3875篇 |
1979年 | 6689篇 |
1978年 | 4982篇 |
1977年 | 4710篇 |
1976年 | 4368篇 |
1975年 | 4828篇 |
1974年 | 5231篇 |
1973年 | 5243篇 |
1972年 | 4842篇 |
1971年 | 4502篇 |
1970年 | 3920篇 |
1969年 | 3883篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
R. Borges-Argez L. Balnbury A. Flowers A. Gimnez-Turba G. Ruiz P.G. Waterman L.M. Pea-Rodríguez 《Phytomedicine》2007,14(7-8):530-533
A number of flavonoids isolated from Lonchocarpus spp. were evaluated for their antiprotozoal and cytotoxic activity. Flavone 6 and chalcone 7 were found to be the most active against Leishmania parasites and against cell cultures of Leukemia P388DI and adenocarcinoma prostate PC-3. 相似文献
122.
123.
Páraic ó Cuív Rajesh Gupta Hareshwar P. Goswami Mark Morrison 《Applied and environmental microbiology》2013,79(19):6173-6175
Clostridium thermocellum encodes a cellulosomal, modular, and thermostable serine protease inhibitor (serpin), PinA. PinA stability but not inhibitory activity is affected by the Fn(III) and Doc(I) domains, and PinA is a broad inhibitor of subtilisin-like proteases and may play a key role in protecting the cellulosome from protease attack. 相似文献
124.
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
125.
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
126.
127.
The relations between the saccus lacrimalis and different portions of the musculus orbicularis oculi were studied in orbital regions of human fetuses sectioned into numbered series. No insertions of the pars lacrimalis or Horner's muscle on the saccus were found. These muscular fibres pass along the dorsal wall of the saccus and are separated from it by the reflex tendon of the ligamentum palpebrale mediale. The only muscular fibres that insert on the saccus are those that approach the anterior face of the saccus and the fornix. The fibres that insert on the anterior face proceed from the deep bundles of the pars preseptalis of the lower eyelids, and those that insert on the fornix derive from the deep bundles of the pars preseptalis of the upper eyelid. 相似文献
128.
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
129.
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
130.