全文获取类型
收费全文 | 31321篇 |
免费 | 136篇 |
国内免费 | 264篇 |
专业分类
系统科学 | 453篇 |
丛书文集 | 477篇 |
教育与普及 | 96篇 |
理论与方法论 | 113篇 |
现状及发展 | 11214篇 |
研究方法 | 1249篇 |
综合类 | 17330篇 |
自然研究 | 789篇 |
出版年
2014年 | 165篇 |
2013年 | 448篇 |
2012年 | 651篇 |
2011年 | 1447篇 |
2010年 | 445篇 |
2009年 | 380篇 |
2008年 | 724篇 |
2007年 | 863篇 |
2006年 | 869篇 |
2005年 | 787篇 |
2004年 | 629篇 |
2003年 | 548篇 |
2002年 | 553篇 |
2001年 | 1030篇 |
2000年 | 1057篇 |
1999年 | 658篇 |
1992年 | 539篇 |
1991年 | 455篇 |
1990年 | 475篇 |
1989年 | 472篇 |
1988年 | 447篇 |
1987年 | 430篇 |
1986年 | 433篇 |
1985年 | 505篇 |
1984年 | 442篇 |
1983年 | 366篇 |
1982年 | 337篇 |
1981年 | 319篇 |
1980年 | 368篇 |
1979年 | 876篇 |
1978年 | 680篇 |
1977年 | 687篇 |
1976年 | 524篇 |
1975年 | 605篇 |
1974年 | 850篇 |
1973年 | 700篇 |
1972年 | 694篇 |
1971年 | 859篇 |
1970年 | 1012篇 |
1969年 | 792篇 |
1968年 | 793篇 |
1967年 | 781篇 |
1966年 | 729篇 |
1965年 | 519篇 |
1959年 | 266篇 |
1958年 | 434篇 |
1957年 | 327篇 |
1956年 | 241篇 |
1955年 | 250篇 |
1954年 | 232篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
64.
1 Results The photosynthetic bacterial reaction center (RC) is a membrane protein complex.The RC is composed of three protein subunits and redox components such as bacteriochlorophylls, bacteriopheophytins,and quinones.The RC performs the photochemical electron transfer from the bacteriochlorophyll dimer through a series of electron donor and acceptor molecules to a secondary quinone,QB.QB accepts electrons from a primary quinone,QA,in two sequential electron transfer reactions.The second electron trans... 相似文献
65.
66.
67.
68.
69.
70.
Acquired immunity and epidemiology of Schistosoma haematobium 总被引:1,自引:0,他引:1
Human immune responses to schistosome infection have been characterized in detail. But there has been controversy over the relative importance of ecological factors (variation in exposure to infection) and immunological factors (acquired immunity) in determining the relationships between levels of infection and age typically found in areas where infection is endemic. Independent effects of exposure and age on the rates of reinfection with Schistosoma haematobium after chemotherapy have been demonstrated in the Gambia and Zimbabwe. This age effect could be the result of acquired immunity to infection. Indeed, allowing for variation in exposure and age, low rates of reinfection in the Gambia are correlated with high amounts of specific IgE antibodies--human IgE can kill S. mansoni schistosomulae in vitro. Further, animals can acquire immunologically mediated resistance to S. mansoni infection, although nonimmunological factors could also be involved. Acquisition of this immunity seems to be related to the cumulative effects of repeated infection and provides only partial protection. These characteristics are consistent with immuno-epidemiological data for both S. mansoni and S. haematobium infections of humans. We have now analysed age-prevalence data for human infection with S. haematobium, and find patterns of variation that are indeed consistent with the epidemiological effects of acquired immunity predicted by mathematical models. 相似文献