全文获取类型
收费全文 | 670701篇 |
免费 | 58082篇 |
国内免费 | 1096篇 |
专业分类
729879篇 |
出版年
2018年 | 16865篇 |
2017年 | 15621篇 |
2016年 | 14493篇 |
2015年 | 9389篇 |
2014年 | 11085篇 |
2013年 | 16197篇 |
2012年 | 22046篇 |
2011年 | 30697篇 |
2010年 | 23973篇 |
2009年 | 19160篇 |
2008年 | 25897篇 |
2007年 | 27766篇 |
2006年 | 16861篇 |
2005年 | 16183篇 |
2004年 | 16540篇 |
2003年 | 16062篇 |
2002年 | 15536篇 |
2001年 | 26021篇 |
2000年 | 25882篇 |
1999年 | 20655篇 |
1998年 | 7067篇 |
1997年 | 7263篇 |
1996年 | 6931篇 |
1995年 | 6291篇 |
1994年 | 6366篇 |
1993年 | 6209篇 |
1992年 | 17091篇 |
1991年 | 16766篇 |
1990年 | 16595篇 |
1989年 | 16594篇 |
1988年 | 15218篇 |
1987年 | 14419篇 |
1986年 | 13319篇 |
1985年 | 13553篇 |
1984年 | 10969篇 |
1983年 | 9387篇 |
1982年 | 6911篇 |
1981年 | 6076篇 |
1980年 | 5904篇 |
1979年 | 10317篇 |
1978年 | 8016篇 |
1977年 | 7237篇 |
1976年 | 7016篇 |
1975年 | 7837篇 |
1974年 | 8352篇 |
1973年 | 8248篇 |
1972年 | 7686篇 |
1971年 | 6940篇 |
1970年 | 5872篇 |
1969年 | 5558篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
V V Sviridov E V Kozhevnikova 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1985,(9):67-70
The immunization of mice with the protein fraction of B. pertussis strain 305 has made it possible to obtain hybridomas producing monoclonal antibodies to B. pertussis antigens. Ascitic fluids containing monoclonal antibodies react in the ELISA in high titers and actively agglutinate B. pertussis strains 305 and 475. 相似文献
32.
U Mura A M Osman A S Mohamed D Di Martino P L Ipata 《Comparative biochemistry and physiology. B, Comparative biochemistry》1987,87(1):157-160
The preservation of purine ring as purine bases appears to be a common feature of camel liver. Hepatic guanine appears to be actively converted into GMP in the camel rather than further degraded. The limiting step of guanine degradation appears to be the lack of hepatic guanase activity. Higher purine bases over uric acid ratios were found in camel urine with respect to those of zebu. 相似文献
33.
Purification of smooth-muscle myosin free of calmodulin and myosin light-chain kinase. Susceptibility to oxidation. 下载免费PDF全文
Smooth-muscle myosin purified as described by Persechini & Hartshorne [(1983) Biochemistry 22, 470-476] contains trace amounts of calmodulin and myosin light-chain kinase, which can be removed by Ca2+-dependent hydrophobic-interaction chromatography followed by calmodulin-Sepharose affinity chromatography. The resultant column-purified myosin exhibits properties similar to those of the non-purified myosin, e.g. actin activation of the Mg2+-ATPase requires Ca2+/calmodulin-dependent phosphorylation of the two 20 kDa light chains. However, unlike the non-purified myosin, the column-purified myosin undergoes a time-dependent transition to a form which no longer requires phosphorylation for actin activation of the myosin Mg2+-ATPase. This transition is identified as a time-dependent change in conformation of the column-purified myosin from a 10 S to 6 S form and is caused by slow oxidation of the column-purified myosin, since it could be prevented by storage under N2 and reversed by 5 mM-dithiothreitol. 相似文献
34.
35.
Abstract. Nutrient conservation in vegetation affects rates of litter decomposition and soil nutrient availability. Although resorption has been traditionally considered one of the most important plant strategies to conserve nutrients in temperate forests, long leaf life‐span and low nutrient requirements have been postulated as better indicators. We aimed at identifying nutrient conservation strategies within characteristic functional groups of NW Patagonian forests on Andisols. We analysed C‐, N‐, P‐, K‐ and lignin‐concentrations in mature and senescent leaves of ten native woody species within the functional groups: broad‐leaved deciduous species, broad‐leaved evergreens and conifers. We also examined mycorrhizal associations in all species. Nutrient concentration in mature leaves and N‐ resorption were higher in broad‐leaved deciduous species than in the other two functional groups. Conifers had low mature leaf nutrient concentrations, low N‐resorption and high lignin/N ratios in senescent leaves. P‐ and K‐resorptions did not differ among functional groups. Broad‐leaved evergreens exhibited a species‐dependent response. Nitrogen in mature leaves was positively correlated with both N resorption and soil N‐fertility. Despite the high P‐retention capacity of Andisols, N appeared to be the more limiting nutrient, with most species being proficient in resorbing N but not P. The presence of endomycorrhizae in all conifers and the broad‐leaved evergreen Maytenus boaria, ectomycorrhizae in all Nothofagus species (four deciduous, one evergreen), and cluster roots in the broad‐leaved evergreen Lomatia hirsuta, would be possibly explaining why P is less limiting than N in these forests. 相似文献
36.
A A Sukhopiatkina O S Bat A V Levitskaia V G Potapova 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1985,(4):80-81
The study of the specific epidemiological and clinical features of Q fever revealed the existence of an active focus of infection among humans due to their contacts with agricultural animals in one of the districts of the region. The focus was manifested by group morbidity among the cattle-tending personnel of a dairy farm. The source of this infection was cattle. The infection was transferred mainly through the air. The disease took a moderately severe course. The study of the rickettsial contamination of humans, animals and ticks suggested the presence of the active epidemic process and made it possible to work out concrete antiepidemic measures. 相似文献
37.
38.
39.
40.
F F Dias M K Shaikh Y B Bhatt D C Modi V R Subramanyam 《The Journal of applied bacteriology》1986,60(4):271-275
Mutants of Bacillus amyloliquefaciens resistant to at least 10 micrograms/ml of tunicamycin were isolated and shown to be pleiotropic. The mutants were more resistant to streptomycin, chloramphenicol, kanamycin and neomycin than was the parent strain but less resistant to penicillin G and tetracycline. They were more autolytic, presumably due to an altered cell wall. The mutants produced reduced levels of amylase, penicillinase and both metal and serine protease besides having an enhanced sporulation frequency and being more motile. 相似文献