全文获取类型
收费全文 | 432篇 |
免费 | 6篇 |
国内免费 | 1篇 |
专业分类
系统科学 | 7篇 |
教育与普及 | 3篇 |
现状及发展 | 93篇 |
研究方法 | 29篇 |
综合类 | 283篇 |
自然研究 | 24篇 |
出版年
2019年 | 5篇 |
2018年 | 3篇 |
2016年 | 2篇 |
2015年 | 3篇 |
2014年 | 3篇 |
2013年 | 6篇 |
2012年 | 9篇 |
2011年 | 31篇 |
2010年 | 4篇 |
2008年 | 11篇 |
2007年 | 11篇 |
2006年 | 15篇 |
2005年 | 24篇 |
2004年 | 8篇 |
2003年 | 10篇 |
2002年 | 17篇 |
2001年 | 9篇 |
2000年 | 14篇 |
1999年 | 12篇 |
1997年 | 3篇 |
1995年 | 2篇 |
1992年 | 13篇 |
1991年 | 10篇 |
1990年 | 3篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1979年 | 13篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 10篇 |
1975年 | 10篇 |
1974年 | 13篇 |
1973年 | 11篇 |
1972年 | 9篇 |
1971年 | 9篇 |
1970年 | 12篇 |
1969年 | 8篇 |
1968年 | 7篇 |
1967年 | 11篇 |
1966年 | 13篇 |
1965年 | 4篇 |
1960年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有439条查询结果,搜索用时 15 毫秒
51.
We compared a simple complement-dependent lymphocytotoxicity test with a widely used indirect immunofluorescence procedure to enumerate total T, T helper, and T suppressor lymphocytes in normal blood samples. Results with the two techniques were closely similar. 相似文献
52.
53.
The chromosomes of four species of Falconiformes 总被引:4,自引:0,他引:4
Summary Leucocyte cultures were used in four species of Falconiformes for the purpose of karyotypic sex determination and the establishment of a breeding pair. The Andean condor has 80 Guiana eagle 54, Crane hawk 66, and Turkey vulture 76 chromosomes with readily distinguished ZW elements in the female.Our cordial thanks are extended toA. Risser, Ph. D. Assistant Curator of Birds, San Diego Zoo;Warren Thomas, D.V.M., Director, Los Angeles Zoo for their cooperation and assistance in the collection of blood samples for chromosome study. We are also grateful toK. Benirschke, M.D., Director of Research, San Diego Zoo for his kind assistance. 相似文献
54.
W N Kuo J L Williams T Floyd-Jones C F Duggans D L Boone S O Smith R F Copeland 《Experientia》1979,35(8):997-998
Decreased activities of both the inhibitory modulator of adenosine 3':5'-monophosphate (cAMP)-dependent protein kinase (A-PK) as well as the stimulatory modulator of guanosine 3':5'-monophosphate (cGMP)-dependent protein kinase (G-PK) from the mouse cerebellum were noted due to the administration of excessive doses of ethanol, caffeine, and phenobarbital for up to 28 days. The dose-dependent of the inhibition of A-PK or the stimulation of G-PK was observed as a function of the amount of protein kinase modulators in the cerebellum of mice receiving different doses of ethanol. 相似文献
55.
56.
Rifampicin inhibits the growth of some mammalian viruses 总被引:29,自引:0,他引:29
57.
D. W. Cushman J. Pluščec N. J. Williams E. R. Weaver E. F. Sabo O. Kocy H. S. Cheung M. A. Ondetti 《Cellular and molecular life sciences : CMLS》1973,29(8):1032-1035
Zusammenfassung Nachweis mit Analogen der im Gifte vonBothrops jararaca gefundenen Peptide, dass die Inhihibition des Angiotensins «converting enzyme» von zwei eindeutigen Teilsequenzen dieser Peptide abhängig ist. Die hohe spezifische kompetitive Inhibition, hervorgerufen durch die Peptide vonBothrops jararaca, wird der Bindung ihrer Tripeptidreste vom Carboxyterminus mit dem aktiven Zentrum des Enzyms zugeschrieben, die in gleicher Weise wie die Peptidsubstrate mit dem Enzym gebunden werden. Die Wirksamkeit der Giftpeptide hängt von der Bindung eines zweiten Teiles der Peptide mit dem Enzym ab. 相似文献
58.
Williams TN Mwangi TW Wambua S Peto TE Weatherall DJ Gupta S Recker M Penman BS Uyoga S Macharia A Mwacharo JK Snow RW Marsh K 《Nature genetics》2005,37(11):1253-1257
The hemoglobinopathies, disorders of hemoglobin structure and production, protect against death from malaria. In sub-Saharan Africa, two such conditions occur at particularly high frequencies: presence of the structural variant hemoglobin S and alpha(+)-thalassemia, a condition characterized by reduced production of the normal alpha-globin component of hemoglobin. Individually, each is protective against severe Plasmodium falciparum malaria, but little is known about their malaria-protective effects when inherited in combination. We investigated this question by studying a population on the coast of Kenya and found that the protection afforded by each condition inherited alone was lost when the two conditions were inherited together, to such a degree that the incidence of both uncomplicated and severe P. falciparum malaria was close to baseline in children heterozygous with respect to the mutation underlying the hemoglobin S variant and homozygous with respect to the mutation underlying alpha(+)-thalassemia. Negative epistasis could explain the failure of alpha(+)-thalassemia to reach fixation in any population in sub-Saharan Africa. 相似文献
59.
60.
Block BA Teo SL Walli A Boustany A Stokesbury MJ Farwell CJ Weng KC Dewar H Williams TD 《Nature》2005,434(7037):1121-1127
Electronic tags that archive or transmit stored data to satellites have advanced the mapping of habitats used by highly migratory fish in pelagic ecosystems. Here we report on the electronic tagging of 772 Atlantic bluefin tuna in the western Atlantic Ocean in an effort to identify population structure. Reporting electronic tags provided accurate location data that show the extensive migrations of individual fish (n = 330). Geoposition data delineate two populations, one using spawning grounds in the Gulf of Mexico and another from the Mediterranean Sea. Transatlantic movements of western-tagged bluefin tuna reveal site fidelity to known spawning areas in the Mediterranean Sea. Bluefin tuna that occupy western spawning grounds move to central and eastern Atlantic foraging grounds. Our results are consistent with two populations of bluefin tuna with distinct spawning areas that overlap on North Atlantic foraging grounds. Electronic tagging locations, when combined with US pelagic longline observer and logbook catch data, identify hot spots for spawning bluefin tuna in the northern slope waters of the Gulf of Mexico. Restrictions on the time and area where longlining occurs would reduce incidental catch mortalities on western spawning grounds. 相似文献