全文获取类型
收费全文 | 2351篇 |
免费 | 114篇 |
国内免费 | 4篇 |
出版年
2023年 | 22篇 |
2022年 | 19篇 |
2021年 | 74篇 |
2020年 | 46篇 |
2019年 | 52篇 |
2018年 | 86篇 |
2017年 | 58篇 |
2016年 | 69篇 |
2015年 | 102篇 |
2014年 | 131篇 |
2013年 | 182篇 |
2012年 | 178篇 |
2011年 | 164篇 |
2010年 | 108篇 |
2009年 | 105篇 |
2008年 | 104篇 |
2007年 | 91篇 |
2006年 | 91篇 |
2005年 | 74篇 |
2004年 | 63篇 |
2003年 | 63篇 |
2002年 | 68篇 |
2001年 | 49篇 |
2000年 | 43篇 |
1999年 | 36篇 |
1998年 | 13篇 |
1997年 | 7篇 |
1996年 | 15篇 |
1995年 | 9篇 |
1994年 | 12篇 |
1993年 | 6篇 |
1992年 | 21篇 |
1991年 | 22篇 |
1990年 | 16篇 |
1989年 | 27篇 |
1988年 | 24篇 |
1987年 | 23篇 |
1986年 | 17篇 |
1985年 | 18篇 |
1984年 | 21篇 |
1983年 | 7篇 |
1982年 | 15篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1979年 | 19篇 |
1978年 | 12篇 |
1977年 | 13篇 |
1976年 | 9篇 |
1975年 | 7篇 |
1970年 | 5篇 |
排序方式: 共有2469条查询结果,搜索用时 16 毫秒
41.
The effect of population size, redox potential, exogenous ATP and complexing agents on Cu uptake by free and immobilized cyanobacteriumNostoc calcicola
Bréb. has been studied. Cu uptake was regulated by the population size. In such comparisons, the immobilized cells had a greater
longevity. Low pH conditions enhanced Cu uptake. Exogenous ATP (10 μmol/L) supplied to dark-grown free and immobilized cells
did not support Cu uptake to the extent of light-grown cells. Experiments involving natural as well as synthetic complexing
agents clearly established the superiority of soil extract and spent medium over EDTA (10 μmol/L), in sequestering Cu in free
as well as immobilized cells. 相似文献
42.
F M Salzano F L Black S M Callegari-Jacques S E Santos T A Weimer M A Mestriner R R Kubo J P Pandey M H Hutz 《American journal of physical anthropology》1991,85(1):51-60
Data on 31 genetic systems were obtained for 421 individuals belonging to the Arara, Araweté, Mundurucu, and Jamamadi tribes of northern Brazil. The Jamamadi depart farthest, and the Mundurucu least, from South American Indian averages. These data are analyzed together with those of 24 other Amazonian groups. Genetic distances and corresponding dendrograms indicate a cluster of 14 related tribes living north of the Amazon river. These genetic results show only a modest correlation with linguistic and geographic relationships among these groups. 相似文献
43.
The pattern of arterial supply to the various parts (clavicular, sternocostal and aponeurotic) of the pectoralis major muscle was studied in 7 cadaver dissections and 10 angiograms by injecting a radio-opaque substance. Three main arteries supplied the muscle, i.e. the pectoral branch of the thoracoacromial trunk (TAT-PB), the lateral thoracic artery and the perorating branch of the internal thoracic artery, supported by other branches of the TAT and the superior thoracic artery. It is observed that the TAT-PB, a chief vascular pedicle, anastomoses freely with other arteries and supplies most parts of the muscle. The present study is mainly focussed on the exclusion of the chief vascular pedicle of muscle to eliminate the confusion of previous studies and prevent the unnecessary hindrance and complications of the muscle flap. 相似文献
44.
Using agar gel électrophoresis, the number and relative mobility of seric protein fractions has been determined for twelve species of fishes belonging to the Elasmobranchii, Dipnoi and Actinopterygii.The study of relative mobilities has shown both similitudes and divergences between some of the proteinograms. Immunoelectrophoretic cross tests using the twelve sera and five antisera have shown that these similitudes did not result from protein homology and thus agar gel electrophoresis could not be used to determine phylogenetic relationships between the species considered.
Laboratoire d'Hydrobiologie et de Pisci culture, Université de Kinshasa (Zaïre) 相似文献
45.
A new alkaloid, 3-methoxy-4,6-dihydroxymorphinandien-7-one, and norsinoacutine have been isolated from extracts of Croton bonplandianum. 相似文献
46.
47.
48.
A strain of Fusarium solani (Mart.) Sacc. (IMI-216517), isolated from a patient of mycotic keratitis, produced experimental keratomycosis in albino rabbit cornea and survived in internal tissues of albino mice for varying periods. Alantolactone, isolated from the plant — Inula racemosa Hook. f. exhibited marked in vitro fungistatic activity against this strain of F. solani at 100–200 g/ml concentrations. The strain was less sensitive to amphotericin B and showed more acid than alkaline proteinase and phosphatase activities.Communication No. 2526. 相似文献
49.
50.
K B Lee G N La Mar R K Pandey I N Rezzano K E Mansfield K M Smith 《Biochemistry》1991,30(7):1878-1887
1H nuclear magnetic resonance spectroscopy was used to assign the hyperfine-shifted resonances and determine the position of a side chain in the heme cavity of wild-type rat apocytochrome b5 reconstituted with a series of synthetic hemins possessing systematically perturbed carboxylate side chains. The hemins included protohemin derivatives with individually removed or pairwise shortened and lengthened carboxylate side chains, as well as (propionate)n(methyl)8-nporphine-iron(III) isomers with n = 1-3 designed to force occupation of nonnative propionate sites. The resonance assignments were effected on the basis of available empirical heme contact shift correlations and steady-state nuclear Overhauser effect measurements in the low-spin oxidized proteins. The failure to detect holoproteins with certain hemins dictates that the stable holoproteins, unlike the case of myoglobin, demand the axial iron-His bonds and cannot accommodate carboxylate side chains at interior positions in the binding pocket. Hence, the heme pocket interior in cytochrome b5 is judged much less polar and less sterically accommodating than that of myoglobin. The propionate occupational preference was greatest as the native 7-propionate site, but also possible at the nonnative crystallographic 5-methyl or 8-methyl positions. Only for a propionate at the crystallographic 8-methyl position was a significant perturbation of the native molecular/electronic structure observed, and this was attributed to an alternative propionate-protein hydrogen bond at the crystallographic 8-methyl position. The structures of the transient protein complexes detected only shortly after reconstitution reveal that the initial encounter complexes during assembly of holoprotein from apoprotein and hemin involve one of the two alternate propionate-protein links at either the 7-propionate or native 8-methyl position. In a monopropionate hemin, this leads to the characterization of a new type of heme orientational disorder involving rotation about a N-Fe-N axis. 相似文献