全文获取类型
收费全文 | 464篇 |
免费 | 10篇 |
国内免费 | 12篇 |
专业分类
486篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 3篇 |
2020年 | 5篇 |
2019年 | 12篇 |
2018年 | 4篇 |
2017年 | 8篇 |
2016年 | 7篇 |
2015年 | 8篇 |
2014年 | 19篇 |
2013年 | 29篇 |
2012年 | 7篇 |
2011年 | 8篇 |
2010年 | 5篇 |
2009年 | 12篇 |
2008年 | 21篇 |
2007年 | 19篇 |
2006年 | 22篇 |
2005年 | 16篇 |
2004年 | 14篇 |
2003年 | 12篇 |
2002年 | 16篇 |
2001年 | 14篇 |
2000年 | 15篇 |
1999年 | 8篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1993年 | 16篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 11篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1984年 | 15篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 12篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有486条查询结果,搜索用时 15 毫秒
41.
MARIÁN PERNÝ VLADISLAV KOLARIK L'UBO MAJESKÝ PAVOL MÁRTONFI 《Botanical journal of the Linnean Society. Linnean Society of London》2008,157(3):475-485
Cytogeographical variability within the Phleum pratense group in the Carpathians and adjacent part of Pannonian lowland, based on 132 populations analysed by flow cytometry, is described. Only diploid and hexaploid plants were detected among 635 samples from the studied area. Diploids were found to be less frequent (127 plants, 20%) than hexaploids (508, 80%). With the exception of the single pure diploid population, diploids always co-occured with hexaploids (30 localities, 22.7%). The majority of populations (101, 76.5%) consisted of hexaploid plants. Most mixed populations occur in the Western Carpathians (26). In the Eastern Carpathians, mixed populations are much rarer, with three populations in Ukraine and one in Romania. In the Southern Carpathians, only hexaploids occur. The conventional taxonomic concept of the two species, diploid P. bertolonii and hexaploid P. pratense , was followed in spite of their sympatric occurence. Distribution maps based on chromosome number data from previous studies and on ploidy level estimates are given for both species in the studied area. The pattern of different distribution of the two taxa within the Carpathians is discussed. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 475–485. 相似文献
42.
The effects of urea and glycine-betaine (GB) osmolytes on the hydrophobic interactions of neopentane in water have been studied using molecular dynamics simulations. From the study of the potentials of mean force, it is observed that both urea and GB decrease the association and solvation of neopentane. The calculated equilibrium constants show that urea and GB decrease the population of solvent-separated minima of neopentane. The hydrophobic association as well as solvation of neopentane molecules are stabilised by entropy and enthalpy in the mixtures. The radial distribution functions (RDFs) and running coordination numbers of water, urea and GB molecules show that neopentane shows salting-in behaviour in aqueous-GB, aqueous-urea and aqueous-urea-GB mixtures. Neopentane is preferentially solvated by GB in aqueous-GB and preferentially solvated by urea in aqueous-urea-GB solutions. The preferential solvation of neopentane by GB suggests that GB decreases the interaction between neopentane molecules i.e. salting-in of neopentane. The calculated solvation free energies and radial density profiles of neopentane also support the salting-in behaviour of neopentane in the mixtures of these osmolytes. 相似文献
43.
44.
45.
In a review of chromosome numbers in the genus Potamogeton, we highlight numerous errors that have crept into the literature. These have resulted chiefly from reliance on abstracts in chromosome number indices and compilations, rather than on the original publications, but partly also because of misleading summaries even in the primary literature. We present a list of counts that we believe are original and genuine, and a list of those that were never made but which nevertheless appear in the literature. Scrutiny of the list of accepted counts indicates that aneuploidy is widespread in the genus and that transition between the two common chromosome numbers (2n=26 and 2n=28) has occurred several times. Currently available data are insufficient to resolve the question of the ancestral base number. We also present details of the first chromosome counts from English populations of five taxa: P. polygonifolius Pourr. (2n=28), P. pectinatus L. (2n=ca. 78), P. perfoliatus L. (2n=ca. 52), P.×nitens Weber (P. gramineus×P. perfoliatus) (2n=ca. 52) and P.×salicifolius Wolfg. (P. lucens×P. perfoliatus) (2n=ca. 52). 相似文献
46.
Monica Boşcaiu Oscar Vicente Friedrich Ehrendorfer 《Plant Systematics and Evolution》1999,218(1-2):13-21
Somatic chromosome numbers have been determined for the followingCerastium taxa:C. eriophorum (2n = 36),C. alpinum (2n = 72),C. transsylvanicum (2n = 108),C. arcticum (2n = 108),C. latifolium (2n = 36),C. carinthiacum (2n = 36),C. banaticum (2n = 36),C. arvense subsp.glandulosum (2n = 36),C. arvense subsp.arvense (2n = 72) andC. fontanum (2n = 144). Karyotypes of three diploid species (C. eriophorum, C. banaticum andC. latifolium), belonging to three different taxonomic groups, were analysed and found to be similar. The relative nuclear DNA contents of all taxa were determined by flow cytometry and, for five species, also by Feulgen cytophotometry. The values obtained by the two methods are similar. A comparison of nuclear DNA contents among diploids shows that values differ significantly between different taxonomic groups, and are correlated with average chromosome size. Within closely related polyploid groups nuclear DNA amounts increase from 2x- to 4x- and 6x taxa as 1 : 1.4 : 2.4 in theC. alpinum complex, whereas DNA amounts are doubled comparing 2x- and 4x-subspecies in theC. arvense complex. 相似文献
47.
48.
49.
KATSUYUKI SATO 《The Journal of eukaryotic microbiology》1989,36(1):35-38
Two new phenomena were observed during macronuclear development in E. patella. During the formation of giant chromosomes, the number of chromosomes decreased while individual chromosomes gradually became longer and thicker. Immediately before macronuclear elongation, ring-like anlagen appeared, which did not contain chromatin at their centers. The course of macronuclear development in Euplotes is reconsidered in light of these findings. 相似文献
50.
Infections with the nematode Trichinella spiralis induce unresponsiveness in mice. A study was made to determine whether suppression could be due to a deficiency in the cells responsible for the immunological response. Mice were given low or moderate infections and were killed 7, 14, 28, or 56 days after inoculation; spleen macrophages and leucocytes, θ cells, and Con A- and LPS-sensitive cells were determined in the thymus, spleen, and the mesenteric and axillary lymph nodes. Spleen macrophages are diminished throughout the course of the infection, reaching significantly low levels on the 14th day. The thymus loses, whereas the spleen and the axillary node gain, cells bearing the θ antigen. In spite of the increase in leucocytes and θ cells in the secondary lymphoid tissue, the cells of these organs are insensitive to the blastogenic action of Con A in the heavier infections. In lower infections, however, spleen cells show an enhanced response to Con A and LPS; mesenteric cells, on the other hand, show an early enhanced susceptibility to LPS and a reduced susceptibility to Con A and, in the later phases of parasitism, an enhanced Con A and a reduced LPS susceptibility. It is suggested that these phenomena contribute to the immunosuppression phenomena which are characteristic of T. spiralis infections. 相似文献