全文获取类型
收费全文 | 3864篇 |
免费 | 207篇 |
国内免费 | 273篇 |
出版年
2023年 | 38篇 |
2022年 | 48篇 |
2021年 | 126篇 |
2020年 | 84篇 |
2019年 | 85篇 |
2018年 | 93篇 |
2017年 | 78篇 |
2016年 | 69篇 |
2015年 | 104篇 |
2014年 | 195篇 |
2013年 | 262篇 |
2012年 | 183篇 |
2011年 | 149篇 |
2010年 | 122篇 |
2009年 | 159篇 |
2008年 | 157篇 |
2007年 | 161篇 |
2006年 | 190篇 |
2005年 | 159篇 |
2004年 | 159篇 |
2003年 | 167篇 |
2002年 | 167篇 |
2001年 | 160篇 |
2000年 | 152篇 |
1999年 | 103篇 |
1998年 | 110篇 |
1997年 | 86篇 |
1996年 | 94篇 |
1995年 | 74篇 |
1994年 | 66篇 |
1993年 | 60篇 |
1992年 | 58篇 |
1991年 | 38篇 |
1990年 | 46篇 |
1989年 | 41篇 |
1988年 | 40篇 |
1987年 | 48篇 |
1986年 | 21篇 |
1985年 | 23篇 |
1984年 | 34篇 |
1983年 | 11篇 |
1982年 | 17篇 |
1981年 | 20篇 |
1980年 | 17篇 |
1979年 | 21篇 |
1978年 | 17篇 |
1977年 | 9篇 |
1976年 | 7篇 |
1974年 | 4篇 |
1972年 | 3篇 |
排序方式: 共有4344条查询结果,搜索用时 15 毫秒
31.
Summary In order to obtain markers for the Y chromosome ofSilene latifolia, we pooled equal weights of leaf tissue from 18 female siblings into one sample and repeated the process with 18 male siblings. Pooling was intended to provide a common genetic background for each sample, leaving the absence or presence of the Y chromosome as the primary difference between the two samples. DNA was extracted from each sample and subjected to polymerase chain reaction (PCR) amplification with arbitrary 10 bp primers. Four of 60 primers used gave an amplification with the male DNA not found among those from the female DNA. Each of these was subsequently shown to provide a reliable marker for the Y chromosome. 相似文献
32.
栽培中华猕猴桃的染色体观察 总被引:5,自引:0,他引:5
对原产地位于赣鄂边界幕阜山地区的十二个大果型中华猕猴桃优株或株系的染色体数目观察表明,这些栽培类型全部为四倍体,2n=4x=116。讨论了染色体倍性与果实大小的关系及几种可能的育种方法。 相似文献
33.
CAT SHUTAO CONGMEI ZENG JINGYAN LI ZHONGHE ZHAI Department of Biology Beijing University Beijing China. Kunming Institute of Zoology Academia Sinica Kunming China. 《Cell research》1992,(2)
Dinoflagellate is one of the primitive eukaryotes,whosenucleus may represent one of the transition stages fromprokaryotic nucleoid to typical eukaryotic nucleus.Usingselective extraction together with embeddment-free sectionand whole mount electron microscopy,a delicate nuclearmatrix filament network was shown,for the first time,indinoflagellate Crypthecodinium cohnii nucleus.Chromosomeresidues are connected with nuclear matrix filaments to forma complete network spreading over the nucleus.Moreover,we demonstrated that the dinoflagellate chromosome retainsa protein scaffold after the depletion of DNA and solubleproteins.This scaffold preserves the characteristic mor-phology of the chromosome.Two dimensional elec-trophoreses indicated that the nuclear matrix and chromo- some scaffold are mainly composed of acidic proteins.Ourresults demonstrated that a framework similar to the nuclearmatrix and chromosome scaffold in mammalian cells appearsin this primitive eukaryote,suggesting that these structuresmay have been originated from the early stages of eukaryoteevolution. 相似文献
34.
Averell Gnatt Dalia Ginzberg Judy Lieman-Hurwitz Ronit Zamir Haim Zakut Hermona Soreq 《Cellular and molecular neurobiology》1991,11(1):91-104
1. Various hybridization approaches were employed to investigate structural and chromosomal interrelationships between the human cholinesterase genes CHE and ACHE encoding the polymorphic, closely related, and coordinately regulated enzymes having butyrylcholinesterase (BuChE) and acetylcholinesterase (AChE) activities. 2. Homologous cosmid recombination with a 190-base pair 5' fragment from BuChEcDNA resulted in the isolation of four overlapping cosmid clones, apparently derived from a single gene with several introns. The Cosmid CHEDNA included a 700-base pair fragment known to be expressed at the 3' end of BuChEcDNA from nervous system tumors and which has been mapped by in situ hybridization to the unique 3q26-ter position. In contrast, cosmid CHEDNA did not hybridize with full-length AChEcDNA, proving that the complete CHE gene does not include AChE-encoding sequences either in exons or in its introns. 3. The chromosomal origin of BuChE-encoding sequences was further examined by two unrelated gene mapping approaches. Filter hybridization with DNA from human/hamster hybrid cell lines revealed BuChEcDNA-hybridizing sequences only in cell lines including human chromosome 3. However, three BuChEcDNA-homologous sequences were observed at chromosomal positions 3q21, 3q26-ter, and 16q21 by a highly stringent in situ hybridization protocol, including washes at high temperature and low salt. 4. These findings stress the selectivity of cosmid recombination and chromosome blots, raise the possibility of individual differences in BuChEcDNA-hybridizing sequences, and present an example for a family highly similar proteins encoded by distinct, nonhomologous genes. 相似文献
35.
J. W. Kadereit 《Plant Systematics and Evolution》1991,175(1-2):93-99
The genomic evolution of triploid plants with regular bivalent formation is discussed. The conclusion is reached that although all the progeny of an originally triploid individual will be triploid numerically, only part of the progeny will be triploid genomically. The consequences of this for triploid identification by means of chromosome morphology and isozyme numbers is discussed. 相似文献
36.
Callus cultures were established from stem explants of Ruscus hypophyllum on a modified basal medium of Murashige and Skoog (1962) supplemented with 1 mg l-1 2,4-D+0.1 mg l-1 BAP. The optimal 2,4-D concentration for promoting shoot bud formation and growth was 0.05 mg l-1 along with 0.5 mg l-1 BAP. Sixty percent of rootless shoots produced flowers on the regenerating medium. Rooting was induced when shoots were transferred to half strength MS inorganic salts supplemented with 2 mg l-1 IBA. Eighty percent of plants transferred to soil have survived. 相似文献
37.
Guatteria, Guatteriopsis, Guatteriella andHeteropetalum share the same conspicuous pollen type which is new for theSpermatophyta. It is zonoaperturate with a folded aperture region and an extremely reduced exine. First chromosome counts and karyotype analyses forGuatteriopsis (4 species investigated) andGuatteriella (1 species) are identical with those ofGuatteria (19 species seen): 2n = 28. The genome is characterized by diploidization and partly telocentric chromosomes. Sequentially Giemsa C- and fluorochrome banded chromosomes and interphase nuclei are described. The cuticular folding pattern is distinct forHeteropetalum only. Growth forms and ecology are reported for many species. The evolutionary pattern of theGuatteria group is discussed and compared with other genera and families. 相似文献
38.
B. L. Turner 《Plant Systematics and Evolution》1985,150(3-4):237-262
Verbesina sect.Pseudomontanoa is revised. The last treatment of the group byRobinson & Greenman (1899) recognized 5 species; the present treatment recognizes 12 species, 3 of which (V. breedlovei, V. cronquistii andV. olsenii) are described as new. A key to species, phyletic diagram and distribution maps are provided. 相似文献
39.
40.