全文获取类型
收费全文 | 3816篇 |
免费 | 219篇 |
国内免费 | 270篇 |
出版年
2023年 | 38篇 |
2022年 | 39篇 |
2021年 | 119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 | 100篇 |
1998年 | 106篇 |
1997年 | 75篇 |
1996年 | 89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4305条查询结果,搜索用时 15 毫秒
51.
52.
随着人类基因组计划的迅猛发展,已有越来越多的 Y 染色体多态性遗传标记被发现,它们在探索人类起源、进化和迁移规律等方面,提供了非常有价值的遗传标记,同样在法医学中也有着广阔的应用前景.对 Y-DNA 的多态性及其相关应用的研究进展进行了综述. 相似文献
53.
54.
Y. Zhang S. G. Zhang L. W. Qi B. Liu J. M. Gao C. B. Chen X. L. Li W. Q. Song 《Plant Molecular Biology Reporter》2005,23(2):129-138
A method for single-chromosome microdissection and microcloning was established in forest plants using poplar (Populus tremula) as a model. By use of meristematic cell division in root tip and the wall degradation hypotonic method, well-spread poplar
metaphase chromosome spreads showing low contamination were quickly prepared and fitted for chromosome microdissection. An
individual chromosome 1 was microdissected from the metaphase spreads of poplar root-tip cells with a fine glass needle controlled
by a micromanipulator. The dissected chromosome was amplified in vitro by theSau3A linker adaptor-mediated PCR technique, by which 200- to 3000-bp smear DNA fragments were obtained. Southern hybridization
results showed that the PCR products from the single poplar chromosome were homogeneous with poplar genomic DNA, indicating
that DNA from the single chromosome has been successfully amplified. Next, the second-round PCR products from the single chromosome
1 were cloned into T-easy vectors to generate a DNA library of the chromosome 1. About 3×105 recombinant clones were obtained. Evaluation based on 160 randomly selected clones showed that the sizes of the cloned inserts
varied from 230–2200 bp, with an average of 800 bp. Therefore, this research suggests that microdissection and microcloning
of single small chromosomes in forest plants is feasible. 相似文献
55.
《植物学报(英文版)》2005,47(3)
A better understanding of the mechanisms of water uptake by plant roots should be vital for improving drought resistance and water use efficiency (WUE). In the present study, we have demonstrated correlations between root system hydraulic conductivity and root characteristics during evolution using six wheat evolution genotypes (solution culture) with different ploidy chromosome sets (Triticum boeoticum Bioss., T. monococcum L.: 2n = 2x = 14; T. dicoccides Koern., T. dicoccon (Schrank) Schuebl.: 2n = 4x = 28;T. vulgare Vill., T. aestivum L. cv. Xiaoyan No. 6: 2n = 6x = 42). The experimental results showed that significant correlations were found between root system hydraulic conductivity and root characteristics of the materials with the increase in ploidy chromosomes (2x→6x) during wheat evolution. Hydraulic conductivity of the wheat root system at the whole-plant level was increased with chromosome ploidy during evolution, which was positively correlated with hydraulic conductivity of single roots, whole plant biomass,root average diameter, and root growth (length, area), whereas the root/shoot ratio had an inverse correlation with the hydraulic conductivity of root system with increasing chromosome ploidy during wheat evolution. Therefore, it is concluded that that the water uptake ability of wheat roots was strengthened from wild to modern cultivated species during evolution, which will provide scientific evidence for genetic breeding to improve the WUE of wheat by genetic engineering. 相似文献
56.
Mapping of a Wheat Resistance Gene to Yellow Mosaic Disease by Amplified Fragment Length Polymorphism and Simple Sequence Repeat Markers 总被引:3,自引:0,他引:3
Wei-Hua LIU Huan NIE Zhen-Tian HE Xiu-Lan CHEN Yue-Peng HAN Jin-Rong WANG Xin LI Cheng-Gui HAN Jia-Lin YU 《植物学报(英文版)》2005,47(9):1133-1139
Wheat (Triticum aestivum L.) yellow mosaic virus (WYMV) is transmitted by a fungal vector through soil and causes serious wheat yield losses due to yellow mosaic disease, with yellow-streaked leaves and stunted plants. In the present study, the amplified fragment length polymorphisms (AFLP) and simple sequence repeat (SSR) were used to identify the molecular linkages with the resistance gene against WYMV. Bulked segregant analysis was performed with an F2 population derived from the cross of cultivar Ningmai 9 (resistant) × cultivar Yangmai 10 (susceptible). By screening among the resistant or susceptible parents, the F2 pools and the individuals in the F2 population with 64 combined selective AFLP primers (EcoRI/MseI) or 290 reported SSR primers, a polymorphic DNA segment (approximately 120 bp) was amplified using the primer pair E2/M5, and an SSR marker (approximately 180 bp) was located on wheat chromosome 2A using the primer Xgwm328. Analysis with MAPMAKER/Exp Version 3.0b (Whitehead institute for Biomedical Research, Cambridge, MA, USA) indicated that these two markers were dominantly associated with the resistance gene at distances of 5.4 cM or 17.6 cM, respectively. The resistance gene to WYMV derived from Ningmai 9, is temporarily named YmNM, and was mapped to wheat chromosome 2A. 相似文献
57.
Seven hundred and fourteen individuals of the Scilla sinensis (Louriro) Merrill complex were sampled from 21 populations at 19 localities in 10 provinces and two cities of China and investigated cytologically in order to test its cytotype composition and cytogeographical variation still further. Five cytotypes were found (I.e. AA (2n = 16), BB (2n = 18), AABB (2n = 34), AAA (2n = 24), and AABB 9 (2n = 43)). Until now, nine of the 12 cytotypes have been identified on the continent, which indicates that it is an important place for the cytotypic differentiation of the complex. The cytotype AABB 9 is a new record on the continent. AAA was recorded for the second time in this complex. The majority of populations are composed of only one cytotype (AA, BB, or AABB), whereas another four populations consist of more than two cytotypes involving AA, BB, AAA, AABB, and AABB 9. The distribution of BB covers the entire region south to Huai River, whereas AA populations are distributed in Taiwan, Fujian, Hong Kong, and Gungdong and are isolated from its major distribution. The appearance of AABB 9 is possibly evidence for the degeneration of the subglobular bulb type of AABB and the fact that AAA and AAAA exist in the interior border regions of the range of this complex probably suggests that drought is a major factor promoting plant polyploidization. In addition, the mean numbers of B chromosomes per individual, the percentage of individuals with the B chromosome in each population, and the correlation coefficients between the latter and their latitude/longitude were calculated. Generally speaking, the B chromosome number is higher in BB populations compared with AA populations and there is a prominent tendency that the B chromosome content in either AA or BB populations correlates with the latitude and longitude of the populations. 相似文献
58.
陕西汉族人群12号染色体上7个STR基因座的遗传多态性分析 总被引:1,自引:0,他引:1
分析了中国汉族人群中12号染色体上7个短串联重复序列(short tandem repeat,STR)基因座的多态性。 采用荧光标记基因扫描对12号染色体上D12S1718、D12S1675、D12S358、D12S367、D12S1638、D12S1646和D12S1682基因座在80名陕西咸阳、榆林汉族人中的遗传多态性进行分析。结果在中国汉族人群中, D12S1718、D12S1675、D12S358、D12S367、D12S1638、D12S1646和D12S1682基因座分别检出7、10、8、8、6、9和11个等位基因,10、17、18、18、14、18和26个基因型,杂合度分别为44.28%、66.10%、78.89%、77.89%、73.69%、74.55%和82.39%。表明这7个STR基因座在中国人群中有较好的多态性,其基因型分布均符合Hard-Weinberg平衡(P>0.05)。 相似文献
59.
JANICE BRITTON-DAVIDIAN FABIENNE FEL-CLAIR JOËLLE LOPEZ PAUL ALIBERT PIERRE BOURSOT 《Biological journal of the Linnean Society. Linnean Society of London》2005,84(3):379-393
We assessed the fertility (reproductive success, litter size, testis weight, spermatocyte-to-spermatid ratio) of F1 s and backcrosses between different wild-derived outbred and inbred strains of two mouse subspecies, Mus musculus domesticus and M. m. musculus . A significant proportion of the F1 females between the outbred crosses did not reproduce, suggesting that female infertility was present. As the spermatocyte-to-spermatid ratio was correlated with testis weight, the latter was used to attribute a sterile vs. fertile phenotype to all males. Segregation proportions in the backcrosses of F1 females yielded 11 (inbred) to 17% (outbred) sterile males, suggesting the contribution of two to three major genetic factors to hybrid male sterility. Only one direction of cross between the inbred strains produced sterile F1 males, indicating that one factor was borne by the musculus X-chromosome. No such differences were observed between reciprocal crosses in the outbred strains. The involvement of the X chromosome in male sterility thus could not be assessed, but its contribution appears likely given the limited introgression of X-linked markers through the hybrid zone between the subspecies. However, we observed no sterile phenotypes in wild males from the hybrid zone, although testis weight tended to decrease in the centre of the transect. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 379–393. 相似文献
60.