全文获取类型
收费全文 | 110753篇 |
免费 | 8642篇 |
国内免费 | 9234篇 |
专业分类
128629篇 |
出版年
2024年 | 245篇 |
2023年 | 1444篇 |
2022年 | 3326篇 |
2021年 | 5618篇 |
2020年 | 3865篇 |
2019年 | 4770篇 |
2018年 | 4530篇 |
2017年 | 3306篇 |
2016年 | 4699篇 |
2015年 | 6841篇 |
2014年 | 8030篇 |
2013年 | 8472篇 |
2012年 | 10240篇 |
2011年 | 9177篇 |
2010年 | 5687篇 |
2009年 | 5079篇 |
2008年 | 5837篇 |
2007年 | 5267篇 |
2006年 | 4573篇 |
2005年 | 3604篇 |
2004年 | 3078篇 |
2003年 | 2828篇 |
2002年 | 2393篇 |
2001年 | 1949篇 |
2000年 | 1770篇 |
1999年 | 1736篇 |
1998年 | 1069篇 |
1997年 | 1034篇 |
1996年 | 966篇 |
1995年 | 840篇 |
1994年 | 810篇 |
1993年 | 628篇 |
1992年 | 838篇 |
1991年 | 639篇 |
1990年 | 479篇 |
1989年 | 452篇 |
1988年 | 363篇 |
1987年 | 350篇 |
1986年 | 269篇 |
1985年 | 290篇 |
1984年 | 159篇 |
1983年 | 162篇 |
1982年 | 102篇 |
1981年 | 86篇 |
1980年 | 60篇 |
1979年 | 77篇 |
1977年 | 60篇 |
1975年 | 57篇 |
1974年 | 52篇 |
1973年 | 58篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
81.
W. L. Li P. D. Chen L. L. Qi D. J. Liu 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1995,90(3-4):526-533
A species-specific repeated sequence, pHvNAU62, was cloned from Haynaldia villosa, a wheat relative of great importance. It strongly hybridized to H. villosa, but not to wheat. In situ hybridization localized this sequence to six of seven H. villosa chromosome pairs in telomeric or sub-telomeric regions. Southern hybridization to whea-H. villosa addition lines showed that chromosomes 1V through 6V gave strong signals in ladders while chromosome 7V escaped detection. In addition to H. villosa, several Triticeae species were identified for a high abundance of the pHvNAU62 repeated sequence, among which Thinopyrum bassarabicum and Leymus racemosus produced the strongest signals. Sequence analysis indicated that the cloned fragment was 292 bp long, being AT rich (61%), and showed 67% homology of pSc7235, a rye repeated sequence. Isochizomer analysis suggested that the present repeated sequence was heavily methylated at the cytosine of the CpG dimer in the genome of H. villosa.It was also demonstrated that pHvNAU62 is useful in tagging the introduced 6VS chromosome arm, which confers a resistance gene to wheat powdery mildew, in the segregating generations. 相似文献
82.
R. Bender R. Fundele M. A. Surani L-L. Li R. Kothary D. O. Fürst B. Christ 《Development genes and evolution》1995,204(7-8):436-443
Parthenogenetic cells are lost from fetal chimeras. This may be due to decreased proliferative potential. To address this question, we have made use of combined cell lineage and cell proliferation analysis. Thus, the incorporation of bromodeoxyuridine in S-phase was determined for both parthenogenetic and normal cells in several tissues of fetal day 13 and 17 chimeras. A pronounced reduction of bromodesoxyuridine incorporation by parthenogenetic cells at both developmental stages was only observed in cartilage. In brain, skeletal muscle, heart and intestinal epithelium, this reduction was either less pronounced or observed only at one of the developmental stages analysed. No difference between parthenogenetic and normal cells was observed in epidermis and ganglia. Our results show that a loss of proliferative potential of parthenogenetic cells during fetal development contributes to their rapid elimination in some tissues. The analysis of the fate of parthenogenetic cells in skeletal muscle and cartilage development demonstrated different selection mechanisms in these tissues. In skeletal muscle, parthenogenetic cells were largely excluded from the myogenic lineage proper by early post-midgestation. In primary hyaline cartilage, parthenogenetic cells persisted into adulthood but were lost from cartilages that undergo ossification during late fetal development. 相似文献
83.
Isolation of two novel myb-like genes from Arabidopsis and studies on the DNA-binding properties of their products 总被引:2,自引:0,他引:2
Two novel myb-like genes (atmyb6 and atmyb7) were isolated from an Arabidopsis thaliana cDNA library. The entire proteins or the Myb domains encoded by the genes were expressed as fusion proteins in Escherichia coli. The DNA-binding domain of the murine c-Myb was also expressed in the same way for use in comparative studies. The fusion proteins were examined for their DNA-binding activity using the animal c-Myb DNA-binding site (MBS) and the binding site of the maize P gene product (PBS). The Myb domain of Atmyb6 bound to PBS more efficiently than to MBS. Complete Atmyb6 and Atmyb7 proteins preferentially bound to PBS but not MBS. This suggests that the in vitro binding consensus sequences for both Atmyb6 and Atmyb7 are similar to PBS. The binding of the Myb domain of Atmyb6 to both PBS and MBS raises the possibility that the protein recognizes multiple sequences in vivo. The third α-helix and three adjacent amino acids in the third repeat (R3) of c-Myb were replaced with the analogous sequence of Atmyb6 to create a chimeric Myb protein. This chimeric protein bound to PBS with a low affinity but failed to bind to MBS. Thus the binding pattern of the chimeric Myb protein is similar to that of the Atmyb6. This result suggests that the last 20 amino acids in the R3 repeat of Atmyb6 play a major role in DNA-binding. 相似文献
84.
85.
Microbial uptake of radiolabeled substrates: estimates of growth rates from time course measurements. 下载免费PDF全文
W K Li 《Applied microbiology》1984,47(1):184-192
The uptake of [3H]glucose and a mixture of 3H-labeled amino acids was measured, in time course fashion, in planktonic microbial assemblages of the eastern tropical Pacific Ocean. The average generation times of those portions of the assemblages able to utilize these substrates were estimated from a simple exponential growth model. Other workers have independently used this model in its integrated or differential form. A mathematical verification and an experimental demonstration of the equivalence of the two approaches are presented. A study was made of the size distribution of heterotrophic activity, using time course measurements. It was found that the size distribution and the effect of sample filtration before radiolabeling were dependent on time of incubation. In principle, it was possible to ascribe these time dependences to differences in the specific growth rate and initial standing stock of the microbial assemblages. 相似文献
86.
87.
88.
89.
90.
本文选用金黄地鼠的微血管,利用显微高速摄影技术,放大微观流场和血细胞,连续地“冻结”短瞬间的变化状态,把物理图象呈现在胶片上,经图像分析和数据处理,从定性及定量方面研究血液微流变学,为生命科学和医学研究提供了又一种新的方法。 相似文献