全文获取类型
收费全文 | 1332篇 |
免费 | 127篇 |
专业分类
1459篇 |
出版年
2022年 | 18篇 |
2021年 | 24篇 |
2020年 | 21篇 |
2019年 | 24篇 |
2018年 | 37篇 |
2017年 | 24篇 |
2016年 | 34篇 |
2015年 | 57篇 |
2014年 | 63篇 |
2013年 | 79篇 |
2012年 | 129篇 |
2011年 | 92篇 |
2010年 | 60篇 |
2009年 | 50篇 |
2008年 | 64篇 |
2007年 | 66篇 |
2006年 | 50篇 |
2005年 | 52篇 |
2004年 | 53篇 |
2003年 | 46篇 |
2002年 | 39篇 |
2001年 | 28篇 |
2000年 | 16篇 |
1999年 | 13篇 |
1998年 | 12篇 |
1996年 | 6篇 |
1994年 | 10篇 |
1993年 | 8篇 |
1992年 | 18篇 |
1991年 | 14篇 |
1990年 | 16篇 |
1989年 | 16篇 |
1988年 | 5篇 |
1987年 | 11篇 |
1986年 | 14篇 |
1985年 | 5篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 14篇 |
1978年 | 14篇 |
1977年 | 18篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1974年 | 7篇 |
1973年 | 11篇 |
1972年 | 13篇 |
1968年 | 5篇 |
排序方式: 共有1459条查询结果,搜索用时 15 毫秒
21.
22.
23.
24.
The structural features of calcium guanosine-3′,5′-cytidine monophosphate (GpC) have been elucidated by X-ray diffraction analysis. The molecule was crystallized in space group P21 with cell constants of a = 21.224 Å, b = 34.207 Å, c = 9.327 Å, and β = 90.527°, Z = 8. The hydration of the crystal is 21% by weight with 72 water molecules in the unit cell. The four GpC molecules in the asymmetric unit occur as two Watson-Crick hydrogen-bonded dimers related by a pseudo-C face centering. Each dimer consists of two independent GpC molecules whose bases are hydrogen bonded to each other in the traditional Watson-Crick fashion. Each dimer possesses a pseudo twofold axis broken by a calcium ion and associated solvent. The four molecules are conformationally similar to helical RNA, but are not identical to it or to each other. Instead, values of conformational angles reflect the intrinsic flexibility of the molecule within the range of basic helical conformations. All eight bases are anti, sugars are all C3′-endo, and the C4′-C5′ bond rotations are gauche-gauche. The R factor is 12.6% for 2918 observed reflections at 1.2-Å resolution. 相似文献
25.
Significant transition/transversion mutation bias is a well-appreciated aspect of mammalian nuclear genomes; however, patterns of bias among genes within a genome and among species remain largely uncharacterized. Understanding these patterns is important for understanding similarities and differences in mutational patterns among genomes and genomic regions. Therefore, we have conducted an analysis of 7,587 pairs of sequences of 4,347 mammalian protein-coding genes from seven species (human, mouse, rat, cow, sheep, pig, and macaque) and from the introns of 51 gene pairs and multiple intergenic regions (37 kbp, 52 kbp and 65 kbp) from the human, chimpanzee, and baboon genomes. Our analyses show that genes and regions with widely varying base composition exhibit uniformity of transition mutation rate both within and among mammalian lineages, as long as the transitional mutations caused by CpG hypermutability are excluded. The estimates show no relationship to potential intrachromosomal or interchromosomal effects. This uniformity points to similarity in point mutation processes in genomic regions with substantially different GC-content biases. 相似文献
26.
Ryan M. Summers Jennifer L. Seffernick Erik M. Quandt Chi Li Yu Jeffrey E. Barrick Mani V. Subramanian 《Journal of bacteriology》2013,195(17):3933-3939
Caffeine and other N-methylated xanthines are natural products found in many foods, beverages, and pharmaceuticals. Therefore, it is not surprising that bacteria have evolved to live on caffeine as a sole carbon and nitrogen source. The caffeine degradation pathway of Pseudomonas putida CBB5 utilizes an unprecedented glutathione-S-transferase-dependent Rieske oxygenase for demethylation of 7-methylxanthine to xanthine, the final step in caffeine N-demethylation. The gene coding this function is unusual, in that the iron-sulfur and non-heme iron domains that compose the normally functional Rieske oxygenase (RO) are encoded by separate proteins. The non-heme iron domain is located in the monooxygenase, ndmC, while the Rieske [2Fe-2S] domain is fused to the RO reductase gene, ndmD. This fusion, however, does not interfere with the interaction of the reductase with N1- and N3-demethylase RO oxygenases, which are involved in the initial reactions of caffeine degradation. We demonstrate that the N7-demethylation reaction absolutely requires a unique, tightly bound protein complex composed of NdmC, NdmD, and NdmE, a novel glutathione-S-transferase (GST). NdmE is proposed to function as a noncatalytic subunit that serves a structural role in the complexation of the oxygenase (NdmC) and Rieske domains (NdmD). Genome analyses found this gene organization of a split RO and GST gene cluster to occur more broadly, implying a larger function for RO-GST protein partners. 相似文献
27.
Gobinath M. Subramanian N. Alagarsamy V. Nivedhitha S. Solomon Viswas Raja 《Russian Journal of Bioorganic Chemistry》2020,46(3):403-408
Russian Journal of Bioorganic Chemistry - Some new 1-substituted-4-(4-nitrophenyl)-[1,2,4]triazolo[4,3-a]quinazolin-5(4H)-ones were synthesized and screened for their H1-antihistaminic activity.... 相似文献
28.
29.
Neha S. Joshi R.B. Subramanian 《Archives Of Phytopathology And Plant Protection》2013,46(15):1773-1789
Roots of the susceptible “JG-62” and resistant “WR-315” chickpeas (Cicer arietinum L.) were inoculated with a conidial suspension of Fusarium oxysporum f. sp. ciceris. Anatomical and biochemical studies were carried out in a time-course manner to elucidate the infection process and plant defence reactions. Scanning electron microscope images revealed fungal colonisation in the root hair region. Early occurrence of fungal biofilms associated with the infected “JG-62” root epidermis was also visualised. After 96 h of inoculation, a gradual accumulation of polysaccharide positive deposits was observed in the xylem vessels of the infected “JG-62” roots. Fungal mycelium was observed in the vessel lumen of infected “JG-62” after 22 days of inoculation. Due to fungal invasion during this period, some of the vessels also appeared collapsed in “JG-62”, whereas vessels in “WR-315” remained intact. The host plant defence responses specifically linked to the susceptible interactions were the induction of ascorbate peroxidase, guaiacol peroxidase and superoxide dismutase in roots and shoots. 相似文献
30.