全文获取类型
收费全文 | 5175篇 |
免费 | 438篇 |
国内免费 | 3篇 |
专业分类
5616篇 |
出版年
2023年 | 32篇 |
2022年 | 85篇 |
2021年 | 136篇 |
2020年 | 72篇 |
2019年 | 102篇 |
2018年 | 101篇 |
2017年 | 100篇 |
2016年 | 178篇 |
2015年 | 293篇 |
2014年 | 317篇 |
2013年 | 399篇 |
2012年 | 468篇 |
2011年 | 480篇 |
2010年 | 281篇 |
2009年 | 269篇 |
2008年 | 373篇 |
2007年 | 339篇 |
2006年 | 329篇 |
2005年 | 289篇 |
2004年 | 246篇 |
2003年 | 225篇 |
2002年 | 186篇 |
2001年 | 27篇 |
2000年 | 19篇 |
1999年 | 31篇 |
1998年 | 34篇 |
1997年 | 26篇 |
1996年 | 29篇 |
1995年 | 11篇 |
1994年 | 6篇 |
1993年 | 11篇 |
1992年 | 6篇 |
1991年 | 14篇 |
1990年 | 13篇 |
1989年 | 8篇 |
1988年 | 11篇 |
1987年 | 5篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1969年 | 4篇 |
排序方式: 共有5616条查询结果,搜索用时 0 毫秒
71.
72.
73.
Kevin Lewellyn Dobroslawa Bialonska Melissa J. Loria Stephen W. White Kenneth J. Sufka Jordan K. Zjawiony 《Bioorganic & medicinal chemistry》2013,21(22):7083-7090
Aplysinopsins are tryptophan-derived natural products that have been isolated from a variety of marine organisms and have been shown to possess a range of biological activities. In vitro receptor binding assays showed that of the 12 serotonin receptor subtypes, analogues showed a high affinity for the 5-HT2B and 5-HT2C receptor subtypes, with selectivity for 5-HT2B over 5-HT2C. While no conclusions could be drawn about the number and position of N-methylations, bromination at C-4 and C-5 of the indole ring resulted in greater binding affinities, with Ki’s as low as 35 nM. This data, combined with previous knowledge of the CNS activity of aplysinopsin analogs, suggested that these compounds may have potential as leads for antidepressant drugs. Compounds 3c, 3u, and 3x were evaluated in the chick anxiety–depression model to assess their in vivo efficacy. Compound 3c showed a modest antidepressant effect at a dose of 30 nM/kg in the animal model. 相似文献
74.
Christiane Baumert Marianne Günthel Sören Krawczyk Marc Hemmer Tom Wersig Andreas Langner Joséf Molnár Hermann Lage Andreas Hilgeroth 《Bioorganic & medicinal chemistry》2013,21(1):166-177
Novel series of N-benzyl 1,4-dihydropyridines have been prepared by facile syntheses. All relevant substituents of the molecular scaffold have been varied. The resulting compounds were biologically evaluated as P-glycoprotein (P-gp) inhibitors. Substitutions of the N-benzyl residue favour biological activity beside respective 3-ester functions. Most active compounds were further evaluated as multidrug resistance (MDR) modulators to restore the cytotoxic properties of varying daunorubicin applications. 相似文献
75.
76.
77.
Abstract Sexually mature male and female Rana esculenta L. were captured in their natural habitat in six phases of the annual cycle. Nuclear volumes in APOA cells were found to fluctuate distinctly in the course of the year. In both sexes nuclear volumes were maximal in the phases preceding the breeding season (IIIrd decade of January, and 1st decade of April), and minimal throughout the phases of active life (IIIrd decade of May, IInd decade of July, and 1st decade of September). No aldehydefuchsin or Gomori‐positive material was found in the APOA perikaryons. 相似文献
78.
79.
Melissa R. Christopherson Garret Suen Shanti Bramhacharya Kelsea A. Jewell Frank O. Aylward David Mead Phillip J. Brumm 《PloS one》2013,8(1)
Actinobacteria in the genus Cellulomonas are the only known and reported cellulolytic facultative anaerobes. To better understand the cellulolytic strategy employed by these bacteria, we sequenced the genome of the Cellulomonas fimi ATCC 484T. For comparative purposes, we also sequenced the genome of the aerobic cellulolytic “Cellvibrio gilvus” ATCC 13127T. An initial analysis of these genomes using phylogenetic and whole-genome comparison revealed that “Cellvibrio gilvus” belongs to the genus Cellulomonas. We thus propose to assign “Cellvibrio gilvus” to the genus Cellulomonas. A comparative genomics analysis between these two Cellulomonas genome sequences and the recently completed genome for Cellulomonas flavigena ATCC 482T showed that these cellulomonads do not encode cellulosomes but appear to degrade cellulose by secreting multi-domain glycoside hydrolases. Despite the minimal number of carbohydrate-active enzymes encoded by these genomes, as compared to other known cellulolytic organisms, these bacteria were found to be proficient at degrading and utilizing a diverse set of carbohydrates, including crystalline cellulose. Moreover, they also encode for proteins required for the fermentation of hexose and xylose sugars into products such as ethanol. Finally, we found relatively few significant differences between the predicted carbohydrate-active enzymes encoded by these Cellulomonas genomes, in contrast to previous studies reporting differences in physiological approaches for carbohydrate degradation. Our sequencing and analysis of these genomes sheds light onto the mechanism through which these facultative anaerobes degrade cellulose, suggesting that the sequenced cellulomonads use secreted, multidomain enzymes to degrade cellulose in a way that is distinct from known anaerobic cellulolytic strategies. 相似文献
80.
Melissa A. Napolitano Sharon Hayes Gary G. Bennett Allison K. Ives Gary D. Foster 《Obesity (Silver Spring, Md.)》2013,21(1):25-31