全文获取类型
收费全文 | 21040篇 |
免费 | 1706篇 |
国内免费 | 1745篇 |
出版年
2024年 | 32篇 |
2023年 | 272篇 |
2022年 | 680篇 |
2021年 | 1173篇 |
2020年 | 777篇 |
2019年 | 990篇 |
2018年 | 929篇 |
2017年 | 625篇 |
2016年 | 925篇 |
2015年 | 1352篇 |
2014年 | 1532篇 |
2013年 | 1588篇 |
2012年 | 1950篇 |
2011年 | 1706篇 |
2010年 | 999篇 |
2009年 | 925篇 |
2008年 | 1091篇 |
2007年 | 907篇 |
2006年 | 832篇 |
2005年 | 655篇 |
2004年 | 508篇 |
2003年 | 449篇 |
2002年 | 371篇 |
2001年 | 323篇 |
2000年 | 321篇 |
1999年 | 324篇 |
1998年 | 208篇 |
1997年 | 242篇 |
1996年 | 191篇 |
1995年 | 190篇 |
1994年 | 162篇 |
1993年 | 129篇 |
1992年 | 181篇 |
1991年 | 143篇 |
1990年 | 146篇 |
1989年 | 98篇 |
1988年 | 90篇 |
1987年 | 87篇 |
1986年 | 63篇 |
1985年 | 65篇 |
1984年 | 43篇 |
1983年 | 47篇 |
1982年 | 21篇 |
1981年 | 16篇 |
1980年 | 14篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1969年 | 9篇 |
1968年 | 8篇 |
1965年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
921.
Chaoqun Li Xiaojia Zhao Pengtao Xie Junping Hu Huimin Bi 《Journal of molecular recognition : JMR》2019,32(1)
Riboswitches are RNA molecules that regulate gene expression using conformation change, affected by binding of small molecule ligands. Although a number of ligand‐bound aptamer complex structures have been solved, it is important to know ligand‐free conformations of the aptamers in order to understand the mechanism of specific binding by ligands. In this paper, we use dynamics simulations on a series of models to characterize the ligand‐free and ligand‐bound aptamer domain of the c‐di‐GMP class I (GEMM‐I) riboswitch. The results revealed that the ligand‐free aptamer has a stable state with a folded P2 and P3 helix, an unfolded P1 helix and open binding pocket. The first Mg ions binding to the aptamer is structurally favorable for the successive c‐di‐GMP binding. The P1 helix forms when c‐di‐GMP is successive bound. Three key junctions J1/2, J2/3 and J1/3 in the GEMM‐I riboswitch contributing to the formation of P1 helix have been found. The binding of the c‐di‐GMP ligand to the GEMM‐I riboswitch induces the riboswitch's regulation through the direct allosteric communication network in GEMM‐I riboswitch from the c‐di‐GMP binding sites in the J1/2 and J1/3 junctions to the P1 helix, the indirect ones from those in the J2/3 and P2 communicating to P1 helix via the J1/2 and J1/3 media. 相似文献
922.
923.
924.
Wasim Ahmed Xiaojing Yan Dekun Hu Muhammad Adnan Ri-Yuan Tang Zi-Ning Cui 《Bioorganic & medicinal chemistry》2019,27(19):115048
Pyrazole constitutes an important heterocyclic family covering a broad range of synthetic as well as natural products that exhibit numerous chemical, biological, agrochemical and pharmacological properties. In order to explore compounds with good fungicidal activity, a series of new pyrazole derivatives containing 5-phenyl-2-furan were designed and synthesized. In vitro and in vivo fungicidal activities were evaluated and the compound ethyl-1-(5-phenylfuran-2-carbonyl)-5-propyl-1H-pyrazole-3-carboxylate (I8) displayed significant fungicidal activity against various fungi, especially against P. infestans. The structures of the novel pyrazole derivatives were confirmed by 1H NMR, 13C NMR, MS, elemental analysis and X-ray single crystal diffraction. Further study showed that compound I8 might act on the synthesis of cell walls from morphological and ultrastructural studies by SEM and TEM. The results also revealed that compound I8 could block the nutritional transportation leading to cells senescence and death. These results suggested that the novel pyrazole derivatives proved to be promising lead compounds. 相似文献
925.
926.
927.
928.
SSU‐rRNA Gene Sequencing Survey of Benthic Microbial Eukaryotes from Guaymas Basin Hydrothermal Vent
Alexis Pasulka Sarah K. Hu Peter D. Countway Kathryn J. Coyne Stephen C. Cary Karla B. Heidelberg David A. Caron 《The Journal of eukaryotic microbiology》2019,66(4):637-653
Microbial eukaryotes have important roles in marine food webs, but their diversity and activities in hydrothermal vent ecosystems are poorly characterized. In this study, we analyzed microbial eukaryotic communities associated with bacterial (Beggiatoa) mats in the 2,000 m deep‐sea Guaymas Basin hydrothermal vent system using 18S rRNA gene high‐throughput sequencing of the V4 region. We detected 6,954 distinct Operational Taxonomic Units (OTUs) across various mat systems. Of the sequences that aligned with known protistan phylotypes, most were affiliated with alveolates (especially dinoflagellates and ciliates) and cercozoans. OTU richness and community structure differed among sediment habitats (e.g. different mat types and cold sediments away from mats). Additionally, full‐length 18S rRNA genes amplified and cloned from single cells revealed the identities of some of the most commonly encountered, active ciliates in this hydrothermal vent ecosystem. Observations and experiments were also conducted to demonstrate that ciliates were trophically active and ingesting fluorescent bacteria or Beggiatoa trichomes. Our work suggests that the active and diverse protistan community at the Guaymas Basin hydrothermal vent ecosystem likely consumes substantial amounts of bacterial biomass, and that the different habitats, often defined by distances of just a few 10s of cm, select for particular assemblages and levels of diversity. 相似文献
929.
Qian Chen Tian Sun Jin Wang James Jia Yan‐Hua Yi Yu‐Xin Chen Yong Miao Zhi‐Qi Hu 《Journal of biochemical and molecular toxicology》2019,33(9)
Hydroxytyrosol (HT), a primary phenolic antioxidant in olive oil, can afford protection from oxidative stress (OS) in different cells, including skin cells. In particular, it regulates several inflammation‐associated processes as well as in improving the antioxidant defense system. However, there is no information about HT used in the treatment of hair loss. This work aimed at exploring the potential protective actions of HT against OS in rat dermal papilla cells. After treatment, the related expression of protein and messenger RNA were detected using morphological and molecular analyses. The results showed that HT significantly reduced intracellular reactive oxygen species level, apoptotic markers and inflammation induced by OS and enhanced cell survival by regulating autophagy. Furthermore, HT enhanced the secretion of hair growth factors in the anti‐inflammation process. These results suggest that HT has a significant protective ability against OS and encourage the use of this biological ingredient as a possible tool to prevent alopecia. 相似文献
930.
Haoli Yu Junyan Li Xiaolong Hu Jiahao Feng Hao Wang Fei Xiong 《Journal of biochemical and molecular toxicology》2019,33(8)
Cynaroside is a flavonoid compound proved to possess antioxidant activity, but its protective effect on age‐related macular degeneration still remains unclear. In this study, the protective effects of cynaroside on oxidative stress and apoptosis in retinal pigment epithelial (RPE) cells induced by hydrogen peroxide (H2O2) were investigated. Results showed that cynaroside effectively attenuated the decrease of cell activity induced by H2O2. The total reactive oxygen species can be remitted by decreasing malondialdehyde level, as well as increasing glutathione level, and superoxide dismutase and catalase activities. In addition, Western blot analysis indicated that cynaroside protected ARPE‐19 cells from apoptosis through downregulation of caspase‐3 protein activation which was controlled by the upstream proteins Bcl‐2 and Bax. It was finally proved that cynaroside could enhance the antioxidant and antiapoptotic ability in ARPE‐19 cells by promoting the expression of p‐Akt. 相似文献