全文获取类型
收费全文 | 508552篇 |
免费 | 54016篇 |
国内免费 | 9042篇 |
出版年
2021年 | 7885篇 |
2020年 | 5533篇 |
2019年 | 6773篇 |
2018年 | 7835篇 |
2017年 | 6643篇 |
2016年 | 9169篇 |
2015年 | 12719篇 |
2014年 | 14880篇 |
2013年 | 18892篇 |
2012年 | 21773篇 |
2011年 | 20915篇 |
2010年 | 13575篇 |
2009年 | 12453篇 |
2008年 | 16584篇 |
2007年 | 16168篇 |
2006年 | 15079篇 |
2005年 | 13576篇 |
2004年 | 12952篇 |
2003年 | 12402篇 |
2002年 | 11713篇 |
2001年 | 20442篇 |
2000年 | 20499篇 |
1999年 | 16952篇 |
1998年 | 6405篇 |
1997年 | 6627篇 |
1996年 | 6388篇 |
1995年 | 5776篇 |
1994年 | 5877篇 |
1993年 | 5556篇 |
1992年 | 13638篇 |
1991年 | 12873篇 |
1990年 | 12685篇 |
1989年 | 12631篇 |
1988年 | 11453篇 |
1987年 | 10903篇 |
1986年 | 10058篇 |
1985年 | 10131篇 |
1984年 | 8134篇 |
1983年 | 7102篇 |
1982年 | 5378篇 |
1981年 | 4739篇 |
1980年 | 4594篇 |
1979年 | 7727篇 |
1978年 | 5970篇 |
1977年 | 5338篇 |
1976年 | 5151篇 |
1975年 | 5581篇 |
1974年 | 5824篇 |
1973年 | 5750篇 |
1972年 | 5207篇 |
排序方式: 共有10000条查询结果,搜索用时 406 毫秒
991.
The isolation and characterisation of mutants of Aspergillus nidulans showing resistance to MNNG is described. Such isolates were stable through prolonged subculture in the absence of the selective agent, and resistance segregated as an allele of a single gene in meiotic and mitotic analysis. MNNG-resistant strains showed an increase in resistance to EMS and UV irradiation but no cross-resistance to MMS was detected. Possible mechanisms of resistance to alkylating agents are discussed. 相似文献
992.
V Franceschini P Del Grande F Ciani G Caniato G Minelli 《Basic and applied histochemistry》1984,28(3):281-289
The ultrastructural localization of alkaline phosphatase and K+-NPPase was investigated in brain capillaries of newt by a cytochemical study using whole brain perfusion. The alkaline phosphatase activity was present in both luminal and antiluminal membranes of the endothelial cells. By contrast, the K+-NPPase was located only in antiluminal membranes of the brain capillaries. This distinct enzymatic distribution suggested that the luminal and antiluminal membranes are functionally different. The role of alkaline phosphatase and K+-NPPase in the blood brain barrier is discussed. 相似文献
993.
994.
Role of superoxide in deoxyribonucleic acid strand scission 总被引:28,自引:0,他引:28
995.
Ohne Zusammenfassung 相似文献
996.
997.
998.
B Müller D Besser P Kleinw?chter O Arad S Reissmann 《The journal of peptide research》1999,54(5):383-393
To improve the assembly of backbone cyclic peptides, N-functionalized dipeptide building units were synthesized. The corresponding N-aminoalkyl or N-carboxyalkyl amino acids were formed by alkylation or reductive alkylation of amino acid benzyl or tert-butyl esters. In the case of N-aminoalkyl amino acid derivatives the aldehydes for reductive alkylation were obtained from N,O-dimethyl hydroxamates of N-protected amino acids by reduction with LiAlH4. N-carboxymethyl amino acids were synthesized by alkylation using bromoacetic acid ester and the N-carboxyethyl amino acids via reductive alkylation using aldehydes derived from formyl Meldrums acid. Removal of the carboxy protecting group leads to free N-alkyl amino acids of very low solubility in organic solvents, allowing efficient purification by extraction of the crude product. These N-alkyl amino acids were converted to their tetramethylsilane-esters by silylation with N,O-bis-(trimethylsilyl)acetamide and could thus be used for the coupling with Fmoc-protected amino acid chlorides or fluorides. To avoid racemization the tert-butyl esters of N-alkyl amino acids were coupled with the Fmoc-amino acid halides in the presence of the weak base collidine. Both the N-aminoalkyl and N-carboxyalkyl functionalized dipeptide building units could be obtained in good yield and purity. For peptide assembly on the solid support, the allyl type protection of the branching moiety turned out to be most suitable. The Fmoc-protected N-functionalized dipeptide units can be used like any amino acid derivative under the standard conditions for Fmoc-solid phase synthesis. 相似文献
999.
Ying Jin Dan Long Juan Li Ruichao Yu Yueming Song Jie Fang Xi Yang Shu Zhou Shishu Huang Zhihe Zhao 《Journal of cellular physiology》2019,234(9):14838-14851
Bone and tooth, fundamental parts of the craniofacial skeleton, are anatomically and developmentally interconnected structures. Notably, pathological processes in these tissues underwent together and progressed in multilevels. Extracellular vesicles (EVs) are cell-released small organelles and transfer proteins and genetic information into cells and tissues. Although EVs have been identified in bone and tooth, particularly EVs have been identified in the bone formation and resorption, the concrete roles of EVs in bone and tooth development and diseases remain elusive. As such, we review the recent progress of EVs in bone and tooth to highlight the novel findings of EVs in cellular communication, tissue homeostasis, and interventions. This will enhance our comprehension on the skeletal biology and shed new light on the modulation of skeletal disorders and the potential of genetic treatment. 相似文献