全文获取类型
收费全文 | 7079篇 |
免费 | 499篇 |
国内免费 | 1篇 |
专业分类
7579篇 |
出版年
2023年 | 40篇 |
2022年 | 119篇 |
2021年 | 185篇 |
2020年 | 140篇 |
2019年 | 168篇 |
2018年 | 214篇 |
2017年 | 165篇 |
2016年 | 288篇 |
2015年 | 455篇 |
2014年 | 449篇 |
2013年 | 583篇 |
2012年 | 668篇 |
2011年 | 631篇 |
2010年 | 352篇 |
2009年 | 317篇 |
2008年 | 406篇 |
2007年 | 376篇 |
2006年 | 348篇 |
2005年 | 305篇 |
2004年 | 268篇 |
2003年 | 217篇 |
2002年 | 240篇 |
2001年 | 51篇 |
2000年 | 36篇 |
1999年 | 49篇 |
1998年 | 55篇 |
1997年 | 33篇 |
1996年 | 36篇 |
1995年 | 24篇 |
1994年 | 31篇 |
1993年 | 25篇 |
1992年 | 34篇 |
1991年 | 20篇 |
1990年 | 17篇 |
1989年 | 20篇 |
1988年 | 14篇 |
1987年 | 15篇 |
1986年 | 7篇 |
1985年 | 15篇 |
1984年 | 15篇 |
1983年 | 6篇 |
1982年 | 13篇 |
1981年 | 9篇 |
1980年 | 14篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1977年 | 11篇 |
1976年 | 7篇 |
1974年 | 7篇 |
1973年 | 17篇 |
排序方式: 共有7579条查询结果,搜索用时 10 毫秒
941.
942.
943.
Alessia Griglio Enza Torre Marta Serafini Alice Bianchi Roberta Schmid Giulia Coda Zabetta Alberto Massarotti Giovanni Sorba Tracey Pirali Silvia Fallarini 《Bioorganic & medicinal chemistry letters》2018,28(4):651-657
Indoleamine 2,3-dioxygenase plays a crucial role in immune tolerance and has emerged as an attractive target for cancer immunotherapy. In this study, the Passerini and Ugi multicomponent reactions have been employed to assemble a small library of imidazothiazoles that target IDO1. While the p-bromophenyl and the imidazothiazole moieties have been kept fixed, a full SAR study has been performed on the side-chain, leading to the discovery of nine compounds with sub-micromolar IC50 values in the enzyme-based assay. Compound 7d, displaying a α-acyloxyamide substructure, is the most potent compound, with an IC50 value of 0.20?µM, but a low activity in a cell-based assay. Compound 6o, containing a α-acylaminoamide moiety, shows an IC50 value of 0.81?µM in the IDO1-based assay, a full biocompatibility at 10?µM, together with a modest inhibitory activity in A375 cells. Molecular docking studies show that both 7d and 6o display a unique binding mode in the IDO1 active site, with the side-chain protruding in an additional pocket C, where a crucial hydrogen bond is formed with Lys238. Overall, this work describes an isocyanide based-multicomponent approach as a straightforward and versatile tool to rapidly access IDO1 inhibitors, providing a new direction for their future design and development. 相似文献
944.
945.
Cappellozza S Saviane A Tettamanti G Squadrin M Vendramin E Paolucci P Franzetti E Squartini A 《Journal of invertebrate pathology》2011,106(3):386-393
Enterococcus mundtii was shown to be directly correlated with flacherie disease of the silkworm larvae reared on artificial diet supplemented with chloramphenicol. Its identification was carried out by means of light and electron microscopy and nucleotide sequencing of 16S gene. The bacterium is capable of rapidly multiplying in the silkworm gut and of invading other body tissues, as demonstrated by deliberate infection of germfree larvae and by subsequent TEM observations. E. mundtii can endure alkaline pH of the silkworm gut and it has been proved to adapt in vitro to commonly applied doses of chloramphenicol, whose use can further contribute to reduce competition by other bacteria in Bombyx mori alimentary canal.The modality of transmission of the infection to the larvae was among the objectives of the present research. Since contamination of the progeny by mother moths can be avoided through routine egg shell disinfection, a trans-ovarian vertical transmission can be ruled out. On the other hand the bacterium was for the first time identified on mulberry leaves, and therefore artificial diet based on leaf powder could be a source of infection. We showed that while microwaved diet could contain live E. mundtii cells, the autoclaved diet is safe in this respect. Being E. mundtii also part of the human-associated microbiota, and since B. mori is totally domestic species, a possible role of man in its epidemiology can be postulated. 相似文献
946.
947.
Johannes G. Achatz Marta Chiodin Willi Salvenmoser Seth Tyler Pedro Martinez 《Organisms Diversity & Evolution》2013,13(2):267-286
Acoels are among the simplest worms and therefore have often been pivotal in discussions of the origin of the Bilateria. Initially thought primitive because of their “planula-like” morphology, including their lumenless digestive system, they were subsequently dismissed by many morphologists as a specialized clade of the Platyhelminthes. However, since molecular phylogenies placed them outside the Platyhelminthes and outside all other phyla at the base of the Bilateria, they became the focus of renewed debate and research. We review what is currently known of acoels, including information regarding their morphology, development, systematics, and phylogenetic relationships, and put some of these topics in a historical perspective to show how the application of new methods contributed to the progress in understanding these animals. Taking all available data into consideration, clear-cut conclusions cannot be made; however, in our view it becomes successively clearer that acoelomorphs are a “basal” but “divergent” branch of the Bilateria. 相似文献
948.
949.
Microstructure and nanomechanical properties of single stalks from diatom Didymosphenia geminata and their change due to adsorption of selected metal ions 下载免费PDF全文
Izabela Zgłobicka Adrian Chlanda Michał Woźniak Maciej Łojkowski Robert Szoszkiewicz Marta Mazurkiewicz‐Pawlicka Wojciech Święszkowski Elżbieta Wyroba Krzysztof J. Kurzydłowski 《Journal of phycology》2017,53(4):880-888
We present topographical and nanomechanical characterization of single Didymosphenia geminata stalk. We compared the samples before and after adsorption of metal ions from freshwater samples. Transmission electron microscopy studies of single stalk cross‐sections have shown three distinct layers and an additional thin extra coat on the external layer (called “EL”). Using scanning electron microscopy and atomic force microscopy (AFM), we found that topography of single stalks after ionic adsorption differed significantly from topography of pristine stalks. AFM nanoindentation studies in ambient conditions yielded elastic moduli of 214 ± 170 MPa for pristine stalks and 294 ± 108 MPa for stalks after ionic adsorption. Statistical tests showed that those results were significantly different. We conducted only preliminary comparisons between ionic adsorption of several stalks in air and in water. While the stalks with ions were on average stiffer than the pristine stalks in air, they became more compliant than the pristine stalks in water. We also heated the stalks and detected EL softening at 50°C ± 15°C. AFM nanoindentation in air on the softened samples yielded elastic moduli of 26 ± 9 MPa for pristine samples and 43 ± 22 MPa for stalks with absorbed metal ions. Substantial decrease of the EL elastic moduli after heating was expected. Significantly different elastic moduli for the samples after ionic adsorption in both cases (i.e., for heated and nonheated samples), as well as behavior of the stalks immersed in water, point to permanent structural EL changes due to ions. 相似文献
950.
Xavier Solé Marta Crous-Bou David Cordero David Olivares Elisabet Guinó Rebeca Sanz-Pamplona Francisco Rodriguez-Moranta Xavier Sanjuan Javier de Oca Ramon Salazar Victor Moreno 《PloS one》2014,9(9)