全文获取类型
收费全文 | 6354篇 |
免费 | 551篇 |
国内免费 | 1篇 |
出版年
2023年 | 48篇 |
2022年 | 82篇 |
2021年 | 187篇 |
2020年 | 160篇 |
2019年 | 169篇 |
2018年 | 204篇 |
2017年 | 188篇 |
2016年 | 260篇 |
2015年 | 339篇 |
2014年 | 365篇 |
2013年 | 449篇 |
2012年 | 503篇 |
2011年 | 465篇 |
2010年 | 289篇 |
2009年 | 273篇 |
2008年 | 315篇 |
2007年 | 332篇 |
2006年 | 251篇 |
2005年 | 262篇 |
2004年 | 268篇 |
2003年 | 213篇 |
2002年 | 217篇 |
2001年 | 125篇 |
2000年 | 96篇 |
1999年 | 92篇 |
1998年 | 55篇 |
1997年 | 61篇 |
1996年 | 39篇 |
1995年 | 34篇 |
1994年 | 37篇 |
1993年 | 33篇 |
1992年 | 50篇 |
1991年 | 42篇 |
1990年 | 44篇 |
1989年 | 32篇 |
1988年 | 35篇 |
1987年 | 32篇 |
1986年 | 31篇 |
1985年 | 30篇 |
1984年 | 25篇 |
1983年 | 22篇 |
1982年 | 21篇 |
1981年 | 22篇 |
1980年 | 14篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1977年 | 17篇 |
1976年 | 15篇 |
1974年 | 10篇 |
1961年 | 5篇 |
排序方式: 共有6906条查询结果,搜索用时 156 毫秒
991.
992.
993.
Bego?a Euba Javier Moleres Cristina Viadas Igor Ruiz de los Mozos Jaione Valle José Antonio Bengoechea Junkal Garmendia 《PloS one》2015,10(4)
Nontypable Haemophilus influenzae (NTHi) is a major cause of opportunistic respiratory tract disease, and initiates infection by colonizing the nasopharynx. Bacterial surface proteins play determining roles in the NTHi-airways interplay, but their specific and relative contribution to colonization and infection of the respiratory tract has not been addressed comprehensively. In this study, we focused on the ompP5 and hap genes, present in all H. influenzae genome sequenced isolates, and encoding the P5 and Hap surface proteins, respectively. We employed isogenic single and double mutants of the ompP5 and hap genes generated in the pathogenic strain NTHi375 to evaluate P5 and Hap contribution to biofilm growth under continuous flow, to NTHi adhesion, and invasion/phagocytosis on nasal, pharyngeal, bronchial, alveolar cultured epithelial cells and alveolar macrophages, and to NTHi murine pulmonary infection. We show that P5 is not required for bacterial biofilm growth, but it is involved in NTHi interplay with respiratory cells and in mouse lung infection. Mechanistically, P5NTHi375 is not a ligand for CEACAM1 or α5 integrin receptors. Hap involvement in NTHi375-host interaction was shown to be limited, despite promoting bacterial cell adhesion when expressed in H. influenzae RdKW20. We also show that Hap does not contribute to bacterial biofilm growth, and that its absence partially restores the deficiency in lung infection observed for the ΔompP5 mutant. Altogether, this work frames the relative importance of the P5 and Hap surface proteins in NTHi virulence. 相似文献
994.
995.
B Radhakrishnamurthy S R Srinivasan K Eberle H Ruiz E R Dalferes C Sharma G S Berenson 《Biochimica et biophysica acta》1988,964(2):231-243
The synthesis of proteoglycans by aorta explants from rabbits with diet-induced atherosclerosis and controls was studied by 35S-incorporation. Proteoglycans were isolated under dissociative conditions from incubation medium and from arterial explants. Additionally, the tissue proteoglycans that were not extracted by 4 M guanidine-HCl were solubilized by digestion of the tissue by elastase in the presence of proteinase inhibitors. The residual tissue was hydrolyzed by papain and glycosaminoglycans were isolated. The atherosclerotic aorta tissue incorporated twice the amount of 35S into proteoglycans than observed for controls; in both groups about 70% of the label incorporated into the tissue was noted in the proteoglycans extracted by guanidine-HC;, while about 30% of the total 35S-labeled proteoglycans synthesized by the explants were found in the media. Atherosclerotic tissue incorporated 35S predominantly into chondroitin sulfate proteoglycans when compared to control tissue. The chondroitinase ABC-digestable proteoglycans that were extracted by guanidine-HCl from atherosclerotic tissues were of larger molecular size than those from control tissue, but the core proteins from these preparations were similar. The heparan sulfate proteoglycan that was obtained by dissociative extraction from atherosclerotic tissue had greater amounts of N-acetyl and lesser amounts of N-sulfate ester groups than the preparation from control tissue. Digestion of the tissue by elastase yielded heparan sulfate proteoglycan as the major constituent in both groups, although atherosclerotic tissue contained relatively small amounts of this proteoglycan. The residual tissue from both groups contained chondroitin sulfate and heparan sulfate as the major glycosaminoglycans with the latter showing a decrease with atherosclerosis. Atherosclerotic tissue secreted into the medium about two-fold more 35S-labeled proteoglycans with larger molecular size than control tissue; proteoglycans of the heparan sulfate and chondroitin sulfate types were the major constituents in the culture medium of both tissues. Thus, proteoglycans undergo both quantitative and qualitative changes in atherosclerosis, reflecting the enhanced smooth muscle cell activity. These changes are potentially important in modulating lipoprotein binding and hemostatic properties, as well as fibrillogenesis of the arterial wall. 相似文献
996.
Davis W. Cheng Alejandro Calderón-Urrea 《Nucleosides, nucleotides & nucleic acids》2013,32(11):979-990
DNA synthesis is the cornerstone of all life forms and is required to replicate and restore the genetic information. Usually, DNA synthesis is carried out only by DNA polymerases semiconservatively to copy preexisting DNA templates. We report here that DNA strands were synthesized ab initio in the absence of any DNA or RNA template by thermophilic DNA polymerases at (a) a constant high temperature (74°C), (b) alternating temperatures (94°C/60°C/74°C), or (c) physiological temperatures (37°C). The majority of the ab initio synthesized DNA represented short sequence blocks, repeated sequences, intergenic spacers, and other unknown genetic elements. These results suggest that novel DNA elements could be synthesized in the absence of a nucleic acid template by thermophilic DNA polymerases in vitro. Biogenesis of genetic information by thermophilic DNA polymerase-mediated nontemplate DNA synthesis may explain the origin of genetic information and could serve as a new way of biosynthesis of genetic information that may have facilitated the evolution of life. Supplemental materials are available for this article. Go to the publisher's online edition of Nucleosides, Nucleotides, and Nucleic Acids to view the free supplemental file. 相似文献
997.
998.
Enrique M Arribas Julia Castro Ian R Clemens Juan C Cuevas Jesús Chicharro Ma Teresa Fraile Silvestre García-Ochoa Federico Gómez de las Heras José R Ruiz 《Bioorganic & medicinal chemistry letters》2002,12(2):117-120
A number of novel 3'-O-acyl and alkyl sordarins were synthesised for structure-activity relationship studies. Many of these derivatives exhibit high activity against Candida albicans, Candida pseudotropicalis, Candida tropicalis and Cryptococcus neoformans. 相似文献
999.
Background
Genome-wide association studies (GWAS) using Copy Number Variation (CNV) are becoming a central focus of genetic research. CNVs have successfully provided target genome regions for some disease conditions where simple genetic variation (i.e., SNPs) has previously failed to provide a clear association. 相似文献1000.
Ainara Pealver‐Cruz Elisa Garzo Ins Prieto‐Ruiz Miguel Díaz‐Carro Ana Winters Arnzazu Moreno Alberto Fereres 《Insect Science》2020,27(3):558-570
The continuous rise of CO2 concentrations in the atmosphere is reducing plant nutritional quality for herbivores and indirectly affects their performance. The whitefly (Bemisia tabaci, Gennadius) is a major worldwide pest of agricultural crops causing significant yield losses. This study investigated the plant‐mediated indirect effects of elevated CO2 on the feeding behavior and life history of B. tabaci Mediterranean species. Eggplants were grown under elevated and ambient CO2 concentrations for 3 weeks after which plants were either used to monitor the feeding behavior of whiteflies using the Electrical Penetration Graph technique or to examine fecundity and fertility of whiteflies. Plant leaf carbon, nitrogen, phenols and protein contents were also analyzed for each treatment. Bemisia tabaci feeding on plants exposed to elevated CO2 showed a longer phloem ingestion and greater fertility compared to those exposed to ambient CO2 suggesting that B. tabaci is capable of compensating for the plant nutritional deficit. Additionally, this study looked at the transmission of the virus Tomato yellow leaf curl virus (Begomovirus) by B. tabaci exposing source and receptor tomato plants to ambient or elevated CO2 levels before or after virus transmission tests. Results indicate that B. tabaci transmitted the virus at the same rate independent of the CO2 levels and plant treatment. Therefore, we conclude that B. tabaci Mediterranean species prevails over the difficulties that changes in CO2 concentrations may cause and it is predicted that under future climate change conditions, B. tabaci would continue to be considered a serious threat for agriculture worldwide. 相似文献