全文获取类型
收费全文 | 8086篇 |
免费 | 771篇 |
国内免费 | 1篇 |
出版年
2022年 | 45篇 |
2021年 | 105篇 |
2020年 | 64篇 |
2019年 | 77篇 |
2018年 | 87篇 |
2017年 | 93篇 |
2016年 | 161篇 |
2015年 | 274篇 |
2014年 | 338篇 |
2013年 | 350篇 |
2012年 | 472篇 |
2011年 | 482篇 |
2010年 | 341篇 |
2009年 | 287篇 |
2008年 | 403篇 |
2007年 | 419篇 |
2006年 | 392篇 |
2005年 | 346篇 |
2004年 | 340篇 |
2003年 | 344篇 |
2002年 | 352篇 |
2001年 | 185篇 |
2000年 | 158篇 |
1999年 | 168篇 |
1998年 | 126篇 |
1997年 | 97篇 |
1996年 | 98篇 |
1995年 | 97篇 |
1994年 | 85篇 |
1993年 | 99篇 |
1992年 | 129篇 |
1991年 | 100篇 |
1990年 | 126篇 |
1989年 | 108篇 |
1988年 | 93篇 |
1987年 | 92篇 |
1986年 | 81篇 |
1985年 | 66篇 |
1984年 | 62篇 |
1983年 | 66篇 |
1982年 | 70篇 |
1981年 | 61篇 |
1980年 | 59篇 |
1979年 | 65篇 |
1977年 | 52篇 |
1976年 | 58篇 |
1975年 | 40篇 |
1974年 | 49篇 |
1973年 | 41篇 |
1971年 | 41篇 |
排序方式: 共有8858条查询结果,搜索用时 515 毫秒
11.
12.
Lyndsey R. Buckner Angela M. Amedee Hannah L. Albritton Pamela A. Kozlowski Nedra Lacour Chris L. McGowin Danny J. Schust Alison J. Quayle 《PloS one》2016,11(1)
Chlamydia trachomatis causes a predominantly asymptomatic, but generally inflammatory, genital infection that is associated with an increased risk for HIV acquisition. Endocervical epithelial cells provide the major niche for this obligate intracellular bacterium in women, and the endocervix is also a tissue in which HIV transmission can occur. The mechanism by which CT infection enhances HIV susceptibility at this site, however, is not well understood. Utilizing the A2EN immortalized endocervical epithelial cell line grown on cell culture inserts, we evaluated the direct role that CT-infected epithelial cells play in facilitating HIV transmission events. We determined that CT infection significantly enhanced the apical-to-basolateral migration of cell-associated, but not cell-free, HIVBaL, a CCR5-tropic strain of virus, across the endocervical epithelial barrier. We also established that basolateral supernatants from CT-infected A2EN cells significantly enhanced HIV replication in peripheral mononuclear cells and a CCR5+ T cell line. These results suggest that CT infection of endocervical epithelial cells could facilitate both HIV crossing the mucosal barrier and subsequent infection or replication in underlying target cells. Our studies provide a mechanism by which this common STI could potentially promote the establishment of founder virus populations and the maintenance of local HIV reservoirs in the endocervix. Development of an HIV/STI co-infection model also provides a tool to further explore the role of other sexually transmitted infections in enhancing HIV acquisition. 相似文献
13.
Rapid degradation of D- and L-succinimide-containing peptides by a post-proline endopeptidase from human erythrocytes 总被引:1,自引:0,他引:1
We have been interested in the metabolic fate of proteins containing aspartyl succinimide (Asu) residues. These residues can be derived from the spontaneous rearrangement of Asp and Asn residues and from the spontaneous demethylation of enzymatically methylated L-isoAsp and D-Asp residues. Incubation of the synthetic hexapeptide N-Ac-Val-Tyr-Pro-Asu-Gly-Ala with the cytosolic fraction of human erythrocytes resulted in rapid cleavage of the prolyl-aspartyl succinimide bond producing the tripeptide N-Ac-Val-Tyr-Pro. The rate of this reaction is equal for both L- and D-Asu-containing peptides and is 10-fold greater than the rate of cleavage of a corresponding peptide containing a normal Pro-Asp linkage. When the aspartyl succinimide ring was replaced with an isoaspartyl residue, the cleavage rate was about 5 times that of the normal Pro-Asp peptide. The tripeptide-producing activity copurified on DEAE-cellulose chromatography with an activity that cleaves N-carbobenzoxy-Gly-Pro-4-methylcoumarin-7-amide, a post-proline endopeptidase substrate. These two activities were both inhibited by an antiserum to rat brain post-proline endopeptidase, and it appears that they are catalyzed by the same enzyme. This enzyme has a molecular weight of approximately 80,000 and is covalently labeled and inhibited by [3H]diisopropyl fluorophosphate. The facile cleavage of the succinimide- and isoaspartyl-containing peptides by this post-proline endopeptidase suggests that it may play a role in the metabolism of peptides containing altered aspartyl residues. 相似文献
14.
Cory Bystrom Shijun Sheng Ke Zhang Michael Caulfield Nigel J. Clarke Richard Reitz 《PloS one》2012,7(9)
Measurement of insulin-like growth factor-1 (IGF-I) has utility for the diagnosis and management of growth disorders, but inter-assay comparison of results has been complicated by a multitude of reference standards, antibodies, detection methods, and pre-analytical preparation strategies. We developed a quantitative LC-MS method for intact IGF-I, which has advantages in throughput and complexity when compared to mass spectrometric approaches that rely on stable isotope dilution analysis of tryptic peptides. Since the method makes use of full-scan data, the assay was easily extended to provide quantitative measurement of IGF-II using the same assay protocol. The validated LC-MS assay for IGF-I and IGF-II provides accurate results across the pediatric and adult reference range and is suitable for clinical use. 相似文献
15.
16.
17.
18.
S. Clarke 《BMJ (Clinical research ed.)》1992,304(6832):961-963
OBJECTIVE--To identify the attitudes of general practitioners towards the use of thermometers in general practice. DESIGN--Postal questionnaire survey. SETTING--All general practitioners in the catchment area of Frimley Park Hospital, Surrey. SUBJECTS--145 general practitioners. MAIN OUTCOME MEASURES--Answers to questions covering a variety of aspects concerning the use of thermometers in general practice. RESULTS--116 (80%) doctors replied. Seven doctors did not have any method of taking a patient''s temperature; up to 12 more doctors did not use their thermometers and 56 doctors used them infrequently, less than once a fortnight. Mercury glass thermometers were most commonly used (80 doctors; 69%), but only 8% of doctors used them correctly. Six doctors failed to clean their thermometers between patients. The study failed to identify the roles of axillary and rectal temperature readings. CONCLUSION--There is a wide variation in attitudes towards the use of thermometers in general practice. 相似文献
19.