全文获取类型
收费全文 | 2729篇 |
免费 | 370篇 |
出版年
2022年 | 15篇 |
2021年 | 37篇 |
2020年 | 24篇 |
2019年 | 28篇 |
2018年 | 42篇 |
2017年 | 38篇 |
2016年 | 67篇 |
2015年 | 115篇 |
2014年 | 144篇 |
2013年 | 144篇 |
2012年 | 144篇 |
2011年 | 140篇 |
2010年 | 110篇 |
2009年 | 93篇 |
2008年 | 133篇 |
2007年 | 127篇 |
2006年 | 90篇 |
2005年 | 105篇 |
2004年 | 114篇 |
2003年 | 122篇 |
2002年 | 111篇 |
2001年 | 94篇 |
2000年 | 89篇 |
1999年 | 69篇 |
1998年 | 37篇 |
1997年 | 35篇 |
1996年 | 37篇 |
1995年 | 36篇 |
1994年 | 39篇 |
1993年 | 31篇 |
1992年 | 69篇 |
1991年 | 60篇 |
1990年 | 47篇 |
1989年 | 58篇 |
1988年 | 44篇 |
1987年 | 28篇 |
1986年 | 36篇 |
1985年 | 34篇 |
1984年 | 27篇 |
1983年 | 20篇 |
1982年 | 19篇 |
1981年 | 21篇 |
1980年 | 23篇 |
1979年 | 15篇 |
1978年 | 19篇 |
1975年 | 21篇 |
1974年 | 17篇 |
1973年 | 14篇 |
1972年 | 11篇 |
1968年 | 13篇 |
排序方式: 共有3099条查询结果,搜索用时 156 毫秒
211.
Raghavan S Yang Z Mosley RT Schleif WA Gabryelski L Olsen DB Stahlhut M Kuo LC Emini EA Chapman KT Tata JR 《Bioorganic & medicinal chemistry letters》2002,12(20):2855-2858
A 1X22X41 combinatorial library or 902 compounds of indinavir analogues was synthesized on the solid support to identify a replacement for the aminoindanol moiety at P2'. 2,6-Dimethyl-4-hydroxy phenol was discovered to be a good replacement for aminoindanol. 相似文献
212.
Franzyk H Jensen SR Olsen CE Rasmussen JH 《Nucleosides, nucleotides & nucleic acids》2002,21(1):23-43
Two enantiomerically pure hydroxymethyl substituted cyclopentene nucleoside analogues (42 and 53) related to carbovir and neplanocin A, respectively, were prepared from the chiral pool of iridoid glucosides. In addition two saturated hydroxymethylated analogues (44 and 45) were obtained from a protected intermediate. 相似文献
213.
Olsen GS Hansen BF 《American journal of physiology. Endocrinology and metabolism》2002,283(5):E965-E970
We examined whether acute activation of 5'-AMP-activated protein kinase (AMPK) by 5'-aminoimidazole-4-carboxamide-1-beta-D-ribonucleoside (AICAR) ameliorates insulin resistance in isolated rat skeletal muscle. Insulin resistance was induced in extensor digitorum longus (EDL) muscles by prolonged exposure to 1.6 mM palmitate, which inhibited insulin-stimulated glycogen synthesis to 51% of control after 5 h of incubation. Insulin-stimulated glucose transport was less affected (22% of control). The decrease in glycogen synthesis was accompanied by decreased glycogen synthase (GS) activity and increased GS phosphorylation. When including 2 mM AICAR in the last hour of the 5-h incubation with palmitate, the inhibitory effect of palmitate on insulin-stimulated glycogen synthesis and glucose transport was eliminated. This effect of AICAR was accompanied by activation of AMPK. Importantly, AMPK inhibition was able to prevent this effect. Neither treatment affected total glycogen content. However, glucose 6-phosphate was increased after inclusion of AICAR, indicating increased influx of glucose. No effect of AICAR on the inhibited insulin-stimulated GS activity or increased GS phosphorylation by palmitate could be detected. Thus the mechanism by which AMPK activation ameliorates the lipid-induced insulin resistance probably involves induction of compensatory mechanisms overriding the insulin resistance. Our results emphasize AMPK as a promising molecular target for treatment of insulin resistance. 相似文献
214.
Transcriptome changes during intestinal cell differentiation 总被引:4,自引:0,他引:4
215.
AIMS: To investigate contamination of surfaces on a poultry slaughter line from infected poultry and subsequent cross-contamination of non-infected poultry. METHODS AND RESULTS: A broiler slaughterhouse was investigated for the presence of Salmonella on 17 defined points over two 1-week periods. Flocks supplied to slaughter and neck skin samples from processed chicken were likewise investigated. Salmonella was detected in 10 out of 18 flocks at ante-mortem inspection, while seven flocks tested positive in the finished products. Equipment at all but one control point at the slaughter line tested positive at least once during the study. The chicken receiving area was the most contaminated. By comparison of typing results from serotyping, plasmid profile typing and phage typing, direct evidence for cross-contamination with Salm. serotype Typhimurium, Salm. Serotype 4.12:b:- and Salm. serotype Virchow on the slaughter line was obtained for four of the flocks. The cleaning procedure in place did not remove all Salmonella from the contaminated areas. CONCLUSIONS: Evidence for contamination of equipment on a slaughter line and subsequent cross-contamination to non-infected chicken was provided by typing methods. SIGNIFICANCE AND IMPACT OF THE STUDY: This study has provided detailed information on cross-contamination on a slaughter line by the use of phage typing and plasmid profiling. The study stresses the importance of controlling Salmonella in the primary production, as contamination of the equipment on the slaughter line will act as a vehicle to contaminate finished products. Cleaning procedures on slaughter lines cannot be expected to control this problem with the current equipment. 相似文献
216.
Which genetic loci have greater population assignment power? 总被引:5,自引:0,他引:5
SUMMARY: WHICHLOCI is a program that determines the relative discriminatory power of alternate genetic loci and loci combinations for population assignment of individuals. AVAILABILITY: http://www.oregonstate.edu/dept/comes/genetics/software.htm 相似文献
217.
Henriksen TF Hölmich LR Friis S McLaughlin JK Fryzek JP Pernille Høyer A Kjøller K Olsen JH 《Plastic and reconstructive surgery》2003,111(7):2182-9; discussion 2190-1
Although numerous epidemiologic studies have examined the long-term safety of silicone breast implants during the past decade, there is a relative lack of surveillance data on short-term health effects and complications following cosmetic surgery of the breast. The Danish Registry for Plastic Surgery of the Breast, established in May of 1999, provides plastic surgeons with a nationwide system for the collection of preoperative, perioperative, and postoperative data on women undergoing breast implantation, breast reduction, or mastopexy. The purpose of the Registry is to examine short-term and, eventually, long-term local complications and possible health effects, and to contribute to an ongoing evaluation of surgical results and surveillance of the products. Furthermore, the Registry will allow the identification of new areas for research into cosmetic and reconstructive breast surgery. Women accepting registration in the Danish Registry for Plastic Surgery of the Breast complete a self-administered questionnaire focusing on medical history and demographic and behavioral factors. Preoperative blood samples are drawn for storage. Surgical data, postoperative results, and complications are registered following surgery and at postoperative visits. Currently, registration has been initiated at 24 private and public clinics, representing more than 80 percent of the plastic surgery clinics in Denmark. As of November of 2001, a total of 1472 women with breast implants and 560 women with breast reduction were included in the Registry. These figures are expected to increase annually by 1000 women undergoing breast implantation and 500 women undergoing breast reduction or mastopexy. The authors present their experience of establishing the first nationwide comprehensive clinical-epidemiologic database and biological bank for cosmetic and reconstructive surgery procedures. 相似文献
218.
Most peroxisomal matrix proteins possess a carboxy-terminal tripeptide targeting signal, termed peroxisomal targeting signal type 1 (PTS1), and follow a relatively well-characterized pathway of import into the organelle. The peroxisomal targeting signal type 2 (PTS2) pathway of peroxisomal matrix protein import is less well understood. In this study, we investigated the mechanisms of PTS2 protein binding and import using an optimized in vitro assay to reconstitute the transport events. The import of the PTS2 protein thiolase differed from PTS1 protein import in several ways. Thiolase import was slower than typical PTS1 protein import. Competition experiments with both PTS1 and PTS2 proteins revealed that PTS2 protein import was inhibited by addition of excess PTS2 protein, but it was enhanced by the addition of PTS1 proteins. Mature thiolase alone, lacking the PTS2 signal, was not imported into peroxisomes, confirming that the PTS2 signal is necessary for thiolase import. In competition experiments, mature thiolase did not affect the import of a PTS1 protein, but it did decrease the amount of radiolabeled full-length thiolase that was imported. This is consistent with a mechanism by which the mature protein competes with the full-length thiolase during assembly of an import complex at the surface of the membrane. Finally, the addition of zinc to PTS2 protein imports increased the level of thiolase bound and imported into the organelles. 相似文献
219.
Collaborative and in-house laboratory trials were conducted to evaluate Cryptosporidium oocyst and Giardia cyst recoveries from source and finished-water samples by utilizing the Filta-Max system and U.S. Environmental Protection Agency (EPA) methods 1622 and 1623. Collaborative trials with the Filta-Max system were conducted in accordance with manufacturer protocols for sample collection and processing. The mean oocyst recovery from seeded, filtered tap water was 48.4% +/- 11.8%, while the mean cyst recovery was 57.1% +/- 10.9%. Recovery percentages from raw source water samples ranged from 19.5 to 54.5% for oocysts and from 46.7 to 70.0% for cysts. When modifications were made in the elution and concentration steps to streamline the Filta-Max procedure, the mean percentages of recovery from filtered tap water were 40.2% +/- 16.3% for oocysts and 49.4% +/- 12.3% for cysts by the modified procedures, while matrix spike oocyst recovery percentages ranged from 2.1 to 36.5% and cyst recovery percentages ranged from 22.7 to 68.3%. Blinded matrix spike samples were analyzed quarterly as part of voluntary participation in the U.S. EPA protozoan performance evaluation program. A total of 15 blind samples were analyzed by using the Filta-Max system. The mean oocyst recovery percentages was 50.2% +/- 13.8%, while the mean cyst recovery percentages was 41.2% +/- 9.9%. As part of the quality assurance objectives of methods 1622 and 1623, reagent water samples were seeded with a predetermined number of Cryptosporidium oocysts and Giardia cysts. Mean recovery percentages of 45.4% +/- 11.1% and 61.3% +/- 3.8% were obtained for Cryptosporidium oocysts and Giardia cysts, respectively. These studies demonstrated that the Filta-Max system meets the acceptance criteria described in U.S. EPA methods 1622 and 1623. 相似文献
220.
Waldenström J On SL Ottvall R Hasselquist D Harrington CS Olsen B 《Applied and environmental microbiology》2003,69(12):7523-7526
A polyphasic identification approach was used to investigate the taxonomic position of Campylobacter-like isolates recovered from barnacle geese (Branta leucopsis) and Canada geese (Branta candensis). Seven strains were selected from a collection of 21 isolates and analyzed by extensive phenotypic testing; four strains were characterized by 16S rRNA gene sequence analysis. The results clearly identified the bird isolates as Helicobacter canadensis, recently described as an emerging human pathogen. This is the first report of an animal reservoir for this organism and of its presence in Europe and confirms the zoonotic potential of H. canadensis. 相似文献