全文获取类型
收费全文 | 357篇 |
免费 | 43篇 |
出版年
2022年 | 3篇 |
2021年 | 9篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2018年 | 2篇 |
2017年 | 8篇 |
2016年 | 6篇 |
2015年 | 15篇 |
2014年 | 21篇 |
2013年 | 23篇 |
2012年 | 23篇 |
2011年 | 19篇 |
2010年 | 15篇 |
2009年 | 16篇 |
2008年 | 17篇 |
2007年 | 21篇 |
2006年 | 21篇 |
2005年 | 15篇 |
2004年 | 20篇 |
2003年 | 19篇 |
2002年 | 15篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 11篇 |
1998年 | 9篇 |
1997年 | 11篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 2篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1973年 | 3篇 |
排序方式: 共有400条查询结果,搜索用时 15 毫秒
11.
One series of 12 rats was exposed to X-irradiation (1500 R) of the stomach 19 days before implantation of Walker tumour cells in the gastric mucosa, and the frequency of tumour take and the extent of tumour growth after 10 days were compared with a second series with the same tumour implantation, but without X-ray exposure. In a third series simple gastric ulcers without tumour were produced by clamping the gastric wall with a heated (80 degrees) surgical needle holder, and the animals were killed 5-7 day later. All the rats were given injections of vinblastine sulfate 3 hours and of 3H-TDR 1 hour before sacrifice. In viewfields with diameter 180 mu the vinblastine-arrested mitoses and labelled cells on the tumour side of the tumour/mucosa border were calculated as percentages of all tumour cells. In the mucosa the total number of proliferating cells was counted at various distances from the border of the tumour or ulcer. No clear differences in the frequency of tumour take and the extent of tumour growth were found between the X-irradiated and the normal rat stomachs, and it is concluded that the X-ray exposure 3 weeks prior to tumour implantation did not reduce the normal mucosal resistance to tumour growth. The percentage of arrested mitoses and labelled cells in the tumour decreased one view field away from the mucosal border, and the number of proliferating cells in the mucosa bordering on the tumours showed a gradual fall with increasing distance up to 0.8-1.0 mm from the tumour border; within these distances, however, the numbers were much higher than at corresponding distances from edges of the ulcers. The Walker tumour thus seems to stimulate cell proliferation in mucosa to a much greater extent than a simple ulcer does. The causes of this phenomenon and the possible roles of "chalones" or "anti-chalones" are discussed. 相似文献
12.
Krishna M. Talasila Narve Brekka Kjersti Mangseth Daniel Stieber Lasse Evensen Gro V. Rosland Anja Torsvik Marek Wagner Simone P. Niclou Rupavathana Mahesparan Olav K. Vintermyr Rolf Bjerkvig Janice M. Nigro Hrvoje Miletic 《PloS one》2013,8(12)
Two of the signature genetic events that occur in human gliomas, EGFR amplification and IDH mutation, are poorly represented in experimental models in vitro. EGFR amplification, for example, occurs in 40 to 50% of GBM, and yet, EGFR amplification is rarely preserved in cell cultures derived from human tumors. To analyze the fate of EGFR amplified and IDH mutated cells in culture, we followed the development over time of cultures derived from human xenografts in nude rats enriched for tumor cells with EGFR amplification and of cultures derived from patient samples with IDH mutations, in serum monolayer and spheroid suspension culture, under serum and serum free conditions. We observed under serum monolayer conditions, that nestin positive or nestin and SMA double positive rat stromal cells outgrew EGFR amplified tumor cells, while serum spheroid cultures preserved tumor cells with EGFR amplification. Serum free suspension culture exhibited a more variable cell composition in that the resultant cell populations were either predominantly nestin/SOX2 co-expressing rat stromal cells or human tumor cells, or a mixture of both. The selection for nestin/SMA positive stromal cells under serum monolayer conditions was also consistently observed in human oligodendrogliomas and oligoastrocytomas with IDH mutations. Our results highlight for the first time that serum monolayer conditions can select for stromal cells instead of tumor cells in certain brain tumor subtypes. This result has an important impact on the establishment of new tumor cell cultures from brain tumors and raises the question of the proper conditions for the growth of the tumor cell populations of interest. 相似文献
13.
Atle van Beelen Granlund Arnar Flatberg Ann E. ?stvik Ignat Drozdov Bj?rn I. Gustafsson Mark Kidd Vidar Beisvag Sverre H. Torp Helge L. Waldum Tom Christian Martinsen Jan Kristian Dam?s Terje Espevik Arne K. Sandvik 《PloS one》2013,8(2)
Background
In inflammatory bowel disease (IBD), genetic susceptibility together with environmental factors disturbs gut homeostasis producing chronic inflammation. The two main IBD subtypes are Ulcerative colitis (UC) and Crohn’s disease (CD). We present the to-date largest microarray gene expression study on IBD encompassing both inflamed and un-inflamed colonic tissue. A meta-analysis including all available, comparable data was used to explore important aspects of IBD inflammation, thereby validating consistent gene expression patterns.Methods
Colon pinch biopsies from IBD patients were analysed using Illumina whole genome gene expression technology. Differential expression (DE) was identified using LIMMA linear model in the R statistical computing environment. Results were enriched for gene ontology (GO) categories. Sets of genes encoding antimicrobial proteins (AMP) and proteins involved in T helper (Th) cell differentiation were used in the interpretation of the results. All available data sets were analysed using the same methods, and results were compared on a global and focused level as t-scores.Results
Gene expression in inflamed mucosa from UC and CD are remarkably similar. The meta-analysis confirmed this. The patterns of AMP and Th cell-related gene expression were also very similar, except for IL23A which was consistently higher expressed in UC than in CD. Un-inflamed tissue from patients demonstrated minimal differences from healthy controls.Conclusions
There is no difference in the Th subgroup involvement between UC and CD. Th1/Th17 related expression, with little Th2 differentiation, dominated both diseases. The different IL23A expression between UC and CD suggests an IBD subtype specific role. AMPs, previously little studied, are strongly overexpressed in IBD. The presented meta-analysis provides a sound background for further research on IBD pathobiology. 相似文献14.
Tomá? Albrecht Oddmund Kleven Jakub Kreisinger Terje Laskemoen Taiwo C. Omotoriogun Ulf Ottosson Ji?í Reif Ond?ej Sedlá?ek David Ho?ák Raleigh J. Robertson Jan T. Lifjeld 《Proceedings. Biological sciences / The Royal Society》2013,280(1752)
Sperm competition represents an important component of post-copulatory sexual selection. It has been argued that the level of sperm competition declines in birds towards the equator. However, to date, sperm competition estimates have been available mainly for avian species inhabiting the northern temperate zone. Here we apply a novel approach, using the coefficient of between-male variation (CVbm) in sperm size as an index for sperm competition risk, in a comparative analysis of 31 Afrotropical and 99 northern temperate zone passerine species. We found no difference in sperm competition risk between the two groups, nor any relationship with migration distance. However, a multivariate model indicated that sperm competition risk was highest in species with a combination of low body mass and few eggs per clutch. The effect of clutch size was most pronounced in tropical species, which indicates that sperm competition risk in tropical and temperate species is differently associated with particular life-history traits. Although tropical species had lower sperm competition risk than temperate zone species for overlapping clutch sizes, the idea of a generally reduced risk of sperm competition in tropical birds was not supported by our analysis. 相似文献
15.
Terje D Josefsen Karen K Sørensen Torill Mørk Svein D Mathiesen Kathrine A Ryeng 《Acta veterinaria Scandinavica》2007,49(1):27
Background
In a project to determine the causes of winter mortality in reindeer in Finnmark County, northern Norway, the most frequent diagnosis turned out to be complete emaciation, despite several of the reindeer having been given silage for up to 4 weeks before they died. The present paper describes autopsy results and other findings in these animals. 相似文献16.
Knudsen Rune Eloranta Antti P. Siwertsson Anna Paterson Rachel A. Power Michael Sandlund Odd Terje 《Hydrobiologia》2019,829(1):245-263
Hydrobiologia - Understanding the concordance between aquatic assemblages in ecological assessments and their responses to human-induced disturbances are fundamental steps toward achieving... 相似文献
17.
18.
Is confidence in the monitoring of GE foods justified? 总被引:1,自引:0,他引:1
Often the limits of detection of genetically engineered organisms (GEOs, LMOs, GMOs) determine what legislation sets as thresholds of allowable contamination of the human food chain with GEOs. Many countries have legislation that is triggered by certain thresholds of contamination. Importantly, international trade in food and animal feed is becoming increasingly vulnerable to interruptions caused by the ambiguity GEOs can create when shipments are monitored at the border. We examine the tools available for detection. Four key error-generating stages are identified with the aim of prompting a higher uniform standard of routine analysis at export and import points. Contamination of the New Zealand corn crop with GEOs is used as a case study for the application of monitoring tools and vulnerability to errors. These tools fail to meet emerging food safety requirements, but some improvements are in development. 相似文献
19.
Structure of the nucleocapsid protein of porcine reproductive and respiratory syndrome virus 总被引:6,自引:0,他引:6
Porcine reproductive and respiratory syndrome virus (PRRSV) is an enveloped RNA virus of the Arteriviridae family, genomically related to the coronaviruses. PRRSV is the causative agent of both severe and persistent respiratory disease and reproductive failure in pigs worldwide. The PRRSV virion contains a core made of the 123 amino acid nucleocapsid (N) protein, a product of the ORF7 gene. We have determined the crystal structure of the capsid-forming domain of N. The structure was solved to 2.6 A resolution by SAD methods using the anomalous signal from sulfur. The N protein exists in the crystal as a tight dimer forming a four-stranded beta sheet floor superposed by two long alpha helices and flanked by two N- and two C-terminal alpha helices. The structure of N represents a new class of viral capsid-forming domains, distinctly different from those of other known enveloped viruses, but reminiscent of the coat protein of bacteriophage MS2. 相似文献
20.
Almaas R Pytte M Lindstad JK Wright M Saugstad OD Pleasure D Rootwelt T 《Journal of neurochemistry》2003,84(5):1018-1027
To study the effect of extracellular acidosis on apoptosis and necrosis during ischemia and reoxygenation, we exposed human post-mitotic NT2-N neurones to oxygen and glucose deprivation (OGD) followed by reoxygenation. In some experiments, pH of the cell medium was lowered to 5.9 during either OGD or reoxygenation or both. Staurosporine, used as a positive control for apoptosis, caused Poly(ADP-ribose)-polymerase (PARP) cleavage and nuclear fragmentation, but no PARP cleavage and little fragmentation were seen after OGD. Low molecular weight DNA fragments were found after staurosporine treatment, but not after OGD. No protective effect of caspase inhibitors was seen after 3 h of OGD and 21 h of reoxygenation, but after 45 h of reoxygenation caspase inhibition induced a modest improvement in 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide (MTT) cleavage. While acidosis during OGD accompanied by neutral medium during reoxygenation protected the neurones (MTT: 228 +/- 117% of neutral medium, p < 0.001), acidosis during reoxygenation only was detrimental (MTT: 38 +/- 25%, p < 0.01). We conclude that apoptotic mechanisms play a minor role after OGD in NT2-N neurones. The effect of acidosis on neuronal survival depends on the timing of acidosis, as acidosis was protective during OGD and detrimental during reoxygenation. 相似文献