首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   307篇
  免费   28篇
  2021年   4篇
  2020年   6篇
  2019年   2篇
  2018年   2篇
  2017年   2篇
  2016年   5篇
  2015年   10篇
  2014年   14篇
  2013年   15篇
  2012年   20篇
  2011年   22篇
  2010年   17篇
  2009年   12篇
  2008年   16篇
  2007年   13篇
  2006年   19篇
  2005年   22篇
  2004年   11篇
  2003年   20篇
  2002年   20篇
  2001年   5篇
  2000年   2篇
  1999年   5篇
  1998年   7篇
  1997年   2篇
  1996年   4篇
  1995年   2篇
  1994年   7篇
  1993年   10篇
  1992年   10篇
  1991年   4篇
  1989年   5篇
  1988年   6篇
  1986年   1篇
  1985年   3篇
  1983年   2篇
  1982年   1篇
  1981年   1篇
  1980年   1篇
  1979年   1篇
  1970年   1篇
  1969年   1篇
  1966年   1篇
  1963年   1篇
排序方式: 共有335条查询结果,搜索用时 31 毫秒
1.
2.
This study aimed to investigate the effect of conditioned media (CM) from osteo‐differentiating and adipo‐differentiating human mesenchymal stem cells (MSCs) isolated from lipoaspirates of healthy female donors on the viability of triple‐negative breast cancer cells MDA‐MB231. The CM of undifferentiated and differentiating MSCs were collected after 7, 14, 21 and 28 days of culture. The effects of MSC CM on cell proliferation were assessed using an 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assay after 24 h. The effects of osteo‐differentiating cell CM on apoptotic promotion, cell cycle impairment, mitochondrial transmembrane potential dissipation, production of reactive oxygen species and autophagosome accumulation were analysed by flow cytometry and Western blot. MTT assay showed that only CM collected from osteo‐induced cells at day 28 (d28O‐CM) reduced tumour cell viability. Treatment with d28O‐CM restrained cell cycle progression through G2 phase, elicited a caspase‐8‐driven apoptotic effect already after 5 h of culture, and down‐regulated autophagosome accumulation and beclin‐1 expression. The finding that factor(s) secreted by osteo‐differentiating MSCs shows properties of an apoptotic inducer and autophagy inhibitor on triple‐negative breast cancer cells may have an important applicative potential that deserves further investigation. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
3.
Neurocysticercosis (NC) is a clinically and radiologically heterogeneous parasitic disease caused by the establishment of larval Taenia solium in the human central nervous system. Host and/or parasite variations may be related to this observed heterogeneity. Genetic differences between pig and human-derived T. solium cysticerci have been reported previously. In this study, 28 cysticerci were surgically removed from 12 human NC patients, the mitochondrial gene that encodes cytochrome b was amplified from the cysticerci and genetic variations that may be related to NC heterogeneity were characterised. Nine different haplotypes (Ht), which were clustered in four haplogroups (Hg), were identified. Hg 3 and 4 exhibited a tendency to associate with age and gender, respectively. However, no significant associations were found between NC heterogeneity and the different T. solium cysticerci Ht or Hg. Parasite variants obtained from patients with similar NC clinical or radiological features were genetically closer than those found in groups of patients with a different NC profile when using the Mantel test. Overall, this study establishes the presence of genetic differences in the Cytb gene of T. solium isolated from human cysticerci and suggests that parasite variation could contribute to NC heterogeneity.  相似文献   
4.
Sap Concentrations in Halophytes and Some Other Plants   总被引:9,自引:2,他引:7  
Freezing point depression in xylem sap of mangroves was found to range from 0.05 to 0.5 degrees , in desert plants from 0.01 to 0.16 degrees . In crush juices from leaves of Batis and Salicornia, 90% or more of the freezing point depression was made up of sodium and chlorine ions; in mangroves they constituted 50 to 70%, the rest probably being organic solutes. Plants growing in seawater have -30 to -60 atmospheres pressure in the xylem sap. As shown earlier, at zero turgor pressure the intracellular freezing point of the parenchyma cells matches closely the negative pressure in the xylem sap. This agrees with the present data, that the fluid which exudes from the xylem by applying gas pressure on the leaves is practically pure water; freezing point is rarely above 0.01 to 0.02 degrees . To perform this ultrafiltration, the plasma membrane is subjected to a hydrostatic pressure gradient which in some cases may exceed 100 atmospheres.  相似文献   
5.
6.
The neuronal Ca2+-binding protein Recoverin has been shown to regulate phototransduction termination in mammalian rods. Here we identify four recoverin genes in the zebrafish genome, rcv1a, rcv1b, rcv2a and rcv2b, and investigate their role in modulating the cone phototransduction cascade. While Recoverin-1b is only found in the adult retina, the other Recoverins are expressed throughout development in all four cone types, except Recoverin-1a, which is expressed only in rods and UV cones. Applying a double flash electroretinogram (ERG) paradigm, downregulation of Recoverin-2a or 2b accelerates cone photoresponse recovery, albeit at different light intensities. Exclusive recording from UV cones via spectral ERG reveals that knockdown of Recoverin-1a alone has no effect, but Recoverin-1a/2a double-knockdowns showed an even shorter recovery time than Recoverin-2a-deficient larvae. We also showed that UV cone photoresponse kinetics depend on Recoverin-2a function via cone-specific kinase Grk7a. This is the first in vivo study demonstrating that cone opsin deactivation kinetics determine overall photoresponse shut off kinetics.  相似文献   
7.
Culture, Medicine, and Psychiatry - In this article, we explore the power of shared embodiment for the constitution of an affective community. More specifically, we examine how people afflicted by...  相似文献   
8.
Oocyte maturation is a prerequisite for successful fertilization. Growing evidence suggests that not only the oocyte but also the surrounding zona pellucida has to undergo maturational changes. In the pig, two-dimensional electrophoretic analysis demonstrated an acidic shift of the zona pellucida glycoproteins of about 1.5–2.0 pH units during the maturation process. These findings were corroborated by histological studies that indicated the synthesis of acidic glycoconjugates in the cumulus cells and an increased occurrence of acidic glycans in the zona pellucida after oocyte maturation. In order to provide structural data on prepuberal zona pellucida N-glycosylation, N-glycans were released from prepuberal zona pellucida glycoproteins by N-glycosidase F and studied by mass spectrometry before and after desialylation and treatment with endo-β-galactosidase. Our results verified the presence of high-mannose-type Man5GlcNAc2 compounds as well as diantennary N-glycans as major neutral species, whereas sialylated diantennary and triantennary species constituted the dominant non-sulfated acidic sugar chains. The major acidic N-glycans of prepuberal animals, however, represented mono-sulfated diantennary, triantennary and tetraantennary oligosaccharides carrying, in part, N-acetyllactosamine repeating units as well as additional Neu5Ac or Neu5Gc residues. Glycans comprising more than one sulfate residue were not detected. In contrast to the literature data on zona pellucida glycoprotein-N-glycans of cyclic animals, our data thus reveal a lower degree in glycan sulfation of the prepuberal zona pellucida.  相似文献   
9.

Background  

Translating a known metabolic network into a dynamic model requires rate laws for all chemical reactions. The mathematical expressions depend on the underlying enzymatic mechanism; they can become quite involved and may contain a large number of parameters. Rate laws and enzyme parameters are still unknown for most enzymes.  相似文献   
10.
Numerous outbreak investigations and case-control studies for campylobacteriosis have provided evidence that handling Campylobacter-contaminated chicken products is a risk factor for infection and illness. There is currently extremely limited quantitative data on the levels of Campylobacter cross-contamination in the kitchen, hindering risk assessments for the pathogen commodity combination of Campylobacter and chicken meat. An exposure assessment needs to quantify the transfer of the bacteria from chicken to hands and the kitchen environment and from there onto ready-to-eat foods. We simulated some typical situations in kitchens and quantified the Campylobacter transfer from naturally contaminated chicken parts most commonly used in Germany. One scenario simulated the seasoning of five chicken legs and the reuse of the same plate for cooked meat. In another, five chicken breast filets were cut into small slices on a wooden board where, without intermediate cleaning, a cucumber was sliced. We also investigated the transfer of the pathogen from chicken via hands to a bread roll. The numbers of Campylobacter present on the surfaces of the chicken parts, hands, utensils, and ready-to-eat foods were detected by using Preston enrichment and colony counting after surface plating on Karmali agar. The mean transfer rates from legs and filets to hands were 2.9 and 3.8%. The transfer from legs to the plate (0.3%) was significantly smaller (P < 0.01) than the percentage transferred from filets to the cutting board and knife (1.1%). Average transfer rates from hands or kitchen utensils to ready-to-eat foods ranged from 2.9 to 27.5%.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号