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   357篇
  免费   22篇
  2023年   4篇
  2022年   10篇
  2021年   18篇
  2020年   12篇
  2019年   5篇
  2018年   18篇
  2017年   7篇
  2016年   14篇
  2015年   11篇
  2014年   12篇
  2013年   22篇
  2012年   37篇
  2011年   38篇
  2010年   16篇
  2009年   10篇
  2008年   41篇
  2007年   35篇
  2006年   11篇
  2005年   22篇
  2004年   6篇
  2003年   6篇
  2002年   2篇
  2001年   4篇
  2000年   2篇
  1999年   1篇
  1998年   1篇
  1997年   1篇
  1996年   1篇
  1995年   1篇
  1994年   1篇
  1992年   1篇
  1990年   1篇
  1989年   1篇
  1987年   1篇
  1982年   1篇
  1971年   2篇
  1970年   1篇
  1968年   1篇
  1966年   1篇
排序方式: 共有379条查询结果,搜索用时 15 毫秒
11.
Variability in the number of tandem repeats of the insulin gene (INS VNTR) is probably involved in the genetic regulation of insulin secretion. The aim of this study was to investigate the association of INS VNTR polymorphism with the presence of glutamic acid decarboxylase antibodies (GADA) and C-peptide levels in patients with the onset of diabetes after 35 years of age. We investigated 117 patients, median of age 63 (range 40-83) years, median of diabetes duration 8 (range 1-30) years; 31 GADA-positive and 86 GADA-negative subjects. INS VNTR polymorphism was typed indirectly using - 23HphI (T/A) polymorphism, which is in complete linkage disequilibrium with INS VNTR. The I/I, I/III and III/III genotypes were found in 22 (71 %), 8 (26 %), 1 (3 %) GADA-positive individuals and in 39 (45 %), 35 (41 %), 12 (14 %) GADA-negative individuals, respectively. The Class I allele and the genotype I/I were significantly associated with the presence of GADA (OR=2.72, CI 95 %=1.29-5.73 and OR=2.95, CI 95 %=1.22-7.13). The presence of Class III allele was significantly associated with a higher level of postprandial C-peptide in GADA-positive subjects, even when regarding the duration of diabetes. Our results of INS VNTR polymorphism in patients with the onset of diabetes after 35 years of age confirm the association of Class I INS VNTR with autoimmune diabetes and the protective effect of Class III INS VNTR on the insulin secretion in GADA-positive subjects.  相似文献   
12.
The radio-ecological model ECOSYS-87 developed for German ecological conditions, has been adapted to the conditions of two sub-regions in the Slovak Republic. In particular, the selection of plant varieties used for animal feeding, the plants’ growing cycles and harvests, the animal feeding practices and the human consumption rates were subjected to adaptation. Measurements of caesium and iodine radioactivity in soil, plants and animal products that have mainly been performed in the vicinity of the Bohunice nuclear power plant after the Chernobyl accident, are compared with the results of the adapted model. Data from various locations with dry, mixed or predominantly wet deposition show in general good agreement. Received: 10 April 2000 / Accepted: 23 October 2000  相似文献   
13.
Exposure of algae or higher plants to bright light can result in a photoinhibitory reduction in the number of functional PS II reaction centers (n) and a consequential decrease in the maximum quantum yield of photosynthesis. However, we found that light-saturated photosynthetic rates (Pmax) in natural phytoplankton assemblages sampled from the south Pacific ocean were not reduced despite photoinhibitory decreases in n of up to 52%. This striking insensitivity of Pmax to photoinhibition resulted from reciprocal increases in electron turnover ( )through the remaining functional PS II centers. Similar insensitivity of Pmax was also observed in low light adapted cultures of Thalassiosira weissflogii (a marine diatom), but not in high light adapted cells where Pmax decreased in proportion to n. This differential sensitivity to decreases in n occurred because was close to the maximum achievable rate in the high light adapted cells, whereas was initially low in the low light adapted cells and could thus increase in response to decreases in n. Our results indicate that decreases in plant productivity are not necessarily commensurate with photoinhibition, but rather will only occur if decreases in n are sufficient to maximize or incident irradiance becomes subsaturating.  相似文献   
14.
15.
Poor outcome of extramedullary disease in multiple myeloma patients and lack of outcome predictors prompt continued search for new markers of the disease. In this report, we show circulating microRNA distinguishing multiple myeloma patients with extramedullary disease from myeloma patients without such manifestation and from healthy donors. MicroRNA-130a was identified by TaqMan Low Density Arrays and verified by quantitative PCR on 144 serum samples (59 multiple myeloma, 55 myeloma with extramedullary disease, 30 healthy donors) in test and validation cohorts as being down-regulated in myeloma patients with extramedullary disease. Circulating microRNA-130a distinguished myeloma patients with extramedullary disease from healthy donors with specificity of 90.0% and sensitivity of 77.1%, patients with extramedullary disease from newly diagnosed multiple myeloma patients with specificity of 77.1% and sensitivity of 34.3% in the test cohort and with specificity of 91.7% and sensitivity of 30.0% in the validation cohort of patients. Circulating microRNA-130a in patients with extramedullary myeloma was associated with bone marrow plasma cells infiltration. Further, microRNA-130a was decreased in bone marrow plasma cells obtained from patients with extramedullary myeloma in comparison to bone marrow plasma cells of myeloma patients without such manifestation, but it was increased in tumor site plasma cells of patients with extramedullary disease compared to bone marrow plasma cells of such patients (p<0.0001). Together, our data suggest connection between lower level of microRNA-130a and extramedullary disease and prompt further work to evaluate this miRNA as a marker of extramedullary disease in multiple myeloma.  相似文献   
16.

Aim

To compare the prognostic accuracy of six scoring models for up to three-year mortality and rates of hospitalisation due to acute decompensated heart failure (ADHF) in STEMI patients.

Methods and Results

A total of 593 patients treated with primary PCI were evaluated. Prospective follow-up of patients was ≥3 years. Thirty-day, one-year, two-year, and three-year mortality rates were 4.0%, 7.3%, 8.9%, and 10.6%, respectively. Six risk scores—the TIMI score and derived dynamic TIMI, CADILLAC, PAMI, Zwolle, and GRACE—showed a high predictive accuracy for six- and 12-month mortality with area under the receiver operating characteristic curve (AUC) values of 0.73–0.85. The best predictive values for long-term mortality were obtained by GRACE. The next best-performing scores were CADILLAC, Zwolle, and Dynamic TIMI. All risk scores had a lower prediction accuracy for repeat hospitalisation due to ADHF, except Zwolle with the discriminatory capacity for hospitalisation up to two years (AUC, 0.80–0.83).

Conclusions

All tested models showed a high predictive value for the estimation of one-year mortality, but GRACE appears to be the most suitable for the prediction for a longer follow-up period. The tested models exhibited an ability to predict the risk of ADHF, especially the Zwolle model.  相似文献   
17.
Lens formation in mouse is critically dependent on proper development of the retinal neuroectoderm that is located close beneath the head surface ectoderm. Signaling from the prospective retina triggers lens‐specific gene expression in the surface‐ectoderm. Supression of canonical Wnt/β‐catenin signaling in the surface ectoderm is one of the prerequisites for lens development because, as we show here, ectopic Wnt activation in the retina and lens abrogates lens formation. Wnt inhibiton is mediated by signals coming from the retina but its exact mechanism is unknown. We show that Pax6 directly controls expression of several Wnt inhibitors such as Sfrp1, Sfrp2, and Dkk1 in the presumptive lens. In accordance, absence of Pax6 function leads to aberrant canonical Wnt activity in the presumptive lens that subsequently impairs lens development. Thus Pax6 is required for down‐regulation of canonical Wnt signaling in the presumptive lens ectoderm. genesis 48:86–95, 2010. © 2009 Wiley‐Liss, Inc.  相似文献   
18.
A novel alcohol oxidase (AOX) has been purified from mycelial pellets of the wood-degrading basidiomycete Gloeophyllum trabeum and characterized as a homooctameric nonglycosylated protein with native and subunit molecular masses of 628 and 72.4 kDa, containing noncovalently bonded flavin adenine dinucleotide. The isolated AOX cDNA contained an open reading frame of 1,953 bp translating into a polypeptide of 651 amino acids displaying 51 to 53% identity with other published fungal AOX amino acid sequences. The enzyme catalyzed the oxidation of short-chain primary aliphatic alcohols with a preference for methanol (K(m) = 2.3 mM, k(cat) = 15.6 s(-1)). Using polyclonal antibodies and immunofluorescence staining, AOX was localized on liquid culture hyphae and extracellular slime in sections from degraded wood and on cotton fibers. Transmission electron microscopy immunogold labeling localized the enzyme in the hyphal periplasmic space and wall and on extracellular tripartite membranes and slime, while there was no labeling of hyphal peroxisomes. AOX was further shown to be associated with membranous or slime structures secreted by hyphae in wood fiber lumina and within the secondary cell walls of degraded wood fibers. The differences in AOX targeting compared to the known yeast peroxisomal localization were traced to a unique C-terminal sequence of the G. trabeum oxidase, which is apparently responsible for the protein's different translocation. The extracellular distribution and the enzyme's abundance and preference for methanol, potentially available from the demethylation of lignin, all point to a possible role for AOX as a major source of H(2)O(2), a component of Fenton's reagent implicated in the generally accepted mechanisms for brown rot through the production of highly destructive hydroxyl radicals.  相似文献   
19.
Clear-cut areas formed after forest decline due to acid deposition, pest attacks, or wind-breaks in temperate mountainous regions are often populated by grass (mainly Calamagrostis villosa). This study focused on the changes of soil chemical characteristics under the grass cover replacing the forest, focusing mainly on aluminium (Al) speciation. Clear-cut area due to strong acid deposition in the Jizera Mountains (Northern Bohemia) was studied. The soils under grass cover exhibit higher pH values and lower exchangeable Al content compared to adjacent surviving forest. Mobile Al species under the grass have larger proportion of non-toxic organic complexes. The content of exchangeable base cations is slightly higher under the grass. The positive effect of grass on soil chemistry was enhanced by liming. The temporary grass cover can therefore improve soil chemical quality for following reforestation. However, the differences are generally limited to surface organic horizons. Similar results were found also on a bark-beetle clear-cut area in the Bohemian Forest (Southern Bohemia) with smaller acid deposition; nevertheless, most differences were not significant there.  相似文献   
20.
Denaturing high-performance liquid chromatography (DHPLC) has been used for rapid and accurate DNA mutation analysis; to extend the DNA fragment lengths analysis. Recently, polymorphism in polyglutamine-coding region of Amplified In Breast cancer gene 1 (AIB1) was analyzed as an independent genetic risk factor influencing breast cancer onset in carriers of mutation in breast cancer predisposing gene 1 (BRCA1). We have implemented efficient, cost-effective and rapid method for analysis of the AIB1 polyglutamine repeat polymorphism based on DHPLC analysis (WAVE system) of unlabeled PCR products. This strategy can be useful for genotyping of other trinucleotide repeat polymorphisms using DHPLC in medium/high throughput settings.  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