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   6623篇
  免费   435篇
  国内免费   11篇
  7069篇
  2024年   20篇
  2023年   78篇
  2022年   269篇
  2021年   384篇
  2020年   146篇
  2019年   181篇
  2018年   273篇
  2017年   179篇
  2016年   261篇
  2015年   394篇
  2014年   382篇
  2013年   488篇
  2012年   485篇
  2011年   462篇
  2010年   281篇
  2009年   235篇
  2008年   274篇
  2007年   290篇
  2006年   231篇
  2005年   182篇
  2004年   177篇
  2003年   137篇
  2002年   136篇
  2001年   95篇
  2000年   70篇
  1999年   56篇
  1998年   41篇
  1997年   37篇
  1996年   29篇
  1995年   30篇
  1994年   24篇
  1993年   24篇
  1992年   54篇
  1991年   39篇
  1990年   50篇
  1989年   48篇
  1988年   37篇
  1987年   31篇
  1986年   35篇
  1985年   29篇
  1984年   38篇
  1983年   33篇
  1982年   32篇
  1981年   34篇
  1980年   40篇
  1979年   18篇
  1978年   28篇
  1977年   20篇
  1974年   22篇
  1973年   20篇
排序方式: 共有7069条查询结果,搜索用时 0 毫秒
991.
We aimed to study MLH1 and MGMT methylation status in Helicobacter pylori-associated chronic gastritis in Egyptian patients with and without gastric cancer. 39 patients were included in our study. They were divided into 2 groups; patients without (group I) and with gastric adenocarcinoma (group II). Patients were subjected to clinical examination, abdominal ultrasound and upper endoscopy for gastric biopsy. Biopsies were subjected to urease test, histological examination, and DNA purification. H. pylori, Braf, Kras, MLH1 and MGMT methylation were assessed by quantitative PCR. DNA sequencing was performed to assess Braf and Kras genes mutation. qPCR of H. pylori was significantly higher in patients with adenocarcinoma (group II) than those without adenocarcinoma (group I); with a p < 0.001 as well as in patients with age above 50 years with a p value = 0.008. By applying logistic regression analysis it was reported that the H. pylori qPCR is a significant predictor to the adenocarcinoma with OR = 1.025 (95 % CI: 1. 002–1.048), with sensitivity of 90 % and specificity of 100 %. Adenocarcinoma patients had a significantly higher mean age and levels of H. Pylori, Braf, K-ras, methylated MGMT and methylated MLH1 than those of gastritis patients. DNA sequence analysis of Braf (codon 12) and Kras (codon 600) had genes mutation in gastric adenocarcinoma versus chronic gastritis. Conclusion: H. pylori may cause epigenetic changes predisposing the patients to cancer stomach. Estimation of H. pylori by qPCR can be a good predictor to adenocarcinoma. Braf and Kras genes mutation were reveled in gastritis and adenocarcinoma patients.  相似文献   
992.
Eight sweet pepper plant samples showing viral and viral like symptoms were collected from open field and used for detecting viral infections through biological, serological and biochemical methods. DAS-ELISA, DBIA and TPIA have relative effectiveness for detecting parenchymal viruses (CMV, TMV and PVY) and vascular virus (TYLCV), and the DAS-ELISA and TPIA are found more efficient (87.5%) than DBIA (78.1%). The examined leaf samples were found co-infected with different mixed types of viruses including (CMV, TMV, PVY and TYLCV), (CMV, PVY and TYLCV), (TMV, PVY and TYLCV) and (TMV and TYLCV) that enhanced different degrees of severe external symptoms. There are 2 out of 8 samples infected with Phytoplasma sp. by Diene’s stain and PCR using generated 16S rDNA gene primer with expected amplicon size of 680?bp. The co-infections with various viruses and phytoplasma has 12.5% frequency that reduced the levels of protein content, peroxidase and polyphenol oxidase activity quantitatively and qualitatively in 2 samples in comparison with other mixed categories. The sweet pepper plant can be considered as a reservoir for parenchymal and vascular viruses and Phytoplasma sp. due to the synergistic and antagonistic effects causing unusual and unpredictable biological and epidemiological, viral and viral-like via host biochemical effects.  相似文献   
993.
994.
995.
996.
997.
Infant mortality in Bangladesh: a review of recent evidence   总被引:1,自引:0,他引:1  
Estimates of child mortality are mainly based on reports by mothers on the survival status of their children. Infant mortality estimates from such data do not seem to have declined in recent years. The Bangladesh Bureau of Statistics sample registration infant mortality estimates appear to be suspiciously low.  相似文献   
998.
1. Platelet phospholipid compositions were studied in four species of phocid seals consuming herring or herring and shrimp and in human subjects consuming a normal mixed diet. 2. There were no major differences in platelet phospholipid, cholesterol and protein levels between different species of seal nor between seals and human subjects, nor in the relative abundance of the individual types of phospholipid. 3. The seal platelet phospholipids (phosphatidylcholine (PC) and phosphatidylethanolamine (PE), were greatly enriched in the omega 3 fatty acid, eicosapentaenoic acid (EPA) and depressed in arachidonic acid (AA) relative to the corresponding human platelet phospholipids. 4. Much less accumulation of EPA in phosphatidylserine (PS) and phosphatidylinositol (PI) was found. 5. The EPA contents of the individual seal platelet phospholipids exhibited considerable differences (including EPA discrimination from PI) but gave patterns which were generally similar to those reported for human volunteers consuming fish/fish oils enriched in EPA. 6. These results suggest that the seal platelet may be a useful model for studying the metabolism and function of the omega 3 fatty acids, such as EPA, in relation to platelet reactivity, phospholipid turnover and the formation of AA- and EPA-derived eicosanoids.  相似文献   
999.
1000.
We have previously demonstrated a depression of airway H2-receptor function in sheep allergic to Ascaris suum antigen. To investigate whether this is a generalized defect, we studied the H1- and H2- histamine receptor functions in the pulmonary and systemic circulations of allergic and nonallergic sheep. Pulmonary arterial pressure, and cardiac output were measured for calculation of pulmonary vascular resistance (PVR) and systemic vascular resistance (SVR) before and immediately after a rapid intrapulmonary infusion of histamine (10 micrograms/kg), with and without pretreatment with H1- (chlorpheniramine) and H2- (metiamide) antagonists. Histamine alone increased mean PVR to 435 and 401% of base line and decreased mean SVR by 51 and 54% in the nonallergic and allergic sheep, respectively (P less than 0.001). In the nonallergic sheep following pretreatment with chlorpheniramine (selective H2 stimulation) or metiamide (selective H1 stimulation), histamine decreased SVR by 18 and 36%, respectively, suggesting that approximately two-thirds of the vasodepressor response was mediated by H1-receptors and one-third by H2-receptors. Combined H1- and H2-antagonists completely blocked the histamine response. In allergic sheep the histamine-induced decrease in SVR was primarily mediated by H1-receptors, because the response was blocked by H1-antagonist, chlorpheniramine, and the H2-antagonist, metiamide, had no effect. In the pulmonary circulation selective H1-stimulation caused a similar increase in PVR in allergic (365%) and nonallergic sheep (424%), whereas selective H2-stimulation caused a significant decrease in PVR in the nonallergic group (14%) but not in the allergic group.(ABSTRACT TRUNCATED AT 250 WORDS)  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