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   1181篇
  免费   91篇
  国内免费   2篇
  1274篇
  2022年   14篇
  2021年   31篇
  2020年   24篇
  2019年   17篇
  2018年   23篇
  2017年   25篇
  2016年   45篇
  2015年   49篇
  2014年   46篇
  2013年   71篇
  2012年   61篇
  2011年   79篇
  2010年   37篇
  2009年   41篇
  2008年   54篇
  2007年   53篇
  2006年   48篇
  2005年   46篇
  2004年   44篇
  2003年   29篇
  2002年   38篇
  2001年   28篇
  2000年   34篇
  1999年   29篇
  1998年   17篇
  1997年   11篇
  1996年   9篇
  1995年   15篇
  1994年   8篇
  1993年   7篇
  1992年   16篇
  1991年   16篇
  1990年   11篇
  1989年   14篇
  1988年   9篇
  1987年   10篇
  1986年   14篇
  1985年   11篇
  1984年   8篇
  1982年   7篇
  1980年   11篇
  1979年   14篇
  1978年   9篇
  1977年   11篇
  1975年   6篇
  1974年   7篇
  1973年   10篇
  1969年   5篇
  1968年   8篇
  1966年   13篇
排序方式: 共有1274条查询结果,搜索用时 9 毫秒
61.
Thermoprecipitation of lysozyme from egg white was demonstrated using copolymers of N-isopropylacrylamide with acrylic acid, methacrylic acid, 2-acryloylamido-2-methylpropane-sulfonic acid and itaconic acid, respectively. Polymers synthesized using molar feed ratio of N-isopropylacrylamide:acidic monomers of 98:2 exhibited lower critical solution temperatures in the range of 33--35 degrees C. These polymers exhibited electrostatic interactions with lysozyme and inhibited its bacteriolytic activity. The concentration of acidic groups required to attain 50% relative inhibition of lysozyme by the polymers, was 10(4)--10(5) times lower than that required for the corresponding monomers. This was attributed to the multimeric nature of polymer-lysozyme binding. More than 90% lysozyme activity was recovered from egg white. Polymers exhibited reusability up to at least 16 cycles with retention of >85% recovery of specific activity from aqueous solution. In contrast, copolymer comprising natural inhibitor of lysozyme i.e. poly (N-isopropylacrylamide-co-O-acryloyl N-acetylglucosamine) lost 50% recovery of specific activity. Thermoprecipitation using these copolymers, which enables very high recovery of lysozyme from egg white, would be advantageous over pH sensitive polymers, which generally exhibit lower recovery.  相似文献   
62.
Inflammatory bowel disease (IBD) is a relapsing inflammation of intestine, which is mediated by release of inflammatory mediators. Both cyclo-oxygenase product prostaglandin (PGE2) and lipo-oxygenase product leukotriene (LTB4), may contribute to the pathogenesis of the inflammatory response. Nimesulide, a preferential COX-2 inhibitor was evaluated for its efficacy against experimental colitis in two different models (acetic acid- and LTB4-induced IBD) in rats. Inflammatory response was induced by intrarectal single administration of acetic acid or LTB4. Nimesulide (9 and 18 mg/kg, p.o.) significantly prevented development of inflammatory changes, decreased myeloperoxidase (MPO) activity, and also restored the altered contractility response of the isolated colon segment to KCl. The results suggested the involvement of both cyclo-oxygenase (COX) and lipo-oxygenase-mediated proinflammatory agents in colonic inflammatory process associated with IBD. Further, this study suggests that such therapeutic interventions may be of value in the treatment of IBD.  相似文献   
63.
The phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway plays an important role in mediating survival signals in wide variety of neurons and cells. Recent studies show that Akt also regulates metabolic pathways to regulate cell survival. In this study, we reported that cyclin-dependent kinase-5 (Cdk5) regulates Akt activity and cell survival through the neuregulin-mediated PI 3-kinase signaling pathway. We found that brain extracts of Cdk5-/-mice display a lower PI 3-kinase activity and phosphorylation of Akt compared with that in wild type mice. Moreover, we demonstrated that Cdk5 phosphorylated Ser-1176 in the neuregulin receptor ErbB2 and phosphorylated Thr-871 and Ser-1120 in the ErbB3 receptor. We identified the Ser-1120 sequence RSRSPR in ErbB3 as a novel phosphorylation consensus sequence of Cdk5. Finally, we found that Cdk5 activity is involved in neuregulin-induced Akt activity and neuregulin-mediated neuronal survival. These findings suggest that Cdk5 may exert a key role in promoting neuronal survival by regulating Akt activity through the neuregulin/PI 3-kinase signaling pathway.  相似文献   
64.
In vitro studies were initiated with Withania somnifera (L.) Dun. for rapid micropropagation of selected chemotypes using nodes, internodes, hypocotyls and embryo explants. Direct regeneration of shoot buds was observed in MS basal medium supplemented with various concentrations of either benzyladenine (BA) or thidiazouron (TDZ) depending on the explant. Nodal explants formed multiple shoots both from pre-existing and de novo buds on Murashige and Skoog's medium (MS) containing 0.1–5.0 mg l−1 BA and a ring of de novo shoot buds on MS medium containing 0.2 and 0.3 mg l−1 TDZ. Internodal explants formed shoot buds on MS with 1.0 and 5.0 mg l−1 BA while the hypocotyl explants gave rise to multiple shoots only on MS with 0.5 mg l−1 BA. Isolated embryos gave rise to many shoot buds on MS with 0.2 and 0.3 mg l−1 TDZ. The shoot buds elongated and rooted either on MS medium with 0.01 mg l−1 BA or on half strength MS medium lacking growth regulators, which depended upon the growth regulator used in the shoot bud induction medium. Except for the embryo-derived plantlets, all other plantlets could be acclimatized with 100% success. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   
65.
The efficient delivery of plasmids encoding antigenic determinants into dendritic cells (DCs) that control immune response is a promising strategy for rapid development of new vaccines. In this study, we prepared a series of targeted cationic lipoplex based on two synthetic lipid components, mannose-poly(ethylene glycol, MW3000)-1,2-distearoyl-sn-glycero-3-phosphoethanolamine (Mannose-PEG3000-DSPE) and O-(2R-1,2-di-O-(1'Z-octadecenyl)-glycerol)-3-N-(bis-2-aminoethyl)-carbamate (BCAT), that were formulated with 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) for evaluation as nonviral vectors for transgene expression in DCs. First, we optimized the N/P ratio for maximum transfection and then screened the effects of mannose targeting for further enhancement of transfection levels. Our results indicate that efficient delivery of gWIZ GFP plasmid into DCs was observed for mannose compositions of ~10%, whereas low transfection efficiencies were observed with nontargeted formulations. Mannose-targeted lipofectamine complexes also showed high GFP expression levels in DCs relative to nontargeted lipofectamine controls. The best transfection performance was observed using 10 mol % Mannose-PEG3000-DSPE, 60 mol % BCAT, and 30 mol % DOPE, indicating that the most efficient delivery into DCs occurs via synergistic interaction between mannose targeting and acid-labile, fusogenic BCAT/DOPE formulations. Our data suggest that mannose-PEG3000-DSPE/BCAT/DOPE formulations may be effective gene delivery vehicles for the development of DC-based vaccines.  相似文献   
66.
67.
A disturbed fatty acid metabolism increases the risk of adult non-communicable diseases. This study examines the effect of maternal micronutrients on the fatty acid composition, desaturase activity, mRNA levels of fatty acid desaturases and transport proteins in the liver. Pregnant female rats were divided into 6 groups at 2 levels of folic acid both in the presence and absence of vitamin B(12). The vitamin B(12) deficient groups were supplemented with omega 3 fatty acid. An imbalance of maternal micronutrients reduces liver docosahexaenoic acid, increases Δ5 desaturase activity but decreases mRNA levels, decreases Δ6 desaturase activity but not mRNA levels as compared to control. mRNA level of Δ5 desaturase reverts back to the levels of the control group as a result of omega 3 fatty acid supplementation. Our data for the first time indicates that maternal micronutrients differentially alter the activity and expression of fatty acid desaturases in the liver.  相似文献   
68.
The molecular pathogenesis of avian influenza infection varies greatly with individual bird species and virus strain. The molecular pathogenesis of the highly pathogenic avian influenza virus (HPAIV) or the low pathogenic avian influenza virus (LPAIV) infection in avian species remains poorly understood. Thus, global immune response of chickens infected with HPAI H5N1 (A/duck/India/02CA10/2011) and LPAI H9N2 (A/duck/India/249800/2010) viruses was studied using microarray to identify crucial host genetic components responsive to these infection. HPAI H5N1 virus induced excessive expression of type I IFNs (IFNA and IFNG), cytokines (IL1B, IL18, IL22, IL13, and IL12B), chemokines (CCL4, CCL19, CCL10, and CX3CL1) and IFN stimulated genes (OASL, MX1, RSAD2, IFITM5, IFIT5, GBP 1, and EIF2AK) in lung tissues. This dysregulation of host innate immune genes may be the critical determinant of the severity and the outcome of the influenza infection in chickens. In contrast, the expression levels of most of these genes was not induced in the lungs of LPAI H9N2 virus infected chickens. This study indicated the relationship between host immune genes and their roles in pathogenesis of HPAIV infection in chickens.  相似文献   
69.
IntroductionAccording to Joint National Committee-7 (JNC-7) guidelines, a systolic blood pressure (SBP) of 120 to 139 mm Hg and/or diastolic blood pressure (DBP) of 80 to 89 mm Hg is considered as pre-hypertension. Existing evidence suggest that the cardiovascular morbidities are increasing among pre-hypertensive individuals compared to normal.ObjectiveTo assess the magnitude and factors associated with pre-hypertension among young adults (20–30 years) in coastal villages of Udupi Taluk (an area of land with a city or town that serves as its administrative centre and usually a number of villages), Udupi District, Karnataka state, India.DesignCommunity based cross sectional studySetting6 (out of total 14) coastal villages of Udupi Taluk, Karnataka state, India.Sample1,152 young adults (age group: 20–30 years) selected by stratified random sampling in 6 coastal villages of Udupi Taluk, Karnataka state, IndiaMethodA semi structured pre-tested questionnaire was used to elicit the details on socio-demographic variables, dietary habits, tobacco use, alcohol consumption, physical activity, family history of hypertension and stress levels. Anthropometric measurements and blood pressure were recorded according to standard protocols. Serum cholesterol was measured in a sub sample of the study population. Multivariate logistic regression was applied to identify the independent correlates of pre-hypertension among young adults (20–30 years).ResultsThe prevalence of pre-hypertension in the study population was 45.2% (95%CI: 42.4–48). Multivariate logistic regression analysis revealed that age group of 25–30 years (adj OR: 4.25, 95% CI: 2.99–6.05), white collared (adj OR: 2.29, 95% CI: 1.08–4.85) and skilled occupation (adj OR: 3.24, 95% CI: 1.64–6.42), students (adj OR: 2.46, 95% CI: 1.22–4.95), using refined cooking oil (adj OR: 0.53, 95% CI: 0.29–0.95), extra salt in meals (adj OR: 2.46, 95% CI: 1.52–3.99), salty food items (adj OR: 6.99, 95% CI: 3.63–13.48), pre-obese (adj OR: 1.66, 95% CI: 1.03–2.67) and obese (adj OR: 9.16, 95% CI: 2.54, 36.4) were the significant correlates of pre-hypertension.ConclusionIn the study population, prevalence of pre-hypertension among young adults (20–30 years) was high (45.2%). Biological (age 25–30 years, pre-obesity and obesity) and behavioral (sedentary occupation, intake of extra salt in meals/salty food and not using refined cooking oil) factors were associated with pre-hypertension. Study emphasizes the need of community based screening of pre-hypertension under National Rural Health Mission. It also provides apt information for the evidence based designing of interventions for lifestyle modifications among high risk young adults in the study area.  相似文献   
70.
Maternal nutrition is an important determinant of one-carbon metabolism that lies at the heart of intrauterine epigenetic programming. Exchange of nutrients and other vital molecules between the mother and fetus takes place across the placenta and hence may play direct role in fetal programming. Pre-eclampsia (PE) originates in the placenta and altered maternal nutrition may influence epigenetic patterns in the placenta, thereby affecting birth outcome. In the present study, we investigated the global DNA methylation levels in placentas of pre-eclampsia women (i.e., women delivering at term and those delivering preterm) and studied their associations with maternal blood pressure and birth outcome. Increased homocysteine and global DNA methylation levels were seen in the pre-eclampsia group (term and preterm PE) when compared with the normotensive group (p?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