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   18848篇
  免费   1279篇
  国内免费   741篇
耳鼻咽喉   77篇
儿科学   324篇
妇产科学   185篇
基础医学   2158篇
口腔科学   127篇
临床医学   1709篇
内科学   2537篇
皮肤病学   189篇
神经病学   828篇
特种医学   403篇
外国民族医学   2篇
外科学   909篇
综合类   3421篇
预防医学   1713篇
眼科学   165篇
药学   4058篇
  8篇
中国医学   1593篇
肿瘤学   462篇
  2024年   39篇
  2023年   213篇
  2022年   375篇
  2021年   677篇
  2020年   515篇
  2019年   450篇
  2018年   440篇
  2017年   579篇
  2016年   616篇
  2015年   596篇
  2014年   1002篇
  2013年   1355篇
  2012年   995篇
  2011年   1115篇
  2010年   874篇
  2009年   808篇
  2008年   905篇
  2007年   842篇
  2006年   826篇
  2005年   702篇
  2004年   638篇
  2003年   579篇
  2002年   451篇
  2001年   488篇
  2000年   426篇
  1999年   352篇
  1998年   323篇
  1997年   316篇
  1996年   330篇
  1995年   309篇
  1994年   267篇
  1993年   236篇
  1992年   222篇
  1991年   180篇
  1990年   163篇
  1989年   171篇
  1988年   133篇
  1987年   136篇
  1986年   107篇
  1985年   169篇
  1984年   137篇
  1983年   77篇
  1982年   134篇
  1981年   96篇
  1980年   69篇
  1979年   67篇
  1978年   55篇
  1977年   55篇
  1976年   71篇
  1973年   44篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Cationic polymer PEI-CyD is doped with Nd by plasma technology to produce the gene vector: Nd@PEI-CyD. Luciferase expression and EGFP transfection experiments performed in vitro reveal that Nd@PEI-CyD has significantly higher transfection efficiency than lipofectamine 2000 and PEI-CyD and the mechanism is studied and proposed. The rare-earth element, Nd, stimulates the energy metabolism of cells, enhances cell uptake of complexes/pDNA, and regulates the cellular pathways. These special features suggest a new strategy involving metal-incorporated non-viral gene vectors.  相似文献   
993.
Cationic lipid-incorporated liposomes modified with pH-sensitive polymers were prepared by introducing 3, 5-didodecyloxybenzamidine as a cationic lipid to egg yolk phosphatidylcholine liposomes modified with 3-methylglutarylated hyperbranched poly(glycidol) (MGlu-HPG) as a pH-sensitive polymer. These liposomes were stable at neutral pH, but were destabilized below pH 6.0 because MGlu-HPG changed its characteristics from hydrophilic to hydrophobic in response to the pH decrease. Cationic lipid inclusion improved their pH sensitivity at weakly acidic pH and association of liposomes with murine dendritic cell (DC) lines. Cationic lipid-incorporated liposomes delivered entrapped ovalbumin (OVA) molecules not only to cytosol but also to endosome/lysosome. Treatment with cationic lipid-incorporated liposomes induced up-regulation of antigen presentation-involved molecules on DCs, the promotion of cytokine production, and antigen presentation via both major histocompatibility complex (MHC) class I and II molecules. Especially, antigen presentation via MHC class II was promoted by cationic lipid inclusion, which might correspond to efficient endosome/lysosome delivery of OVA. Subcutaneous administration of OVA-loaded cationic lipid-incorporated liposomes induced antigen-specific antibody production in serum and Th1-dominant immune responses in the spleen. Furthermore, administration of the cationic lipid-incorporated liposomes to mice bearing E.G7-OVA tumor more significantly reduced the tumor volume than liposomes without cationic lipids. Therefore, cationic lipid inclusion into pH-sensitive polymer-modified liposomes, which can achieve both efficient antigen intracellular delivery and activation of antigen presenting cell, is an effective approach to develop antigen carriers for efficient cancer immunotherapy.  相似文献   
994.

Background

Natural products from plants have received considerable attention in recent years due to their diverse pharmacological properties, including antioxidants and hepatoprotective activities. The protective effects of aqueous extract of Persea americana (AEPA) against carbon tetrachloride (CCl4)-induced hepatotoxicity in male albino rats was investigated.

Materials and Methods

Liver damage was induced in rats by administering a 1:1 (v/v) mixture of CCl4 and olive oil [3 ml/kg, subcutaneously (sc)] after pre-treatment for 7 days with AEPA. Hepatoprotective effects of AEPA was evaluated by estimating the activities of alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP) and levels of total bilirubin (TBL). The effects of AEPA on biomarkers of oxidative damage (lipid peroxidation) and antioxidant enzymes namely, catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione S-transferase (GST) were measured in liver post mitochondrial fraction.

Results

AEPA and Reducdyn® showed significant (p<0.05) hepatoprotective activity by decreasing the activities of ALT, AST, ALP and reducing the levels of TBL. The activities of antioxidant enzymes, levels of malondialdehyde and protein carbonyls were also decreased dose-dependently in the AEPA-treated rats. Pre-treatment with AEPA also decreased the serum levels of glutathione significantly.

Conclusion

These data revealed that AEPA possesses significant hepatoprotective effects against CCl4-induced toxicity attributable to its constituent phytochemicals. The mechanism of hepatoprotection seems to be through modulation of antioxidant enzyme system.  相似文献   
995.

Background

The antioxidant properties of ethanolic root extract of pepper fruit (Donnetia tripetala), and its effect on lipid peroxidation of some fresh beef tissues during frozen storage were investigated.

Materials and Methods

The antioxidant parameters were assessed using standard methods, while malondialdehyde levels of different fresh beef tissue sections treated with the extract prior to freezing, were estimated in a colorimetric reaction with thiobarbituric acid.

Results

The H2O2-scavenging ability of the extract was similar to that of ascorbic acid, with a maximum scavenging power of 55.61 ±4.98%, and an IC50 value of 86µg/ml. The extract exhibited a concentration-dependent ferric ion-reducing power, although this was significantly lower relative to that of the ascorbic acid (p < 0.05). The total phenolic content was 212.5 ± 0.002 mg/g, while the nitric oxide-scavenging ability was 64.33 ± 0.2% after 150 min. The capacity of the extract to inhibit lipid peroxidation in frozen heart muscle slices was significantly higher than that of vitamin C (p < 0 .05), but comparable to vitamins C and E in frozen testes and kidney slices.

Conclusion

These results suggest that the root extract of D. tripetala is rich in antioxidants which can be applied to meat preservation during refrigerated storage.  相似文献   
996.
目的探讨影响健康孕妇新生儿体重的相关因素。方法本研究为前瞻性研究,选择2013年3-8月在青岛市市立医院检查并决定在本院分娩的早孕妇女480例,排除个别妊娠合并症和并发症,共376例进入研究,追踪调查至孕妇分娩。详细记录孕妇年龄、孕前体质量、身高、分娩孕周、分娩前体质量、孕期体质量增长、新生儿体质量,并检测妊娠32~34周孕妇血脂及血糖水平,分析各因素与新生儿体质量的相关性。结果孕期体质量增长、甘油三酯水平与新生儿体质量呈正相关(r=0.213,P〈0.01;r=0.244,P〈0.001)。甘油三酯与孕前体重指数、孕期体质量增长呈正相关(r=0.172,P〈0.05;r=0.178,P〈0.01)。巨大儿组孕妇甘油三酯水平为(3.82±1.47)mmol/L,正常儿组孕妇为(3.21±1.26)mmol/L,差异有统计学意义(P〈0.05)。巨大儿组孕妇空腹血糖水平为(4.45±0.063)mmol/L,正常儿组孕妇血糖水平为(4.17±0.50)mmol/L,差异有统计学意义(P〈0.01)。结论孕妇血脂、血糖水平及孕期增重显著影响新生儿出生体重,孕期应该平衡膳食、合理增重,并进行血脂、血糖监测,对控制新生儿的体重有重要的临床意义。  相似文献   
997.
Background: Patients with chronic kidney disease (CKD) is a very high risk cardiovascular disease population and should be treated aggressively. We investigated lipid management in CKD patients with atherosclerosis in Taiwan.Methods: 3057 patients were enrolled in a multi-center study (T-SPARCLE). Lipid goal are defined as total cholesterol (TC) < 160mg/dl, low-density lipoprotein (LDL) <100 mg/dl, high-density lipoprotein (HDL) > 40 mg/dl in men, HDL > 50 mg/dl in women, non-HDL cholesterol < 130mg/dl, and triglyceride < 150 mg/dl.Results: Compared with those without CKD (n=2239), patients with CKD (n=818) had more co-morbidities (hypertension, glucose intolerance, stroke and heart failure) and lower HDL but higher triglyceride levels. Overall 2168 (70.5%) patients received lipid-lowering agents. There was similar equivalent statin potency between CKD and non-CKD groups. The goal attainment is lower in HDL and TG in the CKD group as compared with non-CKD subjects (47.1 vs. 51.9% and 63.2 vs. 68.9% respectively, both p < 0.02). Analysis of sex and CKD interaction on goals attainment showed female CKD subjects had lower non-HDL and TG goals attainment compared with non-CKD males (both p < 0.019).Conclusion: Although presenting with more comorbidities, the CKD population had suboptimal lipid goal attainment rate as compared with the non-CKD population. Further efforts may be required for better lipid control especially on the female CKD subjects.  相似文献   
998.
999.
1000.
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