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   45047篇
  免费   16782篇
  国内免费   5篇
  2022年   192篇
  2021年   648篇
  2020年   2325篇
  2019年   3890篇
  2018年   4041篇
  2017年   4275篇
  2016年   4429篇
  2015年   4657篇
  2014年   4341篇
  2013年   5070篇
  2012年   2968篇
  2011年   2635篇
  2010年   3773篇
  2009年   2501篇
  2008年   1696篇
  2007年   1386篇
  2006年   1293篇
  2005年   1367篇
  2004年   1321篇
  2003年   1341篇
  2002年   1415篇
  2001年   464篇
  2000年   353篇
  1999年   397篇
  1998年   347篇
  1997年   267篇
  1996年   261篇
  1995年   241篇
  1994年   219篇
  1993年   189篇
  1992年   229篇
  1991年   172篇
  1990年   153篇
  1989年   157篇
  1988年   117篇
  1987年   130篇
  1986年   116篇
  1985年   145篇
  1984年   164篇
  1983年   132篇
  1982年   194篇
  1981年   189篇
  1980年   147篇
  1979年   144篇
  1978年   138篇
  1977年   128篇
  1976年   129篇
  1975年   87篇
  1974年   98篇
  1973年   106篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
993.
994.
Acetaminophen (APAP) overdose leads to liver injury. NLRP3 inflammasome is a key player in APAP‐induced inflammation. Also, apoptosis and liver regeneration play an important role in liver injury. Therefore, we assessed allicin's protective effect on APAP‐induced hepatotoxicity and studied its effect on NLRP3 inflammasome and apoptosis. Mice in the APAP group were injected by APAP (250 mg/kg, intraperitoneal). The allicin‐treated group received allicin orally (10 mg/kg/d) during 7 days before APAP injection. Serum and hepatic tissues were separated 24 hours after APAP injection. Serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), albumin, alkaline phosphatase (ALP), and hepatic malondialdehyde (MDA) were assessed using the colorimetric method. Hepatic NLRP3 inflammasome, caspase‐1, and interleukin‐1β (IL‐1β) were estimated using enzyme‐linked immunosorbent assay. Hepatic Bcl‐2 and Ki‐67 were investigated by immunohistochemistry. APAP significantly increased AST, ALT, and ALP, whereas allicin significantly decreased their levels. Also, APAP significantly decreased albumin and allicin significantly improved it. APAP produced changes in liver morphology, including inflammation and massive coagulative necrosis. Allicin protected the liver from APAP‐induced necrosis, apoptosis, and hepatocellular degeneration via increasing Bcl‐2 and Ki‐67 levels. APAP significantly increased the hepatic MDA, whereas allicin significantly prevented this increase. APAP markedly activated the NLRP3 inflammasome pathway and consequently increased the production of caspase‐1 and IL‐1β. Interestingly, we found that allicin significantly inhibited NLRP3 inflammasome activation, which resulted in decreased caspase‐1 and IL‐1β levels. Allicin has a hepatoprotective effect against APAP‐induced liver injury via the decline of oxidative stress and inhibition of the inflammasome pathway and apoptosis. Therefore, allicin might be a novel tool to halt the progression of APAP‐stimulated hepatotoxicity.  相似文献   
995.
996.
The purpose of this study was to investigate the biological effect of miR‐16 on myocarditis and the underlying molecular mechanism. H9c2 cells were treated with 10 µg/mL lipopolysaccharide (LPS) for 12 hours to form a myocarditis injury model. We observed that LPS treatment distinctly decreased the level of miR‐16 in H9c2 cells. Upregulation of miR‐16 increased cell proliferation and reduced cell apoptosis. Then, CD40 was predicted and verified as a target gene of miR‐16 by TargetScan and luciferase reporter assay, respectively. Furthermore, the messenger RNA and protein expression of CD40 are negatively regulated by miR‐16. The relative expression of inflammatory factors was dramatically decreased by the miR‐16 mimic. Cells cotransfected with miR‐16 mimic and si‐CD40 could significantly abolish the injury of cardiomyocytes caused by myocarditis. Our study illustrated that the upregulation of miR‐16 has a protective effect on LPS‐damaged H9c2 cells, which may be achieved by regulating CD40 and the nuclear factor kappa B pathway.  相似文献   
997.
The aim of this study was to evaluate the impact that 6‐O‐(3″, 4″‐di‐Otrans‐cinnamoyl)‐α‐ l ‐rhamnopyranosylcatalpol (Dicinn) and verbascoside (Verb), two compounds simultaneously reported in Verbascum ovalifolium, have on tumor cell viability, apoptosis, cell cycle kinetics, and intracellular reactive oxygen species (ROS) level. At 100 µg/mL and 48 hours incubation time, Dicinn and Verb produced good cytotoxic effects in A549, HT‐29, and MCF‐7 cells. Dicinn induced cell‐cycle arrest at the G0/G1 phase and apoptosis, whereas Verb increased the population of subG1 cells and cell apoptosis rates. Furthermore, the two compounds exhibited time‐dependent ROS generating effects in tumor cells (1‐24 hours). Importantly, no cytotoxic effects were induced in nontumor MCF‐10A cells by the two compounds up to 100 µg/mL. Overall, the effects exhibited by Verb in tumor cells were more potent, which can be correlated with its structural features, such as the presence of phenolic hydroxyl groups.  相似文献   
998.
Heart failure (HF) is a medical condition inability of the heart to pump sufficient blood to meet the metabolic demand of the body to take place. The number of hospitalized patients with cardiovascular diseases is estimated to be more than 1 million each year, of which 80% to 90% of patients ultimately progress to decompensated HF. Digitalis glycosides exert modest inotropic actions when administered to patients with decompensated HF. Although its efficacy in patients with HF and atrial fibrillation is clear, its value in patients with HF and sinus rhythm has often been questioned. A series of recent studies have cast serious doubt on the benefit of digoxin when added to contemporary HF treatment. We are hypothesizing the role and mechanism of exosome and its biological constituents responsible for worsening the disease state and mortality in decompensated HF patients on digitalis.  相似文献   
999.
Life cycle assessment (LCA) and environmentally extended input–output analyses (EEIOA) are two techniques commonly used to assess environmental impacts of an activity/product. Their strengths and weaknesses are complementary, and they are thus regularly combined to obtain hybrid LCAs. A number of approaches in hybrid LCA exist, which leads to different results. One of the differences is the method used to ensure that mixed LCA and EEIOA data do not overlap, which is referred to as correction for double counting. This aspect of hybrid LCA is often ignored in reports of hybrid assessments and no comprehensive study has been carried out on it. This article strives to list, compare, and analyze the different existing methods for the correction of double counting. We first harmonize the definitions of the existing correction methods and express them in a common notation, before introducing a streamlined variant. We then compare their respective assumptions and limitations. We discuss the loss of specific information regarding the studied activity/product and the loss of coherent financial representation caused by some of the correction methods. This analysis clarifies which techniques are most applicable to different tasks, from hybridizing individual LCA processes to integrating complete databases. We finally conclude by giving recommendations for future hybrid analyses.  相似文献   
1000.
Calcium sulfoaluminate‐based cements (CSA) are proposed as a cement alternative with a low carbon footprint. The nature of CSA makes the manufacturing process to require lower temperature, less fuel, and less calcite. However, it requires aluminum oxide, Al2O3, which would be originated from bauxite and bauxite‐derived wastes, and sulfur, coming from calcium sulfate or elemental sulfur. An eco‐efficiency assessment of CSA cements, benchmarked against the conventional Portland cement, has been performed following the principles of ISO 14045 on eco‐efficiency for a total of 240 CSA clinker production scenarios. The eco‐efficiency indicator relates an environmental indicator with a product system value indicator, and it is calculated for each of the studied parameters: bauxite geographical origin, the fuel used for clinkering, the source of sulfur, and the composition of the clinker. Eco‐efficiency results show a strong dependence on the origin of bauxite, while other parameters, as the fuel used, its content in sulfur, or the supply of other raw materials, are of less importance. The most eco‐efficient solutions are those with certain closeness to bauxite sources. To achieve global solutions, that is, cement‐making based on CSA independently of the origin of the raw materials, the amount of bauxite needs to be minimized and CSA composition restricted.  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