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   27567篇
  免费   350篇
  国内免费   134篇
教育   19051篇
科学研究   3381篇
各国文化   235篇
体育   2306篇
综合类   17篇
文化理论   210篇
信息传播   2851篇
  2021年   235篇
  2020年   387篇
  2019年   557篇
  2018年   760篇
  2017年   682篇
  2016年   714篇
  2015年   457篇
  2014年   606篇
  2013年   4797篇
  2012年   559篇
  2011年   627篇
  2010年   492篇
  2009年   441篇
  2008年   494篇
  2007年   501篇
  2006年   480篇
  2005年   440篇
  2004年   455篇
  2003年   429篇
  2002年   403篇
  2001年   648篇
  2000年   530篇
  1999年   484篇
  1998年   254篇
  1997年   285篇
  1996年   300篇
  1995年   276篇
  1994年   261篇
  1993年   237篇
  1992年   370篇
  1991年   383篇
  1990年   394篇
  1989年   436篇
  1988年   357篇
  1987年   366篇
  1986年   362篇
  1985年   433篇
  1984年   364篇
  1983年   343篇
  1982年   292篇
  1981年   277篇
  1980年   260篇
  1979年   382篇
  1978年   302篇
  1977年   284篇
  1976年   236篇
  1975年   228篇
  1974年   239篇
  1973年   232篇
  1971年   199篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
本文对秦始皇兵马俑博物馆室内采集的长短期降尘、大气悬浮颗粒物和彩绘漆层进行了SEM-EDX研究,在大气悬浮颗粒、短期和长期降尘中,含硫颗粒的粒径分别为0.9~22.8μm、1.0~29.0μm和1.2~37.7μm,多为石膏与粘土或石英以内部混合的状态存在。降尘中的附着型絮状硫酸钙多于大气悬浮颗粒物中,显示降尘和大气中的二氧化硫发生了累进的化学反应。彩绘漆层表面的坑和裂隙附近观察到原位生长的硫酸钙晶体,显示漆层材料或降尘颗粒物与大气二氧化硫之间的酸化学反应,可能是彩绘漆层表面受侵蚀形成微小坑和裂隙的原因之一。  相似文献   
972.
Folic acid is used for preventing and treating multiple diseases and disorders, administered in the form of oral supplements. The present research work was aimed to study the influence of two non-ionic surfactants Poloxamer and Tween 80 (Polysorbate 80) on pectin submicrospheres formulations. Typical natural polymer pectin was used to encapsulate folic acid by cross linking method. The resultant submicrospheres contributed to improve the aqueous solubility to enhance the bioavailability of folic acid. During investigation, it was observed that pectin polymers influenced kinetics of the rate of reaction more intensively than the surfactants. The physical phenomenon caused the change in their size, shape and chemistry of pectin polymers transforming into submicrospheres in aqueous condition. The characteristic differences of submicrospheres were assessed by scanning electron microscopy, differential scanning calorimetry and Fourier-transform infrared spectroscopy. The average diameters of the submicrospheres ranged between 250 and 500 nm. The encapsulation efficiency of submicrospheres ranged between 80 and 96 %. The characteristic swelling behavior of lyophilized submicrospheres was influenced by the ratio of pectin polymers and folic acid used in the formulations. The submicrospheres systems exhibited controlled release of folic acid due to the pH-dependent solubility of pectin polymers in aqueous medium. The submicrospheres showed good haemocompatibility suggesting them to be promising candidates for oral delivery.  相似文献   
973.
Aim of present study was to compare the adenosine deaminase (ADA) activity in various types of arthritis conditions with synovial effusion. No. significant difference was observed in ADA activity in serum of control and study groups but results have shown a definite pattern of ADA activity in synovial fluid in various arthritic conditions. The highest value of ADA activity was observed in synovial fluid of patients with tubercular arthritis followed by rheumatoid, septic, osteo and post traumatic arthritis. Thus measurement of ADA activity in synovial fluid can be used as a parameter of differential diagnosis of arthritis specially tubercular in initial stages.  相似文献   
974.
Proteins and glutathione (GSH) levels were estimated in the experimental groups. Levels of both proteins and glutathione in the control and the treated groups were found to be significantly decreased compared to the normal group. The results show that supplementation of riboflavin has beneficial effect by alleviating the oxidant injuries to GSH and proteins, which are involved in the maintenance of transparency and protection of thiol groups of the lens. Thus, riboflavin has an active role in the lens metabolism and has a potential to improve the metabolic activity of the cataractous lenses.  相似文献   
975.
Serum Beta human chorionic gonadotropin (BhCG) was measured in 25 healthy controls and 75 cases with gestational trophoblastic neoplasms and testicular tumor using RIA kit from BARC, Bombay and ELISA kit from Abbott Diagnostics, USA. Regression Analysis of the values obtained for controls and cases by both the methods were statistically significant P 0.001.  相似文献   
976.
Serum total cholesterol and triglyceride levels were estimated in 45 dilated cardiomyopathy (DCM) patients and were compared with 31 healthy controls. The total serum cholesterol (215±50 mg/dl) and serum triglyceride (162±76 mg/dl) levels in DCM patients did not show any significant changes as compared to normal controls. The cholesterol and triglyceride and the individual lipoprotein fractions, viz HDL, VLDL, LDL and chylomicrons were analysed in 10 patients. The values did not differ significantly when compared to those of controls. These findings suggest that serum lipids may not play a role in the antietiopathogenesis of DCM.  相似文献   
977.
PCOS is a heterogeneous endocrine disorder with diverse clinical presentation. Oxidative stress plays a key role in the pathophysiology of this disease. Serumhigh sensitive C-reactive protein (hsCRP), a marker of chronic low grade inflammation, is indicative of future development of cardiovascular disease. Our aim is to evaluate the oxidant status and hsCRP levels in PCOS. The study involved 61 cases and 61 controls in the age group of 18–40 years diagnosed with PCOS. Erythrocyte malondialdehyde (MDA), superoxide dismutase (SOD), serum hsCRP, gonadotrophins, thyroid stimulating hormone, prolactin, glycemic status and lipid profile were estimated. Erythrocyte MDA (p < 0.001), SOD (p = 0.007) and serum hsCRP (p < 0.001) were significantly elevated in PCOS patients than controls. Oxidative stress is present in women with PCOS along with elevated hsCRP.  相似文献   
978.
With the rise of microfluidics for the past decade, there has come an ever more pressing need for a low-cost and rapid prototyping technology, especially for research and education purposes. In this article, we report a rapid prototyping process of chromed masks for various microfluidic applications. The process takes place out of a clean room, uses a commercially available video-projector, and can be completed in less than half an hour. We quantify the ranges of fields of view and of resolutions accessible through this video-projection system and report the fabrication of critical microfluidic components (junctions, straight channels, and curved channels). To exemplify the process, three common devices are produced using this method: a droplet generation device, a gradient generation device, and a neuro-engineering oriented device. The neuro-engineering oriented device is a compartmentalized microfluidic chip, and therefore, required the production and the precise alignment of two different masks.  相似文献   
979.
980.
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