首页 | 官方网站   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   195205篇
  免费   2367篇
  国内免费   628篇
工业技术   198200篇
  2021年   1193篇
  2019年   1280篇
  2018年   2123篇
  2017年   2104篇
  2016年   2171篇
  2015年   1489篇
  2014年   2615篇
  2013年   7949篇
  2012年   4463篇
  2011年   6113篇
  2010年   4932篇
  2009年   5772篇
  2008年   6147篇
  2007年   6198篇
  2006年   5634篇
  2005年   5304篇
  2004年   5252篇
  2003年   5089篇
  2002年   4892篇
  2001年   5036篇
  2000年   4568篇
  1999年   5190篇
  1998年   15440篇
  1997年   10138篇
  1996年   7715篇
  1995年   5746篇
  1994年   4979篇
  1993年   4984篇
  1992年   3347篇
  1991年   3228篇
  1990年   3197篇
  1989年   2997篇
  1988年   2755篇
  1987年   2202篇
  1986年   2270篇
  1985年   2591篇
  1984年   2297篇
  1983年   2046篇
  1982年   1885篇
  1981年   2023篇
  1980年   1778篇
  1979年   1643篇
  1978年   1644篇
  1977年   2015篇
  1976年   2692篇
  1975年   1416篇
  1974年   1358篇
  1973年   1305篇
  1972年   1113篇
  1971年   941篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
α-Tocopherol (α-Toc) has valuable biological activity, but its activity is limited when exposed to environmental factors. Nanocapsules can be used to overcome this problem. Using nanocapsules in the range of 100–200 nm is more beneficial. A 24 full factorial design was carried out to optimize the size of nanocapsules using the complex coacervation method. The four factors were the amount of the wall material, the ratio of core material to wall material, the pH of the solution, and the speed of the homogenizer. The smallest nanocapsules (176 nm) were obtained at a wall content (gelatine and pectin) of 0.8 mg, a percentage of core material (α-Toc) to wall material of 20%, a pH = 4.5, and a homogenizer speed of 12,000 rpm. The encapsulation efficiency was 90.6 ± 1.1%, and the encapsulation yield was 83.4 ± 1.6%. Assessment of the stability of α-Toc after 1 month showed that encapsulation could improve its stability in the presence of three influential factors: humidity, light, and temperature.  相似文献   
994.
995.
Information on a solar photovoltaic plant that has been created and commissioned on the roof of the administrative building in the town of Kamyshin (Volgograd oblast, Russia) is given, which is useful for further development in this area and identifies some problematic matters connected with creation of the solar plants of such type.  相似文献   
996.
997.
998.
999.
The influence of the type of solvent on the formability of acetate fibers by free-surface electrospinning has been studied. Defect-free ultrafine acetate fibers were produced using an acetic acid–formic acid binary solvent and polyethylene oxide added into the spinning solution. It has been established that using a one-layer paper filter with electrospun acetate fibers in a cigarette filter increases the efficiency of the filtration of tars and nicotine by 2.2–2.4 times.  相似文献   
1000.
To identify potential biomarkers for improving diagnosis of melioidosis, we compared plasma metabolome profiles of melioidosis patients compared to patients with other bacteremia and controls without active infection, using ultra-high-performance liquid chromatography-electrospray ionization-quadruple time-of-flight mass spectrometry. Principal component analysis (PCA) showed that the metabolomic profiles of melioidosis patients are distinguishable from bacteremia patients and controls. Using multivariate and univariate analysis, 12 significant metabolites from four lipid classes, acylcarnitine (n = 6), lysophosphatidylethanolamine (LysoPE) (n = 3), sphingomyelins (SM) (n = 2) and phosphatidylcholine (PC) (n = 1), with significantly higher levels in melioidosis patients than bacteremia patients and controls, were identified. Ten of the 12 metabolites showed area-under-receiver operating characteristic curve (AUC) >0.80 when compared both between melioidosis and bacteremia patients, and between melioidosis patients and controls. SM(d18:2/16:0) possessed the largest AUC when compared, both between melioidosis and bacteremia patients (AUC 0.998, sensitivity 100% and specificity 91.7%), and between melioidosis patients and controls (AUC 1.000, sensitivity 96.7% and specificity 100%). Our results indicate that metabolome profiling might serve as a promising approach for diagnosis of melioidosis using patient plasma, with SM(d18:2/16:0) representing a potential biomarker. Since the 12 metabolites were related to various pathways for energy and lipid metabolism, further studies may reveal their possible role in the pathogenesis and host response in melioidosis.  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-23

京公网安备 11010802026262号