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   26880篇
  免费   4267篇
  国内免费   4534篇
化学   21419篇
晶体学   423篇
力学   1280篇
综合类   345篇
数学   3110篇
物理学   9104篇
  2024年   59篇
  2023年   506篇
  2022年   655篇
  2021年   880篇
  2020年   1057篇
  2019年   1088篇
  2018年   866篇
  2017年   817篇
  2016年   1216篇
  2015年   1292篇
  2014年   1616篇
  2013年   2143篇
  2012年   2412篇
  2011年   2521篇
  2010年   1903篇
  2009年   1688篇
  2008年   1941篇
  2007年   1809篇
  2006年   1619篇
  2005年   1397篇
  2004年   1097篇
  2003年   937篇
  2002年   947篇
  2001年   844篇
  2000年   627篇
  1999年   554篇
  1998年   449篇
  1997年   360篇
  1996年   379篇
  1995年   326篇
  1994年   302篇
  1993年   244篇
  1992年   196篇
  1991年   183篇
  1990年   151篇
  1989年   120篇
  1988年   100篇
  1987年   59篇
  1986年   57篇
  1985年   67篇
  1984年   60篇
  1983年   37篇
  1982年   26篇
  1981年   19篇
  1980年   17篇
  1979年   5篇
  1977年   4篇
  1976年   5篇
  1973年   4篇
  1957年   6篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Herein, we successfully construct the 3D biocompatible graphene through crosslinking 2D graphene nanosheet onto carbon fiber paper with poly(diallyldimethylammonium chloride) (PDDA) as anode of the alcohol biofuel cell. Compared with the bioanode without 3D graphene, the current density and output power of PDDA-graphene-ADH bioanode is increased by 23 % and 41 % at a high concentration of ethanol at pH 8.9, suggesting the stabilization role of graphene in enzyme loading. The study provides us a deep analysis on structures and performances of the bioanode incl. electrochemistry, X-ray photoelectron spectra, and atomic force microscopy images, which is significant to develop the new methods to construct 3D porous electrodes in energy conversion device.  相似文献   
12.
Yu  Yangyang  Li  Jiajia  Yuan  Zhixuan  Fan  Yongchen  Wu  Ying 《Nonlinear dynamics》2022,109(4):3113-3132
Nonlinear Dynamics - Epilepsy is the second largest neurological disease which seriously threatens human life and health. The one important reason of inducing epileptic seizures is ischemic stroke...  相似文献   
13.
In the present research, field-amplified sample injection–CZE (FASI–CZE) coupled with a diode array detector was established to determine trace level sulfa antibiotic. Sulfathiazole, sulfadiazine, sulfamethazine, sulfadimethoxine, sulfamethoxazole, and sulfisoxazole were selected as analytes for the experiments. The background electrolyte solution consisted of 70.0 mmol/L borax and 60.0 mmol/L boric acid (including 10% methanol, pH 9.1). The plug was 2.5 mmol/L borax, which was injected into the capillary at a pressure of 0.5 psi for 5 s. Then the sample was injected into the capillary at an injection voltage of –10 kV for 20 s. The electrophoretic separation was carried out under a voltage of +19 kV. The capillary temperature was maintained at 20˚C throughout the analysis, and six sulfonamides were completely separated within 35 min. Compared with pressure injection-CZE, the sensitivity of FASI-CZE was increased by 6.25–10.0 times, and the LODs were reduced from 0.2–0.5 to 0.02–0.05 μg/mL. The method was applied to the determination of sulfonamides in river water and particulate matter samples. The recoveries were 78.59–106.59%. The intraday and interday precisions were 2.89–7.35% and 2.77–7.09%, respectively. This provides a simpler and faster method for the analysis of sulfa antibiotic residues in environmental samples.  相似文献   
14.
钙钛矿/硅叠层太阳电池可以充分利用太阳光谱,提高光电转换效率.平面硅异质结太阳电池可以作为叠层电池的底电池,其性能直接影响叠层电池的性能表现.采用传统反应热蒸发技术,在低温(170 ℃)条件下制备了掺锡氧化铟薄膜,并在170 ℃的氧气氛围下后退火处理,对ITO薄膜的特性进行了详细的表征和分析.结果表明:后退火工艺改善了ITO的结晶特性,使得材料的光学特性和电学特性得到明显提高,将其应用于平面硅异质结太阳电池,短路电流密度得到极大提高,尤其红外光响应改善明显.引入MgF2薄膜作为减反射层,进一步增强了电池的光响应,转换效率达到19.04;.  相似文献   
15.
In the paper, the authors establish several integral representations for the generating functions of the large and little Schröder numbers and for the large and little Schröder numbers.  相似文献   
16.
17.
18.
JPC – Journal of Planar Chromatography – Modern TLC - A new high-performance thin-layer chromatographic (HPTLC) method has been developed for the simultaneous estimation of...  相似文献   
19.
Journal of Thermal Analysis and Calorimetry - Based on innovative design, a liquid–vapor separation plate condenser with excellent heat transfer performance is invented. It takes less time to...  相似文献   
20.
Natural products with a variety of pharmacological effects are important sources for commercial drugs, and it is very crucial to develop effective techniques to selectively extract and isolate bioactive natural components from the plants against the background of sustainable development. Ionic liquids (ILs) are a kind of designable material with unique physicochemical properties, including good thermal stability, negligible vapor pressure, good solvation ability, etc. ILs have already been used in pharmaceuticals for extraction, purification, drug delivery, etc. It has been reported that multi-interactions, like hydrogen bonding, hydrophobic interactions, play important roles in the extraction of bioactive components from the plants. In this review, recent progress in the understanding of scientific essence of hydrogen bonding, the special interaction, in ILs was summarized. The extraction of various natural products, one important area in pharmaceutical, by conventional and functional ILs as well as the specific roles of multi-interactions in this process were also reviewed. Moreover, problems existing in bioactive compound extraction by ILs and the future developing trends of this area are given, which might be helpful for scientists, especially beginners, in this field.  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