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   104893篇
  免费   17799篇
  国内免费   10227篇
化学   71463篇
晶体学   1232篇
力学   6884篇
综合类   537篇
数学   12187篇
物理学   40616篇
  2024年   240篇
  2023年   2092篇
  2022年   3076篇
  2021年   3719篇
  2020年   4255篇
  2019年   4095篇
  2018年   3467篇
  2017年   3212篇
  2016年   5085篇
  2015年   4777篇
  2014年   5843篇
  2013年   7642篇
  2012年   9353篇
  2011年   9886篇
  2010年   6506篇
  2009年   6242篇
  2008年   6620篇
  2007年   6090篇
  2006年   5545篇
  2005年   4664篇
  2004年   3446篇
  2003年   2703篇
  2002年   2445篇
  2001年   2014篇
  2000年   1800篇
  1999年   2100篇
  1998年   1868篇
  1997年   1742篇
  1996年   1923篇
  1995年   1531篇
  1994年   1486篇
  1993年   1187篇
  1992年   1089篇
  1991年   1011篇
  1990年   813篇
  1989年   577篇
  1988年   478篇
  1987年   394篇
  1986年   383篇
  1985年   325篇
  1984年   251篇
  1983年   158篇
  1982年   150篇
  1981年   111篇
  1980年   80篇
  1979年   48篇
  1978年   35篇
  1976年   36篇
  1975年   35篇
  1974年   45篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
We conducted measurements of black carbon(BC) aerosol in Jiaxing,China during autumn from September 26 to November 30,2013.We investigated temporal and diurnal variations of BC,and its correlations with meteorological parameters and other major pollutants.Results showed that hourly mass concentrations of BC ranged from 0.2 to 22.0 μg/m3,with an average of 5.1 μg/m3.The diurnai variation of BC exhibited a bimodal distribution,with peaks at 07:00 and 18:00.The morning peak was larger than the evening peak.The mass percentages of BC in PM2.5 and PM10 were 7.1%and 4.8%,respectively.The absorption coefficient of BC was calculated to be 44.4 Mm-1,which accounted for 11.1%of the total aerosol extinction.BC was mainly emitted from local sources in southwestern Jiaxing where BC concentrations were generally greater than 11 μg/m3 during the measurement period.Correlation analysis indicated that the main sources of BC were motor vehicle exhaust,and domestic and industrial combustion.  相似文献   
44.
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   
45.
46.
Hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) have been deemed as clean and sustainable strategies to solve the energy crisis and environmental problems. Various catalysts have been developed to promote the process of HER and OER. Among them, two-dimensional covalent organic frameworks (2D COFs) have received great attention due to their diverse and designable structure. In this minireview, we mainly summarize the diverse linkages of 2D COFs and strategies for enhancing the catalytic performance of 2D COFs for HER and OER, such as introducing active building blocks, metal ions and tailored linkages. Furthermore, a brief outlook for the development directions of COFs in the field of HER and OER is provided, expecting to stimulate new opportunities in future research.  相似文献   
47.
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   
48.
A photoluminescent bimetallic cluster [Ag10Cu6(bdppthi)2(C≡CPh)12(MeOH)2(H2O)](ClO4)4 ( 1 , bdppthi=N,N’-bis(diphenylphosphanylmethyl)-tetrahydroimidazole} was synthesized from the PNNP type ligand bdppthi generated in-situ. Upon excitation at 365 nm, 1 exhibited strong phosphorescent emission at 630 nm, which was selectively quenched by NH3 in air or water. The sensing of NH3 was rapid and recoverable, with detection limits of 53 ppm (v/v) in N2 and 21 μmol/L (0.36 ppm, w/w) for NH3 ⋅ H2O in water. Cluster 1 could potentially serve as a bifunctional chemical sensor for the efficient detection of ammonia in waste-gas and waste-water.  相似文献   
49.
Journal of Thermal Analysis and Calorimetry - Coal O2/CO2 combustion is a promising carbon capture and storage technology for coal-fired power plant. Char consumption rate prediction is essential...  相似文献   
50.
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