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   25378篇
  免费   597篇
  国内免费   154篇
化学   16847篇
晶体学   192篇
力学   660篇
综合类   1篇
数学   4393篇
物理学   4036篇
  2021年   142篇
  2020年   213篇
  2019年   286篇
  2018年   233篇
  2017年   207篇
  2016年   442篇
  2015年   344篇
  2014年   456篇
  2013年   1329篇
  2012年   1195篇
  2011年   1509篇
  2010年   785篇
  2009年   616篇
  2008年   1359篇
  2007年   1404篇
  2006年   1412篇
  2005年   1409篇
  2004年   1233篇
  2003年   994篇
  2002年   886篇
  2001年   293篇
  2000年   247篇
  1999年   197篇
  1998年   207篇
  1997年   263篇
  1996年   333篇
  1995年   287篇
  1994年   270篇
  1993年   282篇
  1992年   265篇
  1991年   233篇
  1990年   226篇
  1989年   240篇
  1988年   259篇
  1987年   247篇
  1986年   240篇
  1985年   385篇
  1984年   435篇
  1983年   322篇
  1982年   428篇
  1981年   404篇
  1980年   341篇
  1979年   329篇
  1978年   348篇
  1977年   331篇
  1976年   275篇
  1975年   271篇
  1974年   263篇
  1973年   241篇
  1972年   143篇
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
1.
2.
Journal of Chemical Crystallography - Four different rare-earth oxyapatites of Ca2RE8(SiO4)6O2 (RE?=?Pr, Tb, Ho, Tm) were synthesized using a solution-based method followed by drying,...  相似文献   
3.
Journal of Fluorescence - This report describes a combined immunofluorescence and fluorescence viability stain applied as one staining solution for rapid detection of live Legionella...  相似文献   
4.
5.
Algebras and Representation Theory - We would like to correct two errors in our paper Involutions of type G2 over a field of characteristic 2 [2].  相似文献   
6.
Journal of Thermal Analysis and Calorimetry - In this study, beeswax is studied as a phase change material (PCM) to store heat due to its high latent heat. The disadvantages of using beeswax were...  相似文献   
7.
Conversion of CO2 into valuable molecules is a field of intensive investigation with the aim of developing scalable technologies for making fuels using renewable energy sources. While electrochemical reduction into CO and formate are approaching industrial maturity, a current challenge is obtaining more reduced products like methanol. However, literature on the matter is scarce, and even more for the use of molecular catalysts. Here, we demonstrate that cobalt phthalocyanine, a well‐known catalyst for the electrochemical conversion of CO2 to CO, can also catalyze the reaction from CO2 or CO to methanol in aqueous electrolytes at ambient conditions of temperature and pressure. The studies identify formaldehyde as a key intermediate and an unexpected pH effect on selectivity. This paves the way for establishing a sequential process where CO2 is first converted to CO which is subsequently used as a reactant to produce methanol. Under ideal conditions, the reaction shows a global Faradaic efficiency of 19.5 % and chemical selectivity of 7.5 %.  相似文献   
8.
Curcumin is known to display pronounced anticancer effects and a variety of other biological activities. However, the low bioavailability and fast metabolism of this molecule present an issue of concern with respect to its medicinal applications. To address this issue, structural modifications of the curcumin scaffold can be envisioned as a strategy to improve both the solubility and stability of this chemical entity, without compromising its biological activities. Previous work in our group targeted the synthesis of symmetrical azaheteroaromatic curcuminoids, which showed better solubility and cytotoxicity profiles compared to curcumin. In continuation of that work, we now focused on the synthesis of non-symmetrical nitrogen-containing curcuminoids bearing both a phenolic and an azaheteroaromatic moiety. In that way, we aimed to combine good solubility, antioxidant potential and cytotoxic properties into one molecule. Some derivatives were selected for further chemical modification of their rather labile β-diketone scaffold to the corresponding pyrazole moiety. In this way, thirteen new non-symmetrical aza-aromatic curcuminoids and four pyrazole-based analogues were successfully synthesized in a yield of 11–69 %. All newly synthesized analogues were evaluated for their antioxidant properties, reactive oxygen species (ROS) production, water solubility and anticancer activities. Several novel derivatives displayed good cytotoxicity profiles compared to curcumin, in combination with an improved water solubility and stability, and were thus identified as potential hit scaffolds for further optimization studies.  相似文献   
9.
The boom in growth of 1,4‐disubstituted triazole products, in particular, since the early 2000’s, can be largely attributed to the birth of click chemistry and the discovery of the CuI‐catalyzed azide–alkyne cycloaddition (CuAAC). Yet the synthesis of relatively simple, albeit important, 1‐substituted‐1,2,3‐triazoles has been surprisingly more challenging. Reported here is a straightforward and scalable click‐inspired protocol for the synthesis of 1‐substituted‐1,2,3‐triazoles from organic azides and the bench stable acetylene surrogate ethenesulfonyl fluoride (ESF). The new transformation tolerates a wide selection of substrates and proceeds smoothly under metal‐free conditions to give the products in excellent yield. Under controlled acidic conditions, the 1‐substituted‐1,2,3‐triazole products undergo a Michael addition reaction with a second equivalent of ESF to give the unprecedented 1‐substituted triazolium sulfonyl fluoride salts.  相似文献   
10.
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