全文获取类型
收费全文 | 26188篇 |
免费 | 4320篇 |
国内免费 | 2698篇 |
专业分类
化学 | 18626篇 |
晶体学 | 318篇 |
力学 | 1582篇 |
综合类 | 132篇 |
数学 | 3035篇 |
物理学 | 9513篇 |
出版年
2024年 | 14篇 |
2023年 | 540篇 |
2022年 | 608篇 |
2021年 | 819篇 |
2020年 | 1128篇 |
2019年 | 1110篇 |
2018年 | 905篇 |
2017年 | 821篇 |
2016年 | 1285篇 |
2015年 | 1247篇 |
2014年 | 1419篇 |
2013年 | 1910篇 |
2012年 | 2500篇 |
2011年 | 2574篇 |
2010年 | 1697篇 |
2009年 | 1610篇 |
2008年 | 1752篇 |
2007年 | 1586篇 |
2006年 | 1427篇 |
2005年 | 1192篇 |
2004年 | 875篇 |
2003年 | 670篇 |
2002年 | 599篇 |
2001年 | 448篇 |
2000年 | 434篇 |
1999年 | 511篇 |
1998年 | 424篇 |
1997年 | 427篇 |
1996年 | 446篇 |
1995年 | 354篇 |
1994年 | 303篇 |
1993年 | 233篇 |
1992年 | 234篇 |
1991年 | 201篇 |
1990年 | 170篇 |
1989年 | 142篇 |
1988年 | 95篇 |
1987年 | 109篇 |
1986年 | 88篇 |
1985年 | 82篇 |
1984年 | 47篇 |
1983年 | 43篇 |
1982年 | 35篇 |
1981年 | 18篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1976年 | 9篇 |
1975年 | 11篇 |
1936年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 20 毫秒
81.
82.
High‐Nuclear Organometallic Copper(I)–Alkynide Clusters: Thermochromic Near‐Infrared Luminescence and Solution Stability 下载免费PDF全文
Hong‐Yan Zhuo Dr. Hai‐Feng Su Zhao‐Zhen Cao Wei Liu Prof. Shu‐Ao Wang Lei Feng Dr. Gui‐Lin Zhuang Dr. Shui‐Chao Lin Prof. Mohamedally Kurmoo Prof. Chen‐Ho Tung Dr. Di Sun Prof. Lan‐Sun Zheng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(49):17619-17626
Cu(CF3COO)2 reacts with tert‐butylacetylene (tBuC≡CH) in methanol in the presence of metallic copper powder to give two air‐stable clusters, [CuI15(tBuC≡C)10(CF3COO)5]?tBuC≡CH ( 1 ) and [CuI16(tBuC≡C)12(CF3COO)4(CH3OH)2] ( 2 ). The assembly process involves in situ comproportionation reaction between Cu2+ and Cu0 and the formation of two different clusters is controlled by reactants concentration. The clusters consist of Cu15 and Cu16 cores co‐stabilized by strong by σ‐ and π‐bonded tert‐butylethynide and CF3COO? (together with methanol molecule in 2 ). Their stabilities in solution were confirmed using electrospray ionization mass spectrometry in which the cluster core remains intact for 1 in chloroform and acetone, and for 2 in acetonitrile. Strong thermochromic luminescence in the near infrared (NIR) region was observed in the solid‐state. Of particular interest, the emission maximum of 1 is red‐shifted from 710 nm at 298 K to 793 nm at 93 K, along with a 17‐fold fluorescence enhancement. In contrast, 2 exhibits red shift from 298 to 123 K followed by blue shift from 123 to 93 K. The emission wavelength was correlated with the structural parameters using variable‐temperature X‐ray single‐crystal analyses. The rich cuprophilic interaction plays a significant role in the formation of 3LMCT (tBuC≡C→Cux) excited state mixed with cluster‐centered (3CC) characters, which can be considerably influenced by temperature, leading to thermochromic luminescence. The present work provides 1) a new synthetic protocol for the high‐nuclear CuI–alkynyl clusters; 2) a comprehensive insight into the mechanism of thermochromic luminescence; 3) unusual emissive materials with the characters of NIR and thermochromic luminescence simultaneously. 相似文献
83.
Sulfur and Nitrogen Codoped Carbon Tubes as Bifunctional Metal‐Free Electrocatalysts for Oxygen Reduction and Hydrogen Evolution in Acidic Media 下载免费PDF全文
Tao Sun Prof. Qiang Wu Yufei Jiang Zhiqi Zhang Lingyu Du Prof. Lijun Yang Prof. Xizhang Wang Prof. Zheng Hu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(30):10261-10261
Invited for the cover of this issue is the group of Qiang Wu and Zheng Hu at Nanjing University. The image depicts sulfur and nitrogen codoped carbon tubes as bifunctional metal‐free electrocatalysts for oxygen reduction and hydrogen evolution in acidic media. Read the full text of the article at 10.1002/chem.201601535 . 相似文献
84.
85.
Changyong Sun Guangzong Fang Xiaoguang Guo Yuanli Hu Shuqi Ma Tianhua Yang Jie Han Hao Ma Dali Tan Xinhe Bao 《天然气化学杂志》2015,(3):257-263
Long-term stability test of Mo/HZSM-5-N catalysts(HZSM-5-N stands for nano-sized HZSM-5) in methane dehydroaromatization(MDA)reaction has been performed with periodic CH4-H2 switch at 1033-1073 K for more than 1000 h.During this test,methane conversion ranges from 13% to 16%,and mean yield to aromatics(i.e.benzene and naphthalene) exceeds 10%.N2-physisorption,XRD,NMR and TPO measurements were performed for the used Mo/HZSM-5 catalysts and coke deposition,and the results revealed that the periodic hydrogenation can effectively suppress coke deposition by removing the inert aromatic-type coke,thus ensuring Mo/HZSM-5 partly maintained its activity even in the presence of large amount of coke deposition.The effect of zeolite particle size on the catalytic activity was also explored,and the results showed that the nano-sized zeolite with low diffusion resistance performed better.It is recognized that the size effect was enhanced by reaction time,and it became more remarkable in a long-term MDA reaction even at a low space velocity. 相似文献
86.
Metal‐Free Reaction of ortho‐Carbonylated Alkynyl‐Substituted Arylaldehydes with Common Amines: Selective Access to Functionalized Isoindolinone and Indenamine Derivatives 下载免费PDF全文
Dr. Ziping Cao Hongbo Zhu Dr. Xin Meng Jun Guan Qiang Zhang Laijin Tian Xuejun Sun Guang Chen Prof. Dr. Jinmao You 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(47):16979-16985
Herein we describe a reaction of ortho‐carbonylated alkynyl‐substituted arylaldehydes with common primary amines that can provide functionalized isoindolinone and 3‐hydroxylindenamine products in high yields. Depending on the substituent size of primary amines, two distinct reaction pathways were exploited selectively, that are, an initial aza‐conjugate addition followed by hydrogen transfer to access isoindolinone framework and a unique oxa‐conjugate addition followed by Petasis–Ferrier rearrangement to afford indenamine derivatives. In the presence of Et3N, the reaction property of small primary amines was changed, proceeding to afford 3‐hydroxylindenamine derivatives efficiently. These products contain interesting substructures that exist in many natural products and bioactive molecules. The reaction features contain the use of transition‐metal‐free catalysts, simple operation, broad substrate scope, and product diversity. 相似文献
87.
A Preliminary Study of Diastereoselectivity in the PdII‐Catalyzed C(sp3)‐H Alkoxylation of Cyclic Systems 下载免费PDF全文
Xinglin Yang Tian‐Yu Sun Prof. Yu Rao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(10):3273-3277
Primary mechanism of a PdII‐catalyzed 8‐aminoquinoline‐directed C?H alkoxylation was investigated. It was understood that the PdII‐catalyzed C(sp3)?O bond formation proceeded through a concerted reductive elimination from the PdIV intermediate in the cyclic system. Deuteration experiments and related computational studies elucidate that intrinsic conformation determined the diastereoselectivity of the PdII‐catalyzed C?H alkoxylation of cyclic carboxylic acids. 相似文献
88.
Inside Back Cover: Deciphering a Nanocarbon‐Based Artificial Peroxidase: Chemical Identification of the Catalytically Active and Substrate‐Binding Sites on Graphene Quantum Dots (Angew. Chem. Int. Ed. 24/2015) 下载免费PDF全文
89.
90.
Dawei Chen Ridao Chen Ruishan Wang Jianhua Li Kebo Xie Chuancai Bian Lili Sun Xiaolin Zhang Jimei Liu Lin Yang Fei Ye Xiaoming Yu Jungui Dai 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(43):12869-12873
The catalytic promiscuity of the novel benzophenone C‐glycosyltransferase, MiCGT, which is involved in the biosynthesis of mangiferin from Mangifera indica, was explored. MiCGT exhibited a robust capability to regio‐ and stereospecific C‐glycosylation of 35 structurally diverse druglike scaffolds and simple phenolics with UDP‐glucose, and also formed O‐ and N‐glycosides. Moreover, MiCGT was able to generate C‐xylosides with UDP‐xylose. The OGT‐reversibility of MiCGT was also exploited to generate C‐glucosides with simple sugar donor. Three aryl‐C‐glycosides exhibited potent SGLT2 inhibitory activities with IC50 values of 2.6×, 7.6×, and 7.6×10−7 M , respectively. These findings demonstrate for the first time the significant potential of an enzymatic approach to diversification through C‐glycosidation of bioactive natural and unnatural products in drug discovery. 相似文献