全文获取类型
收费全文 | 25702篇 |
免费 | 4843篇 |
国内免费 | 3886篇 |
专业分类
化学 | 19087篇 |
晶体学 | 430篇 |
力学 | 1615篇 |
综合类 | 274篇 |
数学 | 2664篇 |
物理学 | 10361篇 |
出版年
2024年 | 62篇 |
2023年 | 513篇 |
2022年 | 878篇 |
2021年 | 957篇 |
2020年 | 1159篇 |
2019年 | 1150篇 |
2018年 | 998篇 |
2017年 | 986篇 |
2016年 | 1325篇 |
2015年 | 1401篇 |
2014年 | 1616篇 |
2013年 | 2056篇 |
2012年 | 2547篇 |
2011年 | 2572篇 |
2010年 | 1789篇 |
2009年 | 1868篇 |
2008年 | 1906篇 |
2007年 | 1660篇 |
2006年 | 1573篇 |
2005年 | 1326篇 |
2004年 | 972篇 |
2003年 | 699篇 |
2002年 | 687篇 |
2001年 | 587篇 |
2000年 | 467篇 |
1999年 | 432篇 |
1998年 | 351篇 |
1997年 | 312篇 |
1996年 | 245篇 |
1995年 | 231篇 |
1994年 | 178篇 |
1993年 | 179篇 |
1992年 | 152篇 |
1991年 | 132篇 |
1990年 | 96篇 |
1989年 | 58篇 |
1988年 | 56篇 |
1987年 | 40篇 |
1986年 | 38篇 |
1985年 | 42篇 |
1984年 | 27篇 |
1983年 | 24篇 |
1982年 | 10篇 |
1981年 | 13篇 |
1980年 | 9篇 |
1979年 | 12篇 |
1975年 | 5篇 |
1971年 | 5篇 |
1965年 | 4篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
941.
Da Quan Zhang Xing Jin Bin Xie Hyung Goun Joo Li Xin Gao Kang Yong Lee 《Surface and interface analysis : SIA》2012,44(1):78-83
The corrosion inhibition of ammonium heltamolybdate (AH) and calcium gluconate (CG) for AA6061 alloy in 3% NaCl solution was investigated by the electrochemical measurements. It indicates that AH inhibits the corrosion of AA6061 alloy and acts as an anodic inhibitor. Maximum inhibition efficiency reaches 74.3% at the concentration of 1 × 10?4 mol.l?1 AH. The results of the electrochemical studies reveal AH is physically adsorbed on the AA6061 alloy surface and the adsorption follows Langmuir isotherm. The combination of AH and CG enhances the inhibition efficiency to 95.9%. The enhanced inhibition is attributed to the promotion of AH adsorption by CG. The mixture of AH and CG is a mixed‐type inhibitor and renders the corrosion potential to more positive values. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
942.
Copper Causes Regiospecific Formation of C4F8‐Containing Six‐Membered Rings and their Defluorination/Aromatization to C4F4‐Containing Rings in Triphenylene/1,4‐C4F8I2 Reactions
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Kerry C. Rippy Dr. Eric V. Bukovsky Dr. Tyler T. Clikeman Dr. Yu‐Sheng Chen Dr. Gao‐Lei Hou Dr. Xue‐Bin Wang Dr. Alexey A. Popov Dr. Olga V. Boltalina Prof. Steven H. Strauss 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(3):874-877
The presence of Cu in reactions of triphenylene (TRPH) and 1,4‐C4F8I2 at 360 °C led to regiospecific substitution of TRPH ortho C(β) atoms to form C4F8‐containing rings, completely suppressing substitution on C(α) atoms. In addition, Cu caused selective reductive‐defluorination/aromatization (RD/A) to form C4F4‐containing aromatic rings. Without Cu, the reactions of TRPH and 1,4‐C4F8I2 were not regiospecific and no RD/A was observed. These results, supported by DFT calculations, are the first examples of Cu‐promoted 1) regiospecific perfluoroannulation, 2) preparative C?F activation, and 3) RD/A. HPLC‐purified products were characterized by X‐ray diffraction, low‐temperature PES, and 1H/19F NMR. 相似文献
943.
Engyodontochones,Antibiotic Polyketides from the Marine Fungus Engyodontium album Strain LF069
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Prof. Dr. Bin Wu Dr. Jutta Wiese Arlette Wenzel‐Storjohann Susan Malien Dr. Rolf Schmaljohann Prof. Dr. Johannes F. Imhoff 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(22):7452-7462
Six new ( 2 , 4 – 8 ) and two known polyketides with a basic structure of an anthraquinone‐xanthone were isolated from mycelia and culture broth of the fungus Engyodontium album strain LF069. The structures and relative configurations of these compounds were established by spectroscopic means, and their absolute configurations were defined mainly by comparison of quantum chemical TDDFT calculated and experimental ECD spectra. Compounds 2 and 4 – 8 were given the trivial names engyodontochone A ( 2 ) and B–F ( 4 – 8 ). Compounds 5 – 8 represent the first example of a 23,28 seco‐beticolin carbon skeleton. The relative and absolute configurations of two known substances JBIR‐97/98 ( 1 ) and JBIR‐99 ( 3 ) were determined for the first time. All isolated compounds were subjected to bioactivity assays. Compounds 1 – 4 exhibited inhibitory activity against methicillin‐resistant Staphylococcus aureus (MRSA) that was 10‐fold stronger than chloramphenicol. 相似文献
944.
In this paper, the implementation of research-oriented teaching mode in coordination chemistry was introduced, including the strategies, main contents and evaluation. 相似文献
945.
946.
The quasi-ferrite model is proposed and an appropriate PBE exchange functional with the spin density functional theory(SDFT) is selected for the calculation of the relation between magnetic moment and residual stress in ferrite using a quantum mechanics code. The relationship between ferrite magnetism and the carbon content is determined,and then a ferrite interstitial solid solution(ISS) model in a low carbon concentration state is replaced with an α- Fe model in the case of majority magnetic calculation. The band structure of the loaded-Fe is compared with that of the unloaded α-Fe. The comparison shows that the energy of Fe atomic 3d orbital changes a little,while the energy of electron orbital of iron core below 3d almost keeps unchanged. The relationship between the magnetic moment and the stress appears intermittent due to the Bragg total reflection. The change in the magnetic moment due to lattice mismatch is much larger than that caused by mechanical loading. 相似文献
947.
948.
949.
In this Letter, we construct the quasi-normal modes of three-dimensional extremal black holes in an algebraic way. We show that the infinite towers of the quasi-normal modes of scalar, vector and tensor could be constructed as the descendents of the highest weight modes. Our investigation shows that the hidden conformal symmetry suggested in Chen et al. (2010) [5] is an intrinsic property of the extremal black hole. Moreover, we notice that we need to fix the freedom in defining the local vector fields and find the right hidden conformal symmetry to obtain the physical quasi-normal modes. 相似文献
950.