全文获取类型
收费全文 | 2322篇 |
免费 | 207篇 |
国内免费 | 239篇 |
专业分类
化学 | 1894篇 |
晶体学 | 8篇 |
力学 | 182篇 |
综合类 | 1篇 |
数学 | 253篇 |
物理学 | 430篇 |
出版年
2024年 | 4篇 |
2023年 | 34篇 |
2022年 | 41篇 |
2021年 | 58篇 |
2020年 | 78篇 |
2019年 | 82篇 |
2018年 | 79篇 |
2017年 | 67篇 |
2016年 | 112篇 |
2015年 | 130篇 |
2014年 | 128篇 |
2013年 | 164篇 |
2012年 | 142篇 |
2011年 | 178篇 |
2010年 | 151篇 |
2009年 | 186篇 |
2008年 | 187篇 |
2007年 | 161篇 |
2006年 | 119篇 |
2005年 | 96篇 |
2004年 | 99篇 |
2003年 | 66篇 |
2002年 | 119篇 |
2001年 | 41篇 |
2000年 | 24篇 |
1999年 | 27篇 |
1998年 | 29篇 |
1997年 | 25篇 |
1996年 | 13篇 |
1995年 | 22篇 |
1994年 | 11篇 |
1993年 | 5篇 |
1992年 | 10篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 3篇 |
排序方式: 共有2768条查询结果,搜索用时 8 毫秒
41.
Thioketone‐Directed Palladium(II)‐Catalyzed C−H Arylation of Ferrocenes with Aryl Boronic Acids 下载免费PDF全文
Zhong‐Jian Cai Chen‐Xu Liu Dr. Qing Gu Prof. Dr. Shu‐Li You 《Angewandte Chemie (International ed. in English)》2018,57(5):1296-1299
A palladium(II)‐catalyzed thioketone‐chelation‐assisted direct C?H arylation of ferrocenes is described. With thioketone as an efficient directing group, various monoaryl‐ and diaryl‐substituted thiocarbonylferrocenes were obtained by palladium‐catalyzed direct C?H functionalization in high yields under mild and base‐free reaction conditions. Furthermore, the arylated thiocarbonylferrocene could undergo diverse transformations. 相似文献
42.
Herein we report, a series of new benzimidazolium chlorides as N-heterocyclic carbene (NHC) ligand and their corresponding palladium(II)-NHC complexes with the general formula [PdCl2(NHC)2] were synthesized. All new compounds were characterized by 1H NMR, 13C NMR, IR spectroscopy and elemental analysis techniques. The catalytic activity of palladium(II)-NHC complexes was investigated in the direct C2- or C5-arylation of thiazoles with aryl bromides in presence of palladium(II)-NHC at 150?°C for 1?h. These complexes exhibited the good catalytic performance for the direct arylation of thiazoles. The arylation of thiazoles regioselectively produced C2- or C5-arylated thiazoles in moderate to high yields. 相似文献
43.
Axial chirality of biaryls is found in natural products, bioactive molecules, ligands and catalysts and their synthesis is therefore highly appealing. Thus, the atroposelective palladium-catalyzed C-H functionalization of chiral biaryl sulfoxides was extended to a direct arylation reaction, affording ortho-terphenyls bearing one atropisomeric axis. The high stereoselectivities, good yields and operational simplicity, along with the traceless character of the sulfoxide moiety allows access to a wide range of optically active o-terphenyls. 相似文献
44.
Selective C vs N-arylation of 2-aminonaphthoquinone was achieved using different transition metal salts and arylboronic acids. Mn(OAc)3·2H2O provided C-arylated product whereas NiCl2·6H2O and Cu(OAc)2·H2O provided N-mono arylated and N,N-diarylated products respectively. Usefulness of the C and N arylated product was demonstrated by converting it into benzocarbazoledione. 相似文献
45.
Prof. Dr. Michio Yamada Prof. Dr. Takeshi Akasaka Prof. Dr. Shigeru Nagase 《Angewandte Chemie (International ed. in English)》2018,57(41):13394-13405
The awesome allotropy of carbon yields innumerable topologically possible cage structures of molecular carbon. This field is also related to endohedral metallofullerenes constructed by metal‐atom encapsulation. Stable and soluble empty fullerenes and endohedral metallofullerenes are available in pure form in macroscopic amounts from carbon arc production or other physical processes followed by extraction and subsequent chromatographic separation. However, many other unidentified fullerene species, which must be reactive and insoluble in their pristine forms, remain in soot. These “missing” species must have extremely small HOMO–LUMO gaps and may have unconventional cage structures. Recent progress in this field has demonstrated that reactive fullerenes can be salvaged by exohedral derivatization, which can stabilize the reactive carbon cages. This concept provides a means of preparing macroscopic amounts of unconventional fullerenes as their derivatives. 相似文献
46.
Perfluoroaryl Bicyclic Cell‐Penetrating Peptides for Delivery of Antisense Oligonucleotides 下载免费PDF全文
Justin M. Wolfe Colin M. Fadzen Rebecca L. Holden Monica Yao Gunnar J. Hanson Prof. Bradley L. Pentelute 《Angewandte Chemie (International ed. in English)》2018,57(17):4756-4759
Exon‐skipping antisense oligonucleotides are effective treatments for genetic diseases, yet exon‐skipping activity requires that these macromolecules reach the nucleus. While cell‐penetrating peptides can improve delivery, proteolytic instability often limits efficacy. It is hypothesized that the bicyclization of arginine‐rich peptides would improve their stability and their ability to deliver oligonucleotides into the nucleus. Two methods were introduced for the synthesis of arginine‐rich bicyclic peptides using cysteine perfluoroarylation chemistry. Then, the bicyclic peptides were covalently linked to a phosphorodiamidate morpholino oligonucleotide (PMO) and assayed for exon skipping activity. The perfluoroaryl cyclic and bicyclic peptides improved PMO activity roughly 14‐fold over the unconjugated PMO. The bicyclic peptides exhibited increased proteolytic stability relative to the monocycle, demonstrating that perfluoroaryl bicyclic peptides are potent and stable delivery agents. 相似文献
47.
Irina Iovel Lena Golomba Juris Popelis Alexander Gaukhman Edmunds Lukevics 《应用有机金属化学》2001,15(1):67-74
The conjugate addition of some (hetero)aromatic amides to an α,β‐unsaturated ester (ethyl acrylate) proceeds efficiently in the presence of an equimolar amount of the CsF–Si(OEt)4 system to afford the corresponding ethyl esters of N‐substituted β‐amino acids. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
48.
E. Delée L. Le Garrec I. Jullien S. Béranger J. C. Pascal H. Pinhas 《Chromatographia》1987,24(1):357-359
Summary A routine chiral analysis has been developed to control the optical purity of chiral drugs and to monitor their asymmetric
synthesis. The recent advent of new chiral stationary phases for HPLC enabled us to achieve the direct resolution of chiral
drugs without any derivatization.
The factors affecting chiral resolution on a new alpha1-acid glycoprotein column (EnantioPac, LKB) were assessed with three beta-aminoalcohols. 相似文献
49.
Summary Procedures for the quantitative analysis of industrial effluents which involve concentration by solvent extraction or the
purge-and-trap method are time-consuming, labor-intensive, and prone to error. Direct aqueous injection gas chromatography
using an electron-capture detector for the analysis of volatile halocarbons at the ppb level is in routine use in many laboratories.
We now discuss the development of a similar protocol for the analysis of volatile polar organics such as acetone, methyl ethyl
ketone, methyl isobutyl ketone, and tretrahydrofuran using a flame-ionization detector. 相似文献
50.
直接甲酸燃料电池Pd阳极催化剂及其电催化稳定性 总被引:1,自引:0,他引:1
直接甲酸燃料电池(DFAFC)中Pd阳极催化剂对甲酸氧化具有很好的电催化活性, 但电催化稳定性较差, 因此, 对Pd催化剂电催化活性和稳定性的影响原因和机理的研究已经成为DFAFC阳极催化剂的研究重点, 本文综述了DFAFC中Pd催化剂和Pd基复合催化剂的研究和发展概况. 主要介绍了Pd催化剂的优缺点、稳定性及提高稳定性的方法和机理等, 为Pd催化剂和Pd基复合催化剂的实际应用奠定基础. 相似文献