全文获取类型
收费全文 | 22747篇 |
免费 | 2835篇 |
国内免费 | 2541篇 |
专业分类
化学 | 11432篇 |
晶体学 | 126篇 |
力学 | 874篇 |
综合类 | 143篇 |
数学 | 1603篇 |
物理学 | 5309篇 |
综合类 | 8636篇 |
出版年
2024年 | 104篇 |
2023年 | 381篇 |
2022年 | 701篇 |
2021年 | 740篇 |
2020年 | 767篇 |
2019年 | 748篇 |
2018年 | 597篇 |
2017年 | 595篇 |
2016年 | 821篇 |
2015年 | 967篇 |
2014年 | 1113篇 |
2013年 | 1349篇 |
2012年 | 1549篇 |
2011年 | 1647篇 |
2010年 | 1126篇 |
2009年 | 1145篇 |
2008年 | 1277篇 |
2007年 | 1087篇 |
2006年 | 1059篇 |
2005年 | 985篇 |
2004年 | 787篇 |
2003年 | 849篇 |
2002年 | 1064篇 |
2001年 | 904篇 |
2000年 | 610篇 |
1999年 | 725篇 |
1998年 | 587篇 |
1997年 | 492篇 |
1996年 | 489篇 |
1995年 | 451篇 |
1994年 | 404篇 |
1993年 | 336篇 |
1992年 | 330篇 |
1991年 | 308篇 |
1990年 | 263篇 |
1989年 | 232篇 |
1988年 | 184篇 |
1987年 | 135篇 |
1986年 | 83篇 |
1985年 | 48篇 |
1984年 | 24篇 |
1983年 | 22篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1959年 | 2篇 |
1957年 | 3篇 |
1955年 | 1篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Qian Lei Yawen Wei Dinesh Talwar Prof. Chao Wang Prof. Dong Xue Prof. Jianliang Xiao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(12):4021-4029
Reductive amination of various ketones and aldehydes by transfer hydrogenation under aqueous conditions has been developed, by using cyclometallated iridium complexes as catalysts and formate as hydrogen source. The pH value of the solution is shown to be critical for a high catalytic chemoselectivity and activity, with the best pH value being 4.8. In comparison with that in organic solvents, the reductive amination in an aqueous phase is faster, and the molar ratio of the substrate to the catalyst (S/C) can be set as high as 1×105, the highest S/C value ever reported in reductive amination reactions. The catalyst is easy to access and the reaction is operationally simple, allowing a wide range of ketones and aldehydes to react with various amines in high yields. The protocol provides a practical and environmental friendly new method for the synthesis of amine compounds. 相似文献
992.
Zhen Wang Zuliang Zhang Qian Yao Prof. Dr. Xiaohua Liu Yunfei Cai Dr. Lili Lin Prof. Dr. Xiaoming Feng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(26):8591-8596
The highly Z‐selective asymmetric conjugate addition of 3‐substituted oxindoles to alkynyl carbonyl compounds has been developed by using scandium complexes of chiral N,N′‐dioxides under mild conditions. The thermodynamically unstable Z‐olefin derivatives were obtained in excellent yields and high enantiomeric and geometric control. The catalyst was also found to be effective in the asymmetric acetylenic substitution reaction of 3‐substituted oxindoles, giving excellent enantioselectivities. 相似文献
993.
Dr. Xiaolong Liang Xiaoda Li Lijia Jing Peng Xue Lingdong Jiang Prof. Qiushi Ren Prof. Dr. Zhifei Dai 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(47):16113-16121
This paper reports the facile design and synthesis of a series of lipidic organoalkoxysilanes with different numbers of triethoxysilane headgroups and hydrophobic alkyl chains linked by glycerol and pentaerythritol for the construction of cerasomes with regulated surface siloxane density and controlled release behavior. It was found that the number of triethoxysilane headgroups affected the properties of the cerasomes for encapsulation efficiency, drug loading capacity, and release behavior. For both water‐soluble doxorubicin (DOX) and water‐insoluble paclitaxel (PTX), the release rate from the cerasomes decreased as the number of triethoxysilane headgroups increased. The slower release rate from the cerasomes was attributed to the higher density of the siloxane network on the surface of the cerasomes, which blocks the drug release channels. In contrast to the release results with DOX, the introduction of one more hydrophobic alkyl chain into the cerasome‐forming lipid resulted in a slower release rate of PTX from the cerasomes due to the formation of a more compact cerasome bilayer. An MTT viability assay showed that all of these drug‐loaded cerasomes inhibited proliferation of the HepG2 cancer cell line. The fine tuning of the chemical structure of the cerasome‐forming lipids would foster a new strategy to precisely regulate the release rate of drugs from cerasomes. 相似文献
994.
Tao Cai Zhen Yang Haijiang Li Hu Yang Aimin Li Rongshi Cheng 《Cellulose (London, England)》2013,20(5):2605-2614
In this present work, a series of hydrolyzed polyacrylamide grafted carboxymethyl cellulose (CMC-g-HPAM) was prepared. The structure and solution properties of CMC-g-HPAM were characterized by FTIR, 1H-NMR, elemental analysis and zeta potential measurements. The graft copolymers were applied as flocculants to remove methylene blue (MB), a cationic dye, from aqueous solutions. In comparison with its precursors, carboxymethyl cellulose (CMC) and polyacrylamide CMC-g-PAM, CMC-g-HPAM exhibited higher removal efficiencies. Furthermore, the flocculation performance of the copolymers was significantly improved with the increase of the hydrolysis degree, and the MB removal efficiency was more than 90 % when the hydrolysis degree of CMC-g-HPAM was higher than 80 %. More importantly, image analysis in combination with fractal theory demonstrated that the graft copolymers could produce notably denser and larger flocs, which was of great significance in practical water treatment. The improved flocculation performance was ascribed to both charge neutralization and bridging effects. 相似文献
995.
996.
以3,5-二硝基苯甲酸,咪唑为配体,合成了新化合物[Cd(H2O)2(DNBA)(Im)2](DNBA)·H2O,(DNBA=3,5-二硝基苯甲酸阴离子)。该配合物属正交晶系,空间群为Ccc2,晶胞参数:a=1.324 99(4) nm,b=1.516 01(5) nm,c=2.789 22(8) nm;V=5.602 7(3) nm3,Dc=1.719 g·cm-3,Z=8,μ=0.866 mm-1,F(000)=2 912,最终偏离因子R1=0.058 3,wR2=0.146 4。该配合物中包含两个单核镉(Ⅱ)配合物,且配合物中还包含未配位的3,5-二硝基苯甲酸,金属中心均是六配位变形八面体结构。并测定和研究了标题化合物的热重和荧光性能。 相似文献
997.
998.
A Supersymmetric AKNS Problem and Its Darboux‐Bäcklund Transformations and Discrete Systems
下载免费PDF全文
![点击此处可从《Studies in Applied Mathematics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In this paper, we consider a supersymmetric AKNS spectral problem. Two elementary and a binary Darboux transformations are constructed. By means of reductions, Darboux and Bäcklund transformations are given for the supersymmetric modified Korteweg‐de Vries, sinh‐Gordon, and nonlinear Schrödinger equations. These Darboux and Bäcklund transformations are adopted for the constructions of integrable discrete super systems, and both semidiscrete and fully discrete systems are presented. Also, the continuum limits of the relevant discrete systems are worked out. 相似文献
999.
1000.
In the presence of a water-soluble pillar[6]arene WP6 containing 12 imidazolium groups, silver nanoparticles were successfully prepared and investigated in detail by ultraviolet visible spectroscopy, X-ray diffraction, and transmission electron microscopy. Excitingly, these pillar[6]arene stabilized silver nanoparticles were demonstrated to function as a colorimetric sensor to selectively probe glutamic acid in water. 相似文献