全文获取类型
收费全文 | 4611篇 |
免费 | 704篇 |
国内免费 | 637篇 |
专业分类
化学 | 3808篇 |
晶体学 | 36篇 |
力学 | 274篇 |
综合类 | 62篇 |
数学 | 604篇 |
物理学 | 1168篇 |
出版年
2024年 | 7篇 |
2023年 | 76篇 |
2022年 | 112篇 |
2021年 | 119篇 |
2020年 | 169篇 |
2019年 | 166篇 |
2018年 | 143篇 |
2017年 | 121篇 |
2016年 | 225篇 |
2015年 | 209篇 |
2014年 | 280篇 |
2013年 | 351篇 |
2012年 | 395篇 |
2011年 | 344篇 |
2010年 | 322篇 |
2009年 | 282篇 |
2008年 | 276篇 |
2007年 | 247篇 |
2006年 | 257篇 |
2005年 | 205篇 |
2004年 | 190篇 |
2003年 | 193篇 |
2002年 | 298篇 |
2001年 | 256篇 |
2000年 | 139篇 |
1999年 | 119篇 |
1998年 | 87篇 |
1997年 | 50篇 |
1996年 | 46篇 |
1995年 | 38篇 |
1994年 | 45篇 |
1993年 | 10篇 |
1992年 | 17篇 |
1991年 | 27篇 |
1990年 | 25篇 |
1989年 | 17篇 |
1988年 | 15篇 |
1987年 | 16篇 |
1986年 | 11篇 |
1985年 | 11篇 |
1984年 | 9篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1972年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有5952条查询结果,搜索用时 15 毫秒
201.
An Unprecedented Two‐Fold Nested Super‐Polyrotaxane: Sulfate‐Directed Hierarchical Polythreading Assembly of Uranyl Polyrotaxane Moieties
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)
Dr. Lei Mei Dr. Qun‐yan Wu Dr. Li‐yong Yuan Dr. Lin Wang Shu‐wen An Zhen‐ni Xie Dr. Kong‐qiu Hu Prof. Zhi‐fang Chai Prof. Peter C. Burns Prof. Wei‐qun Shi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(32):11329-11338
The hierarchical assembly of well‐organized submoieties could lead to more complicated superstructures with intriguing properties. We describe herein an unprecedented polyrotaxane polythreading framework containing a two‐fold nested super‐polyrotaxane substructure, which was synthesized through a uranyl‐directed hierarchical polythreading assembly of one‐dimensional polyrotaxane chains and two‐dimensional polyrotaxane networks. This special assembly mode actually affords a new way of supramolecular chemistry instead of covalently linked bulky stoppers to construct stable interlocked rotaxane moieties. An investigation of the synthesis condition shows that sulfate can assume a vital role in mediating the formation of different uranyl species, especially the unique trinuclear uranyl moiety [(UO2)3O(OH)2]2+, involving a notable bent [O=U=O] bond with a bond angle of 172.0(9)°. Detailed analysis of the coordination features, the thermal stability as well as a fluorescence, and electrochemical characterization demonstrate that the uniqueness of this super‐polyrotaxane structure is mainly closely related to the trinuclear uranyl moiety, which is confirmed by quantum chemical calculations. 相似文献
202.
Shu‐Ting Wu Zhen‐Wen Cai Qiao‐Yan Ye Chen‐Hao Weng Xi‐He Huang Xiao‐Lin Hu Chang‐Cang Huang Nai‐Feng Zhuang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(47):13074-13078
Circular dichroism is known to be the feature of a chiral agent which has inspired scientist to study the interesting phenomena of circularly polarized light (CPL) modulated molecular chirality. Although several organic molecules or assemblies have been found to be CPL‐responsive, the influence of CPL on the assembly of chiral coordination compounds remains unknown. Herein, a chiral coordination polymer, which is constructed from achiral agents, was used to study the CPL‐induced enantioselective synthesis. By irradiation with either left‐handed or right‐handed CPL during the reaction and crystallization, enantiomeric excesses of the crystalline product were obtained. Left‐handed CPL resulted in crystals with a left‐handed helical structure, and right‐handed CPL led to crystals with a right‐handed helical structure. It is exciting that the absolute asymmetric synthesis of a chiral coordination polymer could be enantioselective when using CPL, and provides a strategy for the control of the chirality of chiral coordination polymers. 相似文献
203.
204.
205.
Titanium tetrachloride in ethyl acetate can be reduced by Mg powder to the corresponding low‐valent titanium complexes, which can reduce some aromatic aldehydes and ketones to the corresponding pinacols in 38–85% yields within 15–60 min at rt with stirring. 相似文献
206.
缆机是大坝浇筑过程中的主要运输设备之一,缆机驾驶员操作水平直接关系缆机起重作业安全.为有效提高缆机起重作业驾驶员操作行为可靠性,预防起重作业安全事故,针对缆机起重作业周期性多维运动的特点,分解驾驶员操作流程;剖析操作行为失误,建立驾驶员行为模式;从时间角度量化操作流程,计算缆机驾驶员操作行为响应失误概率;构建操作行为可靠性分析模型,定量表达操作行为可靠性,分析人因失误对缆机起重作业安全事故的影响.结果表明,吊具与吊罐对接、混凝土卸料等作业过程的缆机驾驶员操作行为可靠性低,需加强安全培训,严格考核制度,从根本上提高缆机驾驶员操作行为的可靠性,以期提升缆机生产效率,实现预防安全事故的目标. 相似文献
207.
208.
Dr. Tao Shu Prof. Janine Cossy 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(43):11021-11029
This review highlights the recent achievements of iron- and cobalt-catalyzed enantioselective cross-couplings of halide derivatives with organometallic reagents for the construction of C-C bonds. Synthetic applications of enantioselective cross-couplings to natural products and biologically active compounds are also covered showing the power of these cross-couplings in organic synthesis. 相似文献
209.
Gold‐Catalyzed Tandem Cycloisomerization–Halogenation of Chiral Homopropargyl Sulfonamides
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)
Chao Shu Long Li Cang‐Hai Shen Peng‐Peng Ruan Chao‐Yue Liu Prof. Dr. Long‐Wu Ye 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(7):2282-2290
Two new gold‐catalyzed tandem cycloisomerization–halogenation reactions of chiral homopropargyl sulfonamides have been developed. Various enantioenriched 3,3‐diiodopyrrolidin‐2‐ols and 3‐fluoropyrrolidin‐2‐ols were obtained in moderate‐to‐good yields with excellent enantio‐ and diastereoselectivity. 相似文献
210.
A novel one-pot protocol for the synthesis of substituted 2-aminooxazoline from isonitriles and 2-aminoethanol was developed and the reactions involved imidoyl diiodide intermediates,which were generated by mixing isonitriles and iodine in CH2C12 at room temperature. 相似文献