全文获取类型
收费全文 | 30973篇 |
免费 | 5253篇 |
国内免费 | 5943篇 |
专业分类
化学 | 22670篇 |
晶体学 | 638篇 |
力学 | 1832篇 |
综合类 | 650篇 |
数学 | 3960篇 |
物理学 | 12419篇 |
出版年
2024年 | 49篇 |
2023年 | 479篇 |
2022年 | 1055篇 |
2021年 | 1133篇 |
2020年 | 1141篇 |
2019年 | 1224篇 |
2018年 | 992篇 |
2017年 | 1135篇 |
2016年 | 1291篇 |
2015年 | 1475篇 |
2014年 | 1772篇 |
2013年 | 2341篇 |
2012年 | 2680篇 |
2011年 | 2759篇 |
2010年 | 2201篇 |
2009年 | 2174篇 |
2008年 | 2453篇 |
2007年 | 2135篇 |
2006年 | 2039篇 |
2005年 | 1597篇 |
2004年 | 1359篇 |
2003年 | 1105篇 |
2002年 | 1165篇 |
2001年 | 977篇 |
2000年 | 916篇 |
1999年 | 712篇 |
1998年 | 488篇 |
1997年 | 417篇 |
1996年 | 394篇 |
1995年 | 319篇 |
1994年 | 288篇 |
1993年 | 321篇 |
1992年 | 240篇 |
1991年 | 213篇 |
1990年 | 176篇 |
1989年 | 162篇 |
1988年 | 137篇 |
1987年 | 119篇 |
1986年 | 93篇 |
1985年 | 94篇 |
1984年 | 64篇 |
1983年 | 52篇 |
1982年 | 54篇 |
1981年 | 31篇 |
1980年 | 23篇 |
1979年 | 29篇 |
1978年 | 14篇 |
1977年 | 15篇 |
1976年 | 9篇 |
1974年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
21.
Peng-Yan Gui Xiao-Hui Yan Wen-Juan Yuan Yuan-Liang Ma Xiao Ding Shuai Liu 《Natural product research》2019,33(19):2830-2836
A new A, D-seco limonoid, named 12-acetyloxyperforatin (1), along with three known ones, were isolated from the leaves of Harrisonia perforata. Their structures were elucidated on the basis of spectroscopic analysis, including extensive NMR techniques and computational modelling. These compounds showed no inhibitory activity against the 11β-HSD1 enzyme. 相似文献
22.
Sun Yuan Luo Shunlong Lei Xiangyun 《International Journal of Theoretical Physics》2021,60(9):3211-3224
International Journal of Theoretical Physics - Gram matrices arise naturally in the consideration of pair-wise overlap of a family of vectors or quantum pure states, and play an important role in... 相似文献
23.
在管式反应器中采用苯甲酸、聚乙二醇、固体古马隆树脂(S)、液体古马隆树脂(L)为添加剂来降低煤沥青中有害物质苯并芘的含量,以期使得煤沥青可绿色化应用。采用紫外-可见分光光度计分析煤沥青中苯并芘含量。考察了反应温度、反应时间、添加剂添加量、催化剂等工艺条件对添加剂脱除煤沥青中苯并芘的影响。结果表明,不同工艺条件能降低煤沥青中苯并芘的含量。在优化条件下,不同添加剂对苯并芘脱除率由高到低依次为:液体古马隆树脂、聚乙二醇、苯甲酸和固体古马隆树脂。分析其反应机理,这与催化剂的酸性相关,发生亲电取代反应。结果表明,液体古马隆树脂(L)在催化剂存在下对煤沥青中苯并芘脱除率可达73.0%,显示了良好的应用前景。 相似文献
24.
25.
26.
27.
28.
29.
DFT mechanistic study of the H2‐assisted chain transfer copolymerization of propylene and p‐methylstyrene catalyzed by zirconocene complex
下载免费PDF全文
![点击此处可从《Journal of polymer science. Part A, Polymer chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Cheng‐Gen Zhang Shu‐Yuan Yu Liaoyun Zhang Huayi Li Zhi‐Xiang Wang 《Journal of polymer science. Part A, Polymer chemistry》2015,53(4):576-585
DFT computations have been performed to investigate the mechanism of H2‐assisted chain transfer strategy to functionalize polypropylene via Zr‐catalyzed copolymerization of propylene and p‐methylstyrene (pMS). The study unveils the following: (i) propylene prefers 1,2‐insertion over 2,1‐insertion both kinetically and thermodynamically, explaining the observed 1,2‐insertion regioselectivity for propylene insertion. (ii) The 2,1‐inserion of pMS is kinetically less favorable but thermodynamically more favorable than 1,2‐insertion. The observation of 2,1‐insertion pMS at the end of polymer chain is due to thermodynamic control and that the barrier difference between the two insertion modes become smaller as the chain length becomes longer. (iii) The pMS insertion results in much higher barriers for subsequent either propylene or pMS insertion, which causes deactivation of the catalytic system. (iv) Small H2 can react with the deactivated [Zr]?pMS?PPn facilely, which displace functionalized pMS?PPn chain and regenerate [Zr]? H active catalyst to continue copolymerization. The effects of counterions are also discussed. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 576–585 相似文献
30.
Dr. Feifan Wang Jie Tian Dr. Mengzhu Li Dr. Weizhen Li Dr. Lifang Chen Xiaozhi Liu Dr. Jian Li Aidaer Muhetaer Prof. Dr. Qi Li Prof. Dr. Yuan Wang Prof. Dr. Lin Gu Prof. Dr. Ding Ma Prof. Dr. Dongsheng Xu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(21):8280-8286
Fully utilizing solar energy for catalysis requires the integration of conversion mechanisms and therefore delicate design of catalyst structures and active species. Herein, a MOF crystal engineering method was developed to controllably synthesize a copper–ceria catalyst with well-dispersed photoactive Cu-[O]-Ce species. Using the preferential oxidation of CO as a model reaction, the catalyst showed remarkably efficient and stable photoactivated catalysis, which found practical application in feed gas treatment for fuel cell gas supply. The coexistence of photochemistry and thermochemistry effects contributes to the high efficiency. Our results demonstrate a catalyst design approach with atomic or molecular precision and a combinatorial photoactivation strategy for solar energy conversion. 相似文献