全文获取类型
收费全文 | 11698篇 |
免费 | 1683篇 |
国内免费 | 1118篇 |
专业分类
化学 | 10778篇 |
晶体学 | 265篇 |
力学 | 213篇 |
综合类 | 84篇 |
数学 | 707篇 |
物理学 | 2452篇 |
出版年
2024年 | 10篇 |
2023年 | 151篇 |
2022年 | 297篇 |
2021年 | 484篇 |
2020年 | 627篇 |
2019年 | 474篇 |
2018年 | 447篇 |
2017年 | 400篇 |
2016年 | 627篇 |
2015年 | 606篇 |
2014年 | 603篇 |
2013年 | 1050篇 |
2012年 | 629篇 |
2011年 | 742篇 |
2010年 | 576篇 |
2009年 | 652篇 |
2008年 | 653篇 |
2007年 | 771篇 |
2006年 | 726篇 |
2005年 | 603篇 |
2004年 | 534篇 |
2003年 | 456篇 |
2002年 | 462篇 |
2001年 | 230篇 |
2000年 | 211篇 |
1999年 | 174篇 |
1998年 | 150篇 |
1997年 | 178篇 |
1996年 | 154篇 |
1995年 | 121篇 |
1994年 | 123篇 |
1993年 | 93篇 |
1992年 | 91篇 |
1991年 | 50篇 |
1990年 | 50篇 |
1989年 | 41篇 |
1988年 | 34篇 |
1987年 | 42篇 |
1986年 | 28篇 |
1985年 | 28篇 |
1984年 | 15篇 |
1983年 | 13篇 |
1982年 | 12篇 |
1981年 | 12篇 |
1980年 | 15篇 |
1979年 | 12篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1972年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
《Mendeleev Communications》2022,32(4):467-470
Isomeric forms of indoline spiropyrans show unusual behavior compared with similar compounds, according to experimental data. DFT modeling for gas phase was made to consider the simplest case without environmental effects, which revealed the intramolecular reasons for occurrence of ring opening reaction depending on the particular structure of the compound. The questions of charge redistributions, the changes of geometry and chemical bonds in the structures are also discussed. 相似文献
2.
Yaoli Wang Yan Liang Huixiang Sheng Jin Wang Junjie Wang Shunhao He Mengdan Guan Yaqi Chen Prof. Gang Lu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(2):e202103709
Surface plasmon can trigger or accelerate many photochemical reactions, especially useful in energy and environmental industries. Recently, molecular adsorption has proven effective in modulating plasmon-mediated photochemistry, however the realized chemical reactions are limited and the underlying mechanism is still unclear. Herein, by using in situ dark-field optical microscopy, the plasmon-mediated oxidative etching of silver nanoparticles (Ag NPs), a typical hot-hole-driven reaction, is monitored continuously and quantitatively. The presence of thiol or thiophenol molecules is found essential in the silver oxidation. In addition, the rate of silver oxidation is modulated by the choice of different thiol or thiophenol molecules. Compared with the molecules having electron donating groups, the ones having electron accepting groups accelerate the silver oxidation dramatically. The thiol/thiophenol modulation is attributed to the modulation of the charge separation between the Ag NPs and the adsorbed thiol or thiophenol molecules. This work demonstrates the great potential of molecular adsorption in modulating the plasmon-mediated photochemistry, which will pave a new way for developing highly efficient plasmonic photocatalysts. 相似文献
3.
4.
Kento Nishikibe Keisuke Nishikawa Momochika Kumagai Matsumi Doe Yoshiki Morimoto 《化学:亚洲杂志》2022,17(1):e202101137
There are marine cytotoxic bromotriterpenoids, named the thyrsiferol family that are structurally characterized by some tetrahydropyran (THP) and tetrahydrofuran (THF) rings. The thyrsiferol family belongs to natural products that are often difficult to determine their stereostructures even by the current, highly advanced spectroscopic methods, especially in acyclic systems including stereogenic tetrasubstituted carbon centers. In such cases, it is effective to predict and synthesize the possible stereostructures. Herein, to elucidate ambiguous stereostructures and unassigned absolute configurations of aplysiol B, laurenmariannol, and saiyacenol A, members of the thyrsiferol family, we carried out their asymmetric chemical syntheses featuring 6-exo and 5-exo oxacyclizations of epoxy alcohol precursors and 6-endo bromoetherification of a bishomoallylic alcohol. In this paper, we report total assignments of their stereostructures through their asymmetric chemical syntheses and also their preliminary cytotoxic activities against some tumor cells. These results could not have been achieved without depending on asymmetric total synthesis. 相似文献
5.
Wacker oxidation is an industry-adopted process to transform olefins into value-added epoxides and carbonyls. However, traditional Wacker oxidation involves the use of homogeneous palladium and copper catalysts for the olefin addition and reductive elimination. Here, we demonstrated an ultrahigh loading Cu single atom catalyst(14% Cu, mass fraction) for the palladium-free Wacker oxidation of 4-vinylanisole into the corresponding ketone with N-methylhydroxylamine hydrochloride as an additive under mild conditions. Mechanistic studies by 18O and deuterium isotope labelling revealed a hydrogen shift mechanism in this palladium-free process using N-methylhydroxylamine hydrochloride as the oxygen source. The reaction scope can be further extended to Kucherov oxidation. Our study paves the way to replace noble metal catalysts in the traditional homogeneous processes with single atom catalysts. 相似文献
6.
7.
Bohuai Xiao Jianqiao Dong Zhiye Wang Xu Wang Mingjun Sun Jing Guo Gongming Qian Yunchuan Li Shuai Chang 《Chemphyschem》2022,23(7):e202100833
One important prerequisite for the fabrication of molecular functional device strongly relies on the understanding the conducting behaviors of the metal-molecule-metal junction that can respond to an external stimulus. The model Lewis basic molecule 4,4′-(pyridine-3,5-diyl)dibenzonitrile (DBP), which can react with Lewis acid and protic acid, was synthesized. Then, the molecular conducting behavior of DBP, DBP-B(C6F5)3, and DBP-TfOH (DBP-B(C6F5)3, and DBP-TfOH were produced by Lewis acid and protonic acid treatment of DBP) was researched and compared. Given that their identical physical paths for DBP, DBP-B(C6F5)3, and DBP-TfOH to sustain charge transport, our results indicate that modifying the molecular electronic structure, even not directly changing the conductive physical backbone, can tune the charge transporting ability by nearly one order of magnitude. Furthermore, the addition of another Lewis base triethylamine (of stronger alkaline than DBP), to Lewis acid-base pair reverts the electrical properties back to that of a single DBP junction, that is constructive to propose a useful but simple strategy for the design and construction of reversible and controllable molecular device based on pyridine derived molecule. 相似文献
8.
ZHANG Xinyu TANG Pengpeng ZHAI Guangyao LIN Xiu ZHANG Qiang CHEN Jiesheng WEI Xiao 《高等学校化学研究》2022,38(5):1292-1300
In this study, we have provided a facile solution to synthesize well-aligned titanium dioxide nanorods by using hydrothermal reaction. By calcining the materials under different atmospheres and temperatures, a batch of titanium dioxides with excellent oxygen evolution reaction(OER) catalytic efficiency were obtained. This new structured TiO2 photoanode material yields a high photocurrent density of 5.69 mA/cm2 at 1.23 V vs. reversible hydrogen electrode(RHE) under simulated solar light(100 mW/cm2). Surface photovoltage techniques and other measurements were carried out to confirm that the enhanced photoelectrochemical performances were attributed to the synergistic effect of the phase junction and a certain content of surface states, which accelerate the separation and transmission of the photogenerated charges. This material with phase junction and surface states promises a potential application in the field of photoelectric catalysis under solar light. 相似文献
9.
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
10.