全文获取类型
收费全文 | 4642篇 |
免费 | 534篇 |
国内免费 | 499篇 |
专业分类
化学 | 4245篇 |
晶体学 | 48篇 |
力学 | 145篇 |
综合类 | 32篇 |
数学 | 79篇 |
物理学 | 1126篇 |
出版年
2024年 | 11篇 |
2023年 | 49篇 |
2022年 | 84篇 |
2021年 | 123篇 |
2020年 | 172篇 |
2019年 | 174篇 |
2018年 | 123篇 |
2017年 | 182篇 |
2016年 | 221篇 |
2015年 | 178篇 |
2014年 | 247篇 |
2013年 | 502篇 |
2012年 | 310篇 |
2011年 | 282篇 |
2010年 | 239篇 |
2009年 | 255篇 |
2008年 | 234篇 |
2007年 | 268篇 |
2006年 | 225篇 |
2005年 | 209篇 |
2004年 | 194篇 |
2003年 | 159篇 |
2002年 | 125篇 |
2001年 | 109篇 |
2000年 | 93篇 |
1999年 | 112篇 |
1998年 | 91篇 |
1997年 | 82篇 |
1996年 | 88篇 |
1995年 | 69篇 |
1994年 | 67篇 |
1993年 | 63篇 |
1992年 | 36篇 |
1991年 | 38篇 |
1990年 | 39篇 |
1989年 | 30篇 |
1988年 | 32篇 |
1987年 | 20篇 |
1986年 | 17篇 |
1985年 | 14篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 14篇 |
1981年 | 8篇 |
1980年 | 16篇 |
1979年 | 21篇 |
1978年 | 9篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1973年 | 3篇 |
排序方式: 共有5675条查询结果,搜索用时 0 毫秒
1.
《Mendeleev Communications》2022,32(3):395-396
A new method for assembling 1,3-selenazolines by the iodine- mediated reaction of the simplest building blocks such as elemental selenium, alkenes and acetonitrile has been discovered. A proposed mechanism includes the addition of the intermediate selenium iodides to alkene with subsequent solvent interception by the formed seleniranium ion. 相似文献
2.
3.
Solvent Influence on Cellulose 1,4‐β‐Glycosidic Bond Cleavage: A Molecular Dynamics and Metadynamics Study 下载免费PDF全文
Claudia Loerbroks Eliot Boulanger Prof. Dr. Walter Thiel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(14):5477-5487
We explore the influence of two solvents, namely water and the ionic liquid 1‐ethyl‐3‐methylimidazolium acetate (EmimAc), on the conformations of two cellulose models (cellobiose and a chain of 40 glucose units) and the solvent impact on glycosidic bond cleavage by acid hydrolysis by using molecular dynamics and metadynamics simulations. We investigate the rotation around the glycosidic bond and ring puckering, as well as the anomeric effect and hydrogen bonds, in order to gauge the effect on the hydrolysis mechanism. We find that EmimAc eases hydrolysis through stronger solvent–cellulose interactions, which break structural and electronic barriers to hydrolysis. Our results indicate that hydrolysis in cellulose chains should start from the ends and not in the centre of the chain, which is less accessible to solvent. 相似文献
4.
Yuyang Ji Rebekka S. Klausen 《Journal of polymer science. Part A, Polymer chemistry》2021,59(21):2521-2529
The synthesis of vinyl alcohol copolymers is limited due to the poor radical reactivity of vinyl acetate (VAc), the traditional precursor to polyvinyl alcohol (PVA). Main group monomers such as BN 2-vinylnaphthalene (BN2VN) have attracted attention as alternatives to VAc to form side chain hydroxyls via oxidation, but outstanding questions of molecular weight control remain. Herein we report systematic investigation of solvent, temperature, and initiator concentration as factors influencing BN2VN degree of polymerization. We find increased chain transfer to toluene, hypothesized to arise from differences in radical stabilization and reactivity by aromatic and BN aromatic rings. As a result of these combined efforts, high molecular weight (Mw ~ 105 g mol−1) BN2VN homopolymers and BN2VN-styrene copolymers were obtained. 相似文献
5.
Facile non‐lithographic route to highly aligned silica nanopatterns using unidirectionally aligned polystyrene‐block‐polydimethylsiloxane films 下载免费PDF全文
Zhe Qiang Maurice L. Wadley Bryan D. Vogt Kevin A. Cavicchi 《Journal of Polymer Science.Polymer Physics》2015,53(15):1058-1064
Thin films (monolayer and bilayer) of cylinder forming polystyrene‐block‐polydimethylsiloxane (PS‐b‐PDMS) were shear aligned by the swelling and deswelling of a crosslinked PDMS pad that was physically adhered to the film during solvent vapor annealing. The nanostructures formed by self‐assembly were exposed to ultraviolet‐ozone to partially oxidize the PDMS, followed by calcination in air at 500 °C. In this process, the PS segments were fully decomposed, while the PDMS yielded silica nanostructures. The highly aligned PDMS cylinders were thus deposited as silica nanolines on the silicon substrate. Using a bilayer film, the center‐to‐center distance of these features were effectively halved from 38 to 19 nm. Similarly, by sequential shear‐alignment of two distinct layers, a rhombic array of silica nanolines was fabricated. This methodology provides a facile route to fabricating complex topographically patterned nanostructures. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1058–1064 相似文献
6.
7.
许雪松 《原子与分子物理学报》2006,23(1):137-142
应用密度泛函B3LYP/6—31+G(d,p)方法对C8H80-(H2O)n(n=1~5)团簇这种弱相互作用体系进行垒自由度能量梯度优化,得到该系列团簇的稳定蛄构.计算结果表明。在该系列二元团簇中,一方面水分子数目的多少对苯基丙酮分子的结构影响很小,另一方面由于苯基丙酮分子的存在,破坏了团簇中水分子的对称性结构,在团簇内部极力形成O—H—O这样弯曲的有方向性的氢键.对苯基丙酮-水这样结构复杂的团簇,指认光谱的难度非常大,本文只讨论了与C=O有关的振动峰和水分子的对称伸缩振动的最强峰. 相似文献
8.
离子阱中热库诱导退相干的控制 总被引:1,自引:1,他引:0
王中结 《原子与分子物理学报》2006,23(4):757-761
对单个囚禁离子在热库作用下的退相干的控制问题进行了研究.本文提出的控制方法是基于消除自由哈密顿技术和脉冲重聚技术的结合.前者是利用一个经典大失谐激光场作用于囚禁离子来实现的,而后者是利用一系列的激光π脉冲来实现的.解析与数值表明,应用这种控制方法可以有效消除量子退相干且比纯粹应用脉冲重聚技术要好. 相似文献
9.
For more than 25 yearsJΨ production has helped to sharpen our understanding of QCD. In proton induced reaction some observations are rather well understood
while others are still unclear. The current status of the theory ofJΨ production will be sketched, paying special attention to the issues of formation time andJΨ re-interaction in a nuclear medium. 相似文献
10.