全文获取类型
收费全文 | 5057篇 |
免费 | 507篇 |
国内免费 | 496篇 |
专业分类
化学 | 4093篇 |
晶体学 | 43篇 |
力学 | 375篇 |
综合类 | 61篇 |
数学 | 624篇 |
物理学 | 864篇 |
出版年
2024年 | 7篇 |
2023年 | 47篇 |
2022年 | 102篇 |
2021年 | 143篇 |
2020年 | 165篇 |
2019年 | 185篇 |
2018年 | 133篇 |
2017年 | 206篇 |
2016年 | 236篇 |
2015年 | 190篇 |
2014年 | 254篇 |
2013年 | 543篇 |
2012年 | 314篇 |
2011年 | 283篇 |
2010年 | 232篇 |
2009年 | 273篇 |
2008年 | 278篇 |
2007年 | 304篇 |
2006年 | 244篇 |
2005年 | 223篇 |
2004年 | 216篇 |
2003年 | 172篇 |
2002年 | 149篇 |
2001年 | 113篇 |
2000年 | 108篇 |
1999年 | 113篇 |
1998年 | 101篇 |
1997年 | 90篇 |
1996年 | 85篇 |
1995年 | 70篇 |
1994年 | 63篇 |
1993年 | 65篇 |
1992年 | 44篇 |
1991年 | 32篇 |
1990年 | 37篇 |
1989年 | 25篇 |
1988年 | 36篇 |
1987年 | 29篇 |
1986年 | 22篇 |
1985年 | 18篇 |
1984年 | 17篇 |
1983年 | 9篇 |
1982年 | 14篇 |
1981年 | 7篇 |
1980年 | 13篇 |
1979年 | 14篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 6篇 |
1973年 | 4篇 |
排序方式: 共有6060条查询结果,搜索用时 250 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.
数据包络分析(DEA)是评价供应链系统(Supply chain system)间相对有效性的一种重要的工具,但是传统的DEA不考虑供应链的内部结构,对系统效率评价偏高;而本文所研究两阶段串联供应链系统,考虑把部分中间产品作为最终产品输出,增加额外中间投入的情形.基于所提出的供应链系统结构,本文建立相应的串联结构下的网络DEA模型,并针对所建立模型进行相关理论的研究,给出了串联结构下的生产可能集和规模收益情况判定方法.最后,进行数值实验,以验证我们提出的结论. 相似文献
6.
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
7.
8.
理想气体在热力学中的作用 总被引:1,自引:1,他引:0
指出热力学理论是普遍的,不依赖于理想气体.理想气体为热力学理论提供了一个简单的实例,为测量热力学温度提供了一种简单的温度计. 相似文献
9.
E. A. Bailov N. Temirgaliev 《Computational Mathematics and Mathematical Physics》2006,46(9):1515-1525
Sharp estimates (in the power scale) are obtained for the discretization error in the solutions to Poisson’s equation whose right-hand side belongs to a Korobov class. Compared to the well-known Korobov estimate, the order is almost doubled and has an ultimate value in the power scale. 相似文献
10.
The Boltzmann distribution used in the steady-state analysis of the simulated annealing algorithm gives rise to several scale invariant properties. Scale invariance is first presented in the context of parallel independent processors and then extended to an abstract form based on lumping states together to form new aggregate states. These lumped or aggregate states possess all of the mathematical characteristics, forms and relationships of states (solutions) in the original problem in both first and second moments. These scale invariance properties therefore permit new ways of relating objective function values, conditional expectation values, stationary probabilities, rates of change of stationary probabilities and conditional variances. Such properties therefore provide potential applications in analysis, statistical inference and optimization. Directions for future research that take advantage of scale invariance are also discussed. 相似文献