全文获取类型
收费全文 | 223960篇 |
免费 | 35548篇 |
国内免费 | 29190篇 |
专业分类
化学 | 154696篇 |
晶体学 | 3023篇 |
力学 | 14764篇 |
综合类 | 2207篇 |
数学 | 28779篇 |
物理学 | 85229篇 |
出版年
2024年 | 672篇 |
2023年 | 3762篇 |
2022年 | 7072篇 |
2021年 | 7458篇 |
2020年 | 8058篇 |
2019年 | 8001篇 |
2018年 | 7190篇 |
2017年 | 7164篇 |
2016年 | 9943篇 |
2015年 | 10288篇 |
2014年 | 12502篇 |
2013年 | 16379篇 |
2012年 | 19283篇 |
2011年 | 19910篇 |
2010年 | 14366篇 |
2009年 | 14055篇 |
2008年 | 15308篇 |
2007年 | 13560篇 |
2006年 | 12854篇 |
2005年 | 10730篇 |
2004年 | 8726篇 |
2003年 | 7143篇 |
2002年 | 7266篇 |
2001年 | 5960篇 |
2000年 | 5190篇 |
1999年 | 4898篇 |
1998年 | 3861篇 |
1997年 | 3457篇 |
1996年 | 3586篇 |
1995年 | 3038篇 |
1994年 | 2710篇 |
1993年 | 2296篇 |
1992年 | 2063篇 |
1991年 | 1725篇 |
1990年 | 1515篇 |
1989年 | 1180篇 |
1988年 | 996篇 |
1987年 | 820篇 |
1986年 | 703篇 |
1985年 | 691篇 |
1984年 | 477篇 |
1983年 | 367篇 |
1982年 | 270篇 |
1981年 | 212篇 |
1980年 | 162篇 |
1979年 | 118篇 |
1978年 | 86篇 |
1977年 | 87篇 |
1976年 | 71篇 |
1975年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Star copolymers have attracted significant interest due to their different characteristics compared with diblock copolymers, including higher critical micelle concentration, lower viscosity, unique spatial shape, or morphologies. Development of synthetic skills such as anionic polymerization and controlled radical polymerization have made it possible to make diverse architectures of polymers. Depending on the molecular architecture of the copolymer, numerous morphologies are possible, for instance, Archimedean tiling patterns and cylindrical microdomains at symmetric volume fraction for miktoarm star copolymers as well as asymmetric lamellar microdomains for star‐shaped copolymers, which have not been reported for linear block copolymers. In this review, we focus on morphologies and microphase separations of miktoarm (AmBn and ABC miktoarm) star copolymers and star‐shaped [(A‐b‐B)n] copolymers with nonlinear architecture. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1–21 相似文献
92.
以4-羟基吲哚为原料,经吲哚环4位乙酰基化、3位亲电取代、酰胺化和还原加氢等反应合成目标化合物7.通过核磁共振氢谱及碳谱对化合物进行结构表征,并对目标化合物进行体外抗氧化生物活性测试.初步生物活性测试结果表明,化合物7a,7b,7c和7d对DPPH·均有很强的清除作用(清除率为85.25%~90.73%),7e,7f,7g,7h作用较差;目标化合物与Vc相比,对·OH的清除作用稍差,最高清除率25.66%(Vc的最高清除率为34.67),但各化合物整体水平相当;在清除O-2·能力上化合物7a,7d,7g,7h最大清除率(分别为19.34,35.35,27.93和31.74)均强于同等浓度的Vc(17.58). 相似文献
93.
We investigate terahertz radiation(T-rays) from a pentacene organic diode at room temperature. The quantum chemistry calculation for frequency-related Huang–Rhys factor of pentacene is also carried out. The results demonstrate that the T-rays can come from a bending vibration of pentacene skeleton after the energy of pentacene exciton transferring to the vibrational excited state via electron–phonon coupling. Frequency and natural bond orbital analytics of pentacene and its derivatives are performed in order to explain the result and develop new materials to get higher emission. This work provides a new way to produce T-rays with a simple device at room temperature. 相似文献
94.
Synthesis and Photophysical Properties of a Sc3N@C80‐Corrole Electron Donor–Acceptor Conjugate 下载免费PDF全文
Bin Liu Hongyun Fang Prof. Xiaofang Li Wenting Cai Lipiao Bao Marc Rudolf Fabian Plass Prof. Louzhen Fan Prof. Xing Lu Prof. Dirk M. Guldi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(2):746-752
Embedding endohdedral metallofullerenes (EMFs) into electron donor–acceptor systems is still a challenging task owing to their limited quantities and their still largely unexplored chemical properties. In this study, we have performed a 1,3‐dipolar cycloaddition reaction of a corrole‐based precursor with Sc3N@C80 to regioselectively form a [5,6]‐adduct ( 1 ). The successful attachment of the corrole moiety was confirmed by mass spectrometry. In the electronic ground state, absorption spectra suggest sizeable electronic communications between the electron acceptor and the electron donor. Moreover, the addition pattern occurring at a [5,6]‐bond junction is firmly proven by NMR spectroscopy and electrochemical investigations performed with 1 . In the electronically excited state, which is probed in photophysical assays with 1 , a fast electron‐transfer yields the radical ion pair state consisting of the one‐electron‐reduced Sc3N@C80 and of the one‐electron‐oxidized corrole upon its exclusive photoexcitation. As such, our results shed new light on the practical work utilizing EMFs as building blocks in photovoltaics. 相似文献
95.
96.
YuanYuan Liu 《中国科学 数学(英文版)》2015,58(12):2633-2642
We investigate perturbation for continuous-time Markov chains(CTMCs) on a countable state space. Explicit bounds on ?D and D are derived in terms of a drift condition, where ? and D represent the perturbation of the intensity matrices and the deviation matrix, respectively. Moreover, we obtain perturbation bounds on the stationary distributions, which extends the results by Liu(2012) for uniformly bounded CTMCs to general(possibly unbounded) CTMCs. Our arguments are mainly based on the technique of augmented truncations. 相似文献
97.
98.
99.
Recyclable and reusable Pd(OAc)2/PPh3/PEG‐2000 system for homocoupling reaction of arylboronic acids under air without base 下载免费PDF全文
A stable and efficient Pd(OAc)2/PPh3/PEG‐2000 catalytic system for homocoupling of arylboronic acids has been developed. In the presence of Pd(OAc)2 and PPh3, the homocoupling reaction of arylboronic acids was carried out smoothly in PEG‐2000 at 70 °C under air without base to afford a variety of symmetric biaryls in good to excellent yields. The isolation of the products was readily performed by extraction with diethyl ether, and the Pd(OAc)2/PPh3/PEG‐2000 system could be easily recycled and reused six times without significant loss of catalytic activity. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
100.