全文获取类型
收费全文 | 49018篇 |
免费 | 7839篇 |
国内免费 | 5742篇 |
专业分类
化学 | 34629篇 |
晶体学 | 571篇 |
力学 | 3170篇 |
综合类 | 573篇 |
数学 | 5798篇 |
物理学 | 17858篇 |
出版年
2024年 | 104篇 |
2023年 | 896篇 |
2022年 | 1130篇 |
2021年 | 1490篇 |
2020年 | 1899篇 |
2019年 | 1860篇 |
2018年 | 1565篇 |
2017年 | 1450篇 |
2016年 | 2118篇 |
2015年 | 2156篇 |
2014年 | 2688篇 |
2013年 | 3462篇 |
2012年 | 4364篇 |
2011年 | 4606篇 |
2010年 | 3048篇 |
2009年 | 3061篇 |
2008年 | 3256篇 |
2007年 | 2966篇 |
2006年 | 2737篇 |
2005年 | 2261篇 |
2004年 | 1815篇 |
2003年 | 1449篇 |
2002年 | 1425篇 |
2001年 | 1143篇 |
2000年 | 1010篇 |
1999年 | 1050篇 |
1998年 | 889篇 |
1997年 | 891篇 |
1996年 | 935篇 |
1995年 | 740篇 |
1994年 | 678篇 |
1993年 | 545篇 |
1992年 | 474篇 |
1991年 | 444篇 |
1990年 | 357篇 |
1989年 | 277篇 |
1988年 | 232篇 |
1987年 | 197篇 |
1986年 | 171篇 |
1985年 | 150篇 |
1984年 | 116篇 |
1983年 | 88篇 |
1982年 | 66篇 |
1981年 | 54篇 |
1980年 | 34篇 |
1979年 | 22篇 |
1977年 | 25篇 |
1976年 | 26篇 |
1975年 | 36篇 |
1974年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 828 毫秒
21.
22.
Xiaoxia Yang Hongyan Xie Zhiguang Xu Jiabing Feng Qiwei Fu Haidong Li Yongtang Jia 《Journal of polymer science. Part A, Polymer chemistry》2021,59(9):813-823
An efficient, atom-economic, oxygen-tolerant, and water-tolerant strategy has been established to synthesize cyano-rich polyesters. Four kinds of organic bases, 1,1,3,3-tetramethylguanidine (TMG), 4-dimethylaminopyridine, triethylamine, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) were explored for accelerating Michael addition polymerization of malononitrile and 1,4-butandiol diacrylate. TMG can promote the polymerization efficiently under mild conditions to quantitatively afford polyester with high-molecular weight and moderate polydispersity. The comparison of the kinetic studies of TMG and TBD reveals that TMG shows better catalytic performance, while the catalysis of TBD brings about oligomers in spite of the higher efficiency at early age of the polymerization. Moreover, other diacrylate compounds could also be quantitatively polymerized to afford polyesters with high molecular weight. When dimethacrylate is chose as the monomer, the polymerization becomes sluggish. All the afforded polyesters display programmable thermal and mechanical properties that are closely related to their chemical structures. 相似文献
23.
Journal of Thermal Analysis and Calorimetry - In the present work, pyrolysis kinetic mechanism was studied for regenerated cellulosic fiber (RCF) and composite RCF containing silicon/nitrogen flame... 相似文献
24.
在中国科学技术大学夏季学期的研究型实验课程"化学科研基础训练"中开设"壳聚糖的制备与表征"综合实验,以龙虾壳为原料,通过除蛋白、脱盐、脱色、脱乙酰等一系列反应,制备得到目标产物壳聚糖。运用红外光谱、核磁共振仪、黏度法、滴定等对产品的结构及性能进行表征。 相似文献
25.
26.
27.
Sulfur hexafluoride (SF6) is considered as a potent greenhouse gas, whose effective degradation is challenging. Here we report a computational study on the nucleophilic activation of sulfur hexafluoride by N-heterocyclic carbenes and N-heterocyclic olefins. The result shows that the activation of SF6 is both thermodynamically and kinetically favorable at mild condition using NHOs with fluoro-substituted azolium and sulfur pentafluoride anion being formed. The Gibbs free energy barrier during the activation of SF6 has a linear relationship with the energy of HOMO of substrates, which could be a guideline for applying those compounds that feature higher energy in HOMO to activate SF6 in high efficiency. 相似文献
28.
In the view of substrate availability, atomic efficiency and cost, directly using arenols as coupling partners in cross‐coupling, would be one of the most attractive goals. Up to date, many efforts have been made to activate the C—O bond of phenols with different strategies, for example, through in‐situ formed intermediates, through a catalytic reductive dearomatization‐condensation‐rearomatization sequence or catalytic deoxygenation. In this review, we summarized recent advances in cross‐couplings of arenols as the electrophiles via C—O activation. 相似文献
29.
Polypyrrole Shell@3D‐Ni Metal Core Structured Electrodes for High‐Performance Supercapacitors
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Gao‐Feng Chen Yu‐Zhi Su Pan‐Yong Kuang Zhao‐Qing Liu Dao‐Yi Chen Xu Wu Nan Li Prof. Shi‐Zhang Qiao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(12):4614-4621
Three‐dimensional (3D) nanometal films serving as current collectors have attracted much interest recently owing to their promising application in high‐performance supercapacitors. In the process of the electrochemical reaction, the 3D structure can provide a short diffusion path for fast ion transport, and the highly conductive nanometal may serve as a backbone for facile electron transfer. In this work, a novel polypyrrole (PPy) shell@3D‐Ni‐core composite is developed to enhance the electrochemical performance of conventional PPy. With the introduction of a Ni metal core, the as‐prepared material exhibits a high specific capacitance (726 F g?1 at a charge/discharge rate of 1 A g?1), good rate capability (a decay of 33 % in Csp with charge/discharge rates increasing from 1 to 20 A g?1), and high cycle stability (only a small decrease of 4.2 % in Csp after 1000 cycles at a scan rate of 100 mV s?1). Furthermore, an aqueous symmetric supercapacitor device is fabricated by using the as‐prepared composite as electrodes; the device demonstrates a high energy density (≈21.2 Wh kg?1) and superior long‐term cycle ability (only 4.4 % and 18.6 % loss in Csp after 2000 and 5000 cycles, respectively). 相似文献
30.