全文获取类型
收费全文 | 20611篇 |
免费 | 3185篇 |
国内免费 | 2353篇 |
专业分类
化学 | 11437篇 |
晶体学 | 164篇 |
力学 | 1156篇 |
综合类 | 64篇 |
数学 | 1661篇 |
物理学 | 6296篇 |
无线电 | 5371篇 |
出版年
2024年 | 83篇 |
2023年 | 553篇 |
2022年 | 664篇 |
2021年 | 845篇 |
2020年 | 811篇 |
2019年 | 722篇 |
2018年 | 675篇 |
2017年 | 652篇 |
2016年 | 969篇 |
2015年 | 933篇 |
2014年 | 1169篇 |
2013年 | 1439篇 |
2012年 | 1783篇 |
2011年 | 1774篇 |
2010年 | 1247篇 |
2009年 | 1208篇 |
2008年 | 1372篇 |
2007年 | 1170篇 |
2006年 | 1117篇 |
2005年 | 997篇 |
2004年 | 673篇 |
2003年 | 566篇 |
2002年 | 541篇 |
2001年 | 452篇 |
2000年 | 428篇 |
1999年 | 455篇 |
1998年 | 364篇 |
1997年 | 311篇 |
1996年 | 345篇 |
1995年 | 343篇 |
1994年 | 253篇 |
1993年 | 204篇 |
1992年 | 193篇 |
1991年 | 175篇 |
1990年 | 162篇 |
1989年 | 121篇 |
1988年 | 97篇 |
1987年 | 77篇 |
1986年 | 56篇 |
1985年 | 44篇 |
1984年 | 31篇 |
1983年 | 25篇 |
1982年 | 15篇 |
1981年 | 17篇 |
1980年 | 9篇 |
1978年 | 2篇 |
1972年 | 1篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 135 毫秒
61.
62.
Da Quan Zhang Xing Jin Bin Xie Hyung Goun Joo Li Xin Gao Kang Yong Lee 《Surface and interface analysis : SIA》2012,44(1):78-83
The corrosion inhibition of ammonium heltamolybdate (AH) and calcium gluconate (CG) for AA6061 alloy in 3% NaCl solution was investigated by the electrochemical measurements. It indicates that AH inhibits the corrosion of AA6061 alloy and acts as an anodic inhibitor. Maximum inhibition efficiency reaches 74.3% at the concentration of 1 × 10?4 mol.l?1 AH. The results of the electrochemical studies reveal AH is physically adsorbed on the AA6061 alloy surface and the adsorption follows Langmuir isotherm. The combination of AH and CG enhances the inhibition efficiency to 95.9%. The enhanced inhibition is attributed to the promotion of AH adsorption by CG. The mixture of AH and CG is a mixed‐type inhibitor and renders the corrosion potential to more positive values. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
63.
Hong‐Juan Deng Yu‐Jing Fang Gao‐Wei Chen Miao‐Chang Liu Hua‐Yue Wu Jiu‐Xi Chen 《应用有机金属化学》2012,26(4):164-167
An efficient and convenient copper‐catalyzed Clauson–Kass reaction of 2,5‐dimethoxytetrahydrofuran with amines in aqueous media has been developed, providing a wide range of N‐substituted pyrroles in good yields. It is noteworthy that the Clauson–Kass reaction of 2,5‐dimethoxytetrahydrofuran with p‐phenylenediamine or m‐phenylenediamine proceeds smoothly to afford the corresponding monopyrroles and bispyrroles with high selectivity in impressive yields. A plausible mechanism for the formation of N‐substituted pyrroles has been proposed. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
64.
Styrene–norbornene (S‐N) copolymerizations were carried out using β‐diketiminato nickel complexes CH{C(CF3)NAr}2NiBr (Ar = 2,6‐iPr2C6H3, 1 ; Ar = 2,6‐Me2C6H3, 2 ) in the presence of methylaluminoxane. The influence of the comonomer feed content and polymerization temperature on the conversion and composition of the copolymers with the catalytic system was investigated. An increase in the feed ratio of S/N led to an increase in the incorporated styrene content of the resulting copolymer. NMR characterization of the copolymers generated with the catalytic systems showed that the random S‐N copolymers are produced. Differential scanning calorimetric determination of the copolymers shows higher Tg values than polystyrene, and gel permeation chromatographic measurements have shown that the copolymers possess rather narrow molecular weight distributions, suggesting that the copolymerization take place at a single active site. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
65.
Xinzhi Chen Shaodong Zhou Yuehan Chen Zehan Dong Yeyu Gao Chao Qian Chaohong He 《Research on Chemical Intermediates》2012,38(9):2255-2269
Alcoholate was utilized in catalytic transfer hydrogenation of unsaturated nitrogen compounds. In the reduction of nitro compounds, oximes and imines, alkoxide was used as the promoter, with alcohol as the hydrogen source, while in the reduction of nitriles, alkoxide was used as the hydrogen source. 相似文献
66.
Yue Shao Hong-Ping Zhao Xi-Qiao Feng Huajian Gao 《Journal of the mechanics and physics of solids》2012,60(8):1400-1419
Studying the structure–property relation of biological materials can not only provide insight into the physical mechanisms underlying their superior properties and functions but also benefit the design and fabrication of advanced biomimetic materials. In this paper, we present a microstructure-based fracture mechanics model to investigate the toughening effect due to the crack-bridging mechanism of platelets. Our theoretical analysis demonstrates the crucial contribution of this mechanism to the high toughness of nacre. It is found that the fracture toughness of nacre exhibits distinct dependence on the sizes of platelets, and the optimized ranges for the thickness and length of platelets required to achieve higher fracture toughness are given. In addition, the effects of such factors as the mechanical properties of the organic phase (or interfaces), the effective elastic modulus of nacre, and the stacking pattern of platelets are also examined. Finally, some guidelines for the biomimetic design of novel materials are proposed based on our theoretical analysis. 相似文献
67.
Syed?Faraz?HasanEmail author Nazmul?H.?Siddique Shyam?Chakraborty Xuemei?Ding Wei?Gao 《Wireless Personal Communications》2013,68(4):1415-1433
WLAN-based roadside-to-vehicle communications is an increasingly popular research trend. This paper examines the applicability of WLANs in the Intelligent Transportation Systems with focus on reducing the scanning phase delay and the address allocation delay. The handover delays become intolerable when the indoor WLAN Access Poins are accessed from by the outdoor mobile nodes at vehicular speeds. In this work, we propose a baseline scheme which calls for passively scanning only the orthogonal channels to reduce the scanning phase delay in the overall handover latency. We argue that the interference free orthogonal channels are ideal for conveying time critical information in vehicular environments. Secondly, this paper evaluates the delays incurred by the Dynamic Host Configuration Protocol (DHCP) in the handover process. The focus on establishing the amount of delay contributed by each DHCP phase and make some meaningful comments at the end. The conclusions made in this paper are based on real-world experiments and tests. 相似文献
68.
69.
Capillary‐Bridge Mediated Assembly of Conjugated Polymer Arrays toward Organic Photodetectors 下载免费PDF全文
Hanfei Gao Jiangang Feng Bo Zhang Chengyi Xiao Yuchen Wu Xiaonan Kan Bin Su Zhaohui Wang Wenping Hu Yanming Sun Lei Jiang Alan J. Heeger 《Advanced functional materials》2017,27(34)
Large‐scale patterning of high‐quality organic semiconductors is crucial for the fabrication of optoelectronic devices with high efficiency and low cost. Yet, owing to the uncontrollable dewetting dynamics of organic liquid in conventional solution patterning techniques, large defect density of organic architectures is inevitable, which is detrimental to the device performance. To address this challenge, herein a capillary‐bridge‐mediated assembly technique is developed for regulating the dewetting process, yielding large‐scale 1D microstructure ordered arrays. The 1D arrays organic photodetectors exhibit a high optoelectronic performance of light on/off ratio exceeding 100, responsivity of 3.24 A W?1, detectivity of 3.20 × 1011 Jones and fast response speed, showing a great improvement compared with spin‐coated membrane devices. In addition, the significant enhancement of the device photodetection under the electronic field modulation is investigated by applying a back‐gate voltage and explained with the photocurrent predominating in the OFF state and the neglected thermocurrent and tunneling current promoting in the ON state of the phototransistor devices. The research offers a new insight for the facile fabrication of large‐scale integrated photodetectors and other organic devices based on patterned conjugated polymers. 相似文献
70.
Batteries: Enhanced Electrocatalysis via 3D Graphene Aerogel Engineered with a Silver Nanowire Network for Ultrahigh‐Rate Zinc–Air Batteries (Adv. Funct. Mater. 18/2017) 下载免费PDF全文