全文获取类型
收费全文 | 83673篇 |
免费 | 10894篇 |
国内免费 | 7959篇 |
专业分类
化学 | 58098篇 |
晶体学 | 775篇 |
力学 | 4863篇 |
综合类 | 525篇 |
数学 | 10637篇 |
物理学 | 27628篇 |
出版年
2023年 | 1464篇 |
2022年 | 1423篇 |
2021年 | 2343篇 |
2020年 | 2771篇 |
2019年 | 2707篇 |
2018年 | 2393篇 |
2017年 | 2149篇 |
2016年 | 3488篇 |
2015年 | 3453篇 |
2014年 | 4071篇 |
2013年 | 5924篇 |
2012年 | 7123篇 |
2011年 | 7457篇 |
2010年 | 4905篇 |
2009年 | 5064篇 |
2008年 | 5214篇 |
2007年 | 4789篇 |
2006年 | 4423篇 |
2005年 | 3983篇 |
2004年 | 3641篇 |
2003年 | 2678篇 |
2002年 | 2292篇 |
2001年 | 1801篇 |
2000年 | 1588篇 |
1999年 | 1680篇 |
1998年 | 1459篇 |
1997年 | 1278篇 |
1996年 | 1342篇 |
1995年 | 1214篇 |
1994年 | 1113篇 |
1993年 | 995篇 |
1992年 | 872篇 |
1991年 | 738篇 |
1990年 | 629篇 |
1989年 | 545篇 |
1988年 | 429篇 |
1987年 | 401篇 |
1986年 | 359篇 |
1985年 | 389篇 |
1984年 | 291篇 |
1983年 | 240篇 |
1982年 | 202篇 |
1981年 | 171篇 |
1980年 | 132篇 |
1979年 | 79篇 |
1978年 | 84篇 |
1977年 | 87篇 |
1976年 | 76篇 |
1975年 | 81篇 |
1974年 | 76篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
71.
72.
Recent advances in photocatalysis focus on the development of materials with hierarchical structure and on the surface plasmon resonance (SPR) phenomenon exhibited by metal nanoparticles (NPs). In this work, both are combined in a material where size‐controllable Ag‐NPs are uniformly loaded onto the hierarchical microporous and mesoporous and nanocolumnar structures of ZnO, resulting in Ag‐NP/ZnO nanocomposites. The embedded Ag‐NPs slightly decrease the hydrophobicity of fibrous ZnO, improve its wettability, and increase the absorption of formaldehyde (H2CO) onto the photocatalyst, all of this resulting in excellent photodegradation of formaldehyde in aqueous solution. Besides, we found that Ag‐NPs with optimal size not only accelerate the charge transfer to the surface of ZnO, but also strengthen the SPR effect in the intercolumnar channels of fibrous ZnO particles combining with high concentration of photo‐generated radical species. The micro‐to‐mesoporous ZnO is like a nanoarray packed Ag‐NPs. With Ag‐NPs of diameter 2.5 < ? < 6.5 nm, ZnO exhibits the most superior photodegradation rate constant value of 0.0239 min?1 with total formaldehyde removal of 97%. This work presents a new feasible approach involving highly sophisticated Ag‐NP/ZnO architecture combining the SPR effect and hierarchically ordered structures, which results in high photocatalytic activity for formaldehyde photodegradation. 相似文献
73.
Maribel Rodríguez‐Aguilar Sofía Ramírez‐García Cesar Ilizaliturri‐Hernndez Alejandro Gmez‐Gmez Evelyn Van‐Brussel Fernando Díaz‐Barriga Susanna Medellín‐Garibay Rogelio Flores‐Ramírez 《Biomedical chromatography : BMC》2019,33(12)
An analytical method to identify volatile organic compounds (VOCs) in the exhaled breath from patients with a diagnosis of chronic obstructive pulmonary disease (COPD) using a ultrafast gas chromatography system equipped with an electronic nose detector (FGC eNose) has been developed. A prospective study was performed in 23 COPD patients and 33 healthy volunteers; exhalation breathing tests were performed with Tedlar bags. Each sample was analyzed by FCG eNose and the identification of VOCs was based on the Kovats index. Raw data were reduced by principal component analysis (PCA) and canonical discriminant analysis [canonical analysis of principal coordinates (CAP)]. The FCG eNose technology was able to identify 17 VOCs that distinguish COPD patients from healthy volunteers. At all stages of PCA and CAP the discrimination between groups was obvious. Chemical prints were correctly classified up to 82.2%, and were matched with 78.9% of the VOCs detected in the exhaled breath samples. Receiver operating characteristic curve analysis indicated the sensitivity and specificity to be 96% and 91%, respectively. This pilot study demonstrates that FGC eNose is a useful tool to identify VOCs as biomarkers in exhaled breath from COPD patients. Further studies should be performed to enhance the clinical relevance of this quick and ease methodology for COPD diagnosis. 相似文献
74.
75.
76.
Chang Mingning Wang He Zheng Yonglei Li Ningning Chen Siheng Wan Yong Yuan Feng Shao Weiquan Xu Sheng 《Journal of Solid State Electrochemistry》2019,23(2):607-613
Journal of Solid State Electrochemistry - Li1.2Ni1/3Co1/3Mn1/3O2 was synthesized as a cathode material for lithium-ion batteries and coated with various amounts of CoAl2O4 (0–5 wt%)... 相似文献
77.
Chen Qinlei Xia Zhengbin Zhang Yanhong Wang Shumin 《Journal of Solid State Electrochemistry》2019,23(12):3399-3408
Journal of Solid State Electrochemistry - Polyaniline/diazonium salt/TiO2 nanotube arrays (PANI/DZ/TiO2 NAs), as a supercapacitor electrode material, are fabricated by two-step anodic oxidation of... 相似文献
78.
79.
Tenghao Yin Lei Wu Tonghao Wu Guoyong Mao Guodong Nian Zhe Chen Xiaocheng Hu Peng Wang Yuhai Xiang Honghui Yu Shaoxing Qu Wei Yang 《Journal of Polymer Science.Polymer Physics》2019,57(5):272-280
Conductive hydrogels with ionic compounds possess great potential for the development of soft smart devices. A dielectric scarfskin is typically required for these devices to prevent short circuiting, leading to devices with lower stretchability than the hydrogel. Henceforth, commonly used dielectric materials, such as PDMS and Ecoflex, cannot be largely stretched. Hydrogel devices with ultrastretchability are required to accommodate hostile application environments. Herein, we propose a hydrogel fiber coated with a dielectric layer that can be stretched to over 2000% of its initial length. The fiber remains conductive when stretched to ~1300%. In addition, the core/sheath hydrogel fiber can be endowed with a variety of functional properties, such as electroluminescence (EL), photoluminescence (PL), and magnetic‐responsiveness, demonstrating scalability of the resultant fiber. The present work can pave the way for numerous next‐generation soft devices, such as smart textiles and wearable electronics. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 272–280 相似文献
80.