全文获取类型
收费全文 | 185850篇 |
免费 | 2477篇 |
国内免费 | 641篇 |
专业分类
化学 | 98192篇 |
晶体学 | 3139篇 |
力学 | 7563篇 |
综合类 | 3篇 |
数学 | 22185篇 |
物理学 | 57886篇 |
出版年
2021年 | 1501篇 |
2020年 | 1765篇 |
2019年 | 1906篇 |
2018年 | 2222篇 |
2017年 | 2275篇 |
2016年 | 3737篇 |
2015年 | 2339篇 |
2014年 | 3641篇 |
2013年 | 8480篇 |
2012年 | 6778篇 |
2011年 | 8100篇 |
2010年 | 5650篇 |
2009年 | 5556篇 |
2008年 | 7436篇 |
2007年 | 7315篇 |
2006年 | 6940篇 |
2005年 | 6284篇 |
2004年 | 5759篇 |
2003年 | 5049篇 |
2002年 | 4928篇 |
2001年 | 5386篇 |
2000年 | 3996篇 |
1999年 | 3105篇 |
1998年 | 2594篇 |
1997年 | 2511篇 |
1996年 | 2391篇 |
1995年 | 2218篇 |
1994年 | 2196篇 |
1993年 | 2113篇 |
1992年 | 2384篇 |
1991年 | 2335篇 |
1990年 | 2257篇 |
1989年 | 2190篇 |
1988年 | 2202篇 |
1987年 | 2193篇 |
1986年 | 2082篇 |
1985年 | 2723篇 |
1984年 | 2780篇 |
1983年 | 2439篇 |
1982年 | 2600篇 |
1981年 | 2423篇 |
1980年 | 2376篇 |
1979年 | 2506篇 |
1978年 | 2571篇 |
1977年 | 2478篇 |
1976年 | 2508篇 |
1975年 | 2428篇 |
1974年 | 2389篇 |
1973年 | 2567篇 |
1972年 | 1638篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
73.
Following a thermal reduction method, platinum nanoparticles were synthesized and stabilized by polyvinylpyrrolidone. The colloidal platinum nanoparticles were stable for more than 3 months. The micrograph analysis unveiled that the colloidal platinum nanoparticles were well dispersed with an average size of 2.53 nm. The sol–gel‐based inverse micelle strategy was applied to synthesize mesoporous iron oxide material. The colloidal platinum nanoparticles were deposited on mesoporous iron oxide through the capillary inclusion method. The small‐angle X‐ray scattering analysis indicated that the dimension of platinum nanoparticles deposited on mesoporous iron oxide (Pt‐Fe2O3) was 2.64 nm. X‐ray photoelectron spectroscopy (XPS) data showed that the binding energy on Pt‐Fe2O3 surface decreased owing to mesoporous support–nanoparticle interaction. Both colloidal and deposited platinum nanocatalysts improved the degradation of methyl orange under reduction conditions. The activation energy on the deposited platinum nanocatalyst interface (2.66 kJ mol?1) was significantly lowered compared with the one on the colloidal platinum nanocatalyst interface (40.63 ± 0.53 kJ mol?1). 相似文献
74.
75.
Susana Estopiñá-Durán Liam J. Donnelly Euan B. Mclean Bryony M. Hockin Prof. Alexandra M. Z. Slawin Dr. James E. Taylor 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(15):3950-3956
A combination of pentafluorophenylboronic acid and oxalic acid catalyses the dehydrative substitution of benzylic alcohols with a second alcohol to form new C−O bonds. This method has been applied to the intermolecular substitution of benzylic alcohols to form symmetrical ethers, intramolecular cyclisations of diols to form aryl-substituted tetrahydrofuran and tetrahydropyran derivatives, and intermolecular crossed-etherification reactions between two different alcohols. Mechanistic control experiments have identified a potential catalytic intermediate formed between the aryl boronic acid and oxalic acid. 相似文献
76.
Plasma Chemistry and Plasma Processing - The hydrocarbons present in diesel exhaust, although treated as minor pollutants, are equivalent to some of the major pollutants in terms of toxicity,... 相似文献
77.
Daniel Heinz Annette Meister Hazrat Hussain Karsten Busse Jörg Kressler 《Journal of polymer science. Part A, Polymer chemistry》2020,58(23):3322-3335
Adding perfluoroalkyl (PF) segments to amphiphilic copolymers yields triphilic copolymers with new application profiles. Usually, PF segments are attached as terminal blocks via Cu(I) catalyzed azide-alkyne cycloaddition (CuAAC). The purpose of the current study is to design new triphilic architectures with a PF segment in central position. The PF segment bearing bifunctional atom transfer radical polymerization (ATRP) initiator is employed for the fabrication of triphilic poly(propylene oxide)-b-poly(glycerol monomethacrylate)-b-PF-b-poly(glycerol monomethacrylate)-b-poly(propylene oxide) PPO-b-PGMA-b-PF-b-PGMA-b-PPO pentablock copolymers by a combined ATRP and CuAAC reaction approach. Differential scanning calorimetry indicates the PF-initiator to undergo a solid–solid phase transition at 63°C before the final crystal melting at 95°C. This is further corroborated by polarized optical microscopy and X-ray diffraction studies. The PF-initiator could successfully polymerize solketal methacrylate (SMA) under typical ATRP conditions producing well-defined Br-PSMA-b-PF-b-PSMA-Br triblock copolymers that are then converted into PPO-b-PSMA-b-PF-b-PSMA-b-PPO pentablock copolymer via CuAAC reaction. Subsequently, acid hydrolysis of the PSMA blocks afforded water soluble well-defined triphilic pentablock copolymers PPO-b-PGMA-b-PF-b-PGMA-b-PPO with fluorophilic central segment, hydrophilic middle blocks, and lipophilic outer blocks. The triphilic block copolymers could self-assemble, depending upon the preparatory protocol, into spherical and filament-like phase-separated nanostructures as revealed by transmission electron microscopy. 相似文献
78.
79.
80.
Markus Bödenler Ludovic de Rochefort P. James Ross Nicolas Chanet Geneviève Guillot Gareth R. Davies 《Molecular physics》2019,117(7-8):832-848
ABSTRACTFast field-cycling (FFC) nuclear magnetic resonance relaxometry is a well-established method to determine the relaxation rates as a function of magnetic field strength. This so-called nuclear magnetic relaxation dispersion gives insight into the underlying molecular dynamics of a wide range of complex systems and has gained interest especially in the characterisation of biological tissues and diseases. The combination of FFC techniques with magnetic resonance imaging (MRI) offers a high potential for new types of image contrast more specific to pathological molecular dynamics. This article reviews the progress in FFC-MRI over the last decade and gives an overview of the hardware systems currently in operation. We discuss limitations and error correction strategies specific to FFC-MRI such as field stability and homogeneity, signal-to-noise ratio, eddy currents and acquisition time. We also report potential applications with impact in biology and medicine. Finally, we discuss the challenges and future applications in transferring the underlying molecular dynamics into novel types of image contrast by exploiting the dispersive properties of biological tissue or MRI contrast agents. 相似文献