全文获取类型
收费全文 | 4999篇 |
免费 | 276篇 |
国内免费 | 671篇 |
专业分类
化学 | 5164篇 |
晶体学 | 89篇 |
力学 | 75篇 |
综合类 | 30篇 |
数学 | 16篇 |
物理学 | 572篇 |
出版年
2024年 | 2篇 |
2023年 | 29篇 |
2022年 | 33篇 |
2021年 | 57篇 |
2020年 | 81篇 |
2019年 | 77篇 |
2018年 | 92篇 |
2017年 | 124篇 |
2016年 | 151篇 |
2015年 | 143篇 |
2014年 | 190篇 |
2013年 | 426篇 |
2012年 | 282篇 |
2011年 | 258篇 |
2010年 | 238篇 |
2009年 | 380篇 |
2008年 | 400篇 |
2007年 | 384篇 |
2006年 | 306篇 |
2005年 | 355篇 |
2004年 | 315篇 |
2003年 | 261篇 |
2002年 | 214篇 |
2001年 | 212篇 |
2000年 | 140篇 |
1999年 | 93篇 |
1998年 | 104篇 |
1997年 | 82篇 |
1996年 | 54篇 |
1995年 | 75篇 |
1994年 | 91篇 |
1993年 | 60篇 |
1992年 | 47篇 |
1991年 | 25篇 |
1990年 | 15篇 |
1989年 | 14篇 |
1988年 | 12篇 |
1987年 | 23篇 |
1986年 | 15篇 |
1985年 | 21篇 |
1984年 | 16篇 |
1983年 | 5篇 |
1982年 | 21篇 |
1981年 | 8篇 |
1980年 | 9篇 |
1979年 | 5篇 |
1978年 | 1篇 |
排序方式: 共有5946条查询结果,搜索用时 93 毫秒
31.
Xingzhong Guo Zixiao Li Wei Lei Ronghua Ding Yun Zhang Hui Yang 《Molecules (Basel, Switzerland)》2021,26(7)
Microwave heating technology is known as an alternative to traditional gas and electric heating sources. In this work, mesoporous methylsilsesquioxane (MSQ) aerogels were prepared via a sol–gel process accompanied by microwave heating technology, and microwave heating was used in the gelation of sol and the drying of wet gels, respectively. The effects of hexadecyltrimethylammonium chloride (CTAC) as a surfactant and template, hydrochloric acid (HCl) as a catalyst, ethanol as a solvent, sodium hydroxide (NaOH) as a gelation agent, and microwave power on the pore structure of as-prepared MSQ aerogels were investigated in detail. Microwave heating at low power results in the acceleration of sol–gel transition and achieves the gelation within a few minutes. Appropriate amounts of chemical reagents and microwave heating at high power allow the preparation of mesoporous MSQ aerogels with a BET-specific surface area of 681.6 m2·g−1 and a mesopore size of 19 nm, and the resultant MSQ aerogel still has a BET specific surface area as high as 134 m2·g−1 after heat treatment at 600 °C for 2 h, showing high thermal stability. The MSQ aerogels/fibre composite possesses a low thermal conductivity of 0.039 W/(m·k)−1, displaying good thermal insulation. Microwave heating technology is a promising heating method for the preparation of other aerogels. 相似文献
32.
Simon Muench René Burges Alexandra Lex-Balducci Johannes C. Brendel Michael Jäger Christian Friebe Andreas Wild Ulrich S. Schubert 《Journal of polymer science. Part A, Polymer chemistry》2021,59(6):494-501
Despite intensive scientific efforts on the development of organic batteries, their full potential is still not being realized. The individual components, such as electrode materials and electrolytes, are in most cases developed independently and are not adjusted to each other. In this context, we report on the performance optimization of a full-organic solid-state battery system by the mutual adaptation of the electrode materials and an ionic liquid (IL)-based gel polymer electrolyte (GPE). The formulation of the latter was designed for a one-step manufacturing approach and can be applied directly to the electrode surface, where it is UV-cured to yield the GPE without further post-treatment steps. Herein, a special focus was placed on the applicability in industrial processes. A first significant capacity increase was achieved by the incorporation of the IL into the electrode composite. Furthermore, the GPE composition was adapted applying acrylate- and methacrylate-based monomers and combinations thereof with the premise of a fast curing step. Furthermore, the amount of IL was varied, and all combinations were evaluated for their final performance in cells. The latter variation revealed that a high ionic conductivity is not the only determining factor for a good cell performance. Next to a sufficient conductivity, the interaction between electrode and electrolyte plays a key role for the cell performance as it enhances the accessibility of the counter ions to the redox-active sites. 相似文献
33.
Dr. Yanhui Wang Dr. Maroua Bouchneb Rimeh Mighri Dr. Johan G. Alauzun Dr. P. Hubert Mutin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(8):2670-2682
Several non-hydrolytic sol–gel syntheses involving different precursors, oxygen donors, and conditions have been screened aiming to selectively produce mesoporous t-ZrO2 or m-ZrO2 with significant specific surface areas. The in situ water formation was systematically investigated by Karl Fisher titration of the syneresis liquids. XRD and nitrogen physisorption were employed to characterize the structure and texture of the ZrO2 samples. Significant amounts of water were found in several cases, notably in the reactions of Zr(OnPr)4 with ketones (acetone, 2-pentanone, acetophenone), and of ZrCl4 with alcohols (benzyl alcohol, ethanol) or acetone. Conversely, the reactions of Zr(OnPr)4 with acetic anhydride or benzyl alcohol at moderate temperature (200 °C) and of ZrCl4 with diisopropyl ether appear strictly non-hydrolytic. Although reaction time and reaction temperature were also important parameters, the presence of water played a crucial role on the structure of the final zirconia: t-ZrO2 is favored in strictly non-hydrolytic routes, while m-ZrO2 is favored in the presence of significant amounts of water. 1H and 13C NMR analysis of the syneresis liquids allowed us to identify the main reactions responsible for the formation of water and of the oxide network. The morphology of the most interesting ZrO2 samples was further investigated by electron microscopy (SEM, TEM). 相似文献
34.
The catalytic performance of rare-earth metal dialkyl complexes in combination with DMAO(dry methylaluminoxane)is explored.In the presence of 60 equivalents of DMAO,the half-sandwich complex(C13H8CH2Ph)Sc(CH2SiMe3)2(THF)(1)is inert for styrene polymerization,but(C5Me4Ph)Sc(CH2C6H4NMe2-o)2(2)converts 18%styrene into syndiotactic polystyrene.Under the same conditions,the constrained-geometry configuration sandium complex(C13H8CH2Py)Sc(CH2SiMe3)2(3a)displays extremely high catalytic activity(>6420 kg·molSC-1·h-1)and perfect syndiospecific(rrrr>99%)for styrene polymerization,while its lutetium(3b)and yttrium(3c)analogues are nearly inactive.Although the binary catalytic system 3a/DMAO exhibits very low activity for 4-methoxystyrene polymerization,it is an efficient catalyst for the syndioselective polymerization of other styrene derivatives such as 2-methoxystyrene,4-methylthiostyrene,4-fluorostyrene,4-dimethylhydrosilylstyrene,alkyne-susbstituted styrenes and 4-methylstyrene.In addition,the binary system 3a/DMAO can copolymerize ethylene and styrene to give alternating copolymers with a single glass transition at 80℃and 0.4 MPa ethylene pressures.By increasing styrene feed amount from 20 mmol to 60 mmol,the styrene content slight increases from 48.2 mol%to 53.8 mol%,but the polymerization activity is obviously promoted from 240 kg·molSc-1·h-1 to 532 kg·molSc-1·h-1. 相似文献
35.
Qing Liu Zheyu Li Qingyun Ma Xuetian Li Guangyu Li Fanfei Zeng Zhongcai Shao 《印度化学会志》2022,99(6):100491
Polymer network gel method combines the advantages of solid-phase method and liquid phase method, triggering acrylamide (AM) radical polymerization in aqueous solution and N, N′- methylene bis acrylamide (MBAM) active double bond cross-linking reaction, forming polymer chains to form a three-dimensional network. The polymer network space formed by the gel is bound and evenly distributed to the ions in the solution, thereby reducing the contact and aggregation of molecules and achieving the purpose of uniform particle size and small particle size. The principle diagram of network gel is shown in Figure. Using cubic zinc acetate and ammonium molybdate tetrahydrate as raw materials, cubic ZnMoO4 negative electrode materials were prepared with polymer network gel method. The polymer network gel method has various effects on the structure, morphology and electrochemical properties of materials. Besides, the calcination temperature and calcination time were also the key factors to the electrochemical properties of the materials. In this paper, the effects of the ratio of monomer and crosslinker, calcination temperature and calcination time on ZnMoO4 materials were studied by single variable method, the preparation process was optimized, and its characterization and electrochemical tests were carried out. After 100 cycles, the optimized ZnMoO4 electrode has a discharge capacity of 374.0 mAh· g?1, 332.5, 263.5 and 177.1 mAh · g?1 at current densities of 0.1, 0.5, 1.0 and 2.0 A g?1, respectively. The electrochemical results show that the optimized ZnMoO4 has high capacity, large rate capability and excellent cycle stability. 相似文献
36.
Sivaiah Areti Jayshree K. Khedkar Sateesh Bandaru Rohit Teotia Jayesh Bellare Chebrolu Pulla Rao 《Analytica chimica acta》2015
A coumarine–imino–C2-glucosyl conjugate (L) was synthesized and characterized. The conjugate L is found to recognize Cu2+ in aqueous HEPES buffer by exhibiting a 95% fluorescence quenching in pH range 7–10 even in the presence of several biologically and ecologically relevant metal ions. Fluorescence on–off behavior has been clearly demonstrated on the basis of the binding variability of Cu2+ to L. The binding has been elicited through the changes observed in fluorescence, absorption, ESI-MS and 1H NMR titrations. All the other thirteen metal ions studied did not show any change in the fluorescence emission. These ions do not interfere with the recognition of Cu2+ by L. The structural features of [CuL]2 complex in both the isomeric forms were established by DFT computational calculations. The utility of L has been demonstrated by showing its sensitivity toward Cu2+ on a thin layer of silica gel. The L gives sensitive fluorescence signals for Cu2+ even in blood serum and exhibits appropriate fluorescence responses in living cells. 相似文献
37.
将氧化石墨凝胶超声不同时间制备氧化石墨烯(GO)溶胶,再以GO溶胶为前驱体采用一步水热法制备了三维还原氧化石墨烯(3DRGO),采用X射线衍射(XRD)、拉曼光谱、原子力显微镜(AFM)、扫描电子显微镜(SEM)和电化学测试等研究了不同超声时间对3DRGO的形貌、结构及超级电容性能的影响.结果表明,当超声时间不超过120 min时,经水热反应后还原氧化石墨烯均能形成稳定的三维结构,但随着超声时间的延长,三维结构尺寸不断减小,强度增加,样品的内部结构也由片状逐渐向多孔网状转化;当超声时间超过120 min时,还原氧化石墨烯虽具有网状结构,但在宏观上不利于形成稳定的三维结构.电化学测试结果表明,经不同超声时间所制备的还原氧化石墨烯均表现出较好的超级电容性能,其中超声时间为120 min时制备的3DRGO具有更均匀的多孔网状结构,表现出了最佳的超级电容性能,在1 A/g电流密度下其比电容可达328 F/g,即使在20 A/g的大电流密度条件下,其比电容仍可高达240 F/g. 相似文献
38.
39.
Stabilization of Titanium Dioxide Nanoparticles at the Surface of Carbon Nanomaterials Promoted by Microwave Heating 下载免费PDF全文
Rui Zhang Prof. Dr. Saveria Santangelo Dr. Enza Fazio Prof. Dr. Fortunato Neri Dr. Massimiliano D'Arienzo Prof. Dr. Franca Morazzoni Prof. Dr. Yihe Zhang Prof. Dr. Nicola Pinna Dr. Patrícia A. Russo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(42):14901-14910
TiO2 is frequently combined with carbon materials, such as reduced graphene oxide (RGO), to produce composites with improved properties, for example for photocatalytic applications. It is shown that heating conditions significantly affect the interface and photocatalytic properties of TiO2@C, and that microwave irradiation can be advantageous for the synthesis of carbon‐based materials. Composites of TiO2 with RGO or amorphous carbon were prepared from reaction of titanium isopropoxide with benzyl alcohol. During the synthesis of the TiO2 nanoparticles, the carbon is involved in reactions that lead to the covalent attachment of the oxide, the extent of which depends on the carbon characteristics, heating rate, and mechanism. TiO2 is more efficiently stabilized at the surface of RGO than amorphous carbon. Rapid heating of the reaction mixture results in a stronger coupling between the nanoparticles and carbon, more uniform coatings, and smaller particles with narrower size distributions. The more efficient attachment of the oxide leads to better photocatalytic performance. 相似文献
40.