全文获取类型
收费全文 | 5613篇 |
免费 | 133篇 |
国内免费 | 670篇 |
专业分类
化学 | 3370篇 |
晶体学 | 23篇 |
力学 | 237篇 |
综合类 | 32篇 |
数学 | 1786篇 |
物理学 | 968篇 |
出版年
2024年 | 9篇 |
2023年 | 153篇 |
2022年 | 68篇 |
2021年 | 86篇 |
2020年 | 157篇 |
2019年 | 111篇 |
2018年 | 99篇 |
2017年 | 193篇 |
2016年 | 194篇 |
2015年 | 119篇 |
2014年 | 183篇 |
2013年 | 503篇 |
2012年 | 221篇 |
2011年 | 299篇 |
2010年 | 221篇 |
2009年 | 365篇 |
2008年 | 387篇 |
2007年 | 373篇 |
2006年 | 321篇 |
2005年 | 295篇 |
2004年 | 255篇 |
2003年 | 191篇 |
2002年 | 185篇 |
2001年 | 157篇 |
2000年 | 158篇 |
1999年 | 134篇 |
1998年 | 121篇 |
1997年 | 128篇 |
1996年 | 113篇 |
1995年 | 75篇 |
1994年 | 88篇 |
1993年 | 78篇 |
1992年 | 62篇 |
1991年 | 40篇 |
1990年 | 37篇 |
1989年 | 33篇 |
1988年 | 26篇 |
1987年 | 30篇 |
1986年 | 22篇 |
1985年 | 17篇 |
1984年 | 22篇 |
1983年 | 6篇 |
1982年 | 19篇 |
1981年 | 19篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1973年 | 3篇 |
1972年 | 3篇 |
排序方式: 共有6416条查询结果,搜索用时 93 毫秒
931.
Determination of the heats of gasification of polymers using differential scanning calorimetry 总被引:1,自引:0,他引:1
The amount of heat that is required to gasify unit mass of material is one of the key properties that define its ignition resistance and fire response. Knowledge of this property is necessary to assess a material's fire hazard in a particular fire scenario. Nevertheless, even for the most common polymers the values of this property are not well established. Here we present a method for determining the heat of gasification using differential scanning calorimetry and apply this method to a set of ten common plastics and engineering polymers. 相似文献
932.
A series of acrylic acid and 4(5)-vinylimidazole copolymers for a non-hydrous proton transferring membrane used in polymer electrolyte membrane for fuel cell (PEMFC) are reported. The feed ratio of each monomer results in the variation of copolymer as evaluated by Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance spectroscopy (1H-NMR). Differential scanning calorimeter and thermal gravimetric analyzer confirm the thermal properties of copolymer films with Tg at 105-177 °C and Td above 230 °C. The simultaneous analysis of wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) suggests the thermal performance about the decrease in domain size as a consequence of the loss of moisture content in the membrane and the increase in domain size as a consequence of chain mobility after Tg. The proton conductivities under anhydrous condition of the copolymer membranes are in the range of 10−2 S/cm even up to 120 °C. 相似文献
933.
Jorge G. Ibanez Alejandro Alatorre-Ordaz Nikola Batina 《Polymer Degradation and Stability》2008,93(4):827-837
Atomic force microscopy (AFM) is employed to monitor the surface morphology of polypyrrole (PPy) films grown on vitreous carbon substrates during the catalytic reduction of Cr(VI) to Cr(III). The morphology of freshly-prepared films depends on substrate characteristics. Upon reaction, uniform nodules of aggregated PPy clusters appear. No significant differences in surface morphology are found between its oxidized and reduced forms. Loss of catalytic activity after 8-9 oxidation/reduction cycles of exposure to the chromate solution (oxidation) and electrochemical recharging of the film at negative potentials (reduction) correlates well with the observed polymer film dissolution/detachment from the carbon substrate. Formation of well-defined circular features (PPy rings) at different stages leads to a model for the film degradation process that includes formation of Cl2 gas inside the polymer matrix. In the final stages, the bulk of the film typically fractures and detaches from the electrode. A catalytically inactive, ultrathin PPy layer remains on the substrate even after prolonged exposure to the target solution. A review of techniques for the study of PPy aging/degradation is given. 相似文献
934.
Ramon Carbó-Dorca 《Journal of mathematical chemistry》2008,44(1):228-234
An Aufbau recursive algorithm, leading to the construction of molecular Quantum similarity matrices (QSM) with positive definite
structure is described. As a consequence, Molecular Quantum Similarity measures optimization has to be restricted by a recursive
constraint, related to the Euclidian norm of the QSM column elements in Quantum Object density tag reciprocal space. 相似文献
935.
《印度化学会志》2023,100(4):100962
In the proposed work, an investigation of shielding effectiveness (SE) for varying compositions of Graphene, Multiwall carbon nanotubes (MWCNT), and Iron nanoparticles coated on Graphite (Fe@Graphite) was conducted in X-band (8.2 GHz–12.4 GHz). All these are mixed in an LDPE matrix. The nanomaterial was subjected to chemical characterization, i.e., Scanning electron microscopy (SEM), X-ray diffraction (XRD), and vibrating sample magnetometry (VSM). The shielding observed is dominantly due to absorption. The lattice structure which facilitates the shielding due to absorption was the hexagonal graphite structure on whose surface iron nanoparticles were embedded and used as the magnetic filler. At the same time, Graphene and MWCNT act as electrically conducting fillers. The Total shielding effectiveness(SET) was maximum for LDPE, MWCNT, Graphene, and Fe@Graphite, in the ratio of 50: 5: 25: 20 by weight %, and is 49 dB at 9.65 GHz for a sample thickness of 3 mm. 相似文献
936.
ZHAO Jinjin LI Wei WANG Xuechen WEI Xiao ZHU Huiwen QU Wenshan MEN Dandan GAO Zhixiang WEI Bin GAO Hanfei WU Yuchen 《高等学校化学研究》2023,39(1):121-126
Organic memristors with low power consumption, fast write/erasure speed, and complementary metal-oxide-semiconductor(CMOS) compatibility have attracted tremendous attention to mimic biological synapses to realize neuromorphic computation in recent years. In this paper, organic resistive switching memory(ORSM) based on (Z)-3-(naphthalen-2-yl)-2-(4-nitrophenyl)acrylonitrile(NNA) and polymer poly(N-vinylcarbazole)(PVK) composite film was prepared by spin-coating method. Device performance based on NNA:PVK composite films with different mass fractions of NNA were systematically investigated. The ORSM based on PVK:40%(mass fraction) NNA composite film exhibited non-volatile and bipolar memory properties with a switching ratio(Ion/Ioff) of 24.1, endurance of 68 times and retention time of 104 s, a “SET” voltage(Vset) of -0.55 V and a “RESET” voltage(Vreset) of 2.35 V. The resistive switching was ascribed to the filling and vacant process of the charge traps induced by NNA and the inherent traps in PVK bulk. The holes trapping and de-trapping process occurred when the device was applied with a negative or positive bias, which caused the transforming of the conductive way of charges, that is the resistive behaviors in the macroscopic. This study provides a promising platform for the fabrication of ORSM with high performance. 相似文献
937.
Makoto Yonenaga Yusuke Kaiwa Dr. Kouki Oka Prof. Dr. Kenichi Oyaizu Prof. Dr. Kenji Miyatake 《Angewandte Chemie (International ed. in English)》2023,62(30):e202304366
A proof-of-concept study was conducted on an all-solid-state rechargeable air battery (SSAB) using redox-active 2,5-dihydroxy-1,4-benzoquinone (DHBQ) and its polymer (PDBM) and a proton-conductive polymer (Nafion). DHBQ functioned well in the redox reaction with the solid Nafion ionomer at 0.47 and 0.57 V vs. RHE, similar to that in acid aqueous solution. The resulting air battery exhibited an open circuit voltage of 0.80 V and a discharge capacity of 29.7 mAh gDHBQ−1 at a constant current density (1 mA cm−2). With PDBM, the discharge capacity was much higher, 176.1 mAh gPDBM−1, because of the improved utilization of the redox-active moieties. In the rate characteristics of the SSAB-PDBM, the coulombic efficiency was 84 % at 4 C, which decreased to 66 % at 101 C. In a charge/discharge cycle test, the capacity remaining after 30 cycles was 44 %, which was able to be significantly improved, to 78 %, by tuning the Nafion composition in the negative electrode. 相似文献
938.
Yutong Pi Linxia Cui Prof. Wenhao Luo Dr. Haitao Li Dr. Yanfu Ma Dr. Na Ta Xinyao Wang Prof. Rui Gao Prof. Dan Wang Prof. Qihua Yang Prof. Jian Liu 《Angewandte Chemie (International ed. in English)》2023,62(43):e202307096
Mimicking the structures and functions of cells to create artificial organelles has spurred the development of efficient strategies for production of hollow nanoreactors with biomimetic catalytic functions. However, such structure are challenging to fabricate and are thus rarely reported. We report the design of hollow nanoreactors with hollow multishelled structure (HoMS) and spatially loaded metal nanoparticles. Starting from a molecular-level design strategy, well-defined hollow multishelled structure phenolic resins (HoMS-PR) and carbon (HoMS-C) submicron particles were accurately constructed. HoMS-C serves as an excellent, versatile platform, owing to its tunable properties with tailored functional sites for achieving precise spatial location of metal nanoparticles, internally encapsulated (Pd@HoMS-C) or externally supported (Pd/HoMS-C). Impressively, the combination of the delicate nanoarchitecture and spatially loaded metal nanoparticles endow the pair of nanoreactors with size–shape-selective molecular recognition properties in catalytic semihydrogenation, including high activity and selectivity of Pd@HoMS-C for small aliphatic substrates and Pd/HoMS-C for large aromatic substrates. Theoretical calculations provide insight into the pair of nanoreactors with distinct behaviors due to the differences in energy barrier of substrate adsorption. This work provides guidance on the rational design and accurate construction of hollow nanoreactors with precisely located active sites and a finely modulated microenvironment by mimicking the functions of cells. 相似文献
939.
Jing Chen Xuetian Deng Yiyang Gao Yuanjun Zhao Xiangpeng Kong Qiang Rong Junqiao Xiong Demei Yu Shujiang Ding 《Angewandte Chemie (International ed. in English)》2023,62(35):e202307255
All-solid-state lithium metal batteries (LMBs) are considered as the promising higher-energy and improved-safety energy-storage systems. Nevertheless, the electrolyte-electrodes interfacial issues due to the limited solid physical contact lead to discontinuous interfacial charge transport and large interfacial resistance, thereby suffering from unsatisfactory electrochemical performance. Herein, we construct an integrated cathode/polymer electrolyte for all-solid-state LMBs under the action of polymer chains exchange and recombination originating from multiple dynamic bonds in our well-designed dynamic supramolecular ionic conductive elastomers (DSICE) molecular structure. The DSICE acts as polymer electrolytes with excellent electrochemical performance and mechanical properties, achieving the ultrathin pure polymer electrolyte thickness (12 μm). Notably, the DSICE also functions as lithium iron phosphate (LiFePO4, LFP) cathode binders with enhanced adhesive capability. Such well-constructed Li|DSICE|LFP-DSICE cells generate delicate electrolyte-electrodes interfacial contact at the molecular level, providing continuous Li+ transport pathways and promoting uniform Li+ deposition, further delivering superior long-term charge/discharge stability (>600 cycles, Coulombic efficiency, >99.8 %) and high capacity retention (80 % after 400 cycles). More practically, the Li|DSICE|LFP-DSICE pouch cells show stable electrochemical performance, excellent flexibility and safety under abusive tests. 相似文献
940.
共轭聚合物发光和光伏材料研究进展 总被引:5,自引:1,他引:4
聚合物光电功能材料与器件因其广阔的应用前景,1990年以年来吸引了世界各国学术界的广泛关注和兴趣.聚合物光电子器件主要包括聚合物电致发光二极管、聚合物场效应晶体管和聚合物太阳能电池等,其使用的关键材料是共轭聚合物光电子材料,包括共轭聚合物发光材料、场效应晶体管材料和光伏材料等.本文主要对共轭聚合物电致发光材料和光伏材料的研究进展进行综述,介绍了这些聚合物材料的种类、结构和性质以及在聚合物电致发光器件和聚合物太阳能电池中的应用.并讨论了当前共轭聚合物光电子材料中的关键科学问题和今后的发展方向. 相似文献