全文获取类型
收费全文 | 1489篇 |
免费 | 44篇 |
国内免费 | 421篇 |
专业分类
化学 | 1586篇 |
晶体学 | 42篇 |
力学 | 34篇 |
综合类 | 1篇 |
数学 | 6篇 |
物理学 | 285篇 |
出版年
2023年 | 9篇 |
2022年 | 28篇 |
2021年 | 26篇 |
2020年 | 31篇 |
2019年 | 29篇 |
2018年 | 42篇 |
2017年 | 48篇 |
2016年 | 62篇 |
2015年 | 73篇 |
2014年 | 80篇 |
2013年 | 85篇 |
2012年 | 240篇 |
2011年 | 139篇 |
2010年 | 119篇 |
2009年 | 155篇 |
2008年 | 122篇 |
2007年 | 146篇 |
2006年 | 96篇 |
2005年 | 92篇 |
2004年 | 110篇 |
2003年 | 63篇 |
2002年 | 33篇 |
2001年 | 26篇 |
2000年 | 16篇 |
1999年 | 11篇 |
1998年 | 14篇 |
1997年 | 7篇 |
1996年 | 14篇 |
1995年 | 8篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有1954条查询结果,搜索用时 15 毫秒
1.
《中国化学快报》2020,31(9):2353-2357
NiS2 has become a research hotspot of anode materials for Na-ion batteries due to its high theoretical specific capacity. However, the volume effect, the dissolution of polysulfide intermediates and the low conductivity during the charge/discharge process lead to the low specific capacity and poor cycling stability. NiS2/rGO nanocomposite was prepared by a facile two-step process: GO was prepared by modified Hummers method, and then NiS2/rGO nanocomposite was synthesized by l-cys assisted hydrothermal method. NiS2/rGO nanocomposite shows excellent cycle performance and rate performance, which could be attributed to the mesoporous structure on the graphene skeleton with high conductivity. Besides, the chemical constraint of a unique SO bond on NiS2 could inhibit the dissolution of intermediates and the loss of irreversible capacity. 相似文献
2.
《中国化学快报》2020,31(5):1124-1128
In this study,flower-like MoS_2 constructed by nanosheets was synthesized by a simple hydrothermal method.The hydrothermal process was optimized and the effects of hydrothermal condition,including reaction temperature,reaction time and the ratio of Mo source to S source(Mo:S) in precursor,on microwave absorption performances and dielectric properties were investigated.Our results showed that when the reaction temperature was 180℃,the reaction time was 18 h,and the Mo:S was 1:3.5,the synthesized MoS_2 had the best performance:Its minimum reflection loss could reach-55.78 dB,and the corresponding matching thickness was 2.30 mm with a wide effective bandwidth of 5.17 GHz.Further researches on the microwave absorption mechanism revealed that in addition to the destructive interference of electromagnetic waves,various polarization phenomena such as defect dipole polarization were the main reasons for microwave loss.We believe that MoS_2 is a candidate for a practical microwave absorbent. 相似文献
3.
Single crystals of a new silicate carbonate, K2Ca[Si2O5](CO3), have been synthesized in a multi-components hydrothermal solution with a pH value close to neutral and a high concentration of a carbonate mineralizer. The new compound has an axial structure (s.g. P6322) with unit cell parameters a = 5.04789 (15), c = 17.8668 (6) Å. Pseudosymmetry of the structure corresponds to s.g. P63/mmc which is broken only by one oxygen position. The structure consists of two layered fragments: one of the type of the mineral kalsilite (KAlSiO4) and the other of the high-temperature soda-like α-Na2CO3, Ca substituting for Na. The electro-neutral layer K2[Si2O5] (denoted K) as well as the layer Ca(CO3) (denoted S) may separately correspond to individual structures. In K2Ca[Si2O5](CO3) the S-K layers are connected together via Ca-O interactions between Ca atoms from the carbonate layer and apical O atoms from the silicate one, and also via K-O interlayer interactions. A hypothetical acentric structure, sp.gr. P-62c, is predicted on the basis of the order-disorder theory. It presents another symmetrical option for the arrangement of K-layers relative to S-layers. The K,Ca-silicate-carbonate powder produces a moderate SHG signal that is two times larger that of the α-quartz powder standard and close to other silicates with acentric structures and low electronic polarizability. 相似文献
4.
《Arabian Journal of Chemistry》2023,16(2):104494
The dispersion of nickel catalysts is crucial for the catalytic ability of CO2 methanation, which can be influenced by the fabrication method and the operation process of the catalysts. Therefore, a series of fabrication methods, including ultrasonic, hydrothermal, microwave, and co-precipitation, have been applied to prepare 25Ni-5Er-Al2O3 catalysts. The fabrication method can partially influence the structural and catalytic activity of the nickel aluminate catalysts. Among the catalysts modified by Erbium prepared with various methods, the catalyst fabricated by ultrasonic pathway exhibited better catalytic performance and CH4 selectivity especially, at a temperature (400 ℃). The impact of the temperature of the reaction (200–500 °C) was examined under a stoichiometric precursor ratio of (H2:CO2) = 4: 1, atmospheric pressure, and space velocity (GHSV) of 25000 mL/gcath. The results demonstrate that the ultrasonic method is strongly efficient for fabricating Ni-based catalysts with a high BET surface area of about 190.33 m2g?1. The catalyst composed via the ultrasonic technique has 69.38 % carbon dioxide conversion and 100 % methane selectivity at 400 °C for excellent catalytic performance in CO2 methanation reactions. The fabrication effect can be associated with its high surface area, which is achieved via the hot spot mechanism. Besides, the addition of Erbium promotes the Ni dispersion on the supports and stimulates the positive reaction because of the erbium oxygen vacancies. 相似文献
5.
通过两步水热法合成了一种新型的还原氧化石墨烯(RGO)修饰的Bi2WO6(Bi2WO6-RGO), 结果表明其在可见光下的光催化性能得到了显著的提高. 研究了RGO在Bi2WO6-RGO中的含量对其光催化性能的影响, 从而确定出RGO相对于Bi2WO6的最佳掺杂质量比值为1%. 通过扫描电镜(SEM)研究发现, RGO并没有改变Bi2WO6光催化剂的结构和形貌. Bi2WO6-RGO在可见光下的光催化性能得以提高可以归功于RGO. 其可能的机理是石墨烯的存在有利于光生载流子(激子)的分离, 从而导致产生更多的O2·-用于有机染料污染物(如罗丹明B (RhB))的降解. RhB分子在石墨烯上的有效吸附可能也是导致Bi2WO6-RGO光催化性能提高的另一原因. 相似文献
6.
Syntheses,Structures, and Luminescent Properties of d10 Coordination Polymers with 2‐(4‐Carboxyphenyl)‐imidazo[4, 5‐f]‐1, 10‐phenanthroline and 1, 3‐Benzenedicarboxylate Derivatives 下载免费PDF全文
Jie‐Fang Fang Jing‐Xiang Cheng Shu‐Ting Huang Jing Zhang Chang‐Qiong Ni Yan‐Ju Xiong Qian Cheng Fei‐Fei Zhu Yun Li Shan‐Tang Yue 《无机化学与普通化学杂志》2015,641(15):2657-2663
Four ZnII/CdII coordination polymers (CPs) based on 2‐(4‐carboxy‐phenyl)imidazo[4, 5‐f]‐1, 10‐phenanthroline (HNCP) and different derivatives of 5‐R‐1, 3‐benzenedicarboxylate (5‐R‐1, 3‐BDC) (R = NO2, H, OH), [Zn(HNCP)(5‐NO2‐1, 3‐BDC)]n ( 1 ), [Cd(HNCP)(5‐NO2‐1, 3‐BDC)]n ( 2 ), [Zn(HNCP)(1, 3‐BDC)(H2O)2]n ( 3 ), and {[Zn(HNCP)(5‐OH‐1, 3‐BDC)(H2O) · H2O}n ( 4 ) were synthesized under hydrothermal conditions. Compounds 1 – 4 were determined by elemental analyses, IR spectroscopy, and single‐crystal and powder X‐ray diffraction. Compounds 1 and 2 are isomorphous, presenting a 4‐connected uninodal (4, 4)‐sql 2D framework with threefold interpenetration, which are further extended into the three‐dimensional (3D) supramolecular architecture through π ··· π stacking interactions between the aryl rings of 5‐NO2‐1, 3‐BDC. Compared to compound 1 , 3 is obtained by using different reaction temperatures and metal‐ligand ratios, generating a 3D framework with –ABAB– fashion via π ··· π stacking interactions. Compound 4 is a 1D chain, which is further extended into a 3D supramolecular net by hydrogen bonds and π ··· π stacking interactions. The thermogravimetric and fluorescence properties of 1 – 4 were also explored. 相似文献
7.
Two Uranyl Complexes with Pyromellitic Acid. A Heterometallic Complex with U=O–CuII Interaction 下载免费PDF全文
Lingling Liang Yige Cai Xiang Li Ronglan Zhang Jianshe Zhao Chiyang Liu Ng Seik Weng 《无机化学与普通化学杂志》2015,641(10):1744-1748
Two uranyl complexes based on pyromellitic acid were hydrothermally synthesized, and their X‐ray single‐crystal diffraction structures were determined. Complex [UO2(Hbtec)]–(Himd)+ · H2O ( 1 ) (H4btec = pyromellitic acid, imd = imidazole), is an ionic complex, which shows a typical (4, 4) topological structure in the space. A heterometallic complex, UO2Cu(btec)(phen) ( 2 ) (phen = 1,10‐phenanthroline) results from the reaction of uranyl nitrate and copper(II) bromide with pyromellitic acid. The structure of complex 2 revealed that the chains of UO7 and CuO3N2 units were connected to each other through the carboxyl groups and U=O–Cu interactions to create a two‐dimensional framework. 相似文献
8.
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
9.
采用水热法合成了一个钨-钒簇聚物[Cu(en)2]2[WⅥ4.5WV2 VVVⅣ9.5O44{Cu(en)2(H2O)}2]·3H2O(1, en=乙二胺),并通过X射线单晶衍射、元素分析、傅里叶变换红外光谱、X射线粉末衍射、热重分析、价键计算、X射线光电子能谱、电子顺磁共振和磁性分析对其结构和性能进行了表征.结果表明,化合物1是以双支撑的四帽Keggin结构[WⅥ4.5WV2 VⅣ9.5O40(VVO4){Cu(en)2(H2O)}2]4-钨-钒簇合物阴离子为基本结构单元,与4个[ Cu( en)2]2+配合物阳离子以共价键和弱键相连接形成二维层状结构,相邻层又通过氢键连接成三维超分子网络.研究了化合物1的磁性及光催化降解罗丹明B的活性. 相似文献
10.
《Journal of Saudi Chemical Society》2022,26(4):101514
A facile, single-step hydrothermal route is followed to prepare ZnS nanowires with large aspect ratios. The obtained ZnS nanowires deposited on nickel foam (ZnS/Ni-foam) exhibit a specific capacitance of 781 F/g at a current density of 0.5 A/g. An asymmetric supercapacitor fabricated from ZnS/Ni-foam as a positive electrode and jute derived activated carbon coated on Ni-foam (JAC/Ni-foam) as a negative electrode attains a high specific capacitance of 573 F/g at a current density of 0.5 A/g, with an accompanying high energy density of 51 Wh/kg at a power density of 200 W/kg in an extensive operating potential window of 1.2 V. In addition, the ZnS//JAC asymmetric supercapacitor reveals long-term cyclic stability, after 10,000 GCD cycles the device sustain around ~87 % of the initial specific capacitance. These results shed enlighten a new opportunity for promising electrode materials in supercapacitors. 相似文献