全文获取类型
收费全文 | 1382篇 |
免费 | 264篇 |
国内免费 | 144篇 |
专业分类
化学 | 940篇 |
晶体学 | 9篇 |
力学 | 137篇 |
综合类 | 27篇 |
数学 | 173篇 |
物理学 | 504篇 |
出版年
2024年 | 4篇 |
2023年 | 39篇 |
2022年 | 55篇 |
2021年 | 42篇 |
2020年 | 66篇 |
2019年 | 56篇 |
2018年 | 35篇 |
2017年 | 37篇 |
2016年 | 63篇 |
2015年 | 65篇 |
2014年 | 74篇 |
2013年 | 97篇 |
2012年 | 130篇 |
2011年 | 119篇 |
2010年 | 93篇 |
2009年 | 93篇 |
2008年 | 93篇 |
2007年 | 78篇 |
2006年 | 89篇 |
2005年 | 45篇 |
2004年 | 54篇 |
2003年 | 40篇 |
2002年 | 31篇 |
2001年 | 19篇 |
2000年 | 25篇 |
1999年 | 14篇 |
1998年 | 25篇 |
1997年 | 20篇 |
1996年 | 24篇 |
1995年 | 20篇 |
1994年 | 10篇 |
1993年 | 19篇 |
1992年 | 23篇 |
1991年 | 10篇 |
1990年 | 12篇 |
1989年 | 13篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
排序方式: 共有1790条查询结果,搜索用时 46 毫秒
81.
In this work, various Co3O4-ZSM-5 catalysts were prepared by the microwave hydrothermal method (MH-Co3O4@ZSM-5), dynamic hydrothermal method (DH-Co3O4@ZSM-5), and conventional hydrothermal method (CH-Co3O4/ZSM-5). Their catalytic oxidation of dichloromethane (DCM) was analyzed. Detailed characterizations such as X-ray diffractometer (XRD), scanning microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET), H2 temperature-programmed reduction (H2-TPR), temperature-programmed desorption of O2 (O2-TPD), temperature-programmed desorption of NH3 (NH3-TPD), diffuse reflectance infrared Fourier-transform spectra with NH3 molecules (NH3-DRIFT), and temperature-programmed surface reaction (TPSR) were performed. Results showed that with the assistance of microwave, MH-Co3O4@ZSM-5 formed a uniform core-shell structure, while the other two samples did not. MH-Co3O4@ZSM-5 possessed rich surface adsorbed oxygen species, higher ratio of Co3+/Co2+, strong acidity, high reducibility, and oxygen mobility among the three Co3O4-ZSM-5 catalysts, which was beneficial for the improvement of DCM oxidation. In the oxidation of dichloromethane, MH-Co3O4@ZSM-5 presented the best activity and mineralization, which was consistent with the characterizations results. Meanwhile, according to the TPSR test, HCl or Cl2 removal from the catalyst surface was also promoted in MH-Co3O4@ZSM-5 by their abundant Brønsted acid sites and the promotion of Deacon reaction by Co3O4 or the synergistic effect of Co3O4 and ZSM-5. According to the results of in situ DRIFT studies, a possible reaction pathway of DCM oxidation was proposed over the MH-Co3O4@ZSM-5 catalysts. 相似文献
82.
Promotion Effect of Bismuth on Nickel Electrodeposition and Its Electrocatalysis to Glucose Oxidation 下载免费PDF全文
Metallic Bi and Ni were co‐deposited onto the surface of glass carbon electrode (GCE) from the electrolyte solution containing their respective nitrate to fabricate a Bi/Ni alloy modified GCE (Bi/Ni‐GCE). The purpose is to study the influence of Bi3+ on the deposition of Ni and that of deposited Bi on the electrocatalytic performance of Ni to glucose in alkali solution. The results show that both redox signal of Ni(OH)2/NiOOH and Ni(OH)2/NiOOH mediated electrocatalysis to glucose is remarkably increased in the presence of Bi. It seems that there is a synergistic effect between Bi and Ni on each other’s redox electrochemistry. It’s possible that the firstly deposited Bi on GCE surface helps to the following nucleation and growth of Ni, leading to the deposition of more metallic Ni on GCE surface. An extremely attractive feature of Bi/Ni‐GCE is reflected by the fast response time to the electrocatalytic oxidation of glucose. The electrode nearly responses immediately after glucose is added and it reaches a steady‐state level within only 2 seconds, demonstrating a good electrocatalytic property of Bi/Ni‐GCE. The calibration plot is linear over the wide concentration range of 0–5.8 mM with a sensitivity of 33.96 µA/mM and a correlation coefficient of 0.9985. The detection limit of the glucose was found to be 0.59 µM at a signal‐to‐noise ratio of 3. The fabricated Bi/Ni‐GCE was successfully employed to analyze the glucose level in blood samples, exhibiting high accuracy, strong resistance against inference and good reliability in the practical applications. 相似文献
83.
Synthesis of CuI Trifluoromethylselenates for Trifluoromethylselenolation of Aryl and Alkyl Halides 下载免费PDF全文
Chaohuang Chen Li Ouyang Quanfu Lin Yanpin Liu Chuanqi Hou Prof. Dr. Yaofeng Yuan Prof. Dr. Zhiqiang Weng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(3):657-661
The development of new strategies for synthesis of trifluoromethylthiolate compounds is of considerable importance in pharmaceuticals, agrochemicals, and advanced materials. Accordingly, currently much attention is being devoted to the development of effective methods and reagents for their synthesis. In contrast, considerably less effort has been afforded to the development of preparing C?SeCF3 bonds. Herein we report a concise route to synthesize a family of copper(I) trifluoromethylselenolate reagents by the reaction of CuI with the Ruppert’s reagent (Me3SiCF3), KF, and elemental selenium in the presence of dinitrogen ligands in CH3CN at room temperature. The reagent [Cu(bpy)(SeCF3)]2 was proven to be air‐stable and highly efficient for nucleophilic trifluoromethylthselenolation of a broad range of (hetero)aryl halides and alkyl halides. This method represents a powerful protocol for the construction trifluoromethylselenolate compounds. 相似文献
84.
We present a coarse-grained molecular dynamics simulation study of phase behavior of amphiphilic monolayers at the liquid crystal (LC)/water interface. The results revealed that LCs at interface can influence the lateral ordering of amphiphiles. Particularly, the amphiphile tails along with perpendicularly penetrated LCs between tails undergo a two-dimension phase transition from liquid-expanded into a liquid-condensed phase as their area density at interface reaches 0.93. While, the liquid-condensed phase of the monolayer never appears at oil/water interface with isotropic shape oil particles. These findings reveal the penetration of anisotropic LC can promote ordered lateral organization of amphiphiles. Moreover, we find the phase transition point is shifted to lower surface coverage of amphiphiles when the LCs have larger affinity to the amphiphile tails. 相似文献
85.
Dr. Xiangyuan Ouyang Meifang Wang Linjie Guo Chengjun Cui Ting Liu Yongan Ren Yan Zhao Dr. Zhilei Ge Xiniu Guo Prof. Gang Xie Dr. Jiang Li Prof. Chunhai Fan Prof. Lihua Wang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(29):11934-11942
Fluorescent copper nanoclusters (CuNCs) have been widely used in chemical sensors, biological imaging, and light-emitting devices. However, individual fluorescent CuNCs have limitations in their capabilities arising from poor photostability and weak emission intensities. As one kind of aggregation-induced emission luminogen (AIEgen), the formation of aggregates with high compactness and good order can efficiently improve the emission intensity, stability, and tunability of CuNCs. Here, DNA nanoribbons, containing multiple specific binding sites, serve as a template for in situ synthesis and assembly of ultrasmall CuNCs (0.6 nm). These CuNC self-assemblies exhibit enhanced luminescence and excellent fluorescence stability because of tight and ordered arrangement through DNA nanoribbons templating. Furthermore, the stable and bright CuNC assemblies are demonstrated in the high-sensitivity detection and intracellular fluorescence imaging of biothiols. 相似文献
86.
Lisi Xie Dr. Jia Tian Yingjie Ouyang Xinai Guo Prof. Dr. Weian Zhang Prof. Dr. Ulf-Peter Apfel Prof. Dr. Wei Zhang Prof. Dr. Rui Cao 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(37):15978-15982
Molecular design to improve catalyst performance is significant but challenging. In enzymes, residue groups that are close to reaction centers play critical roles in regulating activities. Using this bioinspired strategy, three water-soluble polymers were designed with appending Co porphyrins and different side-chain groups to mimic enzyme reaction centers and activity-controlling residue groups, respectively. With these polymers, high hydrogen evolution efficiency was achieved in neutral aqueous media for electro- (turnover frequency >2.3×104 s−1) and photocatalysis (turnover number >2.7×104). Porphyrin units are surrounded and protected by polymer chains, and more importantly, the activity can be tuned with different side-chain groups. Therefore, instead of revising molecular structures that is difficult from both design and synthesis points of view, polymers can be used to improve molecular solubility and stability and simultaneously regulate activity by using side-chain groups. 相似文献
87.
88.
Fengjun Liu Zihan Wu Boshang Hou Zhiqiang Dong Yuhua Weng Rui Pan Zhenling Xu Chunyan Zhang Yinyun Lü Xiaoqing Ouyang Chanzi Ruan 《大学化学》2020,35(9):83-88
By using light sensors of the cellphone, we build a simple photometer which can be used in quantitative analysis experiments. We have performed 5 replicate measurements of iron with phenanthroline to verify reproducibility and stability. We find the absorbance of the sample has a good linear relationship with the concentrations of iron with a R2 value around 0.999 and the RSD of 2.81%. The result is 4.94 μg·mL-1 with spectrophotometer and 5.11 μg·mL-1 with our photometer. The photometer is simple, convenient, accurate and realistic by using a phone as detector, which can replace the traditional spectrophotometer in the laboratory class. The students can enhance their understanding of the structure and principle of spectrophotometer by the DIY photometer experiment. 相似文献
89.
作为最小的不饱和环状分子,环丙烯独特的刚性结构和多变的反应活性吸引了化学家的研究兴趣.自1922年Demjanov[1]报道了环丙烯化合物的首例合成以来,现已发展了一系列环丙烯的合成方法.手性环丙烯的合成是通过炔烃和重氮化合物的[2+1]不对称环加成反应.根据底物的不同,这些不对称环加成反应可以分为四类:(a)末端炔烃和单取代重氮化合物的反应,(b)末端炔烃和双取代重氮化合物的反应,(c)非末端炔烃和双取代重氮化合物的反应,(d)非末端炔烃和单取代重氮化合物的反应.在这四类反应中,末端炔烃和单取代重氮化合物的不对称反应相对容易进行.1992年,Doyle和Müller等[2]报道了手性铑催化剂[Rh2(5R-MEPY)4]促进的末端炔烃和重氮醋酸酯之间的不对称环丙烯基化反应(Scheme 1a).随后各种手性催化剂包括[Rh2(OAc)-(DPTI)3][3]、Ir(salen)衍生物[4]和[Co(3,5-diMes-Chen-Phyrin)][5]等被先后报道用于末端炔烃和单取代重氮化合物的不对称[2+1]环加成反应. 相似文献
90.
Yuebin Lian Wenjuan Yang Chufeng Zhang Hao Sun Zhao Deng Wenjie Xu Li Song Zhongwen Ouyang Zhenxing Wang Jun Guo Yang Peng 《Angewandte Chemie (International ed. in English)》2020,59(1):286-294
Reversible oxygen conversion is important for various green energy technologies. Herein we synthesize a series of bimetallic coordination polymers by varying the Ni/Co ratio and using HITP (HITP=2,3,6,7,10,11‐hexaiminotriphenylene) as the ligand, to interrogate the role of metal centres in modulating the activity of the oxygen reduction reaction (ORR). Co3HITP2 and Ni3HITP2 are compared. Unpaired 3d electrons in Co3HITP2 result in less coplanarity but more radical character. Thus, despite of a reduced crystallinity and conductivity, the best ORR activity, comparable to 20 % Pt/C, is obtained for Co3HITP2, showing the 3d orbital configuration of the metal centre promotes ORR. Experimental and DFT studies show a transition of ORR pathway from four‐electron for Co3HITP2 to two‐electron for Ni3HITP2. Rechargeable zinc–air batteries using Co3HITP2 as the air cathode catalyst demonstrate excellent energy efficiency and stability. 相似文献