全文获取类型
收费全文 | 5564篇 |
免费 | 1038篇 |
国内免费 | 601篇 |
专业分类
化学 | 3861篇 |
晶体学 | 56篇 |
力学 | 221篇 |
综合类 | 80篇 |
数学 | 475篇 |
物理学 | 2510篇 |
出版年
2024年 | 23篇 |
2023年 | 115篇 |
2022年 | 183篇 |
2021年 | 203篇 |
2020年 | 199篇 |
2019年 | 194篇 |
2018年 | 195篇 |
2017年 | 154篇 |
2016年 | 267篇 |
2015年 | 272篇 |
2014年 | 295篇 |
2013年 | 368篇 |
2012年 | 525篇 |
2011年 | 600篇 |
2010年 | 346篇 |
2009年 | 356篇 |
2008年 | 369篇 |
2007年 | 311篇 |
2006年 | 286篇 |
2005年 | 223篇 |
2004年 | 200篇 |
2003年 | 135篇 |
2002年 | 164篇 |
2001年 | 119篇 |
2000年 | 128篇 |
1999年 | 119篇 |
1998年 | 102篇 |
1997年 | 116篇 |
1996年 | 101篇 |
1995年 | 87篇 |
1994年 | 70篇 |
1993年 | 79篇 |
1992年 | 45篇 |
1991年 | 68篇 |
1990年 | 47篇 |
1989年 | 38篇 |
1988年 | 15篇 |
1987年 | 16篇 |
1986年 | 20篇 |
1985年 | 16篇 |
1984年 | 12篇 |
1983年 | 11篇 |
1982年 | 7篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有7203条查询结果,搜索用时 15 毫秒
981.
An electrode of hydrated tungsten oxide (WO3?nH2O) embedded chitosan‐co‐polyaniline (CHIT‐co‐PANI) composite was electrochemically prepared on an indium tin oxide (ITO) coated glass surface using mineral acid as a supporting electrolyte. The resulting CHIT‐co‐PANI/WO3?nH2O/ITO electrode was characterized using ultraviolet‐visible spectroscopy (UV‐vis), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), and scanning electron microscopy (SEM). The composite electrode exhibited a three‐dimensional nanofibrous structure with the diameter of the nanofibers ranging from 20 to 100 nm. The CHIT‐co‐PANI/WO3?nH2O/ITO electrode allowed for the low potential detection of NO2 gas in acidic medium. The NO2 gas sensing characteristics were studied by measuring change in the current with respect to concentration and time. Using the CHIT‐co‐PANI/WO3?nH2O/ITO electrode, NO2 gas was detected electrochemically without interference at pH 2.0 and 0.25 V vs. Ag/AgCl. The current of the electrochemical cell with the CHIT‐co‐PANI/WO3?nH2O/ITO electrode decreased linearly with an increase in NO2 gas concentration in a range from 100 to 500 ppb with a response time of eight seconds. 相似文献
982.
A new Keggin polyoxometalate-based polymer, formulated as (Hppy)2Cu2(ppy)4[SiMo12O40] (1) ppy = 4-(5-phenylpyridin-2-yl)pyridine, had been synthesized under hydrothermal conditions. Complex 1 exhibits a one-dimensional polyoxometalate-based chain constructed from Keggin anions of [SiMo12O40]4? weakly connected by dinuclear [Cu(ppy)2] groups. This complex crystallizes in the triclinic space group P-1, a = 12.621(3) Å, b = 13.168(3) Å, c = 17.467(4) Å, α = 86.09(3)°, β = 85.35(3)°, γ = 64.10(3)°, V = 2601.1(9) Å3, Z = 1. The elemental analyses, FT-IR, TG-DTA for this compound were also determined. 相似文献
983.
Yingliang Liu Jianghui Li Huayu Cao Shaokui Cao Zhijian Chen Lixin Xiao Qihuang Gong 《先进技术聚合物》2008,19(11):1584-1589
Two phenothiazine‐based polymers were synthesized by the Heck reaction of 3,7‐divinyl‐N‐octyl‐phenothiazine with 3,7‐diiodo‐N‐octyl‐phenothiazine and 5,8‐dibromo‐2,3‐diethylquinoxaline. The polymers were characterized by the measurements of 1H‐NMR, IR, TG, GPC, CV, UV–Vis, and FL. The results indicated that the introduction of quinoxaline group makes the absorption, PL, and EL emission maxima red‐shifted. The EL emission maximum and the CIE 1931 coordinate value are stabilized at a constant value with the increase in operating voltages. Therefore, the polymers have a stable electroluminescent emission property. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
984.
Tominaga T Tirumala VR Lee S Lin EK Gong JP Wu WL 《The journal of physical chemistry. B》2008,112(13):3903-3909
Double-network hydrogels (DN-gels) prepared from the combination of a moderately cross-linked anionic polyelectrolyte (PE) and an uncross-linked linear polymer solution (NP) exhibit mechanical properties such as fracture toughness that are intriguingly superior to that of their individual constituents. The scheme of double-network preparation, however, is not equally successful for all polyelectrolyte/neutral polymer pairs. A successful example is the combination of poly(2-acrylamido-2-methyl-1-propane sulfonic acid) (PAMPS) cross-linked network and linear polyacrylamide (PAAm), which results in DN-gels with fracture strength under compression approaching that of articular cartilage ( approximately 20 MPa). Small-angle neutron scattering was used to determine the thermodynamic interaction parameters for PAMPS and PAAm in water as a first step to elucidate the molecular origin responsible for this superior property. Measurements on PAMPS/PAAm DN-gels and their solution blend counterparts indicate that the two polymers interact favorably with each other while in water. This favorable PAMPS/PAAm interaction given by the condition chi(PE-NP) < chi(PE-water) 相似文献
985.
Wen-Yan Xu Zhe-Yuan Xu Ze-Kuan Zhang Tian-Jun Gong Yao Fu 《Angewandte Chemie (International ed. in English)》2023,62(40):e202310125
Divergent synthesis of fluorine-containing scaffolds starting from a suite of raw materials is an intriguing topic. Herein, we report the solvent-controlled rhodium-catalyzed tunable arylation of 1-bromo-2,2-difluoroethylene. The selection of the reaction solvents provides switchable defluorinated or debrominated arylation from readily available feedstock resources (both arylboronic acids/esters and 1-bromo-2,2-difluoroethylene are commercially available). This switch is feasible because of the difference in coordination ability between the solvent (CH2Cl2 or CH3CN) and the rhodium center, resulting in different olefin insertion. This protocol allows the convenient synthesis of monofluoroalkenes and gem-difluoroalkenes, both of which are important scaffolds in the fields of medicine and materials. Moreover, this newly developed solvent-regulated reaction system can be applied to the site-selective dechlorinated arylation of trichloroethylene. Overall, this study provides a useful strategy for the divergent synthesis of fluorine-containing scaffolds and provides insight into the importance of solvent selection in catalytic reactions. 相似文献
986.
Jing Cao Tong Mou Bingbao Mei Pengfei Yao Ce Han Xue Gong Ping Song Prof. Zheng Jiang Prof. Thomas Frauenheim Prof. Jianping Xiao Prof. Weilin Xu 《Angewandte Chemie (International ed. in English)》2023,62(43):e202310973
Full understanding to the origin of the catalytic performance of a supported nanocatalyst from the points of view of both the active component and support is significant for the achievement of high performance. Herein, based on a model electrocatalyst of single-iridium-atom-doped iron (Fe)-based layered double hydroxides (LDH) for oxygen evolution reaction (OER), we reveal the first completed origin of the catalytic performance of such supported nanocatalysts. Specially, besides the activity enhancement of Ir sites by LDH support, the stability of surface Fe sites is enhanced by doped Ir sites: DFT calculation shows that the Ir sites can reduce the activity and enhance the stability of the nearby Fe sites; while further finite element simulations indicate, the stability enhancement of distant Fe sites could be attributed to the much low concentration of OER reactant (hydroxyl ions, OH−) around them induced by the much fast consumption of OH− on highly active Ir sites. These new findings about the interaction between the main active components and supports are applicable in principle to other heterogeneous nanocatalysts and provide a completed understanding to the catalytic performance of heterogeneous nanocatalysts. 相似文献
987.
Cong Liu Chunshao Mo Linfeng Zhong Xiaoqi Gong Yang Zhang Xiaotong Wang Fan Yang Jing Li Prof. Jiang Lu Prof. Dingshan Yu 《Angewandte Chemie (International ed. in English)》2023,62(43):e202312016
Here, we for the first time introduce ethoxylation chemistry to develop a new octupolar cyano-vinylene-linked 2D polymer framework (Cyano-OCF-EO) capable of acting as efficient mixed electron/ion conductors and metal-free sulfur evolution catalysts for dual-promoted Li and S electrochemistry. Our strategy creates a unique interconnected network of strongly-coupled donor 3-(acceptor-core) octupoles in Cyano-OCF-EO, affording enhanced intramolecular charge transfer, substantial active sites and crowded open channels. This enables Cyano-OCF-EO as a new versatile separator modifier, which endows the modified separator with superior catalytic activity for sulfur conversion and rapid Li ion conduction with the high Li+ transference number up to 0.94. Thus, the incorporation of Cyano-OCF-EO can concurrently regulate sulfur redox reactions and Li-ion flux in Li−S cells, attaining boosted bidirectional redox kinetics, inhibited polysulfide shuttle and dendrite-free Li anodes. The Cyano-OCF-EO-involved Li−S cell is endowed with excellent overall electrochemical performance especially large areal capacity of 7.5 mAh cm−2 at high sulfur loading of 8.7 mg cm−2. Mechanistic studies unveil the dominant multi-promoting effect of the triethoxylation on electron and ion conduction, polysulfide adsorption and catalytic conversion as well as previously-unexplored −CN/C−O dual-site synergistic effect for enhanced polysulfide adsorption and reduced energy barrier toward Li2S conversion. 相似文献
988.
Dr. Qingpei Liu Dan Zhang Shuaibiao Gao Xianhua Cai Dr. Ming Yao Yao Xu Yifu Gong Ke Zheng Yigui Mao Liyan Yang Dr. Dengfeng Yang Dr. István Molnár Dr. Xiaolong Yang 《Angewandte Chemie (International ed. in English)》2023,62(6):e202214379
Orsellinic acid (OA) derivatives are produced by filamentous fungi using nonreducing polyketide synthases (nrPKSs). The chain-releasing thioesterase (TE) domains of such nrPKSs were proposed to also catalyze dimerization to yield didepsides, such as lecanoric acid. Here, we use combinatorial domain exchanges, domain dissections and reconstitutions to reveal that the TE domain of the lecanoric acid synthase Preu6 of Preussia isomera must collaborate with the starter acyl transferase (SAT) domain from the same nrPKS. We show that artificial SAT-TE fusion proteins are highly effective catalysts and reprogram the ketide homologation chassis to form didepsides. We also demonstrate that dissected SAT and TE domains of Preu6 physically interact, and SAT and TE domains of OA-synthesizing nrPKSs may co-evolve. Our work highlights an unexpected domain–domain interaction in nrPKSs that must be considered for the combinatorial biosynthesis of unnatural didepsides, depsidones, and diphenyl ethers. 相似文献
989.
Qiuyu Li Yunchu Zhang Pengyun Liu Jing Zhong Baihui Gong Prof. Dr. Hequan Yao Prof. Dr. Aijun Lin 《Angewandte Chemie (International ed. in English)》2023,62(4):e202211988
We herein disclose a mild and efficient access to chiral 3-azabicyclo[3.1.0]hexanes via a Pd-catalyzed asymmetric 5-exo-trig cyclization/cyclopropanation/carbonylation of 1,6-enynes. Various nucleophiles, such as alcohols, phenols, amines and water, are well compatible with the reaction system. This reaction forms three C−C bonds, two rings, two adjacent quaternary carbon stereocenters as well as one C−O/C−N bond with excellent regio- and enantioselectivities. The products could be further functionalized to generate a library of 3-azabicyclo[3.1.0]hexane frameworks. 相似文献
990.
Rui Liu Meng-Lan Shen Lian-Feng Fan Xiao-Le Zhou Pu-Sheng Wang Liu-Zhu Gong 《Angewandte Chemie (International ed. in English)》2023,62(4):e202211631
Allylamines are important building blocks in the synthesis of bioactive compounds. The direct coupling of allylic C−H bonds and commonly available amines is a major synthetic challenge. An allylic C−H amination of 1,4-dienes has been accomplished by palladium catalysis. With aromatic amines, branch-selective allylic aminations are favored to generate thermodynamically unstable Z-allylamines. In addition, more basic aliphatic cyclic amines can also engage in the reaction, but linear dienyl allylic amines are the major products. 相似文献