全文获取类型
收费全文 | 4431篇 |
免费 | 732篇 |
国内免费 | 422篇 |
专业分类
化学 | 3158篇 |
晶体学 | 44篇 |
力学 | 277篇 |
综合类 | 46篇 |
数学 | 436篇 |
物理学 | 1624篇 |
出版年
2024年 | 11篇 |
2023年 | 122篇 |
2022年 | 171篇 |
2021年 | 171篇 |
2020年 | 210篇 |
2019年 | 164篇 |
2018年 | 141篇 |
2017年 | 121篇 |
2016年 | 197篇 |
2015年 | 174篇 |
2014年 | 241篇 |
2013年 | 275篇 |
2012年 | 384篇 |
2011年 | 361篇 |
2010年 | 267篇 |
2009年 | 266篇 |
2008年 | 287篇 |
2007年 | 277篇 |
2006年 | 276篇 |
2005年 | 182篇 |
2004年 | 127篇 |
2003年 | 111篇 |
2002年 | 98篇 |
2001年 | 88篇 |
2000年 | 87篇 |
1999年 | 100篇 |
1998年 | 90篇 |
1997年 | 89篇 |
1996年 | 65篇 |
1995年 | 90篇 |
1994年 | 74篇 |
1993年 | 44篇 |
1992年 | 58篇 |
1991年 | 45篇 |
1990年 | 40篇 |
1989年 | 26篇 |
1988年 | 16篇 |
1987年 | 14篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有5585条查询结果,搜索用时 15 毫秒
141.
142.
Xujiao Ma Yajie Yang Rongchen Ma Yunfeng Zhang Xiaoqin Zou Shoujun Zhu Xin Ge Ye Yuan Wei Zhang Guangshan Zhu 《Chemical science》2020,11(44):12187
Despite their remarkable mechanical, optical, and electrical properties, inorganic particles and dynamic polymer assemblies encounter difficulties in their compatibility with regards to structural order and complexity. Here, covalent organic frameworks (COFs) constructed through reversible coupling reactions were exploited as dynamic porous polymers to prepare inorganic nanocrystal-polymer assemblies. Under an in situ growth process, carbon quantum dots (CDs) were gradually prepared in the COF cavity, with a narrow size distribution (2 ± 0.5 nm). The well-established assemblies achieve effective energy transfer from the inorganic to the organic part (efficiency > 80%), thus rendering a ∼130% increase in quantum yield compared with the pristine COF network. Notably, the hybrid material realizes a simple, selective, and sensitive diagnostic tool for urine copper, surpassing the detection limit of COF solid by 150 times. Beyond the scientific and fundamental interests, such hybrid assemblies are attractive from technological perspectives as well, for example, in energy storage, electronics, catalysis, and optics.Despite their remarkable mechanical, optical, and electrical properties, inorganic particles and dynamic polymer assemblies encounter difficulties in their compatibility with regards to structural order and complexity. 相似文献
143.
Furostanol saponins with inhibitory action against COX-2 production from Tupistra chinensis rhizomes
Kun Zou Jun Zhi Wang Jun Wu Yuan Zhou Chuang Liu Fei Jun Dan Ya Xiong Zhang Jin Yang 《中国化学快报》2007,18(10):1239-1242
Two furostanol saponins were obtained from the n-butanol fraction of methanol extract from Tupistra chinensis rhizomes,a folk medicine of Shennongjia Forest District of Hubei Province.Their structures were determined as (25S)-26-O-(β-D-glucopyranosyl)- furost-1β,3β,22α,26-tetrol-3-O-β-D-glucopyranosyl-(1→4)-β-D-glucopyranosyl-(1→2)-β-D-glucopyranoside (1) and (25R)- 26-O-(β-D-glucopyranosyl)-furost-1β,3β22α,26-tetrol 3-O-β-D-glucopyranosyl-(1→4)-β-D-glucopyranosyl-(1→2)-β-D-glu- copyranoside (2),on basis of chemical and spectroscopic evidences.1 and 2 displayed marked inhibitory action towards COX-2 production in macrophages of the rat abdomen induced by LPS at 20μg/mL. 相似文献
144.
Zhang B Li JF Zhong QL Ren B Tian ZQ Zou SZ 《Langmuir : the ACS journal of surfaces and colloids》2005,21(16):7449-7455
Core-shell Au-Pt nanoparticles were synthesized by using a seed growth method and characterized by transmission electron microscopy, X-ray diffraction, and UV-vis spectroscopy. Au(core)-Pt(shell)/GC electrodes were prepared by drop-coating the nanoparticles on clean glassy carbon (GC) surfaces, and their electrochemical behavior in 0.5 M H2SO4 revealed that coating of the Au core by the Pt shell is complete. The electrooxidation of carbon monoxide and methanol on the Au(core)-Pt(shell)/GC was also examined, and the results are similar to those obtained on a bulk Pt electrode. High quality surface-enhanced Raman scattering (SERS) spectra of both adsorbed CO and thiocyanate were observed on the Au(core)-Pt(shell)/GC electrodes. The potential-dependent SERS features resemble those obtained on electrochemically roughened bulk Pt or Pt thin films deposited on roughened Au electrodes. For thiocyanate, the C-N stretching frequency increases with the applied potential, yielding two distinctly different dnu(CN)/dE. From -0.8 to -0.2 V, the dnu(CN)/dE is ca. 50 cm(-1)/V, whereas it is 90 cm(-1)/V above 0 V. The bandwidth along with the band intensity increases sharply above 0 V. At the low-frequency region, Pt-NCS stretching mode at 350 cm(-1) was observed at the potentials from -0.8 to 0 V, whereas the Pt-SCN mode at 280 cm(-1) was largely absent until around 0 V and became dominant at more positive potentials. These potential-dependent spectral transitions were attributed to the adsorption orientation switch from N-bound dominant at the negative potential region to S-bound at more positive potentials. The origin of the SERS activity of the particles is briefly discussed. The study demonstrates a new method of obtaining high quality SERS on Pt-group transition metals, with the possibility of tuning SERS activity by varying the core size and the shell thickness. 相似文献
145.
Xu X Zhao Z Song P Zhou G Xu J Deng P Bourdet G Chanteloup JC Zou JP Fulop A 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(11-12):2444-2447
Infrared (1.2-1.6 microm) luminescence in a ytterbium aluminium garnet (YbAG) crystal, doped with Cr (0.05at.%) ions, was investigated under CW laser diode pumping (lambda=940 nm). The Cr4+ emission band was observed with its peak at 1.34 microm and measured to be about 1.3 times with respect to Yb3+ IR luminescence (lambda=1.03 microm). We demonstrate that for the excitation wavelength of 940 nm Yb3+ ions act as sensitizers of the 3B2(3T2)-3B1(3A2) emission of Cr4+ ions. This crystal is promising as a high-efficient system for tunable laser (1.2-1.6 microm) output. 相似文献
146.
Zou Jianzhong Hu Xiaodong Duan Chenying Xu Zheng You Xiaozeng Mak Thomas C. W. 《Transition Metal Chemistry》1998,23(4):477-480
Reaction of either K3[Fe(CN)6] or K4[Fe(CN)6] with a macrocyclic CuII complex, [Cu(teta)](ClO4)2 (teta = 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacylotetradecane), in aqueous solution gave the same product as shown by spectroscopic and physicochemical characterisation. The crystal structure of the complex shows that it is a one-dimensional linear chain type heterobinuclear FeIII–CuII polymer. The unit is composed of a [Cu(teta)(H2O)2]2+ cationic complex, a FeIII–CuII alternate linear chain unit, a ClO
4
–
ion and four water molecules. The Cu atom is coordinated in a distorted octahedral arrangement by four nitrogen atoms from one teta ligand and two nitrogen atoms of the bridging cyanide groups. The Cu—N bond distances involving the cyanide bridges, 2.522(7) and 2.608(7)Å, respectively, indicate weak antiferromagnetic interactions between the FeIII and CuII atoms. 相似文献
147.
本文提出平行催化体系的对位叠式循环方波伏安法,并对共作了系统的研究,推导了这一方法的催化电流理论方程,并用验验证这理论的正确性,得到其各脉冲电流皆为同方向,对位叠式循环催化电流相当于将电流叠加4次,而波形不受方波幅度大小的影响,因而灵敏度和分辨率有较大提高,优于其它方波伏安法。 相似文献
148.
Weiping Gan Xiaosong Cao Yi Shi Lei Zou Haifeng Gao 《Journal of polymer science. Part A, Polymer chemistry》2018,56(19):2238-2244
Copper-catalyzed azide-alkyne cycloaddition polymerization (CuAACP) of AB2 monomers demonstrated a chain-growth mechanism without any external ligand because of the complexation of in situ formed triazole groups with Cu catalysts. In this study, we explored the use of various ligands that affected the polymerization kinetics to tune the polymers’ molecular weights and the degree of branching (DB). Eight ligands were studied, including polyethylene glycol monomethyl ether (PEG350, Mn = 350), tris(benzyltriazolylmethyl)amine (TBTA), 2,6-bis(1-undecyl-1H-benzo[d]imidazol-2-yl)pyridine (Py(DBim)2), 2,2′-bipyridyl (bpy), 4,4′-di-n-nonyl-2,2′-bipyridine (dNbpy), N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA), N,N,N′,N″,N″-penta(n-butyl)diethylenetriamine (PBuDETA), and N,N,N′,N″,N″-pentabenzyldiethylenetriamine (PBnDETA). All ligands except PEG350 exhibited stronger coordination with Cu(I) than the polytriazole polymer, which freed the Cu catalyst from polymers and resulted in dominant step-growth polymerization with simultaneous chain-growth feature. Meanwhile, the use of PEG350 ligand retained the confined Cu in the polymer, demonstrating a chain-growth mechanism, but lower polymer molecular weights as compared with the no-external-ligand polymerization. Results indicated that aliphatic substituent groups on ligands had little effect on the molecular weights and DB of the polymers, but rigid aromatic substituent groups decreased both values. By varying the ligand species and amounts, hyperbranched polymers with DB value ranging from 0.53 ([TBTA]0/[Cu]0 = 5) to 0.98 ([PMDETA]0/[Cu]0 = 2) have been achieved. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2238–2244 相似文献
149.
Eleven triazolyl substituted tetrahydrobenzofuran derivatives were synthesized in high yields as novel H+/K+‐ATPase inhibitor via one‐pot CuI‐catalyzed three‐component click reaction of azide, secondary amine and 3‐bromopropyne under mild conditions in water. Their structures were characterized by NMR, IR, ESI‐MS, elemental analysis and single‐crystal X‐ray diffraction analysis. Most of the target compounds exhibited better H+/K+‐ATPase inhibitory activity than commercial omeprazole with IC50 values less than 15 µmol·L?1. The initial structure‐activity analysis suggested that the triazole substituted by cycloalkyl, aromatic ring or O‐containing side‐chain seemed to be beneficial for enhancing the activity. 相似文献
150.
Zirui Song Kangyu Zou Xuhuan Xiao Xinglan Deng Shuo Li Prof. Dr. Hongshuai Hou Prof. Dr. Xiaoming Lou Prof. Dr. Guoqiang Zou Prof. Dr. Xiaobo Ji 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(65):16082-16092
Nowadays sodium-based energy storage systems (Na-based ESSs) have been widely researched as it possesses the possibility to replace traditional energy storage media to become next generation energy storage system. However, due to the irreversible loss of sodium ions in the first cycle, development of Na-based ESSs is limited. Presodiation, as a strategy of adding excess sodium ions to the system in advance, accomplishes the enhancement of electrochemical performance. In this minireview, different presodiation strategies applied in sodium-based energy storage systems will be summarized in detail, their functions and corresponding mechanisms will be discussed as well. Furthermore, the current novel application of presodiation method in other aspects of Na-based ESSs will be mentioned additionally. At last, in the view of present research status of presodiation, issues that can be mitigated are put forward and guidelines are given on how to deliberate in-depth presodiation technology in the future, dedicating to promote the further development of Na-based ESSs. 相似文献