全文获取类型
收费全文 | 2577篇 |
免费 | 250篇 |
国内免费 | 818篇 |
专业分类
化学 | 3335篇 |
晶体学 | 49篇 |
力学 | 22篇 |
综合类 | 31篇 |
数学 | 1篇 |
物理学 | 207篇 |
出版年
2024年 | 4篇 |
2023年 | 88篇 |
2022年 | 103篇 |
2021年 | 186篇 |
2020年 | 176篇 |
2019年 | 136篇 |
2018年 | 121篇 |
2017年 | 131篇 |
2016年 | 159篇 |
2015年 | 118篇 |
2014年 | 142篇 |
2013年 | 226篇 |
2012年 | 233篇 |
2011年 | 149篇 |
2010年 | 135篇 |
2009年 | 190篇 |
2008年 | 155篇 |
2007年 | 190篇 |
2006年 | 166篇 |
2005年 | 152篇 |
2004年 | 116篇 |
2003年 | 102篇 |
2002年 | 90篇 |
2001年 | 49篇 |
2000年 | 45篇 |
1999年 | 53篇 |
1998年 | 41篇 |
1997年 | 35篇 |
1996年 | 15篇 |
1995年 | 33篇 |
1994年 | 27篇 |
1993年 | 21篇 |
1992年 | 19篇 |
1991年 | 5篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 1篇 |
1982年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有3645条查询结果,搜索用时 16 毫秒
81.
82.
Dr. Xingwen Yu Prof. Arumugam Manthiram 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(11):4233-4237
A unique sodium sulfide (Na2S) cathode is developed, which will allow the use of sodium‐free anodes for room‐temperature sodium–sulfur (Na–S) batteries. To overcome the “inert” nature of the Na2S, a special cathode structure is developed by spreading the multi‐walled carbon nanotube (MWCNT)‐wrapped Na2S particles onto MWCNT fabrics. Spectroscopic and electrochemical analyses reveal a series of polysulfide intermediates involved in the charge/discharge of the cell. The Na–S battery prepared in full discharge state with the Na2S/MWCNT cathode provides a remarkable capacity of 500 A h kg?1 (based on sulfur mass) after 50 cycles. 相似文献
83.
The electrochemical bromination of 4-methoxy toluene by two-phase electrolysis yields 3-bromo 4-methoxy toluene at first, which subsequently undergoes side-chain bromination to give 3-bromo 4-methoxy benzyl bromide as a final product in 86% yield. The two-phase electrolysis consists of 25–50% NaBr as aqueous electrolyte and CHCl3 containing aromatic compound as organic phase. The reaction temperature is maintained at 10–25 °C. The probable orientation of bromine atom in an alkyl aromatic compound (nuclear versus side chain) is explained from the experimental result. 相似文献
84.
85.
Roshanak Hatamvand Azim Shams Ehsan Mohammadifar Abdollah Yari Mohsen Adeli 《Journal of polymer science. Part A, Polymer chemistry》2019,57(13):1430-1439
Despite the outstanding properties of hyperbranched polyglycerols such as biocompatibility and multifunctionality, enough attention has not been paid to the synthesis of their functional copolymers. This problem has limited the structural diversity of hyperbranched polyglycerols and hampers further developments and their practical usage. In this work, butyrolactone segments were incorporated into the backbone of polyglycerols by one‐pot ring‐opening copolymerization of a mixture of glycidol and γ‐butyrolactone in the presence of tin(II) 2‐ethylhexanoate. Poly(glycerol‐oligoγ‐butyrolactone)s were then crosslinked by 2,5‐thiophenediylbisboronic acid to obtain polymeric nanonetworks with 140 nm average size. Afterwards, the gold electrode was modified by the polymeric nano‐networks, and it was used for the determination of glucose, glycated hemoglobin, and Escherichia coli in phosphate buffer solution (pH = 9.0) through cyclic voltammetry and impedance spectroscopic. Taking advantage of the straightforward synthesis, cheap precursors and multifunctionality of poly(glycerol‐oligoγ‐butyrolactone)s, they could be used for real‐time sensing of a wide range of biosystems. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1430–1439 相似文献
86.
The dissolution behavior of carbon steel in ammonium chloride (NH4Cl) solution containing sodium thiosulfate (Na2S2O3) of various concentrations (0.01 and 0.1 M) was investigated using electrochemical impedance spectroscopy (EIS) and other nonelectrochemical techniques. The weight loss and polarization measurements indicate a significant increase in the NH4Cl corrosion rate of carbon steel on addition of Na2S2O3. The EIS measurements exhibited two capacitive loops at multiple direct current (dc) potentials for both the concentrations. Electrical equivalent circuit (EEC) and reaction mechanism analysis (RMA) were employed to analyze the impedance data. A four-step mechanism with two intermediate adsorbate species of same charge was proposed to explain the dissolution behavior of carbon steel in the given system. The surface coverage values enumerated that the surface was entirely covered with adsorbed species unlike in the pure NH4Cl system. Charge transfer resistance and polarization resistance values estimated from RMA parameters indicate the increase in a dissolution rate with dc potential. The surface morphology was inspected via field emission scanning electron microscopy, and the corrosion products including surface state of carbon steel electrode were analyzed using energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. 相似文献
87.
Electrochemical oxidation of 2,3‐dihydroxypyridine in aqueous phosphate buffer solution at a glassy carbon electrode has been studied using cyclic voltammetry and controlled potential coulometry. The results indicate that oxidation of 2,3‐dihydroxypyridine on glassy carbon electrode shows an irreversible feature in aqueous solution. This data indicates that the electrochemically generated pyridindione is unstable and via an oxidative conversion pathway converts to a novel highly oxygenated heterocyclic compound. By means of the obtained electrochemical data, an efficient, one‐pot method for the synthesis of this heterocyclic compound based on the oxidative cyclization of 2,3‐dihydroxypyridine under green conditions, and in a good yield and purity is described. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
88.
89.
《Journal of Coordination Chemistry》2012,65(1-4):77-89
Abstract A steric effect in the carbon-skeleton rearrangement catalyzed by heptamethyl cobyrinate perchlorate, [Cob(II)7C1ester]C104, was investigated under electrochemical conditions. The controlled-potential electrolyses of alkyl halides having two carboxylic ester groups of different bulkiness on the same carbon atom, such as 2,2-bis(ethoxycarbonyl)-l-bromopropane, l-bromo-2-tert-butoxycarbonyl-2-ethoxy-carbonylpropane, l-bromo-2-cyclohexyloxycarbonyl-2-ethoxycarbonylpropane, and l-bromo-2-ethoxy-carbonyl-2-phenoxycarbonylpropane, were carried out in N,N-dimethylformamide, as catalyzed by [Cob(II)7C1ester]CIO4, to give the corresponding ester-migrated products in the dark at—1.5 V vs SCE in the presence of acetic acid and at—2.0 V vs SCE without acetic acid. As regards a correlation between bulkiness of an ester group and a migration aptitude, a smaller ester group tends to migrate to the adjacent carbon atom more readily than a larger one. The origin of such a steric effect is discussed with attention to the rate-determining step. 相似文献
90.
《Mendeleev Communications》2021,31(5):726-727
Low-temperature XRD measurements were performed to confirm the phase composition and structural parameters of the electrochemically deposited Cu2ZnSnSe4 thin films on flexible metal substrates. 相似文献