全文获取类型
收费全文 | 5300篇 |
免费 | 965篇 |
国内免费 | 752篇 |
专业分类
化学 | 3972篇 |
晶体学 | 77篇 |
力学 | 431篇 |
综合类 | 67篇 |
数学 | 557篇 |
物理学 | 1913篇 |
出版年
2024年 | 12篇 |
2023年 | 107篇 |
2022年 | 181篇 |
2021年 | 216篇 |
2020年 | 268篇 |
2019年 | 237篇 |
2018年 | 197篇 |
2017年 | 214篇 |
2016年 | 261篇 |
2015年 | 283篇 |
2014年 | 349篇 |
2013年 | 412篇 |
2012年 | 505篇 |
2011年 | 514篇 |
2010年 | 361篇 |
2009年 | 353篇 |
2008年 | 336篇 |
2007年 | 269篇 |
2006年 | 249篇 |
2005年 | 241篇 |
2004年 | 201篇 |
2003年 | 163篇 |
2002年 | 170篇 |
2001年 | 175篇 |
2000年 | 109篇 |
1999年 | 111篇 |
1998年 | 89篇 |
1997年 | 64篇 |
1996年 | 83篇 |
1995年 | 48篇 |
1994年 | 63篇 |
1993年 | 35篇 |
1992年 | 23篇 |
1991年 | 25篇 |
1990年 | 18篇 |
1989年 | 12篇 |
1988年 | 15篇 |
1987年 | 8篇 |
1986年 | 13篇 |
1985年 | 7篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1975年 | 1篇 |
排序方式: 共有7017条查询结果,搜索用时 688 毫秒
131.
The molar heat capacity of the azeotropic mixture composed of ethanol and toluene was measured by a high precision adiabatic calorimeter from 80 to 320 K. The glass transition and phase transitions of the azeotropic mixture were determined based on the heat capacity measurements. A glass transition at 103.350 K was found. A solid-solid phase transition at 127.282 K, two solid-liquid phase transitions at 153.612 and 160.584 K were observed, which correspond to the transition of metastable crystal to stable crystal of ethanol and the melting of ethanol and toluene, respectively. The thermodynamic functions and the excess ones of the mixture relative to the standard temperature 298.15 K were derived based on the relationships of the thermodynamic functions and the function of the measured heat capacity with respect to temperature. 相似文献
132.
Yong Hong Wang Ting Fang Tian Xing Qin Liu Guang Yao Meng 《Journal of membrane science》2006,280(1-2):261-269
The high-quality tubular titania MF membranes are successfully prepared by dip-coating techniques and systematically investigated with regard to their corrosive resistances. The experiments show that dispersants PAA and anatase powder were preferably employed to prepare desired suspensions with solid loading 10–15 wt.% and that suspensions properties significantly affect the final membranes quality. The titania MF membranes with pure water permeability 742.42 l m−2 h−1 bar−1 and 0.1 μm pore diameter have been obtained using the prepared suspensions. The corrosion resistance of titania membranes exhibits that the anatase layers are more stable than the alumina supports in boiling corrosive medium and that the poor quality titania MF membranes become more deteriorated due to its top layer pore blockages and fouling layer formation, which provides a wide range of practical application fields in very hash environments with reliable data supports. 相似文献
133.
The Schiff base‐containing pendant monoaza crown ether HL1, HL2, HL3 and HL4 have been synthesized by condensation of salicylaldehyde with N‐(4‐aminoaryl) monoaza crown ethers, which were prepared conveniently from 4‐nitro‐N, N‐di(hydroxyethyl) aniline or 4‐nitrobenzyl chloride via cyclization or condensation and reduction. The structures of HL1—HL4 were verified by 1H NMR, IR spectra, MS and elemental analysis. Moreover, the oxygenation constants (KO2) and thermodynamic parameters (δH0 and δS0) of their cobalt(II) complexes were determined in the range of ?5 °C to 25 °C, and the effect of crown ring bonded to a Schiff base on the dioxygen affinities of cobalt(II) complexes was also observed as compared to the uncrowned analogue (CoL). 相似文献
134.
Oligomerization and Polymerization of Ethylene Initiated by a Novel Ni(Ⅱ)-Based Acetyliminopyridine Complexes as Single-Site Catalysts
下载免费PDF全文
![点击此处可从《天然气化学杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Baojun Zhang Yanji Wang Gang Wang Jun Cao Shukun Sun Lihua Xing Yongcheng Sun Yunguang Han Hebei University of Technology Tianjin China Research Institute of Daqing Petrochemical Company Daqing Heilongjiang China College of Chemical Science Engineering China University of Petroleum Beijing China 《天然气化学杂志》2007,16(1):64-69
Novel Ni(Ⅱ)-based acetyliminopyridine complexes 1b, 2b, 3b (1-3b), which are synthesized from ligands 1a, 2a, 3a (1-3a) and [NiCl2(DME)], are suitable precursors for the catalysts that are necessary for ethylene oligomerization and polymerization reactions, activated by methylaluminoxane (MAO). The MAO-treated 1-3b presents an active catalytic center, which may oligomerize and polymerize ethylene to produce linearα-olefins and polyethylene, respectively. The molecular weight distributions of oligomers that are obtained are in good agreement with the Schulz-Flory rules for oligomers>C4. The activity of 3b-MAO complex is 6.3×107 g/(molNi·h) at 50℃. The activities and molecular weight distributions of oligomers show significant reliance on the structures of catalyst precursors. 相似文献
135.
A sensitive catalytic method is developed for the spectrophotometric determination of oxalic acid. The procedure is based on the effect of oxalate on the oxidation of Victoria blue B by dichromate in dilute sulfuric acid medium. The reaction is quantitatively estimated by measuring the decrease in absorbance of Victoria blue B at the maximum wavelength of 610nm after quenching the reaction with tap water. The factors effecting the sensitivity and reproducibility of the reaction were studied. The method is not interfered with by foreign species generally associated with oxalate and oxalic acid. The described method is simple, specific, inexpensive and suitable for oxalic acid concentrations of between 0.06 and 9.0µgmL–1. It was validated with satisfactory results by determining oxalic acid content in water extracts from plant materials such as spinach and Lathyrus sativus. 相似文献
136.
Synthesis of poly(thiocarbonate)s from the copolymerization of epoxides and carbon disulfide (CS2) remains a tough challenge, due to inevitable oxygen‐sulfur atom scrambling process. In this work, we utilized the oxygen‐sulfur exchange reaction (O‐S ER) to synthesize a random copolymer with monothiocarbonate and trithiocarbonate units from CS2 and phenyl glycidyl ether (PGE) via metal‐free Lewis pairs. The copolymers contained monothiocarbonate and trithiocarbonate units of which the molar fraction could be tuned by varying either the types of Lewis pairs or the reaction temperature. Keeping track on the intermediate provided an insight in the process of O‐S ER and thus gave a hint to control the product structure. Production and consumption of phenyl thioglycidyl ether was the key process to regulate the chain structure. Remarkably, the oxygen atoms of PGE could be excluded out of the chain, resulting in the nearly complete production of poly(trithiocarbonate)s. Correspondingly, the refractive index of this kind of copolymer could be regulated in a wide range of 1.73—1.79 (at 590 nm). 相似文献
137.
138.
Xian Rong Cai Hao Chen Tao Zhang Xing Xu Ying Li Qing Jiang 《中国化学快报》2007,18(11):1342-1346
A novel oxadiazole-based copolymer has been successfully synthesized through the palladium-catalyzed cross-coupling polycondensation method.The copolymer P is soluble in common organic solvents.Its structure has characterized by ~1H NMR,~(13)C NMR,gel permeation chromatagraphy (GPC),UV-vis absorbance (Abs) and photoluniminescence (PL) spectroscopy,and cyclic voltammetry (CV).Investigation of its optical properties revealed that it is yellow emitting material,and the electrochemical analysis showed that P was well suited poly (2,5-dioctyloxy-p-phenylenevinylene) (PDOCPV) for photovoltaic devices,so the copolymer P is able to act as an electron acceptor in combination with PDOCPV as the electron donor to quench photoluminescence of the copolymer in the blend,indicative of the efficient photoinduced electron transfer from the PDOCPV to the P. 相似文献
139.
A novel protocol for assembling polycyclic ethers was developed and successfully applied to the synthesis of the EFGH ring system of ciguatoxin CTX3C. A key transformation involves construction of an O,S-acetal through coupling of alpha-chlorosulfide and a secondary alcohol under mild conditions. The method is highly applicable to use with sensitive substrates and will enable the synthesis of various natural and artificial polycyclic ethers. [reaction: see text] 相似文献
140.
Jing CHAO Xing Yuan ZHANG Jia Bing DAI Zhen GE Lin Lin FENG 《中国化学快报》2006,17(8):1121-1124
Aqueous acrylic-polyurethane dispersions have become one of the major types of materials used in coating, paint and adhesive industries, because of excellent properties and environmental advantages1-5. However, some properties for cured film such as water… 相似文献