全文获取类型
收费全文 | 745篇 |
免费 | 45篇 |
国内免费 | 28篇 |
专业分类
化学 | 724篇 |
晶体学 | 3篇 |
力学 | 17篇 |
综合类 | 6篇 |
数学 | 15篇 |
物理学 | 53篇 |
出版年
2023年 | 1篇 |
2022年 | 7篇 |
2021年 | 18篇 |
2020年 | 22篇 |
2019年 | 13篇 |
2018年 | 9篇 |
2017年 | 17篇 |
2016年 | 21篇 |
2015年 | 25篇 |
2014年 | 20篇 |
2013年 | 57篇 |
2012年 | 25篇 |
2011年 | 23篇 |
2010年 | 34篇 |
2009年 | 17篇 |
2008年 | 28篇 |
2007年 | 41篇 |
2006年 | 46篇 |
2005年 | 36篇 |
2004年 | 48篇 |
2003年 | 31篇 |
2002年 | 21篇 |
2001年 | 29篇 |
2000年 | 24篇 |
1999年 | 36篇 |
1998年 | 23篇 |
1997年 | 26篇 |
1996年 | 22篇 |
1995年 | 21篇 |
1994年 | 21篇 |
1993年 | 21篇 |
1992年 | 15篇 |
1991年 | 3篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有818条查询结果,搜索用时 15 毫秒
101.
The standard partial molar free energies, enthalpies, and entropies of sorption of the methylene units in the homologous series
of alkylcyclohexanes andN-alkylsubstituted sixmembered heterocycles (piperidines, morpholines, and thiomorpholines) were determined on a capillary
column with the methylsiloxane OV-101 stationary phase at 70–150°C. A characteristic feature of all series under study is
an abnormally high increase in the values of thermodynamic parameters of sorption on going from the methyl to the ethyl homolog.
This peculiarity is believed to be associated with the presence of thegauche butane orgauche methylethylamine fragments in the ethyl homolog. Thesegauche fragments have an increased sorption activity under conditions of gas chromatography in comparison with the correspondingtrans form.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 500–503, March, 1997. 相似文献
102.
Clarence J. Wolf John A. Bornmann Michael A. Grayson David P. Anderson 《Journal of Polymer Science.Polymer Physics》1992,30(3):251-257
The amount and structure of the crystals formed by the solvent-induced crystallization (SIC) following a sorption-desorption cycle of five fluids (benzene, toluene, chloroform, methylene chloride, and carbon disulfide) in amorphous PEEK was determined by wideangle x-ray scattering (WAXS). The SIC crystal structure was compared with that produced by thermal methods, both those formed at low temperature by heating the amorphous material 10–20°C above Tg or by cooling from the melt. Although smaller in size, the SIC crystals are tighter and more organized than those produced thermally. The WAXS data indicates that all five fluids produce approximately 35% crystallinity in PEEK. Gravimetric data suggest that a low-density region, consisting of either microvoids or highly disordered amorphous region, surrounds the crystals. 相似文献
103.
Kazukiyo Nagai Lora G. Toy Benny D. Freeman Masahiro Teraguchi Giseop Kwak Toshio Masuda Ingo Pinnau 《Journal of Polymer Science.Polymer Physics》2002,40(19):2228-2236
The gas permeability and n‐butane solubility in glassy poly(1‐trimethylgermyl‐1‐propyne) (PTMGP) are reported. As synthesized, the PTMGP product contains two fractions: (1) one that is insoluble in toluene and soluble only in carbon disulfide (the toluene‐insoluble polymer) and (2) one that is soluble in both toluene and carbon disulfide (the toluene‐soluble polymer). In as‐cast films, the gas permeability and n‐butane solubility are higher in films prepared from the toluene‐soluble polymer (particularly in those films cast from toluene) than in films prepared from the toluene‐insoluble polymer and increase to a maximum in both fractions after methanol conditioning. For example, in as‐cast films prepared from carbon disulfide, the oxygen permeability at 35 °C is 330 × 10?10 cm3 (STP) cm/(cm2 s cmHg) for the toluene‐soluble polymer and 73 × 10?10 cm3 (STP) cm/(cm2 s cmHg) for the toluene‐insoluble polymer. After these films are conditioned in methanol, the oxygen permeability increases to 5200 × 10?10 cm3 (STP) cm/(cm2 s cmHg) for the toluene‐soluble polymer and 6200 × 10?10 cm3 (STP) cm/(cm2 s cmHg) for the toluene‐insoluble polymer. The rankings of the fractional free volume and nonequilibrium excess free volume in the various PTMGP films are consistent with the measured gas permeability and n‐butane solubility values. Methanol conditioning increases gas permeability and n‐butane solubility of as‐cast PTMGP films, regardless of the polymer fraction type and casting solvent used, and minimizes the permeability and solubility differences between the various films (i.e., the permeability and solubility values of all conditioned PTMGP films are similar). © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2228–2236, 2002 相似文献
104.
We consider transport of a solute obeying linear kinetic sorption under unsteady flow conditions. The study relies on the
vertical unsaturated flow model developed by Indelman et al. [J. Contam. Hydrol. 32 (1998), 77–97] to account for a cycle of infiltration and redistribution. One of the main features of this type of transport,
as compared with the case of a continuous water infiltration, is the finite depth of solute penetration. In the infiltration
stage an analytical solution that generalizes the previous results of Lassey [Water Resour. Res. 24 (1988), 343–350] and Severino and Indelman [J. Contam. Hydrol. 70 (2004), 89–115] is derived. This solution accounts for quite general initial solute distributions in both the mobile and
immobile concentration. When the redistribution is also considered, two timescales become relevant, namely: (i) the desorption
rate k−1, and (ii) the water application time tap. In particular, we have assumed that the quantity ε =(k tap)−1 can be regarded as a small parameter so that a perturbation analytical solution is obtained. At field-scale the concentration
is calculated by means of the column model of Dagan and Bresler [Soil Sci. Soc. Am. J. 43 (1979), 461–467], i.e. as ensemble average over an infinite series of randomly distributed and uncorrelated soil columns.
It is shown that the heterogeneity of hydraulic properties produces an additional spreading of the plume. An unusual phenomenon
of plume contraction is observed at long times of solute propagation during the drying period. The mean solute penetration
depth is studied with special emphasis on the impact of the variability of the saturated conductivity upon attaining the maximum
solute penetration depth. 相似文献
105.
Postsynthetic Improvement of the Physical Properties in a Metal–Organic Framework through a Single Crystal to Single Crystal Transmetallation
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Thais Grancha Dr. Jesús Ferrando‐Soria Prof. Dr. Hong‐Cai Zhou Prof. Dr. Jorge Gascon Dr. Beatriz Seoane Dr. Jorge Pasán Dr. Oscar Fabelo Prof. Dr. Miguel Julve Dr. Emilio Pardo 《Angewandte Chemie (International ed. in English)》2015,54(22):6521-6525
A single crystal to single crystal transmetallation process takes place in the three‐dimensional (3D) metal–organic framework (MOF) of formula MgII2{MgII4[CuII2(Me3mpba)2]3}?45 H2O ( 1 ; Me3mpba4?=N,N′‐2,4,6‐trimethyl‐1,3‐phenylenebis(oxamate)). After complete replacement of the MgII ions within the coordination network and those hosted in the channels by either CoII or NiII ions, 1 is transmetallated to yield two novel MOFs of formulae Co2II{CoII4[CuII2(Me3mpba)2]3}?56 H2O ( 2 ) and Ni2II{NiII4[CuII2(Me3mpba)2]3}? 54 H2O ( 3 ). This unique postsynthetic metal substitution affords materials with higher structural stability leading to enhanced gas sorption and magnetic properties. 相似文献
106.
《Comptes Rendus Chimie》2015,18(1):88-99
The performance of a microporous activated carbon prepared chemically from olive stones for removing Cu(II), Cd(II) and Pb(II) from single and binary aqueous solutions was investigated via the batch technique. The activated carbon sample was characterized using N2 adsorption–desorption isotherms, SEM, XRD, FTIR, and Boehm titration. The effect of initial pH and contact time were studied. Adsorption kinetic rates were found to be fast and kinetic experimental data fitted very well the pseudo-second-order equation. The adsorption isotherms fit the Redlich–Peterson model very well and maximum adsorption amounts of single metal ions solutions follow the trend Pb(II) > Cd(II) > Cu(II). The adsorption behavior of binary solution systems shows a relatively high affinity to Cu(II) at the activated carbon surface of the mixture with Cd(II) or Pb(II). An antagonistic competitive adsorption phenomenon was observed. Desorption experiments indicated that about 59.5% of Cu(II) and 23% of Cd(II) were desorbed using a diluted sulfuric acid solution. 相似文献
107.
Tuning CO2 Uptake and Reversible Iodine Adsorption in Two Isoreticular MOFs through Ligand Functionalization
下载免费PDF全文
![点击此处可从《化学:亚洲杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Srinivasulu Parshamoni Suresh Sanda Dr. Himanshu Sekhar Jena Prof. Dr. Sanjit Konar 《化学:亚洲杂志》2015,10(3):653-660
The synthesis and characterization of two isoreticular metal–organic frameworks (MOFs), {[Cd(bdc)(4‐bpmh)]}n?2 n(H2O) ( 1 ) and {[Cd(2‐NH2bdc)(4‐bpmh)]}n?2 n(H2O) ( 2 ) [bdc=benzene dicarboxylic acid; 2‐NH2bdc=2‐amino benzene dicarboxylic acid; 4‐bpmh=N,N‐bis‐pyridin‐4‐ylmethylene‐hydrazine], are reported. Both compounds possess similar two‐fold interpenetrated 3D frameworks bridged by dicarboxylates and a 4‐bpmh linker. The 2D Cd‐dicarboxylate layers are extended along the a‐axis to form distorted square grids which are further pillared by 4‐bpmh linkers to result in a 3D pillared‐bilayer interpenetrated framework. Gas adsorption studies demonstrate that the amino‐functionalized MOF 2 shows high selectivity for CO2 (8.4 wt % 273 K and 7.0 wt % 298 K) over CH4, and the uptake amounts are almost double that of non‐functional MOF 1 . Iodine (I2) adsorption studies reveal that amino‐functionalized MOF 2 exhibits a faster I2 adsorption rate and controlled delivery of I2 over the non‐functionalized homolog 1 . 相似文献
108.
Water sorption in polyamide 6.6 has been characterized for a wide range of temperature (25°C to 80°C) and various water activities using a Dynamic Vapor Sorption testing machine. Complex sorption mechanisms govern the water uptake in the material. The competition between two main temperature dependant mechanisms has been observed: a Henry's sorption mechanism that mainly governs the sorption curve at low water activities, and a second mechanism at high water activities that could be related to the formation of water clusters. It is observed that the temperature dependency can mainly be attributed to the Henry's contribution. Four physically based models are then used and identified thanks to the extended experimental database. It is shown that a simple Flory-Huggins model is not able to capture the experimental observations at very high water activities for all the temperatures tested. The ENSIC model is a better choice, but good prediction for very high water activity cannot be obtained. Both modified Park and GAB models can accurately predict the volume fraction of water for the whole ranges of water activity and temperature, although the modified Park model should be preferred considering the number of parameters and the mathematical simplicity. 相似文献
109.
110.