全文获取类型
收费全文 | 743篇 |
免费 | 45篇 |
国内免费 | 28篇 |
专业分类
化学 | 722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 | 5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816条查询结果,搜索用时 203 毫秒
91.
Karen L. Mulfort Omar K. Farha Dr. Christos D. Malliakas Dr. Mercouri G. Kanatzidis Prof. Joseph T. Hupp Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(1):276-281
A new, twofold interpenetrated metal–organic framework (MOF) material has been synthesized that demonstrates dramatic steps in the adsorption and hysteresis in the desorption of CO2. Measurement of the structure by powder X‐ray diffraction (PXRD) and pair distribution function (PDF) analysis indicates that structural changes upon CO2 sorption most likely involve the interpenetrated frameworks moving with respect to each other. 相似文献
92.
Robens E. Keller J. U. Massen C. H. Staudt R. 《Journal of Thermal Analysis and Calorimetry》1999,55(2):383-387
In sorption measurements, volumetric or gravimetric procedures are commonly used to determine the amount adsorbed. At low
pressures, thermomolecular flow and pressure differences according to Knudsen's law disturb measurements. In volumetry, calibration
of the dead space is required; in gravimetry, the influence of buoyancy has to be taken into account. In both cases, adsorption
of the calibrating gas, usually helium, may disturb the measurements [1]. From the calibration measurements, the density of
the sample can in principle be calculated. However, it has been observed in many experiments that its value depends on the
calibrating gas.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
93.
S. V. Bel'tyukova E. I. Tselik A. V. Egorova O. I. Teslyuk 《Journal of Applied Spectroscopy》2003,70(2):307-310
The luminescence of the sorbates of the Eu(III) and Tb(III) complexes on the CaA-type zeolite with derivatives of aliphatic and aromatic carbonic acids has been studied. It is shown that the luminescent materials obtained can be used as light regulators and transformers which absorb energy in the UV spectral region and transform it into visible radiation. 相似文献
94.
羧甲基交联壳聚糖树脂的合成、表征及其应用 总被引:1,自引:0,他引:1
羧甲基交联壳聚糖树脂(C-C-CTS)与普通壳聚糖树脂相比,既能在酸性介质中不溶又不失去其螯合性能.其合成采用简单的2步法,首先用还氧氯丙烷交联,然后羧甲基化.C-C-CTS的结构用红外光谱和X-ray光电子能谱进行表征.C-C-CTS树脂对重金属离子有很好的螯合吸附能力,每种树脂对Pb(Ⅱ),Cu(Ⅱ)和Zn(Ⅱ)的吸附能力分别为8.73,10.12和4.89 mg·g-1,并且在不同的pH条件下对Pb(Ⅱ)、Cu(Ⅱ)和Zn(Ⅱ)有很好的选择性吸附,最后还讨论了C-C-CTS树脂对Pb(Ⅱ)的吸附机理. 相似文献
95.
G. N. Dalimova 《Chemistry of Natural Compounds》2006,42(4):479-482
The ability to form intermolecular coordination of lignin macromolecules and metal ions through both ionic and coordinative
metal—ligand bonds was shown by studying the sorption activity of hydrolyzed lignin from cotton seed husks (HLCSH) and its
aminated derivatives. The studied lignins exhibited high sorption activity for metal ions over the whole range of concentrations
used. The heavy-metal ions fell in the following order of decreasing lignin sorption activity: Fe > Pb > Cu > Cd > Zn.
__________
Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 386–388, July–August, 2006. 相似文献
96.
Y. S. Hu R. Y. F. Liu M. Rogunova D. A. Schiraldi S. Nazarenko A. Hiltner E. Baer 《Journal of Polymer Science.Polymer Physics》2002,40(22):2489-2503
This study examined the oxygen‐transport properties of poly(ethylene terephthalate‐co‐bibenzoate) (PETBB55) crystallized from the melt (melt crystallization) or quenched to glass and subsequently isothermally crystallized by heating above the glass‐transition temperature (cold crystallization). The gauche–trans conformation of the glycol linkage was determined by infrared analysis, and the crystalline morphology was examined by atomic force microscopy. Oxygen solubility decreased linearly with volume fraction crystallinity. For melt‐crystallized PETBB55, extrapolation to zero solubility corresponded to an impermeable crystal with 100% trans glycol conformations, a density of 1.396 g cm?3, and a heat of melting of 83 J g?1. From the melt, PETBB55 crystallized as space‐filling spherulites with loosely organized lamellae and pronounced secondary crystallization. The morphological observations provided a structural model for permeability consisting of impermeable platelets randomly dispersed in a permeable matrix. In contrast, cold‐crystallized PETBB55 retained the granular texture of the quenched polymer despite the high level of crystallinity, as measured by the density and heat of melting. Oxygen solubility decreased linearly with volume fraction crystallinity, but zero solubility corresponded to an impermeable defective crystal with a trans fraction of 0.83 and a density of 1.381 g cm?3. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2489–2503, 2002 相似文献
97.
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
98.
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
99.
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
100.
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