全文获取类型
收费全文 | 2189篇 |
免费 | 153篇 |
国内免费 | 472篇 |
专业分类
化学 | 1858篇 |
晶体学 | 71篇 |
力学 | 152篇 |
综合类 | 30篇 |
数学 | 497篇 |
物理学 | 206篇 |
出版年
2024年 | 4篇 |
2023年 | 34篇 |
2022年 | 50篇 |
2021年 | 90篇 |
2020年 | 69篇 |
2019年 | 64篇 |
2018年 | 54篇 |
2017年 | 85篇 |
2016年 | 101篇 |
2015年 | 70篇 |
2014年 | 82篇 |
2013年 | 167篇 |
2012年 | 113篇 |
2011年 | 104篇 |
2010年 | 101篇 |
2009年 | 111篇 |
2008年 | 103篇 |
2007年 | 116篇 |
2006年 | 117篇 |
2005年 | 106篇 |
2004年 | 125篇 |
2003年 | 106篇 |
2002年 | 110篇 |
2001年 | 88篇 |
2000年 | 87篇 |
1999年 | 76篇 |
1998年 | 81篇 |
1997年 | 49篇 |
1996年 | 53篇 |
1995年 | 41篇 |
1994年 | 39篇 |
1993年 | 42篇 |
1992年 | 31篇 |
1991年 | 24篇 |
1990年 | 15篇 |
1989年 | 15篇 |
1988年 | 13篇 |
1987年 | 13篇 |
1986年 | 9篇 |
1985年 | 14篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1978年 | 1篇 |
1977年 | 5篇 |
1976年 | 1篇 |
1973年 | 3篇 |
排序方式: 共有2814条查询结果,搜索用时 15 毫秒
61.
The influence of spent catalyst from catalytic cracking in fluidized bed on the hydration process of cement and the properties
of cement mortars were studied. The spent catalyst was used as an additive to cement in the mortars (10 and 20% of cement).
The samples of mortars kept in water for28 days, then they were placed in sulfate and chloride media for 2 months (the control
samples were kept in water for 3 months). After this time they were subjected to bending strength and compressive strength
determinations. Thermogravimetric and infrared absorption studies were performed and capillary elevation, capability of binding
heavy metals, and changes in mass and apparent density were determined too. The studies disclosed the pozzolana nature of
spent catalyst and its influence on cement mortars being in contact with corrosive media.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
62.
Y. B. Tewari D. E. Martire S. P. Wasik M. M. Miller 《Journal of solution chemistry》1982,11(6):435-445
From thermodynamics and certain assumptions it is shown that, under the usual experimental conditions, the octanol-water partition coefficient (Ko/w) of a given organic liquid should be the same whether the substance is partitioned neat or as part of a mixture. Measurements of several mixtures of n-propylbenzene (log Ko/w=3.71±0.04)+ethylbenzene (log Ko/w=3.16±0.01) clearly confirm this. It is also shown that the aqueous solubility (Sw) of a neat organic liquid can be related to its aqueous solubility (S
w
), when it is present at volume fraction in an organic liquid mixture, by S
w
=Sw, where is its activity coefficient in the organic mixture. The measured S
w
values for n-propylbenzene + ethylbenzene (1), n-hexane + nitrobenzene (>1) and di-isopropyl ether + chloroform (<1) are found to be in good agreement with the predicted values (average differences of, respectively, <2%, 8% and 6%). In general, the bounds on S
w
are expected to be 0w
w. 相似文献
63.
W. Libuś B. Janaszewski R. Pastewski H. Twardowska 《Journal of solution chemistry》1980,9(10):737-752
Solubility isotherms are reported for the NiCl2·4py, MnCl2·4py, and MnCl2·2py solid pyridinates in a number of pyridine+diluent mixtures at 25°C. Activity coefficients of the solvent components have been derived from the total vapor pressures measured by a static method. The standard free energies of transfer for the NiCl2py4 and MnCl2py4 complexes are the same, within the experimental error, in the pyridine+aprotic diluent mixtures, while marked differences are observed in the pyridine+chloroform mixtures. Marked deviations are observed for chloroform and 1,2-dichloroethane from a correlation between the standard free energy of transfer of the complexes, on one hand, and the Hildebrand's solubility parameter of the solvent, on the other, the latter correlation being roughly valid for aprotic solvents. The deviations are tentatively ascribed to hydrogen bond formation of the type H... between the protic solvents and the coordinated pyridine molecules, enhanced by the d electron delocalization. 相似文献
64.
Hans-Jürgen Buschmann Achim Zielesny Eckhard Schollmeyer 《Journal of inclusion phenomena and macrocyclic chemistry》2006,54(3-4):181-185
The complex formation of the macrocyclic ligand hemicucurbit[6]uril with various salts has been studied in aqueous solution. Due to the low solubility of this ligand the formation of complexes results in an increase of the amount of ligand present in solution. From these measurements the stability constants of the complexes formed are calculated. Hemicucurbit[6]uril only forms cation complexes with cobalt(II), nickel(II) and the uranylion. All other cations examined e.g. silver(I), lead(II) and copper(II) do not form detectable complexes in aqueous solution. For a better understanding of the complexation behaviour some quantum mechanical chemical calculations are performed with Gaussian.Dedicated to Prof. H. Möhwald on the occasion of his 60th birthday. 相似文献
65.
Summary The solubility isotherm of the system Tb2O3-SeO2-H2O at 100° was studied. The compounds of the three-component system were identified by the Schreinemakers’ method as well as by chemical and X-ray phase analyses. Simultaneous TG and DTA analyses of all compounds of the system were made. The mechanism of thermal decomposition was described. 相似文献
66.
We generalize the well-known Baker's superstability result for exponential mappings with values in the field of complex numbers to the case of an arbitrary commutative complex semisimple Banach algebra. It was shown by Ger that the superstability phenomenon disappears if we formulate the stability question for exponential complex-valued functions in a more natural way. We improve his result by showing that the maximal possible distance of an -approximately exponential function to the set of all exponential functions tends to zero as tends to zero. In order to get this result we have to prove a stability theorem for real-valued functions additive modulo the set of all integers .
67.
Based on thermodynamic analysis of interfacial segregation, the segregation enthalpy H
o of a solute I in a given matrix was found to depend linearly on two mutually independent terms reflecting the type of interface and the solid solubility limit X
infI
sup*
at temperature T and can be written as In this equation, the structural dependence of interfacial segregation is contained in H
*() which corresponds to the extrapolated segregation enthalpy of a solute with unlimited solubility in the matrix. The product [Tln(X
infI
sup*
)] is essentially constant with temperature, and can therefore be obtained from data for maximum solid solubility, [Tln(X
infI
sup*
)]max. The parameter v>0 represents the relationship between the activity a
infI
sup*
of a solute at the bulk solid solubility limit in a given matrix and X
infI
sup*
, a
infI
sup*
=(X
infI
sup*
)
v
, and is characteristic for the matrix. Using recent experimental data for silicon, phosphorus, and carbon segregation at well-characterized grain boundaries in oriented bicrystals of -iron, the averaged value
was determined. Values of H
*() range from -8 kJ/mol (general grain boundaries) up to +8 kJ/mol (special grain boundaries). These values are discussed and used for a more precise and generalized construction of grain boundary segregation diagrams of -iron. 相似文献
68.
A model, based on inverse gas chromatography experiments, has been developed for intermolecular interaction and its temperature dependence. The model ascribes to each substance a four-component solubility parameter; the four components reflect the van der Waals, polar, electron donor, and electron acceptor interactive properties. Their values depend on temperature in the same manner as does the cohesive energy. The latter was found to depend only on the critical temperature, the acentric factor, and the reduced temperature. The model was used for evaluation of the solubility parameters from polymer-solvent interaction coefficients and their temperature dependence with high accuracy. For binary solventsolvent mixtures, the free energy of mixing and its temperature dependence, as well as enthalpy of mixing can be derived from this model with a good accuracy. 相似文献
69.
The COSMO-RS method, originally developed for the prediction of liquid-liquid and liquid-vapor equilibrium constants based on quantum chemical calculations, has been extended to solid compounds by addition of a heuristic expression for the Gibbs free energy of fusion. By this addition, COSMO-RS is now capable of a priori prediction of aqueous solubilities of a wide range of typical neutral drug and pesticide compounds. Only three parameters in the heuristic expression have been fitted on a data set of 150 drug-like compounds. On these data an rms deviation of 0.66 log-units was achieved. Later, the model was tested on a set of 107 pesticides, which have been critically selected based on two experimental data sources and by a crosscheck with an independent HQSAR model. On this data set an rms of 0.61 log-units was achieved, without any adjustments to the structurally extremely diverse pesticides. This result verifies the ability of this extended COSMO-RS to predict aqueous solubilities of drugs and pesticides of almost arbitrary structural classes. The new method is COSMO-RSol. 相似文献
70.
S.?BabootaEmail author S.?P.?Agarwal 《Journal of inclusion phenomena and macrocyclic chemistry》2005,51(3-4):219-224
Meloxicam is a non steroidal anti inflammatory drug, used in the treatment of rheumatoid and osteoarthiritis. It is practically insoluble in water and its prolonged use is associated with the incidence of side effects like gastro intestinal perforations, ulcerations and bleeding. Therefore, an attempt has been made to improve the aqueous solubility of the drug by making an inclusion complex using hydroxy propyl β cyclodextrin(HPβ-CD). The complexes were prepared by physical mixture and freeze drying method. The different methods employed for evaluation such as DSC, XRD, SEM and FT-IR studies indicated complete formation of the complex by freeze drying method in a molar ratio of 1:2. The prepared complexes showed improved in-vitro dissolution profile as compared to the pure drug. 相似文献