全文获取类型
收费全文 | 572篇 |
免费 | 11篇 |
国内免费 | 50篇 |
专业分类
化学 | 574篇 |
晶体学 | 7篇 |
力学 | 9篇 |
综合类 | 2篇 |
数学 | 3篇 |
物理学 | 38篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 7篇 |
2019年 | 5篇 |
2018年 | 1篇 |
2017年 | 6篇 |
2016年 | 7篇 |
2015年 | 3篇 |
2014年 | 4篇 |
2013年 | 19篇 |
2012年 | 9篇 |
2011年 | 12篇 |
2010年 | 7篇 |
2009年 | 25篇 |
2008年 | 55篇 |
2007年 | 59篇 |
2006年 | 39篇 |
2005年 | 45篇 |
2004年 | 31篇 |
2003年 | 39篇 |
2002年 | 32篇 |
2001年 | 34篇 |
2000年 | 40篇 |
1999年 | 41篇 |
1998年 | 18篇 |
1997年 | 14篇 |
1996年 | 13篇 |
1995年 | 13篇 |
1994年 | 8篇 |
1993年 | 13篇 |
1992年 | 9篇 |
1991年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有633条查询结果,搜索用时 15 毫秒
71.
M.C.C. Peters I.F. de Oliveira M.G.M. Machado D.C. Ferreira M.H.A. Zanin N. Bou-Chacra 《Materials Today Chemistry》2021
The glucocorticoid derivative of budesonide with a phthalimide group is a drug candidate to treat inflammatory eye diseases; nevertheless, it presents low water solubility. Drug nanocrystals have been proposed to overcome this hurdle. The development of an innovative ophthalmic anti-inflammatory nanosuspension was performed using a design space approach. We obtained the particle size reduction of this glucocorticoid derivative on a nanometer scale (approximately 165.0 nm), applying wet bead milling on a super reduced scale. The design of experiment supported the optimization of the formula evaluating the parameters that influence reducing the particle size and also allowed determining the design space. Considering the two statistical models developed and the size range obtained, we proposed that the optimized formulation for the glucocorticoid derivative nanosuspension may be 1.0 wt% glucocorticoid derivative and 0.092 wt% cetylpyridinium chloride. This formulation was characterized by the morphological, physical–chemical, and mucoadhesive in vitro test and showed potential for ophthalmic use with reduced frequency of product application, improved efficiency, and safety, which may promote better patient compliance. 相似文献
72.
The author gives a detailed survey on thermogravimetric investigations under quasi-isothermal — quasi-isobaric conditions (Q-TG). According to the principle of the technique the heating of the sample is governed by the transformation itself according to the feed-back principle in a way that the transformations should take place at a strictly constant rate, slower by orders of magnitude than in the case of the conventional techniques. Due to this, the transformations take place under ideal conditions, near to physico-chemical requirements.Based on the obtained advantageous results further methods were elaborated, like thermo-dilatometry (Q-TD), evolved gas analysis (Q-EGA) and microdistillation under quasi-isothermal conditions.The second part of the present review deals with DTA and DSC techniques under quasi-isothermal conditions elaborated recentlyThis revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
73.
From a model for isothermal oxidation kinetics in nanosized ferrite spinels based on a diffusion-induced stress effect, the
authors present a modeling of the DTG curves for the oxidation of Fe2+ and Mo3+ cations on octahedral sites of a molybdenum ferrite. This has been made by considering that the chemical diffusion coefficient
is given by the relation
, when D
o is a pre-exponential factor, E
a
′
an activation energy and V
a an activation energy induced by the oxidation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
74.
Wang H.-D. Li Y.-T. Ma P.-H. Zeng X.-C. 《Journal of Thermal Analysis and Calorimetry》2002,69(2):575-581
A complex of N,N'-ethylenebis(salicylideneiminato)diaquochromium(III) nitrate, [Cr(salen)(H2O)2]NO3 was characterized and its decomposition mechanism was studied by TG. The IR spectrum and X-ray analysis were examined for the complex. The non-isothermal kinetic data were analyzed by means of the Achar method and the Coats—Redfern method. The most probable kinetic model function was suggested by comparison of the kinetic parameters.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
75.
Holubová J. Černošek Z. Černošková E. 《Journal of Thermal Analysis and Calorimetry》2000,62(3):715-719
The applicability of the kinetic analysis of data obtained by non-isothermal differential scanning calorimetry (DSC) is discussed.
The Johnson-Mehl-Avrami (JMA) model was used for the computer simulation of DSC traces subsequently analysed by common methods
of kinetic analysis of non-isothermal data. For the temperature-independent kinetic exponent n of the JMA equation, the kinetic
analysis was shown to provide correct results, e.g. a correct kinetic model and apparent activation energy. On the other hand,
for the temperature-dependent kinetic exponent, there is a great possibility of erroneous determination of the correct kinetic
model and apparent activation energy, especially at higher heating rates. Since the temperature dependence of n cannot be determined on the basis of non-isothermal DSC experiments, conclusions must be drawn with appropriate caution.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
76.
煤沥青改质非等温动力学研究 总被引:4,自引:1,他引:3
The non-isothermal kinetics for mesophase transformation of Baogang-I coal tar pitch (I-CTP), soft pitch consisted of I-CTP and 18% phenanthrene residue oil (PRO) or I-CTP and 30% PRO have been studied in a thermal conversion unit. Kinetic parameters were calculated by using an integral method. Results showed that the process of mesophase pitch transformation could be described in first order reaction. The activation energy of I-CTP is 175.36kJ/ mol. But adding 30% PRO, which improved the reactivity of I-CTP with activation energy is 138.07kJ/mol, is not beneficial to mesophase transformation. 相似文献
77.
Blue vitriol (copper(II) sulfate pentahydrate), CuSO4·5H2O has been chosen and investigated for its effectiveness as a flame-retardant, when impregnated into cotton fabric (cotton
with a plain structure; woven 180 g m−2, with 22 numbers of yarns per 10 mm). Using the vertical flame test, the extent of resistance to burning of the specimens
has been determined. The impregnation was accomplished via dipping and stirring of bone-dried, weighed fabrics into the individual
and suitable concentrations of the salt at room temperature. Afterwards the samples were squeeze rolled and dried horizontally
at 110°C for 30 min in an oven and cooled in a desiccator and reweighed with an analytical precision. They were then kept
under ordinary conditions overnight prior the fulfillment of the vertical flame test. The efficient quantities of the aforesaid
salt expressed in g per 100 g dry fabric have been determined in an average figure of 12.75%. Estimation of uniformity in
a selected sample was carried out via a spectrophotometer and results are in favor of the heterogeneous distribution of the
salt in the fabric’s middle sectors. However initial and final parts of specimen showed to be rather uniformed. Thermogravimetric
analysis of the pure cotton and the treated ones with insufficient and effective amounts of the salt were fulfilled and their
thermograms were compared and commented. The results obtained for the effect of copper(II) sulfate comply with ‘The Dust or
Wall Effect Theory’. This action is also assigned to the condensed phase retardation. 相似文献
78.
L. Q. Ji 《Journal of Thermal Analysis and Calorimetry》2008,91(3):885-889
Three rational fraction approximations for the temperature integral have been proposed using the pattern search method. The
validity of the new approximations has been tested by some numerical analyses. Compared with several published approximating
formulas, the new approximations is more accurate than all approximations except the approximations proposed by Senum and
Yang in the range of 5≤E/RT≤100. For low values of E/RT, the new approximations are superior to Senum-Yang approximations as solutions of the temperature integral. 相似文献
79.
Bernardi M. Inês B. Araújo Vinícius D. Mesquita Alexandre Frigo Geraldo J. M. Maia Lauro J. Q. 《Journal of Thermal Analysis and Calorimetry》2009,95(3):923-928
Novel zinc(II) complex compounds of general formula Zn(C6H5COO)2·L2 (where L=caffeine (caf) and urea (u)) were synthesized and characterized by elemental analysis and IR spectroscopy. The thermal behaviour
of the complexes was studied during heating in air by thermogravimetry. It was found that the thermal decomposition of the
anhydrous Zn(II) benzoate compounds with bioactive ligands was initiated by the release of organic ligands at various temperatures.
On further heating of the compounds up to 400°C the thermal degradation of the benzoate anions took place. Zinc oxide was
found as the final product of the thermal decomposition of all zinc(II) benzoate complex compounds heated to 600°C. Results
of elemental analysis, infrared spectroscopy, mass spectroscopy and thermogravimetry are presented. 相似文献
80.
P. Budrugeac 《Journal of Thermal Analysis and Calorimetry》2008,92(1):291-296
The thermo-oxidative degradation of poly(vinyl alcohol) (PVA) has been investigated by TG+DTG+DTA simultaneous analysis performed
in static air atmosphere, at four heating rates, namely 3, 5, 10 and 15 K min−1. TG, DTG and DTA curves showed that, in the temperature range 25–700°C, four successive processes occur. The first process
consisting in the loss of physical adsorbed water is followed by three processes of thermal and/or thermo-oxidative degradations.
The processing of the non-isothermal data corresponding to the second process (the first process of thermo-oxidation) was
performed by using Netzsch Thermokinetics — A Software Module for Kinetic Analysis.
The dependence of the activation energy evaluated by Friedman’s isoconversional method on the conversion degree shows that
the investigated process is complex one. The mechanism of this process and the corresponding kinetic parameters were determined
by Multivariate Non-linear Regression Program and checked for quasi-isothermal experimental data. It was pointed out that
the first process of thermo-oxidation of PVA consists in three consecutive steps having Avrami-Erofeev kinetic model. The
obtained results can be used for prediction of the thermal lifetime of PVA corresponding to a certain temperature of use and
an endpoint criterion. 相似文献