全文获取类型
收费全文 | 5043篇 |
免费 | 605篇 |
国内免费 | 269篇 |
专业分类
化学 | 2012篇 |
晶体学 | 61篇 |
力学 | 514篇 |
综合类 | 63篇 |
数学 | 846篇 |
物理学 | 2421篇 |
出版年
2024年 | 9篇 |
2023年 | 29篇 |
2022年 | 94篇 |
2021年 | 104篇 |
2020年 | 110篇 |
2019年 | 101篇 |
2018年 | 113篇 |
2017年 | 140篇 |
2016年 | 169篇 |
2015年 | 121篇 |
2014年 | 199篇 |
2013年 | 412篇 |
2012年 | 249篇 |
2011年 | 279篇 |
2010年 | 222篇 |
2009年 | 273篇 |
2008年 | 333篇 |
2007年 | 308篇 |
2006年 | 266篇 |
2005年 | 269篇 |
2004年 | 220篇 |
2003年 | 231篇 |
2002年 | 172篇 |
2001年 | 169篇 |
2000年 | 148篇 |
1999年 | 166篇 |
1998年 | 113篇 |
1997年 | 108篇 |
1996年 | 81篇 |
1995年 | 91篇 |
1994年 | 59篇 |
1993年 | 70篇 |
1992年 | 74篇 |
1991年 | 56篇 |
1990年 | 51篇 |
1989年 | 34篇 |
1988年 | 42篇 |
1987年 | 38篇 |
1986年 | 24篇 |
1985年 | 26篇 |
1984年 | 21篇 |
1983年 | 11篇 |
1982年 | 16篇 |
1981年 | 20篇 |
1980年 | 19篇 |
1979年 | 11篇 |
1978年 | 12篇 |
1977年 | 14篇 |
1976年 | 5篇 |
1974年 | 5篇 |
排序方式: 共有5917条查询结果,搜索用时 270 毫秒
991.
992.
C. -W. Chang Y. -C. Chou J. -M. Tseng M. -Y. Liu C. -M. Shu 《Journal of Thermal Analysis and Calorimetry》2009,95(2):639-643
Many concerns over unsafe or unknown properties of multi-walled carbon nanotubes (MWNTs) have been raised. The thermal characteristics
regarding stability would represent potential hazards during the production or utilization stage and could be determined by
calorimetric tests for various thermokinetic parameters. Differential scanning calorimetry (DSC) was employed to evaluate
the thermokinetic parameters for MWNTs at various compositions.
Thermoanalytical curves showed that the average heat of decomposition (ΔH
d) of the MWNTs samples in a manufacturing process was about 31,723 J g−1, by identifying them as an inherently hazardous material. In this study, significant thermal analysis appeared in the presence
of sulfuric acid (H2SO4). From the DSC experiments, the purification process of MWNTs could induce an unexpected reaction in the condition of batch
addition with reactants of H2SO4. The results can be applied for designing emergency relief system and emergency rescue strategies during a perturbed situation
or accident. 相似文献
993.
A singularly perturbed problem of third order equation with two parameters is studied. Using singular perturbation method, the structure of asymptotic solutions to the problem is discussed under three possible cases of two related small parameters. The results obtained reveal the different structures and limit behaviors of the solutions in three different cases. And in comparison with the exact solutions of the autonomous equation they are relatively perfect. 相似文献
994.
995.
杨渭清 《纯粹数学与应用数学》2009,25(2):315-320
引入了多尺度向量值多分辨分析.利用矩阵理论,给出多尺度紧支撑向量值正交小波存在的必要条件及其构造方法. 相似文献
996.
The study of properties in waste polymeric materials is important for a further recycling and eventual reuse. The determination of thermal properties of PC-ABS mixtures obtained from waste electric and electronic equipment (WEEE) by using thermogravimetric analysis (TGA) has been carried out in this work. Kinetic parameters, such as apparent activation energies, have been calculated by using the autocatalytic model, which has shown a good correlation with experimental data. A good agreement between calculated and experimental results was observed for PC-based mixtures. This is an indication that the addition of a high amount of ABS permits the creation of a network formed by elastomeric domains which leads to a general increase in heterogeneity of the mixture. 相似文献
997.
Two new charge-scaling methods for efficient modeling of the solvated macromolecular environment in hybrid QM/MM calculations of biological reactions are presented. The methods are extensions of the variational electrostatic projection (VEP) method, and allows a subset of atomic charges in the external environment to be adjusted to mimic, in the active dynamical region, the electrostatic potential and field due to the large surrounding macromolecule and solvent. The method has the advantages that it offers improved accuracy, does not require the use of a three-dimensional grid or auxiliary set of fitting points, and requires only minor molecular simulation code modifications. The VEP-cs and VEP-RVM+cs methods are able to attain very high accuracy (relative force errors of 10(-7) or better with appropriate choice of control parameters), and take advantage of a recently introduced set of high-order discretization schemes and Gaussian exponents for boundary element solvation and VEP methods. The methods developed here serve as potentially powerful tools in the arsenal of computational techniques used in multiscale computational modeling problems. 相似文献
998.
Aminzadeh S Naderi-Manesh H Khajeh K Naderi-Manesh M 《Applied biochemistry and biotechnology》2006,135(3):193-208
For the first time, a polygalacturonase from the culture broth of Tetracoccosporium sp. was isolated and incubated at 30°C in an orbital shaker at 160 rpm for 48h. The enzyme was purified by ammonium sulfate
precipitation and two-step ion-exchange chromatography and had an apparent molecular mass of 36 kDa, as shown by sodium dodecyl
sulfate (SDS)-polyacrylamide gel electrophoresis. Its optimum activity was at pH 4.3 and 40°C, and the K
m
and V
max values of this enzyme (for polygalacturonic acid) were 3.23 mg/mL and 0.15 μmol/min, respectively. Ag+, Co2+, EDTA, Tween-20, Tween-80, and Triton X-100 stimulated polygalacturonase activity whereas Al3+, Ba2+, Ca2+, Fe2+, Fe3+, Ni2+, Mg2+, Mn2+, and SDS inhibited it. In addition, iodoacetamide and iodoacetic acid did not inhibit enzyme activity at a concentration
of 1 mM, indicating that cysteine residues are not part of the catalytic site of polygalacturonase. We studied the kinetic properties
and thermal inactivation of polygalacturonase. This enzyme exhibited a t
1/2 of 63 min at 60°C and its specific activity, turnover number, and catalytic efficiency were 6.17 U/mg, 113.64 min−1, and 35.18 mL/(min·mg), respectively. The activation energy (ΔE
#) for heat inactivation was 5.341 kJ/mol, and the thermodynamic activation parameters ΔG
#, ΔH
#, and ΔS
# were also calculated, revealing a potential application for the industry. 相似文献
999.
1000.
Electron beam evaporation technique was used to prepare TiO2 and Ti2O3 thin films onto glass substrates of thicknesses 50, 500 and 1000 nm for each sample. The structural investigations revealed that the as-deposited films are amorphous in nature. Transmittance measurements in the wavelength range (350-2000 nm) were used to calculate the refractive index n and the absorption index k using Swanepoel's method. The optical constants such as optical band gap , optical conductivity σopt, complex dielectric constant, relaxation time τ and dissipation factor tan δ were determined. The analysis of the optical absorption data revealed that the optical band gap Eg was indirect transitions. The optical dispersion parameters Eo and Ed were determined according to Wemple and Didomenico method. 相似文献