全文获取类型
收费全文 | 3825篇 |
免费 | 202篇 |
国内免费 | 283篇 |
专业分类
化学 | 914篇 |
力学 | 304篇 |
综合类 | 42篇 |
数学 | 2363篇 |
物理学 | 687篇 |
出版年
2023年 | 20篇 |
2022年 | 36篇 |
2021年 | 41篇 |
2020年 | 57篇 |
2019年 | 63篇 |
2018年 | 65篇 |
2017年 | 98篇 |
2016年 | 111篇 |
2015年 | 75篇 |
2014年 | 156篇 |
2013年 | 282篇 |
2012年 | 123篇 |
2011年 | 187篇 |
2010年 | 195篇 |
2009年 | 187篇 |
2008年 | 264篇 |
2007年 | 257篇 |
2006年 | 201篇 |
2005年 | 212篇 |
2004年 | 190篇 |
2003年 | 180篇 |
2002年 | 165篇 |
2001年 | 136篇 |
2000年 | 123篇 |
1999年 | 118篇 |
1998年 | 109篇 |
1997年 | 103篇 |
1996年 | 88篇 |
1995年 | 50篇 |
1994年 | 55篇 |
1993年 | 20篇 |
1992年 | 42篇 |
1991年 | 31篇 |
1990年 | 25篇 |
1989年 | 27篇 |
1988年 | 13篇 |
1987年 | 16篇 |
1986年 | 19篇 |
1985年 | 18篇 |
1984年 | 19篇 |
1983年 | 11篇 |
1982年 | 22篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 18篇 |
1978年 | 18篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1975年 | 6篇 |
1973年 | 9篇 |
排序方式: 共有4310条查询结果,搜索用时 842 毫秒
81.
二组分混合物的最小流化特性 Ⅰ.混合/分离状态与最小流化空隙率 总被引:1,自引:0,他引:1
分析了二组分混合物的3种混合/分离状态及在完全混合时发生连续相转变的极限组成。提出一个判别非等密度体系混合/分离状态的法则与确定混合物空隙率简易可行的随意松散堆积方法。 相似文献
82.
Simultaneous optimization of separation quality and analysis time of the micellar liquid chromatography of nine chlorophenol isomers was investigated. The effect on retention of three experimental parameters was studied using multivariate analysis. The factors studied were the concentration of sodium dodecyl sulfate, propanol content and pH of the mobile phase. The experiments were performed according to the face-centred cube central composite design and the inverse form of the experimental retention times for analytes were fitted to the polynomial models. The results of the analysis of variance showed that the models obtained explain greater than 99% of the variance observed in the chromatograms. Good predictive ability of the models was verified as high values of the statistics R2 and F were obtained for the linear relationship between predicted cross-validated and experimental values of the dependent variable. The study showed that the use of Pareto-optimality method, an approach from multi-criteria decision-making, allows the selection of the best possible combinations of separation and analysis time in micellar liquid chromatography of chlorophenols. 相似文献
83.
In this study, local least squares (LLS) and principal component analysis (PCA) were applied to deal with the disturbances in a data set of chromatographic fingerprints after necessary data transformations. It has been demonstrated that PCA with standard normal variate (SNV) transformation of data led to meaningful classification of 33 different Erigeron breviscapus herbal samples. The result was also corroborated by variance squares discriminant method. The quality of herbal objects was further evaluated, and the causes of this fact have been explained from a chemical point of view. At the same time, it implied an idea for qualitative evaluation of the herbal objects with a common class pattern of chromatographic fingerprints. 相似文献
84.
Martí MP Pino J Boqué R Busto O Guasch J 《Analytical and bioanalytical chemistry》2005,382(2):440-443
The aromatic composition of sugar cane spirits and, in general, of alcoholic beverages, is mainly influenced by the ageing process in wood barrels. There are several factors that affect the quality of the final aged product, but the time of the storage in the barrel is perhaps the most important one. Ageing time must therefore be controlled in order to detect counterfeits; however, this parameter is very difficult to control and, at present, there is no analytical method available to determine it. We propose a quantitative method for determining the ageing time of sugar cane spirits in oak barrels by using an electronic nose based on coupling directly a headspace sampler to a mass spectrometer (HS-MS), and multivariate calibration. The method developed is simple and provides, in 5 min, the ageing time of spirits with an accuracy of about 1 month. 相似文献
85.
86.
Direct CI mass spectrometry profiling of fatty acid methyl esters (FAMEs) from in situ thermal hydrolysis/methylation (THM) of whole bacterial cells with tetramethylammonium hydroxide (TMAH) has been demonstrated as a potential method for real time and fieldable detection/identification of microorganisms. Bacillus anthracis (Ames), Yersinia pestis (Nair. Kenya), Vibrio cholerae (E1 Tor), Brucella melitensis (Abortus wild) and Francisella tularensis (LVS vaccine) were profiled by this method during a 10-month period. Repeatability of the in situ FAME data was calculated using one-way analysis of variance (ANOVA) and a t-test. Artificial neural network (ANN) and multivariate statistics of the FAME profiles were also compared for bacterial identification/classification. Equivalent results were obtained with a multivariate rule building expert system (MuRES) and the ANN. However, the ANN analysis required much less computer time and was deemed the best choice for this application. In situ THM FAME profiles of the bacterial samples provided comparable results with those obtained from the Microbial Identification System (MIDI) (Newark, DE) wet chemistry-gas chromatographic based system. 相似文献
87.
Alexander S. Bondarenko Genady A. Ragoisha 《Journal of Solid State Electrochemistry》2005,9(12):845-849
Potentiodynamic electrochemical impedance spectroscopy provides extraction of potential-dependent space charge layer capacitance
from potentiodynamic impedance spectra of non-stationary semiconductor–electrolyte interface. The new technique has been applied
for acquisition of Mott-Schottky plots of cathodically treated TiO2 anodic films. Cathodic treatment in 1 M H2SO4 increases donor density and flat band potential of TiO2. Freshly doped films show hysteresis in the space charge layer capacitance in cyclic potential scans. The subsequent cycling
eliminates the hysteresis but preserves the greater part of the doping effect.
Presented at the 4th Baltic Conference on Electrochemistry, Greifswald, 13–16 March 2005 相似文献
88.
K. Osaki T. Inoue T. Uematsu Y. Yamashita 《Journal of Polymer Science.Polymer Physics》2002,40(10):1038-1045
Linear viscoelasticity behavior is described with the sum of two terms for polystyrene solutions in tricresyl phosphate around the coil overlapping concentration (K. Osaki, T. Inoue, & T. Uematsu, J Polym Sci Part B: Polym Phys 2001, 39, 211). One is a Rouse–Zimm (RZ) term represented by the Zimm theory with arbitrarily chosen values of the hydrodynamic interaction parameter and the longest relaxation time (τRZ). The other (the L term) consists of a relaxation mode with a single relaxation time (τL > τRZ) and a high‐frequency limiting modulus proportional to the square of the concentration. In this study, we describe the viscosity (η) and first normal stress coefficient (Ψ1) in steady shear with simple formulas. The stress due to the L term is assumed to be given by a Kaye, Bernstein, Kearsley, and Zapas (K‐BKZ) equation with the damping function h(γ) = (1 + 0.2γ2)?1/2, where γ is the magnitude of shear. Contributions to η and Ψ1 from the RZ term are derived from the RZ model, in which the relaxation time in steady flow is given by τst = τ + (τRZ ? τ)/(1 + 0.35τRZ γ˙) instead of τRZ. Here, γ˙ is the rate of shear, and τ is the τRZ value at the infinite dilution limit. η and Ψ1 at various concentrations for two polystyrene samples (with molecular weights of 2890 and 8420 kg mol?1) are well described with parameters derived from dynamic viscoelasticity. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1038–1045, 2002 相似文献
89.
A new quantum scattering approach (linear combination of arrangement channels-scattering wavefunction, LCAC-SW) proposed by Deng and his co-workers is used to calculate collinear state-to-state reaction probabilities for the F + H2(v) → HF(v') + H system. Several interesting problems such M threshold energy, compound states and enhance by translational energy of the reactants and the vibration excitation of products are discussed and they are compared with other theoretical investigations reported in the literature. It is shown that the LCAC-SW approach is the successful one of quantum scattering methods. 相似文献
90.
This research applies semiconductor photocatalysts, which are formed by metal ion exchange on the surface of kaolinite catalyst with cations, to the study of photocatalytic degradation of 4‐chlorophenol. The analysis results of catalyst properties shows that, after sintering at 400 °C, kaolinite catalyst has a particle size of between 10–100 nm indicating the nano level of synthesized catalysts. Under the same condition, kaolinite‐Ag/Zn catalyst works better in degradation efficiency than single kaolinite‐Ag and kaolinite‐Zn catalysts. Kaolinite‐Zn catalyst declines in degradation efficacy after 150 minutes and performs poorer than the other three types of kaolinite catalysts. In the experiments of different amounts of catalysts, when the concentration exceeds 0.1 wt%, utilization of light energy and degradation efficiency will be reduced due to shielding effect. When at different pH values, the higher the pH value, the more OH‐will be released and that is beneficial for reaction with substances and the increase of reaction rate. Finally multivariate analysis proves that there is one determining factor that influences the photocatalytic degradation of 4‐chlorophenol in kaolinite catalysts, named as “the factor with intermediates competition degree,” the one affecting the 4‐CP degradation at different weight percentages that is referred to as the “shielding effect factor.” 相似文献