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排序方式: 共有7641条查询结果,搜索用时 31 毫秒
31.
基于一阶非线性梁理论和物理中面概念,导出了纵横向载荷作用下功能梯度材料(FGM)梁非线性弯曲和过屈曲问题的控制方程,并获得了该问题的精确解;据此解研究了梯度材料性质、外载荷、横向剪切变形以及边界条件等因素对功能梯度材料梁非线性力学行为的影响,分析中假设功能梯度材料性质只沿梁厚度方向,并按成分含量的幂指数函数形式变化。结果表明:纵横载荷共同作用下,功能梯度梁的弯曲构形将有无限多个;随着梯度指数的增大,梁的变形减小,临界载荷升高;随着长高比的增大,横向剪切变形的影响减小。 相似文献
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Nitin P. Lobo K.V. Ramanathan T. Narasimhaswamy 《Magnetic resonance in chemistry : MRC》2020,58(11):988-1009
In this review, methods to obtain the orientational order of topologically variant molecular mesogens using by one- and two-dimensional (2D) solid-state 13C nuclear magnetic resonance (NMR) spectroscopy are described. Besides 13C chemical shifts, the 13C─1H dipolar couplings measured from 2D-separated local field (SLF) technique are used for computing the order parameters of a variety of mesogens. The investigated molecules are composed of a variable number of rings in the core, that is, core ranging from simply one ring to five rings. Among the mesogens investigated, a special focus has been placed on mesogens with thiophene rings, which are gaining popularity as liquid crystalline organic semiconductors. The replacement of a phenyl ring by thiophene in the core has a dramatic influence on molecular topology, as observed from the measured order parameters. The review highlights the advantages of the 2D SLF method for understanding the local dynamics and for mapping the topology of mesogens through the measured order parameters. SLF NMR studies of as many as 24 molecular mesogens that vary in terms of the molecular structure as well as topology are covered in the review. Order parameters of the rings have been estimated from the 13C─1H dipolar couplings in the nematic, smectic A, smectic C, and tilted hexatic phases as well as in B1 and B2 mesophases of various mesogens. It is anticipated that, in the years to come, the 2D SLF method would provide advanced molecular information on structurally complex mesogens that are emerging in liquid crystal science through the incessant efforts of synthetic chemists. The mini review covers the orientational order of topologically variant molecular mesogens determined by 1D and 2D solid-state 13C NMR spectroscopy. Accordingly, rod-like, bent-core, and thiophene mesogens were subjected to 2D SLF measurements to get the order parameters from which the topology was established. The replacement of phenyl ring by thiophene and its influence on order parameters as well as on molecular topology is also discussed. 相似文献
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Simultaneous application of multiple sinusoidal waveforms perturbations superimposed onto DC staircase step significantly enriches current response. The measured current is characterized by a matrix of data rather than a conventional voltammetric output in a form of a vector. This increase of the dimensionality of the current response and therefore the wealth of analytical information is achieved without compromising the time of analysis. The natural approach for compression of such data and extraction of relevant information is by utilizing multi-way chemometric decomposition techniques. An electroplating solution presents a very challenging analyte for electroanalysis as its constituents interact synergistically with each other during both the plating process and its simulation during electroanalysis. For some components the mechanism is not entirely understood. Therefore, the only way to benefit from the analytical data is by employing soft modeling. The electrode processes involving additives rely heavily on adsorption and, indirectly, on electron transfer kinetics for which AC voltammetry is an analytical technique capable of delivering informative signals. This paper presents a rigorous universal method for calculating and validating an exemplary multi-way calibration of a leveler component in a copper electroplating bath used in the semiconductor industry. The method presented employs comparatively Parallel Factor Analysis coupled with Inverse Least Squares Regression and multi-linear Partial Least Squares. The calibration training set consists of multi-frequency AC voltammetric data subjected to pretreatments aiming to select informative independent variables and exclude outliers. 相似文献
36.
《印度化学会志》2023,100(1):100860
This study investigates the influence of synthesis processes such as sonication, sol-gel, and microwave on the production of highly crystalline Lanthanum oxide nanoparticles (La2O3) employing Lanthanum nitrate and Ammonium hydroxide (NH4OH) as precursors. X-ray diffraction (XRD), particle size analysis (DLS), Field emission scanning electron microscopy (FESEM), Fourier-transform infrared spectroscopy (FTIR), ultraviolet–visible absorption spectroscopy (UV–Vis), and electrochemical impedance spectroscopy (EIS) were used to examine the most effective processing method and its effects on the nanoparticle characteristics, such as structure, morphology, and optical and electrical behavior. Sonication produces La2O3 NPs with a smaller crystalline size, an agglomerated nanorod structure, a higher bandgap, and better electrical responsiveness than sol-gel and microwave techniques. Structural and optical characterization tests discovered this. The photocatalytic degradation activity of cationic Safranin and anionic Congo red dye exhibits degradation efficiency of around 90.13% and 89.66%, respectively. 相似文献
37.
Amlan J. Kalita Namrata Gohain Abhik Bordoloi Dr. Kusum K. Bania Dr. Ankur K. Guha 《Chemphyschem》2023,24(9):e202200873
Number of bonds formed by sharing an electron pair between two atoms is not restricted to one, it can go beyond four and six is the maximum. While homopolar sextuple bond in Mo2 and W2 has been reported, such a high bond order in heteropolar diatomics has remained elusive. In the pursuit of the sextuple bond in polar diatomics, the present study depicts the existence of such multiple bonds in Rhodium-Scandium hetero-diatom based on relativistic quantum chemical calculations. The bonding comprises of three normal electron sharing covalent bonds and three dative covalent bonds. 相似文献
38.
With the aid of Riemann–Liouville fractional calculus theory,fractional order Savitzky–Golay differentiation(FOSGD) is calculated and applied to pretreat near infrared(NIR) spectra in order to improve the performance of multivariate calibrations.Similar to integral order Savitzky–Golay differentiation(IOSGD),FOSGD is obtained by fitting a spectral curve in a moving window with a polynomial function to estimate its coefficients and then carrying out the weighted average of the spectral curve in the window with the coefficients.Three NIR datasets including diesel,wheat and corn datasets were utilized to test this method.The results showed that FOSGD,which is easy to compute,is a general method to obtain Savitzky–Golay smoothing,fractional order and integral order differentiations.Fractional order differentiation computation to the NIR spectra often improves the performance of the PLS model with smaller RMSECV and RMSEP than integral order ones,especially for physical properties of interest,such as density,cetane number and hardness. 相似文献
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针对物理化学教材中有关光化学初级过程和次级过程、初级过程的量子产率、初级过程的反应速率表示以及是否是零级反应等问题发表了看法。 相似文献
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