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991.
Talebpour Z Ghassempour A Zendehzaban M Bijanzadeh HR Mirjalili MH 《Analytica chimica acta》2006,576(2):290-296
Trichlorfon is an organophosphorus insecticide, which is extensively being used for protection of fruit crops. Trichlorfon is a thermal labile compound, which cannot be easily determined by gas chromatography (GC) and has no suitable group for sensitive detection by high performance liquid chromatography (HPLC). In this study, a 31P nuclear magnetic resonance (31P NMR) has been described for monitoring of trichlorfon without any separation step. The quantitative works of 31P NMR spectroscopy has been performed in the presence of an internal standard (hexamethylphosphoramide). Limit of detection (LOD) for this method has been found to be 55 mg L−1, without any sample preparation, and the linear working range was 150-5500 mg L−1. Relative standard deviation (R.S.D.%) of the method for three replicates within and between days was obtained ≤9%. The average recovery efficiency was approximately 99-112%. This method was applied for monitoring trichlorfon in a commercial insecticide sample and tomato sample. 相似文献
992.
A new automated headspace solid-phase microextraction (HS-SPME) sampling device was developed, with the capability of heating the sample matrix and simultaneously cooling the fiber coating. The device was evaluated for the quantitative extraction of polycyclic aromatic hydrocarbons (PAHs) from solid matrices. The proposed device improves the efficiency of the release of analytes from the matrix, facilitates the mass transfer into the headspace and significantly increases the partition coefficients of the analytes, by creating a temperature gap between the cold-fiber (CF) coating and the hot headspace. The reliability and applicability of previously reported cold-fiber devices are significantly enhanced by this improvement. In addition, it can be easily adopted for full automation of extraction, enrichment and introduction of different samples using commercially available autosampling devices. Sand samples spiked with PAHs were used as solid matrices and the effect of different experimental parameters were studied, including the extraction temperature, extraction time, moisture content, and the effect of sonication and modifier under optimal experimental conditions, linear calibration curves were obtained in the range of 0.0009-1000 ng/g, with regression coefficients higher than 0.99 and detection limits that ranged from 0.3 to 3 pg/g. Reproducible, precise and high throughput extraction, monitoring and quantification of PAHs were achieved with the automated cold-fiber headspace solid-phase microextraction (CF-HS-SPME) device coupled to GC-flame ionization detection. Determination of PAHs in certified reference sediments using the proposed approach exhibited acceptable agreement with the standard values. 相似文献
993.
Khodabakhsh Niknam Seyed Mehdi Razavian Mohammah Ali Zolfigol Iraj Mohammahpoor‐Baltork 《Journal of heterocyclic chemistry》2006,43(1):199-202
A combination of methanesulfonic acid and sodium nitrite in the presence of wet SiO2 was used as an effective oxidizing agent for the oxidation of 1,4‐dihydropyridines to the corresponding pyridine derivatives under mild and heterogeneous conditions in excellent yields. 相似文献
994.
We describe a method for the correction of slowly varying wavefront aberrations of low-quality telescope mirrors by using a DM in an active optical compensation system. Our goal is to reduce the surface wavefront error of low-cost multimeter-diameter mirrors from approximately 10 waves peak-to-valley (P-V), at a 1 microm wavelength, to approximately 1 wave or less. In a proof-of-concept demonstration using a 0.3m telescope at a wavelength of 633 nm, the rms wavefront error improved to 0.05 waves (0.26 waves P-V) from the original value of 1.4 waves rms (6.5 waves P-V). The Strehl ratio improved to 89% from the original value of 0.08%. The types of aberrations corrected include astigmatism, coma, defocus, trefoil, and higher-order aberrations. 相似文献
995.
The three-dimensional spin-1 Ising superlattice consisting of two different ferromagnetic materials with two different crystal fields Δ1 and Δ2 is considered in the mean field approximation. The phase diagrams are considered in the (t,d2) plane for different ranges of variation of d1(t=T/J,d1=Δ1/J, d2=Δ2/J are the reduced temperature and crystal fields respectively). The phase diagrams exhibit a variety of multicritical points and reentrant and double reentrant behaviours. They are found to depend qualitatively and/or quantitatively on the thicknesses of the materials in a supercell. This has direct consequences on the nature of the magnetic states of superlattices with different thicknesses. 相似文献
996.
Seyyed Javad Sabounchei Parisa Shahriary Zabiholla Bolboli Nojini Hamid Reza Khavasi Cengiz Arici Hakan Dal 《Heteroatom Chemistry》2010,21(7):475-485
Stable phosphoranes, Ar3P = CHCOR (R = C6H5, C6H4NO2, C6H4OCH3, CH3, OCH2C6H5; Ar = p‐tolyl or phenyl), have been C‐acylated by acetic anhydride to obtain new types of phosphorus ylides. Synthesis and characterization of six phosphorus ylides of the type Ar3PC(COCH3)(COR) are reported. The reaction of {(p‐tolyl)3PCHCOC6H5} ( I ), {(p‐ tolyl)3PCHCOC6H4NO2} ( II ), {Ph3PCHCOC6H4NO2} ( III ), {Ph3PCHCOC6H4OCH3} ( IV ), {(p‐tolyl)3PCHCOCH3} ( V ), and {Ph3PCHCOOCH2C6H5} ( VI ) with acetic anhydride in dry chloroform as solvent gives (p‐tolyl)3PC(COMe)(COC6H5), α‐acetyl‐α‐benzoylmethy‐lenetriphenylphosphorane ( 1 ), {(p‐tolyl)3PC(COMe) (COC6H4NO2)} ( 2 ), {Ph3PC(COMe)(COC6H4NO2)} ( 3 ), {Ph3PC(COMe)(COC6H4OCH3)} ( 4 ), {(p‐tolyl)3 PC(COCH3)2} ( 5 ), and {Ph3PC(COMe)(COOCH2 C6H5)} ( 6 ). Single crystal X‐ray analyses for ylides 2 , 5 , and 6 reveal the monoclinic ( 2, 5 ) and triclinic ( 6 ) crystal systems. Characterization of the obtained compounds was also performed by elemental analysis, IR, 1H, 31P, and 13C NMR. The geometries of these compounds have been investigated using density functional theory (DFT). In addition, electronic parameters of these compounds such as HOMO and LUMO energy, Mulliken partial charge, and dipole moment were obtained. In this paper, the reactivity of these ylides is discussed in regard to the aforementioned data. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:475–485, 2010; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20633 相似文献
997.
V. Mohammadi R. Ansari M. Faghih Shojaei R. Gholami S. Sahmani 《Nonlinear dynamics》2013,73(3):1515-1526
In the present study, the dynamic pull-in instability and free vibration of circular microplates subjected to combined hydrostatic and electrostatic forces are investigated. To take size effects into account, the strain gradient elasticity theory is incorporated into the Kirchhoff plate theory to develop a nonclassical plate model including three internal material length scale parameters. By using Hamilton’s principle, the higher-order governing equation and the corresponding boundary conditions are obtained. Afterward, a generalized differential quadrature (GDQ) method is employed to discritize the governing differential equations along with simply supported and clamped edge supports. To evaluate the pull-in voltage and vibration frequencies of actuated microplates, the hydrostatic-electrostatic actuation is assumed to be calculated by neglecting the fringing field effects and utilizing the parallel plate approximation. Also, a comparison between the pull-in voltages predicted by the strain gradient theory and the degenerated ones is presented. It is revealed that increasing the dimensionless internal length scale parameter or decreasing the applied hydrostatic pressures leads to higher values of the pull-in voltage. Moreover, it is found that the value of pull-in hydrostatic pressure decreases corresponding to higher dimensionless internal length scale parameters and applied voltages. 相似文献
998.
Mostafa Keshavarz Moraveji Mona Ebrahimi Fakhari Elmira Mohsenzadeh Reza Davarnejad 《Heat and Mass Transfer》2013,49(1):11-19
In this article, the influences of alcohols on the hydrodynamics and oxygen mass transfer characteristics in an airlift reactor equipped with packing were investigated. The hydrodynamic parameters and mass transfer coefficient in 1 % (v/v) aqueous solutions of four aliphatic alcohols were tested. It was concluded that alcohols addition increased gas holdup and gas–liquid mass transfer coefficient. The packing installation increased mass transfer coefficient, gas holdup and liquid circulation velocity, as well. 相似文献
999.
1000.
Hamid Reza Shaker 《Nonlinear dynamics》2012,70(2):999-1005
The filtering problem is among the fundamental issues in control and signal processing. Several approaches such as H 2 optimal filtering and H ?? optimal filtering have been developed to address this issue. While the optimal H 2 filtering problem has been extensively studied in the past for linear systems, to the best of our knowledge, it has not been studied for bilinear systems. This is indeed surprising, since bilinear systems are important class of nonlinear systems with well-established theories and applications in various fields. The problem of H 2 optimal filtering for both discrete-time and continuous bilinear systems is addressed in this paper. The filter design problem is formulated in the optimization framework. The problem for the discrete-time case is expressed in terms of linear matrix inequalities which can be efficiently solved. The results are used for the optimal filtering of a bilinear model of an electro-hydraulic drive. 相似文献