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41.
为了解决现有短波无线电监测定位系统中存在接收机系统复杂、定位精度不高的问题,设计了一种基于TDOA高精度短波定位系统;该系统采用软件无线电设计架构,射频前端采用直接带通采样,通过FPGA和CPU进行基带IQ数据提取和传输,采用TDOA和粒子算法对位置干扰源进行估计和定位;并且采用了GPS和PLL相结合时钟方案,以及VPN的数据传输通道;给出了短波定位系统的框图,分析了系统子模块和工作原理;采用该系统对已知的短波信号进行定位,实验结果证明优于传统的定位手段;说明该系统具有使用方便、布站灵活和定位精度高的特点。 相似文献
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Antioxidant activity of papaya seed extracts 总被引:1,自引:0,他引:1
The antioxidant activities of the ethanol, petroleum ether, ethyl acetate, n-butanol and water extract fractions from the seeds of papaya were evaluated in this study. The ethyl acetate fraction showed the strongest DPPH and hydroxyl free radical-scavenging activities, and its activities were stronger than those of ascorbic acid and sodium benzoate, respectively. The n-butanol fraction demonstrated the greatest ABTS? radicals scavenging activity. The ethyl acetate fraction and the n-butanol fraction not only showed higher antioxidant activities than the petroleum ether fraction, water fraction and ethanol fraction, but also showed higher superoxide anion and hydrogen peroxide radicals scavenging activities than those of the other extract fractions. The high amount of total phenolics and total flavonoids in the ethyl acetate and n-butanol fractions contributed to their antioxidant activities. The ethyl acetate fraction was subjected to column chromatography, to yield two phenolic compounds, p-hydroxybenzoic acid and vanillic acid, which possessed significant antioxidant activities. Therefore, the seeds of papaya and these compounds might be used as natural antioxidants. 相似文献
44.
有限维李三系称为二次的,如果它容许一个非退化的不变对称双线性型.无论是李三系分解为不可分解理想的直和,还是二次李三系分解为不可分解非退化理想的正交直和,证明了这两类分解在同构意义下都是唯一的. 相似文献
45.
The analytical energy gradient of the normalized elimination of the small component (NESC) method is derived for the first time and implemented for the routine calculation of NESC geometries and other first order molecular properties. Essential for the derivation is the correct calculation of the transformation matrix U relating the small component to the pseudolarge component of the wavefunction. The exact form of ?U/?λ is derived and its contribution to the analytical energy gradient is investigated. The influence of a finite nucleus model and that of the picture change is determined. Different ways of speeding up the calculation of the NESC gradient are tested. It is shown that first order properties can routinely be calculated in combination with Hartree-Fock, density functional theory (DFT), coupled cluster theory, or any electron correlation corrected quantum chemical method, provided the NESC Hamiltonian is determined in an efficient, but nevertheless accurate way. The general applicability of the analytical NESC gradient is demonstrated by benchmark calculations for NESC/CCSD (coupled cluster with all single and double excitation) and NESC/DFT involving up to 800 basis functions. 相似文献
46.
The title compound, 1′,3′-dihydrospiro[fluorene-9,2′-perimidine] has been synthesized and characterized by NMR, ESI-MS, IR, elemental analysis, UV–vis and fluorescence spectroscopy. The crystal structures of the title compound and its co-crsytal with 9-fluorenone have also been determined by X-ray single crystal diffraction. Density functional theory (DFT) calculations and vibrational frequencies have been performed at B3LYP/6-31G* level. The comparisons between the experimental vibrational frequencies and the predicted data show that B3LYP/6-31G* method can simulate the IR of the title compound on the whole. The theoretical electronic absorption spectra have been calculated by using TD-DFT method and compared with the experimental result. The solid-fluorescence determination of the title compound reveals two emission bans at 430 and 590 nm while its co-crystal reveals only one emission band at 590 nm. 相似文献
47.
Phytohemical investigation on the heartwood of Dalbergia odorifera resulted in the isolation of nine flavonoids. Their structures were elucidated as sativanone (1), (3R)-vestitone (2), (3R)-2',3',7-trihydroxy-4'-methoxyisoflavanone (3), (3R)-4'-methoxy-2',3,7-trihydroxyisoflavanone (4), carthamidin (5), liquiritigenin (6), isoliquiritigenin (7), (3R)-vestitol (8), and sulfuretin (9) based on their spectral data. All compounds were evaluated for their inhibitory activity against Ralstonia solanacearum. This is the first report about anti-R. solanacearum activity of the compounds from D. odorifera. 相似文献
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1.INTRODUCTIONThechromatographicproblemistorelatetheconcentrationprofileofthebandattheoutletofthecolumntotheequilibriumisothelm,themasstransferkineticsandtheprofileoftheinjectionbandandperformtheoptimumdesignofseparationprocess['J.Togettheobjective,Itisnecessarytoidentifythesystemof.ProjectsupPOrtedbyTheNationalNaturalScienceFoundationofChinatheliquidadsorptionchromatographylinearornon-linear,andthendeterminethethermodynamicanddynamicsparametersofthesystemaccuratelysothatthecomputersim… 相似文献
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