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991.
Attenuation of Biologically Effective UV Radiation in Tropical Atlantic Waters Measured with a Biochemical DNA Dosimeter 总被引:2,自引:0,他引:2
Peter Boelen Ingrid Obernostere Arie A. Vink Anita G. J. Buma 《Photochemistry and photobiology》1999,69(1):34-40
Abstract— A biochemical dosimeter was developed to study the attenuation of biologically effective UV radiation in marine tropical waters. Small quartz vials were used containing a solution of DNA molecules; the vials were incubated at discrete water depths. Subsequently, DNA damage was determined in these samples, using an antibody directed against thymine dimers followed by chemiluminescent detection. Measurements of DNA damage were compared with calculated biologically effective doses, as derived from spectroradiometer measurements. The biodosimeter was found to be a reliable and easy tool to determine levels of harmful UV radiation in marine waters. The highest attenuation coefficient (1.60 m-l ) measured with the biochemical dosimeter was found in eutrophic waters, at a coastal station off Curabcao, Netherlands Antilles. At the other stations attenuation coefficients ranged from 0.18 m-1 in central Atlantic waters to 0.43 m-1 close to the Curapcao coast line. Latter results indicate that biologically effective UV radiation may easily reach ecologically significant depths, e.g. coral reef communities. 相似文献
992.
Patricia R. Richardson Simon P. Bates Jason Crain Anita C. Jones 《Liquid crystals》2013,40(6):845-850
We explore the structure, torsional frequencies and electronic properties of the gas phase 4-cyanobiphenyl molecule, a prototypical liquid crystal core fragment, in its ground and first excited singlet electronic states. We employ a methodology which combines ab initio quantum mechanical calculations and fluorescence spectroscopy of laser-desorbed, jet-cooled molecules. The aim is to test the predictive power of parameter-free calculations of structure and dynamics in an experimental environment which is similar to the computational conditions of low thermal activation and negligible intermolecular interaction. Both spectroscopic and computational results indicate that very large molecular conformational changes accompany the optical pi → pi* transition. These are found to have a significant influence on the molecular flexibility and electronic polarity. 相似文献
993.
The pricing equations for options on assets that follow jump-diffusion processes contain integrals in addition to the usual differential terms. These integrals usually make such equations expensive to solve numerically. Although Fast Fourier Transform methods can be used to to evaluate the integrals at all mesh points simultaneously, they are costly since the computational region must be extended in order to avoid problems with wrap around. Other numerical difficulties arise when the density function for the jump size is not smooth, as in the Kou double exponential model. We present new solution methods which are based on the fact that even when the problems contain time-dependent parameters the integrals often satisfy easily solved ordinary or parabolic partial differential equations. In particular, we show that by using the operator splitting method proposed by Andersen and Andreasen it is possible to reduce the solution of the pricing equation in the Kou and similar models to a sequence of ordinary differential equations at each time step. We discuss the methods and present results of numerical experiments. 相似文献
994.
With a number of advantages, lower partial moments (LPM) serve as alternatives to variance as measures of portfolio risk. For two specific targets, a separation property holds in the context of mean–LPM portfolio optimization that allows investors to separate the decision about investment proportions among risky assets from the decision about how much to invest in risky versus risk-free assets. For other targets, however, separation is not guaranteed, and this case has not received much attention in the literature. We show in the case of non-separation that investment curves are not common to all optimizing investors, but that they are convex in (mean, LPM) space and their lower envelope is the efficient frontier. We consider the interesting behavior of investment curves and optimal risky portfolios. We also show empirically that an investor who mistakenly assumes separation holds will not experience significant excess portfolio risk in all practical cases. 相似文献
995.
N. Kumari S.B. Krupanidhi K.B.R. Varma 《Applied Physics A: Materials Science & Processing》2008,91(4):693-699
Bismuth vanadate (Bi2VO5.5, BVO) thin films have been deposited by a pulsed laser ablation technique on platinized silicon substrates. The surface morphology
of the BVO thin films has been studied by atomic force microscopy (AFM). The optical properties of the BVO thin films were
investigated using spectroscopic ellipsometric measurements in the 300–820 nm wavelength range. The refractive index (n),
extinction coefficient (k) and thickness of the BVO thin films have been obtained by fitting the ellipsometric experimental
data in a four-phase model (air/BVOrough/BVO/Pt). The values of the optical constants n and k that were determined through multilayer analysis at 600 nm were 2.31
and 0.056, respectively. For fitting the ellipsometric data and to interpret the optical constants, the unknown dielectric
function of the BVO films was constructed using a Lorentz model. The roughness of the films was modeled in the Brugmann effective
medium approximation and the results were compared with the AFM observations.
PACS 78.20.-e; 77.84.-s; 77.55.+f 相似文献
996.
The goal of this study is to assess the implications of the choice of correctors for semi-implicit Picard integral deferred correction (SIPIDC) methods. The SIPIDC methods previously developed compute a high-order approximation by first computing a low-order provisional solution using a semi-implicit method and then using a first-order semi-implicit method to solve a series of correction equations, each of which raises the order of accuracy of the solution by one. In this study, we examine the efficiency of SIPIDC methods that instead use standard second-order semi-implicit methods to solve the correction equations. The accuracy, efficiency, and stability of the resulting methods are compared to previously developed methods, in the context of both nonstiff and stiff problems. 相似文献
997.
998.
999.
PoonamPratibha Kumari Sohail AhmadShive Murat Singh Chauhan 《Tetrahedron letters》2011,52(52):7083-7086
A series of functional metallophthalocyanines have been synthesized to study their role as a catalyst towards the reductive dechlorination of atrazine using sodium borohydride as a mild reducing agent. The cobalt(II) phthalocyanine bearing nitro groups at the peripheral position is the most efficient catalyst with exceptionally high catalytic activity in comparison to other functional cobalt(II) phthalocyanines. 相似文献
1000.
Serhat S. Cicek Anita Aberham Markus Ganzera Hermann Stuppner 《Analytical and bioanalytical chemistry》2011,400(8):2597-2605
In this study, a fast and reproducible RRLC-ELSD method for the quantitative analysis of 17 cycloartane glycosides and the
aglycone cimigenol in black cohosh rhizomes and dietary supplements has been developed. Separation of the 18 triterpenes was
achieved within 16 min using reversed phase material and a gradient elution system consisting of water, acetonitrile and methanol.
The method was validated for accuracy (recovery rates from 96.79% to 102.86%), precision (intra-day variation ≤5.98%, inter-day
variation ≤3.74%), repeatability (R.S.D. ≤ 6.94%) and sensitivity, with detection limits below 4.0 μg/mL and quantification
limits lower than 13.2 μg/mL. Calibration curves were established in the range from 5–1,000 μg/mL, with correlation coefficients
higher than 0.998 for all constituents investigated. Peak purity and peak assignment were confirmed by means of RRLC-qTOF-MS
and in comparison with reference compounds. Three different MS sources (ESI, APCI and APPI) were compared for their ionisation
potential regarding cycloartane derivatives. One of the isolated black cohosh constituents, 24-O-acetylhydroshengmanol-3-O-α-l-arabinopyranoside, could be identified as new natural compound. 相似文献