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61.
Uncertainties in Solubility Calculations 总被引:1,自引:0,他引:1
Summary. When considering the possible migration of hazardous elements in groundwater, one has to take into account several phenomena,
e.g. solubility, ion exchange, adsorption, matrix diffusion, and transport paths. Here, we focus upon the solubility which in
turn depends on several more or less uncertain chemical properties. Uncertainties in the data during laboratory experiments
aiming at measurements of thermodynamic constants may cause uncertainties in the amount of some species of several tenths
of the relative mass fraction.
The thermodynamic data may then be used for solubility calculations under different conditions and water compositions. Clearly,
there are several uncertainties associated with solubility calculations in the rock-water system. First, there is the effect
of uncertainties in thermodynamic data such as stability and solubility constants, and also enthalpies of reaction if the
water is not at room temperature. Furthermore, there are the rock-water interactions which will change the water composition
as different minerals come in contact with the water flowing through a system of fractures. Studies in mineralogy to an accuracy
good enough for modeling of water evolution are difficult to perform, and therefore the mineral composition of the rock and
thus the water composition should be treated as parameters subjected to uncertainties. In addition, there are also conceptual
uncertainties with respect to input data. The calculation of a solubility should be an easy task for every chemist, but in
fact results differing by orders of magnitude are found even when the modelers have used the same computer program and the
same data.
In this paper, uncertainties associated with solubility calculations are discussed. The results are exemplified on the calculated
solubilities of some actinides in groundwater from crystalline rock.
Received August 21, 2000. Accepted (revised) May 18, 2001 相似文献
62.
高密度等离子体工艺总体模型初探 总被引:1,自引:0,他引:1
介绍了与高密度等离子体工艺相关的模型和数值模拟方法,即连续流和动力学方法。在漂流-扩散方程的连续流模型和单元粒子/蒙特卡罗碰撞动力学模型的基础上,提出了一个等离子体工艺模型。讨论了对等离子体鞘层、等离子体刻蚀和淀积过程的模拟方法,提出了一个高密度等离子体工艺总体模型的初步方案。 相似文献
63.
64.
《Applied Mathematical Modelling》2014,38(19-20):4574-4585
This paper presents a constructive approach to optimize the availability of a system through modeling the dependency of the components. Our goal is to minimize the system cost under the constraint that system availability must not be less than a given level. In particular, the components are dependent of each other. A function noted as the dependence function is introduced to model the dependency. It is demonstrated that, for a general form of the system cost, the dependence function guarantees a finite set of feasible solutions. An approach is then developed with the help of the dependence function to obtain the optimal solution. The resolution is illustrated by an interesting example, in which the system cost depends on the strength of the dependency. Our study reveals that the dependency is an essential and effective option to improve system reliability. Moreover, the modeling of dependency, i.e. the introduction of the dependence function is valuable for resolving the optimization problem. 相似文献
65.
Binary phase transmission gratings exhibiting a certain number N of central diffraction orders of equal intensity can be used to construct star couplers of the 1-to-N and N-to-N type. The calculation of the grating's groove structure is described, and first experimental results are presented. 相似文献
66.
Effect of polarization on two-dimensional carrier distribution in nitride quantum wells 总被引:1,自引:0,他引:1
Bidisha Lahiri Reshmee Datta Sudakshina Kundu 《Physica E: Low-dimensional Systems and Nanostructures》2005,25(4):449-455
Wide band-gap group-III nitrides are important for the design of optical devices in the blue and blue–green region. Owing to their wurtzite structure, these materials have a strong inherent polarization field that affects carrier distribution, exciton stability and hence influences the optical properties of the devices. So far, carriers have been assumed to have a sheet-like character. In this paper a non sheet-like distribution function for these quasi two-dimensional carriers is proposed that incorporates the effect of the polarization field. Here GaN/InGaN/GaN and AlGaN/GaN/AlGaN quantum wells have been studied. The polarization field causes the electron and hole wave functions to separate out, thus causing decrease of emission strength and strong reduction of exciton binding energy. This treatment explains well the qualitative nature of carrier distribution in the well. The polarization field changes with GaN mole fraction present in the tertiary nitride layer. The effect of mole fraction on carrier distribution has also been studied. It is found that, inside the well, the hole distribution changes a little more with change in mole fraction than the electron distribution, but for all practical purposes the net change in the distribution pattern is negligible. 相似文献
67.
B. Fiorina O. Gicquel L. Vervisch S. Carpentier N. Darabiha 《Proceedings of the Combustion Institute》2005,30(1):867-874
Tabulated chemistry and presumed probability density function (PDF) approaches are combined to perform RANS modeling of premixed turbulent combustion. The chemistry is tabulated from premixed flamelets with three independent parameters: the equivalence ratio of the mixture, the progress of reaction, and the specific enthalpy, to account for heat losses at walls. Mean quantities are estimated from presumed PDFs. This approach is used to numerically predict a turbulent premixed flame diluted by hot burnt products at an equivalence ratio that differs from the main stream of reactants. The investigated flame, subjected to high velocity fluctuations, has a thickened-wrinkled structure. A recently proposed closure for scalar dissipation rate that includes an estimation of the coupling between flame wrinkling and micromixing is retained. Comparisons of simulations with experimental measurements of mean velocity, temperature, and reactants are performed. 相似文献
68.
O.P. Korobeinichev V.M. Shvartsberg A.G. Shmakov T.A. Bolshova T.M. Jayaweera C.F. Melius W.J. Pitz C.K. Westbrook H. Curran 《Proceedings of the Combustion Institute》2005,30(2):2353-2360
Chemical inhibition of laminar propane flames by organophosphorus compounds has been studied experimentally and computationally using a detailed chemical kinetic reaction mechanism. Both fuel-lean and fuel-rich propane flames were studied to examine the role of equivalence ratio in flame inhibition. The experiments examined a wide variety of organophosphorus compounds. We report on experimental species flame profiles for tri-methyl phosphate (TMP) and compare them with modeled species flame profile results of TMP and di-methyl methyl phosphonate (DMMP). Both experiments and kinetic modeling indicate that inhibition efficiency is effectively the same for all of the organophosphorus compounds examined, independent of the molecular structure of the initial inhibitor molecule. Chemical inhibition is due to reactions involving small P-bearing species HOPO2 and HOPO produced by the organophosphorus compounds (OPCs). Ratios of HOPO2 and HOPO concentrations differ between lean and rich flames, with HOPO2 dominant in lean flames while HOPO dominates in rich flames. Resulting HOPO2 and HOPO species profiles do not significantly depend on the initial source of the HOPO2 and HOPO, and thus are relatively insensitive to the initial OPC inhibitor. A more generalized form of the Twarowski mechanism is developed to account for the results observed, and new theoretical values are determined for heats of formation of the important P-containing species, using the BAC-G2 method. 相似文献
69.
讨论了具有混合边界的潜水污染数学模型,在适当条件下,应用Galerkjn方法证明了模型广义解的存在性,并证明了广义解的唯一性和对初边值及自由项的连续依赖性. 相似文献
70.
A new microscopic model, based on DFT/LDA modeling, is suggested for the Langmuir-Hinshelwood reaction of catalytic CO oxidation in coadsorbed O-CO layers on Pt(1 1 1). It has been found that only the oxygen atoms occupying threefold hollow sites of hcp type are chemically active. The potential barrier for the oxidation reaction significantly decreases due to changes in the adlayer oxygen states in the proximity to CO. The oxygen electronic density distribution is affected by approaching CO molecule which alters the oxygen position. Height of the barrier is estimated as 1.15 eV, which may be attributed to the upper limit of activation energy for the net reaction process. 相似文献