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121.
Peter R. Cromwell 《Geometriae Dedicata》2008,137(1):63-84
We extend the classification of pattern types by Grünbaum and Shephard to the 2-sided plane to include patterns having layered
or interlaced motifs. Such patterns may have symmetries that turn the plane over. There are 17 infinite families of pattern
types for 2-sided rosettes (twelve 1-parameter families and five 2-parameter families), 68 types of 2-sided frieze pattern,
and 264 types of 2-sided periodic pattern. The definition of ‘henomeric’ is clarified to ensure that two of the periodic patterns
are distinguished.
相似文献
122.
P. Bot I. Mutabazi 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(1):141-155
The dynamics of defects in a pattern of traveling inclined rolls has been investigated. Two regimes were identified in the
neighborhood of defects: a diffusive regime, with a negative phase diffusion coefficient, and a coalescence regime in which
the phase gradient diverges in time following a power law behavior. The observed periodic nucleation of defects is related
to the frequency inhomogeneity induced by the disymmetry of the wave amplitude. Amplitude holes have been observed in the
secondary modulated pattern.
Received 23 February 1999 and Received in final form 26 May 1999 相似文献
123.
Ulrike Bücking 《Geometriae Dedicata》2008,137(1):163-197
A circle pattern is a configuration of circles in the plane whose combinatorics is given by a planar graph G such that to each vertex of G corresponds a circle. If two vertices are connected by an edge in G, the corresponding circles intersect with an intersection angle in (0, π). Two sequences of circle patterns are employed to approximate a given conformal map g and its first derivative. For the domain of g we use embedded circle patterns where all circles have the same radius decreasing to 0 and with uniformly bounded intersection
angles. The image circle pattern has the same combinatorics and intersection angles and is determined from boundary conditions
(radii or angles) according to the values of g′ (|g′| or arg g′). For quasicrystallic circle patterns the convergence result is strengthened to C
∞-convergence on compact subsets.
相似文献
124.
A monomer design having a bulky terminal tricyclodecane (TCD) unit linked via hydrogen bondable urethane to an ethyleneoxy methacrylate unit, and capable of generating three‐dimensional honeycomb patterns upon solvent casting has been investigated. Random copolymers as well as a diblock copolymer Poly(Sty42‐b‐TCD18) of this monomer with styrene were prepared by free‐radical polymerization route and atom transfer radical polymerization (ATRP) route. Morphology characterization was carried out using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. Particle size was measured by dynamic light scattering measurements (DLS). Irrespective of the wide differences in molecular weight and polydispersity index values, the random copolymers having TCD content >30 mol % were found to form microporous films upon solvent casting from a THF/water 9:1 solvent combination. The amount of TCD in the copolymer was found to have an influence on the pore size formed. The diblock copolymer formed microspheres ~200 nm in diameter. The thermal properties of all the polymers were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), and the copolymers were found to have good thermal stability. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1278–1288, 2008 相似文献
125.
Uniaxial tension tests of semihard copper sheets were studied by means of electronic spekle pattern interferometry (ESPI).
The setup allowed the authors to analyze in detail the transitions from elastic to plastic behavior and from homogeneous to
inhomogeneous plastic deformation. In agreement with the conventional definition of the yield point for copper fully plastic
behavior starded at permanent strains close to 0.005. The strain-hardening coefficient was very low at the early stage of
plastic flow (“easy glide”), increasing progressively until values on the order of 0.13 to 0.14 were reached at maximum load.
A this point, the appearance of unequally spaced fringes signaled the beginning of inhomogeneous deformation. With ESPI, this
occurrence may thus serve as a criterion to establish the forming limit of the material. 相似文献
126.
D. Valenti L. Schimansky-Geier X. Sailer B. Spagnolo 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(1-2):199-203
The dynamics of a spatially extended system of two competing
species in the presence of two noise sources is studied. A
correlated dichotomous noise acts on the interaction parameter and
a multiplicative white noise affects directly the dynamics of the
two species. To describe the spatial distribution of the species
we use a model based on Lotka-Volterra (LV) equations. By writing
them in a mean field form, the corresponding moment equations for
the species concentrations are obtained in Gaussian approximation.
In this formalism the system dynamics is analyzed for different
values of the multiplicative noise intensity. Finally by comparing
these results with those obtained by direct simulations of the
time discrete version of LV equations, that is coupled map lattice
(CML) model, we conclude that the anticorrelated oscillations of
the species densities are strictly related to non-overlapping
spatial patterns. 相似文献
127.
Yiming Zhao Jing Yan Yanxin Wang Qianzhen Jing Tingliang Liu 《Entropy (Basel, Switzerland)》2021,23(4)
A porcelain insulator is an important part to ensure that the insulation requirements of power equipment can be met. Under the influence of their structure, porcelain insulators are prone to mechanical damage and cracks, which will reduce their insulation performance. After a long-term operation, crack expansion will eventually lead to breakdown and safety hazards. Therefore, it is of great significance to detect insulator cracks to ensure the safe and reliable operation of a power grid. However, most traditional methods of insulator crack detection involve offline detection or contact measurement, which is not conducive to the online monitoring of equipment. Hyperspectral imaging technology is a noncontact detection technology containing three-dimensional (3D) spatial spectral information, whereby the data provide more information and the measuring method has a higher safety than electric detection methods. Therefore, a model of positioning and state classification of porcelain insulators based on hyperspectral technology is proposed. In this model, image data were used to extract edges to locate cracks, and spectral information was used to classify the surface states of porcelain insulators with EfficientNet. Lastly, crack extraction was realized, and the recognition accuracy of cracks and normal states was 96.9%. Through an analysis of the results, it is proven that the crack detection method of a porcelain insulator based on hyperspectral technology is an effective non-contact online monitoring approach, which has broad application prospects in the era of the Internet of Things with the rapid development of electric power. 相似文献
128.
Shenghan Zhou Houxiang Liu Bang Chen Wenkui Hou Xinpeng Ji Yue Zhang Wenbing Chang Yiyong Xiao 《Entropy (Basel, Switzerland)》2021,23(6)
The traditional sequential pattern mining method is carried out considering the whole time period and often ignores the sequential patterns that only occur in local time windows, as well as possible periodicity. Therefore, in order to overcome the limitations of traditional methods, this paper proposes status set sequential pattern mining with time windows (SSPMTW). In contrast to traditional methods, the item status is considered, and time windows, minimum confidence, minimum coverage, minimum factor set ratios and other constraints are added to mine more valuable rules in local time windows. The periodicity of these rules is also analyzed. According to the proposed method, this paper improves the Apriori algorithm, proposes the TW-Apriori algorithm, and explains the basic idea of the algorithm. Then, the feasibility, validity and efficiency of the proposed method and algorithm are verified by small-scale and large-scale examples. In a large-scale numerical example solution, the influence of various constraints on the mining results is analyzed. Finally, the solution results of SSPM and SSPMTW are compared and analyzed, and it is suggested that SSPMTW can excavate the laws existing in local time windows and analyze the periodicity of the laws, which solves the problem of SSPM ignoring the laws existing in local time windows and overcomes the limitations of traditional sequential pattern mining algorithms. In addition, the rules mined by SSPMTW reduce the entropy of the system. 相似文献
129.
该文旨在研究损伤位置和程度对自由阻尼加筋层合板声辐射功率和指向性的影响。基于Mindlin和Timoshenko梁理论,建立了自由阻尼层合板-梁组合结构有限元模型。数值求解四边简支边界条件自由阻尼加筋层合板振动响应,继而通过Rayleigh积分计算加筋层合板辐射声功率和指向性。将计算得到的前4阶模态固有频率、声辐射功率与指向性与已有文献进行了对比基本一致,验证了数值模型的正确性。最后,详细讨论了损伤位置和程度对自由阻尼加筋层合板固有频率、振型、声辐射功率和指向性的影响,结果表明:随着结构损伤程度的增大,声辐射功率峰值向低频移动,在更多角度上出现明显的指向性;声辐射功率和指向性对损伤位置比损伤程度更加敏感。 相似文献
130.
B. Peters 《Flow, Turbulence and Combustion》2005,73(3-4):217-229
The objective of this contribution is to investigate whether the mechanism of the thermal diffusion instability in gaseous
flames causing cellular flame structures also occurs during the combustion of porous solid fuel. Based on conservation for
mass and energy, the relevant set of differential equations was derived. Assuming thermal equilibrium between fuel and oxidiser,
a global energy equation was valid for both solid and gaseous phase. The resulting set of differential equations was discretised
by the Collocation method to arrive at a system of algebraic equations. In order to investigate into cellular flame structures,
an infinitesimal disturbance was superimposed onto the plane conversion front. Carrying out a linear instability analysis,
yielded eigenvalues dependent on the wave number of the disturbance. A critical wave number exists below which the real part
of the eigenvalues is positive, thus, indicating a regime of instability. Within this region, eigenvalues with a not-vanishing
imaginary part of the eigen value existed causing cellular flame structures. However, the growth rate of disturbances was
found to be small, which may explain the difficulty to investigate this phenomena experimentally. 相似文献