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991.
Joseph V. Alexander James W. Neely Eric A. Grulke 《Journal of Polymer Science.Polymer Physics》2014,52(20):1366-1373
Chemical treatment of polymeric hollow fiber membranes (HFMs) is used to prepare their exterior surfaces for coatings. Typical treatments can cleave both C? C and C? H bonds of polypropylene, leading to lower mechanical strength of the fibers. This study evaluated the yield strength, maximum strain, ultimate tensile strength, and burst strength of HFMs treated with each of three common oxidizing reagents: ozone as a gas phase system, aqueous solutions of potassium persulfate, and ammonium persulfate for liquid phase systems. The yield strength and ultimate tensile strength of HFMs decreased continuously with increasing ozonation time. Batch treatments with aqueous oxidizing systems showed limiting values of the yield and ultimate tensile strengths with time. Swelling the hollow fibers with methanol prior to oxidation caused less reduction of the mechanical properties after persulfate treatment. Fibers pretreated with methanol showed lower losses of mechanical properties strength with aqueous oxidation systems. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1366–1373 相似文献
992.
A Reissner–Mindlin theory for composite laminates without invoking ad hoc kinematic assumptions is constructed using the variational-asymptotic method. Instead of assuming a priori the distribution of three-dimensional displacements in terms of two-dimensional plate displacements as what is usually done in typical plate theories, an exact intrinsic formulation has been achieved by introducing unknown three-dimensional warping functions. Then the variational-asymptotic method is applied to systematically decouple the original three-dimensional problem into a one-dimensional through-the-thickness analysis and a two-dimensional plate analysis. The resulting theory is an equivalent single-layer Reissner–Mindlin theory with an excellent accuracy comparable to that of higher-order, layer-wise theories. The present work is extended from the previous theory developed by the writer and his co-workers with several sizable contributions: (a) six more constants (33 in total) are introduced to allow maximum freedom to transform the asymptotically correct energy into a Reissner–Mindlin model; (b) the semi-definite programming technique is used to seek the optimum Reissner–Mindlin model. Furthermore, it is proved the first time that the recovered three-dimensional quantities exactly satisfy the continuity conditions on the interface between different layers and traction boundary conditions on the bottom and top surfaces. It is also shown that two of the equilibrium equations of three-dimensional elasticity can be satisfied asymptotically, and the third one can be satisfied approximately so that the difference between the Reissner–Mindlin model and the second-order asymptotical model can be minimized. Numerical examples are presented to compare with the exact solution as well as the classical lamination theory and the first-order shear-deformation theory, demonstrating that the present theory has an excellent agreement with the exact solution. 相似文献
993.
S. J. Matysiak V. J. Pauk A. A. Yevtushenko 《Archive of Applied Mechanics (Ingenieur Archiv)》1998,68(5):297-307
Summary The problems of transient heat conduction in a periodically stratified medium consisting of a large number of alternating
concentric cylinders of two homogeneous isotropic rigid materials and in a rotationally periodic cylinder consisting of a
large number of circular homogeneous isotropic rigid sectors are considered. The equations of the homogenized models with
microlocal parameters are derived by using the homogenization procedure given in [17]. The obtained models take into account
certain microlocal effects connected with the microperiodic structure of the considered composites. Some examples of the application
of the presented models to the problems of temperature distributions in composite cylinders are detailed.
Received 10 March 1997; accepted for publication 23 October 1997 相似文献
994.
An experimental investigation was conducted to determine the influence of postmold trimming and resultant edge quality on
the performance of fiber-reinforced plastics (FRP) under dynamic loads. Graphite/epoxy and graphite/bismaleimide laminates
were machined using three state-of-the-art industrial techniques and subjected to three-point bend impact to failure. The
load load-line displacement records were used to obtain the load, bend deflection and energy absorbed to fracture. High-speed
photography was also employed to identify the initiation and progression of failure and record the time dependent fracture
process. From a comparison of edge quality and subsequent material performance for both polymeric composites, it was found
that the impact response of FRPs is highly process dependent. In general, the load and energy absorbed to fracture decreases
with increasing surface roughness. Reductions in the load and energy to the onset of fracture with degrading surface quality
were as high as 20 percent. The dynamic response was also found to be dependent on the constituents, stacking sequence and
impact velocity. 相似文献
995.
996.
This Note presents a new approximate scheme for nonlinear composites. The approximation which is made preserves certain features of the original second-order scheme of Ponte Castañeda, exactness to second-order in the contrast and existence of an effective energy, but improves on one drawback, which is the gap between the strain-energy formulation and the affine formulation. A numerical example shows the accuracy of the present method. To cite this article: N. Lahellec, P. Suquet, C. R. Mecanique 332 (2004). 相似文献
997.
Ni/聚氨酯纳米复合涂层的制备及其摩擦学性能研究 总被引:13,自引:3,他引:13
用超声化学方法制备了纳米Ni微粒,并在此基础上制备了Ni/聚氨酯纳米复合涂层,用X射线衍射仪和透射电子显微镜表征了纳米Ni微粒的结构和形貌以及纳米复合涂层中Ni微粒的分布;用球—盘摩擦磨损试验机评价了Ni/聚氨酯纳米复合涂层的摩擦磨损性能.结果表明:纳米Ni微粒平均品粒尺寸为10nm;纳米Ni微粒均匀分布在Ni/聚氨酯纳米复合涂层中,其颗粒尺寸约为50nm;Ni/聚氨酯纳米复合涂层的摩擦学性能明显优于聚氨酯涂层. 相似文献
998.
999.
1000.
T. K. Ooi J. A. Gilbert M. V. Bower R. E. Vaughan R. C. Engberg 《Experimental Mechanics》2005,45(3):221-225
In this paper we describe how finite element and experimental modal analyses can be used to characterize the dynamic behavior
of plates made from a new class of graphite reinforced silica/polymer matrix composite (GRSPMC) materials. An agreement is
obtained between both methods, and the results show that GRSPMC materials can be modeled and tested using tools similar to
those applied to the study of classical composite laminates. 相似文献