全文获取类型
收费全文 | 2581篇 |
免费 | 242篇 |
国内免费 | 269篇 |
专业分类
化学 | 2041篇 |
晶体学 | 38篇 |
力学 | 460篇 |
综合类 | 3篇 |
数学 | 97篇 |
物理学 | 453篇 |
出版年
2024年 | 9篇 |
2023年 | 28篇 |
2022年 | 43篇 |
2021年 | 67篇 |
2020年 | 135篇 |
2019年 | 90篇 |
2018年 | 92篇 |
2017年 | 130篇 |
2016年 | 162篇 |
2015年 | 120篇 |
2014年 | 132篇 |
2013年 | 270篇 |
2012年 | 128篇 |
2011年 | 150篇 |
2010年 | 138篇 |
2009年 | 167篇 |
2008年 | 148篇 |
2007年 | 160篇 |
2006年 | 167篇 |
2005年 | 137篇 |
2004年 | 120篇 |
2003年 | 89篇 |
2002年 | 64篇 |
2001年 | 52篇 |
2000年 | 42篇 |
1999年 | 42篇 |
1998年 | 36篇 |
1997年 | 28篇 |
1996年 | 31篇 |
1995年 | 16篇 |
1994年 | 29篇 |
1993年 | 14篇 |
1992年 | 13篇 |
1991年 | 10篇 |
1990年 | 9篇 |
1989年 | 4篇 |
1988年 | 8篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有3092条查询结果,搜索用时 15 毫秒
991.
基于压力隧洞模型的复合材料横向热残余应力分析 总被引:1,自引:1,他引:0
考虑碳纤维横向刚度情况下,将复合材料横向热残余应力问题简化为压力隧洞模型.利用该模型推导出复合材料固化成型过程中形成的横向热残余应力,其中分析得出了单纤维与树脂的接触压力以及该压力传递到纤维和树脂后的分布情况.结果表明接触压力传递到纤维内部后成一固定值,传递到树脂后以正比于r.函数衰减.在其基础上提出场叠加方法,得出纤维之间相互耦合的接触压力与残余应力场.通过有限元模拟,理论模型和数值模拟基本一致. 相似文献
992.
V. G. Ponomareva N. F. Uvarov G. V. Lavrova E. F. Hairetdinov 《Solid State Ionics》1996,90(1-4):161-166
Transport, thermal and structural properties of the composite solid electrolytes (1 −x)CsHSO4---xSiO2 (where x = 0–0.8) were investigated. The composites were prepared by mechanical mixing of components followed by heating at temperatures near CsHSO4 melting point (483 K). The dependence of low temperature phase conductivity on x has a maximum with a value 2.5 orders of magnitude higher than that of pure CsHSO4 and conductivity is governed by protons. Heterogeneous doping is shown to change markedly the thermodynamic parameters of the ionic component. The phase transition temperature CsHSO4 in the composites decreases from 414 to 350 K with the increase of the content of heterogeneous additive SiO2 from 0 to 0.7. As x raises CsHSO4 the amorphization takes place and the relative change of ionic conductivity at phase transition diminishes, the phase transition becomes diffusive and disappears for the 0.2CsHSO4---0.8SiO2 composite. 相似文献
993.
J. Ma. García‐Martínez O. Laguna S. Areso E. P. Collar 《Journal of Polymer Science.Polymer Physics》2002,40(13):1371-1382
This article reports on the interfacial modifications induced by different amounts of a succinyl‐fluorescein grafted atactic polypropylene (a‐PP‐SF) as a truly interfacial agent in polypropylene/talc composite materials. The a‐PP‐SF used, which contains 4% grafts, was previously obtained in our laboratory by chemical modification of a byproduct from industrial polymerization reactors. Thermal and mechanical analyses of composites, performed under dynamic conditions, led to the correlation of parameters at the microscopic scale with others at the macroscopic scale. Thus, the interfacial effect caused by different amounts of a‐PP‐SF in the composite can be concluded by observations made at either scale. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1371–1382, 2002 相似文献
994.
B. Cantor 《Micron (Oxford, England : 1993)》1994,25(6):551-574
This paper gives an overview of the use of process monitoring measurements, computer modelling calculations and electron microscope material characterization techniques to understand and control the manufacture of materials by a variety of advanced solidification processing methods. Examples which are discussed include: (1) spray formed Al alloys and composites for aerospace structures; (2) squeeze cast Al alloys and composites for automotive components; (3) melt spun Al bearing alloys and; (4) melt spun amorphous Fe alloys for distribution transformer cores and structural components; and (5) plasma sprayed Ti composites for aeroengine compressors. 相似文献
995.
P. S. Theocaris G. E. Stavroulakis 《Archive of Applied Mechanics (Ingenieur Archiv)》1998,68(3-4):281-295
Summary Materials with specific microstructural characteristics and composite structures are able to exhibit negative Poisson's ratio.
This fact has been shown to be valid for certain mechanisms, composites with voids and frameworks and has recently been verified
for microstructures optimally designed by the homogenization approach. For microstructures composed of beams, it has been
postulated that nonconvex shapes (with reentrant corners) are responsible for this effect. In this paper, it is numerically
shown that mainly the shape, but also the ratio of shear-to-bending rigidity of the beams do influence the apparent (phenomenological)
Poisson's ratio. The same is valid for continua with voids, or for composites with irregular shapes of inclusions, even if
the constituents are quite usual materials, provided that their porosity is strongly manifested. Elements of the numerical
homogenization theory and first attempts towards an optimal design theory are presented in this paper and applied for a numerical
investigation of such types of materials.
Received 11 March 1997; accepted for publication 12 September 1997 相似文献
996.
C.C. Trapalis M. Kokkoris G. Perdikakis G. Kordas 《Journal of Sol-Gel Science and Technology》2003,26(1-3):1213-1218
In the present work, composite copper containing silicate thin coatings (Cu/SiO2) were prepared on glass substrates by the sol-gel route. The preparation process included hydrolysis and subsequent polycondensation of corresponding alkoxide under refluxing and addition of soluble salt of antibacterial metal to the resulting sol. The coatings deposited by dipping process, were thermally treated in oxidative and reductive conditions up to 500°C for metal nanoparticles formation. The coating structure and the nanoparticles formation were studied by the X-ray Diffraction (XRD), UV-VIS and Heavy Ion Rutherford Backscattering (HIRBS) Spectroscopies. The antibacterial activity against Escherichia Coli was examined by the so-called antibacterial-drop test. The possible correlation between the layer interdiffusion after the thermal treatment and the antibacterial activity was considered and analyzed. The coatings exhibited a high antibacterial activity, which was enhanced with the increase of the metal concentration and was decreased with the increase of temperature of thermal treatment and metal nanoparticles formation. 相似文献
997.
Dweck J. Andrade B. F. Monteiro E. E. C. Fischer R. 《Journal of Thermal Analysis and Calorimetry》2002,67(2):321-326
Plaster composites have been developed by the authors, aiming the manufacture of plasterboards and other building materials
with enhanced properties. Polymeric plaster composites,obtained from hydration of commercial plaster of Paris with aqueous
solutions of a commercial polyester, were characterized by thermogravimetry (TG) and differential thermal analysis (DTA).
A method using derivative thermogravimetry (DTG) was developed to determine the polymer content in the composites and its
distribution. Samples prepared conventionally by hydration of plaster of Paris with water were used as reference. Independently
of the initial solution concentration, all the composites show an even distribution of the polymer, which presence enhances
the composite mechanical strength.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
998.
María Elena Leyva Guilherme M. O. Barra Ana C. F. Moreira Bluma G. Soares Dipak Khastgir 《Journal of Polymer Science.Polymer Physics》2003,41(23):2983-2997
The conductivity of styrene‐butadiene‐styrene block copolymers containing different amounts of extraconductive carbon black (CB) was investigated as a function of the mold temperature. The composites exhibited reduced percolation thresholds (between 1.0 and 2.0 vol % CB). The dynamic mechanical analysis characterization revealed that the glass‐rubber‐transition temperatures of both segments were not affected by the CB addition, although the damping of the polybutadiene phase displayed a progressive drop with an increase in the CB concentration. The normalized curves of tan δ/tan δmax (where tan δ represents the value of the loss tangent at any measurement temperature and tan δmax represents the loss tangent peak value at the corresponding temperature Tmax) versus T/Tmax (where T is the temperature and Tmax is the maximum temperature), corresponding to both polystyrene and polybutadiene phases as well as the activation energy related to the glass‐rubber‐transition process, did not present any significant change with the addition of CB. The dielectric analysis revealed the presence of two relaxation peaks in the composite containing 1.5 vol % CB, the magnitude of which was strongly influenced by the frequency, being attributed to interfacial Maxwell‐Wagner‐Sillars relaxations caused by the presence of different interfaces in the composite. The mechanical properties were not affected by the presence of CB at concentrations of up to 2.5 vol %. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2983–2997, 2003 相似文献
999.
Qinghua Zhang Xianhong Wang Yanhou Geng Dajun Chen Xiabin Jing 《Journal of Polymer Science.Polymer Physics》2002,40(22):2531-2538
Polyaniline (PANI) in an emeraldine‐base form, synthesized by chemical oxidation polymerization, was doped with camphor sulfonic acid (CSA). The conducting complex (PANI–CSA) and a matrix, polyamide‐66, polyamide‐11, or polyamide‐1010, were dissolved in a mixed solvent, and the blend solution was dropped onto glass and dried for the preparation of PANI/polyamide composite films. The conductivity of the films ranged from 10?7 to 100 S/cm when the weight fraction of PANI–CSA in the matrices changed from 0.01 to 0.09, and the percolation threshold was about 2 wt %. The morphology of the composite films before and after etching was studied with scanning electron microscopy, and the thermal properties of the composite films were monitored with differential scanning calorimetry. The results indicated that the morphology of the blend systems was in a globular form. The addition of PANI–CSA to the films resulted in a decrease in the melting temperature of the composite films and also affected the crystallinity of the blend systems. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2531–2538, 2002 相似文献
1000.
Novel high performance aluminum nitride (AlN)/poly(ether-ether-ketone) (PEEK) composites containing 0-50 wt.% fractions of AlN were prepared by solution blending method followed by hot pressing to evaluate their density, melting temperature, crystallization, thermal stability, morphological behavior and Vickers hardness by using different characterization techniques. Differential scanning calorimetry results indicated that the AlN particles are very effective nucleating agent, which results in increase in melting point, hot crystallization temperature and crystallinity of composites as the AlN content increases. Thermogravimetric analysis showed enhanced thermal stability of the composites with respect to PEEK. Density and X-ray diffraction techniques showed that crystallinity of the composites increases as the wt.% of AlN content increases in polymer matrix. Scanning electron microscopy revealed that AlN particles were well dispersed with no porosity in composites. Vickers hardness of the samples increased from 24 kg/mm2 for the pure PEEK to 35 kg/mm2 for AlN/PEEK composites. 相似文献