全文获取类型
收费全文 | 2836篇 |
免费 | 230篇 |
国内免费 | 144篇 |
专业分类
化学 | 557篇 |
晶体学 | 10篇 |
力学 | 1725篇 |
综合类 | 36篇 |
数学 | 254篇 |
物理学 | 628篇 |
出版年
2024年 | 11篇 |
2023年 | 28篇 |
2022年 | 41篇 |
2021年 | 60篇 |
2020年 | 65篇 |
2019年 | 56篇 |
2018年 | 62篇 |
2017年 | 93篇 |
2016年 | 116篇 |
2015年 | 96篇 |
2014年 | 112篇 |
2013年 | 205篇 |
2012年 | 112篇 |
2011年 | 141篇 |
2010年 | 97篇 |
2009年 | 121篇 |
2008年 | 122篇 |
2007年 | 133篇 |
2006年 | 146篇 |
2005年 | 140篇 |
2004年 | 148篇 |
2003年 | 126篇 |
2002年 | 110篇 |
2001年 | 93篇 |
2000年 | 91篇 |
1999年 | 77篇 |
1998年 | 78篇 |
1997年 | 67篇 |
1996年 | 82篇 |
1995年 | 55篇 |
1994年 | 57篇 |
1993年 | 47篇 |
1992年 | 36篇 |
1991年 | 31篇 |
1990年 | 22篇 |
1989年 | 19篇 |
1988年 | 7篇 |
1987年 | 12篇 |
1986年 | 19篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 20篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1976年 | 1篇 |
1973年 | 2篇 |
1957年 | 4篇 |
排序方式: 共有3210条查询结果,搜索用时 15 毫秒
61.
Jian-Cai Huang Hui Xiao Dr. Zhixin Chen Dr. Wenxu Zheng Dr. Chang-Cang Huang Dr. Shu-Ting Wu Zenghong Xie Prof. Naifeng Zhuang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(56):14017-14024
Chiral compounds are known to be important not only because they are the fundamental components of living organisms, but also for their unique chiroptical properties. In recent years, scientists have fabricated several chiral organic supramolecular aggregates by using chiral physical fields, such as vortex flow. Herein, the relationship between dynamic chiroptical properties and rheological nature is discussed, suggesting the shear thinning properties of non-Newtonian fluids might help colloidal particles adopt a chiral arrangement in vortices. Furthermore, the storage modulus of colloids could be increased by adding a linking agent, which successfully kept the dynamic chiroptical properties in the static state. Moreover, the salt effect on the host–guest interaction involved in the colloids was studied, the results suggested a significant enhancement of the transferred dynamic circular dichroism for the achiral guest molecule. 相似文献
62.
《Composite Interfaces》2013,20(5-6):443-458
The mechanism with which the fiber-matrix interfacial strength exerts its influence on the compressive strength of fiber reinforced composites has been studied by measuring the axial compressive strength of carbon fiber/epoxy resin unidirectional composite strands having different levels of interfacial shear strength. The composite strands are used for experiments in order to investigate the compressive strength which is not affected by the delamination taking place at a weak interlayer of the laminated composites. The interfacial strength is varied by applying various degrees of liquid-phase surface treatment to the fibers. The efficiency of the compressive strength of the fibers utilized in the strength of the composite strands is estimated by measuring the compressive strength of the single carbon filaments with a micro-compression test. The compressive strength of the composite strands does not increase monotonically with increasing interfacial shear strength but showes lower values at higher interfacial shear strengths. With increasing interfacial shear strength, the suppression of the interfacial failure in the misaligned fiber region increases the compressive strength, while at higher interfacial shear strengths, the enhancement of the crack sensitivity decreases the compressive strength. 相似文献
63.
Pascal Moucheront François BertrandGeorg Koval Laurent Tocquer Stéphane RodtsJean-Noël Roux Alain CorfdirFrançois Chevoir 《Magnetic resonance imaging》2010
The rheology of granular materials near an interface is investigated through proton magnetic resonance imaging. A new cylinder shear apparatus has been inserted in the magnetic resonance imaging device, which allows the control of the radial confining pressure exerted by the outer wall on the grains and the measurement of the torque on the inner shearing cylinder. A multi-layer velocimetry sequence has been developed for the simultaneous measurement of velocity profiles in different sample zones, while the measurement of the solid fraction profile is based on static imaging of the sample. This study describes the influence of the roughness of the shearing interface and of the transverse confining walls on the granular interface rheology. 相似文献
64.
The rheological behavior of dope solutions of poly(acrylonitrile‐co‐itaconic acid) or poly(AN‐co‐IA) is important from the point of view of deriving the spinning conditions for good quality special acrylic fibers. The viscosity of the resin dope is dictated by the polymer concentration, molar mass, temperature and shear force. The dynamic shear rheology of concentrated poly(AN‐co‐IA) polymer dope solutions in N, N‐dimethylformamide, in the molar mass (M¯v) range of 1×105 to 1×106 g/mol, was investigated in the shear rate (γ′) range of 1×101 to 5×104 min?1. An empirical relation between η and M¯v was found to exist at constant shear rate. The dope viscosity was dependent on the molar mass and the shear rate at a given temperature (T) and concentration. The polymer molar mass index of dope viscosity (m) was calculated as functions of concentration (c), shear rate and temperature. The m values increased with shear rate and temperature. A master equation relating m, with shear rate and temperature was derived for a given dope concentration. At higher shear rates, m tends to the value of 3.4, which is close to the molar mass index of viscosity reported for molten thermoplastics. m increased significantly with shear rate and nominally with temperature, while an increase in concentration decreased it. The onset of shear thinning of the dope shifted to a lower shear rate regime with an increase in polymer concentration and the molar mass. For a given value of molar mass, the increase in viscosity of the dope solution with polymer concentration was dependent on the shear rate. 相似文献
65.
Zhaoxia Dong Jinru Guo Qian Zhao Meiqin Lin Yun Lin Meihua Chen 《Journal of Dispersion Science and Technology》2013,34(12):1786-1792
The salt resistance, temperature resistance, and shear stability of a cross-linked polyacrylamide microsphere system are studied by microfiltration, light diffraction analysis, and optical microscopy. The results show that other conditions being equal, the particle diameter of cross-linked polyacrylamide microspheres decreases with increased NaCl concentration. When NaCl concentration is lower than 10,000 mg/L, its effect on the plugging performance of a cross-linked polyacrylamide microsphere system in regard to the nuclear pore membrane is weak in comparison with a linked polymer solution, but the former system has better salt tolerance. Particle diameter decreases with increased swelling temperature. When the swelling temperature is below 90°C, its effect on the plugging performance of the cross-linked polyacrylamide microsphere system in regard to nuclear pore membrane is weak in comparison with the linked polymer solution, but has better temperature tolerance. Particle size shows little change, with shearing rate being increased, while the shape remains about the same and the effect of shearing on the plugging performance of the cross-linked polyacrylamide microsphere dispersion system in regard to the nuclear pore membrane is weak in comparison with the linked polymer solution, but has better shear stability. The salt tolerance, temperature tolerance, and shear stability of microspheres are associated with a particular cross-linked structure. 相似文献
66.
M. H. Godinho C. Cruz P. I. C. Teixeira A. J. Ferreira C. Costa P. S. Kulkarni 《Liquid crystals》2013,40(2):103-107
The phase behaviour of a number of N‐alkylimidazolium salts was studied using polarizing optical microscopy, differential scanning calorimetry and X‐ray diffraction. Two of these compounds exhibit lamellar mesophases at temperatures above 50°C. In these systems, the liquid crystalline behaviour may be induced at room temperature by shear. Sheared films of these materials, observed between crossed polarisers, have a morphology that is typical of (wet) liquid foams: they partition into dark domains separated by brighter (birefringent) walls, which are approximately arcs of circle and meet at “Plateau borders” with three or more sides. Where walls meet three at a time, they do so at approximately 120° angles. These patterns coarsen with time and both T1 and T2 processes have been observed, as in foams. The time evolution of domains is also consistent with von Neumann's law. We conjecture that the bright walls are regions of high concentration of defects produced by shear, and that the system is dominated by the interfacial tension between these walls and the uniform domains. The control of self‐organised monodomains, as observed in these systems, is expected to play an important role in potential applications. 相似文献
67.
68.
In the present work, the influence of porosity and boron on shear thickening behavior of hybrid mesoporous silica has been studied. Three different levels of boron modification were performed by varying the molar composition of boric acid viz., 1.5 mmol, 2.5 mmol, and 3.5 mmol in a co-condensation approach. The incorporation of boron in mesoporous silica network was confirmed by various techniques such as Fourier transform infra-red (FTIR), and 11B solid- state nuclear magnetic resonance (NMR) spectroscopy. The morphology and particle size were confirmed by using scanning and transmission electron microscopy. To evaluate the effect of boron and porosity on the shear thickening behavior, dispersions were prepared from mesoporous boron- modified silica (MSiB), control mesoporous silica (MSi), non-porous boron-modified silica (SiB), and control non-porous silica (Si) in polyethylene glycol. The shear thickening behavior was studied using steady shear rheology. The dispersion prepared from different loadings of synthesized MSiB containing 1.5 mmol boron showed more than 16 times increase in viscosity (657.7 Pa.s) compared to that of MSi (39.2 Pa.s) at a fairly low volume fraction (φ = 0.15) of silica. It is expected that the highly ordered mesoporous architecture of hybrid silica has improved the interaction between the particle and the dispersing medium through hydrogen bonding. The porous morphology of the hybrid mesoporous silica as well as the incorporation of boron in the silica network favors the formation of a frictional contact network, and a transition from continuous shear thickening (CST) to discontinuous shear thickening (DST) behavior was observed. Therefore, silica prepared via incorporation of boron as well as porosity can be material of interest in variety of applications, for example, soft body armors, sporting goods, and shear thickening electrolytes for high impact resistant batteries. 相似文献
69.
PBO fiber is one of the most promising reinforcements in resin matrix composite because of its excellent mechanical properties. However, the inert and smooth surfaces make it the poor interface adhesion with resin matrix, which seriously limits the application in composites. In this article, we report a method to modify the surface of PBO fibers with 2,2-Bis (3-amino-4-hydroxyphenyl) hexafluoropropane(BisAPAF)in supercritical CO2 to enhance interfacial properties. Chemical structures, surface elemental composition and functional groups, and surface morphology were characterized by FT-IR spectrometer, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM), respectively. The mechanical properties of the samples were tested by a tensile tester. Static contact angle and microdebonding tests were used to characterize the wetting ability and interfacial shear strength (IFSS) of the fiber and epoxy resin. The results showed that the BisAPAF could be solved in scCO2 and introduced more groups, –NH2, –OH, and –CF3 on the fiber surface, resulting in the mechanical properties and the wettability of PBO fiber slightly improved. Moreover, the fiber surface roughness was also increased obviously. The IFSS between the modified PBO fiber and epoxy resin increased from 8.18 MPa to 31.4 MPa when the treating pressure was 14 MPa. In general, the method to modify PBO fibers surface using BisAPAF in scCO2 can effectively improve their interfacial properties. 相似文献
70.
Abstract Homopolymer of linseed oil and its four copolymers with styrene, 1-decene, isodecyl acrylate and octyl acrylate, respectively, have been synthesized in this present context. The prepared polymers are characterized by NMR and FTIR spectroscopy. The molecular weights have been measured by gel permeation chromatography. Their effectiveness as pour point depressant (PPD), viscosity index improver (VII) and their shear stability in terms of permanent shear stability index have been evaluated in lube oil. The copolymers acted as better PPDs than the homopolymer whereas the homopolymer of linseed oil excelled as VII. Further it was observed that all the prepared polymers were stable enough under severe mechanical shear. 相似文献