全文获取类型
收费全文 | 15348篇 |
免费 | 1043篇 |
国内免费 | 50篇 |
专业分类
电工技术 | 224篇 |
综合类 | 38篇 |
化学工业 | 3350篇 |
金属工艺 | 577篇 |
机械仪表 | 1131篇 |
建筑科学 | 273篇 |
矿业工程 | 13篇 |
能源动力 | 570篇 |
轻工业 | 1274篇 |
水利工程 | 89篇 |
石油天然气 | 27篇 |
无线电 | 2856篇 |
一般工业技术 | 3407篇 |
冶金工业 | 784篇 |
原子能技术 | 205篇 |
自动化技术 | 1623篇 |
出版年
2024年 | 15篇 |
2023年 | 186篇 |
2022年 | 281篇 |
2021年 | 510篇 |
2020年 | 354篇 |
2019年 | 424篇 |
2018年 | 462篇 |
2017年 | 537篇 |
2016年 | 586篇 |
2015年 | 522篇 |
2014年 | 720篇 |
2013年 | 1014篇 |
2012年 | 1025篇 |
2011年 | 1245篇 |
2010年 | 892篇 |
2009年 | 919篇 |
2008年 | 888篇 |
2007年 | 674篇 |
2006年 | 599篇 |
2005年 | 525篇 |
2004年 | 481篇 |
2003年 | 458篇 |
2002年 | 448篇 |
2001年 | 346篇 |
2000年 | 296篇 |
1999年 | 303篇 |
1998年 | 403篇 |
1997年 | 258篇 |
1996年 | 204篇 |
1995年 | 141篇 |
1994年 | 133篇 |
1993年 | 106篇 |
1992年 | 76篇 |
1991年 | 67篇 |
1990年 | 57篇 |
1989年 | 60篇 |
1988年 | 36篇 |
1987年 | 47篇 |
1986年 | 23篇 |
1985年 | 33篇 |
1984年 | 21篇 |
1983年 | 12篇 |
1982年 | 8篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1973年 | 5篇 |
1963年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
A poly(perfluoroalkylethyl methacrylate) and a series of poly(n-alkyl methacrylate)s such as poly(methyl methacrylate), poly(ethyl methacrylate), and poly(n-butyl methacrylate) were prepared and used to investigate the surface properties of polymer mixtures containing a fluorinated homopolymer and a nonfluorinated homopolymer and the effect of the side-chain length of poly(n-alkyl methacrylate) on the surface free energy for the polymer mixtures. Contact angles were measured for the surfaces of polymer mixtures by varying the concentration of poly(perfluoroalkylethyl methacrylate). From the contact angle data, it can be inferred that most of the poly(perfluoroalkylethyl methacrylate) added to poly(n-alkyl methacrylate)s is located in the outermost layer of polymer-mixture surface. Surface free energies for the outermost surfaces of polymer mixtures were calculated from the contact angle data using Owen and Wendt's equation. The decrease in the surface free energy for the polymer mixture with the poly(perfluoroalkylethyl methacrylate) addition is more pronounced as the side-chain length of poly(n-alkyl methacrylate) decreases. Due to the steric effect of the side chain of poly(n-alkyl methacrylate), the arrangement of the perfluoroalkylethyl group of poly(perfluoroalkylethyl methacrylate) to the air side is considerably hindered. The ESCA analysis of atomic compositions of the surface for the polymer mixture verified that poly(perfluoroalkylethyl methacrylate) is preferentially arranged and concentrates at the polymer mixture–air interface. The results of functional group compositions obtained by ESCA showed that the functional group composition of CF3 for the outermost layer has a more important effect on the surface free energy than that of CF2 and confirmed the hindrance of the arrangement of perfluoroalkylethyl group to the air side by the side chain of poly(n-alkyl methacrylate). © 1994 John Wiley & Sons, Inc. 相似文献
132.
Multifunctional monomers, m‐xylylenedimaleimide, p‐phenylenedimaleimide, m‐phenylenedimaleimide, and p‐phenylenedinadimide, all of which have maleimide groups, were synthesized to increase thermal and radiation stabilities. The synthesized multifunctional monomers showed good compatibility with low‐density polyethylene (LDPE). Mixtures of LDPE and these multifunctional monomers were irradiated with γ‐rays from a Co‐60 source at room temperature in a nitrogen atmosphere. The absorbed dose ranged from 0 to 160 KGy. Among these multifunctional monomers, m‐xylylenedimaleimide was the best in gel fraction enhancement. Crosslinked LDPE with m‐xylylenedimaleimide displayed a higher modulus than that of crosslinked LDPE with triallyl cyanurate. For the elongation property, LDPE with m‐xylylenedimaleimide as a multifunctional monomer showed better results than that with commercial multifunctional monomers such as triallyl cyanurate (TAC) and trimethylol propane triacrylate (TMPTA). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2339–2345, 2003 相似文献
133.
Electrorheological (ER) response of biocompatible particles suspended in an insulating silicone oil, was investigated under several different applied external electric field strengths. Chitosan, a biodegradable polysaccharide, was used as anhydrous ER materials. The effect of particle volume concentration on their ER response was examined by focusing on the measurement for rheological and electrical properties. The yield stress of chitosan suspended in silicone oil system as a function of applied electric field strength showed different value of slopes for different particle concentrations, however, all data points collapse onto a universal scaling function. 相似文献
134.
Jeong-Woo Choi 《Korean Journal of Chemical Engineering》1992,9(3):128-134
The use of suspended and alginate-entrapped XAD-7, polycarboxyl ester resin, for thein situ separation of berberine, isoquinoline alkaloid, produced from plant cell culture ofThalictrum rugosum was investigated. XAD-7 could adsorb the berberine and the amount of berberine adsorbed on XAD-7 depended on pH. The neutral
form of berberine was adsorbed onto XAD-7 and the adsorption isotherm for berberine showed a Langmuir-type appearance.In situ berberine removal enhanced the production of secondary metabolites in cell suspension culture ofThalictrum rugosum. Addition of XAD-7 at the exponential phase of cell growth was the most effective for enhancement of berberine production.
In chitosan-treated cell culture to permeabilize intracellular berberine, berberine secretion was significantly accelerated
by addition of alginate-entrapped XAD-7 at the stationary phase of cell growth and thus more than 70% of the produced berberine
could be adsorbed to alginate-entrapped XAD-7. 相似文献
135.
Structured dispersion particles suitable for pressure sensitive adhesives (PSA) were synthesized via swelling polymerization technique (EP 359562). Particles consisting of poly(n‐butyl acrylate) copolymerized with different types of carboxylic acids were used as seeds. The final particles were synthesized by swelling polymerization process, using 6 wt % styrene or 6 wt % methyl methacylate. The resulting particle morphology was analyzed by atomic force microscopy (AFM) and transmission electron microscopy (TEM). From previous works (Coll Surf A 2001, 183–185, 725–737; J Appl Polym Sci 2004, 91, 2610–2623) where two‐step emulsion polymerization was used on similar particles, it is expected that the particle morphology is affected by the polarity of the monomer used for swelling polymerization because of the phase compatibility (thermodynamic parameter). In this work, the seed particles used were always of a glass transition temperature (Tg) below polymerization temperature. The diffusion of the growing polymer chains from the swelling polymerization is therefore mainly affected by their own Tg and the influence of the carboxy groups on the chain length of the entering radicals (kinetic parameter). The different morphologies of the single particles are discussed qualitatively. The effects of reaction parameters are compared with the results given in the previous work. The structure of the corresponding dispersion films was characterized using AFM. Correlations to macroscopic properties such as the cohesive strength and peel adhesion to different substrates are discussed. The results are also compared with the application properties of the corresponding unmodified particles, statistical copolymers, and to blends with small sized PMMA or PS particles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1444–1455, 2006 相似文献
136.
Young Tae Moon Do Kyung Kim Chong Hee Kim 《Journal of the American Ceramic Society》1995,78(4):1103-1106
Based on the principle that the solubility of a salt decreases as the dielectric constant of the solvent decreases, zirconia powders were prepared by heating a zirconyl chloride solution with a 2-PrOH-water mixture as the solvent. The morphology, size, and size distribution of the resulting particles were highly sensitive to the heating method used on the starting solution. Particles formed under conventional heating methods were polydisperse, agglomerated spherical, or irregularly shaped because of inhomogeneous precipitation through the temperature gradient, the shear force induced by stirring, compositional nonuniformity, and the low heating rate. The present study demonstrated that microwaves provide an excellent means of heating uniformly and rapidly without stirring. The particles resulting from microwave treatment were monodisperse and spherical, with a mean diameter of 0.28 μm. 相似文献
137.
The dynamical behavior of polymers with molecular weight distribution is analyzed from the standpoint of reptation and tube
renewal. In a binary blend where the entanglements between longer chains are prominent, the shorter chain relaxes only by
reptation, whereas the longer chain shows more complex behavior, i.e., reptation in the original tube, short-range tube renewal
causing the tube enlargement, and thereafter reptation again in the expanded tube. Dynamic moduli data from literature are
used for determining the compositional dependence of the relaxation times. Also on the basis of the relaxation mechanism considered
here, the critical composition due to the onset of entanglements between different longer chains is proposed as a function
of their component molecular weighl ratio. 相似文献
138.
Enhancing textile ink-jet printing with chitosan 总被引:1,自引:0,他引:1
Following on from previous research, the possibility of using chitosan in preparing the pretreatment print paste for textile ink-jet printing was investigated but the final colour was not as good as expected. In this study, chitosan was applied separately on cotton fabric for ink-jet printing. A two-bath method was proposed and it was confirmed that a better colour yield was achieved with this method. However, the use of chitosan reduced the tensile strength of the ink-jet printed fabric slightly. 相似文献
139.
Yong?An?Jung Du?Young?Choi Seung?Bum?Hong Kyung?Ho?RowEmail author 《Korean Journal of Chemical Engineering》2003,20(4):705-708
Reversed-phase high-performance liquid chromatography was successfully developed for the simultaneous and rapid separation for the main whey proteins, α-Lactalbumin and β-Lactoglobulin. This method consisted of a linear gradient of the two mobile phases of 0.1% trifluoroacetic acid in water and 0.1% trifluoroacetic acid in acetonitrile. The total run time for this separation was approximately 30 min, and α-Lactalbumin was eluted followed byβ- Lactoglobulin. The injection volume was fixed at 20 μl and the flow rate was 1 ml 1/min. The optimum mobile phase composition and gradient conditions to separate α-Lactalbumin and β-Lactoglobulin (A+B) were experimentally obtained at the 15 μm particle with a pore size of 300 Å on the linear-gradient mode. 相似文献
140.
Polypropylene (PP)/layered silicate nanocomposites were prepared via simple melt mixing of three components, PP, layered silicates modified with octadecylamine (C18-MMT) and antioxidant, to investigate the role of antioxidant. TEM and X-ray scattering results confirmed the intercalated state of silicates in PP/layered silicate nanocomposites with antioxidant. In rheological and mechanical study, the nanocomposites with antioxidant showed higher properties than those of the unfilled PP. The nanocomposite with 5 wt% C18-MMT and 0.5 phr antioxidant exhibited about 1.4 times higher tensile modulus and 1.3 times higher storage modulus than the unfilled PP. However, PP/C18-MMT without antioxidant showed lower rheological values owing to the thermal decomposition of PP and the poor compatibility between PP and C18-MMT. It could be concluded that antioxidants played an important role in enhancing the compatibility between PP and C18-MMT. According to the real time X-ray diffraction, the nanocomposite showed the weak ordering of PP crystals than the unfilled PP in the load-extension plateau region of elongation. 相似文献