全文获取类型
收费全文 | 2982篇 |
免费 | 58篇 |
国内免费 | 14篇 |
专业分类
电工技术 | 40篇 |
综合类 | 12篇 |
化学工业 | 475篇 |
金属工艺 | 53篇 |
机械仪表 | 63篇 |
建筑科学 | 99篇 |
矿业工程 | 26篇 |
能源动力 | 98篇 |
轻工业 | 176篇 |
水利工程 | 36篇 |
石油天然气 | 18篇 |
无线电 | 254篇 |
一般工业技术 | 431篇 |
冶金工业 | 837篇 |
原子能技术 | 48篇 |
自动化技术 | 388篇 |
出版年
2021年 | 23篇 |
2020年 | 16篇 |
2019年 | 26篇 |
2018年 | 30篇 |
2017年 | 34篇 |
2016年 | 35篇 |
2015年 | 28篇 |
2014年 | 44篇 |
2013年 | 169篇 |
2012年 | 89篇 |
2011年 | 115篇 |
2010年 | 81篇 |
2009年 | 103篇 |
2008年 | 126篇 |
2007年 | 114篇 |
2006年 | 95篇 |
2005年 | 95篇 |
2004年 | 90篇 |
2003年 | 69篇 |
2002年 | 71篇 |
2001年 | 59篇 |
2000年 | 71篇 |
1999年 | 68篇 |
1998年 | 158篇 |
1997年 | 131篇 |
1996年 | 115篇 |
1995年 | 78篇 |
1994年 | 72篇 |
1993年 | 58篇 |
1992年 | 45篇 |
1991年 | 39篇 |
1990年 | 41篇 |
1989年 | 36篇 |
1988年 | 33篇 |
1987年 | 47篇 |
1986年 | 42篇 |
1985年 | 43篇 |
1984年 | 38篇 |
1983年 | 34篇 |
1982年 | 30篇 |
1981年 | 24篇 |
1980年 | 27篇 |
1979年 | 30篇 |
1978年 | 28篇 |
1977年 | 39篇 |
1976年 | 54篇 |
1975年 | 16篇 |
1974年 | 22篇 |
1973年 | 16篇 |
1972年 | 18篇 |
排序方式: 共有3054条查询结果,搜索用时 546 毫秒
51.
聚丙烯固相法接枝改性 总被引:3,自引:0,他引:3
聚丙烯固相法接枝不饱和单体是一种简便易行的本体法技术。与其它接枝方法相比,具有成本低、接枝率高、时间短、无溶剂回收、不妨害接枝物的进一步应用等优点。本文介绍了聚丙烯固相法接枝不饱和单体的进展,并较详细地讨论了影响接枝反应的各种因素。 相似文献
52.
The turbulence in the upward gas flow above a gas-fluidised bed was measured by hot wire anemometry. In this region above the bed—defined as the free is the fluidising velocity. The irregularity of the motion is caused by bursting bubbles at the surface of the bed. It appears that the gas within a bu are termed “ghost bubbles”.Ghost bubble mechanics were studied by releasing single bubbles from: (i) stagnant liquid; and (ii) an incipiently fluidised bed. Tle velocity field wa The velocity of a ghost bubble diminishes as it rises, due to fluid entrainment caused by turbulent circulatory flow within the bubble.From the freeboard turbulence measurements for a continuously bubbling fluidised bed, it is clear that the turbulence is due to ghost bubbles, but the ghost bubble. 相似文献
53.
Solvent refined coal (SRC), a coal extract which is highly polyaromatic in character and relatively high in N, O and S content, is derived from the direct liquefaction of coal. SRC contains mineral matter in the form of soluble organometallic compounds which can not be removed by filtration. These soluble species can be detrimental to the hydrocracking catalyst used in the upgrading of the SRC to high-value liquid fuels. These species, however, can be separated from the SRC by extraction with benzene or tetralin as solvents so that the mineral matter is mainly concentrated in the solvent-insoluble fraction, the other fraction are then readily hydrocracked, as demonstrated in this work. 相似文献
54.
Fanqin Meng Steven F. Dec Don Williamson Phat Pham Michael A. Yandrasits Andrew M. Herring 《Electrochimica acta》2007,53(3):1372-1378
A perfluorosulfonic acid (PFSA) polymer with pendant side chain -O(CF2)4SO3H was doped with the heteropoly acids (HPAs), H3PW12O40 and H4SiW12O40. Infrared spectroscopy revealed a strong interaction between the HPA and the PFSA ionomer. Modes associated with the peripheral bonds of the HPA were shifted to lower wave numbers when doped into PFSA membranes. Small-angle X-ray scattering (SAXS) measurements showed the presence of large crystallites of HPA in the membrane with d spacings of ca. 10 Å, close to the lattice spacing observed in bulk HPA crystals. Under wet conditions the HPA was more dispersed and constrained the size of the sulfonic acid clusters to 20 Å at a 5 wt% HPA doping level, the same as in the vacuum treated ionomer samples. Under conditions of minimum hydration the HPA decreased the Ea for the self-diffusion of water from 27 to 15 kJ mol−1. The reverse trend was seen under 100% RH conditions. Proton conductivity measurements showed improved proton conductivity of the HPA doped PFSAs at a constant dew point of 80 °C for all temperatures up to 120 °C and at all relative hummidities up to 80%. The activation energy for proton conduction generally was lower than for the undoped materials at RH ≤80%. Significantly the Ea was 1/2 that of the undoped material at RHs of 40 and 60%. A practical proton conductivity of 113 mS cm−1 was observed at 100 °C and 80% RH. 相似文献
55.
N. S. Ramesh Don H. Rasmussen Gregory A. Campbell 《Polymer Engineering and Science》1994,34(22):1685-1697
The existing models based on classical nucleation theory are not able to explain satisfactorily the nucleation phenomenon of microcellular foams in thermoplastics. Here, we extend the analysis of Kweeder (24), who developed a new model that considers the presence of microvoids, resulting from the thermal processing history of the polymer, as potential nucleation sites. The nucleation model “concentrates” on the stresses and thus void formations in the rubber particles. Since these are pre-existing microvoids, bubble nucleation depends on the survival of these voids to grow rather than the formation of a new phase as modeled by classical nucleation theory. The population of viable microvoids with a sufficiently large radius to survive and overcome surface and elastic forces has been modeled to yield the cell density. A log-normal distribution, which relates to the rubber particle size, has been used to model the distribution of microvoids in the polymer composite material. The model depends on various process parameters such as saturation pressure, foaming temperature, concentration of nucleating agents, solubility of the blowing agent in the polymer, and the modulus. High impact polystyrene (HIPS) was added to polystyrene to obtain polymers with different concentrations of rubber gel particles, the nucleating agent, and used here for this study. 相似文献
56.
This work was undertaken to discuss in depth the vital differences in the morphological development during synthesis, and properties of starch‐g‐poly‐(vinyl acetate) copolymers using two different initiators, potassium persulfate (KPS) and ceric ammonium nitrate (CAN). KPS‐initiated system gave relatively low values of grafting ratio and grafting efficiency, indicating a great tendency for the formation of poly(vinyl acetate) homopolymer (PVAc). Yet, higher values were seen for the CAN‐initiated system. Transmission electron microscope observations indicated a relatively broad distribution of latex particles for the KPS‐initiated system. The surface potential of latex particles was about ?3.5 mV, which turned out to be insufficient to maintain stability of latex particles. On the other hand, a uniform particle size distribution was found for the CAN‐initiated system, as the surface potential of latex particles was 21.5 mV. Moreover, radicals on starch molecules were generated directly through a redox reaction with positively charged ceric ion. The hydrophobic PVAc chains were thus grafted on starch, resulting in an amphiphilic graft copolymer, which provides a sufficient stabilization degree as a role of surfactant to render a relatively uniform distribution of latex particles. The synthesized starch‐g‐poly(vinyl acetate) copolymers were further converted to starch‐g‐poly(vinyl alcohol) through saponification, which were subjected to evaluations regarding the biodegradation and cell culture capability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3017–3027, 2006 相似文献
57.
Methyl 8-[2-(cis-pent-2′-enyl)-3-oxo-cis-cyclopent-4-enyl] octanoate (I) is the methyl ester of a cyclic fatty acid synthesized enzymically from an incubation of
linolenic acid with an extract of flaxseed (Linum usitatissimum L.). A proposed trivial name for I is methyl 12-oxo-cis-10, 15-phytodienoate (12-oxo-PDA). The evidence presented indicated that compound I has thecis configuration of the carbon chains with respect to the cyclopentenone ring. Treatment with acid, base, or heat isomerized
I to a second product (II) that has thetrans configuration of the carbon chains. Prolonged heat treatment of II yielded a third cyclic product, methyl 12-oxo-9(13),cis-15-phytodienoate (III). 相似文献
58.
Reed M. Izatt Steven R. Izatt Don W. Mcbride Jr. Jerald S. Bradshaw James J. Christensen 《Israel journal of chemistry》1985,25(1):27-32
Macrocycle-mediated fluxes of Cd(NO3)2 and of several binary mixtures of Cd(NO3)2 with the nitrate salt of either Na+, K+, Rb+ Cs+, Ag+, Ca2+, Sr2+, Pb2+, Zn2+, or Cu2+ have been determined in a H2O-CHCl3–H2O liquid membrane system. Of the macrocycles studied, 2.2 and 2.2DD most successfully transported Cd2+ In the Cd2+–Mn+ mixtures, Cd2+ was transported selectively with 2.2 when Mn+ was either an alkali or an alkaline earth cation. However, when Mn+ was either Ag+, Pb2+, or Cu2+ the Cd2+ flux was reduced sharply. Generally, cation flux was greater for 2.2DD than for 2.2 with selectivity for Cd2+ being altered also in several cases. Relative fluxes from binary cation mixtures depend on metal cation radius, macrocycle cavity diameter, ligand ring substituent and log K for metal ion-macrocycle interaction. 相似文献
59.
Randomly crosslinked networks with a range of crosslink densities were prepared by γ-irradiation. Quasielastic light scattering measurements were made on the gels swollen to equilibrium in cyclohexane at 308, 318 and 333 K. The longitudinal osmotic modulus Mos was obtained from the intensity of the dynamically scattered light, and the cooperative diffusion coefficient Dc calculated from the relaxation rate of the autocorrelation function. The concentration dependence of these parameters at the theta temperature was found to be consistent with the scaling predictions, but at higher temperatures where excluded volume conditions prevail, deviations from scaling behaviour were observed. These discrepancies are probably caused by defects in the network structure. 相似文献
60.
An axisymmetric model for thread forming in polycarbonate and polypropylene screw and boss fasteners
Plastic boss and screw fasteners are an economical means of securing automotive components, such as instrument or body panels. However, new materials and/or suboptimal design present challenges to the boss/screw effectiveness. Failure of a boss/screw can result is loss of functional performance or increased squeak and rattle. Failure is often controlled by what occurs during the initial thread‐forming process. Thus, the goal of this paper is to develop an FEA model to elucidate the thread‐forming process so that we can facilitate subsequent design and/or process optimization, and understand potential failure modes. The FEA must accommodate nonlinear couplings, such as large strain and heat transfer. Heat generation is present in the forms of interfacial shear heating and plastic work associated with the large deformation of the interface between the boss and screw. Strain rate‐dependent materials are included using the Eyring theory for plastic flow of polymeric materials. Results of the model are presented and compared to experimentally determined torque curves and temperatures. Polym. Eng. Sci. 44:1498–1508, 2004. © 2004 Society of Plastics Engineers. 相似文献