全文获取类型
收费全文 | 20009篇 |
免费 | 1992篇 |
国内免费 | 921篇 |
专业分类
电工技术 | 423篇 |
技术理论 | 1篇 |
综合类 | 260篇 |
化学工业 | 4642篇 |
金属工艺 | 1203篇 |
机械仪表 | 1571篇 |
建筑科学 | 589篇 |
矿业工程 | 134篇 |
能源动力 | 2341篇 |
轻工业 | 1108篇 |
水利工程 | 170篇 |
石油天然气 | 174篇 |
武器工业 | 5篇 |
无线电 | 2296篇 |
一般工业技术 | 4165篇 |
冶金工业 | 483篇 |
原子能技术 | 145篇 |
自动化技术 | 3212篇 |
出版年
2024年 | 147篇 |
2023年 | 1238篇 |
2022年 | 1051篇 |
2021年 | 1120篇 |
2020年 | 1434篇 |
2019年 | 1222篇 |
2018年 | 731篇 |
2017年 | 1282篇 |
2016年 | 1392篇 |
2015年 | 1461篇 |
2014年 | 1466篇 |
2013年 | 1267篇 |
2012年 | 1339篇 |
2011年 | 1083篇 |
2010年 | 726篇 |
2009年 | 955篇 |
2008年 | 338篇 |
2007年 | 713篇 |
2006年 | 829篇 |
2005年 | 394篇 |
2004年 | 195篇 |
2003年 | 243篇 |
2002年 | 251篇 |
2001年 | 280篇 |
2000年 | 164篇 |
1999年 | 195篇 |
1998年 | 80篇 |
1997年 | 47篇 |
1996年 | 70篇 |
1995年 | 71篇 |
1994年 | 56篇 |
1993年 | 56篇 |
1992年 | 57篇 |
1991年 | 51篇 |
1990年 | 62篇 |
1989年 | 63篇 |
1988年 | 103篇 |
1987年 | 232篇 |
1986年 | 203篇 |
1985年 | 43篇 |
1984年 | 34篇 |
1983年 | 26篇 |
1982年 | 19篇 |
1981年 | 39篇 |
1980年 | 19篇 |
1979年 | 33篇 |
1978年 | 16篇 |
1977年 | 7篇 |
1976年 | 12篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
21.
《Sensors and actuators. A, Physical》2006,125(2):223-233
To characterize the thickness of a corrosive fluid system's coated facilities, such as pipes, tubes, tanks, and structural members, a complex ultrasonic transducer capable of measuring multilayered parts was fabricated and the time and frequency responses were evaluated. The target transducer was constructed with two active dual elements made from tape-cast PbNb2O6 sheets and an additional thin-film active element made from sol–gel spin-coated Pb(Zr0.52Ti0.48)O3 films. After adjusting the properties of each active element, a complex transducer was assembled after matching the impedance of each element and considering the minimal interference between the active layers. The impulse response of the assembled complex transducer shows excellent characteristics. Moreover, the assembled transducer's capability of accurately measuring the thickness assures that it can be directly applied to related industries. 相似文献
22.
《International Journal of Heat and Mass Transfer》2006,49(1-2):359-365
Physically substantiated boundary conditions for problems of heat transfer in infiltrated granular beds based on the two-temperature model which allow for the absence of interphase heat transfer on boundaries are formulated. It is shown that classical Dankwerts conditions would be applicable for gas. The problem of porous cooling at the boundary conditions of the 2nd and 3rd kind on the outer boundary is solved in a new formulation. 相似文献
23.
《Materials Letters》2007,61(11-12):2164-2166
By radiating a linear polyethylenimine–HAuCl4 aqueous solution with natural sunlight, we obtained polyelectrolyte-protected gold nanoparticles, and the size of such gold nanoparticles can be controlled by varying the molar ratio of polyelectrolyte to gold. 相似文献
24.
25.
《Sensors and actuators. B, Chemical》2006,113(1):106-111
A stable film made from hydroxyethylcellulose (HEC) on pyrolytic graphite (PG) electrode was employed for incorporating hemoglobin (Hb), myoglobin (Mb) and horseradish peroxidase (HRP), and the electrochemical characteristics of the proteins were studied correspondingly. Experimental results revealed that HEC film could greatly accelerate electron transfer between the proteins and electrode, and the proteins showed a thin layer electrochemical behavior in the film. Moreover, all the proteins in the film exhibited good catalytic activity towards the reduction of hydrogen peroxide (H2O2) in the low H2O2 concentration range. In the high concentration range, H2O2 would exhibit toxicity effect on the proteins. The electrochemical properties and electrocatalytic abilities of the three heme proteins in HEC film have been compared, and the optimal conditions for H2O2 biosensor fabrication have been obtained. 相似文献
26.
《Optical Materials》2005,27(1):99-102
The spin Hamiltonian parameters g∥, g⊥, A∥ and A⊥ for Er3+ ion in LiYF4 are investigated by using the perturbation formulas of these parameters for a 4f11 ion in tetragonal symmetry. In these formulas, the contributions to the spin Hamiltonian parameters from the second-order perturbation terms and the admixtures of different states are considered. The relevant crystal field parameters are calculated from the superposition model and the local structural parameters of the Y3+ site occupied by impurity Er3+. The theoretical optical spectra within 4I15/2 and 4I13/2 states and the spin Hamiltonian parameters obtained in this work are consistent with the observed values. 相似文献
27.
《Hydrometallurgy》2006,81(3-4):190-196
A ligand-containing porous membrane was prepared by radiation-induced graft polymerization of an epoxy-group-containing monomer of glycidyl methacrylate onto a polyethylene porous hollow-fiber membrane and by subsequent conversion of the epoxy group to an N-methylglucamino (NMG) group at a density of 0.78 mmol/g of the membrane. Sb(V) solution was permeated through the NMG-ligand-containing porous hollow-fiber membrane. Optimum pH for Sb(V) recovery was 3.0. Breakthrough curves of Sb (V) overlapped irrespective of residence times of Sb (V) in the membrane, due to negligible diffusional mass-transfer resistance. Maximum amount of Sb (V) adsorbed was 130 mg/g-membrane, which was equivalent to 1.3 binding molar ratio. Repeated usage of the membrane for adsorption and elution was possible. 相似文献
28.
《Hydrometallurgy》2006,81(3-4):234-240
The oxidation of glucose during the reductive leaching of pure MnO2 and manganese ore in sulphuric acid at 90 °C MnO2 was investigated. The aim was to identify the derivatives and the chemical pathway of glucose oxidation. Organic derivatives were monitored by HPLC using an Aminex HPX-78H column and UV detection. Chromatographic patterns of leaching solutions showed that major compound formed was formic acid. Minor quantities of glycolic, glyceric and traces of gluconic acids were identified. Results suggest that during the leaching reaction, the carbon chain of glucose is shortened by detachment of one carbon atom as formic acid. 相似文献
29.
《International Journal of Fatigue》2007,29(9-11):1846-1854
This work presents a survey of the isothermal and anisothermal fatigue behavior of aluminum casting alloys obtained from different processes. Experimental results have shown that porosity, especially large and irregular pores, provides the main factor in decreasing fatigue properties of the tested alloys. In materials with similar porosity levels, other microstructural factors became relevant such as, matrix morphology and the amount of alloying elements. Fractographic analyses showed that fatigue cracks preferentially start to propagate in microcracks or interdendritic shrinkage usually located next to the surface. In most cases, propagation takes place in the eutectic phase, although in the thixoformed material, a transition from transgranular to intergranular mode was observed in the crack propagation mode. 相似文献
30.
《Materials Letters》2007,61(11-12):2502-2505
Carbon microspheres with a diameter of 2 μm were prepared by hydrothermal process. The apatite-formation ability of the carbon microspheres was evaluated by soaking them in a simulated body fluid (SBF) for 5 and 10 d and apatite-formation mechanism was also analyzed. The result showed that bonelike apatite was formed on the surface of carbon microspheres. Our study indicates that the carbon microspheres synthesized by this method possess apatite-formation ability and may be used as a bioactive injectable filler for bone tissue regeneration. 相似文献