全文获取类型
收费全文 | 4815篇 |
免费 | 243篇 |
国内免费 | 121篇 |
专业分类
电工技术 | 150篇 |
综合类 | 174篇 |
化学工业 | 723篇 |
金属工艺 | 177篇 |
机械仪表 | 205篇 |
建筑科学 | 165篇 |
矿业工程 | 45篇 |
能源动力 | 166篇 |
轻工业 | 293篇 |
水利工程 | 54篇 |
石油天然气 | 258篇 |
武器工业 | 20篇 |
无线电 | 592篇 |
一般工业技术 | 786篇 |
冶金工业 | 680篇 |
原子能技术 | 29篇 |
自动化技术 | 662篇 |
出版年
2024年 | 5篇 |
2023年 | 34篇 |
2022年 | 74篇 |
2021年 | 121篇 |
2020年 | 71篇 |
2019年 | 69篇 |
2018年 | 86篇 |
2017年 | 96篇 |
2016年 | 96篇 |
2015年 | 99篇 |
2014年 | 162篇 |
2013年 | 301篇 |
2012年 | 257篇 |
2011年 | 282篇 |
2010年 | 260篇 |
2009年 | 291篇 |
2008年 | 263篇 |
2007年 | 229篇 |
2006年 | 238篇 |
2005年 | 195篇 |
2004年 | 141篇 |
2003年 | 102篇 |
2002年 | 90篇 |
2001年 | 90篇 |
2000年 | 111篇 |
1999年 | 148篇 |
1998年 | 260篇 |
1997年 | 211篇 |
1996年 | 150篇 |
1995年 | 82篇 |
1994年 | 74篇 |
1993年 | 64篇 |
1992年 | 46篇 |
1991年 | 36篇 |
1990年 | 34篇 |
1989年 | 38篇 |
1988年 | 35篇 |
1987年 | 24篇 |
1986年 | 31篇 |
1985年 | 16篇 |
1984年 | 12篇 |
1983年 | 12篇 |
1982年 | 16篇 |
1981年 | 24篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1977年 | 19篇 |
1976年 | 37篇 |
1975年 | 5篇 |
1972年 | 6篇 |
排序方式: 共有5179条查询结果,搜索用时 656 毫秒
71.
Wei-Hao Chen Chia-Yueh Chou Bao-Jhen Li Shao-Liang Cheng Cheng-Yi Liu 《Journal of the American Ceramic Society》2021,104(12):6579-6588
Columnar wurtzite grains were formed in sputtered ZnO thin films deposited on a plastic polyethylene terephthalate substrate. Selected-area diffraction patterns reveal that the columnar grains in the sputtered films present two preferred growth planes, namely, the basal (0002) and prismatic (100) growth planes. The diffraction patterns obtained also confirm that the microstructure of sputtered indium tin oxide thin films is amorphous in nature. Tensile tests indicate that the fracture strain of the ZnO thin film occurs between 1.73% and 2.14%, while the fracture strain of the indium tin oxide thin film occurs between 0.24% and 0.67%. Thus, the fracture toughness of the sputtered ZnO thin film is greater than that of the sputtered indium tin oxide thin film. High-resolution transmission electron microscopic images demonstrate that edge and screw dislocations could be identified in the sputtered ZnO thin films. Moreover, edge and screw dislocation movements may, respectively, be observed in the basal- and prismatic-oriented ZnO columnar grains of the sputtered ZnO thin films. Our results indicate that movements of the edge and screw dislocations in the basal- and prismatic-oriented ZnO columnar grains account for the plastic deformation of the investigated ZnO thin films under tensile stress. 相似文献
72.
Kuo-Chih Chou 《北京科技大学学报(英文版)》2009,16(5):500-504
Electrical conductivity of molten slag is an important physicochemical property for designing the refining process in electric smelting furnaces.Though conductivities of many slag systems have been measured,the quantitative relationships of conductivity with slag composition and temperature are still very limited.In this article,the Arrhenius law was used to describe the experimental data of conductivities for CaO-MgO-Al2O3-SiO2,CaO-Al2O3-SiO2,CaO-MnO-Al2O3-SiO2,as well as CaO-MgO-MnO-Al2O3-SiO2 systems,and... 相似文献
73.
皮慧娟 《齐齐哈尔轻工业学院学报》2009,(2):39-43
为了更好地满足客户需要、提高管理效率、提高客户的满意度和忠诚度,降低企业生产和运营成本,设计了基于Delphi 7.0的保险行业客户关系管理信息系统的技术方案,详细讨论了系统的功能设计以及实现技术。为保险企业提供了一个很好的技术平台,提高了企业的竞争力。 相似文献
74.
以自制的生物浸矿反应器为对象,以反应器内矿浆质量分数分布为评价指标,就搅拌器搅拌方式、外循环流量及曝气大小对矿浆质量分数的分布进行了研究.结果表明:当搅拌速度为1800~2000 r/min,搅拌桨离曝气器顶部2~3 cm,外部循环流量为13 L/min,曝气量为1.2 m3/h时,反应器内矿浆质量分数分布均匀.并对总矿浆质量分数为6 %、10 %、15%和20%的反应器内矿浆质量分数随反应器高度的变化进行了研究. 相似文献
75.
Thick films of superconducting oxides, YBa2Cu3O7-, were successfully made by conventional screen-printing technology on Al2O3, MgO, and ZrO2 substrates. Interdiffusion between the superconductive film and substrate was investigated using analytical electron microscopy. The results indicate that MgO and ZrO2 are superior to Al2O3 for substrate materials. 相似文献
76.
77.
78.
从环境角度研究了敏化1Cr18Ni9Ti不锈钢在高温水中的腐蚀行为.研究指出,在一定浓度Cl~-和(或)O_2存在情况下,在酸性和中性高温高压水中都会出现应力腐蚀破裂.断口电子金相表明,在氯离子为主的环境中,破裂系晶间型;在氧为主的环境中,破裂系以解理为主的混合型.给出了1Cr18Ni9Ti在高温水中腐蚀的表观和真实动力学曲线,表明腐蚀包含溶解和湿氧化两部分,而以湿氧化为主.借Mossbauer内转换电子谱研究了氧化膜结构与腐蚀的关系,指出在一般腐蚀条件下,膜的主要组分为Fe_3O_4,而在应力腐蚀条件下,膜的主要组分为Fe_2O_3,并且系Fe_2O_3和Fe_3O_4多层重叠结构.当水中添加了一定量的硼,在氧化膜中会局部出现FeBO_3相,既不会引起也不会抑制应力腐蚀.硼的这种“惰性”作用和膜结构中Fe_3O_4相的非化学计量比,膜具有阴离子选择性有关.根据腐蚀电化学,认为应力腐蚀系发生在钝化/过钝化区域,增高Cl~-或O_2含量,从不同角度都会使合金的电位接近过钝化区.Cl~-的作用在于改变阳极极化曲线,O_2的作用在于改变阴极极化曲线.在含Cl~-水中,晶界TiC的迅速溶解是应力腐蚀的主要原因,而在含氧水中,晶粒Fe-Cr-Ni中Cr的选择性溶解是应力腐蚀的主要原因.在分析应力腐蚀的特征后,指出应力既是某些严重腐蚀点形 相似文献
79.
In this study, we perform an experimental result for measurements of the body wave phase and group velocities in transversely isotropic media (TIM) by through-transmission technique. After comparing the experimental and theoretical first arrival times of the waves, a difference between the phase velocity and group velocity is observed. When the ratio between propagation distance (d) of the wave and the diameter (D) of transducer is 2.4 for measuring phase velocity and the point probes configuration for measuring group velocity, the accuracy in velocity estimation can reach the limit of system's resolution. However if d/D is 7.8, the wave will propagate with an intermediate velocity between the phase and group velocities. The rapid change of the wave velocity and waveform for qSV-wave propagation with the group velocity has been observed at the propagation direction near the cusps. Therefore, in order to reduce the error in group velocity estimation of qSV-waves, the optimum directions are suggested at 20 and 60°. 相似文献
80.
A figure of merit (FOM) has been developed to define the quality of ceramic (e.g., ZrO2) coatings on metal and alloy [Type 304SS and Alloy 600] surfaces. Zirconia (ZrO2) coatings were developed as a means of protecting the metal/alloy surfaces from stress corrosion cracking (SCC) in boiling water reactor (BWR) primary heat transport circuits, by inhibiting the cathodic reaction (reduction of oxygen and hydrogen peroxide) on the surface external to the crack. The distribution of pores in the coating plays an important role in corrosion prevention, such that the lower the porosity of the coating, the better the protection afforded to the system against SCC. Since the reactors operate at high temperature (e.g., at 288 °C under full power conditions), the temperature dependence of the FOM was investigated. The figure of merit (FOM) was developed by measuring impedance data over a wide range of frequency (10 mHz-5 kHz) at temperatures of 25, 100, 200, and 288 °C in hydrogenated, buffered solutions, with the hydrogen electrode reaction (HER) being used as a “fast” redox couple. An “equivalent circuit” analog was first developed from the bare surface impedance data and this analog was then employed in a second step to model the pore bottom in defining the pore distribution on the coated surface. A lognormal distribution (LND) of the pores was assumed and the parameters of the LND were determined using a constrained optimization technique to fit the model to the experimental data for the coated surface at different temperatures. The results suggest that, as temperature increases, the coating becomes more porous, making the substrate more susceptible to corrosion cracking. At 288 °C, 87% of the SS and 85% of the Ni-alloy surfaces become porous with the pore radius varying from 0.0001 cm to 0.01 cm. 相似文献