全文获取类型
收费全文 | 63307篇 |
免费 | 7890篇 |
国内免费 | 2846篇 |
专业分类
电工技术 | 4799篇 |
综合类 | 2759篇 |
化学工业 | 20013篇 |
金属工艺 | 2455篇 |
机械仪表 | 2217篇 |
建筑科学 | 4785篇 |
矿业工程 | 1731篇 |
能源动力 | 2037篇 |
轻工业 | 7021篇 |
水利工程 | 1111篇 |
石油天然气 | 2397篇 |
武器工业 | 256篇 |
无线电 | 4542篇 |
一般工业技术 | 6156篇 |
冶金工业 | 2772篇 |
原子能技术 | 3295篇 |
自动化技术 | 5697篇 |
出版年
2024年 | 210篇 |
2023年 | 1054篇 |
2022年 | 3677篇 |
2021年 | 4074篇 |
2020年 | 2044篇 |
2019年 | 2085篇 |
2018年 | 2229篇 |
2017年 | 2875篇 |
2016年 | 4040篇 |
2015年 | 4422篇 |
2014年 | 4869篇 |
2013年 | 5332篇 |
2012年 | 3568篇 |
2011年 | 3090篇 |
2010年 | 2557篇 |
2009年 | 2595篇 |
2008年 | 2404篇 |
2007年 | 3556篇 |
2006年 | 3731篇 |
2005年 | 3226篇 |
2004年 | 2143篇 |
2003年 | 2106篇 |
2002年 | 1598篇 |
2001年 | 1143篇 |
2000年 | 975篇 |
1999年 | 713篇 |
1998年 | 459篇 |
1997年 | 386篇 |
1996年 | 352篇 |
1995年 | 310篇 |
1994年 | 295篇 |
1993年 | 222篇 |
1992年 | 168篇 |
1991年 | 199篇 |
1990年 | 196篇 |
1989年 | 143篇 |
1988年 | 91篇 |
1987年 | 106篇 |
1986年 | 79篇 |
1985年 | 84篇 |
1984年 | 79篇 |
1983年 | 48篇 |
1982年 | 40篇 |
1981年 | 40篇 |
1980年 | 49篇 |
1966年 | 25篇 |
1964年 | 34篇 |
1962年 | 64篇 |
1959年 | 53篇 |
1955年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
111.
T. Choi J.‐H. Jang C.K. Ullal M.C. LeMieux V.V. Tsukruk E.L. Thomas 《Advanced functional materials》2006,16(10)
The probing of the micromechanical properties within a two‐dimensional polymer structure with sixfold symmetry fabricated via interference lithography reveals a nonuniform spatial distribution in the elastic modulus “imprinted” with an interference pattern in work reported by Tsukruk, Thomas, and co‐workers on p. 1324. The image prepared by M. Lemieux and T. Gorishnyy shows how the interference pattern is formed by three laser beams and is transferred to the solid polymer structure. The elastic and plastic properties within a two‐dimensional polymer (SU8) structure with sixfold symmetry fabricated via interference lithography are presented. There is a nonuniform spatial distribution in the elastic modulus, with a higher elastic modulus obtained for nodes (brightest regions in the laser interference pattern) and a lower elastic modulus for beams (darkest regions in the laser interference pattern) of the photopatterned films. We suggest that such a nonuniformity and unusual plastic behavior are related to the variable material properties “imprinted” by the interference pattern. 相似文献
112.
Cu-Mg/Al_2O_3催化乙醇和乙二胺合成N-乙基乙二胺 总被引:1,自引:0,他引:1
在固定床反应器内,乙醇和乙二胺经分子间催化胺化反应合成了N-乙基乙二胺(NEED),考察了一系列铜系催化剂的活性,并筛选出催化性能较好的Cu-Mg/A l2O3催化剂;通过X射线衍射和透射扫描电子显微镜方法表征了助剂Mg对Cu/A l2O3催化剂的改性作用;考察了助催化剂Mg含量、反应温度、反应压力、进料量和乙二胺含量等对Cu-Mg/A l2O3催化剂性能的影响。实验结果表明,Cu-Mg/A l2O3催化剂具有很好的活性和选择性;在200℃、3.0MPa、质量分数20%的乙二胺乙醇溶液、进料量1.0mL/m in的条件下,乙二胺的转化率为71.56%,产物NEED的选择性和收率分别为92.62%和69.86%;经过20 d的连续使用表明,Cu-Mg/A l2O3催化剂具有良好的稳定性。 相似文献
113.
114.
光氯化制备对氯三氯甲苯的工艺条件研究 总被引:1,自引:0,他引:1
赵培新 《南京工业职业技术学院学报》2003,3(3):34-37
本研究了在内环流反应器中,以对氯甲苯为原料制备对氯三氯甲苯的新工艺,考察了不同氯气流量、不同氯化温度对对氯甲苯侧链光氯化反应的影响,得出了对氯甲苯的侧链光氯化反应规律。结合正交试验,得出了对氯甲苯侧链光氯化制备对氯三氯甲苯的较优工艺条件。 相似文献
115.
Woo‐Seok Cheong 《ETRI Journal》2003,25(6):503-509
Selective epitaxial growth (SEG) of silicon has attracted considerable attention for its good electrical properties and advantages in building microstructures in high‐density devices. However, SEG problems, such as an unclear process window, selectivity loss, and nonuniformity have often made application difficult. In our study, we derived processing diagrams for SEG from thermodynamics on gas‐phase reactions so that we could predict the SEG process zone for low pressure chemical vapor deposition. In addition, with the help of both the concept of the effective supersaturation ratio and three kinds of E‐beam patterns, we evaluated and controlled selectivity loss and nonuniformity in SEG, which is affected by the loading effect. To optimize the SEG process, we propose two practical methods: One deals with cleaning the wafer, and the other involves inserting dummy active patterns into the wide insulator to prevent the silicon from nucleating. 相似文献
116.
117.
118.
Organic solar cells are a promising route towards large‐area and low‐price photovoltaic systems. The devices are composed of at least two layers: the hole‐transport layer and the electron‐transport layer. The light absorption can occur in one or both layers. At the interface of the layers the excitons are separated into charge carriers, and every layer deals with one type of carrier. Higher efficiencies of the separation process can be obtained by using a mixed layer containing both materials to obtain a very high interface area. Although the structure of the mixed layers used plays a crucial role for the device performance, until now the morphologies have not been elucidated. In order to correlate physical and optical findings with structure and morphology for the materials in question, electron microscopy experiments were performed on the single components as well as on the layer systems. The conventional electron microscope is a poor phase microscope. As consequence, weak‐phase objects like organic molecules have to be stained or imaged under strong defocus to produce an observable contrast. Artifacts caused by chemical staining and the appearance of Fresnel diffraction using the defocus technique represent the main problems of conventional microscopy. These artifacts can be avoided using electron holography. Holograms of ultrathin sections of thin layers composed of organic dye molecules were recorded. Subsequently, the phase images were reconstructed. In this manner, we succeeded in obtaining high‐contrast electron micrographs without applying staining or defocus. In addition, holograms of crystalline C60 and zinc phthalocyanine were successfully recorded. Holography has been shown to be a useful tool to image beam‐sensitive and weak‐phase objects without artifacts. 相似文献
119.
120.
Characterisation of two biomass fuels (pelletised Miscanthus Giganteus and wood) was performed using thermogravimetric analysis with measurement of products by means of Fourier transform infrared spectroscopy (TG-FTIR). Three heating rate profiles were applied (10, 30 and 100 °C/min), with a final temperature of 900 °C. HCN and HNCO were found to be the major N-products, while the NH3 fraction was detected to a minor extent. Kinetic parameters were obtained from the TG-FTIR results using a model based on parallel first-order reactions with a Gaussian distribution of activation energies. On the basis of the above kinetic analysis and product yields, input files for the functional group-devolatilisation, vaporisation, cross-linking biomass-pyrolysis model were prepared. The fit of model parameters to TG-FTIR product-evolution data was found to be generally good, but the model-predicted yields for some species did not fit experimental data at all heating rates. Further improvements in the model are needed to resolve above difficulty. 相似文献