全文获取类型
收费全文 | 30431篇 |
免费 | 4207篇 |
国内免费 | 1808篇 |
专业分类
电工技术 | 1908篇 |
综合类 | 2458篇 |
化学工业 | 8123篇 |
金属工艺 | 640篇 |
机械仪表 | 1060篇 |
建筑科学 | 719篇 |
矿业工程 | 3208篇 |
能源动力 | 823篇 |
轻工业 | 2289篇 |
水利工程 | 308篇 |
石油天然气 | 2570篇 |
武器工业 | 244篇 |
无线电 | 2712篇 |
一般工业技术 | 3297篇 |
冶金工业 | 1720篇 |
原子能技术 | 597篇 |
自动化技术 | 3770篇 |
出版年
2024年 | 145篇 |
2023年 | 520篇 |
2022年 | 876篇 |
2021年 | 1133篇 |
2020年 | 1080篇 |
2019年 | 1002篇 |
2018年 | 913篇 |
2017年 | 1087篇 |
2016年 | 1213篇 |
2015年 | 1287篇 |
2014年 | 1875篇 |
2013年 | 1942篇 |
2012年 | 2442篇 |
2011年 | 2348篇 |
2010年 | 1751篇 |
2009年 | 1798篇 |
2008年 | 1685篇 |
2007年 | 1978篇 |
2006年 | 1762篇 |
2005年 | 1549篇 |
2004年 | 1218篇 |
2003年 | 1204篇 |
2002年 | 966篇 |
2001年 | 800篇 |
2000年 | 688篇 |
1999年 | 593篇 |
1998年 | 453篇 |
1997年 | 387篇 |
1996年 | 346篇 |
1995年 | 296篇 |
1994年 | 259篇 |
1993年 | 177篇 |
1992年 | 119篇 |
1991年 | 106篇 |
1990年 | 93篇 |
1989年 | 64篇 |
1988年 | 69篇 |
1987年 | 36篇 |
1986年 | 33篇 |
1985年 | 30篇 |
1984年 | 26篇 |
1983年 | 20篇 |
1982年 | 16篇 |
1981年 | 6篇 |
1980年 | 10篇 |
1979年 | 7篇 |
1974年 | 3篇 |
1965年 | 2篇 |
1959年 | 4篇 |
1951年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
分子印迹技术及其应用 总被引:3,自引:0,他引:3
分子印迹技术是将高分子科学、材料科学、生物学、化学工程等有机集成。基于分子印迹技术所制备的分子印迹聚合物具有选择性高、稳定性好、应用范围广等特点 ,近年来得到了日益广泛和深入的研究。介绍了分子印迹技术的原理、分子印迹聚合物的制备方法、分子印迹技术的应用场合和实例 ,并简要预测了分子印迹技术领域未来的发展趋势。 相似文献
42.
43.
This paper presents a method to compensate voltage sags with minimum energy injection for a series‐connected voltage restorer using a micro‐SMES. A circuit for extracting the fundamental symmetrical components from sag voltages and a minimum energy injection algorithm is described. Simulations of voltage sag compensation have been carried out using PSCAD/EMTDC for various faults. The simulation results confirm the validity of the proposed method and show the possibility of reducing the size of energy storage devices. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(3): 70–80, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10047 相似文献
44.
Free vibration of partially supported piles with the effects of bending moment, axial and shear force 总被引:1,自引:0,他引:1
The pile parts above the soil and embedded in the soil are called the first region and the second region, respectively. The fourth order partial differential equations of both regions for free vibration of partially supported pile subjected to bending moment, axial force and shear force are obtained using the small-displacement theory and the Winkler model. It is assumed that the behavior of the material is linear-elastic, and that axial force along the pile length and modulus of subgrade reaction for the second region to be constant. Shear effect is included in the partial differential equations by the second derivative of the elastic curve function with respect to shear deformation. Natural circular frequencies and relative stiffness of the pile are calculated for non-trivial solution of linear homogeneous system of equations obtained due to the values of axial forces acting on the pile, the shape factors, and the boundary conditions of the pile with both ends free and both ends simply supported; the results are presented in graphs. 相似文献
45.
46.
47.
本文以济南鲍德气体有限公司 2 0 0 0 0m3 /h空分设备为例 ,从物料平衡的观点出发 ,阐述了操作中一些应注意的问题及解决的措施。 相似文献
48.
The miscibility and phase behavior of ternary blends containing dimethylpolycarbonate (DMPC), tetramethylpolycarbonate (TMPC) and poly[styrene‐co‐(methyl methacrylate)] copolymer (SMMA) have been explored. Ternary blends containing polystyrene (PS) instead of SMMA were also examined. Blends of DMPC with SMMA copolymers (or PS) did not form miscible blends regardless of methyl methacrylate (MMA) content in copolymers. However, DMPC blends with SMMA (or PS) blends become miscible by adding TMPC. The miscible region of ternary blends is compared with the previously determined miscibility region of binary blends having the same chemical components and compositions. The region where the ternary blends are miscible is much narrower than that of binary blends. Based on lattice fluid theory, the observed phase behavior of ternary blends was analyzed. Even though the term representing the Gibbs free energy change of mixing for certain ternary blends had a negative value, blends were immiscible. It was revealed that a negative value of the Gibbs free energy change of mixing was not a sufficient condition for miscible ternary blends because of the asymmetry in the binary interactions involved in ternary blends. Copyright © 2004 Society of Chemical Industry 相似文献
49.
A feasibility analysis methodology adopted from reactive distillation is applied to membrane reactors. A model is formulated to depict the reactive liquid phase composition on the retentate side of a continuous type membrane reactor. The effects of both the chemical reaction kinetics and the membrane mass transfer kinetics on the feasible products are elucidated by means of retentate phase diagrams and bifurcation analysis. The proposed method can be applied to various membrane processes, independent of the specific structure of the membrane. Two quaternary reaction systems are considered to illustrate the methodology. In the first hypothetical system, it is shown how selective membranes can influence the sequence of effective volatilities which in turn affects the feasible products of the system. In the second example of practical importance, i.e. the heterogeneously catalysed synthesis of propyl acetate coupled with permeation through a porous polycarbonate membrane, the dusty gas model is applied to describe the component fluxes through the membrane. For the latter reaction system, the existence of reactive arheotrope is demonstrated. Arheotropes represent mass transfer controlled feasible products of membrane separation process. 相似文献
50.
提出一种配电网电容电流测量的新方法,在零序电压互感器的开口三角侧串联一个可调电感,通过注入一个变频恒流信号寻找配电网的谐振频率,改变可调电感的数值后寻找另一谐振频率,联立2个谐振方程求解电容电流,该方法消除了电压互感器漏抗对测量的影响。开发了配电网电容电流测量仪,经模拟试验和现场测试表明,该方法具有安全、快捷、准确等特点,适用于中性点不接地或经随调式消弧线圈接地配电网。 相似文献