全文获取类型
收费全文 | 89514篇 |
免费 | 6863篇 |
国内免费 | 3478篇 |
专业分类
电工技术 | 4940篇 |
技术理论 | 5篇 |
综合类 | 5701篇 |
化学工业 | 15727篇 |
金属工艺 | 5413篇 |
机械仪表 | 5507篇 |
建筑科学 | 7878篇 |
矿业工程 | 2582篇 |
能源动力 | 2380篇 |
轻工业 | 5373篇 |
水利工程 | 1566篇 |
石油天然气 | 5262篇 |
武器工业 | 684篇 |
无线电 | 9359篇 |
一般工业技术 | 10655篇 |
冶金工业 | 4505篇 |
原子能技术 | 1074篇 |
自动化技术 | 11244篇 |
出版年
2024年 | 361篇 |
2023年 | 1497篇 |
2022年 | 2429篇 |
2021年 | 3376篇 |
2020年 | 2629篇 |
2019年 | 2192篇 |
2018年 | 2544篇 |
2017年 | 2880篇 |
2016年 | 2459篇 |
2015年 | 3273篇 |
2014年 | 4135篇 |
2013年 | 5074篇 |
2012年 | 5565篇 |
2011年 | 5946篇 |
2010年 | 5038篇 |
2009年 | 4970篇 |
2008年 | 4772篇 |
2007年 | 4589篇 |
2006年 | 4884篇 |
2005年 | 4340篇 |
2004年 | 2896篇 |
2003年 | 2499篇 |
2002年 | 2296篇 |
2001年 | 2024篇 |
2000年 | 2303篇 |
1999年 | 2681篇 |
1998年 | 2188篇 |
1997年 | 1777篇 |
1996年 | 1827篇 |
1995年 | 1486篇 |
1994年 | 1212篇 |
1993年 | 859篇 |
1992年 | 700篇 |
1991年 | 554篇 |
1990年 | 402篇 |
1989年 | 332篇 |
1988年 | 270篇 |
1987年 | 184篇 |
1986年 | 123篇 |
1985年 | 88篇 |
1984年 | 57篇 |
1983年 | 36篇 |
1982年 | 40篇 |
1981年 | 35篇 |
1980年 | 23篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1965年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
Experimental Research on the Dynamic Energy Absorbing Capacity of the Honeycomb Paperboard Filled with Polyurethane 总被引:1,自引:0,他引:1
A kind of composite buffering material was made by filling the voids of honeycomb paperboard with polyurethane. Drop tests were performed to evaluate the dynamic energy absorption capacity of the material. Based on the tests results, the mechanical behaviors of the material under low velocity dynamic impact conditions were analyzed. It was shown that the absorbed energy of the composite material varies inversely with the void diameter. The absorbed energy of the composite material is 1 - 2 times than that of honeycomb paperboard and polyurethane. The energy absorption efficiency of the composite material is better than those of honeycomb paperboard and polyurethane. 相似文献
172.
针对水火电联合运行的电力系统,首次利用优化的方法分析水电和火电间的相互作用规律和负荷的空间分布特性对电力系统节能运行的影响规律,揭示了其联合运行时的水电和火电的运行特征.以此为基础,构建了可充分发挥梯级水电站互动特性的优化调度模型.以一个含有梯级水电站的水火电力系统为例进行分析,结果表明可通过充分发挥水电能源的互补作用,实现非可再生能源的节约和促进能源的可持续高效利用. 相似文献
173.
以南拳项目中腾空飞脚动作为例,依据2003版竞技武术套路竞赛规则,建立三维坐标系,将动作质量(A组)评分规则中的腾空飞脚动作的扣分规则进行形式化描述,以利于电子裁判对错误动作进行识别.针对每个动作建立错误函数和基于计算机视觉的腾空飞脚动作扣分模型,并举例说明. 相似文献
174.
海面高程的传递是水准测量中的难题.以宁波市象山县某围堤工程变形测量为例,对全站仪进行跨海面高程测量进行了成功应用,并用GPS拟合高程测量方法和平均海平面法进行了验证,结果合理. 相似文献
175.
176.
Zhiping Zhou 《Polymer》2004,45(4):1313-1320
According to the six-state scheme proposed by Vacatello and Flory, the mean-square dipole moments 〈M2〉/x (x: number of monomeric units) of poly(methyl methacrylate) (PMMA) chains and their temperature dependence were calculated by the matrix algebra method of rotational isomeric state theory. To take account of the orientation effect of polar ester groups, the statistical weight matrices, U′ and U″, were recast into an expanded form. A Bernoullian probability λ introduced to measure the preference between the two alternative orientations (χ=0 and χ=π) of the side ester groups was found to give rise to a large effect on the mean-square dipole moment of polymers. When the skeletal bonds of a meso dyad are both in trans, an exceptionally strong dipole-dipole interaction may take place. If the two adjacent ester groups adopt the same orientation, the dipoles must be situated nearly parallel to each other in a close proximity. Such repulsive interactions may be alleviated by taking a staggered conformation, i.e. (χ,χ′)=(0,π) or (π,0). Such neighbor-dependent correlation inherent to the meso dyad is considered by assigning a parameter λ′ to the proper element of the Um″ matrix. The values of 〈M2〉/x observed at 30 °C were satisfactorily reproduced by adopting λ=0.270 and λ′=0.865. The thermal coefficients were found to be reconciled with the available experimental data by allowing the orientation parameters λ and λ′ to be slightly temperature dependent. The stereochemical characteristics of the chain terminals were examined in order to extend the treatment to include the dipole moment of PMMA oligomers. 相似文献
177.
一、咨询公司进行工程前期沟通的意义
在工程前期咨询过程中沟通的有效性往往能决定该阶段工作的成败,主要体现在以下几方面.
(1)为项目的决策和计划提供信息.项目的相关各方通过工程项目内外部环境之间的有关信息的沟通,获得对自己有价值的信息,并依据这些信息进行项目的决策和计划. 相似文献
178.
Xiaohua Zhou Shuren Zhang Ying Yuan Bo Li Jingsong Liu 《Journal of Materials Science: Materials in Electronics》2006,17(2):133-136
Nonreducible X7R dielectric materials, which can be cofired with Ni electrode, were obtained by doping nanometer additives
to BaTiO3 powders synthesized by employing a sol-gel method. The crystallization process, structure and constituent of nanometer additives,
as well as morphologies were studied via differential thermal and thermogravimetric analyses (DTA/TG), X-ray diffraction (XRD)
and transmission electron microscopy (TEM). The effects of the calcining temperature of dopants on the dielectric properties
were also discussed. The experiment results proved that higher-performance X7R dielectric materials could be obtained via
nanometer doping compared with conventional doping. At room temperature, dielectric constant is more than 3000; dielectric
loss lower than 1.0% and insulation resistance more than 1011Ω ⋅cm. 相似文献
179.
180.