全文获取类型
收费全文 | 78499篇 |
免费 | 8109篇 |
国内免费 | 4672篇 |
专业分类
电工技术 | 5917篇 |
技术理论 | 3篇 |
综合类 | 6760篇 |
化学工业 | 11927篇 |
金属工艺 | 4432篇 |
机械仪表 | 5208篇 |
建筑科学 | 6118篇 |
矿业工程 | 2430篇 |
能源动力 | 2059篇 |
轻工业 | 7579篇 |
水利工程 | 1941篇 |
石油天然气 | 3132篇 |
武器工业 | 869篇 |
无线电 | 8746篇 |
一般工业技术 | 8270篇 |
冶金工业 | 3233篇 |
原子能技术 | 1123篇 |
自动化技术 | 11533篇 |
出版年
2024年 | 468篇 |
2023年 | 1483篇 |
2022年 | 2893篇 |
2021年 | 3803篇 |
2020年 | 2916篇 |
2019年 | 2210篇 |
2018年 | 2501篇 |
2017年 | 2851篇 |
2016年 | 2427篇 |
2015年 | 3516篇 |
2014年 | 4628篇 |
2013年 | 5387篇 |
2012年 | 6055篇 |
2011年 | 6169篇 |
2010年 | 5843篇 |
2009年 | 5339篇 |
2008年 | 5177篇 |
2007年 | 5070篇 |
2006年 | 4421篇 |
2005年 | 3572篇 |
2004年 | 2556篇 |
2003年 | 1980篇 |
2002年 | 1950篇 |
2001年 | 1558篇 |
2000年 | 1391篇 |
1999年 | 1136篇 |
1998年 | 717篇 |
1997年 | 648篇 |
1996年 | 578篇 |
1995年 | 454篇 |
1994年 | 355篇 |
1993年 | 263篇 |
1992年 | 206篇 |
1991年 | 169篇 |
1990年 | 114篇 |
1989年 | 110篇 |
1988年 | 85篇 |
1987年 | 43篇 |
1986年 | 49篇 |
1985年 | 17篇 |
1984年 | 33篇 |
1983年 | 14篇 |
1982年 | 14篇 |
1981年 | 23篇 |
1980年 | 32篇 |
1979年 | 14篇 |
1977年 | 5篇 |
1976年 | 9篇 |
1959年 | 10篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Guo Dong Zhu Jing Xu Xue Jian Yan Jie Li Zhi Gang Zeng Miao Shen Li Zhang 《Thin solid films》2006,510(1-2):181-183
This paper introduces the Force Modulation technique to the study of crystallization process in ferroelectric vinylidene fluoride and trifluoroethylene copolymer films. Using this technique we have successfully visualized ferroelectric crystalline domains and observed that these ferroelectric domains grow out from amorphous phase, unite into strip-like structures, and finally congregate into a union. Force Modulation can weaken the influence of topography on imaging of ferroelectric domains, and reveal more details, which are difficult to be observed in topographical image. 相似文献
82.
间苯二酚溶剂萃取液液相平衡研究 总被引:4,自引:0,他引:4
测定了“醋酸正丁酯-间苯二酚(溶质)-盐水(含0.2质量分率NaCl)”三元系在24℃、101.33kPa下的液液相平衡数据并给出了三角相图,用Hand公式对相平衡数据进行了关联,获得了可供工业连续萃取过程设计使用的关联式。本研究将醋酸正丁酯和正丁醇作为溶剂萃取间苯二酚进行了对比,并指出:醋酸正丁酯优于正丁醇。 相似文献
83.
The objectives of this article is to propose a new drying model for the second falling rate period known as the variable diffusion controlled period that follows after the first falling rate period and to propose a new method to determine the second critical moisture content that separates these two periods. Experimental work on paddy drying at minimum fluidization velocity was carried out in a rapid bin dryer. The effects of operating temperatures (60-120°C) and bed depths (2-6 cm) on the paddy drying characteristics were investigated. It was found that the normalized drying rate of paddy was proportional to the normalized moisture content in the first falling rate period but in the second falling rate period, the normalized drying rate of the material varies exponentially with the normalized moisture content. The different relationship between the normalized drying rate and the normalized moisture content in the first and second falling rate periods indicate that two different mechanism of moisture transport are at work. The new exponential model of the second falling rate period and the linear model of the first falling rate period were found to fit the experimental data very well. Derivation from variable diffusion equation shows that the linear model is the result of constant diffusion coefficient whereas the new exponential model is the result of linear diffusion coefficient. This also implies that the first falling rate period is a constant diffusion controlled period and the second falling rate period is a variable diffusion controlled period. In addition, drying kinetics data of a drying process that fits the exponential model over a very slow drying period will show that the drying process is under the effect of a linear diffusion coefficient. It was also found that the proposed new method to determine the second critical moisture content that distinguishes between the first and second falling rate periods by using a sudden change in the value of the drying rate gradient to a much lower value at that point is more rigorous and yet simpler than the method of determining the specific location of the receding drying boundary since it is based on the behavior of the actual drying kinetic data. 相似文献
84.
FTP是网络系统提供的基本服务之一.用户可以通过FTP上传和下载文件。本文介绍Linux系统的FTP服务器的原理以及建立FTP服务器和对FTP用户的磁盘配额进行设置。 相似文献
85.
A powerful concept to cope with resource limitations and information redundancy in wireless sensor networks is the use of collaboration groups to distill information within the network and suppress unnecessary activities. When the phenomena to be monitored have large geographical extents, it is not obvious how to define these collaboration groups. This article presents the application of geometric duality to form such groups for sensor selection and non-local phenomena tracking. Using a dual-space transformation, which maps a non-local phenomenon (e.g., the edge of a half-plane shadow) to a single point in the dual space and maps locations of distributed sensor nodes to a set of lines that partitions the dual space, one can turn off the majority of the sensors to achieve resource preservation without losing detection and tracking accuracy. Since the group so defined may consist of nodes that are far away in physical space, we propose a hierarchical architecture that uses a small number of computationally powerful nodes and a massive number of power constrained motes. By taking advantage of the continuity of physical phenomena and the duality principle, we can greatly reduce the power consumption in non-local phenomena tracking and extend the lifetime of the network. 相似文献
86.
The technique which is described combines the advantages of the techniques formerly proposed in the literature in each stage of the preparation of transmission electron microscopy (TEM) specimens including a single metal-ceramic interface. It allows easy handling of the thin foils in spite of their brittleness. Preferential thinning of the softer material in the two-phase foil is prevented, and both sides of the interface are thinned down to comparable thicknesses. The nickel-alumina bicrystal interface observed in TEM is neat and free from any reaction layer. This method is easily adaptable to other metal-ceramic systems. 相似文献
87.
88.
本文研究了LF6铝合金的超塑性/扩散连接组合工艺,用变形和再结晶的方法细化晶粒,成功地进行了SPF/DB工艺试验,利用电子探针观察了扩散连接接头的界面微观区域,并从机理上分析了金属的超塑性/扩散连接两种工艺之间的内部联系及其金属学行为。 相似文献
89.
通过分析黑岱沟露天煤矿轮胎消耗的主要原因,制定相应措施,降低轮胎消耗,降低生产成本。 相似文献
90.
Jie Luo Ephremides A. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2006,52(2):414-420
This paper extends our earlier results. We assume that the receiver has the capability of capturing multiple packets so long as the signal-to-interference-plus-noise ratio (SINR) of each packet is above a designed threshold T throughout its transmission period. We prove that, compared with a multiple-power-level system, the single-power-level system in which all nodes transmit at the maximum allowable power level achieves optimal throughput, under a condition that T exceeds the value 3.33. Given a minimum throughput requirement, under the same condition on T, the single-power-level system also achieves the maximum average packet capture probability as well as the optimum energy usage efficiency. If the multiple-power-level systems are constrained such that higher power levels always have shorter packet lengths, then the above results hold for T greater than 2. 相似文献