全文获取类型
收费全文 | 32390篇 |
免费 | 4678篇 |
国内免费 | 3468篇 |
专业分类
电工技术 | 2006篇 |
综合类 | 2704篇 |
化学工业 | 4157篇 |
金属工艺 | 1138篇 |
机械仪表 | 1322篇 |
建筑科学 | 143篇 |
矿业工程 | 238篇 |
能源动力 | 1610篇 |
轻工业 | 307篇 |
水利工程 | 27篇 |
石油天然气 | 81篇 |
武器工业 | 233篇 |
无线电 | 12394篇 |
一般工业技术 | 4197篇 |
冶金工业 | 342篇 |
原子能技术 | 254篇 |
自动化技术 | 9383篇 |
出版年
2024年 | 191篇 |
2023年 | 1700篇 |
2022年 | 1381篇 |
2021年 | 1459篇 |
2020年 | 1754篇 |
2019年 | 1292篇 |
2018年 | 1356篇 |
2017年 | 2274篇 |
2016年 | 2229篇 |
2015年 | 1964篇 |
2014年 | 2537篇 |
2013年 | 2525篇 |
2012年 | 3238篇 |
2011年 | 3349篇 |
2010年 | 2095篇 |
2009年 | 2335篇 |
2008年 | 1154篇 |
2007年 | 2140篇 |
2006年 | 1806篇 |
2005年 | 706篇 |
2004年 | 311篇 |
2003年 | 299篇 |
2002年 | 318篇 |
2001年 | 291篇 |
2000年 | 226篇 |
1999年 | 237篇 |
1998年 | 111篇 |
1997年 | 90篇 |
1996年 | 87篇 |
1995年 | 89篇 |
1994年 | 69篇 |
1993年 | 64篇 |
1992年 | 66篇 |
1991年 | 65篇 |
1990年 | 59篇 |
1989年 | 56篇 |
1988年 | 94篇 |
1987年 | 200篇 |
1986年 | 163篇 |
1985年 | 42篇 |
1984年 | 24篇 |
1983年 | 10篇 |
1982年 | 14篇 |
1981年 | 17篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 11篇 |
1977年 | 5篇 |
1976年 | 8篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
��Ȼ����������ϵͳ�ļ춨��У 总被引:6,自引:3,他引:3
当前我国管道天然气计量系以体积表示,就其计量器具而言,差压式流量计、容积式流量计和速变式流量计都有,但大流量计量大多仍采用标准孔板差压式流量计,其流量计量标准招待我国SY/T6143-1996《天然气流量的标准孔板计量方法》。文章介绍目前常用的三种流量计的优缺点比较;天然气标准孔板差压式流量计算机自动计量系统的检定,其中包括:标准孔板节流装置,静压、差压变送器、温度传感器、数据采集系统等组件的检定;以及计量器具的正确使用和维护。最后,文章指出目前流量计量的发展主要是二次仪表的发展,籍助应用计算机大大提高流量法的测量范围和准确度,但对用户来说,应选择性/价比合适的仪表,并要考虑所选用仪表要便于检定、维护,同时,计量检定部门则应跟上发展,为广大用户提供技术支持。 相似文献
42.
《Optical Materials》2005,27(1):99-102
The spin Hamiltonian parameters g∥, g⊥, A∥ and A⊥ for Er3+ ion in LiYF4 are investigated by using the perturbation formulas of these parameters for a 4f11 ion in tetragonal symmetry. In these formulas, the contributions to the spin Hamiltonian parameters from the second-order perturbation terms and the admixtures of different states are considered. The relevant crystal field parameters are calculated from the superposition model and the local structural parameters of the Y3+ site occupied by impurity Er3+. The theoretical optical spectra within 4I15/2 and 4I13/2 states and the spin Hamiltonian parameters obtained in this work are consistent with the observed values. 相似文献
43.
《Thin solid films》2006,515(2):782-785
We present theoretical photoluminescence (PL) and absorption spectra of p-doped InGaN/AlInGaN and AlInGaN/InGaN multiple quantum wells (MQWs). The calculations were performed within the k.p method by means of solving a full eight-band Kane Hamiltonian together with the Poisson equation in a plane wave representation, including exchange–correlation effects within the local density approximation. Strain effects due to the lattice mismatch and an internal electric field are also taken into account. We show that by changing the In and Al composition we can reach short and long emission wavelengths. The trends in the calculated Stokes shift, due to many-body effects within the quasi-two-dimensional hole gas (2DHG), are analyzed as a function of the acceptor doping concentration. Since the studies of optical properties of quantum wells based on nitrides quaternary alloys are at an early stage, the results reported here will provide guidelines for the interpretation of forthcoming experiments. 相似文献
44.
《Materials Letters》2007,61(4-5):1027-1030
The structure of the melt-spun Cu60Zr30Ti10 metallic glass is investigated by anomalous small angle X-ray scattering (ASAXS). It is confirmed that the compositional segregation in the diameter range of 30–50 nm exists in the as-quenched state. ASAXS results have convincingly shown the aggregation of Cu atoms and the formation of Cu-rich domains in the amorphous matrix. The Cu-rich domains grow slightly with low growth rate below the glass transition temperature, while the sizes of these domains drastically increase with high growth rate in the supercooled liquid temperature region. The Cu-rich domains are presumed to be associated with nucleation for the primary crystallization process. 相似文献
45.
针对传统的非锐化掩模算法的局限性,依据图像中各像素点及以其为中心的若干相邻像素点的均方差值,提出了自适应图像增强算法的原理,并分析其硬件实现方法,然后给出了该算法与其它算法应用于图像增强的对比结果,最后在FPGA(field programmable gate array)实验板上进行验证.实验结果表明,此算法有效的增强图像的细节区域,防止图像边缘区域出现过冲现象,抑制图像平坦区域的噪声放大.因此,该算法取得了良好的视觉效果,硬件实现简单,适合于实时条件下图像的增强. 相似文献
46.
47.
In this paper, a Ka-band thin film microstrip line(TFMS) filter with multi-layer structure on silicon substrate is introduced. The simulated results show that it is possible to design compact millimeter-wave filter on silicon substrate with process compatible to current VLSI technology. 相似文献
48.
The general volume equivalence theorem for bianisotropic scatterers is presented, where the equivalent electric and magnetic currents are determined by a pair of coupled vector integral equations. Moreover, using the general volume equivalence theorem and conventional image principle, image theory is developed for a bianisotropic body over an infinite perfect electric or magnetic conducting ground plane. 相似文献
49.
The lateral shift of focus diffracted and reflected beam and resolving power, insertion loss of a five channel grating spectrometer for 25 to 100 GHz are experimentally investigated. And some analysis for these results are also given. 相似文献
50.
Ling Tong 《Journal of Infrared, Millimeter and Terahertz Waves》1997,18(2):431-436
This paper introduce the experiment about a new type of quasi-optic cavity Making a experimental model, measuring all parameters of the cavity, giving experiment results. It shows that theoritical research in reference[1] is correct Its results coincide with theory. At same time, it also indicates the cavity is hopeful device in MMW. 相似文献