全文获取类型
收费全文 | 25904篇 |
免费 | 2352篇 |
国内免费 | 970篇 |
专业分类
电工技术 | 1377篇 |
综合类 | 2068篇 |
化学工业 | 3444篇 |
金属工艺 | 639篇 |
机械仪表 | 1892篇 |
建筑科学 | 1945篇 |
矿业工程 | 887篇 |
能源动力 | 1024篇 |
轻工业 | 1586篇 |
水利工程 | 472篇 |
石油天然气 | 1158篇 |
武器工业 | 182篇 |
无线电 | 5159篇 |
一般工业技术 | 4530篇 |
冶金工业 | 701篇 |
原子能技术 | 386篇 |
自动化技术 | 1776篇 |
出版年
2025年 | 172篇 |
2024年 | 549篇 |
2023年 | 623篇 |
2022年 | 704篇 |
2021年 | 862篇 |
2020年 | 1039篇 |
2019年 | 968篇 |
2018年 | 819篇 |
2017年 | 961篇 |
2016年 | 1083篇 |
2015年 | 1043篇 |
2014年 | 1514篇 |
2013年 | 1474篇 |
2012年 | 1614篇 |
2011年 | 1734篇 |
2010年 | 1386篇 |
2009年 | 1452篇 |
2008年 | 1296篇 |
2007年 | 1416篇 |
2006年 | 1340篇 |
2005年 | 1113篇 |
2004年 | 934篇 |
2003年 | 871篇 |
2002年 | 678篇 |
2001年 | 610篇 |
2000年 | 558篇 |
1999年 | 420篇 |
1998年 | 387篇 |
1997年 | 287篇 |
1996年 | 233篇 |
1995年 | 189篇 |
1994年 | 185篇 |
1993年 | 152篇 |
1992年 | 108篇 |
1991年 | 68篇 |
1990年 | 79篇 |
1989年 | 54篇 |
1988年 | 39篇 |
1987年 | 31篇 |
1986年 | 25篇 |
1985年 | 24篇 |
1984年 | 32篇 |
1983年 | 19篇 |
1982年 | 20篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1976年 | 4篇 |
1959年 | 8篇 |
1953年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Power devices with high capability have been developed. 8‐kV/3.5‐kA‐class light‐triggered thyristors have the highest capability among power devices. These devices are used in the Kii Channel HVDC transmission system in Japan. In this paper, we report the extracted problems of conventional testing methods of 8‐kV/3.5‐kA‐class light‐triggered thyristors among manufacturers, and the proposed unified testing methods on the basis of element characteristics and operating conditions in the Kii Channel HVDC system. Furthermore, we propose a figure of merit for power devices for the practical use, and try to extract elements used at the Kii Channel HVDC system with small margins and low withstand capabilities. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(3): 61–70, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10024 相似文献
2.
王骊 《数码设计:surface》2008,(3):153-155
任何事物的存在都不是固定的状态和单一的形式,对事物的认识理解也不应是局限的、固有的,经验感知往往使我们对事物存在方式的认识受到限制,应在静中求动,通过关联性寻求可变因素。本文还通过对灯的"开"与"关"状态的联想为例,浅析"静中求动"认识事物的思维方法,"设计不是一个结论,而是一种假设,不是一种宣言,而是一种步骤、一个瞬间,这里没有确定性,只有可能性,没有真实性,只有经验性,没有那是什么,只有发生了什么",设计是实现作品与生活之间的一种可能性关系。 相似文献
3.
Chengkun Xu Richard Killmeyer McMahan L. Gray Shahed U.M. Khan 《Applied catalysis. B, Environmental》2006,64(3-4):312-317
The present research focused on wet process synthesis of visible light active carbon-modified (CM)-n-TiO2 nanoparticles and their photocatalytic activity. The CM-n-TiO2 was synthesized by hydrolysis of TiCl4 in the presence of tetrabutylammonium hydroxide and also in the presence of glucose and sodium hydroxide. UV–vis spectra, X-ray diffraction (XRD), and FT-IR were used to characterize these photocatalysts. It was found that the CM-n-TiO2 nanoparticles synthesized by hydrolysis with tetrabutylammonium hydroxide or with sodium hydroxide and glucose when subjected to extended aging and subsequent calcinations absorb well into the visible to near infrared region up to 800 nm and exhibit enhanced visible light photocatalytic activity on degradation of 4-chlorophenol. CM-n-TiO2 synthesized using glucose as the carbon source generated 13-fold increase in the initial rate of photodegradation of 4-chlorophenol compared to those by regular n-TiO2, whereas, it increased only eight-fold when tetrabutylammonium hydroxide was used as the carbon source. 相似文献
4.
在客源时间分布上,计算乌镇游客游览时间强度指数,得到游客游览时间主要集中在二、三季度,并以7、8月份为最高峰。而在客源市场的分布上,鸟镇已经形成了以浙江为核心,上海、北京等地为一级,安徽、河南等地为二级的国内客源市场。在长三角古村落旅游发展迅速的今天,乌镇与周边的周庄、同里等古镇的竞争日益激烈,而旅游产品的创新、加大宣传迅速占领国内二级客源市场等措施将有助于乌镇在竞争中脱颖而出,占领主导地位。 相似文献
5.
CMC在珠光颜料涂布纸中的应用试验 总被引:4,自引:0,他引:4
对添加羧甲基纤维素钠改善水性珠光涂布纸云母系列珠光涂料的性质做了初步研究.试验结果表明,羧甲基纤维素钠不仅能改善涂料的稳定性,提高涂层的表面拉毛强度,还能起到辅助胶粘剂的作用.通过优化试验得到了较理想的羧甲基纤维素钠配比. 相似文献
6.
We review, unify and extend work pertaining to evaluating mode mixity of interfacial fracture utilizing the virtual crack
closure technique (VCCT). From the VCCT, components of the strain energy release rate (SERR) are obtained using the forces
and displacements near the crack tip corresponding to the opening and sliding contributions. Unfortunately, these components
depend on the crack extension size, Δ, used in the VCCT. It follows that a mode mixity based upon these components also will
depend on the crack extension size. However, the components of the strain energy release rate can be used for determining
the complex stress intensity factors (SIFs) and the associated mode mixity. In this study, we show that several—seemingly
different—suggested methods presented in the literature used to obtain mode mixity based on the stress intensity factors are
indeed identical. We also present an alternative, simpler quadratic equation to this end. Moreover, a Δ-independent strain
energy release based mode mixity can be defined by introducing a “normalizing length parameter.” We show that when the reference
length (used for the SIF-based mode mixity) and the normalizing length (used for Δ-independent SERR-based mode mixity) are
equal, the two mode mixities are only shifted by a phase angle, depending on the bimaterial parameter ε. 相似文献
7.
8.
In the evaluation of accurate weight functions for the coefficients of first few terms of the linear elastic crack tip fields and the crack opening displacement (COD) using the finite element method (FEM), singularities at the crack tip and the loading point need to be properly considered. The crack tip singularity can be well captured by a hybrid crack element (HCE), which directly predicts accurate coefficients of first few terms of the linear elastic crack tip fields. A penalty function technique is introduced to handle the point load. With the use of these methods numerical results of a typical wedge splitting (WS) specimen subjected to wedge forces at arbitrary locations on the crack faces are obtained. With the help of appropriate interpolation techniques, these results can be used as weight functions. The range of validity of the so-called Paris equation, which is widely used in the evaluation of the COD from the stress intensity factors (SIFs), is established. 相似文献
10.
The influences of vegetation on intraseasonal oscillation (ISO) were examined using the Community Atmosphere Model version 3 (CAM3). Two 15-year numerical experiments were completed: the first was performed with a realistic vegetation distribution (VEG run),and the second was identical to the VEG run except without land vegetation (NOVEG run). Generally speaking, CAM3 was able to reproduce the spatial distribution of the ISO, but the ISO intensity in the simulation was much weaker than that observed in nature: the ISO has a relatively much stronger signal. A comparison of the VEG run with the NOVEG run revealed that the presence of vegetation usually produces a weak ISO. The vegetation effects on ISO intensity were significant over West Africa and South Asia, especially in the summer half-year.Vegetation also plays an important role in modulating ISO propagation. The eastward propagation of the ISO in the VEG run was clearer than that in the NOVEG run over the West African and Maritime Continent regions. The northward propagation of the ISO in the VEG run was more consistent with observation than that in the NOVEG run. 相似文献