全文获取类型
收费全文 | 913篇 |
免费 | 115篇 |
国内免费 | 50篇 |
专业分类
电工技术 | 27篇 |
综合类 | 38篇 |
化学工业 | 132篇 |
金属工艺 | 36篇 |
机械仪表 | 75篇 |
建筑科学 | 98篇 |
矿业工程 | 10篇 |
能源动力 | 53篇 |
轻工业 | 62篇 |
水利工程 | 2篇 |
石油天然气 | 5篇 |
武器工业 | 1篇 |
无线电 | 128篇 |
一般工业技术 | 188篇 |
冶金工业 | 14篇 |
原子能技术 | 3篇 |
自动化技术 | 206篇 |
出版年
2024年 | 25篇 |
2023年 | 36篇 |
2022年 | 45篇 |
2021年 | 49篇 |
2020年 | 48篇 |
2019年 | 29篇 |
2018年 | 14篇 |
2017年 | 21篇 |
2016年 | 29篇 |
2015年 | 25篇 |
2014年 | 57篇 |
2013年 | 46篇 |
2012年 | 68篇 |
2011年 | 52篇 |
2010年 | 63篇 |
2009年 | 70篇 |
2008年 | 45篇 |
2007年 | 100篇 |
2006年 | 65篇 |
2005年 | 36篇 |
2004年 | 21篇 |
2003年 | 15篇 |
2002年 | 9篇 |
2001年 | 17篇 |
2000年 | 23篇 |
1999年 | 8篇 |
1998年 | 9篇 |
1997年 | 4篇 |
1996年 | 7篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1970年 | 2篇 |
1967年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有1078条查询结果,搜索用时 15 毫秒
1.
选用实验室制备的四种新型反应型受阻胺类光稳定剂(r-HALS):4-甲基丙烯酰氧基-2,2,6,6-四甲基哌啶醇酯(MTMP)、4-丙烯酰氧基-2,2,6,6-四甲基哌啶醇酯(ATMP)、4-甲基丙烯酰氧基-1,2,2,6,6-五甲基哌啶醇酯(MPMP)和4-丙烯酰氧基-1,2,2,6,6-五甲基哌啶醇酯(APMP),实现了紫外光固化聚合物涂层(膜)的原位(in situ)光稳定化。通过室内人工光老化实验和在光氧化过程中黄度指数(Yellowness Index,YI)的监测,再与典型的商用HALS(Tinuvin770和Tinuvin292)进行平行实验对比,考察了r-HALS对紫外光固化聚合物涂层的光防护效果,探索一条紫外光固化聚合物涂层原位(in situ)光稳定化的新途径。 相似文献
2.
《Thin solid films》1986,141(1):117-127
The formation of the various chromium silicide phases, as predicted by the Cr-Si phase diagram for bulk materials, was studied when thin Cr/a-Si (where a-Si is amorphous silicon) bilayers were annealed in situ in a transmission electron microscope using a limited supply of a-Si. These results are compared with the silicide formed when unlimited a-Si or single-crystal silicon was used. The specimens were analysed using electron micrographs and diffraction patterns.The detailed studies of the bilayers were preceded by studies of single layers of chromium and a-Si. The chromium single layers proved to be continuous for films as thin as approximately 2 nm. The as-deposited films with thickness in excess of about 5 nm were crystalline with b.c.c. structure and comprised very small grains. A phase change occured at about 450°C from the b.c.c to a simple cubic lattice structure. The silicon single layers were completely amorphous in their as-deposited state and crystallized around 600°C. Very large grains formed.The self-supporting Cr/a-Si bilayers with a typical total thickness of about 50 nm, where the relative film thickness were adjusted to yield Cr:a-Si atomic ratios of 1:2, 1:1, 5:3 and 3:1, were prepared by sequential electron gun vacuum deposition of chromium and silicon onto photoresist-covered glass slides. In the early stages of phase formation, when both unreacted chromium and silicon were present, the CrSi2 phase was formed at about 450°C for all of these specimens. This was the end phase for the 1:2 ratio specimen. For all the other specimens the metal- rich Cr5Si3 phase was next to grow at about 550°C. For the 5:3 ratio specimen this was the end phase.Upon further heating of specimens with a Cr:a-Si atomic ration of 3:1, a more chromium-rich phase of Cr3Si was formed at about 650°C. In the 1:1 ratio specimen, however, the next and end phase observed was CrSi, also growing at about 650°C. The end phase was thus determined by the availability of chromium and silicon during the reactions and could be predicted from the phase diagram.When using an unlimited supply of a-Si (or of single-crystal silicon), instead of limiting it to the thickness necessary for the predetermined ratios mentioned above, the only phase that ever formed was CrSi2.The grain sizes observed in the various final phase specimens were as follows: CrSi2, 25 nm; Cr3Si, 40 nm; Cr5Si3, 50 nm; CrSi, 100 nm. 相似文献
3.
《Information Sciences》1986,38(3):271-282
This paper introduces a new type of two-dimensional automaton called a three-way two-dimensional finite automaton with rotated inputs, and investigates a relationship among the accepting powers of these new automata, two-dimensional finite automata, and tape-bounded three-way two-dimensional Turing machines. We show, for example, that m log m space (m2 space) is necessary and sufficient for deterministic three-way two-dimensional Turing machines to simulate deterministic (nondeterministic) three-way two-dimensional finite automata with rotated inputs. 相似文献
4.
《International Journal of Engineering Science》1986,24(5):643-647
A mathematical model is presented to obtain the effective thermal conductivity and the effective heat capacity in composite materials due to oscillating temperature field. An integro-differential equation for temperature field in composites is derived using the Green's function for heat conduction. The ensemble averaged temperature field is determined by a self-consistent scheme to yield algebraic equations for the effective thermal conductivity and the effective heat capacity. The obtained expression for the effective thermal conductivity is not symmetrical with the interchange of the matrix phase and the inclusion phase. 相似文献
5.
A new unstructured mesh coastal water and air quality model has been developed that includes species transport, nonlinear decay, byproduct formation and mass-exchange between sea and atmosphere. The model has been programmed with a graphical interface and is applicable to coastal seawater, lakes and rivers. Focused on species conversion and interaction with the atmosphere, the water and air quality model follows a modular approach. It is a compatible module which simulates distributions based on fluid dynamic field data of underlying existing hydrodynamic and atmospheric simulations. Nonlinear and spline approximations of decay and growth kinetics, byproduct formation and joint sea–atmosphere simulation have been embedded. The Windows application software includes functions allowing error analysis concerning mesh and finite volume approximation. In this work, an anoxic submerged process-water discharge has been simulated. An error analysis has been carried out by varying vertical meshing, time-steps and comparing results based on explicit and implicit finite volume approximation. 相似文献
6.
便携式点对点可见光通信终端的实验研究 总被引:1,自引:13,他引:1
利用开关键控-非归零码(OOK-NRZ)调制编码技术,设计并实现了一对基于ARM7处理器(LPC2148)的便携式点对点可见光通信(VLC)收/发终端。发送端由编码器、光源驱动器及单个白色发光二极管(WLED)构成,接收端由可见光探测器、信号处理电路及解码器构成。实验研究了WLED的发射谱和可见光探测器的响应谱,测试分析了VLC信道的时域和频域的电-光-电(EOE)响应。阐述了系统结构和原理,编写了通信软件并制定了相关协议,实现了系统的软、硬件集成。利用研制出的通信装置,建立了点对点通信链路,并开展了数据通信实验。结果表明,在发送端,为了最大化地降低误码率(BER),WLED的调制系数应设置为0.68~1.00,即在一定的交流调制信号幅度下,需要向WLED提供合适的直流偏置电压;在接收端,在一定的阈值判决门限电压下,VLC传输呈带通特性。在所优化选择的系统参数下,系统的通信距离为0.5m,可达到的最快信息传输速率约为4 Mbps,BER小于10-6。利用多个WLED构成阵列光源,系统可进一步满足更长距离的通信需求,从而在室内、外短途通信方面具有潜在的应用价值。 相似文献
7.
8.
9.
Novel organic dyes containing N-bridged oligothiophene coplanar cores for dye-sensitized solar cells
Three novel organic dyes adopting fully-fused coplanar heteroarene as the donor moieties end-capped with two cyanoacrylic acids as acceptors and anchoring groups have been synthesized, characterized, and used as the sensitizers for dye-sensitized solar cells (DSSCs). The photophysical and electrochemical properties of the novel dyes and the characteristics of the DSSCs based on the novel organic dyes were investigated. The incorporation of the coplanar cores with electron-donating N-bridges are beneficial for the better intramolecular charge transfer (ICT), giving these new dyes good light-harvesting capability. The LUMO energy levels of these coplanar heteroacene-based dyes are sufficiently high for the efficient electron injection to TiO2 upon photo-excitation, while the suitable HOMOs allow the regeneration of oxidized dyes with the electrolyte redox (I−/I3−). The structural features of the coplanar cores (penta vs. hexa heteroarene) as well as the alkyl substitutions play crucial roles in governing the physical properties and device performance. Among these three novel organic sensitizers, the EHTt dye composed of a fully fused hexa-arene core and less bulky N-alkyl groups caused the DSSC to show the best photovoltaic performance with an open-circuit voltage (VOC) of 0.58 V, a short-circuit photocurrent density (JSC) of 13.72 mA/cm2, and a fill factor (FF) of 0.69, yielding an overall power conversion efficiency (PCE) of 5.52% under AM 1.5G solar irradiation. 相似文献
10.
目前网页游戏已成为网络游戏的主流产品,而网页游戏所使用的开发技术也成为研究的热点。基于RIA平台设计的"龙曦"网页游戏软件,使用了当今流行的Flex开发技术。其游戏的动画使用Flash制作,通过ActionScript实现调用;画面层的管理,由ActionScript提供的功能来实现;消息数据以AMF格式封装,客户端与服务器的信息交互则采用线程通信技术。在对目前网页游戏常用开发技术进行综合比较的基础上,就"龙曦"网页游戏软件的开发进行了详细介绍。结果证明,使用Flex技术开发的网页游戏能够极大地提高用户体验。 相似文献