全文获取类型
收费全文 | 11895篇 |
免费 | 879篇 |
国内免费 | 742篇 |
专业分类
电工技术 | 533篇 |
技术理论 | 2篇 |
综合类 | 889篇 |
化学工业 | 1878篇 |
金属工艺 | 872篇 |
机械仪表 | 651篇 |
建筑科学 | 923篇 |
矿业工程 | 343篇 |
能源动力 | 284篇 |
轻工业 | 736篇 |
水利工程 | 239篇 |
石油天然气 | 466篇 |
武器工业 | 112篇 |
无线电 | 1303篇 |
一般工业技术 | 1644篇 |
冶金工业 | 919篇 |
原子能技术 | 154篇 |
自动化技术 | 1568篇 |
出版年
2024年 | 36篇 |
2023年 | 169篇 |
2022年 | 309篇 |
2021年 | 440篇 |
2020年 | 315篇 |
2019年 | 289篇 |
2018年 | 311篇 |
2017年 | 323篇 |
2016年 | 312篇 |
2015年 | 420篇 |
2014年 | 492篇 |
2013年 | 594篇 |
2012年 | 656篇 |
2011年 | 757篇 |
2010年 | 646篇 |
2009年 | 648篇 |
2008年 | 740篇 |
2007年 | 615篇 |
2006年 | 619篇 |
2005年 | 488篇 |
2004年 | 388篇 |
2003年 | 428篇 |
2002年 | 522篇 |
2001年 | 447篇 |
2000年 | 389篇 |
1999年 | 321篇 |
1998年 | 368篇 |
1997年 | 252篇 |
1996年 | 211篇 |
1995年 | 157篇 |
1994年 | 125篇 |
1993年 | 101篇 |
1992年 | 71篇 |
1991年 | 56篇 |
1990年 | 49篇 |
1989年 | 60篇 |
1988年 | 48篇 |
1987年 | 26篇 |
1986年 | 38篇 |
1985年 | 20篇 |
1984年 | 34篇 |
1983年 | 23篇 |
1982年 | 19篇 |
1981年 | 10篇 |
1980年 | 14篇 |
1979年 | 11篇 |
1978年 | 14篇 |
1977年 | 9篇 |
1976年 | 35篇 |
1956年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 338 毫秒
11.
Face centered cubic metals and alloys have multiple slip systems and are characterized by high dislocation velocities. Nevertheless, these materials suffer from transgranular stress corrosion cracking (T-SCC), that occurs by environmentally-induced cleavage. Since plasticity precedes fracture in all T-SCC phenomena, the evolution of deformation patterning during T-SCC is an important element of the local microfracture mode. Experimental observations show that the presence of the SCC-causing environment during straining is promoting localized plastic deformation at the near-surface region and producing an entirely different deformation pattern compared with that developing in laboratory air. The deformation evolving in the presence of the SCC electrolyte is highly localized, exhibiting closely spaced, coarse slip bands. The amount of localized strain developing at the near-surface region prior to nucleation of stress corrosion cracks is equivalent to the strain required for ductile fracture of the material in air, suggesting the existence of a fundamental fracture criterion. The above phenomenology of the deformation evolution is considered in relation to T-SCC initiation and propagation. The T-SCC is suggested to be a macroscopically brittle but microscopically ductile fracture occurring by localized plastic flow. An environment-induced deformation localization mechanism is described where the role of the environment involves generation of vacancies and subsequent dislocation nucleation from the near-surface region at loads well below those required for normal yielding. The evolution of the localized deformation pattern during T-SCC is suggested to be an outcome of nonuniformity and periodicity in the dissolution process.Presented at Fourth Greek National Congress on Mechanics, 26–29 June 1995, held at Xanthi, Greece. 相似文献
12.
VB Lang P Langguth C Ottiger H Wunderli-Allenspach D Rognan B Rothen-Rutishauser JC Perriard S Lang J Biber HP Merkle 《Canadian Metallurgical Quarterly》1997,86(7):846-853
Due to the low effective permeabilities of peptides at many absorption sites, their structure-permeation relations are of high interest. In this work structure-permeation relations of Met-enkephalin analogues are presented using confluent Caco-2 cells as an in vitro permeation model. Four model peptides (Met-enkephalin, [D-Ala2]Met-enkephalin, [D-Ala2]Met-enkephalinamide, and metkephamid) were tested in terms of permeability, lipophilicity, charge, and molecular size. Permeability coefficients (P(eff)) across Caco-2 cells were low, 3.3 x 10(-8) to 9.5 x 10(-8) cm s-1, and were similar to typical paracellular markers. No correlation of permeability and the log(apparent octanol/buffer partition coefficient) was observed. A 40-fold increase of the permeability of metkephamid in the presence of 10 mM EDTA suggested a significant contribution of paracellular transport. Independent support for this conclusion was obtained by visualizing the pathway of the fluorescein isocyanate isomer I 1-metkephamid by confocal laser scanning microscopy (CLSM). The fluorophore-labeled peptide was observed in the intercallular space only. Metkephamid permeabilities were found to be direction-specific. Permeabilities from basolateral to apical (b-to-a) were significantly higher (ca. 4-fold) than in the opposite (a-to-b) direction. The addition of verapamil equalized the permeabilities in the a-to-b and b-to-a directions, suggesting the involvement of a P-glycoprotein-mediated secretion mechanism. Similar observations were obtained with [D-Ala2]Met-enkephalinamide, but not with Met-enkephalin and [D-Ala2]Met-enkephalin. In contrast to the other analogues, metkephamid and [D-Ala2]Met-enkephalinamide are positively charged at neutral pH, as demonstrated by their isoelectric points (pl = 8.6 for [D-Ala2]Met-enkephalinamide and metkephamid and 5.3 for [D-Ala2]Met-enkephalin and Met-enkephalin). The data is in agreement with the literature showing that most compounds secreted by the P-glycoprotein transporter carry a positive charge. 相似文献
13.
湿硫化氢环境下的球罐腐蚀状况分析 总被引:5,自引:0,他引:5
在湿硫化氢环境下 ,尤其储存介质中的硫化氢含量超标时 ,很容易对储存容器壳体 (含焊缝和母材 )造成硫化氢应力腐蚀或氢鼓包。作者较仔细分析了 1 0 0 0m3 丙烯球罐产生硫化氢应力腐蚀开裂和40 0m3 LPG球罐产生氢鼓包的原因。提出了此类设备在设计选材、设备制造、施工安装和使用维护等环节应注意的问题。 相似文献
14.
15.
16.
17.
18.
Yu Shichang Wu Shenqing Gong Youjun Gong Yuansheng Lian Mingsheng Ye Gang Cheng Yijun 《中国稀土学报(英文版)》2006,24(1):120-120
Grain growth behavior of 5Cr21Mn9Ni4NRE steel was experimentally studied at various solid solution treatment temperatures and holding for different times. The experimental results show that the 5Cr21Mn9Ni4NRE steel has the feature of sharp austenite grain coarsening after solid solution treatment at the temperature above 1150 ℃. RE added in the steel has the benefit to restrain grain growth and increase grain growth activation energy. 相似文献
19.
Weiming Shen S.Y.T. Lang Lihui Wang 《IEEE transactions on systems, man and cybernetics. Part C, Applications and reviews》2005,35(3):371-381
Global competition is driving manufacturing companies to change the way they do business. New kinds of shop floor control systems need to be implemented for these companies to respond quickly to changing shop floor environments and customer demands. This paper presents a new concept called iShopFloor-an intelligent shop floor based on the Internet, web, and agent technologies. It focuses on the implementation of distributed intelligence in the manufacturing shop floor. The proposed approach provides the framework for components of a complex control system to work together as a whole rather than as a disjoint set. It encompasses both information architecture and integration methodologies. The paper introduces the basic concept of iShopFloor, a generic system architecture, and system components. It also describes the implementation of eXtensible Markup Language message services in iShopFloor and the application of intelligent agents to distributed manufacturing scheduling. A prototype environment is presented, and some implementation issues are discussed. 相似文献
20.
Out-of-plane microlenses and microoptical fiber holder are two of the most important components for building an integrated
microoptic system with a precise alignment accuracy. In this paper, a simple and convenient method to fabricate these components
from SU-8 by using inclined UV lithography in water is proposed. It consists of two perpendicular exposures in SU-8 at ±45°.
DI water possesses a low absorption coefficient and a moderate and stable value of refractive index in near UV. Using water,
the exposure angle in SU-8 can be increased to 50° from 35° in air necessary to pattern the desired 45° slope of the sidewalls.
The principle of the proposed technique and the detailed fabrication process of the microoptic components will be presented.
The integratability of the fabricated components was demonstrated by the fabrication of the microoptical fiber holder with
a pre-aligned out-of-plane microlens. 相似文献