全文获取类型
收费全文 | 27078篇 |
免费 | 4114篇 |
国内免费 | 2113篇 |
专业分类
电工技术 | 527篇 |
综合类 | 2074篇 |
化学工业 | 3091篇 |
金属工艺 | 11852篇 |
机械仪表 | 1439篇 |
建筑科学 | 993篇 |
矿业工程 | 674篇 |
能源动力 | 265篇 |
轻工业 | 1249篇 |
水利工程 | 365篇 |
石油天然气 | 424篇 |
武器工业 | 314篇 |
无线电 | 1361篇 |
一般工业技术 | 4893篇 |
冶金工业 | 2805篇 |
原子能技术 | 149篇 |
自动化技术 | 830篇 |
出版年
2024年 | 152篇 |
2023年 | 699篇 |
2022年 | 1317篇 |
2021年 | 1369篇 |
2020年 | 1411篇 |
2019年 | 1101篇 |
2018年 | 1100篇 |
2017年 | 1263篇 |
2016年 | 1226篇 |
2015年 | 1333篇 |
2014年 | 1507篇 |
2013年 | 1612篇 |
2012年 | 1990篇 |
2011年 | 2160篇 |
2010年 | 1581篇 |
2009年 | 1638篇 |
2008年 | 1199篇 |
2007年 | 1633篇 |
2006年 | 1574篇 |
2005年 | 1256篇 |
2004年 | 1097篇 |
2003年 | 899篇 |
2002年 | 709篇 |
2001年 | 611篇 |
2000年 | 472篇 |
1999年 | 406篇 |
1998年 | 306篇 |
1997年 | 292篇 |
1996年 | 268篇 |
1995年 | 198篇 |
1994年 | 191篇 |
1993年 | 139篇 |
1992年 | 144篇 |
1991年 | 105篇 |
1990年 | 122篇 |
1989年 | 97篇 |
1988年 | 30篇 |
1987年 | 19篇 |
1986年 | 9篇 |
1985年 | 17篇 |
1984年 | 11篇 |
1983年 | 4篇 |
1982年 | 14篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1959年 | 2篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
41.
Wang Xuegang Yan Fengjie Yan Qian Li Xingeng 《Frontiers of Materials Science in China》2007,1(2):225-227
An iron-based amorphous foil (FeNiCrSiB) was used as an interlayer for the amorphous diffusion bonding of low carbon steel
pipes under argon flux. The microstructure and mechanical properties of the joint were analyzed using an electron probe micro-analyzer
(EPMA), tensile test, bending test and impact test. The results show that the joint microstructure resembles that of the base
metal and no precipitates form at the joint. Melting point depressants (B, Si) diffuse far away from the joint and the base
metal element is homogenous across the joint. The joint impact toughness is greater than the base metal toughness and the
mechanical properties of the joint are similar around the pipe. 相似文献
42.
43.
C. G. Gwie R. J. Griffiths D. T. Cooney M. L. Johns D. I. Wilson 《Journal of the American Oil Chemists' Society》2006,83(12):1053-1062
The spray-freezing of two food fats, tripalmitin (PPP) and cocoa butter (CB) and mixtures thereof, has been modeled experimentally
using a novel single droplet freezing apparatus configured so that temperature profiles or samples for microstructure analysis
can be obtained. For 2 mm diameter droplets suspended in a cold air flow at temperatures around 2–15°C, initial cooling rates
were on the order of 10 K s−1 and the temperature profiles could be correlated directly to DSC data collected at 20 K min−1, indicating that minimal supercooling of the materials occurred in the droplet form. Microstructure analysis confirmed that
PPP crystallized preferentially in mixtures, and that the surface structure was very sensitive to storage conditions. The
bulk structure was much less sensitive, and the internal microstructure of the PPP droplets revealed distinct nucleation sites,
which were absent from the CB: These persisted in the mixtures up to 50 wt%. X-ray analysis indicated that the fats crystallized
in their more stable forms, namely, β for PPP and Form V/V1 in CB. 相似文献
44.
45.
主要研究了Cr对低碳Si-Mn系TRIP钢组织与力学性能的影响。首先利用Formastor-F型膨胀仪测定了含Cr和不含Cr两种低碳钢的连续冷却转变(CCT)曲线,分析指出了Cr对连续退火工艺的潜在影响;然后采用Gleeble-3800热/力模拟试验机对两种钢的薄板试样进行了连续退火模拟实验,并通过拉伸试验测定了力学性能;最后采用金相、扫描电镜、X-射线衍射分析等技术考察分析了两种钢的显微组织。结果表明:含Cr的TRIP钢的组织比较细小,铁素体晶粒近似等轴分布;两种TRIP钢的残余奥氏体含量相近,但含Cr钢的残余奥氏体中的含碳量较高。分析认为这是由于含Cr钢在热轧阶段较易生成细小的组织,而在热处理阶段则抑制贝氏体的生成,最终获得稳定的残余奥氏体。 相似文献
46.
Chris Harty 《Building Research & Information》2005,33(6):512-522
An alternative approach to understanding innovation is made using two intersecting ideas. The first is that successful innovation requires consideration of the social and organizational contexts in which it is located. The complex context of construction work is characterized by inter-organizational collaboration, a project-based approach and power distributed amongst collaborating organizations. The second is that innovations can be divided into two modes: 'bounded', where the implications of innovation are restricted within a single, coherent sphere of influence, and 'unbounded', where the effects of implementation spill over beyond this. Bounded innovations are adequately explained within the construction literature. However, less discussed are unbounded innovations, where many firms' collaboration is required for successful implementation, even though many innovations can be considered unbounded within construction's inter-organizational context. It is argued that unbounded innovations require an approach to understand and facilitate the interactions both within a range of actors and between the actors and technological artefacts. The insights from a sociology of technology approach can be applied to the multiplicity of negotiations and alignments that constitute the implementation of unbounded innovation. The utility of concepts from the sociology of technology, including 'system building' and 'heterogeneous engineering', is demonstrated by applying them to an empirical study of an unbounded innovation on a major construction project (the new terminal at Heathrow Airport, London, UK). This study suggests that 'system building' contains outcomes that are not only transformations of practices, processes and systems, but also the potential transformation of technologies themselves. 相似文献
47.
The effects of yttrium and cerium on microstructures and properties of Nb-Si system composites were investigated by scanning electron microscopy( SEM), energy dispersive spectrum(EDS), X-ray diffraction(XRD) and high temperature oxidation experiments.It is found that the coarse primary silicide phase became finer and more homogeneous with Y and Ce addition.The results of high temperature oxidation experiments show that the oxidation rates of NbSi system composites with an appropriate amount of Y and Ce decrease compared with those of alloys without Y or Ce addition, and oxidation products mainly distribute along the phase boundaries between the Nb solid solution and silicide. 相似文献
48.
Y. MURAKAMI K. TAKAHASHI R. KUSUMOTO 《Fatigue & Fracture of Engineering Materials & Structures》2003,26(6):523-531
ABSTRACT The fatigue crack growth behaviour of 0.47% carbon steel was studied under mode II and III loadings. Mode II fatigue crack growth tests were carried out using specially designed double cantilever (DC) type specimens in order to measure the mode II threshold stress intensity factor range, ΔKIIth. The relationship ΔKIIth > ΔKIth caused crack branching from mode II to I after a crack reached the mode II threshold. Torsion fatigue tests on circumferentially cracked specimens were carried out to study the mechanisms of both mode III crack growth and of the formation of the factory‐roof crack surface morphology. A change in microstructure occurred at a crack tip during crack growth in both mode II and mode III shear cracks. It is presumed that the crack growth mechanisms in mode II and in mode III are essentially the same. Detailed fractographic investigation showed that factory‐roofs were formed by crack branching into mode I. Crack branching started from small semi‐elliptical cracks nucleated by shear at the tip of the original circumferential crack. 相似文献
49.
50.
D. Knig S. Carvajal-Gonzalez A. M. Downs J. Vassy P. Rigaut 《Journal of microscopy》1991,161(3):405-433
Within the concept of point processes, a review is presented of quantities which can be used in studies of three-dimensional (3-D) aggregates of particles. Suitable characteristics and estimators are given for both unmarked and marked point processes. To demonstrate the feasibility of such quantitative approaches, an application in histology, dealing with 3-D arrangements of cell nuclei in rat liver, is described. Using a confocal scanning light microscope, 3-D images are recorded and image analysis used to obtain the coordinates of the centroid, together with the volume and DNA content, of each cell nucleus. Examples of results are given, using both unmarked and marked point processes. In the latter case, cell type, nuclear volume and ploidy group are suitable marks. 相似文献