全文获取类型
收费全文 | 32756篇 |
免费 | 3433篇 |
国内免费 | 2301篇 |
专业分类
电工技术 | 2147篇 |
技术理论 | 6篇 |
综合类 | 2646篇 |
化学工业 | 2077篇 |
金属工艺 | 442篇 |
机械仪表 | 1390篇 |
建筑科学 | 4840篇 |
矿业工程 | 2512篇 |
能源动力 | 907篇 |
轻工业 | 4348篇 |
水利工程 | 2484篇 |
石油天然气 | 1507篇 |
武器工业 | 430篇 |
无线电 | 2840篇 |
一般工业技术 | 2756篇 |
冶金工业 | 885篇 |
原子能技术 | 1061篇 |
自动化技术 | 5212篇 |
出版年
2024年 | 165篇 |
2023年 | 461篇 |
2022年 | 1000篇 |
2021年 | 1202篇 |
2020年 | 1303篇 |
2019年 | 944篇 |
2018年 | 943篇 |
2017年 | 1165篇 |
2016年 | 1338篇 |
2015年 | 1379篇 |
2014年 | 2809篇 |
2013年 | 2360篇 |
2012年 | 3029篇 |
2011年 | 2833篇 |
2010年 | 2149篇 |
2009年 | 2030篇 |
2008年 | 2022篇 |
2007年 | 2318篇 |
2006年 | 1931篇 |
2005年 | 1536篇 |
2004年 | 1136篇 |
2003年 | 1044篇 |
2002年 | 727篇 |
2001年 | 570篇 |
2000年 | 430篇 |
1999年 | 319篇 |
1998年 | 260篇 |
1997年 | 211篇 |
1996年 | 140篇 |
1995年 | 131篇 |
1994年 | 107篇 |
1993年 | 111篇 |
1992年 | 68篇 |
1991年 | 57篇 |
1990年 | 39篇 |
1989年 | 39篇 |
1988年 | 43篇 |
1987年 | 14篇 |
1986年 | 12篇 |
1985年 | 21篇 |
1984年 | 15篇 |
1983年 | 17篇 |
1982年 | 10篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1973年 | 4篇 |
1959年 | 7篇 |
1955年 | 5篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
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
62.
63.
Boundary objects are a critical, but understudied, theoretical construct in CSCW. Through a field study of aircraft technical
support, we examined the role of boundary objects in the practical achievement of safety by service engineers. Their resolution
of repair requests was preserved in the organization’s memory via three compound boundary objects. These crystallizations
did not manifest a static interpretation, but instead were continually reinterpreted in light of meta-negotiations. This suggests
design implications for organizational memory systems which can more fluidly represent the meta-negotiations surrounding boundary
objects. 相似文献
64.
Kinema is a fermented soya bean food of Nepal and the hilly regions of North-eastern States of India. Generally, the fermentation is dominated by Bacillus spp. that often cause alkalinity and desirable stickiness in the product. The present study was undertaken in a limited number of commercial (market) kinema samples to test for the presence of foodborne pathogens and their properties. Bacillus cereus was present in numbers exceeding 104 cfu/g product in five of the tested 15 market samples. Enterobacteriaceae and coliform bacteria exceeded 105 cfu/g in 10 of the 15 samples. Escherichia coli exceeding 105 cfu/g was found in two samples. Staphylococcus aureus was not detected in any of the tested samples. Of 31 isolated typical and atypical strains of B. cereus, 18 representative strains were tested qualitatively for the ability to produce diarrhoeal type enterotoxin (BCET) using an Oxoid BCET-RPLA test kit. Overall, BCET was formed by 12 strains in BHIG (brain heart infusion broth +1% glucose), by seven strains on sterilized cooked rice, and by five strains on sterilized cooked soya beans. Semi-quantitative tests on BCET revealed that levels exceeding 256 ng/g soya beans, produced by single pure culture inoculation with the isolated B. cereus strains, were reduced to ≤ 8 ng/g by frying kinema in oil, a common procedure when making kinema curry. It was also shown in a mixed pure culture experiment that a kinema strain B. Subtilis DK-W1, is able to suppress growth and BCET formation by a selected toxin producing strain (BC7-5) of B. cereus. It is concluded that the traditional way of making kinema and its culinary use in curries is safe. However, for novel applications of kinema, safety precautions are advisable. 相似文献
65.
66.
该文分析某微型起爆器引起的一起误爆事故,指出该起爆器设计上的缺陷及其对作业安全的威胁,提出防患建议。 相似文献
67.
用平均输出功率为1.1W,脉宽为90fs的商用再生锁模Ti:Sapphire激光器作为泵浦源,用KTP作为非线性光学介质,制成一台同步泵浦飞秒光学参量振荡器。其输出调谐范围为1.04μm至1.26μm,平均输出功率在100mw左右,脉宽仅约100fs。 相似文献
68.
文中对影响煤矿许用毫秒延期电雷管沼气安全性与延期时间精度的因素进行了研究。应用正交设计研制了新的延期药配方,确定了合理的雷管结构及装配工艺参数,产品性能达到GB8031《工业电雷管》的规定。 相似文献
69.
本文研究在13SiMnNiCrMoV 结构钢中用尖裂纹的应力强度因子来反映三点弯曲缺口试样的疲劳裂纹萌生规律。当 R=0.1,f=100Hz,试样尺寸 B×W×L=12.5×25×117mm 时,缺口名义应力幅的门槛值为Δσ_(th)=3315ρ~(0.352) MPa,0.5mm≤ρ≤5mmΔK_(th)=250ρ~(0.352) MPam~(1/2)门槛值与ρ有关。同时得到缺口裂纹萌生的循环次数 N_i 与名义应力幅Δσ、缺口曲率半径ρ的定量关系是N_i=3.98×10~(22)ρ~(1.62)/Δσ~(4.85),N_i≤10~(5.5)并讨论了(ΔK_1/ρ~(1/2))_(th)与ρ无关的结论。 相似文献
70.
In the framework of joint effort between the Nuclear Energy Agency (NEA) of OECD, the United States Department of Energy (US DOE), and the Commissariat a l'Energie Atomique (CEA), France a coupled three-dimensional (3D) thermal-hydraulics/neutron kinetics benchmark for VVER-1000 was defined. The benchmark consists of calculation of a pump start-up experiment labelled V1000CT-1 (Phase 1), as well as a vessel mixing experiment and main steam line break (MSLB) transient labelled V1000CT-2 (Phase 2), respectively. The reference nuclear plant is Kozloduy-6 in Bulgaria. The overall objective is to assess computer codes used in the analysis of VVER-1000 reactivity transients. A specific objective is to assess the vessel mixing models used in system codes. Plant data are available for code validation consisting of one experiment of pump start-up (V1000CT-1) and one experiment of steam generator isolation (V1000CT-2). The validated codes can be used to calculate asymmetric MSLB transients involving similar mixing patterns. This paper summarizes a comparison of CATHARE and TRAC-PF1 system code results for V1000CT-1, Exercise 1, which is a full plant point kinetics simulation of a reactor coolant system (RCS) pump start-up experiment. The reference plant data include integral and sector average parameters. The comparison is made from the point of view of vessel mixing and full system simulation. CATHARE used a six-sector multiple 1D vessel thermal-hydraulic model with cross flows and TRAC used a six-sector, 18-channel coarse-mesh 3D vessel model. Good agreement in terms of integral parameters and inter-loop mixing is observed. 相似文献