全文获取类型
收费全文 | 21799篇 |
免费 | 1943篇 |
国内免费 | 1273篇 |
专业分类
电工技术 | 1644篇 |
综合类 | 2094篇 |
化学工业 | 990篇 |
金属工艺 | 2680篇 |
机械仪表 | 1420篇 |
建筑科学 | 5366篇 |
矿业工程 | 826篇 |
能源动力 | 489篇 |
轻工业 | 242篇 |
水利工程 | 1070篇 |
石油天然气 | 586篇 |
武器工业 | 163篇 |
无线电 | 995篇 |
一般工业技术 | 4376篇 |
冶金工业 | 1261篇 |
原子能技术 | 150篇 |
自动化技术 | 663篇 |
出版年
2024年 | 28篇 |
2023年 | 162篇 |
2022年 | 381篇 |
2021年 | 434篇 |
2020年 | 581篇 |
2019年 | 492篇 |
2018年 | 420篇 |
2017年 | 638篇 |
2016年 | 691篇 |
2015年 | 762篇 |
2014年 | 1148篇 |
2013年 | 1027篇 |
2012年 | 1350篇 |
2011年 | 1624篇 |
2010年 | 1254篇 |
2009年 | 1460篇 |
2008年 | 1405篇 |
2007年 | 1792篇 |
2006年 | 1483篇 |
2005年 | 1321篇 |
2004年 | 995篇 |
2003年 | 925篇 |
2002年 | 817篇 |
2001年 | 681篇 |
2000年 | 578篇 |
1999年 | 424篇 |
1998年 | 356篇 |
1997年 | 354篇 |
1996年 | 253篇 |
1995年 | 238篇 |
1994年 | 198篇 |
1993年 | 129篇 |
1992年 | 128篇 |
1991年 | 95篇 |
1990年 | 91篇 |
1989年 | 92篇 |
1988年 | 47篇 |
1987年 | 22篇 |
1986年 | 13篇 |
1985年 | 15篇 |
1984年 | 30篇 |
1983年 | 25篇 |
1982年 | 21篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 13篇 |
1963年 | 1篇 |
1960年 | 2篇 |
1955年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
11.
12.
A high density polyethylene geomembrane (GMB) stabilized with hindered amine (light) stabilizers (HALS or HAS) is immersed in four chlorinated water solutions with a simulated free chlorine concentration range of 0.5–5 ppm at five different temperatures (25, 40, 65, 75, and 85 °C) for 70 months. Standard and high pressure oxidative induction time (OIT) tests are performed to monitor antioxidants depletion while melt flow index, tensile, and stress crack resistance (SCR) tests are conducted to monitor degradation in physical and mechanical properties. Degradation in the GMB properties occurred shortly after immersion in chlorinated water at all temperatures except at 25 °C. Increasing the free chlorine concentration resulted in faster degradation of the tensile properties and SCR. The predicted time to nominal failure based on SCR ranges between 25 years at 40 °C and 5 years at 85 °C in chlorinated water (with 0.5 ppm free chlorine). A comparison between the degradation in SCR of this GMB and a GMB with a different resin and without HALS shows significant difference in their performance in chlorinated water but not in other incubation media. 相似文献
13.
14.
基于声发射和高斯混合模型的灰岩破裂特征识别研究 总被引:3,自引:0,他引:3
通过单轴压缩条件下灰岩破裂过程的声发射试验研究,利用高斯混合模型(GMM)对加载过程声发射信号波形特征进行深入分析,探索性识别灰岩破裂失稳过程的裂纹模式及其前兆特征。分析结果表明,灰岩在单轴加载过程中先后主要存在张拉和剪切两种破裂模式。其中,张拉破裂的声发射信号波形特征在AF-RA坐标空间呈现低A_F值、高R_A值分布;剪切破裂的声发射信号波形特征在AF-RA坐标空间呈现低R_A值、高A_F值,且随着应力的增加分布中心向A_F轴靠拢。GMM分析结果揭示了灰岩在整个应力加载过程中以张拉裂纹为主,在加载前中期几乎全为张拉裂纹,临近破坏阶段过渡到剪切破坏为主。剪切裂纹所占比例的最大值出现在(0.8~0.9)σ_c阶段,也是AF-RA坐标轴分布呈现最大A_F值时。研究结果可为预测早期灰岩破裂失稳提供参考,同时为深入研究识别岩石破裂失稳前兆信号特征提供了一种分析方法。 相似文献
15.
针对100 mm超厚板TC4钛合金电子束焊接接头,采用慢应变速率拉伸方法评价接头在人造海水中的应力腐蚀敏感性,分析接头的显微组织和断口形貌,对接头的腐蚀机制进行研究. 结果表明,室温条件下应变速率为ε=1×10-6 s-1时,母材在海水中未表现出应力腐蚀敏感性;焊缝上部、中部和下部具有轻微应力腐蚀敏感性. 焊缝在海水中发生阳极溶解,产生氢吸附,导致裂纹的萌生. 同时氢扩散诱导α'相界及α'相内发生位错塞积,进而使裂纹在更低的应力水平下发生扩展. 相似文献
16.
Muntasir Hashim Farnoosh Farhad David Smyth‐Boyle Robert Akid Xiang Zhang Philip J. Withers 《工业材料与腐蚀》2019,70(11):2009-2019
The environmental performance of 316L grade stainless steel, in the form of tensile specimens containing a single corrosion pit with various aspect ratios, under cyclic loading in aerated chloride solutions is investigated in this study. Results from environmental tests were compared and contrasted with those obtained using finite element analysis (FEA). Fractography of the failed specimens obtained from experiments revealed that fatigue crack initiation took place at the base of the shallow pit. The crack initiation shifted towards the shoulder and the mouth of the pit for pits of increasing depth. This process is well predicted by FEA, as the strain contour maps show that strain is the highest around the centric strip of the pit. However, for shallow pits, local strain is uniformly distributed around that strip but begins to concentrate more towards the shoulder and the mouth region for increasingly deep pits. 相似文献
17.
18.
《Contact lens & anterior eye》2019,42(6):646-651
PurposeTo evaluate meibomian gland (MG) width and determine its impact on successful contact lens (CL) use and ocular health.MethodsA five-site study was conducted by recruiting 18- to 45-year-old subjects who had dropped out of CLs because of discomfort. CL dropouts were compared to age- and sex-matched successful CL wearers. Right eyes were evaluated for tear break-up time, tear meniscus height, MG expressibility, meibum quality, and meibography. Central MG widths were evaluated with a custom MATLAB program.ResultsCL dropouts (n = 56) and successful CL (n = 56) wearers had similar grades for upper (p = 1.0) and lower (p = 0.22) MG atrophy, upper (p = 0.07) and lower (p = 0.89) MG tortuosity, and upper (p = 0.92) and lower (p = 0.97) MG widths. Upper eyelid MG widths were narrower than lower eyelid MG widths (p = 0.03). Upper and lower MG tortuosity (p < 0.001) and widths (p = 0.03) were associated, but not atrophy (p = 0.42). Lower eyelid MG widths were associated with MG expressibility (p = 0.01), but MG widths were not with any other factors.ConclusionsSuccessful CL wear does not appear to be clinically influenced by MG width or other measures of MG structural integrity. Lower eyelid MGs were wider than upper eyelid MGs and narrower lower eyelid MGs were associated with worse MG expressibility, suggesting that narrower MGs may produce abnormal meibum. Data also suggests that MG factors of both eyelids should be evaluated in practice. 相似文献
19.
ABSTRACTR-curve and controlled stable crack growth behaviour of ZrB2–17vol.-%SiC and ZrB2–45vol.-%SiC ceramic composites was studied on V-notched samples using four-point bending at room temperature. The rising K1R behaviour was determined as a function of the crack extension Δa with a crack bridging mechanism being dominant in such behaviour. Significant differences in crack growth rates were found within the same composition of ceramics simply as the crack length varied during crack growth processes. These differences are indicative of the significant influence of microstructural parameters of the ceramics on crack propagation. The peculiarities of stress intensity factor K1 and the crack growth-specific behaviour in ZrB2–SiC particulate ceramic composites are discussed. 相似文献
20.
在混凝土高拱坝浇筑过程中,影响坝体施工期温度场及温度应力的因素有很多,因此选用适当的浇筑方案对于节约工程成本及提高坝体安全性有着重要意义。以孟底沟水电站工程为例,选用多种施工方案,并利用三维有限元方法进行仿真分析,分析了浇筑季节、浇筑层厚、间歇时间及浇筑温度等因素对坝体施工期的敏感性。结果表明,低温季节浇筑、在防止热量倒灌的前提下尽量减小浇筑层厚度、缩短间歇时间、降低浇筑温度有助于降低温度应力,提高坝体安全性。 相似文献