全文获取类型
收费全文 | 45078篇 |
免费 | 3220篇 |
国内免费 | 2462篇 |
专业分类
电工技术 | 1454篇 |
综合类 | 2588篇 |
化学工业 | 13285篇 |
金属工艺 | 4230篇 |
机械仪表 | 2106篇 |
建筑科学 | 3269篇 |
矿业工程 | 627篇 |
能源动力 | 1371篇 |
轻工业 | 2708篇 |
水利工程 | 281篇 |
石油天然气 | 2563篇 |
武器工业 | 346篇 |
无线电 | 4024篇 |
一般工业技术 | 5823篇 |
冶金工业 | 1894篇 |
原子能技术 | 845篇 |
自动化技术 | 3346篇 |
出版年
2024年 | 147篇 |
2023年 | 608篇 |
2022年 | 1424篇 |
2021年 | 1442篇 |
2020年 | 1235篇 |
2019年 | 1143篇 |
2018年 | 958篇 |
2017年 | 1297篇 |
2016年 | 1618篇 |
2015年 | 1545篇 |
2014年 | 2093篇 |
2013年 | 2454篇 |
2012年 | 2650篇 |
2011年 | 3366篇 |
2010年 | 2437篇 |
2009年 | 2945篇 |
2008年 | 2365篇 |
2007年 | 2923篇 |
2006年 | 2709篇 |
2005年 | 2228篇 |
2004年 | 1900篇 |
2003年 | 1870篇 |
2002年 | 1525篇 |
2001年 | 1182篇 |
2000年 | 1078篇 |
1999年 | 847篇 |
1998年 | 672篇 |
1997年 | 490篇 |
1996年 | 446篇 |
1995年 | 376篇 |
1994年 | 334篇 |
1993年 | 302篇 |
1992年 | 244篇 |
1991年 | 204篇 |
1990年 | 186篇 |
1989年 | 139篇 |
1988年 | 111篇 |
1987年 | 109篇 |
1986年 | 116篇 |
1985年 | 112篇 |
1984年 | 99篇 |
1983年 | 87篇 |
1982年 | 84篇 |
1981年 | 91篇 |
1980年 | 79篇 |
1978年 | 76篇 |
1977年 | 75篇 |
1976年 | 91篇 |
1975年 | 87篇 |
1974年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
3.
For the first time, we present the unique features exhibited by power 4H–SiC UMOSFET in which N and P type columns (NPC) in the drift region are incorporated to improve the breakdown voltage, the specific on-resistance, and the total lateral cell pitch. The P-type column creates a potential barrier in the drift region of the proposed structure for increasing the breakdown voltage and the N-type column reduces the specific on-resistance. Also, the JFET effects reduce and so the total lateral cell pitch will decrease. In the NPC-UMOSFET, the electric field crowding reduces due to the created potential barrier by the NPC regions and causes more uniform electric field distribution in the structure. Using two dimensional simulations, the breakdown voltage and the specific on-resistance of the proposed structure are investigated for the columns parameters in comparison with a conventional UMOSFET (C-UMOSFET) and an accumulation layer UMOSFET (AL-UMOSFET) structures. For the NPC-UMOSFET with 10 µm drift region length the maximum breakdown voltage of 1274 V is obtained, while at the same drift region length, the maximum breakdown voltages of the C-UMOSFET and the AL-UMOSFET structures are 534 and 703 V, respectively. Moreover, the proposed structure exhibits a superior specific on-resistance (Ron,sp) of 2 mΩ cm2, which shows that the on-resistance of the optimized NPC-UMOSFET are decreased by 56% and 58% in comparison with the C-UMOSFET and the AL-UMOSFET, respectively. 相似文献
4.
In the present work, inter-diffusion of nickel and titanium and formation of Ni-Ti intermetallic compounds on Ti-6Al-4V substrate have been studied. Initially, nickel was electrodeposited on the alloy using a modified Watts bath solution at a current density of 2 A dm?2 for 1?h. The coated specimens were then heat treated for different durations at 750, 800 and 850 °C under argon atmosphere. The effects of temperature and time on the characteristics, hardness and wear resistance of intermetallic phases were investigated. The results showed that a multilayer structure was formed after heat treatment, an outer layer of residual nickel, an area of intermetallic layers with different compositions followed by a solid solution of Ni-Ti. It was also observed that an increase in time or temperature at first led to the formation of thicker intermetallic layers; however, after passing a critical point, the intermetallic layers seem to dissolve into the substrate. Furthermore, the wear rates of the diffusion treated samples were four times lower compared to Ti-6Al-4V alloy when sliding against AISI 52100 hardened steel. 相似文献
5.
Effects of breed and age at slaughter on degradation of muscle lipids during processing of dry‐cured hams 下载免费PDF全文
Linda Storrustløkken Hanne Marie Devle Lars Erik Gangsei Carl Fredrik Naess‐Andresen Bjørg Egelandsdal Ole Alvseike Dag Ekeberg 《International Journal of Food Science & Technology》2015,50(8):1933-1943
Hams from Landrace, Duroc and Hampshire pigs slaughtered at ages 6, 7.5 and 9 months were processed to generate Norwegian Parma‐style hams. Lipid contents and the compositions of fatty acid classes (ΣSFA, ΣMUFA, ΣPUFA) within neutral lipids, phospholipids and free fatty acids were determined. Small differences in lipid degradation and composition of the classes were revealed. However, significant sensory differences related to lipids were observed. Breed was more important than age. Dry‐cured Hampshire hams gave a more intense mature odour that may be associated with higher overall lipid degradation. Unexpectedly, these hams also demonstrated high juiciness and tenderness, which could be related to the melting characteristics of the fat. Dry‐cured Duroc hams showed a higher susceptibility towards rancidity, presumably associated with preferential oxidation of n‐6 fatty acids relative to C18:1 n‐9. Dry‐cured Landrace hams showed the lowest juiciness and tenderness, likely due to their lower fat content (marbling). 相似文献
6.
Eight datasets of 1-h black carbon (BC) concentrations measured in Warsaw agglomeration (Poland), at urban background and sub-urban sites, and in Racibórz, a small town in Upper Silesia district (regional background site) were analyzed to evaluate BC levels, daily profiles and statistical distributions of concentrations in Central-Eastern European region. The observed mean levels ranged from 1483 ng m−3 in suburban site during summer to 3358 ng m−3 in regional background site in winter. Observed diurnal patterns were bimodal in the locations dominated by traffic emissions, but unimodal, with elevated evening peak in individually heated residential area. Three theoretical frequency distributions were applied to fit analyzed datasets separately. The lognormal distribution was the most appropriate to represent the middle-range values, while the high concentrations were satisfactorily predicted by the type I two-parameter exponential distribution which was used to estimate the return periods of extreme concentrations for winter months. 相似文献
7.
F. Schröder R. M. Ward A. R. Walpole R. P. Turner M. M. Attallah J.-C. Gebelin 《Materials Science & Technology》2015,31(3):372-384
Linear friction welding of the Ti6Al4V alloy is studied. A new definition of the energy input rate is proposed, based on an integration over time of the in-plane force and velocity; a strong correlation with the upset rate is then found. The effective friction coefficient is estimated to be 0·5±0·1 for varying frequencies and amplitudes, with only a weak dependence on the processing conditions displayed. A model is proposed that accounts for both the conditioning and equilibrium stages of the process, which is shown to be in good agreement with the experimental data. The model is used to study the mechanism by which the flash is formed. A criterion is proposed by which the rippled nature of its morphology can be predicted. 相似文献
8.
9.
《Planning》2015,(12):33-35
目的:探讨IL-27与LTB4在非小细胞肺癌组织中的表达情况及临床意义。方法:采用免疫组化S-P法分别检测60例非小细胞肺癌组织及正常肺组织中的IL-27与LTB4的表达水平。结果:IL-27与LTB4在肺癌组织中的总阳性表达率分别为41.67%、63.33%,各种检测指标的阳性率在肺癌组织与对照组之间均存在着差异性(P<0.05)。IL-27与LTB4的表达均与肿瘤的分化程度有关(P<0.05),IL-27的表达与肺癌的TNM分期相关(P<0.05),与病理类型无关(P>0.05)。LTB4的表达与组织学类型、临床分期无关(P>0.05),IL-27与LTB4之间存在密切相关性。结论:IL-27、LTB4与肺癌发生机制及发展有密切关系,联合进行检测两者表达水平对于肺癌临床诊断、评估恶性程度及判断预后有重要意义。 相似文献
10.