全文获取类型
收费全文 | 36035篇 |
免费 | 4091篇 |
国内免费 | 1916篇 |
专业分类
电工技术 | 2538篇 |
技术理论 | 4篇 |
综合类 | 3239篇 |
化学工业 | 3921篇 |
金属工艺 | 1701篇 |
机械仪表 | 2398篇 |
建筑科学 | 4204篇 |
矿业工程 | 941篇 |
能源动力 | 1272篇 |
轻工业 | 6178篇 |
水利工程 | 1370篇 |
石油天然气 | 1227篇 |
武器工业 | 776篇 |
无线电 | 1854篇 |
一般工业技术 | 5360篇 |
冶金工业 | 1879篇 |
原子能技术 | 610篇 |
自动化技术 | 2570篇 |
出版年
2024年 | 241篇 |
2023年 | 765篇 |
2022年 | 1548篇 |
2021年 | 1661篇 |
2020年 | 1711篇 |
2019年 | 1410篇 |
2018年 | 1397篇 |
2017年 | 1634篇 |
2016年 | 1769篇 |
2015年 | 1791篇 |
2014年 | 2298篇 |
2013年 | 2575篇 |
2012年 | 2814篇 |
2011年 | 2937篇 |
2010年 | 1942篇 |
2009年 | 1831篇 |
2008年 | 1669篇 |
2007年 | 1874篇 |
2006年 | 1690篇 |
2005年 | 1381篇 |
2004年 | 1089篇 |
2003年 | 930篇 |
2002年 | 732篇 |
2001年 | 677篇 |
2000年 | 563篇 |
1999年 | 499篇 |
1998年 | 421篇 |
1997年 | 314篇 |
1996年 | 283篇 |
1995年 | 263篇 |
1994年 | 229篇 |
1993年 | 173篇 |
1992年 | 145篇 |
1991年 | 107篇 |
1990年 | 114篇 |
1989年 | 73篇 |
1988年 | 64篇 |
1987年 | 46篇 |
1986年 | 30篇 |
1985年 | 36篇 |
1984年 | 31篇 |
1983年 | 18篇 |
1982年 | 26篇 |
1980年 | 26篇 |
1979年 | 23篇 |
1965年 | 16篇 |
1964年 | 19篇 |
1963年 | 15篇 |
1961年 | 13篇 |
1957年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
J. W. PARK R.F. TESTIN P. J. VERGANO H.J. PARK C.L. WELLER 《Journal of food science》1996,61(4):766-768
The effects of various stearic-palmitic acid blend concentrations in films, storage temperatures and storage times on potato chip quality were evaluated using Response Surface Methodology. Storage temperature and time affected the quality of potato chips. The maximum storage times for acceptable potato chip quality were: 30 to 43 days, 23 to 25 days, and 11 to 12 days for storage temperatures of 15, 25 and 35°C, respectively. Results were independent of stearic-palmitic acid blend concentrations. 相似文献
102.
STN-LCD采用新的取向层,消除了残象;采用新的驱动波形,消除了串扰;采用二(口恶)烷、卤化物、链烯基、醚和二苯乙炔,改进了液晶料材的性能,使STN-LCD获得高的对比度、快的响应速度、低的驱动电压;采用有源矩阵驱动方法,消除了帧响应,使STN-LCD获得高的对比度、高的亮度及视频响应速度;使用温度跟踪电路,自动跟踪STN-LCD的阀值电压,使STN-LCD获得宽的工作温度。 相似文献
103.
Dynamic elastic-plastic buckling phenomena which might develop in a rod from an axial impact loading are studied in order to identify the conditions for quasi-static behaviour. A discrete model for dynamic elastic-plastic buckling, which retains the axial and the lateral inertia forces, is proposed, and the relationship between the model parameters and the characteristics of an actual structure is given. Examples of different external loadings and boundary conditions are considered in order to clarify the influence of elastic-plastic axial wave propagation on the buckling process. The critical time for the initiation of buckling is obtained and the post-buckling behaviour of the model is analysed. Particular attention is paid to the role of the striking mass on the characteristics of the buckling process and on the development of the buckling shape. The numerical study reveals that the inertia of the striking mass affects considerably the development of the buckling shape causing different patterns of axial strain distributions at the initiation of buckling. The comparisons which are made between the model predictions and some previously published experimental data show that the buckling process is governed by the impact velocity as well as by the external loading history provided by the experimental technique. 相似文献
104.
根据面板堆石坝的结构特点和工作条件,采用动力非线性有限元法,对清平水库面板坝进行了空库和满库条件下地震反应分析与比较、混凝土面板地震抗滑稳定分析及坝基饱和细砂层的地震液化验算,综合评价大坝的安全性. 相似文献
105.
实证分析:上市公司资本结构的影响因素 总被引:13,自引:0,他引:13
在国内外相关研究的基础上,利用我国资本市场的公开数据,对上市公司资本结构的影响因素进行实证研究,得出了若干重要结论。 相似文献
106.
A study of impact toughness of Fe-Cr-X damping alloys 总被引:1,自引:0,他引:1
J. S. Lu X. Liu W. Zheng B. Wu H. Bi G. Wang 《Journal of Materials Engineering and Performance》1994,3(3):409-411
A study was carried out on the impact toughness of Fe- Cr- Х damping alloys. Two measures proved to be effective in improving
impact toughness. One was to lower carbon plus nitrogen content to an ultra- low level. This method is suitable for single-
phase ferrite alloy. The other is to use dual- phase damping alloys. The presence of martensite in Fe- Cr- Х alloys can enhance
impact toughness remarkably, but lower damping capacity drastically. This shows the importance of achieving balance between
mechanical prop-erties and damping capacity by properly controlling martensite volume fraction in dual- phase alloys. 相似文献
107.
The paper addresses the design of two-level power system stabilizers using an optimal reduced order model whose state variables are torque angles and speeds. The reduced order model retains their physical meaning and is used to design a two-level linear feedback controller that takes into account the realities and constraints of electrical power systems. The two-level control strategy is used, and a global control signal is generated from the output variables to minimize the effect of interactions. The effectiveness of this controller is evaluated and a multimachine system is given as an example to illustrate the advantages of the proposed method. Responses of the system with a two-level scheme and an optimal reduced order scheme are included for comparative analysis. 相似文献
108.
根据对黄骅坳陷白水头—唐家河地区东营组钻井资料的统计分析,设计了3种不同地质模型.用于分析不同厚度、不同孔隙度和不同流体性质的储层所表现出的地层速度和密度特性,进而通过地震正演模拟研究,得到不同储层参数状况下的响应曲线。分析响应曲线发现,在该地区,当含水砂岩厚度为20m时.其地震反射振幅最大;而含油帮岩在厚度为18m时达到最大。当孔隙度达到22%时.含油砂岩的地震反射振幅会发生极性反转;而含水砂岩在孔隙度为28%时极性反转。这就为该地区的地震储层预测提供了依据。 相似文献
109.
Tucker Don M.; Luu Phan; Frishkoff Gwen; Quiring Jason; Poulsen Catherine 《Canadian Metallurgical Quarterly》2003,112(4):667
Functional neuroimaging suggests that limbic regions of the medial frontal cortex may be abnormally active in individuals with depression. These regions, including the anterior cingulate cortex, are engaged in both action regulation, such as monitoring errors and conflict, and affect regulation, such as responding to pain. The authors examined whether clinically depressed subjects would show abnormal sensitivity of frontolimbic networks as they evaluated negative feedback. Depressed subjects and matched control subjects performed a video game in the laboratory as a 256-channel EEG was recorded. Speed of performance on each trial was graded with a feedback signal of A, C, or F. By 350 ms after the feedback signal, depressed subjects showed a larger medial frontal negativity for all feedback compared with control subjects with a particularly striking response to the F grade. This response was strongest for moderately depressed subjects and was attenuated for subjects who were more severely depressed. Localization analyses suggested that negative feedback engaged sources in the anterior cingulate and insular cortices. These results suggest that moderate depression may sensitize limbic networks to respond strongly to aversive events. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
110.
Zhen Wang 《Applied Composite Materials》1995,2(4):257-264
A bimodal Weibull distribution function was applied to analyse the strength distribution of glass fibre bundles under tensile impact. The simulation was performed using a one-dimensional damage constitutive model. The results show that there were two concurrent flaw populations in the fracture process. The regression analysis using the bimodal Weibull distribution function was in good agreement with experiment. 相似文献