全文获取类型
收费全文 | 44423篇 |
免费 | 4675篇 |
国内免费 | 2893篇 |
专业分类
电工技术 | 6644篇 |
技术理论 | 2篇 |
综合类 | 4264篇 |
化学工业 | 4937篇 |
金属工艺 | 1811篇 |
机械仪表 | 2196篇 |
建筑科学 | 4389篇 |
矿业工程 | 1501篇 |
能源动力 | 2000篇 |
轻工业 | 2798篇 |
水利工程 | 1780篇 |
石油天然气 | 3402篇 |
武器工业 | 319篇 |
无线电 | 4265篇 |
一般工业技术 | 4405篇 |
冶金工业 | 2205篇 |
原子能技术 | 1089篇 |
自动化技术 | 3984篇 |
出版年
2024年 | 208篇 |
2023年 | 662篇 |
2022年 | 1529篇 |
2021年 | 1808篇 |
2020年 | 1578篇 |
2019年 | 1233篇 |
2018年 | 1200篇 |
2017年 | 1482篇 |
2016年 | 1670篇 |
2015年 | 1750篇 |
2014年 | 2698篇 |
2013年 | 2989篇 |
2012年 | 3060篇 |
2011年 | 3497篇 |
2010年 | 2625篇 |
2009年 | 2682篇 |
2008年 | 2434篇 |
2007年 | 2912篇 |
2006年 | 2557篇 |
2005年 | 2226篇 |
2004年 | 1842篇 |
2003年 | 1513篇 |
2002年 | 1425篇 |
2001年 | 1135篇 |
2000年 | 942篇 |
1999年 | 786篇 |
1998年 | 608篇 |
1997年 | 525篇 |
1996年 | 461篇 |
1995年 | 380篇 |
1994年 | 325篇 |
1993年 | 220篇 |
1992年 | 170篇 |
1991年 | 145篇 |
1990年 | 125篇 |
1989年 | 124篇 |
1988年 | 116篇 |
1987年 | 57篇 |
1986年 | 42篇 |
1985年 | 33篇 |
1984年 | 40篇 |
1983年 | 13篇 |
1982年 | 27篇 |
1981年 | 13篇 |
1980年 | 14篇 |
1964年 | 12篇 |
1961年 | 8篇 |
1960年 | 10篇 |
1959年 | 16篇 |
1955年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
61.
62.
E. I. Leyarovski J. K. Georgiev A. L. Zahariev 《International Journal of Thermophysics》1988,9(3):391-408
A new method for experimental determination of the thermal diffusion factor
T for binary gas mixtures with a thermal diffusion column (TDC) is developed, based on A. M. Rozen's equation of TDC. The experimental results for
T are obtained in a reduced form in this approximation. An experimental reference point, determined in the same TDC with a standard gas mixture, is used for the transformation of the results for
T in absolute units. The proposed method is applicable for arbitrary gas mixtures, irrespective of the mass difference of the components. 相似文献
63.
64.
电感电容损耗电阻的讨论 总被引:3,自引:0,他引:3
通过对电容电感阻抗的测量,发现实验值偏离理论值。定性地分析了误差的来源,得出的结论是电感电容内部的损耗电阻随着频率的变化而变化,变化方向相反而并非相同。 相似文献
65.
In this paper, the author dipped surface vapor oxidized H13 steel specimens into 700℃ molten aluminum liquid for a certain period of time. Analyze the intermetallic phases formed on the H13 samples surface with optical microscope and X-ray diffraction method. The observation of immersion test sample's cross-section shows that Fe3O4 film will protect die substrate from molten aluminum erosion. The identification of the intermetallic phases reveals that they consist of 2parts, which is named as the composite layer and the compact layer. Further investigations are made in order to know the phase constituents of the 2 layers, they are Al8Fe2Si (outer composite layer), (AlCuMg) and Al5Fe2 (compact layer),respectively. The experimental results show that on the same specimen, a convex surface with bigger radius of curvature is more likely to be molten and the melting loss speed is also faster than a flat and smooth surface. The thickness of compact layer on a smooth surface is much bigger than that of the convex surface. Therefore, the author supposes the compact layer is favorable in stabilizing the die surface material from further melting loss, as their formation on the die surface, the melting loss speed will decrease. 相似文献
66.
探讨了该厂化肥生产中碳铵发青的原因,通过硫化氢含量的测定,分析了系统内外影响因素,提出了解决措施,达到了不停车稳定产品质量的目的。 相似文献
67.
《Expert systems with applications》2014,41(7):3444-3449
During early design and development stages, every engineering system has to meet its specific reliability goals. The target reliability of the system is achieved through application of an effective reliability apportionment technique to its subsystems. There are various traditional methods exist to perform the reliability allocation based on engineering factors that are assessed in a subjective manner. The conventional reliability allocation approach requires the assessment of factors like complexity, cost, and maintenance. This may not be realistic in real applications if they are assessed in a crisp manner by the domain experts of their varied expertise and background.In this paper, we treat allocation factors as fuzzy numbers, which are evaluated in fuzzy linguistic terms. As a result, fuzzy proportionality factor scales are proposed for the subsystems. In order to accomplish fuzzy division to evaluate the fuzzy proportionality factor, an approximation method based on linear programming for trapezoidal fuzzy numbers is also proposed in this paper. For the evaluation of weighting factors from fuzzy proportionality factors, centroid method of defuzzification is being employed. The allocated reliability of each subsystem is computed with the help of weighting factor thereafter. An example is provided to illustrate the potential application of the proposed fuzzy based reliability allocation approach. 相似文献
68.
Transport phenomena studies on single phase “model” fluids are of limited value in biochemical engineering if they cannot be translated to the heterogeneous systems encountered in real fermentation processes. In this paper we discuss the utility of polymer solutions as models of filamentous fermentation broths for evaluation of: pipeline friction factors and impeller power numbers (turbine and helical ribbon). To a first approximation, polymer solutions can serve as suitable models for the prediction of laminar flow pressure drop in pipelines and turbulent power consumption in stirred tanks. However, results obtained on polymer solutions do not directly apply to filamentous fermentation broths for predictions of laminar flow impeller power consumption and the transition point for turbulent flow in stirred tanks. These discrepancies are believed to result from the existence of a time dependent yield stress in filamentous fermentation broths. 相似文献
69.
结合现有两种主要群体推荐算法的优势, 建立新的算法框架, 并引入差异度因素对模型进行优化。另外, 考虑到在线社区用户的特点, 定义互动度指标来描述群体成员间的互动程度, 通过分析其与推荐精度之间的关系, 探讨互动度对群体推荐的影响。选取豆瓣网数据进行实验, 并与传统方法进行比较, 结果表明, 融入差异度的算法具有更好的推荐效果, 且有效的互动机制能够保证较高的推荐精度。 相似文献
70.
研究了具有数据包丢失和随机不确定性离散随机线性系统的状态估计问题.其中数据包丢失是随机的,且满足Bernoulli分布,系统矩阵中的随机不确定性由一个白色乘性噪声来描述.首先,通过配方方法,提出了最小均方意义下的无偏最优线性递推满阶滤波器.所提出的滤波器用到了当前时刻和最近时刻接收到的观测来保证线性最优性.与多项式滤波和增广滤波器相比,本文的滤波器具有较小的计算负担.然后,基于所获得的线性滤波器推导了线性最优预报器和平滑器.进一步研究了线性最优估值器的渐近稳定性,给出了稳态特性存在的一个充分条件.最后,通过两个仿真例子验证了所提估计算法的优越性. 相似文献