全文获取类型
收费全文 | 35448篇 |
免费 | 3332篇 |
国内免费 | 2167篇 |
专业分类
电工技术 | 916篇 |
综合类 | 2868篇 |
化学工业 | 7144篇 |
金属工艺 | 1310篇 |
机械仪表 | 3274篇 |
建筑科学 | 1335篇 |
矿业工程 | 1141篇 |
能源动力 | 2048篇 |
轻工业 | 1285篇 |
水利工程 | 716篇 |
石油天然气 | 6601篇 |
武器工业 | 831篇 |
无线电 | 963篇 |
一般工业技术 | 4456篇 |
冶金工业 | 1051篇 |
原子能技术 | 499篇 |
自动化技术 | 4509篇 |
出版年
2024年 | 184篇 |
2023年 | 693篇 |
2022年 | 1193篇 |
2021年 | 1364篇 |
2020年 | 1202篇 |
2019年 | 1157篇 |
2018年 | 1028篇 |
2017年 | 1258篇 |
2016年 | 1444篇 |
2015年 | 1487篇 |
2014年 | 2015篇 |
2013年 | 2323篇 |
2012年 | 2234篇 |
2011年 | 2597篇 |
2010年 | 1759篇 |
2009年 | 1791篇 |
2008年 | 1611篇 |
2007年 | 2065篇 |
2006年 | 2015篇 |
2005年 | 1742篇 |
2004年 | 1521篇 |
2003年 | 1326篇 |
2002年 | 1166篇 |
2001年 | 949篇 |
2000年 | 815篇 |
1999年 | 715篇 |
1998年 | 594篇 |
1997年 | 481篇 |
1996年 | 427篇 |
1995年 | 369篇 |
1994年 | 267篇 |
1993年 | 197篇 |
1992年 | 154篇 |
1991年 | 140篇 |
1990年 | 120篇 |
1989年 | 121篇 |
1988年 | 74篇 |
1987年 | 50篇 |
1986年 | 40篇 |
1985年 | 30篇 |
1984年 | 40篇 |
1983年 | 32篇 |
1982年 | 27篇 |
1981年 | 18篇 |
1980年 | 22篇 |
1979年 | 20篇 |
1978年 | 11篇 |
1959年 | 11篇 |
1955年 | 5篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
阳离子化多元醇防塌剂的研制 总被引:4,自引:0,他引:4
室内研究和现场应用表明,聚乙烯醇类防塌剂表现出较明显的增粘负效应,可引起钻井液粘度的急剧增加,严重影响其推广应用.通过金属盐催化降解和阳离子化反应,研制出了抑制性好且增粘负效应低的阳离子化改性多元醇防塌剂.考察了阳离子化试剂、反应温度、反应时间对取代度、反应效率和产品主要性能的影响,得出了阳离子化多元醇防塌剂最佳制备条件,即:PVA与阳离子化试剂物质的量比为1:1,反应温度为50℃,反应时间为4 h,阳离子度可达0.435. 相似文献
32.
《Drying Technology》2007,25(6):971-983
This article reviews developments in the simulations of spray dryer behavior, including the challenges in modeling the complex flow patterns inside the equipment, which are often highly transient and three-dimensional in nature. There appears to be considerable scope for using CFD simulations for investigating methods to reduce the rates of wall deposition and of thermal degradation for particles by modifying the air flow patterns in the chamber through small changes in the air inlet geometry. Challenges include building particle drying kinetics and reaction processes, as well as agglomeration behavior, into these simulations. The numerical simulations should be valuable supplements to pilot-scale testing, enabling more extensive and accurate optimization to be carried out than hitherto possible. New understanding of reaction processes and materials science, in combination with recent knowledge of the application of CFD to these problems, may enable new engineered powder products to be developed from the one-step spray-drying process. 相似文献
33.
Wei Hui 《Frontiers of Computer Science in China》2007,1(3):361-372
Almost all applications of Artificial Neural Networks (ANNs) depend mainly on their memory ability. The characteristics of
typical ANN models are fixed connections, with evolved weights, globalized representations, and globalized optimizations,
all based on a mathematical approach. This makes those models to be deficient in robustness, efficiency of learning, capacity,
anti-jamming between training sets, and correlativity of samples, etc. In this paper, we attempt to address these problems
by adopting the characteristics of biological neurons in morphology and signal processing. A hierarchical neural network was
designed and realized to implement structure learning and representations based on connected structures. The basic characteristics
of this model are localized and random connections, field limitations of neuron fan-in and fan-out, dynamic behavior of neurons,
and samples represented through different sub-circuits of neurons specialized into different response patterns. At the end
of this paper, some important aspects of error correction, capacity, learning efficiency, and soundness of structural representation
are analyzed theoretically. This paper has demonstrated the feasibility and advantages of structure learning and representation.
This model can serve as a fundamental element of cognitive systems such as perception and associative memory. 相似文献
34.
Intact and ovariectomized oxytocin (OT)-deficient (OT-/-) and wild-type (OT+/+) mice were tested for consumption of 0.5 M NaCl solution or tap water in a 2-bottle choice test. During 3 days of acclimation, voluntary ingestion of NaCl was equal between genotypes. After overnight fluid deprivation, intact OT-/- mice ingested 2 times more NaCl solution than OT+/+ mice in the 6th hr, but not the 1 st hr, after reintroduction of fluid. Ovariectomized mice consumed less than intact mice after overnight fluid deprivation. When a 0.2 M NaCl solution was administered for 6 days in ovariectomized mice, OT-/- mice voluntarily consumed greater amounts than OT+/+ mice. After overnight fluid deprivation, consumption by OT-/- mice was 3 times that of OT+/+ mice at 1 hr and 2-fold greater after 6 hr. Enhanced intake of NaCl-containing solutions in female OT-/- mice suggests that central OT may be an important inhibitor of sodium consumption. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
35.
36.
建(构)筑物机械拆除方法综述 总被引:1,自引:0,他引:1
介绍了几种常用的建(构)筑物机械拆除方法,对其工作原理、特点、应用条件及局限性加以分析和说明。 相似文献
37.
Ramon R. Costa Liu Hsu 《International Journal of Adaptive Control and Signal Processing》1992,6(1):19-33
A variable structure model reference adaptive controller (VS-MRAC) using only input and output measurements was recently proposed and shown to be globally asymptotically stable with superior transient behaviour and disturbance rejection properties. In this paper a singular perturbation approach is used in order to establish the robustness of the controller in the presence of unmodelled dynamics (parasitics) and disturbances. We develop a new Lyapunov-based technique to analyse the overall system and show that for sufficiently small parasitics the system remains stable and the output error is small in some sense. 相似文献
38.
39.
The effect of adsorption on the measurement of diffusion coefficients by the Taylor dispersion technique is investigated by modifying the governing equation to account for reversible, nonequilibrium adsorption. The resulting two-dimensional equations are solved by an explicit finite-difference technique. Experimental data for the acridine carbon dioxide system indicated that acridine adsorbs on the walls on the tubing and these data were investigated with this model. The influence of carious parameters including the number of sites and the rates of adsorption desorption was investigated by conducting a parametric sensitivity analysis on the model. It was found that adsorption of the solute on the wall of the tubing could produce an error as high as 35% on the measured diffusion coefficient compared to the actual diffusion coellicient. Examination of the influence of each of the parameters will enable Inure investigators to reduce the effect of adsorption in the measurement of diffusion coefficients by Taylor dispersion. 相似文献
40.