全文获取类型
收费全文 | 47245篇 |
免费 | 5692篇 |
国内免费 | 2681篇 |
专业分类
电工技术 | 2412篇 |
技术理论 | 5篇 |
综合类 | 3356篇 |
化学工业 | 12589篇 |
金属工艺 | 2901篇 |
机械仪表 | 3637篇 |
建筑科学 | 2657篇 |
矿业工程 | 472篇 |
能源动力 | 4879篇 |
轻工业 | 1928篇 |
水利工程 | 694篇 |
石油天然气 | 1183篇 |
武器工业 | 301篇 |
无线电 | 5295篇 |
一般工业技术 | 7329篇 |
冶金工业 | 1568篇 |
原子能技术 | 1479篇 |
自动化技术 | 2933篇 |
出版年
2024年 | 217篇 |
2023年 | 886篇 |
2022年 | 1367篇 |
2021年 | 1570篇 |
2020年 | 1610篇 |
2019年 | 1551篇 |
2018年 | 1406篇 |
2017年 | 1597篇 |
2016年 | 1649篇 |
2015年 | 1679篇 |
2014年 | 2371篇 |
2013年 | 3076篇 |
2012年 | 2850篇 |
2011年 | 3428篇 |
2010年 | 2520篇 |
2009年 | 2590篇 |
2008年 | 2594篇 |
2007年 | 2856篇 |
2006年 | 2663篇 |
2005年 | 2481篇 |
2004年 | 1999篇 |
2003年 | 1895篇 |
2002年 | 1618篇 |
2001年 | 1213篇 |
2000年 | 1123篇 |
1999年 | 906篇 |
1998年 | 860篇 |
1997年 | 782篇 |
1996年 | 689篇 |
1995年 | 580篇 |
1994年 | 431篇 |
1993年 | 395篇 |
1992年 | 381篇 |
1991年 | 289篇 |
1990年 | 266篇 |
1989年 | 240篇 |
1988年 | 170篇 |
1987年 | 140篇 |
1986年 | 126篇 |
1985年 | 109篇 |
1984年 | 131篇 |
1983年 | 92篇 |
1982年 | 80篇 |
1981年 | 21篇 |
1980年 | 15篇 |
1979年 | 10篇 |
1976年 | 8篇 |
1966年 | 7篇 |
1959年 | 17篇 |
1951年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
A scanning electron microscope (SEM) is a sophisticated equipment employed for fine imaging of a variety of surfaces. In this study, prediction models of SEM were constructed by using a generalized regression neural network (GRNN) and genetic algorithm (GA). The SEM components examined include condenser lens 1 and 2 and objective lens (coarse and fine) referred to as CL1, CL2, OL-Coarse, and OL-Fine. For a systematic modeling of SEM resolution (R), a face-centered Box–Wilson experiment was conducted. Two sets of data were collected with or without the adjustment of magnification. Root-mean-squared prediction error of optimized GRNN models are GA 0.481 and 1.96×10-12 for non-adjusted and adjusted data, respectively. The optimized models demonstrated a much improved prediction over statistical regression models. The optimized models were used to optimize parameters particularly under best tuned SEM environment. For the variations in CL2 and OL-Coarse, the highest R could be achieved at all conditions except a larger CL2 either at smaller or larger OL-Coarse. For the variations in CL1 and CL2, the highest R was obtained at all conditions but larger CL2 and smaller CL1. 相似文献
142.
In non-invasive thermal diagnostics, accurate correlations between the thermal image at skin surface and interior human physiology are desired. In this work, an estimation methodology to determine unknown geometrical parameters of an embedded tumor is proposed. We define a functional that represents the mismatch between a measured experimental temperature profile, which may be obtained by infrared thermography on the skin surface, and the solution of an appropriate boundary problem. This functional is related to the geometrical parameters through the solution of the boundary problem, in such a way that finding the minimum of this functional form also means finding the unknown geometrical parameters of the embedded tumor. Sensitivity analysis techniques coupled with the adjoint method were considered to compute the shape derivative of the functional. Then, a nonmonotone spectral projected gradient method was implemented to solve the optimization problem of finding the optimal geometric parameters. 相似文献
143.
基于FPGA的高速自适应滤波器的实现 总被引:2,自引:0,他引:2
在LMS算法进行变步长处理的基础上,结合驰豫超前流水线技术和时序重构技术提出了创新结构和改进算法,在FPGA的仿真综合环境中设计实现了该高速自适应滤波器,并且在AlteraDE2-70开发板上进行了板级测试。 相似文献
144.
朴光秉 《数字社区&智能家居》2008,3(12):1604-1605
该文在介绍国外农业电子商务发展的背案下,对我国农业电子商务发展的现状作了实例的分析和对策研究。 相似文献
145.
Malatesta M Frigato E Baldelli B Battistelli S Foà A Bertolucci C 《Microscopy research and technique》2007,70(7):578-584
Reptiles represent an interesting animal model to investigate the influence of temperature on molecular circadian clocks. The ruin lizard Podarcis sicula lives in a continental climate and it is subjected to wide range of environmental temperatures during the course of the year. As consequence, ruin lizard daily activity pattern includes either the hibernation or periods of inactivity determined by hypothermia. Here we showed the rhythmic expression of two clock genes, lPer2 and lClock, in the liver of active lizards exposed to summer photo-thermoperiodic conditions. Interestingly, the exposition of lizards to hypothermic conditions, typical of winter season, induced a strong dampening of clock genes mRNA rhythmicity with a coincident decrease of levels. We also examined the qualitative and quantitative distribution of lPER2 and lCLOCK protein in different cellular compartments during the 24-h cycle. In the liver of active lizards both proteins showed a rhythmic expression profile in all cellular compartments. After 3 days at 6 degrees C, some temporal fluctuations of the lCLOCK and lPER2 are still detectable, although, with some marked modifications in respect to the values detected in the liver of active lizards. Besides demonstrating the influence of low temperature on the lizard liver circadian oscillators, present results could provide new essential information for comparative studies on the influence of temperature on the circadian system across vertebrate classes. 相似文献
146.
梯形波脉冲筛板萃取柱传质性能 总被引:1,自引:0,他引:1
本文以UO_2(NO_3)_2—30%TBP(KO)为实验体系,进行了梯形波脉冲筛板柱传质性能的研究。实验中测量了两组分的两相稳态浓度剖面共13组,以扩散模型为基础,求得了梯形波脉冲柱的“真实”传质单元高度HTU_(ox),分散单元高度HDU及表观传质单元高度HTU_(oxp)。通过对实验结果进行分析,选择出了适于本实验体系的较好的操作条件。 相似文献
147.
Morton Litt 《Polymer International》1993,30(2):213-216
We have analyzed the electrical conductivity of a linear high charge density polyelectrolyte aqueous solution, finding that the counterion association order follows the same pattern as that described for a cyclic monomeric polyelectrolyte, i.e. NO > Br? > Cl? > F?. However, these counterions interact in a very different manner with this polyion, making Eisenberg's relationship inapplicable in this system. Consequently, an alternative method is proposed for treating data. 相似文献
148.
A technique to segment pores from a normal backscattered electron (BSE) image of cement-based materials is presented. The upper threshold grey level for porosity is determined from the inflection point of the cumulative brightness histogram of the BSE image. This represents a critical point where a small incremental grey value will cause a sudden increase in thresholded area, a condition termed as overflow. The proposed technique was found to be more consistent and reliable than existing methods. Significantly fewer images are required to achieve a satisfactory level of statistical confidence for quantifying porosity. 相似文献
149.
150.
N,N-二甲基对甲基苯胺的自动氧化 总被引:1,自引:0,他引:1
N,N-二甲基对甲基苯胺(DMT)是一个典型的电子给体,可以和多种电子受体形成称之为CCT(Contact Charge Transfer)的络合物。在光照条件下,这种络合物可以生成离子自由基,从而引起一系列反应。同时,DMT又是一个还原剂,很容易发生氧 相似文献