全文获取类型
收费全文 | 182180篇 |
免费 | 16180篇 |
国内免费 | 8633篇 |
专业分类
电工技术 | 11668篇 |
技术理论 | 13篇 |
综合类 | 12353篇 |
化学工业 | 29225篇 |
金属工艺 | 10179篇 |
机械仪表 | 11686篇 |
建筑科学 | 13943篇 |
矿业工程 | 5554篇 |
能源动力 | 5461篇 |
轻工业 | 12645篇 |
水利工程 | 3442篇 |
石油天然气 | 10709篇 |
武器工业 | 1486篇 |
无线电 | 21867篇 |
一般工业技术 | 21664篇 |
冶金工业 | 8629篇 |
原子能技术 | 1998篇 |
自动化技术 | 24471篇 |
出版年
2024年 | 612篇 |
2023年 | 3253篇 |
2022年 | 5634篇 |
2021年 | 8260篇 |
2020年 | 6289篇 |
2019年 | 4982篇 |
2018年 | 5659篇 |
2017年 | 6289篇 |
2016年 | 5631篇 |
2015年 | 7652篇 |
2014年 | 9560篇 |
2013年 | 11521篇 |
2012年 | 12684篇 |
2011年 | 13435篇 |
2010年 | 11565篇 |
2009年 | 10930篇 |
2008年 | 10508篇 |
2007年 | 9751篇 |
2006年 | 9842篇 |
2005年 | 8438篇 |
2004年 | 5655篇 |
2003年 | 4624篇 |
2002年 | 4083篇 |
2001年 | 3713篇 |
2000年 | 3665篇 |
1999年 | 4167篇 |
1998年 | 3439篇 |
1997年 | 2920篇 |
1996年 | 2718篇 |
1995年 | 2195篇 |
1994年 | 1770篇 |
1993年 | 1280篇 |
1992年 | 1032篇 |
1991年 | 764篇 |
1990年 | 555篇 |
1989年 | 454篇 |
1988年 | 358篇 |
1987年 | 237篇 |
1986年 | 195篇 |
1985年 | 122篇 |
1984年 | 108篇 |
1983年 | 76篇 |
1982年 | 80篇 |
1981年 | 65篇 |
1980年 | 61篇 |
1979年 | 30篇 |
1978年 | 25篇 |
1977年 | 24篇 |
1976年 | 26篇 |
1975年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
集中供热优化节能自动控制系统的特点 总被引:1,自引:0,他引:1
国家十一五规划中明确指出:五年内节能20%。根据供热系统耗能比重和现状,集中供热的节能潜力非常大。安装优化节能集中供热控制系统,并依此提高运行管理水平,可取得事半功倍的节能效果。基于多年持久的调查、研究、试验、产品开发和实际应用,我们体会到:只有从集中供热的特点出发,才能使集中供热控制系统既可靠又简单、价低,达到既确保人体舒适又真正节能的目标。本文将对集中供热优化节能控制系统在热力学模型、计算机控制方案、节能效果、可靠性和软硬件选择原则等方面的特点进行介绍。 相似文献
995.
A Single-Die 124 dB Stereo Audio Delta-Sigma ADC With 111 dB THD 总被引:1,自引:0,他引:1
This paper presents a highly power-efficient stereo delta-sigma ADC designed for high-precision applications, with measured inter-channel isolation over 130 dB. This design adopts a single-loop, fifth-order, 33 level analog modulator with positive and negative feedforward paths. An interpolated multilevel quantizer with unevenly weighted quantization levels replaces a conventional 5-bit flash type quantizer. These new techniques suppress signal dependent energy inside the delta-sigma loop, reduce internal channel coupling and power consumption. Manufactured in 0.35 mum double poly, three metal CMOS process, the single-die chip includes two analog modulators, on-chip bandgap reference circuit, decimation filter and serial interface circuits. The core die area is around 14.8 mm2. The ADC achieves 124 dB dynamic range (A-weighted), -111 dB THD over 20 kHz bandwidth. Total power consumption is less than 330 mW. 相似文献
996.
超低碳奥氏体不锈钢00Cr18Ni10还原脱磷研究 总被引:1,自引:0,他引:1
在 2 5kg真空感应炉上用镁钙合金对超低碳奥氏体不锈钢 0 0Cr18Ni10进行了还原脱磷试验。通过充入工业纯氩使炉内压力为 6 6 .6 6kPa和精炼时的反应温度 14 5 0~ 15 0 0℃ ,加入镁钙合金 5 0kg t和助熔剂CaF2 11kg t,可使精炼后 0 0Cr18Ni10的磷含量进一步降低到 (5 0~ 6 0 )× 10 - 6 ,钢中氧、硫含量分别稳定降到(4~ 6 )× 10 - 6 和 15× 10 - 6 。 相似文献
997.
A thin film of poly(l-serine) was prepared via electropolymerization for the determination of trace levels of estradiol. In pH 5.0 phosphate buffer,
l-serine was oxidized during the cyclic potential sweeps between −0.60 and 2.0 V, forming a thin film at the electrode surface.
The electrochemical behavior of estradiol was investigated. The oxidation peak potential of estradiol shifts negatively at
the poly(l-serine) film-coated glassy carbon electrode (GCE) compared with that at the bare GCE. Otherwise, the oxidation peak current
greatly increases at the poly(l-serine) film-modified GCE. These phenomena suggest that the poly(l-serine) film exhibits catalytic activity towards the electrochemical oxidation of estradiol. Based on this, a sensitive,
rapid and simple electrochemical method was proposed for the determination of estradiol. The limit of detection is evaluated
to be 2.0 × 10−8 mol L−1. Finally, this method was successfully used to determine estradiol in blood serum. 相似文献
998.
The long‐term thermal‐oxidative aging behavior of polyamide 6 (PA6) was studied by comparison with the stabilized sample in this work. The variation of mechanical properties of the pure and the stabilized samples of PA6 with aging time at 110°C, 130°C, and 150°C were investigated, respectively. The aging mechanism of PA6 under heat and oxygen was studied in terms of the reduced viscosity, crystallization behavior, dynamic mechanical behavior, and chemical composition through the methods of polarized light microscopy (PLM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), X‐ray photoelectron energy spectrum (XPS), and so on. The results indicated that at the initial stage of aging, the molecular crosslinking reaction of PA6 dominated resulting in the increase of the mechanical strength, reduced viscosity, and the glass transition temperature of the sample. And the molecular degradation dominated in the subsequent aging process resulting in the decrease of the melting temperature, the increase of the crystallinity, and the formation of the oxides and peroxides products. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
999.
Biphenol monoacrylate (AL) was combined with a traditional hindered phenolic‐based binary antioxidant system to form a ternary stabilization system for the purpose of further improving the thermal–oxidative stability of polyamide 6 (PA6). The thermal stabilization effect of the antioxidant AL on PA6 was studied in terms of the reduced viscosity, the chemical structure, the yellow index, and the mechanical properties. The results showed that the antioxidant AL, with the proper chemical structure, could improve the thermal stability of PA6 effectively through a unique bifunctional stabilizing mechanism. The interaction of the molecules of PA6 with the antioxidant AL was investigated. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
1000.
Using nickel-2,2′-dipyridyl complex as a template, N-vinyl-2-pyrrolidone as the metal coordination functional monomer, and ethylene glycol dimethacrylate as the crosslinker, polyvinylidene fluoride (PVDF) hollow fiber ultrafiltration membrane as the supported membrane, metal complex imprinted polymeric membranes were prepared. The association constant of template-monomer interaction in the prepolymerization solution was estimated to be 4.38 × 104 (L/mol)2 by spectrophotometric titration analysis. The attenuated total reflection Fourier transform infrared spectroscopy and scanning electron micrograph characterization indicated that the surface of the support PVDF membrane was completely coated by the imprinted polymer layer after modification. The imprinted membranes exhibited the selective permeability for the template in certain nickel acetate solution. The molecularly imprinted membranes gave higher permeation separation factors at about pH 6, whereas increasing pressure would lower the separation ability. The effects of ion concentration, cations and counterions, ligand selectivity, pH, and trans-membrane pressure were investigated and the permeation performances of the imprinted membranes could be regarded as facilitated transport mechanism. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献