全文获取类型
收费全文 | 15095篇 |
免费 | 1386篇 |
国内免费 | 1164篇 |
专业分类
电工技术 | 320篇 |
综合类 | 604篇 |
化学工业 | 3054篇 |
金属工艺 | 1781篇 |
机械仪表 | 2193篇 |
建筑科学 | 238篇 |
矿业工程 | 103篇 |
能源动力 | 261篇 |
轻工业 | 738篇 |
水利工程 | 37篇 |
石油天然气 | 206篇 |
武器工业 | 90篇 |
无线电 | 2909篇 |
一般工业技术 | 3367篇 |
冶金工业 | 356篇 |
原子能技术 | 1049篇 |
自动化技术 | 339篇 |
出版年
2024年 | 34篇 |
2023年 | 261篇 |
2022年 | 337篇 |
2021年 | 470篇 |
2020年 | 455篇 |
2019年 | 473篇 |
2018年 | 425篇 |
2017年 | 529篇 |
2016年 | 513篇 |
2015年 | 480篇 |
2014年 | 606篇 |
2013年 | 904篇 |
2012年 | 842篇 |
2011年 | 1128篇 |
2010年 | 797篇 |
2009年 | 832篇 |
2008年 | 907篇 |
2007年 | 894篇 |
2006年 | 822篇 |
2005年 | 740篇 |
2004年 | 622篇 |
2003年 | 565篇 |
2002年 | 523篇 |
2001年 | 344篇 |
2000年 | 375篇 |
1999年 | 328篇 |
1998年 | 297篇 |
1997年 | 296篇 |
1996年 | 276篇 |
1995年 | 214篇 |
1994年 | 162篇 |
1993年 | 153篇 |
1992年 | 154篇 |
1991年 | 131篇 |
1990年 | 122篇 |
1989年 | 113篇 |
1988年 | 82篇 |
1987年 | 71篇 |
1986年 | 68篇 |
1985年 | 63篇 |
1984年 | 74篇 |
1983年 | 54篇 |
1982年 | 57篇 |
1981年 | 11篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 3篇 |
1959年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
151.
152.
Thin film of Ti-Ni alloy has a potential to perform the microactuation functions required in the microelectromechanical system (MEMS).It is essential, however, to have good uniformity in both chemical composition and thickness to realize its full potential as an active component of MEMS devices.Electron beam evaporation technique was employed in this study to fabricate the thin films of Ti-Ni alloy on different substrates.The targets used for the evaporation were first prepared by electron beam melting.The uniformity of composition and microstructure of the thin films were characterized by electron probe microanalysis (EPMA), Auger electron spectroscopy (AES), X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM).The mechanical property of the thin films was evaluated by the nano-indentation test.The martensitic transformation temperature was measured by differential scanning calorimetry (DSC).It is confirmed that the chemical composition of deposited thin films is identical to that of the target materials.Furthermore, results from depth profiling of the chemical composition variation reveal that the electron beam evaporation process yields better compositional homogeneity than other conventional methods such as sputtering and thermal evaporation.Microstructural observation by TEM shows that nanometer size precipitates are preferentially distributed along the grain boundaries of a few micron size grains.The hardness and elastic modulus of thin films decreases with an increase in Ti contents. 相似文献
153.
近年来,新开发的电子背散射衍射技术将多晶材料的显微组织、微区成分与结晶学数据分析联系起来,能对晶界类型、取向、位向差和结构及其分布进行观察、统计测定和定量分析,从而建立了晶界结构、取向和织构等与多晶材料性能的定量和半定量关系,成为现代材料研究的重要实验技术。笔者结合低碳钢生产中的一些实际问题,扼要介绍了电子背散射衍射技术中的晶体取向图在多晶材料显微结构表征中的应用。 相似文献
154.
为了表征二维混凝土的传输过程,制备厚度为1 mm的混凝土薄片. 采用X射线透射成像(TXR)技术,联合扫描电镜、背散射和能谱分析技术(SEM/BSE/EDS)原位追踪水在2维混凝土薄片中的毛细自吸过程. 测试不同质量分数CsCl溶液对X射线透射图像的增强效果. 结果表明,CsCl能够提高吸水过程中混凝土薄片的TXR图像对比度,使得水在混凝土中的渗流路径更清晰、可辨. 水泥浆体在吸收CsCl后,扫描电子背散射图像的对比度显著增强. 不同位置铯原子的EDS能谱结果验证了TXR技术确定吸水前锋位置的准确性. 相似文献
155.
将被焊工件温度模糊控制技术应用于电子束扫描钎焊中,所研发的系统集成了电子束焊接过程控制、电子束扫描轨迹控制、工件温度模糊控制、焊接数据高速采集与存储等多项功能.通过扫描轨迹的编辑与控制,可以适应各种形状曲线钎焊缝的温度场要求;在电子束对工件进行扫描加热的同时,通过温度采集装置实时得到被焊工件的温度信号并与设定值进行对比从而得到温度偏差及偏差的变化率作为模糊控制器的两个输入变量,以模糊控制器输出控制量调节电子束流大小,从而实现钎焊温度的闭环控制.控制系统具有响应速度快、稳定时间短、稳态误差小、超调量小等特点,表明在电子束钎焊过程中采用模糊控制技术可以得到非常理想的控制效果. 相似文献
156.
中压型大功率电子束焊机电控系统的研制 总被引:5,自引:3,他引:5
本文介绍了70kV、30kW电子束焊机电子枪电源──加速电源、灯丝电源、轰击电源和偏压电源的特点及其控制原理。 相似文献
157.
Aleksandra A. Ageeva Ilya M. Magin Alexander B. Doktorov Victor F. Plyusnin Polina S. Kuznetsova Alexander A. Stepanov Alexander A. Alekseev Nikolay E. Polyakov Tatyana V. Leshina 《International journal of molecular sciences》2021,22(12)
The study of the L- and D-amino acid properties in proteins and peptides has attracted considerable attention in recent years, as the replacement of even one L-amino acid by its D-analogue due to aging of the body is resulted in a number of pathological conditions, including Alzheimer’s and Parkinson’s diseases. A recent trend is using short model systems to study the peculiarities of proteins with D-amino acids. In this report, the comparison of the excited states quenching of L- and D-tryptophan (Trp) in a model donor–acceptor dyad with (R)- and (S)-ketoprofen (KP-Trp) was carried out by photochemically induced dynamic nuclear polarization (CIDNP) and fluorescence spectroscopy. Quenching of the Trp excited states, which occurs via two mechanisms: prevailing resonance energy transfer (RET) and electron transfer (ET), indeed demonstrates some peculiarities for all three studied configurations of the dyad: (R,S)-, (S,R)-, and (S,S)-. Thus, the ET efficiency is identical for (S,R)- and (R,S)-enantiomers, while RET differs by 1.6 times. For (S,S)-, the CIDNP coefficient is almost an order of magnitude greater than for (R,S)- and (S,R)-. To understand the source of this difference, hyperpolarization of (S,S)-and (R,S)- has been calculated using theory involving the electron dipole–dipole interaction in the secular equation. 相似文献
158.
Solubility measurements of several oxides in molten NaCl-KCl and NaCl-KCl-Na2SO4-K2SO4 were conducted in three different levels of basicity. The dissolution behavior of the oxides showed almost the same tendency as that shown by the dissolution behavior of the oxides in molten Na2SO4 in literature. In a waste incineration environment, a protective Cr2O3 film easily dissolves in molten chlorides as CrO42− because pO2− of the molten chlorides tends to have a small value due to the effect of water vapor contained in the combustion gas. From the result of the solubility measurement, the addition of molybdenum and/or silicon was expected to improve the corrosion resistance of alloys. Laboratory corrosion tests confirmed this expectation. However, the scale analysis suggested that the effect of molybdenum could not be explained completely by only the mechanism derived from the result of the solubility measurement. 相似文献
159.
The effects of α and β phase interactions on the tensile and creep deformation behavior of β titanium alloys was studied using
Ti-6.0wt.% Mn and Ti-8.1wt.%V as the model two-phase alloys, and Ti-13.0wt.%Mn and Ti-14.8wt.%V as the single-phase β alloys.
The β phase of α-βTi-8.1V deforms by stress-induced hexagonal martensite (α′), while slip and twinning occurs in the single-phase
β alloy with the same chemistry as the β phase. No stress-induced martensite was observed in the β or α-βTi-Mn alloys. This
behavior is modeled in terms of a number of factors, including elastic interaction stresses between the α and β phases, coherency
between the α phase and hexagonal martensite, and β phase stability.
This paper was presented at the Beta Titanium Alloys of the 00’s Symposium sponsored by the Titanium Committee of TMS, held
during the 2005 TMS Annual Meeting & Exhibition, February 13–16, 2005 in San Francisco, CA. 相似文献
160.
The physical metallurgy underlying the development of cast microstructures in abrasion resistant high chromium cast irons, and their structural modification by thermal treatments is relatively complex. Structural characterisation via electron microscopy therefore has a key role to play in furthering our understanding of the phase transformations that control the microstructures and hence the service performances of these irons as wear parts. This paper shows how both scanning and especially transmission electron microscopy can provide valuable information on the nature of eutectic and secondary carbides and on the matrix structures in these irons. Particular attention is given to current characterisation research on conventionally cast 30%Cr irons that are used for applications involving corrosive wear e.g. slurry pumps and on a semi-solid cast 27%Cr iron that has a potential for applications in industry. 相似文献