全文获取类型
收费全文 | 26355篇 |
免费 | 1013篇 |
国内免费 | 163篇 |
专业分类
电工技术 | 431篇 |
综合类 | 35篇 |
化学工业 | 5724篇 |
金属工艺 | 917篇 |
机械仪表 | 821篇 |
建筑科学 | 497篇 |
矿业工程 | 67篇 |
能源动力 | 1683篇 |
轻工业 | 1439篇 |
水利工程 | 214篇 |
石油天然气 | 99篇 |
武器工业 | 1篇 |
无线电 | 3327篇 |
一般工业技术 | 5885篇 |
冶金工业 | 2368篇 |
原子能技术 | 282篇 |
自动化技术 | 3741篇 |
出版年
2024年 | 114篇 |
2023年 | 491篇 |
2022年 | 1119篇 |
2021年 | 1333篇 |
2020年 | 1064篇 |
2019年 | 1066篇 |
2018年 | 1429篇 |
2017年 | 1137篇 |
2016年 | 1128篇 |
2015年 | 705篇 |
2014年 | 1023篇 |
2013年 | 1929篇 |
2012年 | 1123篇 |
2011年 | 1406篇 |
2010年 | 1118篇 |
2009年 | 1107篇 |
2008年 | 989篇 |
2007年 | 819篇 |
2006年 | 702篇 |
2005年 | 532篇 |
2004年 | 426篇 |
2003年 | 387篇 |
2002年 | 336篇 |
2001年 | 318篇 |
2000年 | 312篇 |
1999年 | 293篇 |
1998年 | 578篇 |
1997年 | 426篇 |
1996年 | 367篇 |
1995年 | 317篇 |
1994年 | 259篇 |
1993年 | 287篇 |
1992年 | 220篇 |
1991年 | 242篇 |
1990年 | 197篇 |
1989年 | 191篇 |
1988年 | 161篇 |
1987年 | 163篇 |
1986年 | 158篇 |
1985年 | 185篇 |
1984年 | 164篇 |
1983年 | 159篇 |
1982年 | 132篇 |
1981年 | 127篇 |
1980年 | 97篇 |
1979年 | 79篇 |
1978年 | 78篇 |
1977年 | 92篇 |
1976年 | 121篇 |
1975年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
51.
A systematic investigation was undertaken to measure the solubility of Y2O3 in several LiF-YF2 melts, with the YF3 composition ranging from 20 to 50 mole pct, in the temperature range of 998 to 1273 K. Experimental results showed that the
solubility of Y2O4 in the melts increased with increase in temperature and also with increased YF3 content. The activity of Y2O3 was calculated using the free energy of fusion of Y2O3,
. The
was deduced from the values of enthalpy, heat of fusion, and melting point of Y2O3. From the known values of activity, the activity coefficients of Y2O3 as a function of temperature and melt composition were calculated. Considering the ionic nature of the melt, activity coefficients
were also calculated using Temkin’s ideal mixing and electrically equivalent fraction methods. The thermodynamic data, such
as integral molar enthalpy, entropy, and free energy of formation, were calculated as a function of composition and temperature.
The calculated thermodynamic data showed that the melt exhibited a negative deviation from ideal conditions. 相似文献
52.
This article analyzes the transmission line characteristics of plasmonic hybrid metal insulator metal (HMIM) waveguide, circular ring resonator (CRR) based dual-band band-pass filters with two transmission poles in both pass-bands in the optical regime using coupled line feed. The transmission line characteristics of an HMIM waveguide, such as characteristic impedance (ZPV), effective refractive index (neff) and propagation length (Lspp), have been obtained by using full wave simulation. Using basic HMIM slot waveguide, a CRR with periodic loading of double- and triple-ring CRR is numerically analyzed. Two input ports have been used for excitation, which are located at the separation of 180° positions along the CRR, and are coupled with the ring by parallel coupled lines, producing the dual pass-bands with the synchronous excitation of two transmission poles. The proposed double-ring dual-band band-pass filter (DR-DB-BPF) offers 35 dB extinction ratio (ER), 299.69 nm free spectral range (FSR) and narrow band full width half maximum (FWHM) of 78.057—112.43 nm. The triple-ring DB-BPF (TR-DB-BPF) has 22.5 dB ER, FSR of 292.18 nm and FWHM of 42.751—59.58 nm. The proposed filters are very useful in the development of dual-band filters for electronic photonic integrated circuits (EPICs), as the optical signals are filtered at two wavelengths simultaneously. 相似文献
53.
Baranwal Alok Kumar Sharma Shashibhushan Roy Sanjay Dhar Kundu Sumit 《Wireless Personal Communications》2022,124(2):1281-1296
Wireless Personal Communications - This paper proposes and analyses the power allocation coefficient normalization for successive interference cancellation in power-domain non-orthogonal multiple... 相似文献
54.
Journal of Communications Technology and Electronics - A Compact U-shaped multiple-inputs and multiple-output (MIMO)-antenna with dimensions of 23 × 47 mm2 has been proposed for... 相似文献
55.
The present article is concerned with the investigation of disturbances in a homogeneous transversely isotropic thermoelastic rotating medium with two temperatures, in the presence of the combined effects of Hall currents and magnetic field. The formulation is applied to the thermoelasticity theories developed by Green-Naghdi theories of type-II and type-III. Laplace and Fourier transform techniques are applied to solve the problem. The analytical expressions of displacements, stress components, temperature change, and current density components are obtained in the transformed domain. A numerical inversion technique has been applied to obtain the results in the physical domain. Numerical simulated results are depicted graphically to show the effect of Hall current and two temperatures on resulting quantities. Some special cases are also deduced from the present investigation. 相似文献
56.
Sanjay Sahare Ravi Kant Choubey Gurunath Jadhav Tejashree M. Bhave Samrat Mukherjee Sunil Kumar 《Journal of Superconductivity and Novel Magnetism》2017,30(6):1439-1446
In this report, we studied various structural and optical properties of pure and copper-doped cadmium oxide (CdO) thin films. Nanostructured Cu-doped CdO films were deposited using sol–gel spin-coating technique. The structural and morphological changes have been observed by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM) studies. The optical and electrical properties of the pure and Cu-doped CdO thin films were studied by UV–vis spectroscopy and four-point probe method, respectively. The XRD peaks show the formation of nanocrystalline CdO with cubic face-centered crystal structure. The band gaps of the as deposited films were found in the range of 2.32–2.73 eV, while after doping, it decreases due to structural deformation. The electrical resitivity was found to decrease approximately ~10 in Cu-doped CdO thin films. 相似文献
57.
Microfluidics: Inertial Microfluidic Cell Stretcher (iMCS): Fully Automated,High‐Throughput,and Near Real‐Time Cell Mechanotyping (Small 28/2017) 下载免费PDF全文
58.
59.
Ravi Shanker Vidyarthy Dheerendra Kumar Dwivedi Vasudevan Muthukumaran 《Materials and Manufacturing Processes》2018,33(7):709-717
In the present work, the influence of process parameters such as welding current (I), welding speed (S), and flux coating density (F) on different aspects of weld bead geometry for example depth of penetration (DOP), bead width (BW), depth to width ratio (D/W), and weld fusion zone area (WA) were investigated by using the central composite design (CCD). 9–12% Cr ferritic stainless steel (FSS) plates were welded using A-TIG welding. It was observed that all input variables have a direct influence on the DOP, BW, and D/W. However, flux coating density has no significant effect on WA. Mathematical models were generated from the obtained responses to predict the weld bead geometry. An optimized DOP, BW, D/W, and WA of 6.95?mm, 8.76?mm, 0.80, and 41.99?mm2, respectively, were predicted at the welding current of 213.78 A, the welding speed of 96.22?mm/min, and the flux coating density of 1.99?mg/cm2. Conformity test was done to check the practicability of the developed models. The conformity test results were in good agreement with the predicted values. Arc constriction and reversal in Marangoni convection were considered as major mechanisms for the deep and narrow weld bead during A-TIG welding. 相似文献
60.