首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   195834篇
  免费   2650篇
  国内免费   597篇
电工技术   3412篇
综合类   145篇
化学工业   27212篇
金属工艺   7969篇
机械仪表   5943篇
建筑科学   4625篇
矿业工程   1300篇
能源动力   5065篇
轻工业   16683篇
水利工程   2288篇
石油天然气   4014篇
武器工业   8篇
无线电   22903篇
一般工业技术   39511篇
冶金工业   37224篇
原子能技术   5078篇
自动化技术   15701篇
  2021年   1475篇
  2019年   1562篇
  2018年   2567篇
  2017年   2644篇
  2016年   2766篇
  2015年   1782篇
  2014年   3063篇
  2013年   8925篇
  2012年   5040篇
  2011年   7011篇
  2010年   5580篇
  2009年   6318篇
  2008年   6397篇
  2007年   6476篇
  2006年   5542篇
  2005年   5185篇
  2004年   4973篇
  2003年   4824篇
  2002年   4283篇
  2001年   4405篇
  2000年   4254篇
  1999年   4460篇
  1998年   11129篇
  1997年   7916篇
  1996年   6146篇
  1995年   4636篇
  1994年   4237篇
  1993年   4042篇
  1992年   3175篇
  1991年   3037篇
  1990年   2832篇
  1989年   2907篇
  1988年   2788篇
  1987年   2360篇
  1986年   2279篇
  1985年   2685篇
  1984年   2464篇
  1983年   2304篇
  1982年   2048篇
  1981年   2175篇
  1980年   2003篇
  1979年   2094篇
  1978年   2095篇
  1977年   2343篇
  1976年   3162篇
  1975年   1814篇
  1974年   1736篇
  1973年   1756篇
  1972年   1434篇
  1971年   1320篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Photonic Network Communications - In the present work, a high-speed optical encoder is proposed based on two-dimensional photonic crystal ring resonator using coupled mode theory and resonance...  相似文献   
2.
Journal of Materials Science: Materials in Electronics - Non-volatile organic memory devices were fabricated using polystyrene sulfonate (PSS)?+?nitrogen-doped multi-walled carbon...  相似文献   
3.

InN thin films are grown on sapphire substrates by remote plasma-assisted metal organic chemical vapor deposition while varying the indium pulse length and substrate temperature. The effects of the indium pulse length and temperature on the structural, morphological, electronic, and optical properties of the thin films are studied. The structural parameters are determined by X-ray diffraction and X-ray photoelectron spectroscopy and the effects of incorporating oxygen atoms in the structure is described. The N K-edge X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) measurements are used to determine the band gap and it is found to be 1.80?±?0.25 eV for all samples. A complementary measurement namely, X-ray excited optical luminescence measurement is performed to confirm the band gap value obtained from XAS and XES measurements. O K-edge XAS measurements are performed to determine the presence of oxygen impurities in the samples. Meanwhile, we carry out the density functional theory calculations for Wurtzite InN, hypothetical Wurtzite-type InO0.5N0.5, and InO0.0625N0.9375 structures. We find that the measured N-edge spectra agree well with our Wurtzite InN calculations and the measured O K-edge spectra agree better with hypothetical Wurtzite-type InO0.0625N0.9375 than Wurtzite-type InO0.5N0.5.

  相似文献   
4.
The present article investigates the influence of Joule heating and chemical reaction on magneto Casson nanofluid phenomena in the occurrence of thermal radiation through a porous inclined stretching sheet. Consideration is extended to heat absorption/generation and viscous dissipation. The governing partial differential equations were transformed into nonlinear ordinary differential equations and numerically solved using the Implicit Finite Difference technique. The article analyses the effect of various physical flow parameters on velocity, heat, and mass transfer distributions. For the various involved parameters, the graphical and numerical outcomes are established. The analysis reveals that the enhancement of the radiation parameter increases the temperature and the chemical reaction parameter decreases the concentration profile. The empirical data presented were compared with previously published findings.  相似文献   
5.
We considered the magnetohydrodynamic (MHD) free convective flow of an incompressible electrically conducting viscous fluid past an infinite vertical permeable porous plate with a uniform transverse magnetic field, heat source and chemical reaction in a rotating frame taking Hall current effects into account. The momentum equations for the fluid flow during absorbent medium are controlled by the Brinkman model. Through the undisturbed state, both the plate and fluid are in a rigid body rotation by the uniform angular velocity perpendicular to an infinite vertical plate. The perpendicular surface is subject to the homogeneous invariable suction at a right angle to it and the heat on the surface varies about a non-zero unvarying average whereas the warmth of complimentary flow is invariable. The systematic solutions of the velocity, temperature, and concentration distributions are acquired systematically by utilizing the perturbation method. The velocity expressions consist of steady-state and fluctuating situations. It is revealed that the steady part of the velocity field has a three-layer characteristic while the oscillatory part of the fluid field exhibits a multi-layer characteristic. The influence of various governing flow parameters on the velocity, temperature, and concentration are analyzed graphically. We also discuss computational results for the skin friction, Nusselt number, and Sherwood number in the tabular forms.  相似文献   
6.
Journal of Materials Science - For decades, a wide variety of products have benefitted from the use of flexible PVC, ranging from healthcare to cable to packaging & household items. The...  相似文献   
7.
The thermodynamics modeling of a Reiner–Philippoff-type fluid is essential because it is a complex fluid with three distinct probable modifications. This fluid model can be modified to describe a shear-thinning, Newtonian, or shear-thickening fluid under varied viscoelastic conditions. This study constructs a mathematical model that describes a boundary layer flow of a Reiner–Philippoff fluid with nonlinear radiative heat flux and temperature- and concentration-induced buoyancy force. The dynamical model follows the usual conservation laws and is reduced through a nonsimilar group of transformations. The resulting equations are solved using a spectral-based local linearization method, and the accuracy of the numerical results is validated through the grid dependence and convergence tests. Detailed analyses of the effects of specific thermophysical parameters are presented through tables and graphs. The study reveals, among other results, that the buoyancy force, solute and thermal expansion coefficients, and thermal radiation increase the overall wall drag, heat, and mass fluxes. Furthermore, the study shows that amplifying the space and temperature-dependent heat source parameters allows fluid particles to lose their cohesive force and, consequently, maximize flow and heat transfer.  相似文献   
8.
Wireless Personal Communications - Since the last decade, cloud-based Electronic Health Records (EHRs) have achieved important consideration to facilitate remote access of patient medical records....  相似文献   
9.
The study aims to evaluate the technological properties of autochthonous strains (Lactobacillus sakei S15, Lactobacillus plantarum S24, L. plantarum S91, Pediococcus pentosaceus S128b and Staphylococcus carnosus G109) in Turkish dry fermented sausage (sucuk). After 24 h of fermentaPtion, all lactic acid bacteria strains reduced the pH to below 5.0, while the pH in the control group was above 5.3. The number of lactic acid bacteria strains reached 108–109 cfu g−1 during fermentation. Staphylococcus carnosus G109 remained at the inoculation level of 106 cfu g−1 during ripening. Lactobacillus sakei S15 as mono-culture showed higher TBARS values compared to other strains. The control group had the lowest L* value and autochthonous strains caused no significant difference for a* value. According to principal component analysis results, most volatile compounds were positively correlated with the group containing only L. sakei S15.  相似文献   
10.
Wireless Personal Communications - In this paper, modeling of rain drop size distribution (DSD) and analysis of rain-induced attenuation are analyzed based on Gamma DSD model in a tropical...  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号