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   1159602篇
  免费   16641篇
  国内免费   3161篇
电工技术   20804篇
综合类   1072篇
化学工业   177432篇
金属工艺   44206篇
机械仪表   34583篇
建筑科学   28881篇
矿业工程   6633篇
能源动力   30735篇
轻工业   98467篇
水利工程   12283篇
石油天然气   22684篇
武器工业   73篇
无线电   128976篇
一般工业技术   224404篇
冶金工业   221637篇
原子能技术   23820篇
自动化技术   102714篇
  2021年   10053篇
  2020年   7614篇
  2019年   9402篇
  2018年   15960篇
  2017年   15887篇
  2016年   17052篇
  2015年   11517篇
  2014年   18986篇
  2013年   53488篇
  2012年   29915篇
  2011年   41587篇
  2010年   33229篇
  2009年   37152篇
  2008年   38173篇
  2007年   37601篇
  2006年   33083篇
  2005年   30316篇
  2004年   29010篇
  2003年   28498篇
  2002年   27500篇
  2001年   26989篇
  2000年   25500篇
  1999年   26545篇
  1998年   65587篇
  1997年   47019篇
  1996年   36433篇
  1995年   27583篇
  1994年   24460篇
  1993年   24047篇
  1992年   17757篇
  1991年   16819篇
  1990年   16634篇
  1989年   16205篇
  1988年   15442篇
  1987年   13698篇
  1986年   13384篇
  1985年   15420篇
  1984年   14176篇
  1983年   13169篇
  1982年   12116篇
  1981年   12436篇
  1980年   11709篇
  1979年   11574篇
  1978年   11273篇
  1977年   13257篇
  1976年   17320篇
  1975年   10002篇
  1974年   9502篇
  1973年   9677篇
  1972年   8106篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Fire spread and growth on real‐scale four cushion mock‐ups of residential upholstered furniture (RUF) were investigated with the goal of identifying whether changes in five classes of materials (barrier, flexible polyurethane foam, polyester fiber wrap, upholstery fabric, and sewing thread), referred to as factors, resulted in statistically significant changes in burning behavior. A fractional factorial experimental design plus practical considerations yielded a test matrix with 20 material combinations. Experiments were repeated a minimum of two times. Measurements included fire spread rates derived from video recordings and heat release rates (HRRs). A total of 13 experimental parameters (3 based on the videos and 10 on the HRR results), referred to as responses, characterized the measurements. Statistical analyses based on Main Effects Plots (main effects) and Block Plots (main effects and factor interactions) were used. The results showed that three of the factors resulted in statistically significant effects on varying numbers of the 13 responses. The Barrier and Fabric factors had the strongest main effects with roughly comparable magnitudes. Foam was statistically significant for fewer of the responses and its overall strength was weaker than for Barrier and Fabric. No statistically significant main effects were identified for Wrap or Thread. Multiple two‐term interactions between factors were identified as being statistically significant. The Barrier*Fabric interaction resulted in the highest number of and strongest statistically significant effects. The existence of two‐term interactions means that it will be necessary to consider their effects in approaches designed to predict the burning behavior of RUF.  相似文献   
42.
Theoretical Foundations of Chemical Engineering - Using gas–liquid chromatography, the activity coefficients upon the infinite dilution of the components of the reaction mixture for obtaining...  相似文献   
43.
Ceria-based solid solutions are important materials for high- and medium-temperature electrochemical applications. However, the stabilities of both binary and ternary ceria-based solid solutions are insufficient at elevated temperatures, which limits their application as solid electrolytes or SOFC cathodes. Data on the high-temperature stability of ceria-based ceramics are unavailable in the literature. In the present study, we report a thermodynamic stability investigation of Y2O3-CeO2 and Y2O3-ZrO2-CeO2 solid solutions. The thermal prehistories of binary and ternary systems were investigated using STA, XRD, and ESCA techniques. The vaporization processes were investigated in the temperature range of 1577–2227°С via the Knudsen effusion mass spectrometry technique. Using data on the component activity in solid-phase thermodynamic properties of Y2O3-CeO2 solid solutions, which is represented as the Gibbs energy, the excess Gibbs energy was calculated as a function of the ceria mol. %. It was shown that the reduction of Ce4+ to Ce3+ in Y2O3-CeO2 and Y2O3-ZrO2-CeO2 solid solutions corresponds to less-negative Gibbs energy compared to ZrO2-CeO2 solid solutions.  相似文献   
44.
Theoretical Foundations of Chemical Engineering - The main approaches to developing a reactor block for the hydrodesulfurization of diesel fuels are considered taking into account the reactivity of...  相似文献   
45.
Mobile Networks and Applications - Blockchain applications have continuously improved ever since its first debut on cryptocurrency. From then on, its uses have branched out from the financial...  相似文献   
46.
Journal of Signal Processing Systems - Convolutional Neural Networks (CNNs) have improved several computer vision applications, like object detection and classification, when compared to other...  相似文献   
47.
The phospholipid composition of lipoproteins is determined by the specificity of hepatic phospholipid biosynthesis. Plasma phospholipid 20:4n-6 and 22:6n-3 concentrations are higher in women than in men. We used this sex difference in a lipidomics analysis of the impact of endocrine factors on the phospholipid class and molecular species composition of fasting plasma from young men and women. Diester species predominated in all lipid classes measured. 20/54 Phosphatidylcholine (PtdCho) species were alkyl ester, 15/48 phosphatidylethanolamine (PtdEtn) species were alkyl ester, and 12/48 PtdEtn species were alkenyl ester. There were no significant differences between sexes in the proportions of alkyl PtdCho species. The proportion of alkyl ester PtdEtn species was greater in women than men, while the proportion of alkenyl ester PtdEtn species was greater in men than women. None of the phosphatidylinositol (PtdIns) or phosphatidylserine (PtdSer) molecular species contained ether-linked fatty acids. The proportion of PtdCho16:0_22:6, and the proportions of PtdEtn O-16:0_20:4 and PtdEtn O-18:2_20:4 were greater in women than men. There were no sex differences in PtdIns and PtdSer molecular species compositions. These findings show that plasma phospholipids can be modified by sex. Such differences in lipoprotein phospholipid composition could contribute to sexual dimorphism in patterns of health and disease.  相似文献   
48.
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   
49.
Journal of Communications Technology and Electronics - Abstract—The matrix coefficients of projection models of strip lines obtained using the Chebyshev basis are presented as a sum of...  相似文献   
50.
Analog Integrated Circuits and Signal Processing - This paper presents the complete design of a phase locked loop-based clock synthesizer for reconfigurable analog-to-digital converters. The...  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