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   18773篇
  免费   958篇
  国内免费   137篇
电工技术   326篇
综合类   27篇
化学工业   4018篇
金属工艺   601篇
机械仪表   638篇
建筑科学   374篇
矿业工程   45篇
能源动力   1358篇
轻工业   1184篇
水利工程   147篇
石油天然气   85篇
武器工业   1篇
无线电   2344篇
一般工业技术   4350篇
冶金工业   1445篇
原子能技术   175篇
自动化技术   2750篇
  2024年   23篇
  2023年   419篇
  2022年   867篇
  2021年   1132篇
  2020年   917篇
  2019年   959篇
  2018年   1238篇
  2017年   969篇
  2016年   951篇
  2015年   615篇
  2014年   852篇
  2013年   1524篇
  2012年   901篇
  2011年   1089篇
  2010年   869篇
  2009年   817篇
  2008年   720篇
  2007年   574篇
  2006年   476篇
  2005年   366篇
  2004年   271篇
  2003年   242篇
  2002年   185篇
  2001年   164篇
  2000年   151篇
  1999年   148篇
  1998年   268篇
  1997年   221篇
  1996年   199篇
  1995年   168篇
  1994年   156篇
  1993年   152篇
  1992年   101篇
  1991年   124篇
  1990年   98篇
  1989年   97篇
  1988年   79篇
  1987年   88篇
  1986年   74篇
  1985年   84篇
  1984年   73篇
  1983年   71篇
  1982年   60篇
  1981年   70篇
  1980年   48篇
  1979年   31篇
  1978年   27篇
  1977年   27篇
  1976年   35篇
  1975年   13篇
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
61.
Application of brown titanium dioxide (TiO2-x) and its modified composite forms in the photocatalytic decomposition of organic pollutants in the environment is a promising way to provide solutions for environmental redemption. Herein, we report the synthesis of effective and stable TiO2-x nanoparticles with g-C3N4, RGO, and multiwalled carbon nanotubes (CNTs) using a simple hydrothermal method. Among all the as-synthesized samples, excellent photocatalytic degradation activity was observed for RGO-TiO2-x nanocomposite with high rate constants of 0.075 min?1, 0.083 min?1 and 0.093 min?1 for methylene blue, rhodamine-B, and rosebengal dyes under UV–Visible light irradiation, respectively. The altered bandgap (1.8 eV) and the large surface area of RGO-TiO2-x nanocomposite impacts on both absorption of visible light and efficiency of photogenerated charge electron (e?)/hole (h+) pair separation. This resulted in enhanced photocatalytic property of carbon-based TiO2-x nanocomposites. A systematic study on the influence of different carbon nanostructures on the photocatalytic activity of brown TiO2-x is carried out.  相似文献   
62.
Telecommunication Systems - Wireless sensor networks (WSNs) and Internet of Things domain comprise of numerous small sized battery powered sensor nodes. Energy efficiency and energy balancing are...  相似文献   
63.
In the present study we made an effort to deploy eco-friendly synthesized reduced graphene oxide/Lanthanum Alluminate nanocomposites (RGO-LaAlO3) and Lanthanum Alluminate (LaAlO3) as adsorbents to remove dye from the synthetic media. XRD, SEM, BET surface area and EDX have been used to characterize the above-mentioned adsorbents. The impacts of different factors like adsorbent dosage, the concentration of adsorbate and PH on adsorption were studied. The best fit linear and nonlinear equations for the adsorption isotherms and kinetic models had been examined. The sum of the normalized errors and the coefficient of determination were used to determine the best fit model. The experimental data were more aptly fitted for nonlinear forms of isotherms and kinetic equations. Pseudo-second-order and Freundlich isotherm model fits the equilibrium data satisfactorily. Methyl orange (MO) has been used as model dye pollutant and maximum adsorption capacity was found to be 469.7 and 702.2 mg g?1 for LaAlO3 and RGO-LaAlO3, respectively.  相似文献   
64.
In liver surgery, biliary obstruction can lead to secondary biliary cirrhosis, a life-threatening disease with liver transplantation as the only curative treatment option. Mesenchymal stromal cells (MSC) have been shown to improve liver function in both acute and chronic liver disease models. This study evaluated the effect of allogenic MSC transplantation in a large animal model of repeated biliary obstruction followed by partial hepatectomy. MSC transplantation supported the growth of regenerated liver tissue after 14 days (MSC group, n = 10: from 1087 ± 108 (0 h) to 1243 ± 92 mL (14 days); control group, n = 11: from 1080 ± 95 (0 h) to 1100 ± 105 mL (14 days), p = 0.016), with a lower volume fraction of hepatocytes in regenerated liver tissue compared to resected liver tissue (59.5 ± 10.2% vs. 70.2 ± 5.6%, p < 0.05). Volume fraction of connective tissue, blood vessels and bile vessels in regenerated liver tissue, serum levels of liver enzymes (AST, ALT, ALP and GGT) and liver metabolites (albumin, bilirubin, urea and creatinine), as well as plasma levels of IL-6, IL-8, TNF-α and TGF-β, were not affected by MSC transplantation. In our novel, large animal (pig) model of repeated biliary obstruction followed by partial hepatectomy, MSC transplantation promoted growth of liver tissue without any effect on liver function. This study underscores the importance of translating results between small and large animal models as well as the careful translation of results from animal model into human medicine.  相似文献   
65.
Kumar  Bhavya  Chaujar  Rishu 《SILICON》2021,13(3):919-927
Silicon - This work presents the analog and RF performance evaluation of Junctionless Accumulation Mode (JAM) Gate Stack Gate All Around (GS-GAA) FinFET, and the results acquired have been compared...  相似文献   
66.
Journal of Chemical Ecology - The Oriental fruit fly, Bactrocera dorsalis (Hendel) is an economically devastating pest of fruit crops across the globe with stringent quarantine restrictions to...  相似文献   
67.
68.
Singh  A. K.  Chandra  Devesh  Kattayat  Sandhya  Kumar  Shalendra  Alvi  P. A.  Rathi  Amit 《Semiconductors》2019,53(12):1584-1592
Semiconductors - Compositional variations in GaAs based ternary alloys have exhibited wide range alterations in electronic properties. In the present paper, first-principles study of...  相似文献   
69.
A flower‐shaped ultra‐wideband fractal antenna is presented. It comprises a fourth iterative flower‐shaped radiator, asymmetrical stub‐loaded feeding line, and coplanar quarter elliptical ground planes. A wide operating band of 12.12 GHz (4.58‐16.7 GHz) for S 11 ≤ ? 10 dB is achieved along with an overall antenna footprint of 15.7 × 11.4 mm2. In addition, other desirable characteristics, that is, omnidirectional radiation patterns, peak gain upto 5 dB, and fidelity factor more than 75% are achieved. A good agreement exists between the simulation and measured results. The obtained results illustrate that this antenna has wide operating range and compact dimensions than available structures.  相似文献   
70.
Type 316LN stainless steel (SS) is the principal structural material for the components of sodium cooled fast reactors operating under elevated temperature conditions. In order to assess the degradation in strength of service exposed components using a small specimen testing technique such as automated ball indentation (ABI), it is necessary to carry out prior detailed ABI studies on the virgin material. In this investigation, the tensile behaviour of as-received 316LN SS were investigated at several temperatures in the range 298–973 K using ABI technique. The load-depth of indentation data measured from ABI tests was analyzed using semi-empirical relationships to obtain the tensile properties. The yield stress and the flow curves were determined by correlating ABI results with corresponding uniaxial tensile test results. Trend curve for tensile strength with temperature, as estimated from ABI tests, exhibited a plateau region in the temperature around 823 K, similar to uniaxial tensile tests. The variations of strength coefficient, strain hardening exponent, yield ratio, hardness and uniform ductility with temperature were evaluated from ABI tests. The ABI technique was found to estimate the influence of temperature on tensile properties sensitively.  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