首页 | 官方网站   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   2881篇
  免费   78篇
  国内免费   9篇
工业技术   2968篇
  2023年   27篇
  2022年   62篇
  2021年   77篇
  2020年   70篇
  2019年   65篇
  2018年   86篇
  2017年   60篇
  2016年   66篇
  2015年   58篇
  2014年   78篇
  2013年   176篇
  2012年   105篇
  2011年   107篇
  2010年   75篇
  2009年   88篇
  2008年   87篇
  2007年   77篇
  2006年   84篇
  2005年   61篇
  2004年   46篇
  2003年   45篇
  2002年   45篇
  2001年   22篇
  2000年   41篇
  1999年   64篇
  1998年   200篇
  1997年   135篇
  1996年   101篇
  1995年   60篇
  1994年   63篇
  1993年   58篇
  1992年   38篇
  1991年   31篇
  1990年   22篇
  1989年   42篇
  1988年   33篇
  1987年   30篇
  1986年   26篇
  1985年   22篇
  1984年   20篇
  1983年   18篇
  1982年   30篇
  1981年   31篇
  1980年   26篇
  1979年   21篇
  1978年   17篇
  1977年   29篇
  1976年   41篇
  1974年   15篇
  1973年   24篇
排序方式: 共有2968条查询结果,搜索用时 15 毫秒
81.
Jatropha curcas is an important non feed crop, increasingly important as a biofuel crop. It is hardy and resistant to different stress conditions in the field. In the wastelands of Gujarat (India), it is being grown for land reclamation and for socio-economic benefits. The long coastline in this state also promotes the growth of a large number of halophytes. Exploiting the genetic resource of Jatropha and halophytes for drought and salt-induced gene is an important area of research. For the isolation of genes and to study the molecular mechanism a good qualitative and quantitative RNA is a prerequisite. Jatropha leaves have latex, and therefore isolating RNA using guanidine thiocyanate or cetyltrimethylammonium bromide did not yield desirable quality of RNA. This paper reports a very simple and economical protocol for the isolation of good quality RNA from Jatropha and a few halophytes. The sodium dodecyl sulphate was used as a detergent for lysis of plant cells in the extraction buffer along with bentonite, which inhibits the ribonuclease’s activity. The addition of water saturated phenol in mortar-pestle, during grinding, facilitated better homogenisation of the tissues. Absolute RNA precipitation was obtained with the help of 2-butoxyethanol. Further this RNA was used successfully in preparation of complementary DNA and subsequently used for gene isolation.  相似文献   
82.
83.
Popat  Y.  Orlandi  M.  Gupta  S.  Bazzanella  N.  Pillai  S.  Patel  M. K.  Miotello  A.  Patel  N. 《Catalysis Letters》2022,152(2):438-451
Catalysis Letters - Mixed transition-metals oxide electrocatalysts have shown huge potential for electrochemical water oxidation due to their earth abundance, low cost and excellent...  相似文献   
84.
Devi  Neena  Patel  Sanjay K. S.  Kumar  Pradeep  Singh  Archana  Thakur  Nandita  Lata  Jeevan  Pandey  Deepak  Thakur  Vikram  Chand  Duni 《Catalysis Letters》2022,152(4):944-953
Catalysis Letters - In this study, Rhodococcus pyridinivorans cells containing hyperactive acyltransferase was immobilized on various macromolecules based-polymeric matrices and used to improve...  相似文献   
85.
Doke  Suhas D.  Patel  C. M.  Lad  V. N. 《SILICON》2022,14(3):913-922
Silicon - Abundant applications of silica nanoparticles (SiNPs) have motivated many research groups for silica nanoparticles synthesis with tuned properties. Here we show the formation of SiNPs...  相似文献   
86.
We present the different elaboration steps of a composite formed of carbon nanotubes (CNT) carpet embedded in an epoxy polymer. Detailed characterization at each step of the elaboration process is performed. The good alignment of CNT in as‐grown carpets is kept all along the elaboration process of the composite, as it is measured at both macro and microscopic scales by X‐ray scattering. We also ensured by X‐ray fluorescence measurements that the iron‐based catalyst particles used for the synthesis were removed from the carpet after a high temperature post‐annealing treatment. These measurements give valuable information for further applications involving unidirectional nanotube composites and membranes, where CNT alignment is a key parameter. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39730.  相似文献   
87.
Nanographitic materials are gaining enormous interest as a new class of reinforcement for nanocomposites, promising revolutionary electrical, thermal, and mechanical properties. However, the progress has been quite limited especially in terms of mechanical properties. Here we report a significant leap, >2× increases in tensile strength and modulus of an epoxy composite using surface treated graphite nanoplatelets (GnPs). This corroborated by increases in Tgs as well as the presence of oxygen‐functionalized groups verified by XPS, suggest improved distribution and chemical interaction at the filler‐to‐matrix interface. Toughness values also showed increases with concentration, without compromising the strength or failure strain. However, if solvent levels during degassing were not reduced sufficiently, negligible contributions to strength and stiffness were observed with GnP loading. Subsequent elevated temperature treatments increased the strength of the composite due to cure enhancement of the matrix material, yet did not provide mechanical enhancements due to the incorporation of the filler. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40802.  相似文献   
88.
Teaching-learning-based optimization (TLBO) is a recently developed heuristic algorithm based on the natural phenomenon of teaching-learning process. In the present work, multi-objective improved teaching-learning-based optimization (MO-ITLBO) algorithm is introduced and applied for the multi-objective optimization of plate-fin heat exchangers. The basic TLBO algorithm is improved to enhance its exploration and exploitation capacities by introducing the concept of number of teachers, adaptive teaching factor, tutorial training and self-motivated learning. The MO-ITLBO algorithm uses a grid-based approach to adaptively assess the non-dominated solutions maintained in an external archive. Minimizing total annual cost and the total weight of heat exchanger as well as minimization of total pressure drop and maximization of heat exchanger effectiveness for specific heat duty requirement are considered as objective functions. Two application examples are presented to demonstrate the effectiveness and accuracy of the proposed algorithm.  相似文献   
89.
This two-part paper focuses on the characterization and simulation of two important molding defects in liquid composite molding—poor wetting and void formation. Part I analyzes resin-fiber wettability. This involved characterization of various liquids/resins and fiber filaments/fiber mats by using wicking test and capillary pressure measurement. Methodology to quantify capillary pressurewettability relationships was developed. It was found that the Leverett J function can correlate capillary pressure-saturation relationships for fiber reinforcements with various porosities and fiber architecture.  相似文献   
90.
The grafting of acrylonitrile (AN) onto sodium salt of partially carboxymethylated amylose (Na-PCMA) using ceric ammonium nitrate (CAN) as an initiator has been studied in water/solvent mixtures. The solvents used include methanol, ethanol, propanol, butanol, acetone and carbon tetrachloride. The results have been discussed. The effect of reaction medium on the molecular weight of grafted PAN has also been studied. The chain transfer constants (Cs) for solvents like methanol, ethanol, propanol, butanol, acetone and carbon tetrachloride have been evaluated at 30°C by the help of Mayo's equation.  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-23

京公网安备 11010802026262号