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   1946篇
  免费   85篇
  国内免费   17篇
化学   1393篇
晶体学   23篇
力学   66篇
综合类   3篇
数学   155篇
物理学   408篇
  2024年   7篇
  2023年   12篇
  2022年   66篇
  2021年   86篇
  2020年   54篇
  2019年   60篇
  2018年   57篇
  2017年   46篇
  2016年   83篇
  2015年   69篇
  2014年   80篇
  2013年   159篇
  2012年   120篇
  2011年   157篇
  2010年   76篇
  2009年   86篇
  2008年   81篇
  2007年   85篇
  2006年   80篇
  2005年   81篇
  2004年   58篇
  2003年   61篇
  2002年   48篇
  2001年   29篇
  2000年   25篇
  1999年   15篇
  1998年   14篇
  1997年   13篇
  1996年   11篇
  1995年   10篇
  1994年   11篇
  1993年   18篇
  1992年   12篇
  1991年   12篇
  1990年   16篇
  1989年   8篇
  1988年   10篇
  1987年   11篇
  1986年   16篇
  1985年   11篇
  1984年   10篇
  1983年   6篇
  1982年   14篇
  1981年   9篇
  1980年   8篇
  1979年   8篇
  1978年   4篇
  1977年   10篇
  1976年   6篇
  1975年   4篇
排序方式: 共有2048条查询结果,搜索用时 968 毫秒
61.
This study has presented a performance investigation of an advanced tracked prime mover for the operation of agricultural goods and other operations on peat terrain. The maximum and continuous traction torque of the prime mover has been developed by designing an advanced controller for controlling the intelligent system. The prime mover’s mobility is studied with ultrasonic displacement sensor, torque transducer, National Instrument cRIO-9004 Compact-RIO Real-time Controller Unit (RCU), a National Instrument TPC 2106T Touch Panel Control (TPC), a Trimble AG132 GPS antenna and receiver unit, and a Dlink DIR-655 router. The fuzzy logic controller (FLC) has been equipped with the prime mover hydraulic system to increase the traction torque of the hydraulic motor when the prime mover’s sinkage is more than or equal to 70 mm. The prime mover’s design demonstrates good potential in traversing peat terrain as the measured tractive effort was found to be 48% of the vehicle’s gross weight while the recommended tractive effort is in the range of 30–36% of the vehicle’s gross weight.  相似文献   
62.
Abstract

We have studied the lyotropic liquid-crystalline behaviour of cationic surfactants containing a potentially thermotropic moiety, a terminal cyanobiphenyloxy group. Both mono-alkyl and mid-chain substituted dialkyl surfactants have been examined using optical microscopy and NMR spectroscopy. Incorporation of the cyanobiphenyloxy group destabilizes the hexagonal and bicontinuous cubic phases, with only an extensive lamellar region being observed. For the dialkyl surfactant there is a range of compositions where two lamellar phases co-exist, one water-rich and the second surfactant-rich.  相似文献   
63.
64.
Benzoyl peroxide has been used as a mild and efficient reagent for the preparation of benzoyl ester of oxime in moderate to good yields.  相似文献   
65.
The reaction of different mercapto substituted heterocycles with o,o-dialkyl chlorphosphate or thiophosphates, gave the corresponding S- and N- alkylated derivatives instead of the expected phosphorylated products.  相似文献   
66.
This paper reports a study on the effect of Al2O3 nanoparticles on the adhesion strength of steel-glass/epoxy composite joints bonded by a two-component structural acrylic adhesive. The addition of Al2O3 nanoparticles to the two-component acrylic adhesive led to a remarkable enhancement in the shear and tensile strength of the composite joints. The shear and tensile strength of the adhesive joints increased by addition of Al2O3 up to 1.5 wt%, which decreased by further addition of the nanofiller. Introduction of the nanoparticles caused a reduction in the peel strength of the joints. DSC analysis revealed that the glass transition temperature (Tg) of the adhesives rose by increasing the nanofiller content. The advancing water contact angle was decreased for adhesives containing nanoparticles. SEM micrographs indicated good dispersions of the Al2O3 nanoparticles within the acrylic matrix in the specimens with up to 1.5 wt% Al2O3 and revealed that addition of nanoparticles altered the fracture morphology from smooth to rough fracture surfaces.  相似文献   
67.
Gene silencing is one of the limiting factors for transgene expression in plants. But the plant viruses have learnt to suppress gene silencing by encoding the protein(s), called RNA silencing suppressor(s) (RSS). Hence, these proteins could be used to overcome the limitation for transgene expression. The RNAi suppressors, namely HC-Pro and P19, have been shown to enhance the transgene expression but other RSS proteins have not been screened for similar role. Moreover, none of RSSs from the DNA viruses are known for enhancing the expression of transgenes. The Mungbean Yellow Mosaic India Virus (MYMIV) belonging to the genus Begomovirus within the family of Geminiviridae encodes an RSS called the AC2 protein. Here, we used AC2 to elevate the expression of the transgenes. Upon introduction of MYMIV-AC2 in the silenced GFP transgenic tobacco lines, by either genetic hybridisation or transgenesis, the GFP expression was enhanced several fold in F1 and T0 lines. The GFP-siRNA levels were much reduced in F1 and T0 lines compared with those of the initial parental silenced lines. The enhanced GFP expression was also observed at the cellular level. This approach was also successful in enhancing the expression of another transgene, namely topoisomeraseII.  相似文献   
68.
69.
Cold expansion is a useful process for imposing compressive residual stresses around the holes in riveted and bolted connections. These stresses increase the fatigue life of holed parts. Distribution and amount of exerted residual stress dependent on various parameters as material, distance of adjacent holes, hole diameter, cold expansion ratio and plate thickness. In this study, experimental and numerical results for two different aluminum alloys and various holes distances are investigated and compared. Effects of mentioned parameters on the residual stress are studied.  相似文献   
70.
This paper reviews the use of solid polymeric electrolyte (SPE) and gel polymeric electrolyte (GPE) in photoelectrochemical cell (PEC) and dye-sensitized solar cell (DSSC). The structure of PEC and its working principle are presented. The various types of polymer electrolytes utilized in PEC and DSSC have been highlighted in this review. It also highlights the comparison of performance of PEC and DSSC utilizing those polymer electrolytes. This review is completed with the list of other SPEs that potentially be tested in DSSC.  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