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   6015篇
  免费   564篇
  国内免费   886篇
化学   3919篇
晶体学   36篇
力学   611篇
综合类   77篇
数学   577篇
物理学   2245篇
  2024年   31篇
  2023年   69篇
  2022年   104篇
  2021年   59篇
  2020年   36篇
  2019年   32篇
  2018年   27篇
  2017年   24篇
  2016年   26篇
  2015年   26篇
  2014年   147篇
  2013年   37篇
  2012年   152篇
  2011年   188篇
  2010年   88篇
  2009年   70篇
  2008年   140篇
  2007年   197篇
  2006年   200篇
  2005年   139篇
  2004年   54篇
  2003年   376篇
  2002年   1577篇
  2001年   1333篇
  2000年   470篇
  1999年   379篇
  1998年   299篇
  1997年   67篇
  1996年   133篇
  1995年   187篇
  1994年   126篇
  1993年   172篇
  1992年   122篇
  1991年   114篇
  1990年   144篇
  1989年   106篇
  1988年   3篇
  1987年   2篇
  1986年   3篇
  1985年   5篇
  1965年   1篇
排序方式: 共有7465条查询结果,搜索用时 15 毫秒
41.
杨冰  李瑛 《中国物理快报》2003,20(1):161-163
Perylene and coronene have been synthesized with good yield via the Dields-Alder reaction.They have good photoluminescence properties and could transfer ultraviolet light to visible-loght.To find an easy way of making a better ultraviolet charge coupled device,we blended perylene or coronene with polymers.Then,these blends were analysed by the photoluminescence spectrum.The results indicate that the blends have larger fluorescence intensity than pure perylene or coronene.Through spreading these blends on image detectors,organic image detectors with good ultraviolet photoelectricity capability were prepared.  相似文献   
42.
Quan  Min  LI  Hai  Xin  BAI 《中国化学快报》2003,14(3):290-293
A new method for indirect determination of cetyl-trimethyl ammonium bromide (CTMAB) with NaCl and NH4SCH by floatation and separation of zinc has been studied.The study shows that Zn(Ⅱ) can associate with NH4SCN and CTMAB to form insoluble ternary ion-association complex,and the precipitate can float on the surface of the liquid phase.A good linear relationship is observed between the floatation yield(E%) of Zn(Ⅱ) and the amount of CTMAB.On the ground,CTMAB Can be indirectly determined by determining E% of Zn(Ⅱ).The results were satisfactory.  相似文献   
43.
To describe pulsar spin-down,we present a simple combined torque model that takes into account both the standard magnetic dipole radiation and the electromagnetic radiation from the 3P2 superluid vortex neutrons inside neutron star.Using an ordinary exponential model for the magnetic field decay,we derive an analytical formulae for pulsar evolution tracks,The pulsar evolution on the P-P diagram is quite different from that of the standard magnetic dipole radiation model,especially when the superfluid torque or field decay becomes dominant.  相似文献   
44.
氘作同位素交换气对除氚后的新鲜氘氚化锂残渣[主要成分是硅锂化合物和二氧化硅,渣中含氚约为0.9443mg/g(渣)]中的微量氚进行氚的计量与回收,为氘氚化锂残渣中氚的回收提供技术支持。  相似文献   
45.
We present a new exactly solvable inflation model in which inflation can stop automatically,and in the approximately de sitter limit,we give its power spectrum which can be tested in the future observations of cosmic microwave background anisotropy.  相似文献   
46.
A New High Power Microwave Source Operated at Low Magnetic Field   总被引:2,自引:0,他引:2       下载免费PDF全文
A new tpye of high power microwave souce operated at low magnetic filed is proposed and studied by the particle-in-cell (PIC) method.An oversized uniform backward-wave-oscillator-like structure is connected to a tapered slow-wave structure by a resonalt cavity.In this device,the electron beam current is effectively used to yield microwaves with high efficientcy,and the mode is locked in a wide range of diode voltage to reduce the requirement to the voltage wave form.The PIC siumlation results show that a peak microwave power of 2.1 GW (averaged 1.1GW) with a pure TM01 mode at 10.7GHz is radiated with 4.1GW input beam power,the frequency remains approximately the same when the diode voltage changed from 300kV to 700kV.  相似文献   
47.
The structural evolution of nanostructured γ-Ni-28Fe alloy(n-Ni-Fe)(grain size d-30nm),synthesized by the mechno-chemical method,was investigated by using the internal friction technique combined with differential scanning calorimetry(DSC) in the temperature range from 300K to 670K.An internal friction peak with typical characteristics of the first-order phase transition was observed in the vicinity of 620K,which corresponds to a broad exothermic process revealed by using DSC.Theses results can be explained as the structural changes from the disordering to the ordering transition in the n-Ni-Fe sample.  相似文献   
48.
A water soluble crude polysaccharide has been isolated from the fruiting body of cultivated Cordyceps militarvs(L.)Link.The GC analysis indicated that it contained the monosaccharides of Gal,Man,Glc and GlcA.Their molar ratio is 1.00:1.58:7.89:0.19.The crude polysaccharide was fractionated with ethanol to get three fractions,which were CM-Ⅰand CM-Ⅲ,CM-Ⅱ was further purified to get one homogeneous fraction named CMB.The molecular weight was estimated to be 6000by means of gel filtration.CMB is a greyish white powder.The GC analysis indicated that it was composed of Gal.Man,Glc and the molar ratio is 1.00:1.38:5.10.Partial hydrolysis with an acid.periodate oxidation.Smith degradation.IR,GC and methylation analyses,GC/MS analyses were used for the structure analyses of CMB.Man,(1→6)-linked-Glc,(1→4)-linked-Glc and (1→4)-linked-Gal.Some of (1→4) -linked-Glc and all(1→4)-linked-Gal residues are substituted at 3-O and 6-O respectively,(1→4)-linked-Glc and minor(1→6)-linked-Gle.The nonreduced end is composed of Gal and Glc.The main glycosidic link of CMB is α configuration.  相似文献   
49.
Yao  Dong  HUANG  Xiao  Jie  ZHANG 《中国化学快报》2003,14(1):29-31
A convenient and large-scale preparation of retinoic acid 1 from β-ionone in five steps with 38% overall yield is described.The key steps are the epoxidization of 2 with a new methylated agent and the condensation 4 with tetraethyl methylenediphophonate in one-pot procedure to prepare 6.  相似文献   
50.
PURE STATE APPROACH TO C(x)_αZ_nLIBINGREN;LINQING(InstituteofMathematics,AcademiaSinica,Beijing100080,China.Projectsupportedbyth?..  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