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   15725篇
  免费   1874篇
  国内免费   942篇
化学   8840篇
晶体学   141篇
力学   472篇
综合类   49篇
数学   1102篇
物理学   3657篇
无线电   4280篇
  2024年   45篇
  2023年   327篇
  2022年   383篇
  2021年   515篇
  2020年   528篇
  2019年   495篇
  2018年   404篇
  2017年   362篇
  2016年   705篇
  2015年   625篇
  2014年   756篇
  2013年   1117篇
  2012年   1265篇
  2011年   1267篇
  2010年   812篇
  2009年   872篇
  2008年   1007篇
  2007年   968篇
  2006年   848篇
  2005年   812篇
  2004年   555篇
  2003年   457篇
  2002年   479篇
  2001年   347篇
  2000年   336篇
  1999年   277篇
  1998年   250篇
  1997年   196篇
  1996年   191篇
  1995年   207篇
  1994年   183篇
  1993年   158篇
  1992年   134篇
  1991年   95篇
  1990年   99篇
  1989年   57篇
  1988年   55篇
  1987年   44篇
  1986年   43篇
  1985年   44篇
  1984年   32篇
  1983年   20篇
  1982年   33篇
  1981年   24篇
  1980年   13篇
  1979年   11篇
  1978年   12篇
  1976年   8篇
  1975年   11篇
  1966年   8篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
利用修正的非线性Schrodinger方程研究了单模光纤最小群速度色散波长附近的调制不稳定性,发现了一个新的由光纤四色散导致的调制不稳定性区域,该区域的调制范围与初始入射脉冲的功率和四阶色散有关。  相似文献   
72.
本文论述了帧中继交换的概念、标准,结构、特点网络式样及在互连网中的应用。  相似文献   
73.
The bit error rate (BER) analysis of a direct-sequence code-division multiple-access (DS-CDMA) cellular system over a Rayleigh-fading channel often results in complicated expressions even though the Gaussian approximation is applied. A combined probability density function (pdf) approach for the forward link and a mean-method technique for the reverse link are proposed to significantly reduce the computational complexity. The simplified BER expressions are derived and yield accurate results  相似文献   
74.
The purpose of this paper is to study the relationship between the oxygen concentration and brightness degradation in ZnS:TbOF green thin-film electroluminescent (EL) devices. The characteristics including crystallinity, optical, and electrical properties were discussed. The brightness-voltage (B-V) measurement results shelved that with higher oxygen-content in ZnS:TbOF phosphor layer, lower brightness was measured. It was consistent with the poor crystallinity, worse photoluminescent intensity, and easier to get moisture in the oxygen-rich (O/Tb>1) phosphor film. Furthermore, deep level transient spectroscopy (DLTS) measurements identified that when the O/Tb ratio was greater than 1, the oxygen-related deep hole traps EH1 and/or EH2 could be detected in the ZnS:TbOF phosphor layer. These E H1 and/or EH2 traps were believed to be the main killers for the brightness of the device since they capture most of the holes from the generated electron-hole pairs. This evidence strongly supports that the modified energy transfer model is more dominant than direct impact excitation during the luminescent process  相似文献   
75.
谐振子薛定谔方程的简单解法   总被引:2,自引:0,他引:2  
物质的许多物理与化学性质都可以用线性谐振子模型解释,本文用简单的数学运算求解线性谐振子的薛定谔方程,避免了特殊函数等复杂的数学运算,得出了量子力学教材完全相同的结果。  相似文献   
76.
A series of Gd(1−x)Bx alloys have been prepared by arc melting method. After introducing small quantity of B atom in Gd, the Curie temperature of these alloys increase while the magnetic entropy changes are almost same as that of Gd. The refrigerant capacities of these alloys are also greater than that of Gd. These results suggest that Gd(1−x)Bx alloys may be utilized as refrigerant in household magnetic refrigeration.  相似文献   
77.
78.
Catalytic decomposition of NO over Cu-Os/13X has been carried out in a tubular fixed bed reactor at atmospheric pressure and the results were compared with literature data performed by high-throughput screening (HTS). The activity and durability of Cu-Os/13X prepared by conventional ion-exchange method have been investigated in the presence of H2O and SO2. It was found that Cu-Os/13X prepared by ion-exchange shows a high activity in a wide temperature range in selective catalytic reduction (SCR) of NO with C3H6 compared to Cu/13X, proving the existence of more NO adsorption site on Cu-Os/13X. However, Cu-Os/13X exhibited low activity in the presence of water, and was quite different from the result reported in literature. SO2 resistance is also low and does not recover its original activity when the SO2 was blocked in the feed gas stream. This result suggested that catalytic activity between combinatorial screening and conventional testing should be compared to confirm the validity of high-throughput screening.  相似文献   
79.
We have reported a novel design of surface plasmon resonance (SPR) device, which uses alternating dielectric layers to enhance the SPR signal quality and modulate its resonant position. Admittance loci method of thin film design has been used in the design of such a device. The use of biomolecular thin film, such as DNAs or Porteins, in this design can result in resonant condition of wavelength changes as well. Bio-plasmonics is proposed for the research and development of novel devices, which use biomolecules as a part of the plasmon oscillation system to actively interact with nano/micro structure.  相似文献   
80.
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