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   107596篇
  免费   18363篇
  国内免费   10408篇
化学   72805篇
晶体学   1233篇
力学   7036篇
综合类   554篇
数学   12206篇
物理学   42533篇
  2024年   376篇
  2023年   2167篇
  2022年   3719篇
  2021年   3994篇
  2020年   4327篇
  2019年   4210篇
  2018年   3636篇
  2017年   3357篇
  2016年   5294篇
  2015年   5036篇
  2014年   6138篇
  2013年   7932篇
  2012年   9586篇
  2011年   9936篇
  2010年   6568篇
  2009年   6275篇
  2008年   6690篇
  2007年   6108篇
  2006年   5600篇
  2005年   4721篇
  2004年   3490篇
  2003年   2751篇
  2002年   2504篇
  2001年   2049篇
  2000年   1806篇
  1999年   2119篇
  1998年   1889篇
  1997年   1744篇
  1996年   1912篇
  1995年   1537篇
  1994年   1490篇
  1993年   1194篇
  1992年   1093篇
  1991年   1001篇
  1990年   808篇
  1989年   574篇
  1988年   471篇
  1987年   391篇
  1986年   383篇
  1985年   323篇
  1984年   248篇
  1983年   157篇
  1982年   143篇
  1981年   109篇
  1980年   76篇
  1979年   44篇
  1978年   34篇
  1976年   36篇
  1975年   33篇
  1974年   45篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
We conducted measurements of black carbon(BC) aerosol in Jiaxing,China during autumn from September 26 to November 30,2013.We investigated temporal and diurnal variations of BC,and its correlations with meteorological parameters and other major pollutants.Results showed that hourly mass concentrations of BC ranged from 0.2 to 22.0 μg/m3,with an average of 5.1 μg/m3.The diurnai variation of BC exhibited a bimodal distribution,with peaks at 07:00 and 18:00.The morning peak was larger than the evening peak.The mass percentages of BC in PM2.5 and PM10 were 7.1%and 4.8%,respectively.The absorption coefficient of BC was calculated to be 44.4 Mm-1,which accounted for 11.1%of the total aerosol extinction.BC was mainly emitted from local sources in southwestern Jiaxing where BC concentrations were generally greater than 11 μg/m3 during the measurement period.Correlation analysis indicated that the main sources of BC were motor vehicle exhaust,and domestic and industrial combustion.  相似文献   
13.
JPC – Journal of Planar Chromatography – Modern TLC - A new high-performance thin-layer chromatographic (HPTLC) method has been developed for the simultaneous estimation of...  相似文献   
14.
15.
16.
We investigate terahertz radiation(T-rays) from a pentacene organic diode at room temperature. The quantum chemistry calculation for frequency-related Huang–Rhys factor of pentacene is also carried out. The results demonstrate that the T-rays can come from a bending vibration of pentacene skeleton after the energy of pentacene exciton transferring to the vibrational excited state via electron–phonon coupling. Frequency and natural bond orbital analytics of pentacene and its derivatives are performed in order to explain the result and develop new materials to get higher emission. This work provides a new way to produce T-rays with a simple device at room temperature.  相似文献   
17.
18.
A new approach has been developed to improve SO2 sorption by cyano‐containing ionic liquids (ILs) through tuning the basicity of ILs and cyano–sulfur interaction. Several kinds of cyano‐containing ILs with different basicity were designed, prepared, and used for SO2 capture. The interaction between these cyano‐containing ILs and SO2 was investigated by FTIR and NMR methods. Spectroscopic investigations and quantum chemical calculations showed that dramatic effects on SO2 capacity originate from the basicity of the ILs and enhanced cyano–sulfur interaction. Furthermore, the captured SO2 was easy to release by heating or bubbling N2 through the ILs. This efficient and reversible process, achieved by tuning the basicity of ILs, is an excellent alternative to current technologies for SO2 capture.  相似文献   
19.
20.
Let L be an additive map between (real or complex) matrix algebras sending n×n Hermitian idempotent matrices to m×m Hermitian idempotent matrices. We show that there are nonnegative integers p,q with n(p+q)=rm and an m×m unitary matrix U such thatL(A)=U[(Ip?A)(Iq?At)0m?r]U?,for any n×n Hermitian A with rational trace. We also extend this result to the (complex) von Neumann algebra setting, and provide a supplement to the Dye-Bunce-Wright Theorem asserting that every additive map of Hermitian idempotents extends to a Jordan ?-homomorphism.  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