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   145032篇
  免费   33369篇
  国内免费   23624篇
化学   96544篇
晶体学   1589篇
力学   9701篇
综合类   380篇
数学   17853篇
物理学   75958篇
  2024年   458篇
  2023年   2168篇
  2022年   2324篇
  2021年   3092篇
  2020年   3933篇
  2019年   4207篇
  2018年   3799篇
  2017年   4138篇
  2016年   5539篇
  2015年   5595篇
  2014年   6103篇
  2013年   9038篇
  2012年   10554篇
  2011年   12156篇
  2010年   13296篇
  2009年   13354篇
  2008年   7678篇
  2007年   6748篇
  2006年   6143篇
  2005年   5894篇
  2004年   5925篇
  2003年   4775篇
  2002年   4461篇
  2001年   4518篇
  2000年   3583篇
  1999年   4023篇
  1998年   3350篇
  1997年   3157篇
  1996年   3465篇
  1995年   3664篇
  1994年   3620篇
  1993年   3485篇
  1992年   3010篇
  1991年   2629篇
  1990年   2208篇
  1989年   2200篇
  1988年   2121篇
  1987年   1384篇
  1986年   1415篇
  1985年   1056篇
  1984年   1111篇
  1982年   962篇
  1981年   800篇
  1980年   830篇
  1979年   557篇
  1978年   560篇
  1977年   673篇
  1976年   1071篇
  1973年   463篇
  1972年   543篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Mass concentration and isotopic values δ13C and 14C are presented for the water-insoluble refractory carbon(WIRC) component of total suspended particulates(TSP),collected weekly during 2003,as well as from October 2005 to May 2006 at the WMO-GAW Mt.Waliguan(WLG) site.The overall average WIRC mass concentration was(1183±120)ng/m3(n = 79),while seasonal averages were 2081 ±1707(spring),454±205(summer),650±411(autumn),and 1019±703(winter) ng/m3.Seasonal variations in WIRC mass concentrations were consistent with black carbon measurements from an aethalometer,although WIRC concentrations were typically higher,especially in winter and spring.The δ13C PDB value(-25.3 ± 0.8)%.determined for WIRC suggests that its sources are C3 biomass or fossil fuel combustion.No seasonal change in δ13C PDB was evident.The average percent Modern Carbon(pMC) for 14C in WIRC for winter and spring was(67.2 ± 7.7)%(n = 29).Lower pMC values were associated with air masses transported from the area east of WLG,while higher pMC values were associated with air masses from the Tibetan Plateau,southwest of WLG.Elevated pMC values with abnormally high mass concentrations of TSP and WIRC were measured during a dust storm event.  相似文献   
42.
Liu  Jian-Guo  Zhu  Wen-Hui 《Nonlinear dynamics》2020,100(3):2739-2751
Nonlinear Dynamics - Under investigation is a generalized (3 + 1)-dimensional variable- coefficient Kadomtsev– Petviashvili equation in fluid mechanics. Various exact analytical solutions are...  相似文献   
43.
The European Physical Journal C - We study the isentropic evolution of the matter produced in relativistic heavy-ion collisions for various values of the entropy-per-baryon ratio of interest for...  相似文献   
44.
45.
46.
47.
Journal of Solid State Electrochemistry - The “shuttle effect” of polysulfides is a serious issue, resulting in a decrease in the life-cycle of lithium-sulfur (Li-S) batteries. To...  相似文献   
48.
Embedding endohdedral metallofullerenes (EMFs) into electron donor–acceptor systems is still a challenging task owing to their limited quantities and their still largely unexplored chemical properties. In this study, we have performed a 1,3‐dipolar cycloaddition reaction of a corrole‐based precursor with Sc3N@C80 to regioselectively form a [5,6]‐adduct ( 1 ). The successful attachment of the corrole moiety was confirmed by mass spectrometry. In the electronic ground state, absorption spectra suggest sizeable electronic communications between the electron acceptor and the electron donor. Moreover, the addition pattern occurring at a [5,6]‐bond junction is firmly proven by NMR spectroscopy and electrochemical investigations performed with 1 . In the electronically excited state, which is probed in photophysical assays with 1 , a fast electron‐transfer yields the radical ion pair state consisting of the one‐electron‐reduced Sc3N@C80 and of the one‐electron‐oxidized corrole upon its exclusive photoexcitation. As such, our results shed new light on the practical work utilizing EMFs as building blocks in photovoltaics.  相似文献   
49.
50.
We investigate perturbation for continuous-time Markov chains(CTMCs) on a countable state space. Explicit bounds on ?D and D are derived in terms of a drift condition, where ? and D represent the perturbation of the intensity matrices and the deviation matrix, respectively. Moreover, we obtain perturbation bounds on the stationary distributions, which extends the results by Liu(2012) for uniformly bounded CTMCs to general(possibly unbounded) CTMCs. Our arguments are mainly based on the technique of augmented truncations.  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