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   86741篇
  免费   14446篇
  国内免费   9873篇
化学   61759篇
晶体学   892篇
力学   5280篇
综合类   564篇
数学   10046篇
物理学   32519篇
  2024年   172篇
  2023年   1652篇
  2022年   1848篇
  2021年   2835篇
  2020年   3451篇
  2019年   3264篇
  2018年   2836篇
  2017年   2611篇
  2016年   4018篇
  2015年   3941篇
  2014年   4722篇
  2013年   6269篇
  2012年   7833篇
  2011年   8030篇
  2010年   5502篇
  2009年   5249篇
  2008年   5825篇
  2007年   5246篇
  2006年   4814篇
  2005年   4025篇
  2004年   3282篇
  2003年   2679篇
  2002年   2617篇
  2001年   2184篇
  2000年   1885篇
  1999年   1933篇
  1998年   1550篇
  1997年   1542篇
  1996年   1444篇
  1995年   1217篇
  1994年   1076篇
  1993年   910篇
  1992年   809篇
  1991年   675篇
  1990年   593篇
  1989年   457篇
  1988年   377篇
  1987年   320篇
  1986年   284篇
  1985年   234篇
  1984年   168篇
  1983年   118篇
  1982年   91篇
  1981年   80篇
  1980年   74篇
  1979年   35篇
  1978年   38篇
  1977年   47篇
  1976年   38篇
  1973年   35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.
Silver nanoparticles (NPs) ranging in size from 40 to 100 nm were prepared in high yield by using an improved seed‐mediated method. The homogeneous Ag NPs were used as building blocks for 2D assembled Ag NP arrays by using an oil/water interface. A close‐packed 2D array of Ag NPs was fabricated by using packing molecules (3‐mercaptopropyltrimethoxysilane) to control the interparticle spacing. The homogeneous 2D Ag NP array exhibited a strong quadrupolar cooperative plasmon mode resonance and a dipolar red‐shift relative to individual Ag NPs suspended in solution. A well‐arranged 2D Ag NP array was embedded in polydimethylsiloxane film and, with biaxial stretching to control the interparticle distance, concomitant variations of the quadrupolar and dipolar couplings were observed. As the interparticle distance increased, the intensity of the quadrupolar cooperative plasmon mode resonance decreased and dipolar coupling completely disappeared. The local electric field of the 2D Ag NP array was calculated by using finite difference time domain simulation and qualitatively showed agreement with the experimental measurements.  相似文献   
43.
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   
44.
The research progress of a novel traffic solution,a submerged floating tunnel(SFT),is reviewed in terms of a study approach and loading scenario.Among existing publications,the buoyancy-weight ratio(BWR) is usually predefined.However,BWR is a critical structural parameter that tremendously affects the dynamic behaviour of not only the tunnel tube itself but also the cable system.In the context of a SFT prototype(SFTP) project in Qiandao Lake(Zhejiang Province,China),the importance of BWR is illustrated by finite element analysis and subsequently,an optimized BWR is proposed within a reasonable range in the present study.In the numerical model,structural damping is identified to be of importance.Rayleigh damping and the corresponding Rayleigh coefficients are attained through a sensitivity study,which shows that the adopted damping ratios are fairly suitable for SFTP.Lastly,the human sense of security is considered by quantifying the comfort index,which helps further optimize BWR in the SFTP structural parameter design.  相似文献   
45.
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   
46.
47.
48.
49.
50.
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