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   254348篇
  免费   12102篇
  国内免费   7140篇
化学   149149篇
晶体学   2718篇
力学   12088篇
综合类   518篇
数学   26423篇
物理学   82694篇
  2021年   2881篇
  2020年   3503篇
  2019年   3448篇
  2018年   3350篇
  2017年   3047篇
  2016年   5086篇
  2015年   4571篇
  2014年   5820篇
  2013年   12401篇
  2012年   10802篇
  2011年   12328篇
  2010年   8310篇
  2009年   8193篇
  2008年   9917篇
  2007年   9723篇
  2006年   9224篇
  2005年   8269篇
  2004年   7242篇
  2003年   6199篇
  2002年   5855篇
  2001年   7082篇
  2000年   5280篇
  1999年   4592篇
  1998年   3639篇
  1997年   3613篇
  1996年   3574篇
  1995年   3430篇
  1994年   3258篇
  1993年   3003篇
  1992年   3394篇
  1991年   3166篇
  1990年   3027篇
  1989年   2980篇
  1988年   2810篇
  1987年   2805篇
  1986年   2576篇
  1985年   3462篇
  1984年   3394篇
  1983年   2769篇
  1982年   2937篇
  1981年   2862篇
  1980年   2715篇
  1979年   2859篇
  1978年   3126篇
  1977年   2935篇
  1976年   2887篇
  1975年   2745篇
  1974年   2679篇
  1973年   2718篇
  1967年   2132篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
JETP Letters - The results of the first run (December 2020) for the commissioning of the new superconducting synchrotron Booster at the Joint Institute for Nuclear Research are presented. Vacuum...  相似文献   
23.
Chen  Cui  Wang  Ya-Nan  Yan  Jun 《中国科学 数学(英文版)》2021,64(8):1789-1800
In this paper,we investigate the non-autonomous Hamilton-Jacobi equation ■ where H is 1-periodic with respect to t and M is a compact Riemannian manifold without boundary.We obtain the viscosity solution denoted by T_(t_0)~tφ(x) and show T_(t_0)~tφ(x) converges uniformly to a time-periodic viscosity solution u~*(x,t) of ?_tu+H(t,x,?_xu,u)=0.  相似文献   
24.
Chen  Manling  Liu  Xue 《Journal of fluorescence》2021,31(4):1153-1160
Journal of Fluorescence - Carbon nanodots (CDs) have exhibited excellent sensing capability for various metal ions. However, it is difficult to determine the selectivity of CDs to metal ions. In...  相似文献   
25.
Zhang  F.  Yi  S. H.  Niu  H. B.  Lu  X. G.  Wang  X. X. 《Fluid Dynamics》2021,56(3):383-392
Fluid Dynamics - To predict the boundary layer transition on swept wings, experimental and numerical researches were conducted to obtained the accurate boundary layer transition front and to...  相似文献   
26.
Annals of Operations Research - The main purpose of this study was to explore the impact of peace dividends on global changes in national productivity. First, this study assessed changes in...  相似文献   
27.
Recent success in strain engineering has triggered tremendous interest in its study and potential applications in nanodevice design. In this paper, we establish a coupled piezoelectric/semiconducting model for a wurtzite structure ZnO nanofiber under the local mechanical loading. The energy band structure tuned by the local mechanical loading and local length is calculated via an eight-band k·p method, which includes the coupling of valance and conduction bands. Poisson's effect on the distribution of electric potential inversely depends on the local mechanical loading. Numerical results reveal that both the applied local mechanical loading and the local length exhibit obvious tuning effects on the electric potential and energy band. The band gap at band edges varies linearly with the applied loading. Changing the local length shifts the energy band which is far away from the band edges. This study will be useful in the electronic and optical enhancement of semiconductor devices.  相似文献   
28.
29.
This paper investigates the effect of phosphorus (P) on char structure and reactivity of char prepared from the fast pyrolysis of purposely-prepared P-loaded biomass samples at 1000 °C in absence of other inorganic species. Biomass was first acid-washed then loaded with P of three different occurrence forms (one organic P i.e. phytic acid, and two inorganic P i.e. orthophosphoric acid and polyphosphoric acid) at the same P content of 0.8 wt%. Experimental results show that both organic and inorganic P substantially increase char yields during pyrolysis from 6.2% for the biomass sample without P to 23.0–26.0% for P-loaded samples due to the enhanced crosslinking by P-containing structures in char, leading to increases in the char C and H contents and decrease in O content. The presence of P in biochars from fast pyrolysis of various P-loaded biomass samples plays important role in the evolution of char structure and intrinsic reactivity measured during low-temperature oxidation at 500 °C in air under chemical-reaction-controlled regime. After pyrolysis and subsequent char oxidation, all P in biomass either as organic or inorganic P are found to be present in forms of acid-insoluble organic structures. For char prepared from acid-washed wood, char reactivity increases with char conversion due to the increasing pore surface area at higher conversion. Comparatively, for char prepared from acid-washed wood loaded with various P at char conversion below 60%, the presence of P increases char intrinsic reactivity due to the enhanced crosslinking of reactive carbon structures and reduced condensation of char structures. However, at conversions above 60%, P-containing species in char lead to a significant decrease in char reactivity, due to the formation of abundant CO-P bonds, that is highly resistant to the oxidation in air, in the reacting chars.  相似文献   
30.
Journal of Theoretical Probability - This work presents an infinite-dimensional generalization of the correspondence between the Kullback–Leibler and Rényi divergences between Gaussian...  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