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   454619篇
  免费   4108篇
  国内免费   1153篇
化学   225964篇
晶体学   7022篇
力学   23035篇
综合类   14篇
数学   56340篇
物理学   147505篇
  2021年   4190篇
  2020年   4440篇
  2019年   5141篇
  2018年   7231篇
  2017年   7522篇
  2016年   9893篇
  2015年   5364篇
  2014年   9323篇
  2013年   20733篇
  2012年   16040篇
  2011年   19161篇
  2010年   14632篇
  2009年   14765篇
  2008年   17583篇
  2007年   17431篇
  2006年   15962篇
  2005年   13927篇
  2004年   13135篇
  2003年   11729篇
  2002年   11838篇
  2001年   13817篇
  2000年   10251篇
  1999年   7968篇
  1998年   6794篇
  1997年   6567篇
  1996年   6105篇
  1995年   5399篇
  1994年   5309篇
  1993年   5201篇
  1992年   5585篇
  1991年   6003篇
  1990年   5748篇
  1989年   5714篇
  1988年   5395篇
  1987年   5585篇
  1986年   5233篇
  1985年   6608篇
  1984年   6664篇
  1983年   5620篇
  1982年   5714篇
  1981年   5415篇
  1980年   5217篇
  1979年   5690篇
  1978年   5813篇
  1977年   5868篇
  1976年   5937篇
  1975年   5562篇
  1974年   5500篇
  1973年   5668篇
  1972年   4233篇
排序方式: 共有10000条查询结果,搜索用时 734 毫秒
231.
232.
Radiophysics and Quantum Electronics - We propose and experimentally test a numerical method for correction of the influence of fluctuations in the distance to objects during noncontact probing in...  相似文献   
233.
The aim of the study presented in this paper was to characterize quantitatively the erosion of aluminum cathodes in high-current vacuum arcs. The experimental setup comprised two current generators. The first one, capable of generating a current of amplitude up to 350 kA, was used to produce a plasma jet, that is, the object to be investigated. The second generator was used to produce a source of probe radiation for imaging the object under investigation in soft x rays of energy ?ν ≈ 0.5–3 keV. The findings of the study are based on experimental data obtained by electrophysical and radiographic methods. It has been shown that the cathode erosion rate in a high-current vacuum arc is a function of the charge passed through the cathode.  相似文献   
234.
Nonlinear Dynamics - Introduction of stiffness nonlinearities to broaden the frequency bandwidth of vibratory energy harvesters has the adverse influence of complicating the response behavior of...  相似文献   
235.
Physics of Atomic Nuclei - The article presents the concept of a channel-type reactor with a combined cooled moderator. The moderator consists of ceramic beryllium oxide and a liquid...  相似文献   
236.
We describe the synthesis and the physical properties of polyaromatic hydrocarbons (PAHs) containing a phosphorus atom at the edge. In particular, the impact of the successive addition of aromatic rings on the electronic properties was investigated by experimental (UV/Vis absorption, fluorescence, cyclic voltammetry) and theoretical studies (DFT). The physical properties recorded in solution and in the solid state showed that the P‐containing PAHs exhibit properties expected for an emitter in white organic light‐emitting diodes (WOLEDs).  相似文献   
237.
238.
239.
New aromatic (co)polyesters containing pendant propargyloxy groups were synthesized by phase transfer‐catalyzed interfacial polycondensation of 5‐(propargyloxy)isophthaloyl chloride (P‐IPC) and various compositions of P‐IPC and isophthaloyl chloride with bisphenol A. FTIR and NMR spectroscopic data, respectively, revealed successful incorporation of pendant propargyloxy groups into (co)polyesters and formation of (co)polyesters with desired compositions. (Co)polyesters exhibited good solubility in common organic solvents such as chloroform, dichloromethane, and tetrahydrofuran and could be cast into transparent, flexible, and tough films from chloroform solution. Inherent viscosities and number average molecular weights of (co)polyesters were in the range 0.77–1.33 dL/g and 43,600–118,000 g/mol, respectively, indicating the achievement of reasonably high‐molecular weights. The 10% weight loss temperatures of (co)polyesters were in the range 390–420 °C, demonstrating their good thermal stability. (Co)polyesters exhibited Tg in the range 146–170 °C and Tg values decreased with increase in mol % incorporation of P‐IPC. The study of non‐isothermal curing by DSC indicated thermal crosslinking of (co)polyesters via propargyloxy groups. The utility of pendant propargyloxy group was demonstrated by post‐modification of the selected copolyester with 1‐(4‐azidobutyl)pyrene, 9‐(azidomethyl)anthracene, and azido‐terminated poly(ethyleneglycol) monomethyl ether via copper(I)‐catalyzed Huisgen 1,3‐dipolar cycloaddition reaction. FTIR and 1H NMR spectra confirmed that click reaction was quantitative. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 588–597  相似文献   
240.
Plasma Chemistry and Plasma Processing - The hydrocarbons present in diesel exhaust, although treated as minor pollutants, are equivalent to some of the major pollutants in terms of toxicity,...  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