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   491408篇
  免费   5276篇
  国内免费   1780篇
化学   259825篇
晶体学   7495篇
力学   21790篇
综合类   8篇
数学   58525篇
物理学   150821篇
  2020年   3489篇
  2019年   3728篇
  2018年   4410篇
  2017年   4233篇
  2016年   7193篇
  2015年   5181篇
  2014年   7760篇
  2013年   21842篇
  2012年   16496篇
  2011年   20416篇
  2010年   13530篇
  2009年   13437篇
  2008年   18789篇
  2007年   19023篇
  2006年   18249篇
  2005年   16538篇
  2004年   15039篇
  2003年   13334篇
  2002年   13165篇
  2001年   14832篇
  2000年   11374篇
  1999年   9119篇
  1998年   7491篇
  1997年   7346篇
  1996年   7221篇
  1995年   6580篇
  1994年   6323篇
  1993年   6250篇
  1992年   6735篇
  1991年   6740篇
  1990年   6298篇
  1989年   6097篇
  1988年   6443篇
  1987年   6012篇
  1986年   5746篇
  1985年   8134篇
  1984年   8319篇
  1983年   6855篇
  1982年   7267篇
  1981年   7227篇
  1980年   6913篇
  1979年   7195篇
  1978年   7240篇
  1977年   7203篇
  1976年   7189篇
  1975年   6864篇
  1974年   6781篇
  1973年   6953篇
  1972年   4443篇
  1971年   3487篇
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
141.
A standard model Lagrangian is constructed making the pseudo-Finsleroid generalization of the Yang-Mills field equation by the conformal method. The Higgs field potential is suggested that ensures generation of particle masses caused by the spontaneous symmetry breaking. After transition to the conformal coordinates, the expressions obtained assume the standard form that in many cases allows the results of pseudo-Euclidean theory to be used in calculations of the Feynman diagrams. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 44–51, April, 2006.  相似文献   
142.
For fairly high concentrations, the effective arsenic diffusioncoefficient is known to grow linearly with the concentration.In this paper, we consider the strongly enhanced diffusion ofarsenic by asymptotic methods, and extend the results of a previouspaper (King & Please, 1987) in three ways: we characterizean additional (low-concentration) region; we consider the influenceof the initial data; and we consider the case of constant surfaceconcentration.  相似文献   
143.
144.
A method for suppressing self-modulation in backward-wave tubes is proposed. Additional delay is introduced into the feedback circuit, owing to which the output signal amplitude affects the electron beam current that enters into the interaction space. Numerical simulations demonstrate that the operating current in the single-frequency oscillation mode may be increased roughly twofold.  相似文献   
145.
Ascidia malaca gametes before fertilization incubated in 10?5 or 10?7 M solutions of tributyltin(IV) chloride, TBTCl, for 3 h appear highly damaged under transmission electron microscopy observation. Also, the fertilization process is affected by the compound: the damaged spermatozoa are present in the vitelline coat and the egg does not cleave. An increase of microbodies, structurally similar to peroxisomes, have been detected in the egg peripheral cytoplasm, probably in relation to their role in alleviating damage to some cellular components. The results have shown that the reproduction of ascidians under unfavourable environmental conditions is prevented. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
146.
147.
148.
Optics and Spectroscopy - The fluorescence of the nematic liquid crystal n-butyl-n′-methoxyazoxybenzene (BMAOB) in the form of a layer and in porous glasses with pores of different diameter...  相似文献   
149.
The effects of the blend ratio and initiating system on the viscoelastic properties of nanostructured natural rubber/polystyrene‐based interpenetrating polymer networks (IPNs) were investigated in the temperature range of ?80 to 150 °C. The studies were carried out at different frequencies (100, 50, 10, 1, and 0.1 Hz), and their effects on the damping and storage and loss moduli were analyzed. In all cases, tan δ and the storage and loss moduli showed two distinct transitions corresponding to natural rubber and polystyrene phases, which indicated that the system was not miscible on the molecular level. However, a slight inward shift was observed in the IPNs, with respect to the glass‐transition temperatures (Tg's) of the virgin polymers, showing a certain degree of miscibility or intermixing between the two phases. When the frequency increased from 0.1 to 100 Hz, the Tg values showed a positive shift in all cases. In a comparison of the three initiating systems (dicumyl peroxide, benzoyl peroxide, and azobisisobutyronitrile), the dicumyl peroxide system showed the highest modulus. The morphology of the IPNs was analyzed with transmission electron microscopy. The micrographs indicated that the system was nanostructured. An attempt was made to relate the viscoelastic behavior to the morphology of the IPNs. Various models, such as the series, parallel, Halpin–Tsai, Kerner, Coran, Takayanagi, and Davies models, were used to model the viscoelastic data. The area under the linear loss modulus curve was larger than that obtained by group contribution analysis; this showed that the damping was influenced by the phase morphology, dual‐phase continuity, and crosslinking of the phases. Finally, the homogeneity of the system was further evaluated with Cole–Cole analysis. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1680–1696, 2003  相似文献   
150.
R.J Hand 《Journal of Non》2003,315(3):276-287
Glass may be strengthened by epoxy coatings although the strengthening mechanisms remain unclear. Possible strengthening mechanisms are reviewed and are used to analyse strength data for both a solvent based and a water based coating system. The coatings either fill (solvent based coatings), or partially fill (water based coatings) surface cracks and it is shown that closure stresses arising from the thermal expansion mismatch of the coating within these cracks can account for the observed degrees of strengthening. It is also demonstrated that other suggested mechanisms such as flaw healing cannot fully account for the observed degree of strengthening.  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