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   1149篇
  免费   31篇
  国内免费   3篇
化学   895篇
晶体学   12篇
力学   5篇
数学   38篇
物理学   233篇
  2022年   11篇
  2021年   14篇
  2020年   23篇
  2019年   22篇
  2018年   15篇
  2017年   6篇
  2016年   24篇
  2015年   21篇
  2014年   19篇
  2013年   71篇
  2012年   47篇
  2011年   56篇
  2010年   21篇
  2009年   41篇
  2008年   56篇
  2007年   54篇
  2006年   58篇
  2005年   63篇
  2004年   72篇
  2003年   74篇
  2002年   47篇
  2001年   52篇
  2000年   36篇
  1999年   17篇
  1998年   6篇
  1997年   17篇
  1996年   13篇
  1995年   5篇
  1994年   7篇
  1993年   17篇
  1992年   13篇
  1991年   5篇
  1990年   5篇
  1989年   14篇
  1988年   17篇
  1987年   11篇
  1986年   12篇
  1985年   14篇
  1984年   21篇
  1983年   8篇
  1982年   8篇
  1980年   9篇
  1979年   7篇
  1978年   9篇
  1977年   8篇
  1976年   4篇
  1975年   5篇
  1974年   4篇
  1973年   7篇
  1971年   3篇
排序方式: 共有1183条查询结果,搜索用时 468 毫秒
161.
This study proposes a prediction method for assessing the sound of a passing vehicle that is transmitted through a glass plate, which employs the vibro-acoustic finite-difference time-domain (FDTD) method. The noise that is transmitted through the glass in a building façade, which is affected by the sound-insulation characteristics of its glass plates, can have a psychological influence such as a sleep disorder on the residents. In this study, a prediction method for the spectral characteristics of the transmitting sound through glass plates is proposed. The sound-insulation characteristics of glass plates are obtained using a vibro-acoustic FDTD method, and are then synthesized with the sound of passing vehicles obtained by in situ measurement. Firstly, the sound transmitted through several kinds of glass plates is simulated using the proposed method. Then, in order to confirm the validity of this method, the simulated results are compared to measured sounds transmitted by passing vehicles into a room near the street.  相似文献   
162.
We demonstrated the stimulation of neurons at a single-cell level in cultured neuronal network by a focused femtosecond laser. When the femtosecond laser was focused on a neuron loaded with a fluorescent calcium indicator, the fluorescence intensity immediately increased at the laser spot, suggesting that intracellular Ca2+ increases in the neuronal cell due to the femtosecond laser irradiation. The probability of Ca2+ elevation at the laser spot depended on the average laser power, irradiation time, and position of the focal point along the optical axis, indicating that the femtosecond laser activates neurons because of multiphoton absorption. Moreover, after laser irradiation of a single neuron cultured on multielectrode arrays, the evoked electrical activity of the neurons was demonstrated by electrophysiological systems, which concluded that the focused femtosecond laser could achieve stimulating a single neuron in a neuronal network with high spatial and temporal resolution.  相似文献   
163.
164.
Sakamoto  S.  Nagamine  K. 《Hyperfine Interactions》1996,99(1):277-283
Longitudinal cooling forces have been measured for heavy ions from C6+ to U92+ at various energies from 50 to 360 MeV/u. Two experimental methods are described which offer the opportunity to measure the cooling force over the whole range of relative ion velocities from zero to 107 m/s. Measurements for various ion species are presented which show a pronounced deviation from the expected q2 scaling in the regime of low relative ion velocities. Further investigations concerning the influence of the magnetic field strength in the cooler revealed no significant influence.  相似文献   
165.
A new AB2 type building block for synthesis of dendritic compounds is made starting from Michael addition of 2 equiv of 3-hydroxyacetophenone to acrylate, followed by decarboxylation and deprotection of either carboxyl or hydroxyl protecting groups. [G1]-[G4] dendrons and [G2] dendrimer were synthesized by the reiterative [hydrogenolysis then DCC/DPTS coupling] sequence using a combination of convergent and divergent growth methods.  相似文献   
166.
Syntheses of 3-substituted indazoles and benzoisoxazoles were efficiently accomplished with the aid of Pd-catalyzed intramolecular carbon-nitrogen and carbon-oxygen bond formations. The catalyst system described herein allows the cyclization to proceed under very mild conditions and thus could be applied to a wide range of substrates with acid- or base-sensitive functional groups. A total synthesis for the indazole ring-containing natural product nigellicine is also described.  相似文献   
167.
168.
Summary The purpose of the present paper is to propose a simple but practically useful procedure for the analysis of multidimensional contingency tables of survey data. By the procedure we can determine the predictor on which a specific variable has the strongest dependence and also the optimal combination of predictors. The procedure is very simply realized by the search for the minimum of the statistic AIC within a set of models proposed in this paper. The practical utility of the procedure is demonstrated by the results of some successful applications to the analysis of the survey data of the Japanese national character. The difference between the present procedure and the conventional test procedure is briefly discussed. The Institute of Statistical Mathematics  相似文献   
169.
170.
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