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   940篇
  免费   32篇
  国内免费   6篇
化学   579篇
晶体学   6篇
力学   41篇
数学   131篇
物理学   221篇
  2023年   8篇
  2022年   28篇
  2021年   35篇
  2020年   27篇
  2019年   22篇
  2018年   18篇
  2017年   13篇
  2016年   45篇
  2015年   34篇
  2014年   30篇
  2013年   72篇
  2012年   62篇
  2011年   50篇
  2010年   48篇
  2009年   51篇
  2008年   94篇
  2007年   79篇
  2006年   54篇
  2005年   28篇
  2004年   32篇
  2003年   16篇
  2002年   25篇
  2001年   16篇
  2000年   10篇
  1999年   8篇
  1998年   4篇
  1997年   10篇
  1996年   8篇
  1995年   5篇
  1994年   6篇
  1993年   4篇
  1992年   1篇
  1991年   4篇
  1990年   3篇
  1989年   1篇
  1988年   3篇
  1987年   2篇
  1986年   2篇
  1985年   1篇
  1984年   2篇
  1983年   1篇
  1982年   5篇
  1981年   1篇
  1980年   2篇
  1979年   2篇
  1977年   1篇
  1976年   2篇
  1974年   1篇
  1973年   1篇
  1970年   1篇
排序方式: 共有978条查询结果,搜索用时 46 毫秒
131.
132.
Fractional calculus (FC) is the area of calculus that generalizes the operations of differentiation and integration. FC operators are non-local and capture the history of dynamical effects present in many natural and artificial phenomena. Entropy is a measure of uncertainty, diversity and randomness often adopted for characterizing complex dynamical systems. Stemming from the synergies between the two areas, this paper reviews the concept of entropy in the framework of FC. Several new entropy definitions have been proposed in recent decades, expanding the scope of applicability of this seminal tool. However, FC is not yet well disseminated in the community of entropy. Therefore, new definitions based on FC can generalize both concepts in the theoretical and applied points of view. The time to come will prove to what extend the new formulations will be useful.  相似文献   
133.
134.
135.
Journal of Radioanalytical and Nuclear Chemistry - A procedure for characterizing the activity amount of 125I seed was developed in order to establish a secondary standard activity measurement...  相似文献   
136.
The effects of the main operation variables on the electrochemical oxidation of simulated tributyl phosphate (TBP) waste by a boron-doped diamond anode are individually studied. The optimum operating conditions are obtained as follows: 4 g L?1 initial TBP concentration, 180 min degradation time, 40 mA cm?2 current density, 0.5 mol L?1 Na2SO4 as the supporting electrolyte, and unadjusted pH of the aqueous phase. Under such conditions, a chemical oxygen demand (COD) removal ratio of 82.3% is achieved, and the energy consumption is 26.16 kWh m?3. A degradation mechanism of TBP is tentatively proposed.  相似文献   
137.
The biological activity influence on the mangrove sediment capacity to remove 65Zn and 109Cd from tidal water was evaluated in a site chronically polluted. Benthic Activity Indexes (BAI), corresponding to relative estimates of biological impact on radiotracer accumulation, were higher for 109Cd (~?38%) than for 65Zn (~?10%) in the top centimetre of sediment. However, BAI exceeded 96% for deeper sediment layers. This apparent decrease in radiotracer diffusion into deep sediments through biological activity inhibition is stronger than reported for much less polluted mangrove nearby, suggesting that benthic organisms tolerant of chronic metal pollution may affect metal sorption mechanisms.  相似文献   
138.
We have investigated the role of the retroviral lipid bilayer and envelope proteins in the adsorption of retroviral vectors (RVs) to a Fractogel DEAE matrix. Intact RVs and their degradation components (envelope protein-free vectors and solubilized vector components) were adsorbed to this matrix and eluted using a linear gradient. Envelope protein-free RVs (Env(-)) and soluble envelope proteins (gp70) eluted in a significantly lower range of conductivities than intact RVs (Env(+)) (13.7-30 mS/cm for Env(-) and gp70 proteins vs. 47-80 mS/cm for Env(+)). The zeta (zeta)-potential of Env(+) and Env(-) vectors was evaluated showing that envelope proteins define the pI of the viral particles (pI (Env(+)) < 2 versus 3 < pI (Env(-)) < 4) and that Env(+) and Env(-) vectors have similar zeta-potentials within pH 5 and 8. The results presented herein indicate that the adsorption of retroviral particles occurs through multi-point interaction of the envelope proteins with the cationic groups on the chromatographic matrix. The strength of this adsorption is thus dependent on the amount of envelope protein present in the viral lipid bilayer. In conclusion, AEXc enables the separation of gp70 proteins as well as envelope protein-free vectors constituting a significant improvement to the quality of retroviral preparations for gene therapy applications.  相似文献   
139.
This paper describes the development and optimization, by using multivariate analysis, of a GC-MS-SIM method for evaluation of the 16 polyaromatic hydrocarbons considered as priority pollutants in atmospheric particulate material by the US EPA. In order to assure an adequate separation in the shortest analysis time, a multivariate design was used to set the conditions of the oven temperature program. The optimization process was carried out using factorial fractional design and Box-Behnken design. The following factors were evaluated: initial temperature, temperature rate #1, intermediary temperature, temperature rate #2, and final temperature. The optimized conditions were set at: 70 degrees C (2 min) --> 200 degrees C (30 degrees C/min, 5 min) --> 300 degrees C (5 degrees C/min, 1.67 min). Moreover, we have also optimized the injector temperature as 310 degrees C and sampling time as 0.8 min. The total analysis time was 33 min. Validation of GC-MS-SIM yielded satisfactory results for repetitivity of the detector response and retention times, and linearity of calibration curves. LOD were established as 0.13-0.34 ng/mL (peak area) and 0.18-0.72 ng/mL (peak height). The method has been shown to be appropriate for the analysis of samples of atmospheric particulate material and/or other environmental matrices.  相似文献   
140.
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