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   96829篇
  免费   4006篇
  国内免费   3581篇
化学   38493篇
晶体学   1128篇
力学   7859篇
综合类   227篇
数学   33863篇
物理学   22846篇
  2024年   58篇
  2023年   407篇
  2022年   582篇
  2021年   760篇
  2020年   999篇
  2019年   971篇
  2018年   11063篇
  2017年   10903篇
  2016年   6997篇
  2015年   1876篇
  2014年   1521篇
  2013年   1893篇
  2012年   5640篇
  2011年   12368篇
  2010年   6999篇
  2009年   7337篇
  2008年   8054篇
  2007年   9923篇
  2006年   1292篇
  2005年   2192篇
  2004年   2203篇
  2003年   2527篇
  2002年   1595篇
  2001年   711篇
  2000年   690篇
  1999年   487篇
  1998年   430篇
  1997年   362篇
  1996年   405篇
  1995年   306篇
  1994年   263篇
  1993年   237篇
  1992年   175篇
  1991年   168篇
  1990年   150篇
  1989年   143篇
  1988年   116篇
  1987年   98篇
  1986年   104篇
  1985年   105篇
  1984年   81篇
  1983年   66篇
  1982年   62篇
  1981年   56篇
  1980年   51篇
  1979年   48篇
  1914年   45篇
  1912年   40篇
  1909年   41篇
  1908年   40篇
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
11.
Cinnamaldehyde (CA), an active ingredient isolated from the traditional Chinese medicine Cortex Cinnamomi, has a wide range of bioactivities. To clarify the distribution characteristics of CA, a selective and sensitive method utilizing gas chromatography–mass spetrometry was initially developed for simultaneously determining the concentration of CA and its metabolite cinnamyl alcohol in rat tissues. Selected ion masses of m/z 131, 105 and 92 were chosen, and separation of the analytes was performed on a DB‐5 ms (30 m × 0.25 mm, 0.25 µm, thickness) capillary column by gas chromatography–mass spectrometry. The calibration curves demonstrated good linearity and reproducibility over the range of 20–2000 and 20–4000 ng/mL for various tissue samples. Recoveries ranged from 86.8 to 107.5%, while intra‐ and interday relative standard deviations were all <11.3%. The analysis method was successfully applied in tissue distribution studies for CA and cinnamyl alcohol. As CA and cinnamyl alcohol may inter‐convert to one another, simultaneous determination of both analytes provides a comparative and accurate data for tissue study. The concentrations of CA and cinnamyl alcohol remaining in spleen were the highest among the main organs, including heart, liver, spleen, lung, kidney and brain. In addition, there was no long‐term accumulation of CA in rat tissues. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
12.
Mesoscopic modeling at the pore scale offers great promise in exploring the underlying structure transport performance of flow through porous media. The present work studies the fluid flow subjected to capillarity-induced resonance in porous media characterized by different porous structure and wettability. The effects of porosity and wettability on the displacement behavior of the fluid flow through porous media are discussed. The results are presented in the form of temporal evolution of percentage saturation and displacement of the fluid front through porous media. The present study reveals that the vibration in the form of acoustic excitation could be significant in the mobilization of fluid through the porous media. The dependence of displacement of the fluid on physicochemical parameters like wettability of the surface, frequency along with the porosity is analyzed. It was observed that the mean displacement of the fluid is more in the case of invading fluid with wetting phase where the driving force strength is not so dominant.  相似文献   
13.
14.
We prove that the group of diffeomorphisms of the interval [0, 1] contains surface groups whose action on (0, 1) has no global fix point and such that only countably many points of the interval (0, 1) have non-trivial stabiliser.  相似文献   
15.
A strategy based on covalent organic frameworks for ultrafast ion transport involves designing an ionic interface to mediate ion motion. Electrolyte chains were integrated onto the walls of one-dimensional channels to construct ionic frameworks via pore surface engineering, so that the ionic interface can be systematically tuned at the desired composition and density. This strategy enables a quantitative correlation between interface and ion transport and unveils a full picture of managing ionic interface to achieve high-rate ion transport. Moreover, the effect of interfaces was scaled on ion transport; ion mobility is increased in an exponential mode with the ionic interface. This strategy not only sets a benchmark system but also offers a general guidance for designing ionic interface that is key to systems for energy conversion and storage.  相似文献   
16.
17.
18.
19.
A new spectral problem is proposed, and nonlinear differential equations of the corresponding hierarchy are obtained. With the help of the nonlinearization appr...  相似文献   
20.
The design and exploration of efficient, stable and environmentally compatible organic emitters for an electrochemiluminescence (ECL) sensor is a promising topic. Herein, a novel environmentally-friendly luminophore, ZnBCBTP@MWCNTs, were fabricated via self-assembly of porphyrin molecules (ZnBCBTP) onto multi-walled carbon nanotubes (MWCNTs). The resulting luminophore ZnBCBTP@MWCNTs displayed not only the highly ECL property and but also the good accelerated electron mobility. Then, a label-free ECL biosensor based ZnBCBTP@MWCNTs was constructed for the ultrasensitive detection of uric acid. Excitingly, this proposed ECL biosensor performed a good linear relationship in the range of 0–300 μM with a low detection limit of 1.4 μM, thus offering another reliable and feasible sensing platform for clinical bioanalysis with good selectivity, stability, and repeatability.  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