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   497篇
  免费   60篇
  国内免费   38篇
化学   374篇
晶体学   2篇
力学   10篇
综合类   4篇
数学   49篇
物理学   156篇
  2023年   7篇
  2022年   13篇
  2021年   17篇
  2020年   20篇
  2019年   13篇
  2018年   7篇
  2017年   20篇
  2016年   14篇
  2015年   20篇
  2014年   19篇
  2013年   40篇
  2012年   24篇
  2011年   27篇
  2010年   25篇
  2009年   43篇
  2008年   26篇
  2007年   33篇
  2006年   33篇
  2005年   26篇
  2004年   22篇
  2003年   19篇
  2002年   15篇
  2001年   10篇
  2000年   16篇
  1999年   6篇
  1998年   9篇
  1997年   8篇
  1996年   4篇
  1995年   6篇
  1994年   9篇
  1993年   4篇
  1992年   8篇
  1991年   2篇
  1990年   4篇
  1989年   6篇
  1988年   4篇
  1987年   7篇
  1986年   3篇
  1985年   1篇
  1984年   2篇
  1983年   1篇
  1980年   1篇
  1972年   1篇
排序方式: 共有595条查询结果,搜索用时 921 毫秒
591.
Texture analysis is a subject of intensive focus in research due to its significant role in the field of image processing. However, few studies focus on colored texture analysis and even fewer use information theory concepts. Entropy measures have been proven competent for gray scale images. However, to the best of our knowledge, there are no well-established entropy methods that deal with colored images yet. Therefore, we propose the recent colored bidimensional fuzzy entropy measure, FuzEnC2D, and introduce its new multi-channel approaches, FuzEnV2D and FuzEnM2D, for the analysis of colored images. We investigate their sensitivity to parameters and ability to identify images with different irregularity degrees, and therefore different textures. Moreover, we study their behavior with colored Brodatz images in different color spaces. After verifying the results with test images, we employ the three methods for analyzing dermoscopic images of malignant melanoma and benign melanocytic nevi. FuzEnC2D, FuzEnV2D, and FuzEnM2D illustrate a good differentiation ability between the two—similar in appearance—pigmented skin lesions. The results outperform those of a well-known texture analysis measure. Our work provides the first entropy measure studying colored images using both single and multi-channel approaches.  相似文献   
592.
建立了微波消解电感耦合等离子体发射光谱法测定棉花中微量元素的方法,并用该法分别测定了天然彩棉和普通白棉中Ca,μg,Fe,Cu,Ba,Zn,Al,Sr,Mn和Si等元素的含量。该法检出限为0.9~21 μg·L-1,加标回收率为93%~111%,RSD<4.0%(n=5);研究结果表明天然彩棉中棕色彩棉和绿色彩棉中Ca,Cu,Zn,Al,Fe,Sr和Si等元素含量要明显高于普通白棉。文章的研究结果可为彩棉的显色原理研究以及真假彩棉的鉴定提供一定的科学依据。  相似文献   
593.
This work is concerned with the asymptotic behaviors of solutions to a class of non-autonomous stochastic Ginzburg-Landau equations driven by colored noise and deterministic non-autonomous terms defined on thin domains. The existence and uniqueness of tempered pullback random attractors are proved for the stochastic Ginzburg-Landau systems defined on $(n+1)$-dimensional narrow domain. Furthermore, the upper semicontinuity of these attractors is established, when a family of $(n+1)$-dimensional thin domains collapses onto an $n$-dimensional domain.  相似文献   
594.
Temperature-sensitive filled poly(N-isopropylacrylamide) (PNIPAAm) gel beads with diameters in the range of millimeters were prepared using the alginate technique. The polymerization and cross-linking reaction of NIPAAm in the presence of inorganic filling particles was performed in spherical networks of Ca-alginate forming interpenetrating networks (IPN). Thermo-sensitive gel beads could be obtained by washing these IPN with EDTA solution. The PNIPAAm gel beads were analyzed by optical methods to observe there swollen diameter in dependence on the temperature. The diameters of the swollen gel beads were in the range of 0.1 - 2 mm. The influence of the monomer to cross-linker ratio (MCR) and the filling materials (ferrofluid, BaTiO3, TiO2, and Ni,) were studied. The phase transition temperature (Tpt) was only weakly influenced by the MCR and the filling material remaining at around 34°C.  相似文献   
595.
Temperature-sensitive hydrogel beads were prepared by radiation crosslinking of poly(vinyl methyl ether) PVME spheres wrapped in Ca-alginate. The obtained gel beads have diameters in the sub-millimeter or millimeter range (depending on the PVME concentration). They were characterized by sol-gel analysis, swelling measurements, and differential scanning calorimetry. The gel content g increases with increasing radiation dose D. The swelling degree Qv decreases with increasing PVME concentration cp and increasing D. In comparison to PVME bulkgels the phase-transition temperature of the synthesized PVME gel beads is a little decreased.  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