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   311篇
  免费   3篇
  国内免费   1篇
化学   171篇
晶体学   2篇
力学   8篇
数学   47篇
物理学   87篇
  2024年   1篇
  2023年   1篇
  2022年   4篇
  2021年   5篇
  2020年   7篇
  2019年   15篇
  2018年   14篇
  2017年   15篇
  2016年   18篇
  2015年   6篇
  2014年   15篇
  2013年   42篇
  2012年   22篇
  2011年   23篇
  2010年   15篇
  2009年   12篇
  2008年   18篇
  2007年   20篇
  2006年   13篇
  2005年   6篇
  2004年   7篇
  2003年   4篇
  2002年   10篇
  2001年   3篇
  1998年   2篇
  1997年   2篇
  1996年   1篇
  1995年   1篇
  1992年   1篇
  1991年   1篇
  1989年   1篇
  1988年   2篇
  1985年   3篇
  1984年   1篇
  1981年   2篇
  1978年   1篇
  1976年   1篇
排序方式: 共有315条查询结果,搜索用时 15 毫秒
201.
202.
203.
204.
    
The extra chromosome 21 of Down syndrome (DS) or trisomy 21 patients contains an average of 40 extra copies of rRNA genes and the in vivo/in vitro regulation of the activity of these genes is not fully understood. The objective of this work was to compare the NORs expression pattern in interphase lymphocytes of DS patients with regular trisomy 21 and control individuals according to phytohemagglutinin (PHA) concentration (0.37, 0.75, 1.48 and 2.21 ml) per 100 ml of medium. Because the AgNOR staining is an indicator of the active rRNA genes, comparison of the image analysis values of the AgNOR area in 72 h cultivated lymphocytes for each concentration of PHA between DS patients (N=30) and controls (N=24) provided a plausible conclusion on the regulation of the extra rRNA genes in DS lymphocytes. The nucleolus organizer regions area/total nuclear area (NORa/TNa) was calculated using an in-house computer program. Fifty consecutive interphases per PHA concentration were analysed for each individual, for determination of the NORa/TNa. In contrast to healthy controls, NORa/TNa of lymphocytes from DS patient babies/children (0-8 years old) increased gradually in parallel with the PHA concentration in the culture medium: 10.44+/-1.72% for 0.37 ml of PHA, 11.74+/-1.93% for 0.75 ml of PHA, 13.25+/-2.03% for 1.48 ml of PHA and 13.43+/-2.08% for 2.21 ml of PHA per 100 ml of medium. Contrary to control cells (in which the NORa/TNa ratio according to PHA concentration in the culture medium remains constant), DS interphase lymphocytes in culture do not down-regulate their NOR expression. These results obtained from interphase NORs are consistent with the previous results obtained by evaluating the mean of AgNOR+ chromosome number in metaphase cells, also in relation to the mitogen concentration in the culture medium.  相似文献   
205.
1-Aryl-3-phenethylamino-1-propanone hydrochlorides 1-10, which are potentialpotent cytotoxic agents, were synthesized via Mannich reactions using paraformaldehyde,phenethylamine hydrochloride as the amine component and acetophenone, 4'-methyl-, 4'-methoxy-, 4'-chloro-, 4'-fluoro-, 4'-bromo-, 2',4'-dichloro-, 4'-nitro-, 4'-hydroxyacetophenone or 2-acetylthiophene as the ketone component. Yields were in the87-98 % range. Of the compounds synthesized, compounds 2, 6-8 and 10 were new. Theoptimum reaction conditions were investigated by changing the mol ratios of the reactants,the solvents and the acidity levels using 1 and 10 as representative targets. It was observedthat the best mol ratio of the ketone, paraformaldehyde and phenethylamine hydrochloridewas 1:1.2:1 (compared with a 2:2.1 ratio), and the most suitable reaction medium wasethanol containing concentrated hydrochloric acid (compared with only ethanol or nosolvent). This study may serve as a guide for the conditions of the reactions to synthesizecompounds having similar chemical structures.  相似文献   
206.
Many bar soaps are processed using continuous processing technologies, including single and twin screw extrusion. However, in spite of the industrial importance of the extrusion-based processing of bar soaps the rheological behavior of bar soaps is poorly understood. Here, the shear viscosity and the formation of gross surface irregularities upon extrusion of the bar soap were investigated using steady torsional, rectangular slit, and capillary flows. Furthermore, the structure development aspects were investigated using wide-angle X-ray diffraction and scanning electron microscopy. It is revealed that the flow and deformation behavior of bar soaps is complicated by the ubiquitous presence of wall slip, viscoplasticity, gross surface irregularities, and various structuring aspects. The orientation of crystallites and the shear stress dependent fracture of a crystalline component of the formulation at the wall during flow were identified as some of the contributing effects to the development of the structure of the bar soap during flow and deformation.  相似文献   
207.
208.
In this paper we consider the asymptotic behavior of the Ginzburg–Landau model for superconductivity in three dimensions, in various energy regimes. Through an analysis via Γ-convergence, we rigorously derive a reduced model for the vortex density and deduce a curvature equation for the vortex lines. In the companion paper (Baldo et al. Commun. Math. Phys. 2012, to appear) we describe further applications to superconductivity and superfluidity, such as general expressions for the first critical magnetic field H c1, and the critical angular velocity of rotating Bose–Einstein condensates.  相似文献   
209.
    
The study was to determine selective removal and recovery of Cr(VI) from acidic media by solvent extraction (SX) using asymmetric imidazolium-based room temperature imidazolium bromide salts (ARTILs) as the extractants. The relevant parameters on the extraction and the stripping of Cr(VI) were investigated to identify optimum conditions. The optimum conditions were determined as equilibration time 5 minutes, acid concentration and type 0.5?mol/L H2SO4, stirring speed 1200?rpm, extractant concentration and type 0.5?mol/L ARTIL5, phase ratio 2.0 and stripping reagent type, and concentration 2.0?mol/L NH3. In optimum conditions, decyl substituted ARTIL was best in extraction process about 99.7% of extraction rate, whereas moderately hydrophobic pentyl substituted ARTIL was best in stripping process about 70.0% of stripping rate. Also, the optimized process was found as so selective toward Cr(VI) in the presence of the other metal ions with an environmental-friendly liquid–liquid–based SX method.  相似文献   
210.
    
In the present work, the experimental and the theoretical spectroscopic properties of 1-Methyl-6-Nitro-1H- Benzimidazole were investigated. The FT-IR (400~4 000 cm-1) and FT-Raman spectra (100~4 000 cm-1) of 1-Methyl-6-Nitro-1H- Benzimidazole in the solid phase were recorded. Also, experimental NMR and UV spectra of titled molecule were measured. To interpret the experimental data, geometric parameters, vibrational frequencies, NMR, UV spectra and NLO analysis of the optimized molecule were calculated using ab initio Hartree–Fock (HF) method and density functional theory (B3LYP) method with the 6-31++G(d,p) and 6-311++G(d,p) basis sets. Vibrational bands were assigned based on the potential energy distribution using the VEDA 4 program. The theoretical results showed good agreement with the experimental values.  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