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   341篇
  免费   17篇
  国内免费   3篇
化学   268篇
晶体学   2篇
力学   8篇
数学   30篇
物理学   53篇
  2023年   4篇
  2022年   18篇
  2021年   26篇
  2020年   18篇
  2019年   17篇
  2018年   15篇
  2017年   9篇
  2016年   19篇
  2015年   7篇
  2014年   13篇
  2013年   29篇
  2012年   16篇
  2011年   16篇
  2010年   15篇
  2009年   7篇
  2008年   17篇
  2007年   16篇
  2006年   9篇
  2005年   9篇
  2004年   13篇
  2003年   9篇
  2002年   16篇
  2001年   7篇
  2000年   8篇
  1999年   3篇
  1997年   2篇
  1996年   1篇
  1995年   3篇
  1994年   1篇
  1993年   1篇
  1991年   3篇
  1989年   1篇
  1988年   2篇
  1987年   3篇
  1986年   1篇
  1985年   2篇
  1984年   1篇
  1980年   1篇
  1970年   1篇
  1968年   1篇
  1932年   1篇
排序方式: 共有361条查询结果,搜索用时 46 毫秒
331.
碳纳米管/聚合物纳米复合材料研究进展   总被引:12,自引:0,他引:12  
碳纳米管/聚合物纳米复合材料是近几年发展起来的一个新的研究方向。本文从增强和功能性两个方面评述了碳纳米管/聚合物纳米复合材料的发展过程以及最新进展,详细讨论了碳纳米管在聚合物中的分散、取向和胃面相互作用对复合材料力学性能的影响,介绍了碳纳米管的加入赋予聚合物的一些新的光电性能,并对今后的研究方向进行了展望。  相似文献   
332.
333.
The topological susceptibility 〈Q t 2 〉/V is computed for theCP 3-model appropriately discretized on simplicial lattices onT 2 andS 2, respectively. We concentrate on volumes 1?V2?100, ξ being the correlation length measured onT 2. Approximate scaling behaviour is found presumably not related to the continuum limit but rather to the occurence of dislocations. We observe finite-size effects which are fairly weak on the sphere, however.  相似文献   
334.
基于一类新的胞腔排除遗传算法求解迭代函数系逆问题   总被引:4,自引:1,他引:3  
提出求解迭代函数系(IFS)逆问题的一类有效遗传算法,该算法基于新发展的可拼接/可分解编码,并结合使用胞腔排除技巧,对于典型图像的应用表明;该方法可有效应用于基于矩匹配表示的IFS逆向题求解,从而为IFS逆问题的数值方法研究提供了一条新颖途径。  相似文献   
335.
Antimicrobial resistance is a dramatic global threat; however, the slow progress of new antibiotic development has impeded the identification of viable alternative strategies. Natural antioxidant-based antibacterial approaches may provide potent therapeutic abilities to effectively block resistance microbes’ pathways. While essential oils (EOs) have been reported as antimicrobial agents, its application is still limited ascribed to its low solubility and stability characters; additionally, the related biomolecular mechanisms are not fully understood. Hence, the study aimed to develop a nano-gel natural preparation with multiple molecular mechanisms that could combat bacterial resistance in an acne vulgaris model. A nano-emulgel of thyme/clove EOs (NEG8) was designed, standardized, and its antimicrobial activity was screened in vitro and in vivo against genetically identified skin bacterial clinical isolates (Pseudomonas stutzeri, Enterococcus faecium and Bacillus thuringiensis). As per our findings, NEG8 exhibited bacteriostatic and potent biofilm inhibition activities. An in vivo model was also established using the commercially available therapeutic, adapalene in contra genetically identified microorganism. Improvement in rat behavior was reported for the first time and NEG8 abated the dermal contents/protein expression of IGF-1, TGF-β/collagen, Wnt/β-catenin, JAK2/STAT-3, NE, 5-HT, and the inflammatory markers; p(Ser536) NF-κBp65, TLR-2, and IL-6. Moreover, the level of dopamine, protective anti-inflammatory cytokine, IL-10 and PPAR-γ protein were enhanced, also the skin histological structures were improved. Thus, NEG8 could be a future potential topical clinical alternate to synthetic agents, with dual merit mechanism as bacteriostatic antibiotic action and non-antibiotic microbial pathway inhibitor.  相似文献   
336.
This Note is concerned with the severely ill-posed Cauchy–Stokes problem. This inverse problem is rephrased into an optimization one: An energy-like error functional is introduced. We prove that the optimality condition of the first order is equivalent to solving an interfacial equation which turns out to be a Cauchy–Steklov–Poincaré operator. Numerical trials highlight the efficiency of the present method. To cite this article: A. Ben Abda et al., C. R. Mecanique 337 (2009).  相似文献   
337.
Numerous species of Allium genus have been used in the traditional medicine based on their vast biological effects, e.g., antimicrobial, digestion stimulant, anti-sclerotic, soothing, antiradical or wound healing properties. In this work, unpolar and polar extracts from two lesser-investigated species of Allium growing in Kazakhstan, Allium galanthum Kar. & Kir. (AG) and A. turkestanicum Regel. (AT), were studied for their composition and biological effects. In the HPLC-ESI-QTOF-MS/MS analyses of water and alcoholic extracts simple organic acids, flavonoids and their glycosides were found to be the best represented group of secondary metabolites. On the other hand, in the GC-MS analysis diethyl ether, extracts were found to be rich sources of straight-chain hydrocarbons and their alcohols, fatty acids and sterols. The antimicrobial activity assessment showed a lower activity of polar extracts, however, the diethyl ether extract from AT bulbs and AG chives showed the strongest activity against Bacillus subtilis ATCC 6633, B. cereus ATCC 10876, some species of Staphylococcus (S. aureus ATCC 25923 and S. epidermidis ATCC 12228) and all tested Candida species (Candida albicans ATCC 2091, Candida albicans ATCC 10231, Candida glabrata ATCC 90030, Candida krusei ATCC 14243 and Candida parapsilosis ATCC 22019) with a minimum inhibitory concentration of 0.125–0.5 mg/mL. The highest antiradical capacity exhibited diethyl ether extracts from AG bulbs (IC50 = 19274.78 ± 92.11 mg Trolox eq/g of dried extract) in DPPH assay. In ABTS scavenging assay, the highest value of mg Trolox equivalents, 50.85 ± 2.90 was calculated for diethyl ether extract from AT bulbs. The same extract showed the highest inhibition of mushroom tyrosinase (82.65 ± 1.28% of enzyme activity), whereas AG bulb ether extract was the most efficient murine tyrosinase inhibitor (54% of the enzyme activity). The performed tests confirm possible cosmeceutical applications of these plants.  相似文献   
338.
水相中辣根过氧化物酶的反应动力学和机理研究   总被引:4,自引:0,他引:4  
陈建波  夏春谷 《分子催化》2000,14(2):125-128
利用分光光度法 ,对水相中辣根过氧化物酶与底物反应的最适反应条件进行了研究 .同时 ,用停流法探讨了 2 5℃时辣根过氧化物酶反应过程中各种中间化合物的形成和消失速度 ;并用停流光谱法对稳态动力学的研究结果进行了验证  相似文献   
339.
A macroscopic model is presented aimed at assessing the macroscopic elastic behaviour of materials reinforced by periodically distributed flexible membranes. According to this model, called multiphase model, the reinforced material is described not as a single homogenized continuum as in the classical homogenization approach, but as the superposition of two mutually interacting continuous media, namely the matrix phase and the reinforcement phase. It is shown in particular how such a model allows to capture both scale and boundary effects, which cannot be accounted for in a classical homogenization procedure.  相似文献   
340.
The readily available N-Boc-protected delta-amino alpha,beta-unsaturated gamma-keto ester 1 was diastereoselectively reduced to the corresponding alcohols 2 and 3, using boron- and aluminum-based reducing reagents. Reduction reactions were successful and resulted in anti/syn ratios of alcohols of >95:5 (80% yield), using LiAlH(O-t-Bu)(3) in EtOH at -78 degrees C under chelation control, and 5:95 (98% yield), using NB-Enantride in THF at -78 degrees C under Felkin-Anh control.  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