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   460篇
  免费   16篇
  国内免费   1篇
化学   286篇
晶体学   6篇
力学   15篇
数学   84篇
物理学   86篇
  2023年   1篇
  2022年   25篇
  2021年   9篇
  2020年   9篇
  2019年   5篇
  2018年   4篇
  2017年   3篇
  2016年   14篇
  2015年   11篇
  2014年   23篇
  2013年   16篇
  2012年   30篇
  2011年   31篇
  2010年   26篇
  2009年   17篇
  2008年   22篇
  2007年   26篇
  2006年   28篇
  2005年   19篇
  2004年   11篇
  2003年   17篇
  2002年   16篇
  2001年   11篇
  2000年   15篇
  1999年   5篇
  1998年   7篇
  1997年   5篇
  1996年   6篇
  1995年   5篇
  1994年   8篇
  1993年   6篇
  1992年   4篇
  1991年   3篇
  1989年   3篇
  1988年   2篇
  1987年   3篇
  1986年   3篇
  1985年   5篇
  1984年   5篇
  1983年   1篇
  1982年   1篇
  1981年   3篇
  1980年   3篇
  1978年   2篇
  1975年   1篇
  1974年   3篇
  1972年   2篇
  1971年   1篇
  1965年   1篇
排序方式: 共有477条查询结果,搜索用时 15 毫秒
91.
We report first observations of B(s)(0) → J/ψη and B(s)(0) → J/ψη'. The results are obtained from 121.4 fb(-1) of data collected at the Υ(5S) resonance with the Belle detector at the KEKB e+ e- collider. We obtain the branching fractions B(B(s)(0) → J/ψη)=[5.10±0.50(stat)±0.25(syst)(-0.79)(+1.14)(N(B(s)(*) B(s)(*))]×10(-4), and B(B(s)(0) → J/ψη')=[3.71±0.61(stat)±0.18(syst)(-0.57)(+0.83)(N(B(s)(*) B(s)(*))]×10(-4). The ratio of the two branching fractions is measured to be (B(B(s) → J/ψη'))/(B(B(s) → J/ψη))=0.73±0.14(stat)±0.02(syst).  相似文献   
92.
The synthesis of recyclable ionic liquid-supported imidazolidinone catalyst I and its application in 1,3-dipolar cycloaddition of nitrone with α,β-unsaturated aldehyde with high performance were described. Most importantly, the catalyst I can be recovered and recycled for up to five runs without observing significant decrease in catalytic activity.  相似文献   
93.
Vulcanization kinetics of natural rubber (NR) compounds with efficient vulcanization system was studied through phenomenological approach using the experimentally cure data obtained from a moving die rheometer. The cure kinetic parameters were defined using the proposed models by Claxton?CLiska and Deng?CIsayev with the support of curve fitting software. The effects of the amount of accelerators, sulfur and silica in the formulations on the cure characteristics and cure kinetic parameters at high cure temperatures were investigated. Kinetic data results showed that the above two models were able to describe the curing behaviour of the studied compounds satisfactorily. It showed that the fitting of the experimental data with Claxton?CLiska and Deng?CIsayev could provide a good platform to investigate the cure kinetics of the prepared NR compounds.  相似文献   
94.
The opposed jet configuration presents a canonical geometry suitable for the evaluation of calculation methods seeking to reproduce the impact of strain and re-distribution on turbulent transport in reacting and non-reacting flows. The geometry has the advantage of good optical access and, in principle, an absence of complex boundary conditions. Disadvantages include low frequency flow motion at high nozzle separations and comparatively low turbulence levels causing bulk strain to exceed the turbulent contribution at small nozzle separations. In the current work, fractal generated turbulence has been used to increase the turbulent strain and velocity measurements for isothermal flows are reported with an emphasis on the axis, stagnation plane and the distribution of mean and instantaneous strain rates. Energy spectra were also determined. The instrumentation comprised hot-wire anemometry and particle image velocimetry with the flows to both nozzles seeded with 1  $\upmu$ m silicon oil droplets providing a relaxation time of ? 3 $\upmu$ s. It is shown that fractal grids increase the turbulent Reynolds number range from 48–125 to 109–220 for bulk velocities from 4 to 8 m/s as compared to conventional perforated plate turbulence generators. Low frequency motion of the order 10 Hz could not be completely eliminated and probability density functions were determined for the location of the stagnation plane. Results show that the fluctuation in the position of the stagnation plane is of the order of the integral length scale, which was determined to be 3.1±0.1 mm at the nozzle exits through the use of hot-wire anemometry. Flow statistics close to the fractal plate located upstream of the nozzle exit were also determined using a transparent glass nozzle.  相似文献   
95.
This study aimed to evaluate the effects of peanut varieties cultivated in Morocco (Virginia and Valencia) and extraction methods (cold press, CP; Soxhlet, Sox and maceration, and Mac) on the fatty acid profile, phytosterol, and tocopherol contents, quality characteristics, and antioxidant potential of peanut seed oil. The DPPH method was used to determine the antioxidant activity of the oils. The results revealed that fatty acid content was slightly affected by the extraction technique. However, the CP method was shown to be an excellent approach for extracting oil with desirable quality features compared to the Sox and Mac methods. Furthermore, the peanut oil extracted via CP carried a higher amount of bioactive compounds and exhibited remarkable antioxidant activities. The findings also revealed higher oleic acid levels from the Virginia oil, ranging from 56.46% to 56.99%. Besides, a higher total phytosterol and tocopherol content and DPPH scavenging capacity were obtained from the Valencia oil. Analyzing the study, it can be inferred that extraction method and variety both affect the composition of the peanut oil’s bioactive compounds and antioxidant activity. This information is relevant for extracting peanut oil with a greater level of compounds of industrial interest.  相似文献   
96.
Sophorolipids are well-known glycolipid biosurfactants, produced mainly by non-pathogenic yeast species such as Candida bombicola with high yield. Its unique environmental compatibility and high biodegradable properties have made them a focus in the present review for their promising applications in diverse areas. This study aims to examine current research trends of sophorolipids and evaluate their applications in food and health. A literature search was conducted using different research databases including PubMed, ScienceDirect, EBSCOhost, and Wiley Online Library to identify studies on the fundamental mechanisms of sophorolipids and their applications in food and health. Studies have shown that various structural forms of sophorolipids exhibit different biological and physicochemical properties. Sophorolipids represent one of the most attractive biosurfactants in the industry due to their antimicrobial action against both Gram-positive and Gram-negative microorganisms for applications in food and health sectors. In this review, we have provided an overview on the fundamental properties of sophorolipids and detailed analysis of their applications in diverse areas such as food, agriculture, pharmaceutical, cosmetic, anticancer, and antimicrobial activities.  相似文献   
97.
Pua  Aileen  Goh  Rui Min Vivian  Ee  Kim-Huey  Huang  Yunle  Liu  Shao Quan  Lassabliere  Benjamin  Yu  Bin 《Chromatographia》2021,84(5):507-515
Chromatographia - The separation of isomers is one of the key issues in analysing complex natural matrices, thus commanding a higher separating power from the applied analytical system. In this...  相似文献   
98.
Phosphorene, generally defined as two-dimensional (2D) black phosphorus (BP) with monolayered or few-layered structure, has emerged as a promising member of the family of 2D materials. Since its discovery in 2014, extensive research has been focused on broadening its applications, covering the biological, photoelectric, and electrochemical fields, owing to the unique physicochemical and structural properties. As a single-elemental material, phosphorene has demonstrated its applicability for the preparation of efficient electrocatalysts for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), nitrogen reduction reaction (NRR), and other electrocatalytic applications. In this Minireview, a summary of the very recent research progresses of phosphorene in electrocatalysis is offered, with a special focus on the effective synthetic strategies towards performance improvement. In the concluding section, challenges and perspectives are also discussed.  相似文献   
99.
100.
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