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   705篇
  免费   40篇
  国内免费   12篇
化学   493篇
晶体学   3篇
力学   42篇
数学   85篇
物理学   134篇
  2024年   1篇
  2023年   6篇
  2022年   23篇
  2021年   20篇
  2020年   42篇
  2019年   37篇
  2018年   50篇
  2017年   28篇
  2016年   64篇
  2015年   34篇
  2014年   52篇
  2013年   100篇
  2012年   55篇
  2011年   53篇
  2010年   38篇
  2009年   31篇
  2008年   25篇
  2007年   19篇
  2006年   18篇
  2005年   11篇
  2004年   10篇
  2003年   7篇
  2002年   9篇
  2000年   2篇
  1997年   4篇
  1996年   1篇
  1995年   2篇
  1994年   2篇
  1992年   2篇
  1981年   1篇
  1980年   3篇
  1979年   5篇
  1978年   2篇
排序方式: 共有757条查询结果,搜索用时 62 毫秒
71.

Background

Caspase-3 is one of the most downstream enzymes activated in the apoptotic pathway. In caspase-3 deficient mice, loss of cochlear hair cells and spiral ganglion cells coincide closely with hearing loss. In contrast with the auditory system, details of the vestibular phenotype have not been characterized. Here we report the vestibular phenotype and inner ear anatomy in the caspase-3 deficient (Casp3 -/- ) mouse strain.

Results

Average ABR thresholds of Casp3 -/- mice were significantly elevated (P < 0.05) compared to Casp3 +/- mice and Casp3 +/+ mice at 3 months of age. In DPOAE testing, distortion product 2F1-F2 was significantly decreased (P < 0.05) in Casp3 -/- mice, whereas Casp3 +/- and Casp3 +/+ mice showed normal and comparable values to each other. Casp3 -/- mice were hyperactive and exhibited circling behavior when excited. In lateral canal VOR testing, Casp3 -/- mice had minimal response to any of the stimuli tested, whereas Casp3 +/- mice had an intermediate response compared to Casp3 +/+ mice. Inner ear anatomical and histological analysis revealed gross hypomorphism of the vestibular organs, in which the main site was the anterior semicircular canal. Hair cell numbers in the anterior- and lateral crista, and utricle were significantly smaller in Casp3 -/- mice whereas the Casp3 +/- and Casp3 +/+ mice had normal hair cell numbers.

Conclusions

These results indicate that caspase-3 is essential for correct functioning of the cochlea as well as normal development and function of the vestibule.  相似文献   
72.
In this study, we have investigated the antifungal activity of ZnO nanorods prepared by the chemical solution method against Candida albicans. In the study, Zinc oxide nanorods have been deposited on glass substrates using the chemical solution method. The as-grown samples are characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). X-ray diffraction (XRD) showed zinc oxide nanorods grown in (0 0 2) orientation. The antifungal results indicated that ZnO nanorod arrays exhibit stable properties after two months and play an important role in the growth inhibitory of Candida albicans.  相似文献   
73.
The nonlinear propagation of dust ion-acoustic (DIA) shock waves is studied in a charge varying dusty plasma with electrons having kappa velocity distribution. We use hot ions with equilibrium streaming speed and a fast superthermal electron charging current derived from orbit limited motion (OLM) theory. It is found that the presence of superthermal electrons does not only significantly modify the basic properties of shock waves, but also causes the existence of shock profile with only positive potential in such plasma with parameter ranges corresponding to Saturn?s rings. It is also shown that the strength and steepness of the shock waves decrease with increase of the size of dust grains and ion temperature.  相似文献   
74.
This article has investigated a new multiobjective allocation of optimal sizing and sitting of distributed generation (DG) units and capacitor banks in simultaneous mode to improve reliability and reduce energy losses. The proposed method consists of four objectives, that is, cost of energy not supplied, system average interruption duration index, costs of energy loss and investment. A novel structure differential evolution has been suggested to solve this nonlinear complex problem and its results are compared with related values of genetic algorithm and simple differential evolutionary algorithm. In addition to the novel objective function, the other contribution of this article is proposing a new model for load and energy cost. Three types of DGs, that is, wind turbine, solar cell, and diesel generator have been used in placement process. To verify the comprehensiveness of the proposed function, three scenarios have been introduced: scenario i: first, placement of DGs, then capacitor banks, scenario ii: first, placement of capacitor banks, and then DGs, and scenario iii: simultaneous placement of DGs and capacitor banks. Simulations have been carried out on one part of practical distribution network in Metropolitan Tabriz in North West of Iran. The results of simulations have been discussed and analyzed using the five novel indices. The obtained simulation results using proposed function shows that the simultaneous placement of DGs and capacitor banks results in more reduction of the energy losses and increase improvements of reliability indices as well as voltage profile. © 2013 Wiley Periodicals, Inc. Complexity 19: 40–54, 2014  相似文献   
75.
We prove the classification of joinings for maximal horospherical subgroups acting on homogeneous spaces without any restriction on the characteristic. Using the linearization technique, we deduce a special case of Raghunathan’s orbit closure conjecture. In the appendix, quasi-isometries of higher rank lattices in semisimple algebraic groups over fields of positive characteristic are characterized.  相似文献   
76.
Let K be a number field and let A be its ring of integers. Let G be a connected, noncommutative, absolutely almost simple algebraic K-group. If the K-rank of G equals 2, then G(A[t]) is not finitely presented.  相似文献   
77.
78.
Aerogels prepared from aqueous dispersions of anionic and cationic cellulose nanofibrils (CNFs) were investigated as solid supports for enzymes and silver nanoparticles and to elicit a sustained antibacterial effect. The imparted stabilization in dry conditions was studied with aerogels that were cast after mixing the enzymes with CNFs followed by dehydration (freeze-drying). The activity of lysozyme immobilized in the given CNF system was analyzed upon storage in liquid and air media. In contrast with aqueous solutions of free, unbound enzyme, which lost activity after the first day, the enzyme immobilized physically in unmodified and cationic CNF presented better stability (activity for a longer time). However, the enzyme activity was reduced in the case of anionic CNF, which was prepared by TEMPO-mediated oxidation (TO-CNF). Both humidity and temperature reduced the stability of the enzyme immobilized in the respective CNF aerogel. The antibacterial activity of CNF aerogels carrying lysozyme was also tested against gram-negative and gram-positive bacteria. The results were compared with those obtained from CNF systems loaded with silver nanoparticles (AgNP) after in situ synthesis via UV reduction. Storage in cold or dry conditions preserved the activity and antibacterial performance of enzyme-loaded CNF aerogels. As expected, the lysozyme-containing aerogels showed lower inhibition than the AgNP-containing aerogel. In this latter case, the antibacterial activity depended on the concentration and size of the nanoparticles. Compared to unmodified CNF and TO-CNF, the aerogels prepared with cationic CNF, loaded with either lysozyme or AgNPs, showed remarkably better antibacterial activity. Similar experiments were conducted with horseradish peroxidase, which confirmed, to different degrees, the observations derived from the lysozyme systems. Overall, the results indicate that non-toxic and biodegradable CNF is a suitable support for bio-active materials and is effective in protecting and retaining enzymatic and antibacterial activities.  相似文献   
79.
80.
TiO 2 nanorods have been successfully grown into a track-etched polycarbonate (PC) membrane by a particulate sol-electrophoretic deposition from an aqueous medium.The prepared sols had a narrow particle size distribution around 17 nm and excellent stability against aging,with zeta potentials in the range of 47-50 mV at pH 2.It was found that TiO 2 nanorods were grown from dilute aqueous sol with a low,0.1-M concentration.Fourier transform infrared spectroscopy (FT-IR) analysis confirmed that a full conversi...  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