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   312篇
  免费   2篇
化学   213篇
晶体学   2篇
力学   9篇
数学   34篇
物理学   56篇
  2024年   8篇
  2023年   2篇
  2022年   20篇
  2021年   24篇
  2020年   8篇
  2019年   18篇
  2018年   13篇
  2017年   10篇
  2016年   11篇
  2015年   8篇
  2014年   15篇
  2013年   36篇
  2012年   13篇
  2011年   7篇
  2010年   10篇
  2009年   9篇
  2008年   12篇
  2007年   8篇
  2006年   10篇
  2005年   7篇
  2004年   7篇
  2003年   8篇
  2002年   9篇
  2001年   7篇
  2000年   1篇
  1999年   1篇
  1998年   1篇
  1997年   1篇
  1996年   2篇
  1995年   3篇
  1993年   3篇
  1992年   1篇
  1991年   1篇
  1990年   4篇
  1988年   1篇
  1987年   1篇
  1986年   1篇
  1985年   1篇
  1984年   3篇
  1983年   3篇
  1982年   1篇
  1979年   1篇
  1978年   1篇
  1975年   1篇
  1968年   1篇
  1936年   1篇
排序方式: 共有314条查询结果,搜索用时 0 毫秒
201.
In?vitro antifungal activity and phytochemical constituents of essential oil, aqueous, methanol and chloroform extract of Eucalyptus citriodora Hook leaves were investigated. A qualitative phytochemical analysis was performed for the detection of alkaloids, cardiac glycosides, flavonoids, saponins, sterols, tannins and phenols. Methanolic extract holds all identified biochemical constituents except for the tannin. While these biochemical constituents were found to be absent in essential oil, aqueous and chloroform extracts with the exception of sterols, cardiac glycosides and phenols in essential oil and sterols and phenols in aqueous and chloroform extracts. Antimycotic activity of four fractions of E. citriodora was investigated through agar-well diffusion method against four post-harvest fungi, namely, Aspergillus flavus Link ex Gray, Aspergillus fumigatus Fres., Aspergillus nidulans Eidam ex Win and Aspergillus terreus Thom. The results revealed maximum fungal growth inhibition by methanolic extract (14.5%) followed by essential oil (12.9%), chloroform extract (10.15%) and aqueous extract (10%).  相似文献   
202.
203.
The synthesis of both enantiomers of 1,4-benzodioxan-2-carboxylic acid 1, a key synthetic intermediate for the therapeutic agents piperoxan, prosympal, dibozane, and doxazosin was achieved with good yields and high enantioselectivities via the Arthrobacter sp. lipase catalyzed kinetic resolution of ester (±)-17a. The influence of the co-solvents and the immobilization of the lipase upon kinetic resolution demonstrated that immobilized whole cells, in the presence of n-butanol as a co-solvent, resulted in the optimal resolution of the substrate (ee ~99%, E = 535) at 258 mmol (50 g/L) substrate concentration.  相似文献   
204.
205.
    
Cancer stands as a leading cause of global mortality, with chemotherapy being a pivotal treatment approach, either alone or in conjunction with other therapies. The primary goal of these therapies is to inhibit the growth of cancer cells specifically, while minimizing harm to healthy dividing cells. Conventional treatments, often causing patient discomfort due to side effects, have led researchers to explore innovative, targeted cancer cell therapies. Thus, biopolymer-based aerogels emerge as innovative platforms, showcasing unique properties that respond intelligently to diverse stimuli. This responsiveness enables precise control over the release of anticancer drugs, enhancing therapeutic outcomes. The significance of these aerogels lies in their ability to offer targeted drug delivery with increased efficacy, biocompatibility, and a high drug payload. In this comprehensive review, the author discuss the role of biopolymer-based aerogels as an emerging functionalized platforms in anticancer drug delivery. The review addresses the unique properties of biopolymer-based aerogels showing their smart behavior in responding to different stimuli including temperature, pH, magnetic and redox potential to control anticancer drug release. Finally, the review discusses the application of different biopolymer-based aerogel in delivering different anticancer drugs and also discusses the potential of these platforms in gene delivery applications.  相似文献   
206.
207.
Fission neutron spectrum averaged cross-sections were measured for the reactions64Zn(n, p)64Cu,67Zn(n, p)67Cu and68Zn(n, α)65Ni by the activation technique, using radiochemical separations and γ-spectroscopy. The preparation of64Cu and67Cu in a nuclear reactor was studied. The64, 67Cu was separated from zinc matrix activity using anion exchange column technique.  相似文献   
208.
Enamines derived from cyclic ketones react with arenesulfonyl azides and cyanogen azide, mainly via ring contraction, with formation of the corresponding amidines. The mechanism of this efficient rearrangement, which has not been investigated experimentally, was determined with the aid of quantum-chemical calculations. In the transition state, from the intermediate 5-amino-v-triazolines, the loss of dinitrogen and a cyclic rearrangement occurred in one-step in a quite synchronous manner with a very low transition state energy.  相似文献   
209.
The temperature dependence of the tunneling spectrum of methyl groups in lithium acetate dihydrate has been studied in the temperature range between 1.2 and 8.0 K by inelastic neutron scattering. The results unambiguously prove that it is to a first order approximation correct to describe the tunneling motions by a model of coupled CH3 pairs which are isolated from each other. However, from the fact that the tunneling frequencies shift to higher values with decreasing spin temperature, we conclude that coupling effects are important not only between nearest neighbour CH3 groups. Quantitatively we can describe the observations by a model of coupled pairs with a fixed value for the interaction potentialW 3 and a variable single particle potentialV 3 which depends linearly on the concentration of the spin symmetry species.  相似文献   
210.
Lowest-lying tetra-quark hadrons in anisotropic lattice QCD   总被引:1,自引:0,他引:1  
We present a detailed study of the lowest-lying hadrons in quenched improved anisotropic lattice QCD. Using the π π and diquark–antidiquark local and smeared operators, we attempt to isolate the signal for I(J P )=0(0+),2(0+) and 1(1+) states in two flavour QCD. In the chiral limit of the light-quark mass region, the lowest scalar 4q state is found to have a mass, m 4q I=0=927(12) MeV, which is slightly lower than the experimentally observed f 0(980). The results from our variational analysis do not indicate a signature of a tetraquark resonance in I=1 and I=2 channels. After the chiral extrapolation the lowest 1(1+) state is found to have a mass m 4q I=1=1358(28) MeV. We analysed the static 4q potential extracted from a tetraquark Wilson loop and illustrated the behaviour of the 4q state as a bound state, unbinding at some critical diquark separation. From our analysis we conclude that the scalar 4q system appears as a two-pion scattering state and that there is no spatially-localised 4q state in the light-quark mass region.  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