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   901篇
  免费   19篇
  国内免费   10篇
化学   561篇
晶体学   6篇
力学   7篇
数学   56篇
物理学   300篇
  2023年   4篇
  2022年   5篇
  2020年   5篇
  2019年   11篇
  2018年   4篇
  2016年   11篇
  2015年   15篇
  2014年   15篇
  2013年   29篇
  2012年   50篇
  2011年   44篇
  2010年   29篇
  2009年   39篇
  2008年   39篇
  2007年   40篇
  2006年   43篇
  2005年   43篇
  2004年   37篇
  2003年   33篇
  2002年   42篇
  2001年   30篇
  2000年   32篇
  1999年   10篇
  1998年   10篇
  1997年   9篇
  1996年   14篇
  1995年   16篇
  1994年   24篇
  1993年   8篇
  1992年   10篇
  1991年   6篇
  1990年   8篇
  1989年   13篇
  1988年   13篇
  1987年   11篇
  1986年   7篇
  1985年   20篇
  1984年   6篇
  1983年   11篇
  1982年   8篇
  1981年   12篇
  1980年   6篇
  1979年   12篇
  1978年   9篇
  1977年   6篇
  1976年   7篇
  1975年   9篇
  1974年   7篇
  1973年   9篇
  1972年   13篇
排序方式: 共有930条查询结果,搜索用时 31 毫秒
901.
902.
Metal-organic polyhedra with surface-exposed organic groups have been designed. The polyhedra are based on concentric shells of alternating negative-positive-negative charges and have been used to design homochiral hosts.  相似文献   
903.
Graphite epoxide   总被引:1,自引:0,他引:1  
Oxidation of graphite may be carried out by reaction with meta-chloroperoxybenzoic acid to yield graphite epoxide. Scanning tunneling microscopy (STM) showed that the functionalization occurs at the edges rather than on the basal plane of the graphite. Quantification of the epoxide content is possible through the deepoxidation reaction using MeReO3/PPh3.  相似文献   
904.
The degradation of imazapyr, an imidazolinone herbicide, in aqueous solution has been investigated with TiO2 slurry as photocatalyst at 30°C under UV radiation. The depletion of imazapyr concentration in an aqueous suspension followed 1st order kinetic behavior. The influence of pH and the charge densities of imazapyr geometries were calculated at the semi-empirical AM1 level, and the effect of temperature was investigated. The addition of electron acceptors such as potassium persulfate and hydrogen peroxide showed that the rate constant doubled at least. At higher persulfate concentrations the herbicide degradation was more efficient in direct photolysis than TiO2-photocatalysis. The degradation rate constant increased by 38% upon variation of the temperature between 20.0 and 50.0°C and displayed non-Arrhenius behavior.  相似文献   
905.
Photocatalytic lithography couples light with photoreactive coated mask materials to pattern surface chemistry. We excite porphyrins to create radical species that photocatalytically oxidize, and thereby pattern, chemistries in the local vicinity. The technique advantageously is suited for use with a wide variety of substrates. It is fast and robust, and the wavelength of light does not limit the resolution of patterned features. We have patterned proteins and cells to demonstrate the utility of photocatalytic lithography in life science applications.  相似文献   
906.
Biphenyl dioxygenase-catalysed cis-dihydroxylation of 2-chloroquinoline, 2-chloro-3-methylquinoline and 2-chloro-6-phenylpyridine substrates yielded the corresponding enantiopure cis-dihydrodiols; enantiopure 2,2'-bipyridines, synthesised in four steps from 2-chloroquinoline, proved to be efficient chiral ligands in catalytic asymmetric allylic oxidation and cyclopropanation reactions of alkenes.  相似文献   
907.
We studied the open circuit interaction of methanol and ethanol with oxidized platinum electrodes using in situ infrared spectroscopy. For methanol, it was found that formic acid is the main species formed in the initial region of the transient and that the steep decrease of the open circuit potential coincides with an explosive increase in the CO2 production, which is followed by an increase in the coverage of adsorbed CO. For ethanol, acetaldehyde was the main product detected and only traces of dissolved CO2 and adsorbed CO were found after the steep potential decay. In both cases, the transients were interpreted in terms of (a) the emergence of sub-surface oxygen in the beginning of the transient, where the oxide content is high, and (b) the autocatalytic production of free platinum sites for lower oxide content during the steep decay of the open circuit potential.  相似文献   
908.
Biological rhythms are regulated by homeostatic mechanisms that assure that physiological clocks function reliably independent of temperature changes in the environment. Temperature compensation, the independence of the oscillatory period on temperature, is known to play a central role in many biological rhythms, but it is rather rare in chemical oscillators. We study the influence of temperature on the oscillatory dynamics during the catalytic oxidation of formic acid on a polycrystalline platinum electrode. The experiments are performed at five temperatures from 5 to 25 °C, and the oscillations are studied under galvanostatic control. Under oscillatory conditions, only non-Arrhenius behavior is observed. Overcompensation with temperature coefficient (q(10), defined as the ratio between the rate constants at temperature T + 10 °C and at T) < 1 is found in most cases, except that temperature compensation with q(10) ≈ 1 predominates at high applied currents. The behavior of the period and the amplitude result from a complex interplay between temperature and applied current or, equivalently, the distance from thermodynamic equilibrium. High, positive apparent activation energies were obtained under voltammetric, nonoscillatory conditions, which implies that the non-Arrhenius behavior observed under oscillatory conditions results from the interplay among reaction steps rather than from a weak temperature dependence of the individual steps.  相似文献   
909.
We report here the noncovalent synthesis of thermosensitive dendrimers. Short oligoguanosine strands were linked to the focal point of a dendron by using “click chemistry”, and quadruplex formation was used to drive the self‐assembly process in the presence of metal ions. The dynamic nature of these noncovalent assemblies can be exploited to create combinatorial libraries of dendrimers as demonstrated by the co‐assembly of two components. These supramolecular dendrimers showed thermoresponsive behavior that can be tuned by varying the templating cations or the number of guanines in the oligonucleotide strand.  相似文献   
910.
A recent in situ infrared study on the selective hydrogenation of C5 dienes and monoenes over a Pd/Al(2)O(3) catalyst only reported incomplete vibrational assignments for some of the reagents, intermediates, and products encountered in that study. This work uses a combination of infrared absorption spectroscopy, Raman, and inelastic neutron scattering to characterize the vibrational spectra of pentane, 1-pentene, cis- and trans-2-pentene, cis- and trans-1,3-pentadiene, 1,4-pentadiene, cyclopentane, and cyclopentene. Ab initio calculations of the potential energy surface, geometry, and vibrational transition energies were performed and simulations of the vibrational spectra compared to the experimental data. Complete vibrational assignments for the majority of the molecules are presented. The potential for using gas-phase infrared measurements for studying heterogeneously catalyzed gas-phase reactions is also briefly considered.  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