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   556篇
  免费   12篇
化学   335篇
晶体学   1篇
力学   8篇
数学   36篇
物理学   188篇
  2023年   4篇
  2022年   7篇
  2021年   7篇
  2020年   12篇
  2019年   18篇
  2018年   8篇
  2017年   10篇
  2016年   16篇
  2015年   7篇
  2014年   33篇
  2013年   26篇
  2012年   26篇
  2011年   37篇
  2010年   19篇
  2009年   17篇
  2008年   30篇
  2007年   26篇
  2006年   39篇
  2005年   34篇
  2004年   23篇
  2003年   8篇
  2002年   8篇
  2000年   4篇
  1999年   4篇
  1998年   3篇
  1997年   4篇
  1996年   8篇
  1995年   6篇
  1994年   9篇
  1993年   2篇
  1992年   4篇
  1991年   4篇
  1990年   5篇
  1989年   7篇
  1988年   5篇
  1987年   5篇
  1986年   2篇
  1985年   7篇
  1984年   4篇
  1983年   8篇
  1982年   5篇
  1981年   4篇
  1980年   3篇
  1979年   11篇
  1978年   3篇
  1977年   7篇
  1976年   9篇
  1975年   10篇
  1974年   2篇
  1973年   4篇
排序方式: 共有568条查询结果,搜索用时 0 毫秒
111.
112.
The thermal stability of some boracites, CuB7O13Cl, NiB7O13Br and FeB7O13I, was investigated using thermogravimetry in air up to 1000°, DTA in air to 1200° and evolved gas analysis in vacuum to 1200°C. Only the FeI compound showed weight loss below 1000°C. The endothermic peaks associated with melting were CuCl (1025°C), NiBr (1150°C) and FeI) (965°C). Evolved gas analysis indicated major differences in the decomposition products of the three materials.  相似文献   
113.
Condition monitoring is implementation of the advanced diagnostic techniques to reduce downtime and to increase the efficiency and reliability. The research is for determining the usage of advanced techniques like Vibration analysis, Oil analysis and Thermography to diagnose ensuing problems of the Plant and Machinery at an early stage and plan to take corrective and preventive actions to eliminate the forthcoming breakdown and enhancing the reliability of the system. Nowadays, the most of the industries have adopted the condition monitoring techniques as a part of support system to the basic maintenance strategies. Major condition monitoring technique they follow is Vibration Spectrum Analysis, which can detect faults at a very early stage. However implementation of other techniques like Oil analysis or Ferrography, Thermography etc. can further enhance the data interpretation as they would detect the source of abnormality at much early stage thus providing us with a longer lead time to plan and take the corrective actions. In Large Captive Power Plants and Aluminium Smelters, Integrated Condition Monitoring techniques play an important role as stoppage of primary system and its auxiliaries (boiler, steam turbine, generator, coal and ash handling plants etc.) results into the stoppage of the entire plant, which in turn leads to loss of productivity. From economical and operational point of view, it is desirable to ensure optimum level of system availability.  相似文献   
114.
Diamond-like carbon films are deposited on silicon substrates at different substrate bias using ECR-CVD technique. Raman spectroscopic studies show the presence of broad G and D peaks. In contrast to the position of D peak, the G peak shows a systematic red-shift with increase in the bias voltage. From the analysis it is found that an increase in bias voltage decreases the sp2 cluster diameter. Furthermore, two additional Raman peaks at around 690 and 880 cm?1 are also observed. These peaks, forbidden in the first order Raman scattering, arise due to the breakdown of phonon selection rule in graphitic nanoclusters.  相似文献   
115.
Resonant photoemission from the valence band of a (√3 × √3)R30° reconstructed Mn:Ge(111) metallic interface has been carefully analyzed with the aim to track the transition from resonant Raman to normal Auger emission. The transition energy has been compared with the Mn 2p binding energy, as well as with the Mn L(3) absorption edge energy. Close similarities emerge with respect to the case of elemental Mn thin films, suggesting that the excitation dynamics is dominated by the electronic properties of Mn 3d states, in spite of the bonding with Ge atoms. The switching from the resonant Raman Auger (RRAS) to the normal Auger regime is found about 2 eV below the Mn L(3) absorption edge. A change of the lineshape due to the transition from an overall N - 1 electron final state (RRAS channel) to an N - 2 electron final state (normal Auger channel) is evidenced by the analysis of the experimental data, which also allowed the ratio to be tracked between charge delocalization and core-hole time scales as the photon energy is tuned across the Mn L(3) edge.  相似文献   
116.
Ten derivatives of N1 substituted/unsubstituted 5-(4-chlorophenyl)-3-(2-thienyl) pyrazoline were synthesised from chalcone-like intermediate and substituted phenyl hydrazines, hydrazine hydrate, and semi/thiosemicarbazide. The chemical structure of compounds was confirmed by means of IR, 1H NMR, mass spectroscopy, and elemental analysis. The antidepressant and anticonvulsant activities were investigated by Porsolt’s behavioural despair test (forced swimming) and maximum electroshock seizure test, respectively. Rota-Rod test was performed to assess any probable changes in motor coordination induced by the test compounds. Four compounds (IId, IIg, IIi, and IIj) exhibited good activity profile against depression and docking studies confirmed their consensual interaction with monoamine oxidase A. In addition, compounds IIc and IIe showed protection against MES-induced seizures.  相似文献   
117.
P.C. Dash 《Physics letters. A》1985,109(7):307-312
Two new aspects of a perturbed ?4 equation are introduced: kink plus phonon, and a kink interacting with a phonon wave packet. The ?4-kink in the presence of perturbing forces follows newtonian dynamics unambiguously. The non-newtonian behaviour is due to an improper use of the latter idea, the kink-phonon-wave-packet interaction. The origin and role of the recently discovered defective degenerate mode are also stressed.  相似文献   
118.
Mass difference oft-flavored hadrons is calculated using bag model modified for considering heavy quarks inside the bag. Both electric and magnetic contributions to mass differences are evaluated without the assumption of degenerate intermediate state. Mass differences between up and down quarks inside the bag is taken to be a constant in the absence of a dynamical calculations for the same.  相似文献   
119.
Imidazole(Im), benzimidazole(BzIm), morpholine (Morph) and their derivatives react with Co(CNS)2 and dimethylglyoxime(DH2) in ethanolic medium in presence of air to form a number of new cobalt(III) complexes of the type trans-[Co(DH)2(L)(SCN)], which are characterised on the basis of electronic and IR spectra, NMR (1H and 13C) and mass spectra as well as thermogravimetric (TG-DTA) and conductance measurements. The thiocyanate groups are S-bonded. The NMR observations suggest that in solution these compounds exist as mixtures of the neutral species [Co(DH)2(L)(SCN)] and the salt [Co(DH)2(SCN)2]? [Co(DH)2(L)2]+. The mass spectra does not show the molecular ion peak of the complex. The TG-DTA measurements show that the thermolysis of these complexes proceeds through polymeric intermediates giving CO3O4 as the end product.  相似文献   
120.
The solubility and solubility product of silver permanganate in water have been determined at the temperatures ranging from 15 to 35°C over 5°C intervals in the presence of an added electrolyte, sodium perchlorate. The solubility of silver permanganate ranges from 0.966 x 10?5 mol 1?1 at 15°C to 1.420x10?5 moll?1 at 35°C and the corresponding solubility product 0.933 x 10?10 mol2 1?2 at 15°C to 2.017 x 10?10 mol2 1?2 at 35°C. The standard potentials of the Ag(s)/AgMnO4(s)/ MnO?4 electrode have been calculated at these temperatures. The mean activity coefficients of silver permanganate at various rounded molarities of sodium perchlorate solutions, and the standard thermodynamic quantities for the process AgMnO4(s)→Ag+ (aq)+MnO?4(aq) have been calculated at these temperatures.  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