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   790篇
  免费   18篇
  国内免费   3篇
化学   436篇
晶体学   6篇
力学   25篇
数学   49篇
物理学   295篇
  2023年   13篇
  2022年   15篇
  2021年   21篇
  2020年   23篇
  2019年   24篇
  2018年   19篇
  2017年   17篇
  2016年   23篇
  2015年   12篇
  2014年   25篇
  2013年   39篇
  2012年   30篇
  2011年   38篇
  2010年   31篇
  2009年   24篇
  2008年   35篇
  2007年   37篇
  2006年   38篇
  2005年   32篇
  2004年   33篇
  2003年   24篇
  2002年   12篇
  2001年   20篇
  2000年   13篇
  1999年   8篇
  1998年   4篇
  1997年   6篇
  1995年   7篇
  1994年   10篇
  1993年   9篇
  1992年   8篇
  1991年   12篇
  1990年   13篇
  1989年   9篇
  1988年   13篇
  1987年   10篇
  1986年   7篇
  1985年   10篇
  1984年   11篇
  1983年   6篇
  1982年   5篇
  1981年   10篇
  1980年   13篇
  1979年   3篇
  1978年   7篇
  1977年   5篇
  1976年   3篇
  1974年   5篇
  1973年   3篇
  1933年   3篇
排序方式: 共有811条查询结果,搜索用时 15 毫秒
711.
712.
Anodised aluminium oxide (AAO) templates have been utilised to investigate Cu deposition from a typical sulphate plating bath. The influence of the common additives poly ethylene glycol (PEG), chloride ion (Cl?) and Bis-(sodium sulphopropyl)-disulphide (SPS) on the deposition process has been analysed. The growth of Cu wires or nanotubes (with tube walls of 40–70 nm) is significantly influenced by the action of the additives. In the presence of either Cl? or SPS solid wire growth is observed, however, when PEG is added with Cl? the growth of ordered Cu nanotubes is observed. SPS added to a bath containing Cl? and PEG restores the growth of wires.  相似文献   
713.
Chemical investigation of the stem bark of Saraca indica has resulted in the isolation of a new lignan glycoside, saracoside, along with four known lignan glycosides lyoniside, icariside E3, (+)5'-methoxyisolarciresinol-9'-O-beta-D-glucopyranoside and nudiposide, and a phenolic glucopyranoside, 3,4,5-trimethoxyphenyl-beta-D-glucopyranoside, which has been isolated for the first time from this species. The isolated lignan glycosides exhibit potent DNA topoisomerase IB inhibitory activity.  相似文献   
714.
We derive a closed-form approximate analytical formula for the gain of a Brillouin fiber amplifier operating in the depleted pump regime. We take into account the material loss of the medium, which is a strong effect in optical fibers. We validate obtained results numerically and experimentally. The presented analysis can be used to accurately predict the performance of high-gain Brillouin fiber amplifiers.  相似文献   
715.
In this short paper we report the interactions of silver island films with chemiluminescing species. Our findings show that silver island films can increase the detectability of chemiluminescent reactions/species, with an approximately 5-fold increase in signal intensity. This finding not only suggests the use of silver nanostructures to amplify chemiluminscent signatures in assay platforms, and therefore increase the detectability of analytes or biospecies, but more importantly, suggests that surface plasmons can be directly excited by chemically induced electronically excited molecules. This finding is of significance towards our understanding of fluorophore–metal interactions, a relatively new near-field fluorescence concept, recently named metal-enhanced fluorescence and also radiative decay engineering.  相似文献   
716.
The titanium(IV) complexes of the unsymmetrical Schiff base ligands (L) of ethylenediamine and salicylaldehyde, o‐hydroxyacetophenone, o‐hydroxynapthaldehyde have been prepared and characterized when unsymmetrical ligands are synthesized through in situ partial displacement of the symmetrical bis‐Schiff bases. Compounds have been characterized by elemental analysis, electronic, (Infra‐red) IR, 1H NMR spectral data, magnetic susceptibility measurement and molar conductance and eight coordinated geometry of the complexes was proposed. The complexes have been found to posses 1:2:1 (M:L:B) stoichiometry (B is the secondary ligand). The bio‐efficacy of the prepared complexes has been examined against the growth of bacteria and fungi in vitro to evaluate their anti‐microbial potential.  相似文献   
717.
The intake of leafy vegetables in daily diet is very important to meet our nutritional needs. Vegetables provide the essential elements which are necessary and recommended for human growth. However, due to rapid industrialization and urbanization our environment becomes polluted and this affects the normal growth of agricultural products and composition of environmental species. The elemental concentrations present in the environmental samples are good indicators to assess the toxicological levels due to pollution affects. In the present work we have analysed several vegetable plant samples by instrumental neutron activation analysis to determine the elemental concentrations at major, minor and trace levels. The leafy vegetables like spinach, red leafy veagetable, pui, gourd leaf, lettuce and katoua were chosen as these are extensively consumed by local peple in eastern part of India. We have determined 15 elements in the above mentioned vegetable samples and some of these are essential elements and some are toxic elements. It was found that Na and K were present as major elements, Fe and Zn as minor elements and As, Ce, Cr, Co, La, Mo, Rb, Sc, Sm, Sr as trace elements. The concentration level of Cr was found to be higher than that of recommended value certified by WHO and National environment quality control for human consumption. The validation of our analytical results have been performed by the Z-score tests through the determination of concentrations of the elements of interest in certified reference materials.  相似文献   
718.
We present precision Penning trap mass measurements of neutron-rich calcium and potassium isotopes in the vicinity of neutron number N=32. Using the TITAN system, the mass of ^{51}K was measured for the first time, and the precision of the ^{51,52}Ca mass values were improved significantly. The new mass values show a dramatic increase of the binding energy compared to those reported in the atomic mass evaluation. In particular, ^{52}Ca is more bound by 1.74?MeV, and the behavior with neutron number deviates substantially from the tabulated values. An increased binding was predicted recently based on calculations that include three-nucleon (3N) forces. We present a comparison to improved calculations, which agree remarkably with the evolution of masses with neutron number, making neutron-rich calcium isotopes an exciting region to probe 3N forces.  相似文献   
719.
Manganese sulphide (MnS) thin films have been deposited onto glass substrate by a low cost spray‐pyrolysis technique at 220 °C. The as‐deposited MnS thin films have been characterized using scanning electron microscopy (SEM), energy dispersive X‐ray (EDX) spectroscopy, atomic force microscopy (AFM), X‐ray diffraction, UV visible spectroscopy and photo electrochemical (PEC) measurement. The SEM and AFM images showed that the MnS thin films were well covered onto the substrate surface. The as‐deposited raw thin film was found to be amorphous in nature and perfectly crystalline phase after annealing the sample. Optical band gap of the MnS thin films was found to vary from 3.1 to 3.21 eV and the band gap decreases with the increase in film thickness. Optical constants such as refractive index, extinction coefficient have been evaluated using reflectance and absorbance data. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
720.
High energy nucleon-nucleon collision events are analysed in the light of modified Duller-Walker approach as proposed in a recent paper by Ghosh et al. The result of the analysis clearly justifies the validity of the modified D. W. approach in the cosmic ray energy from 100 to 10,000 GeV.  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