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   631篇
  免费   12篇
  国内免费   6篇
化学   330篇
晶体学   2篇
力学   19篇
数学   84篇
物理学   214篇
  2023年   8篇
  2022年   13篇
  2021年   5篇
  2020年   5篇
  2019年   9篇
  2018年   11篇
  2017年   8篇
  2016年   18篇
  2015年   10篇
  2014年   18篇
  2013年   30篇
  2012年   32篇
  2011年   30篇
  2010年   23篇
  2009年   21篇
  2008年   33篇
  2007年   28篇
  2006年   27篇
  2005年   24篇
  2004年   14篇
  2003年   15篇
  2002年   15篇
  2001年   6篇
  2000年   15篇
  1999年   12篇
  1998年   9篇
  1997年   11篇
  1996年   10篇
  1995年   10篇
  1994年   11篇
  1993年   10篇
  1992年   8篇
  1991年   9篇
  1989年   5篇
  1988年   6篇
  1987年   6篇
  1986年   15篇
  1985年   9篇
  1984年   11篇
  1983年   8篇
  1982年   6篇
  1981年   11篇
  1980年   12篇
  1978年   6篇
  1977年   7篇
  1976年   7篇
  1975年   4篇
  1974年   3篇
  1971年   4篇
  1970年   3篇
排序方式: 共有649条查询结果,搜索用时 15 毫秒
41.
Two new diglycolamide‐based task‐specific ionic liquids (DGA? TSILs) were evaluated for the extraction of actinides and lanthanides from acidic feed solutions. These DGA? TSILs were capable of exceptionally high extraction of trivalent actinide ions, such as Am3+, and even higher extraction of the lanthanide ion, Eu3+ (about 5–10 fold). Dilution of the DGA? TSILs in an ionic liquid, C4mim+ ? NTf2?, afforded reasonably high extraction ability, faster mass transfer, and more efficient stripping of the metal ion. The nature of the extracted species was studied by slope analysis, which showed that the extracted species contained one NO3? anion, along with the participation of two DGA? TSIL molecules. Time‐resolved laser fluorescence spectroscopy (TRLFS) analysis showed a strong complexation with no inner‐sphere water molecule in the EuIII? DGA? TSIL complexes in the presence and absence of C4mim+ ? NTf2? as the diluent. The very high radiolytic stability of DGA? TSIL 6 makes it one of the most‐efficient solvent systems for the extraction of actinides under acidic feed conditions.  相似文献   
42.
The present study investigates the effect of hybrid fillers such as graphene nanoplatelets (GnPs) and Titanium di-oxide (TiO2) in polypropylene (PP) composites on the mechanical properties. The compatibilizing agent of Maleic anhydride grafted polypropylene (MAPP) are used in the polypropylene based composites to increase the interfacial adhesion between matrix and fillers. The experiments are designed according to L16 orthogonal array (OA) based design of experiments (DOE). The parameters selected for this study are GnPs, TiO2 and MAPP with four different levels are used.By using Orthogonal array and Taguchi based experimental design, the performance characteristics of tensile modulus, tensile strength, elongation at break and toughness can be analyzed with more objective through a small set of experiments.Taguchi based analysis are used to find out the optimal parameters to maximize the tensile properties for the GnPs and TiO2 reinforced PP hybrid composites. Further, analysis of variance (ANOVA) is investigated to identify the most significant parameters which influence the mechanical properties.From the analysis it was found that the optimal parameters of 3 ?wt% GnPs, 2 ?wt% TiO2 and 6 ?wt% MAPP for maximum tensile modulus and tensile strength. The most significant parameter for tensile modulus and tensile strength is GnPs followed by TiO2 and MAPP according to ANOVA analysis.  相似文献   
43.
Journal of Radioanalytical and Nuclear Chemistry - Efficient and selective extraction of 137Cs and 90Sr from high level liquid waste (HLLW) is of utmost importance in the back end nuclear fuel...  相似文献   
44.
The in situ Grignard Metalation Method (iGMM) is a straightforward one-pot procedure to quickly produce multigram amounts of Hauser bases R2N-MgBr which are valuable and vastly used metalation reagents and novel electrolytes for magnesium batteries. During addition of bromoethane to a suspension of Mg metal and secondary amine at room temperature in an ethereal solvent, a smooth reaction yields R2N-MgBr under evolution of ethane within a few hours. A Schlenk equilibrium is operative, interconverting the Hauser bases into their solvated homoleptic congeners Mg(NR2)2 and MgBr2 depending on the solvent. Scope and preconditions are studied, and side reactions limiting the yield have been investigated. DOSY NMR experiments and X-ray crystal structures of characteristic examples clarify aggregation in solution and the solid state.  相似文献   
45.
46.
At helium temperatures two sharp lines at 9350 and 9510 cm?1 have been observed for the first tune on the low-energy side of the broad double-peaked absorption corresponding to the 5T2g5Eg transition in Fe2+ at the octahedral site in MgO. The lower energy line has a half width of 4 cm?1; Zeeman measurements show that it is of magnetic dipole origin. The Zeeman spectra are consistent with those expected for a pure electronic transition from the (5T2g)T2g ground state to the 5Eg excited state. The second line, with a halfwidth of ~ 35 cm?1, a vibrational sideband.  相似文献   
47.
D Home  S Sengupta 《Pramana》1981,17(6):509-514
The extensivity property of entropy is clarified in the light of a critical examination of the entropy formula based on quantum statistics and the relevant thermodynamic requirement. The modern form of the Gibbs paradox, related to the discontinuous jump in entropy due to identity or non-identity of particles, is critically investigated. Qualitative framework of a new resolution of this paradox, which analyses the general effect of distinction mark on the Hamiltonian of a system of identical particles, is outlined.  相似文献   
48.
The time-resolved multistage reservoir model well-known for semiconductor optical amplifier (SOA) is extended to analyze the behavior of a bulk homogeneous InP-InGaAsP buried heterostructure reflective semiconductor optical amplifier (RSOA). Parameters for simulation have been extracted from the experimental RSOA characteristics. We have employed the model to explain the steady-state and re-modulation dynamics in the RSOA. Electrical modulation bandwidth and intermodulation distortion in the RSOA have been derived from the model and close agreement is obtained with the reported data. It is found out that the ripples in the upstream output from the RSOA for incomplete modulation erase of downstream modulated data follow Gaussian distribution, which simplifies the calculation of upstream SNR and bit error rate. It is explained in detail that amplitude ripples in the upstream data can be reduced by judicious choice of optical and electrical parameters of the RSOA. In particular, for an average low downstream power level (<−20 dBm) a good downstream modulation erase factor about 89% and 23 dB extinction ratio in the upstream modulated signal can be achieved.  相似文献   
49.
The quantum field measure for gauge fields over a compact surface with boundary, with holonomy around the boundary components specified, is constructed. Loop expectation values for general loop configurations are computed. For a compact oriented surface with one boundary component, let be the moduli space of flat connections with boundary holonomy lying in a conjugacy class in the gauge group G. We prove that a certain natural closed 2-form on , introduced in an earlier work by C. King and the author, is a symplectic structure on the generic stratum of for generic . We then prove that the quantum Yang-Mills measure, with the boundary holonomy constrained to lie in , converges in a natural sense to the corresponding symplectic volume measure in the classical limit. We conclude with a detailed treatment of the case , and determine the symplectic volume of this moduli space. Received: 30 June 1996 / Accepted: 22 July 1996  相似文献   
50.
The Neveu-Schwarz-Ramond type II closed superstring is considered to evolve in a curved space-time manifold. The Krichever-Novikov global operator formalism is used to construct the generators of a super-conformal algebra on a Riemann surface . The computation for the quantum algebra of these generators is explicitly presented. It is shown that the theory is free from super-conformal anomalies if the target manifold is ten dimensional and satisfies the Ricci flatness condition.  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