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   560篇
  免费   17篇
化学   342篇
晶体学   1篇
力学   8篇
数学   36篇
物理学   190篇
  2023年   5篇
  2022年   5篇
  2021年   7篇
  2020年   12篇
  2019年   19篇
  2018年   10篇
  2017年   10篇
  2016年   16篇
  2015年   8篇
  2014年   33篇
  2013年   26篇
  2012年   27篇
  2011年   38篇
  2010年   20篇
  2009年   17篇
  2008年   31篇
  2007年   28篇
  2006年   40篇
  2005年   34篇
  2004年   22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577条查询结果,搜索用时 46 毫秒
141.
This paper deals with a chance constrained programming model, where both fuzziness and randomness are present in the objective function and constraints. The concept of fuzzy random variable, mean and variance of fuzzy random variable, minimum of fuzzy numbers are used in the model. The methodology is verified through a numerical example.  相似文献   
142.
In this paper we use facets of simple mixed-integer sets with three variables to derive a parametric family of valid inequalities for general mixed-integer sets. We call these inequalities two-step MIR inequalities as they can be derived by applying the simple mixed-integer rounding (MIR) principle of Wolsey (1998) twice. The two-step MIR inequalities define facets of the master cyclic group polyhedron of Gomory (1969). In addition, they dominate the strong fractional cuts of Letchford and Lodi (2002).  相似文献   
143.
144.
We report a density functional theory study of the effect of electron-withdrawing groups such as –F, –CN, –NO2 on the geometrical, optoelectronic, intramolecular charge transfer (ICT), and photovoltaic properties of (E)-1,2-bis(5-alkyl-[2,3′-bithiophene]-2′-yl)ethene (TVT-T) based donor-acceptor (D-A) copolymers with different acceptor units, that is, benzo[c][1,2,5]thiadiazole, benzo[c][1,2,5]oxadiazole, and benzo[c][1,2,5]selenadiazole. The computed optical absorption spectra of the designed compounds lie in the visible and near-infrared regions. Of all the studied copolymers, -CN substituted and Se-based compound displays the lowest HOMO-LUMO (E H - L) gap and optical band gap (E opt). The exciton binding energy (E b) is found to be smaller for O-incorporated compounds and -CN substituted copolymer as well, inferring more ICT. The electron-hole coherence concentrated over the D-A units is nearly the same for -CN and -NO2 substituted compounds, but larger in -F derivatives, indicating weak electron-hole coupling in the formers. Comparatively larger dipole moment (6.421 Debye-9.829 Debye) and charge transfer length (D CT) (1.976 Å-3.122 Å) for -CN derivatives lead to enhanced ICT properties. The designed donors yield good hole mobilities (0.127-6.61 cm2 V−1 s−1) and the predicted power conversion efficiencies are calculated to be as high as ~6%-7% for –CN and –NO2 substituted compounds.  相似文献   
145.
Journal of Solid State Electrochemistry - The fission product strontium (Sr), after generation in the reactor due to fission of 233U, might exist as SrF2 in the molten fluoride medium of molten...  相似文献   
146.
An indigenous technology for the production of 125I brachytherapy sources has been developed for the management of intraocular cancer. This indigenous method of producing 125I seeds represents a new paradigm, and a thorough quality evaluation of the seeds in accordance with Atomic Energy Regulatory Board (AERB) of India was carried to ensure their safety during therapy. In this current work, we describe an overview of our experience, the efforts made in establishing enviable quality analysis of 125I seeds to ensure their safety in episcleral plaque brachytherapy.  相似文献   
147.
177Lu-labeled receptor avid peptides and monoclonal antibodies have been effectively used in targeted tumor therapy, owing to the ideally suited decay properties and favourable production logistics of 177Lu [T½ = 6.65 days; Eβ(max) = 497 keV (78.6 %); Eγ = 208 keV (11.0 %)]. The specific activity of 177Lu produced by the (n,γ) route is one of the important criteria, which determines the efficacy of 177Lu-labeled receptor-avid biomolecules. The present article highlights that the specific activity of (n,γ) produced 177Lu cannot be calculated by simply dividing the produced activity by the mass of the target irradiated, unlike other (n,γ) produced medical radioisotopes and there is a significant enhancement of specific activity due to the burn up of the Lu target during irradiation, which is an added advantage towards the utilization of 177Lu in receptor specific therapeutic radiopharmaceuticals.  相似文献   
148.
Two compounds, BaNd2Fe2O7(s) and BaNdFeO4(s) in the quaternary system BaNdFeO were prepared by citrate-nitrate gel combustion route and characterized by X-ray diffraction analysis. Heat capacities of these two oxides were measured in two different temperature ranges: (i) 130-325 K and (ii) 310-845 K, using a heat flux type differential scanning calorimeter. Two different types of solid-state electrochemical cells with CaF2(s) as the solid electrolyte were employed to measure the e.m.f. as a function of temperature. The standard molar Gibbs energies of formation of these quaternary oxides were calculated as a function of temperature from the e.m.f. data. The standard molar enthalpies of formation from elements at 298.15 K, ΔfHm° (298.15 K) and the standard entropies, Sm° (298.15 K) of these oxides were calculated by the second law method. The values of ΔfHm° (298.15 K) and Sm° (298.15 K) obtained for BaNd2Fe2O7(s) are: −2756.9 kJ mol−1 and 234.0 J K−1 mol−1 whereas those for BaNdFeO4(s) are: −2061.5 kJ mol−1 and 91.6 J K−1 mol−1, respectively.  相似文献   
149.
Different N‐benzyl anilines were N‐alkylated with chloroacetonitrile to give the corresponding nitriles, which were subsequently condensed with ethylenediamine in the presence of thioacetamide to afford the corresponding title antazoline derivatives.  相似文献   
150.
We report the first measurements of the doubly charmed baryonic B decays B --> Lambda c+ Lambda c- K. The B+ --> Lambda c+ Lambda c- K+ decay is observed with a branching fraction of (6.5(-0.9)(+1.0)+/-1.1+/-3.4)x10(-4) and a statistical significance of 15.4sigma. The B0 --> Lambda c+ Lambda c- K0 decay is observed with a branching fraction of (7.9(-2.3)(+2.9)+/-1.2+/-4.1)x10(-4) and a statistical significance of 6.6sigma. The branching fraction errors are statistical, systematic, and the error resulting from the uncertainty of the Lambda c+ --> pK- pi+ decay branching fraction. The analysis is based on 357 fb(-1) of data accumulated at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+ e- collider.  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