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   1028篇
  免费   51篇
  国内免费   2篇
化学   743篇
晶体学   13篇
力学   13篇
数学   57篇
物理学   255篇
  2024年   2篇
  2023年   16篇
  2022年   36篇
  2021年   34篇
  2020年   44篇
  2019年   60篇
  2018年   52篇
  2017年   34篇
  2016年   57篇
  2015年   41篇
  2014年   100篇
  2013年   104篇
  2012年   68篇
  2011年   69篇
  2010年   37篇
  2009年   28篇
  2008年   41篇
  2007年   31篇
  2006年   27篇
  2005年   22篇
  2004年   27篇
  2003年   17篇
  2002年   20篇
  2001年   14篇
  2000年   7篇
  1999年   10篇
  1998年   4篇
  1997年   3篇
  1996年   6篇
  1995年   9篇
  1994年   2篇
  1993年   2篇
  1992年   6篇
  1991年   6篇
  1990年   4篇
  1989年   8篇
  1987年   3篇
  1986年   5篇
  1985年   5篇
  1984年   2篇
  1983年   1篇
  1982年   8篇
  1980年   1篇
  1979年   3篇
  1978年   1篇
  1977年   1篇
  1976年   1篇
  1974年   1篇
  1939年   1篇
排序方式: 共有1081条查询结果,搜索用时 31 毫秒
951.
The reaction-based cost effective detection of CN(-) over the most competitive ions, F(-) and Ac(-), by a commercially available dye has been developed. The experimental results are in good agreement with the theory. An application in the form of 'dip-sticks' which provides an instant information, has been demonstrated.  相似文献   
952.
A new stability-indicating reversed-phase LC method has been developed and validated for the assay and identification of betamethasone dipropionate and its related compounds in a dermatological pharmaceutical drug product, namely Diprolene Ointment. Separation of all the peaks of interest was achieved on a Symmetry Shield RP18 (100 mm × 4.6 mm, 3.5 µm) column using a gradient elution at a flow rate of 1.5 mL min?1 with mobile phase A (10 mM monobasic sodium phosphate at pH 2.5) and mobile phase B (acetonitrile) and UV detection at 250 nm. The limit of detection (LOD) and limit of quantitation (LOQ) of this method was 0.00004  and 0.0001 mg mL?1, respectively. The method was successfully validated in accordance with ICH guidelines and was accurate, linear, precise, reproducible, specific, and robust. A simple, reproducible and accurate single step sample extraction procedure using tetrahydrofuran, water, and methanol (40:30:30, v/v/v) was developed to extract betamethasone dipropionate and its related compounds from the ointment. The sample extraction procedure and the LC conditions presented in this report can be used for routine analysis of Diprolene Ointment in quality control laboratories. This method may also be applied to other dermatological pharmaceutical drug products “as-is” or with minor modification.  相似文献   
953.
Europium- and dysprosium-doped barium magnesium silicate powder with different concentrations of dysprosium was synthesized using solid state reactions. The prepared phosphors were characterized using photoluminescence. Prominent green color emissions were obtained under ultraviolet excitation. The thermoluminescence glow curves of the samples were measured after various delay times. With increased delay time, the intensity of the thermoluminescence peak decays, and the position of the thermoluminescence peak shifts to higher temperatures, indicating the considerable retrapping associated with general order kinetics. Refined lattice parameters of monoclinic phosphor were calculated.  相似文献   
954.
Free Space Optics (FSO) link is extremely responsive to the diverse climate state of affairs that bound the FSO range. A demonstration of fading resistant FSO system using a simulated test-bed employing OFDM scheme is reported in this work to realize the prolonged FSO link with acceptable SNR and BER with the highest stream rate of 5 Gb ps under the impact of diverse weather conditions. Simulations point toward that the proposed hybrid OFDM-FSO transmission system incorporating OTSB- and OSSB-schemes promises significantly enhanced FSO link compared to conventional FSO systems.  相似文献   
955.
Ghatee and Hashemi [M. Ghatee, S.M. Hashemi, Ranking function-based solutions of fully fuzzified minimal cost flow problem, Inform. Sci. 177 (2007) 4271–4294] transformed the fuzzy linear programming formulation of fully fuzzy minimal cost flow (FFMCF) problems into crisp linear programming formulation and used it to find the fuzzy optimal solution of balanced FFMCF problems. In this paper, it is pointed out that the method for transforming the fuzzy linear programming formulation into crisp linear programming formulation, used by Ghatee and Hashemi, is not appropriate and a new method is proposed to find the fuzzy optimal solution of multi-objective FFMCF problems. The proposed method can also be used to find the fuzzy optimal solution of single-objective FFMCF problems. To show the application of proposed method in real life problems an existing real life FFMCF problem is solved.  相似文献   
956.
Chromogenic receptors 2 and 3 undergo distinct colour changes from magenta to blue on gradual addition of Cu(II) and can be used as colorimetric probes for spectrophotometric and visual analysis of Cu(II) in the presence of biological metal ions Na(I), K(I), Mg(II), Ca(II), Fe(II), Zn(II) etc. in aqueous solution (methanol-water 1 : 1 v/v). On addition of Cu(II), both 2 and 3 exhibit a bathochromic shift of Delta lambda(max) = 114 nm for 2 and Delta lambda(max)= 150 and 265 nm for receptor 3. The protonation constants and formation constants of Cu(II) complexes of receptors 2 and 3 (at pH 7) and the effect of pH on formation of these complexes has been determined by the combination of UV-vis-pH titrations of receptors 2 and 3 and their Cu(II) complexes. These results and the emergence of only one peak at 610 nm for 2 and two distinct absorption peaks at 715 and 800 nm for 3 on addition of Cu(II) unambiguously point to mono- and di-deprotonation for 2 and 3, respectively.  相似文献   
957.
We demonstrate a new method that makes use of colloidal silica templates to fabricate porous three-dimensional architectures of carbon nanotubes (CNTs). CNTs were grown on monolayered and multilayered structures of colloidal silica using chemical vapor deposition. Porous CNT membranes and three-dimensional carbon nanotube foams were obtained by treating these silica-CNTs structures with HF. The membranes and foams of CNT so obtained were chemically and mechanically stable and were characterized by using scanning electron microscopy and energy dispersive spectroscopy.  相似文献   
958.
A diamide-diamine based sensor 3 possessing anthracene-9,10-dione as a chromogenic moiety has been synthesized and demonstrates a highly selective colour change from red to blue with Cu2+ for visual detection of Cu2+ (5-50 μM). Other metal ions, viz. Fe2+, Cr3+, Co2+, Ni2+, Zn2+, Cd2+, Ag+, Pb2+, Na+, K+, Mg2+, Ca2+, Sr2+ and Ba2+ cations do not lead to any change in colour and their presence does not interfere with the visual and quantitative analysis of Cu2+. The selective deprotonation of an aryl amine NH by Cu2+ is responsible for a bathochromic shift and significant colour changes. Significantly, the stability of the 3·Cu2+ complex between pH 7 and 12 allows Cu2+ estimation under neutral and basic conditions.  相似文献   
959.
The fluorescence measurements of tetraethylene glycol dodecyl ether (C12E4) and triblock polymer (Pluronic P103), poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), (EO)17(PO)60(EO)17, binary mixtures have been performed over the whole mixing range in the temperature range of 20-40 degrees C. The results have been evaluated by computing various micellar parameters and excimer formation. It has been concluded that mixed micelle formation takes place due to unfavorable mixing at lower temperature range, and the magnitude of which decreases with the increase in temperature up to 40 degrees C. The reduction in the unfavorable mixing has been attributed to the dehydration of P103 micelles with the increase in temperature.  相似文献   
960.
An efficient electron transporting layer (ETL) based on single walled carbon nanotube (SWCNT) composites has been developed for poly [2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) based orange polymer light emitting diodes (PLEDs) and its effect on the performance of PLEDs has been examined. It is observed that with increase in SWCNT concentration, in ETL, the luminance and luminous efficiency of the PLEDs increase (about 5 times increase in luminance is observed at 5% w/w SWCNT concentration). The SWCNTs present in the MEH-PPV ETL boost the mobility of electrons injected from the cathode towards the emissive layer by establishing highly conducting percolation paths. This balances the concentration of holes and electrons in the emissive layer, which leads to enhanced emission from the PLEDs.  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