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   214篇
  免费   2篇
化学   127篇
晶体学   1篇
力学   13篇
数学   24篇
物理学   51篇
  2022年   4篇
  2021年   11篇
  2020年   7篇
  2019年   8篇
  2018年   9篇
  2017年   7篇
  2016年   12篇
  2015年   3篇
  2014年   1篇
  2013年   9篇
  2012年   11篇
  2011年   15篇
  2010年   5篇
  2009年   3篇
  2008年   11篇
  2007年   16篇
  2006年   8篇
  2005年   8篇
  2004年   6篇
  2003年   6篇
  2002年   3篇
  2001年   1篇
  2000年   1篇
  1996年   3篇
  1995年   7篇
  1994年   3篇
  1993年   4篇
  1992年   2篇
  1990年   2篇
  1989年   4篇
  1988年   2篇
  1986年   2篇
  1985年   3篇
  1984年   4篇
  1983年   4篇
  1978年   1篇
  1975年   2篇
  1974年   4篇
  1972年   2篇
  1970年   1篇
  1969年   1篇
排序方式: 共有216条查询结果,搜索用时 953 毫秒
81.
A device is developed for automated immunochromatographic assay, designed for one-time tests at the place of occurrence of a disease. The device comprises a turntable platform for up to five strips placed simultaneously, a unit for sample collection and microdosing to a test strip, a detection unit, and a microprocessor control system. A manual, semiautomatic, or automatic operation mode may be selected. Colloidal quantum dots with a luminescence peak from the visible to near-infrared spectral region (600–800 nm) are used as fluorescent labels. A UV-LED or a laser at 365–480 nm can be used as an excitation system; the detection device is a spectrometer with an operation range of 500–800 nm, based on a CCD series of TCD1304DG sensors (Toshiba). RFID tags of samples can re read and the analysis results can be sent to an external computer. The device is made in a plastic case for carrying.  相似文献   
82.
Russian Journal of Coordination Chemistry - The reaction of [Mo3S4(Tu)8(H2O)]Cl4·4H2O (Tu is thiourea) with (PhCH2CH2)2-PCH2CH2SeC5H11) (PSe) followed by purification on a chromatographic...  相似文献   
83.
Journal of Structural Chemistry - A comprehensive study of the electronic structure of trinuclear molybdenum complexes (NH4)2[Mo3S13] and [Mo3S7(dtc)3]Br with cluster core {Mo3S7} and...  相似文献   
84.
Whereas the cluster [Mo3S4(acac)3(py)3]+ ([ 1 ]+, acac=acetylacetonate, py=pyridine) reacts with a variety of alkynes, the cluster [W3S4(acac)3(py)3]+ ([ 2 ]+) remains unaffected under the same conditions. The reactions of cluster [ 1 ]+ show polyphasic kinetics, and in all cases clusters bearing a bridging dithiolene moiety are formed in the first step through the concerted [3+2] cycloaddition between the C?C atoms of the alkyne and a Mo(μ‐S)2 moiety of the cluster. A computational study has been conducted to analyze the effect of the metal on these concerted [3+2] cycloaddition reactions. The calculations suggest that the reactions of cluster [ 2 ]+ with alkynes feature ΔG values only slightly larger than its molybdenum analogue, however, the differences in the reaction free energies between both metal clusters and the same alkyne reach up to approximately 10 kcal mol?1, therefore indicating that the differences in the reactivity are essentially thermodynamic. The activation strain model (ASM) has been used to get more insights into the critical effect of the metal center in these cycloadditions, and the results reveal that the change in reactivity is entirely explained on the basis of the differences in the interaction energies Eint between the cluster and the alkyne. Further decomposition of the Eint values through the localized molecular orbital‐energy decomposition analysis (LMO‐EDA) indicates that substitution of the Mo atoms in cluster [ 1 ]+ by W induces changes in the electronic structure of the cluster that result in weaker intra‐ and inter‐fragment orbital interactions.  相似文献   
85.
The replacement of the iodide ligands in the complex [PtI2(dpa)] (1) (dpa is 2,2′-dipyridylamine) by silver triflate in acetonitrile afforded the compound [Pt(dpa)(MeCN)2](SO3CF3)2 (2). Homoleptic complexes [Pt(dpa)2](X)2 (3·(X)2) were synthesized by the treatment of [PtI2(dpa)] (1) with 2,2′-dipyridylamine in the presence of silver salts AgX in methanol (X = NO3) or acetonitrile (X = SO3CF3). The deprotonation of the complex [3](SO3CF3)2 to give the homoleptic complex [Pt(dpa-H)2] (4) was performed by two methods, e.g., by the treatment of [3](SO3CF3)2 with 2 equiv. of NaOH in methanol or by the addition of excess Et3N to a suspension of [3](SO3CF3)2 in methanol. The structures of compounds 1–4 were established by elemental analyses, high resolution electrospray ionization mass spectrometry, IR and NMR spectroscopy; the crystal structure of complexes [2](SO3CF3)2, [3](NO3)2·H2O, [3](SO3CF3)2·2H2O, and 4 were determined by single-crystal X-ray diffraction.  相似文献   
86.
Akhmedzhanov  R. A.  Bondartsev  A. A.  Gushchin  L. A.  Zelensky  I. V.  Litvak  A. G. 《JETP Letters》2012,94(12):863-867
JETP Letters - Spectral selection, i.e., the separation of a group of particles with a spread in resonance frequencies smaller than the hyperfine splitting of working levels has been implemented by...  相似文献   
87.
The parameters of hydrogen bonds formed during acetalization of poly(vinyl alcohol) with butanal are determined via computer-simulation methods. It is shown that alcohol groups involved in the formation of intermolecular hydrogen bonds are the least active in acetalization reactions. The kinetics of the acetalization reactions in 2,4-pentanediol-water-butanal and (vinyl alcohol)-water-butanal systems are studied at various concentrations of alcohols that model a change in the ratio of hydrogen bonds of various types and are realized in the aqueous solutions of poly(vinyl alcohol) and poly(vinyl butyral). The calculated rate constants are in agreement with the computer-simulation-based order of reactivity of alcohol groups involved in hydrogen bonds of various types. It is proposed that the reactivity of residual alcohol groups in a poly(vinyl butyral) macromolecule should increase when a certain conversion of the polymer is attained.  相似文献   
88.
Reaction of [Mo6I8(CH3COO)6]2– with bis(pentafluorophenyl)phosphinic acid HO(O)P(C6F5)2 yielded a new bright‐red luminescent complex [{Mo6I8}(O2P(C6F5)2)6]2–, isolated as (Bu4N)(H5O2)[{Mo6I8}(O2P(C6F5)2)6] · 3(Et2O) · 1.5(acetone). It was characterized by X‐ray analysis, CV, ESI‐mass spectrometry, and NMR spectroscopy.  相似文献   
89.
Biomimetic materials (biocomposites) with an organic-mineral composition related to natural dental tissues (enamel and dentin) are obtained for the first time and their structural and optical characteristics are studied. It is demonstrated by a complex of structural and spectroscopic methods that in the formation of biocomposites, the introduced organic component, bearing a number of amino acids, does not affect the structure of the inorganic component (carbonate-substituted calcium hydroxyapatite) of the sample. The carbonate-substituted calcium hydroxyapatite synthesized using a biogenic source of calcium, which forms the basis of the biocomposite, has a luminescence spectrum similar to that of apatite tooth enamel. The spectrum of the intact dentin of a human tooth has a broader luminescence band than that for the enamel spectrum. It is determined that both organic and inorganic components contribute to the dentin luminescence band. The features found in the luminescence spectra of intact tissues and in simulating biocomposites can be used to develop a procedure for effective early diagnosis of the demineralization of hard dental tissues and general dental examination.  相似文献   
90.
The parametric generation of low-frequency whistler waves by a pump wave beam formed by high-frequency whistler waves with close frequencies is studied experimentally. The electromagnetic fields excited by the beats of two co- or counterpropagating high-frequency waves, or by an amplitude-modulated pump are studied. It is shown that the nonlinear currents at the beat (modulation) frequency are generated by a transverse ponderomotive force arising due to the finite width of the high-frequency beam. In this case, the nonlinear azimuthal drift currents enclose the pump beam and can radiate low-frequency whistler waves to the surrounding plasma.  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