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   502篇
  免费   8篇
化学   416篇
晶体学   2篇
力学   5篇
数学   14篇
物理学   73篇
  2023年   4篇
  2020年   6篇
  2019年   5篇
  2018年   6篇
  2017年   4篇
  2016年   7篇
  2014年   5篇
  2013年   25篇
  2012年   9篇
  2011年   13篇
  2010年   4篇
  2009年   14篇
  2008年   25篇
  2007年   30篇
  2006年   27篇
  2005年   27篇
  2004年   22篇
  2003年   22篇
  2002年   16篇
  2001年   17篇
  2000年   13篇
  1999年   10篇
  1998年   8篇
  1997年   4篇
  1992年   13篇
  1991年   12篇
  1990年   6篇
  1989年   7篇
  1988年   15篇
  1987年   11篇
  1986年   8篇
  1985年   9篇
  1984年   5篇
  1983年   5篇
  1982年   3篇
  1981年   4篇
  1980年   7篇
  1979年   7篇
  1978年   3篇
  1977年   4篇
  1976年   3篇
  1975年   3篇
  1974年   7篇
  1972年   4篇
  1970年   3篇
  1968年   3篇
  1967年   5篇
  1966年   8篇
  1965年   3篇
  1963年   4篇
排序方式: 共有510条查询结果,搜索用时 15 毫秒
41.
The photoinitiating ability of some sulfur ylides was studied. Diphenylsulfonium bis (methoxycarbony1)methylide (DPSY) could photoinitiate methyl methacrylate and styrene. A free radical mechanism was confirmed by a kinetic study, the inhibiting effect of benzoquinone, and the copolymer composition. From an analysis of the photodecomposition products it is suggested that the phenyl radical generated from the bond fission between the sulfur atom and the phenyl group participates in the initiation of this free radical polymerization. Methylphenylsulfonium bis (methoxycarbonyl) methylide, as well as DPSY, served as a photoinitiator, but dimethylsulfonium bis (methoxycarbony1)methylide did not. The differences are explained based on UV spectra.  相似文献   
42.
43.
The electrochemistry of Hf(IV) and the electrodeposition of Al–Hf alloys were examined in the Lewis acidic 66.7–33.3 mol% aluminum chloride-1-ethyl-3-methylimidazolium chloride molten salt containing HfCl4. When cyclic staircase voltammetry was carried out at a platinum disk electrode in this melt, the deposition and stripping waves for Al shifted to negative and positive potentials, respectively, suggesting that aluminum stripping is more difficult due to the formation of Al–Hf alloys. Al–Hf alloy electrodeposits containing ~13 at.% Hf were obtained on Cu rotating wire and cylinder electrodes. The Hf content in the Al–Hf alloy deposits depended on the HfCl4 concentration in the melt, the electrodeposition temperature, and the applied current density. The deposits were composed of dense crystals and were completely chloride-free. The chloride-induced pitting corrosion potential of the resulting Al–Hf alloys was approximately +0.30 V against pure aluminum when the Hf content was above 10 at.%.  相似文献   
44.
Morpholine enamines 4‐acetyl‐4‐methyl‐1‐morpholinocyclohexene 4a, 4‐acetyl‐4‐phenyl‐1‐morpholinocyclohexene 4b, and 4‐acetyl‐4‐isopropenyl‐1‐morpholinocyclohexene 4c react with methacryloyl chloride to give 1,7‐dimethyl‐4(N‐morpholino) tricyclo[5.3.1.04,9]undecan‐2,6‐dione 9a , 1‐phenyl‐7‐methyl‐4(N‐morpholino) tricyclo[5.3.1.04,9]undecan‐2,6‐dione 9b , and 1‐ispropenyl‐7‐methyl‐4(N‐morpholino) tricyclo[5.3.1.04,9]undecan‐2,6‐dione 9c respectively, along with the corresponding substituted adamandane‐2,4‐diones.  相似文献   
45.
The development of lithium-sulfur batteries is associated with many problems. These problems include polysulfide dissolution, the shuttle phenomenon, the low electric and ionic conductivity of S, and the volume change that occurs during charge and discharge. In this review, various elemental techniques for overcoming these problems are summarized from the standpoints of the supporting materials. These techniques include preventing polysulfide dissolution from the cathodes through physical and chemical adsorption on the supporting materials, the use of electrolytes that do not dissolve polysulfides via the coordination of Li+ and solvents, and the use of ion-exchange polymers to permeate Li+ selectively. The following approaches to enable practical applications of S cathodes in future Li-ion batteries are introduced: the utilization of Li-free anode materials, such as C and Si; the use of Li2S cathodes, which are prepared via a pre-lithiation process; and increasing the areal capacity of the S cathode by using a suitable current collector such as Al foam, thus providing a large amount of space for Li+ to migrate and the electron-conductive path. The utilization of an Al foam current collector is one of the promising approaches to creating a cost-effective Li-ion battery owing to the established mass production of Al foam for use in NiMH batteries; such Li-ion battery can achieve an unprecedentedly high areal capacity of 21.9 mAh cm?2. Owing to the resulting areal capacity, the possibility of developing a lithium-sulfur battery with an energy density greater than 200 Wh kg?1 has been demonstrated. Consequently, the combination of these approaches, as introduced in this review, would help create a bright, sustainable society.  相似文献   
46.
47.
Non‐targeted nuclear magnetic resonance (NMR)‐based metabolic profiling was applied to potato leaves to survey metabolic changes associated with late blight resistance under field conditions. Potato plants were grown in an experimental field, and the compound leaves with no visible symptoms were collected from 20 cultivars/lines at two sampling time points: (i) the time of initial presentation of symptoms in susceptible cultivars and (ii) 12 days before this initiation. 1H NMR spectra of the foliar metabolites soluble in deuterium oxide‐ or methanol‐d4‐based buffers were measured and used for multivariate analysis. Principal component analysis for six cultivars at symptom initiation showed a class separation corresponding to their levels of late blight resistance. This separation was primarily explained by higher levels of malic acid, methanol, and rutin and a lower level of sucrose in the resistant cultivars than in the susceptible ones. Partial least squares regression revealed that the levels of these metabolites were strongly associated with the disease severity measured in this study under field conditions. These associations were observed only for the leaves harvested at the symptom initiation stage, but not for those collected 12 days beforehand. Subsequently, a simple, alternative enzymatic assay for l ‐malic acid was used to estimate late blight resistance, as a model for applying the potential metabolic marker obtained. This study demonstrated the potential of metabolomics for field‐grown plants in combination with targeted methods for quantifying marker levels, moving towards marker‐assisted screening of new cultivars with durable late blight resistance. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
48.
Abstract— Light-dependent phosphorylation of rhodopsin (Rho) is a first step in the desensitization of the signaling state of the receptor during vertebrate and invertebrate visual transduction. We found that only 358Ser of the photoac-tivated octopus Rho (oRho*) was phosphorylated by octopus rhodopsin kinase (oRK). Tryptic truncation of the C-terminal PPQGY repeats of oRho that follow the phosphorylation region did not influence spectral or G-protein activation properties of oRho but abolished phos phorylation. Despite significant structural differences between oRK and mammalian RK, these results provide i further evidence of the importance of singly phosphorylated species of Rho* in the generation of arrestin binding sites.  相似文献   
49.
The voltammetric characteristics of polycrystalline Au and W electrodes cleaned (thermal annealing at 1100 K) and characterized (Auger electron spectroscopy) in ultrahigh vacuum (UHV) have been examined in ultrapure AlCl(3)/1-ethyl-3-methylimidazolium chloride (EtMeImCl) melts in UHV. These experiments were performed using a custom-designed transfer system that allows for the all-Al electrochemical cell to be filled with EtMeImCl in an auxiliary UHV chamber and later transferred under UHV to the main UHV chamber that houses the Auger electron spectrometer. The results obtained for the underpotential (UPD) and bulk deposition of Al on Au were found to be very similar to those reported in the literature for measurements carried out under 1 atm of an inert gas in a glovebox. For the far more reactive W surfaces, voltammetric features ascribed to the stripping of underpotential-deposited Al could be observed following a single scan from 1.0 V vs Al(3+)/Al to a potential negative enough for bulk deposition of Al to ensue. This behavior is unlike that reported in the literature for experiments performed in a glovebox, which required either extensive potential cycling in the Al bulk deposition and stripping region or excursions to potentials positive enough for chlorine evolution to ensue for Al UPD features to be clearly discerned. These observations open new prospects for fundamental electrochemical studies of well-characterized, highly reactive metals, including single crystals, in a variety of low vapor pressure ionic liquids.  相似文献   
50.
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