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81.
The nickel, copper and iron complexes of bis(salicylidene)-meso-1,2-diphenylethylendiaminato (mdpSal2?) and their propensity to form multinuclear complexes similar to those observed for Co(mdpSal) are reported. The syntheses of the primary compounds were carried out with M(OAc)2·xH2O (M = Fe, Ni or Cu) and mdpSalH2 in methanol. The Ni and Cu reactions resulted in the isolation of mononuclear Ni(mdpSal) (1) and Cu(mdpSal) (2) complexes. Both species 1 and 2 adopt approximate square planar geometries in the monoclinic space group P21/n and are iso-structural to the previously reported Co(mdpSal). Although structurally similar, neither 1 nor 2 exhibit comparable reactivity as reported for the cobalt analogue of mdpSal?2 in forming multinuclear complexes. The iron reaction yielded a μ-oxo species [Fe(mdpSal)]2O (3) in which each iron center is oxidized to +3 and ligated to one mdpSal2? ligand frame with each iron center adopting distorted square pyramid geometry. In addition, Co(Salophen) (4) (SalophenH2 = N,N′-bis(salicylidene)-1,2-phenylenediamine) has been synthesized and its reactivity assessed and compared to Co(mdpSal). Complexes 1–3 have been characterized by X-ray crystallography as well as UV–Vis and IR spectroscopy. A detailed comparison of the structural and spectral characteristics of the iso-structural complexes 1 and 2 with Co(mdpSal) are presented along with a discussion of factors that contributed to the unique reactivity observed for [Co(mdpSal)]. 相似文献
82.
Graeme J. Gainsford Richard H. Furneaux Peter C. Tyler Anthony Sauve Vern L. Shramm 《Acta Crystallographica. Section C, Structural Chemistry》2010,66(3):m65-m68
The sodium salt of [immucillin‐A–CO2H]− (Imm‐A), namely catena‐poly[[[triaquadisodium(I)](μ‐aqua)[μ‐(1S)‐N‐carboxylato‐1‐(9‐deazaadenin‐9‐yl)‐1,4‐dideoxy‐1,4‐imino‐d ‐ribitol][triaquadisodium(I)][μ‐(1S)‐N‐carboxylato‐1‐(9‐deazaadenin‐9‐yl)‐1,4‐dideoxy‐1,4‐imino‐d ‐ribitol]] tetrahydrate], {[Na2(C12H13N4O6)2(H2O)7]·4H2O}n, (I), forms a polymeric chain via Na+—O interactions involving the carboxylate and keto O atoms of two independent Imm‐A molecules. Extensive N,O—H...O hydrogen bonding utilizing all water H atoms, including four waters of crystallization, provides crystal packing. The structural definition of this novel compound was made possible through the use of synchrotron radiation utilizing a minute fragment (volume ∼2.4 × 10−5 mm−3) on a beamline optimized for protein data collection. A summary of intra‐ring conformations for immucillin structures indicates considerable flexibility while retaining similar intra‐ring orientations. 相似文献
83.
Perrachione TK Lee J Ha LY Wong PC 《The Journal of the Acoustical Society of America》2011,130(1):461-472
Studies evaluating phonological contrast learning typically investigate either the predictiveness of specific pretraining aptitude measures or the efficacy of different instructional paradigms. However, little research considers how these factors interact--whether different students learn better from different types of instruction--and what the psychological basis for any interaction might be. The present study demonstrates that successfully learning a foreign-language phonological contrast for pitch depends on an interaction between individual differences in perceptual abilities and the design of the training paradigm. Training from stimuli with high acoustic-phonetic variability is generally thought to improve learning; however, we found high-variability training enhanced learning only for individuals with strong perceptual abilities. Learners with weaker perceptual abilities were actually impaired by high-variability training relative to a low-variability condition. A second experiment assessing variations on the high-variability training design determined that the property of this learning environment most detrimental to perceptually weak learners is the amount of trial-by-trial variability. Learners' perceptual limitations can thus override the benefits of high-variability training where trial-by-trial variability in other irrelevant acoustic-phonetic features obfuscates access to the target feature. These results demonstrate the importance of considering individual differences in pretraining aptitudes when evaluating the efficacy of any speech training paradigm. 相似文献
84.
Chon MJ Sethuraman VA McCormick A Srinivasan V Guduru PR 《Physical review letters》2011,107(4):045503
Crystalline to amorphous phase transformation during initial lithiation in (100) Si wafers is studied in an electrochemical cell with Li metal as the counter and reference electrode. During initial lithiation, a moving phase boundary advances into the wafer starting from the surface facing the lithium electrode, transforming crystalline Si into amorphous Li(x)Si. The resulting biaxial compressive stress in the amorphous layer is measured in situ, and it was observed to be ca. 0.5 GPa. High-resolution TEM images reveal a very sharp crystalline-amorphous phase boundary, with a thickness of ~1 nm. Upon delithiation, the stress rapidly reverses and becomes tensile, and the amorphous layer begins to deform plastically at around 0.5 GPa. With continued delithiation, the yield stress increases in magnitude, culminating in a sudden fracture of the amorphous layer into microfragments, and the cracks extend into the underlying crystalline Si. 相似文献
85.
We describe a tunable broadband mid-IR laser source based on difference-frequency mixing of a 100?MHz femtosecond Yb:fiber laser oscillator and a Raman-shifted soliton generated with the same laser. The resulting light is tunable over 3.0?μm to 4.4?μm, with a FWHM bandwidth of 170?nm and maximum average output power up to 125?mW. The noise and coherence properties of this source are also investigated and described. 相似文献
86.
87.
Haiping Qi Manfred Gröning Tyler B. Coplen Bryan Buck Stanley J. Mroczkowski Willi A. Brand Heike Geilmann Matthias Gehre 《Rapid communications in mass spectrometry : RCM》2010,24(13):1821-1827
A new method to seal water in silver tubes for use in a TC/EA (thermal conversion/elemental analyzer) reduction unit using a semi‐automated sealing apparatus can yield reproducibilities (1 standard deviation) of δ2H and δ18O measurements of 1.0‰ and 0.06‰, respectively. These silver tubes containing reference waters may be preferred for the calibration of H‐ and O‐bearing materials analyzed with a TC/EA reduction unit. The new sealing apparatus employs a computer‐controlled stepping motor to produce silver tubes identical in length. The reproducibility of the mass of water sealed in tubes (in a range of 200–400 µg) can be as good as 1%. Approximately 99% of the sealed silver tubes are satisfactory (leak free). Although silver tubes sealed with reference waters are robust and can be shaken or heated to 110°C with no loss of integrity, they should not be frozen because the expansion during the phase transition of water to ice will break the cold seals and all the water will be lost. The tubes should be shipped in insulated containers. This new method eliminates air inclusions and isotopic fractionation of water associated with the loading of water into capsules using a syringe. The method is also more than an order of magnitude faster than preparing water samples in ordinary Ag capsules. Nevertheless, some laboratories may prefer loading water into silver capsules because expensive equipment is not needed, but users of this method are cautioned to apply the necessary corrections for evaporation, back exchange with laboratory atmospheric moisture, and blanks. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
88.
89.
Evaluating the accuracy of theoretical one‐bond 13C─13C scalar couplings and their ability to predict structure in a natural product 下载免费PDF全文
Jacob Powell Domenic Valenti Harley Bobnar Erika Drain Blaine Elliott Sydney Frank Tyler McCullough Sean Moore Andrew Kettring Robbie Iuliucci James K. Harper 《Magnetic resonance in chemistry : MRC》2017,55(11):979-989
This study explores the feasibility of using a combination of experimental and theoretical 1‐bond 13C─13C scalar couplings (1JCC) to establish structure in organic compounds, including unknowns. Historically, nJCC and nJCH studies have emphasized 2 and 3‐bond couplings, yet 1JCC couplings exhibit significantly larger variations. Moreover, recent improvements in experimental measurement and data processing methods have made 1JCC data more available. Herein, an approach is evaluated in which a collection of theoretical structures is created from a partial nuclear magnetic resonance structural characterization. Computed 1JCC values are compared to experimental data to identify candidates giving the best agreement. This process requires knowledge of the error in theoretical methods, thus the B3LYP, B3PW91, and PBE0 functionals are evaluated by comparing to 27 experimental values from INADEQUATE. Respective errors of ±1.2, ±3.8, and ±2.3 Hz are observed. An initial test of this methodology involves the natural product 5‐methylmellein. In this case, only a single candidate matches experimental data with high statistical confidence. This analysis establishes the intramolecular hydrogen‐bonding arrangement, ring heteroatom identity, and conformation at one position. This approach is then extended to hydroheptelidic acid, a natural product not fully characterized in prior studies. The experimental/theoretical approach proposed herein identifies a single best‐fit structure from among 26 candidates and establishes, for the first time, 1 configuration and 3 conformations to complete the characterization. These results suggest that accurate and complete structural characterizations of many moderately sized organic structures (<800 Da) may be possible using only 1JCC data. 相似文献
90.
The retention of polar compounds, the separation of structural isomers and thermal stability make carbonaceous materials very attractive stationary phases for liquid chromatography (LC). Carbon clad zirconia (C/ZrO2), one of the most interesting, exhibits unparalleled chemical and thermal stability, but its characteristically low surface area (20–30 m2/g) limits broader application as a second dimension separation in two-dimensional liquid chromatography (2DLC) where high retentivity and therefore high stationary phase surface area are required. In this work, we used a high surface area commercial HPLC alumina (153 m2/g) as a support material to develop a carbon phase by chemical vapor deposition (CVD) at elevated temperature using hexane vapor as the carbon source. The loading of carbon was varied by changing the CVD time and temperature, and the carbon coated alumina (C/Al2O3) was characterized both physically and chromatographically. The resulting carbon phases behaved as a reversed phase similar to C/ZrO2. At all carbon loadings, C/Al2O3 closely matched the unique chromatographic selectivity of carbon phases, and as expected the retentivity was increased over C/ZrO2. Excess carbon – the amount equivalent to 5 monolayers – was required to fully cover the oxide support in C/Al2O3, but this was less excess than needed with C/ZrO2. Plate counts were 60,000–76,000/m for 5 μm particles. Spectroscopic studies (XPS and FT-IR) were also conducted; they showed that the two materials were chemically very similar. 相似文献