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61.
The pretransitional behaviour of a homologous series of mesomorphic compounds, the alkyl cyanobiphenyls (CNρρC n H 2n + 1) for n = 5–12, has been studied as a function of temperature by light scattering in the isotropic phase. The higher homologues, n = 8–12, exhibit a smectic A phase that becomes increasingly important at the expense of the nematic phase for increasing n and for n = 10 and 12 no nematic phase is observed. We have shown from light scattering and differential scanning calorimetry measurements that the presence of the smectic A phase changes markedly the pretransitional behaviour, and gives rise to two distinct pretransitional regions. The first region is for temperatures greater than ~3°C above the clearing temperature Tc where the systems exhibit a typical pretransitional behaviour adequately described by the phenomenological Landau-de Gennes model of a second order phase transition with an intervering first order transition at Tc . The constants of this model for this region are given and show a distinct odd-even effect. The second region is close to Tc where a strong divergence from the already critical behaviour is observed. This secondary divergence is observed to be a function of the alkyl chain length and its conformation, and is attributed to coupling between smectic A like layers and the orientational order parameter in the isotropic phase. 相似文献
62.
S. P. Perkins D. E. Shoosmith H. J. Coles 《Molecular Crystals and Liquid Crystals》2013,570(1):943-950
Abstract In this paper we present the results of mixing fluorinated and non-fluorinated organosiloxane materials based on ferroelectric and antiferroelectric low molar mass organosiloxane (LMMO) liquid crystals. None of the fluorinated materials exhibit a mesophase, however when mixed with the non-fluorinated analogues a ferroelectric phase is observed. We present the resultant phase diagrams together with the spontaneous polarisation curves of the mixtures. 相似文献
63.
Cecile Schott Steven P. Perkins Harry J. Coles 《Molecular Crystals and Liquid Crystals》2013,570(1):715-724
Abstract In a chiral nematic liquid crystal, the flexoelectric effect consists of a fast and linear coupling with an applied electric field. One difficulty to overcome is the unwinding of the helix that occurs at higher fields due to dielectric coupling. The use of bimesogens, which possess very low molecular dielectric anisotropy can improve flexoelectric characteristics. New bimesogen compounds have recently been synthesised that exhibit switching angles of 45° for applied fields of about 9 V.μm?1. In this paper, results from dielectric, electro-optic and dynamic light scattering measurements are reported for the new bimesogenic mixture. The dielectric anisotropy Δε changes sign with temperature and its values range between -0.2 and 0.3 for the temperature range studied. For Δε weakly positive, no electric field Freedericksz transition could be induced but Williams domains are observed instead. The large decrease in the bend elastic constant to viscosity coefficient ratio is attributed to a large increase in the bend viscosity coefficient. 相似文献
64.
Ryan J. Schwamm Mathew D. Anker Matthias Lein Martyn P. Coles 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(5):1503-1507
The potassium aluminyl complex K[Al(NONAr)] (NON=NONAr=[O(SiMe2NAr)2]2?, Ar=2,6‐iPr2C6H3) reacts with 1,3,5,7‐cyclooctatetraene (COT) to give K[Al(NONAr)(COT)]. The COT‐ligand is present in the asymmetric unit as a planar μ2‐η2:η8‐bridge between Al and K, with additional K???π‐aryl interactions to neighboring molecules that generate a helical chain. DFT calculations indicate significant aromatic character, consistent with reduction to [COT]2?. Addition of 18‐crown‐6 causes a rearrangement of the C8‐carbocycle to form the isomeric 9‐aluminabicyclo[4.2.1]nona‐2,4,7‐triene anion. 相似文献
65.
M. Dimitroff G. Spacu M. Entat E. Vulquin J. Herzog B. van der Burg C. A. Koppejan Erich Müller Florence Fenwick G. Torossian P. M. Dean E. Newcomer O. O. Watts L. A. Congdon W. B. Crabtree H. W. Coles L. L. Smith M. L. Vehalgo H. W. Doughty A. J. Jonas E. Oppenheimer L. J. Curtman C. Kaufman J. M. Kolthoff N. Sasaki J. H. Linschoten V. Thüringer S. Hasselskog H. T. S. Britton F. L. Hibbard 《Analytical and bioanalytical chemistry》1927,72(9-10):375-386
66.
Coles SR Barker G Clark AJ Kirwan K Jacobs D Makenji K Pink D 《Macromolecular bioscience》2008,8(6):526-532
The use of plant oils as industrial feedstocks can often be hampered by their lack of optimization towards a particular process, as well as their development being risky; growing suitable volumes of crops to test can take up to five years. To circumvent this, we aimed to discover a method that would mimic plant oil profiles in the laboratory, and show that they exhibited similar properties to the naturally grown plant oils in a given process. Using the synthesis of polyurethanes as an example, we have synthesized six different polymers and demonstrated that plant oils will produce polymers with similar physical properties to those oils mimicked in the laboratory. The use of this mimicking process can be extended to other types of polymers to obtain a method for predicting the properties of a given material based on the plant oil composition of a crop before it is grown in bulk. 相似文献
67.
Khalaf MS Coles MP Hitchcock PB 《Dalton transactions (Cambridge, England : 2003)》2008,(32):4288-4295
Partial deprotonation of the bicyclic guanidine 1,4,6-triazabicyclo[3.3.0]oct-4-ene (Htbo) is achieved using (n)BuLi. Isolation of the resulting lithium salts has resulted in the structural characterization of the mixed anion complex {[Li(tbo)()(tboH)](2)}(infinity) (where -H = 1-(2-aminoethyl)-2-imidazolidinethione) and the partially deprotonated salt Li(6)(tbo)(6)(Htbo)(3), . The neutral guanidine Htbo reacts cleanly with AlMe(3) and ZnMe(2) to afford the organometallic complexes [Al(tbo)Me(2)](2) [](2), and Zn(3)(tbo)(4)Me(2) (). Structural characterization of these compounds enables comparison between the {5:5}-bicyclic system, [tbo](-), and the previously reported {6:6}-bicyclic system, [hpp](-) (where hppH = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine). Results indicate that delocalization within the [tbo](-) anion is restricted to the CN(2) amidinate component, with retention of electron density in the non-bonding nitrogen lone-pair. These conclusions are supported by a DFT analysis of the neutral guanidines, Htbo and hppH. 相似文献
68.
Skabara PJ Pozo-Gonzalo C Lardiés Miazza N Laguna M Cerrada E Luquin A González B Coles SJ Hursthouse MB Harrington RW Clegg W 《Dalton transactions (Cambridge, England : 2003)》2008,(23):3070-3079
A series of new metal (M) dithiolene complexes bearing terthiophene (3, 12, M = Ni; 4, M = Pd; 5, 6, M = Au) and 2,5-bis(para-methoxyphenyl)thiophene units (14, M = Ni; 15, 16, M = Au; 17, M = Pd) have been synthesised in 38-99% yield. The electrochemical properties of the materials have been characterised by cyclic voltammetry and UV-vis spectroelectrochemistry. The nickel complexes possess low oxidation potentials (-0.12 to -0.25 V vs Ag/AgCl) due to the electron-rich dithiolene centres and all complexes display ligand-based redox activity. The terthiophene derivatives have been polymerised by electrochemical oxidation to give stable films with, in the case of poly(3), broad absorption characteristics. Charge transfer materials have been isolated from 14 and 16 with conductivities in the range 9 x 10(-6) to 7 x 10(-8) S cm(-1). 相似文献
69.
Dr. Xuelin Yao Dr. Heng Zhang Fanmiao Kong Dr. Antoine Hinaut Dr. Rémy Pawlak Prof. Dr. Masanari Okuno Dr. Robert Graf Dr. Peter N. Horton Prof. Dr. Simon J. Coles Prof. Dr. Ernst Meyer Prof. Dr. Lapo Bogani Prof. Dr. Mischa Bonn Prof. Dr. Hai I. Wang Prof. Dr. Klaus Müllen Prof. Dr. Akimitsu Narita 《Angewandte Chemie (International ed. in English)》2023,62(46):e202312610
Structurally defined graphene nanoribbons (GNRs) have emerged as promising candidates for nanoelectronic devices. Low band gap (<1 eV) GNRs are particularly important when considering the Schottky barrier in device performance. Here, we demonstrate the first solution synthesis of 8-AGNRs through a carefully designed arylated polynaphthalene precursor. The efficiency of the oxidative cyclodehydrogenation of the tailor-made polymer precursor into 8-AGNRs was validated by FT-IR, Raman, and UV/Vis-near-infrared (NIR) absorption spectroscopy, and further supported by the synthesis of naphtho[1,2,3,4-ghi]perylene derivatives ( 1 and 2 ) as subunits of 8-AGNR , with a width of 0.86 nm as suggested by the X-ray single crystal analysis. Low-temperature scanning tunneling microscopy (STM) and solid-state NMR analyses provided further structural support for 8-AGNR . The resulting 8-AGNR exhibited a remarkable NIR absorption extending up to ∼2400 nm, corresponding to an optical band gap as low as ∼0.52 eV. Moreover, optical-pump TeraHertz-probe spectroscopy revealed charge-carrier mobility in the dc limit of ∼270 cm2 V−1 s−1 for the 8-AGNR . 相似文献
70.
Coles MP Lee SF Oakley SH Estiu G Hitchcock PB 《Organic & biomolecular chemistry》2007,5(24):3909-3911
The methylene-linked bis{guanidine}, H(2)C{hpp}(2) (hppH = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine), displays nucleophilic activity towards organic halides, including the activation of dichloromethane under ambient conditions affording the cyclic dication, [H(2)C{hpp}(2)CH(2)](2+)[Cl](2). 相似文献