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991.
A new complex Zn(Ⅱ)L2·2CH3OH(H2L = 4-chloro-2-(2,3-dihydro-1H-ben-zoimi-dazol-2-yl)-phenol) has been prepared and characterized by single-crystal X-ray diffraction analysis and elemental analysis.The crystal is of triclinic system,space group P1 with a = 9.2905(10),b = 10.3555(13),c = 14.9590(14) ,α = 101.0340(10),β = 101.261(2),γ = 99.1660(10)o,V = 1356.1(3) 3,Z = 2,C28H24Cl2N4O4Zn,Mr = 616.78,Dc = 1.510 g/cm3,μ = 1.145 mm·1,F(000) = 632,the final R = 0.0379 and wR = 0.0830 for 3606 observed reflections with I 2σ(I).The Zn(Ⅱ) atom presents a distorted square pyramidal coordination involving two H2L ligands.The hydrogen bonds and π···π stacking interactions extend the complex into a two-dimensional framework. 相似文献
992.
Ramaswamy Murugavel Prof. Subramaniam Kuppuswamy Nayanmoni Gogoi Ramamoorthy Boomishankar Dr. Alexander Steiner Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(3):994-1009
In contrast to the well‐known reaction of phosphonic acids RP(O)(OH)2 with divalent transition‐metal ions that yields layered metal phosphonates [RPO3M(H2O)]n, the 2,6‐diisopropylphenyl ester of phosphoric acid, dippH2, reacts with zinc acetate in methanol under ambient conditions to afford tetrameric zinc phosphate [(ArO)PO3Zn(MeOH)]4 ( 1 ). The coordinated methanol in 1 can be readily exchanged by stronger Lewis basic ligands at room temperature. This strategy opens up a new avenue for building double‐four‐ring (D4R) cubane‐based supramolecular assemblies through strong intercubane hydrogen‐bonding interactions. Seventeen pyridinic ligands have been used to synthesize as many D4R cubanes [(ArO)PO3Zn(L)]4 ( 2 – 18 ) from 1 . The ligands have been chosen in such a way that the majority of them contain an additional functional group that could be used for noncovalent synthesis of extended structures. When the ligand does not contain any other hydrogen‐bonding donor–acceptor sites (e.g., 2,4,6‐trimethylpyridine (collidine)), zero‐dimensional D4R cubanes have been obtained. The use of pyridine, lutidine, 2‐aminopyridine, and 2,6‐diaminopyridine, however, results in the formation of linear or zigzag one‐dimensional assemblies of D4R cubanes through strong intermolecular C? H???O or N? H???O interactions. Construction of two‐dimensional assemblies of zinc phosphates has been achieved by employing 2‐hydroxypyridine or 2‐methylimidazole as the exo‐cubane ligand on zinc centers. The introduction of an alcohol side chain on the pyridinic ligand in such a way that the ? CH2OH group cannot participate in intracubane hydrogen bonding (e.g., pyridine‐3‐methanol, pyridine‐4‐methanol, and 3,5‐dimethylpyrazole‐N‐ethanol) leads to the facile noncovalent synthesis of three‐dimensional framework structures. Apart from being useful as building blocks for noncovalent synthesis of zeolite‐like materials, compounds 1 – 18 can also be thermolyzed at approximately 500 °C to yield high‐purity zinc pyrophosphate (Zn2P2O7) ceramic material. 相似文献
993.
Shaun T. Mutter James A. Platts 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(18):5391-5399
A series of ab initio calculations are used to determine the C? H???π and π???π‐stacking interactions of aromatic rings coordinated to transition‐metal centres. Two model complexes have been employed, namely, ferrocene and chromium benzene tricarbonyl. Benchmark data obtained from extrapolation of MP2 energies to the basis set limit, coupled with CCSD(T) correction, indicate that coordinated aromatic rings are slightly weaker hydrogen‐bond acceptors but are significantly stronger hydrogen‐bond donors than uncomplexed rings. It is found that π???π stacking to a second benzene is stronger than in the free benzene dimer, especially in the chromium case. This is assigned, by use of energy partitioning in the local correlation method, to dispersion interactions between metal d and benzene π orbitals. The benchmark data is also used to test the performance of more efficient theoretical methods, indicating that spin‐component scaling of MP2 energies performs well in all cases, whereas various density functionals describe some complexes well, but others with errors of more than 1 kcal mol?1. 相似文献
994.
Michele R. Chierotti Dr. Luca Ferrero Dr. Nadia Garino Dr. Roberto Gobetto Prof. Luca Pellegrino Dr. Dario Braga Prof. Fabrizia Grepioni Prof. Lucia Maini Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(14):4347-4358
Five new polymorphs and one hydrated form of 2‐thiobarbituric acid have been isolated and characterised by solid‐state methods. In both the crystalline form II and in the hydrate form, the 2‐thiobarbituric molecules are present in the enol form, whereas only the keto isomer is present in crystalline forms I (reported in 1967 by Calas and Martinex), III , V and VI . In form IV , on the other hand, a 50:50 ordered mixture of enol/keto molecules is present. All new forms have been characterised by single‐crystal X‐ray diffraction, 1D and 2D (1H, 13C, and 15N) solid‐state NMR spectroscopy, Raman spectroscopy and X‐ray powder diffraction at variable temperature. It has been possible to induce keto–enol conversion between the forms by mechanical methods. The role of hydrogen‐bond interactions in determining the relative stability of the polymorphs and as a driving force in the conversions has been ascertained. To the best of the authors’ knowledge, the 2‐thiobarbituric family of crystal forms represents the richest collection of examples of tautomeric polymorphism so far reported in the literature. 相似文献
995.
Pedro D. Vaz Dr. Mariela M. Nolasco Dr. Francisco P. S. C. Gil Dr. Paulo J. A. Ribeiro‐Claro Prof. John Tomkinson Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(30):9010-9017
Spectroscopic evidence for C? H ??? O hydrogen bonding in chloroform ??? acetone [Cl3CH ??? O?C(CH3)2] mixtures was obtained from vibrational inelastic neutron scattering (INS) spectra. Comparison between the INS spectra of pure samples and their binary mixtures reveals the presence of new bands at about 82, 130 and 170 cm?1. Assignment of the 82 cm?1 band to the νO ??? H anti‐translational mode is considered and discussed. In addition, the βC? H mode of CHCl3 at 1242 cm?1 is split in the spectra of the mixtures, and the high‐wavenumber component is assigned to the hydrogen‐bonded complex. The plot of the integrated intensity of this component shows a maximum for x=0.5, in agreement with the 1:1 stoichiometry of the chloroform ??? acetone complex, with a calculated complexation constant of 0.15 dm3 mol?1. Results also show that the complex behaves as an independent entity, that is, despite being weak, such interactions play a key role in supramolecular chemistry. 相似文献
996.
Sylvain Koeller Dr. Joji Kadota Dr. Frédéric Peruch Dr. Alain Deffieux Dr. Noël Pinaud Isabelle Pianet Dr. Stéphane Massip Dr. Jean‐Michel Léger Dr. Jean‐Pierre Desvergne Dr. Brigitte Bibal Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(14):4196-4205
The mechanism of the ring‐opening polymerization (ROP) of lactide catalyzed by two partner hydrogen‐bonding organocatalysts was explored. New amidoindoles 4 a , c , thioamidoindoles 4 b , d , amidobenzimidazoles 5 a , c , and thioamidobenzimidazoles 5 b , c were synthesized and used as activators of the monomer. In the solid state and in solution, compounds 4 and 5 showed a propensity for self‐association, which was evaluated. (Thio)Amides 4 and 5 do catalyze the ROP of lactide in the presence of a cocatalyst, tertiary amine 3 a or 3 b , which activates the growing polymer chain through hydrogen‐bonding. Reactions were conducted in 2–24 h at 20 °C; conversion yields ranged between 22 and 100 %. A detailed study of the intermolecular interactions undertaken between the participating species showed that, as expected, simultaneous weak hydrogen bonds do exist to activate the reagents. Moreover, interactions have been revealed between the partner catalysts 4 / 5 + 3 . ROP catalyzed by these partner activators is thus governed by multiple dynamic equilibria. The latter should be judiciously adjusted to fine‐tune the catalytic properties of (thio)amides and organocatalysts, more generally. 相似文献
997.
Miguel Maestro Dr. Antonia Mielgo Dr. Itziar Otazo Claudio Palomo Prof. Dr. Irene Velilla 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(18):5333-5342
An anti‐selective Mannich reaction of aldehydes with N‐sulfonyl imines has been developed by using a 4‐hydroxypyrrolidine in combination with an external Brønsted acid. The catalyst design is based on three elements: the α‐substituent of the pyrrolidine, the 4‐hydroxy group, and the Brønsted acid, the combination of which is essential for high chemical and stereochemical efficiency. The reaction works with aromatic aldehyde‐derived imines, which have rarely been employed in previously reported enamine‐based anti‐Mannich reactions. Additionally, both N‐tosyl and N‐nosyl imines can be successfully used and the Mannich adducts can be easily reduced or oxidized, and after N‐deprotection the corresponding β‐amino acids and β‐amino alcohols can be obtained with good yields. The results also show that this ternary catalytic system may be practical in other enamine‐based reactions. 相似文献
998.
Francesca Tancini Dr. Thomas Gottschalk Dr. W. Bernd Schweizer Dr. François Diederich Prof. Dr. Enrico Dalcanale Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(26):7813-7819
The capability of resorcinarenes to bind anions within the alkyl feet at the lower rim has been exploited as the starting point for developing a new cavitand able to engulf contact ion pairs of primary ammonium salts in chlorinated solvents with association constants (Kass) in the range of 103–104 M ?1. Methylene bridges were introduced into the upper rim to freeze the resorcinarene in the cone conformation with the four Hdown protons converging in the lower pocket, thereby maximizing the CH–anion interactions responsible for the anion binding. Four additional phosphate moieties were introduced into the lower rim in close proximity to the anionic site to provide hydrogen‐bonding‐acceptor P?O groups and promote cation complexation at the bottom of the cavitand. The binding ability of the synthesized ligands was analyzed by 1H NMR spectroscopy and, when possible, by isothermal titration calorimetry (ITC); the data were in agreement when complementary techniques were used. 相似文献
999.
Jií ejka Silmarilly Bahfenne Ray L. Frost Jií Sejkora 《Journal of Raman spectroscopy : JRS》2010,41(1):74-77
Raman spectra of vajdakite, [(Mo6+O2)2(H2O)2As O5]·H2O, were studied and interpreted in terms of the structure of the mineral. The Raman spectra were compared with the published infrared spectrum of vajdakite. The presence of dimolybdenyl and diarsenite units and of hydrogen bonded water molecules was inferred from the Raman spectra which supported the known and published crystal structure of vajdakite. Mo O and O H···O bond lengths were calculated from the Raman spectra. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
1000.
Two new organic photochromic compounds based on pyrazolone were synthesized and further characterized by elemental analysis,
MS, IR spectra, and 1H NMR spectra. The photochromic properties and photochemical kinetics of them have been studied by UV absorption spectra under
irradiation of 365 nm light. The photochromism of pyrazolone derivatives in the solid state has been so far explained only
in terms of the light-induced change of absorption and their crystal structures, which is caused by the shift of the tautomeric
equilibrium between the enol and keto forms. In this work, their IR spectra have been measured before and after irradiation.
Based on the IR spectra and crystal structure analysis, a reasonable mechanism was proposed, the photochromic phenomenon may
be due to the photoisomerization from enol-form to keto-form through proton transfer. 相似文献