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971.
Dey A Chow M Taniguchi K Lugo-Mas P Davin S Maeda M Kovacs JA Odaka M Hodgson KO Hedman B Solomon EI 《Journal of the American Chemical Society》2006,128(2):533-541
The geometric and electronic structure of the active site of the non-heme iron enzyme nitrile hydratase (NHase) is studied using sulfur K-edge XAS and DFT calculations. Using thiolate (RS(-))-, sulfenate (RSO(-))-, and sulfinate (RSO(2)(-))-ligated model complexes to provide benchmark spectral parameters, the results show that the S K-edge XAS is sensitive to the oxidation state of S-containing ligands and that the spectrum of the RSO(-) species changes upon protonation as the S-O bond is elongated (by approximately 0.1 A). These signature features are used to identify the three cysteine residues coordinated to the low-spin Fe(III) in the active site of NHase as CysS(-), CysSOH, and CysSO(2)(-) both in the NO-bound inactive form and in the photolyzed active form. These results are correlated to geometry-optimized DFT calculations. The pre-edge region of the X-ray absorption spectrum is sensitive to the Z(eff) of the Fe and reveals that the Fe in [FeNO](6) NHase species has a Z(eff) very similar to that of its photolyzed Fe(III) counterpart. DFT calculations reveal that this results from the strong pi back-bonding into the pi antibonding orbital of NO, which shifts significant charge from the formally t(2)(6) low-spin metal to the coordinated NO. 相似文献
972.
The aggregation behavior of N-(2-hydroxydodecyl)-L-alanine (C12HAla) and N-(n-dodecyl)-L-alanine (C12Ala) was studied in aqueous buffer (pH 12) over a concentration range above their critical aggregation concentration (cac). The C12HAla amphiphile has two cacs in contrast to only one cac value for C12Ala. The micropolarity and microviscosity of the aggregates were studied by use of pyrene and 1,6-diphenyl-1,3,5-hexatriene, respectively, as fluorescent probes. Dynamic light scattering was used to measure the average hydrodynamic diameter and size distribution of the aggregates. Large size, high microviscosity, and low micropolarity values of the aggregates suggested the formation of bilayer structures in dilute solutions of C12HAla. In contrast, C12Ala was observed to form micelles. Transmission electron micrographs of dilute and moderately concentrated solutions of C12HAla revealed the existence of spherical vesicles and branching tubular structures, respectively. Comparison of the aggregation behavior of these amphiphiles to that of C12Ala and the FT-IR spectrum suggested that intermolecular hydrogen-bonding interactions between adjacent hydrocarbon chains through the -OH and -NH- groups of C12HAla are responsible for bilayer formation. The mechanism of nanotube formation was discussed. The temperature dependence of aggregate formation of the amphiphile also was investigated. 相似文献
973.
Subal Dey Tanya K. Todorova Marc Fontecave Victor Mougel 《Angewandte Chemie (International ed. in English)》2020,59(36):15726-15733
Electrocatalytic CO2 reduction to value‐added products provides a viable alternative to the use of carbon sources derived from fossil fuels. Carrying out these transformations at reasonable energetic costs, for example, with low overpotential, remains a challenge. Molecular catalysts allow fine control of activity and selectivity via tuning of their coordination sphere and ligand set. Herein we investigate a series of cobalt(III) pyridine‐thiolate complexes as electrocatalysts for CO2 reduction. The effect of the ligands and proton sources on activity was examined. We identified bipyridine bis(2‐pyridinethiolato) cobalt(III) hexaflurophosphate as a highly selective catalyst for formate production operating at a low overpotential of 110 mV with a turnover frequency (TOF) of 10 s?1. Electrokinetic analysis coupled with density functional theory (DFT) computations established the mechanistic pathway, highlighting the role of metal hydride intermediates. The catalysts deactivate via the formation of stable cobalt carbonyl complexes, but the active species could be regenerated upon oxidation and release of coordinated CO ligands. 相似文献
974.
Cobalt‐Catalyzed sp2‐C−H Activation: Intermolecular Heterocyclization with Allenes at Room Temperature 下载免费PDF全文
Dr. Neetipalli Thrimurtulu Arnab Dey Prof. Debabrata Maiti Prof. Chandra M. R. Volla 《Angewandte Chemie (International ed. in English)》2016,55(40):12361-12365
The reactivity of allenes in transition‐metal‐catalyzed C?H activation chemistry is governed by the formation of either alkenyl–metal (M–alkenyl) or metal–π‐allyl intermediates. Although either protonation or a β‐hydride elimination is feasible with a M–alkenyl intermediate, cyclization has remained unexplored to date. Furthermore, due to the increased steric hindrance, the regioselectivity for the intramolecular cyclization of the metal–π‐allyl intermediate was hampered towards the more substituted side. To address these issues, a unified approach to synthesize a diverse array of biologically and pharmaceutically relevant heterocyclic moieties by cobalt‐catalyzed directed C?H functionalization was envisioned. Upon successful implementation, the present strategy led to the regioselective formation of dihydroisoquinolin‐1(2H)‐ones, isoquinolin‐1(2H)‐ones, dihydropyridones, and pyridones. 相似文献
975.
976.
Kishore S. Jain Muthu K. Kathiravan Jitender B. Bariwal Pratip K. Chaskar Santosh S. Tompe Nikhilesh Arya 《合成通讯》2013,43(5):719-727
The novel dual use of formamide-POCl3 mixture for the incorporation of a C-N fragment to form the pyrimidine nucleus and its subsequent chlorination in an efficient, one-pot synthesis of potentially bioactive condensed 2H-pyrimidin-4-amine libraries under microwave irradiation (MWI) is reported. The one-pot microwave-assisted synthetic protocol is high-yielding, ecofriendly, rapid, and novel as well as eliminates intermittent workups. The protocol can be adapted for the library synthesis of series of a condensed pyrimidines. 相似文献
977.
Nibaran C. Dey Gopu Kumar Birendra K. Saikia Inamul Haque 《Journal of solution chemistry》1985,14(1):49-58
Viscosity and desity data for KCl, KBr, Me4NBr, Et4NBr, Pr4NBr, and Bu4NBr from 0.005 to 3M in aqueous dimethylformamide solutions at 25°C and 35°C are presented. The data for dilute solutions were analyzed by means of the Jones-Dole equation and the ionic B coefficients evaluated. The data for concentrated solutions were analyzed by the Breslau and Miller equation and the effective flow volume, V3 of the electrolytes obtained as a function of concentration. The limiting effective flow volume, V
e
o
was obtained from the Vand equation in the form used by Eagland and Pilling and it is shown that B=2.5 V
e
o
. With increasing DMF concentration V
e
o
increases for Me4NBr but decreases for Pr4NBr and Bu4NBr. The same effect was observed by increasing temperature. This behavior is explained in terms of the structuring effect of the constituent ions and the effect of DMF on the overall structure of the binary solvent. 相似文献
978.
Reddy GR Reddy TR Joseph SC Reddy KS Reddy LS Kumar PM Krishna GR Reddy CM Rambabu D Kapavarapu R Lakshmi C Meda T Priya KK Parsa KV Pal M 《Chemical communications (Cambridge, England)》2011,47(27):7779-7781
A sequential Pd-mediated multi-component reaction followed by Suzuki or Heck or Sonogashira coupling in a single pot has been developed for the synthesis of functionalized pyrroles as potential inhibitors of PDE4. 相似文献
979.
Dey SK Beuerle F Olson MA Stoddart JF 《Chemical communications (Cambridge, England)》2011,47(5):1425-1427
The formation of both [2]- and [7]pseudorotaxanes, which are obtained by mixing of a dibenzylammonium derivative with mono- and hexakis-adducts of [60]fullerene bearing malonato-benzo[25]crown-8 rings, has been monitored in dichloromethane by both 1D and 2D (1)H NMR spectroscopies. 相似文献
980.
Decanuclear Ln10 Wheels and Vertex‐Shared Spirocyclic Ln5 Cores: Synthesis,Structure, SMM Behavior,and MCE Properties 下载免费PDF全文
Dr. Sourav Das Dr. Atanu Dey Dr. Subrata Kundu Sourav Biswas Dr. Ramakirushnan Suriya Narayanan Dr. Silvia Titos‐Padilla Dr. Giulia Lorusso Dr. Marco Evangelisti Prof. Enrique Colacio Prof. Vadapalli Chandrasekhar 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(47):16955-16967
The reaction of a Schiff base ligand (LH3) with lanthanide salts, pivalic acid and triethylamine in 1:1:1:3 and 4:5:8:20 stoichiometric ratios results in the formation of decanuclear Ln10 (Ln=Dy( 1 ), Tb( 2 ), and Gd ( 3 )) and pentanuclear Ln5 complexes (Ln=Gd ( 4 ), Tb ( 5 ), and Dy ( 6 )), respectively. The formation of Ln10 and Ln5 complexes are fully governed by the stoichiometry of the reagents used. Detailed magnetic studies on these complexes ( 1 – 6 ) have been carried out. Complex 1 shows a SMM behavior with an effective energy barrier for the reversal of the magnetization (Ueff)=16.12(8) K and relaxation time (τo)=3.3×10?5 s under 4000 Oe direct current (dc) field. Complex 6 shows the frequency dependent maxima in the out‐of‐phase signal under zero dc field, without achieving maxima above 2 K. Complexes 3 and 4 show a large magnetocaloric effect with the following characteristic values: ?ΔSm=26.6 J kg?1 K?1 at T=2.2 K for 3 and ?ΔSm=27.1 J kg?1 K?1 at T=2.4 K for 4 , both for an applied field change of 7 T. 相似文献