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921.
Novel cobalt (II), nickel (II), copper (II), and zinc (II) complexes were synthesized from Schiff base ligand derived from 4-aminoantipyrine, vanillin, and o-anisidine. The structural features were derived from their elemental analysis, molar conductance, magnetic measurements, and various spectroscopic techniques such as infrared, ultraviolet visible, nuclear magnetic resonance, and electron paramagnetic resonance spectroscopy. Antimicrobial screening tests were performed against bacteria and fungi. The comparative study of the minimum inhibitory concentration values of the Schiff base and its metal complexes indicate that the metal complexes exhibit greater antimicrobial activity than the free ligand. 相似文献
922.
Konstantinos Spiliopoulos Justin A. Sirignano Kay Giesecke 《Stochastic Processes and their Applications》2014
We analyze the fluctuation of the loss from default around its large portfolio limit in a class of reduced-form models of correlated firm-by-firm default timing. We prove a weak convergence result for the fluctuation process and use it for developing a conditionally Gaussian approximation to the loss distribution. Numerical results illustrate the accuracy and computational efficiency of the approximation. 相似文献
923.
Grotevendt AG Lummiss JA Mastronardi ML Fogg DE 《Journal of the American Chemical Society》2011,133(40):15918-15921
The role of ethylene in promoting metathesis of acetylenic enynes is probed within the context of ring-closing enyne metathesis, using first- and second-generation Grubbs catalysts. Under inert atmosphere, rapid catalyst deactivation is observed by calibrated GC-FID analysis for substrates with minimal propargylic bulk. MALDI-TOF mass spectra reveal a Ru(enyne)(2) derivative that exhibits very low reactivity toward both enyne and ethylene. Under ethylene, formation of this species is suppressed. Enynes with bulky propargylic groups are not susceptible to this catalyst deactivation pathway, even under N(2) atmosphere. 相似文献
924.
Oberhumer PM Huang YS Massip S James DT Tu G Albert-Seifried S Beljonne D Cornil J Kim JS Huck WT Greenham NC Hodgkiss JM Friend RH 《The Journal of chemical physics》2011,134(11):114901
We present a spectroscopic and theoretical investigation of the effect of the presence and position of hexyl side-chains in the novel low-bandgap alternating donor-acceptor copolymer poly[bis-N,N-(4-octylphenyl)-bis-N,N-phenyl-1,4-phenylenediamine-alt-5,5'-4',7',-di-2-thienyl-2',1',3'-benzothiadiazole] (T8TBT). We use electronic absorption and Raman spectroscopic measurements supported by calculations of chain conformation, electronic transitions, and Raman modes. Using these tools, we find that sterically demanding side-chain configurations induce twisting in the electronic acceptor unit and reduce the electronic interaction with the donor. This leads to a blue-shifted and weakened (partial) charge-transfer absorption band together with a higher photoluminescence efficiency. On the other hand, sterically relaxed side-chain configurations promote coupling between donor and acceptor units and exhibit enhanced absorption at the expense of luminescence efficiency. The possibility of tuning the donor-acceptor character of conjugated polymers by varying the placement of side-chains has very important ramifications for light emitting diode, Laser, display, and photovoltaic device optimization. 相似文献
925.
Described here are the rotationally resolved S(1)-S(0) electronic spectra of the acid-base complex cis-β-naphthol-H(2)O in the gas phase, both in the presence and absence of an applied electric field. The data show that the complex has a trans-linear O-H???O hydrogen bond configuration involving the -OH group of cis-β-naphthol and the oxygen lone pairs of the attached water molecule in both electronic states. The measured permanent electric dipole moments of the complex are 4.00 and 4.66 D in the S(0) and S(1) states, respectively. These reveal a small amount of photoinduced charge transfer between solute and solvent, as supported by density functional theory calculations and an energy decomposition analysis. The water molecule also was found to tunnel through a barrier to internal motion nearly equal in energy to kT at room temperature. The resulting large angular jumps in solvent orientation produce "flickering dipoles" that are recognized as being important to the dynamics of bulk water. 相似文献
926.
Bozkaya U Turney JM Yamaguchi Y Schaefer HF Sherrill CD 《The Journal of chemical physics》2011,135(10):104103
Using a Lagrangian-based approach, we present a more elegant derivation of the equations necessary for the variational optimization of the molecular orbitals (MOs) for the coupled-cluster doubles (CCD) method and second-order M?ller-Plesset perturbation theory (MP2). These orbital-optimized theories are referred to as OO-CCD and OO-MP2 (or simply "OD" and "OMP2" for short), respectively. We also present an improved algorithm for orbital optimization in these methods. Explicit equations for response density matrices, the MO gradient, and the MO Hessian are reported both in spin-orbital and closed-shell spin-adapted forms. The Newton-Raphson algorithm is used for the optimization procedure using the MO gradient and Hessian. Further, orbital stability analyses are also carried out at correlated levels. The OD and OMP2 approaches are compared with the standard MP2, CCD, CCSD, and CCSD(T) methods. All these methods are applied to H(2)O, three diatomics, and the O(4)(+) molecule. Results demonstrate that the CCSD and OD methods give nearly identical results for H(2)O and diatomics; however, in symmetry-breaking problems as exemplified by O(4)(+), the OD method provides better results for vibrational frequencies. The OD method has further advantages over CCSD: its analytic gradients are easier to compute since there is no need to solve the coupled-perturbed equations for the orbital response, the computation of one-electron properties are easier because there is no response contribution to the particle density matrices, the variational optimized orbitals can be readily extended to allow inactive orbitals, it avoids spurious second-order poles in its response function, and its transition dipole moments are gauge invariant. The OMP2 has these same advantages over canonical MP2, making it promising for excited state properties via linear response theory. The quadratically convergent orbital-optimization procedure converges quickly for OMP2, and provides molecular properties that are somewhat different than those of MP2 for most of the test cases considered (although they are similar for H(2)O). Bond lengths are somewhat longer, and vibrational frequencies somewhat smaller, for OMP2 compared to MP2. In the difficult case of O(4)(+), results for several vibrational frequencies are significantly improved in going from MP2 to OMP2. 相似文献
927.
Daly AM Douglass KO Sarkozy LC Neill JL Muckle MT Zaleski DP Pate BH Kukolich SG 《The Journal of chemical physics》2011,135(15):154304
Microwave spectra of the propiolic acid-formic acid doubly hydrogen bonded complex were measured in the 1 GHz to 21 GHz range using four different Fourier transform spectrometers. Rotational spectra for seven isotopologues were obtained. For the parent isotopologue, a total of 138 a-dipole transitions and 28 b-dipole transitions were measured for which the a-dipole transitions exhibited splittings of a few MHz into pairs of lines and the b-type dipole transitions were split by ~580 MHz. The transitions assigned to this complex were fit to obtain rotational and distortion constants for both tunneling levels: A(0+) = 6005.289(8), B(0+) = 930.553(8), C(0+) = 803.9948(6) MHz, Δ(0+)(J) = 0.075(1), Δ(0+)(JK) = 0.71(1), and δ(0+)(j) = -0.010(1) kHz and A(0-) = 6005.275(8), B(0-) = 930.546(8), C(0-) = 803.9907(5) MHz, Δ(0-)(J) = 0.076(1), Δ(0-)(JK) = 0.70(2), and δ(0-)(j) = -0.008(1) kHz. Double resonance experiments were used on some transitions to verify assignments and to obtain splittings for cases when the b-dipole transitions were difficult to measure. The experimental difference in energy between the two tunneling states is 291.428(5) MHz for proton-proton exchange and 3.35(2) MHz for the deuterium-deuterium exchange. The vibration-rotation coupling constant between the two levels, F(ab), is 120.7(2) MHz for the proton-proton exchange. With one deuterium atom substituted in either of the hydrogen-bonding protons, the tunneling splittings were not observed for a-dipole transitions, supporting the assignment of the splitting to the concerted proton tunneling motion. The spectra were obtained using three Flygare-Balle type spectrometers and one chirped-pulse machine at the University of Virginia. Rotational constants and centrifugal distortion constants were obtained for HCOOH···HOOCCCH, H(13)COOH···HOOCCCH, HCOOD···HOOCCCH, HCOOH···DOOCCCH, HCOOD···DOOCCCH, DCOOH···HOOCCCH, and DCOOD···HOOCCCH. High-level ab initio calculations provided initial rotational constants for the complex, structural parameters, and some details of the proton tunneling potential energy surface. A least squares fit to the isotopic data reveals a planar structure that is slightly asymmetric in the OH distances. The formic OH···O propiolic hydrogen bond length is 1.8 ? and the propiolic OH···O formic hydrogen bond length is 1.6 ?, for the equilibrium configuration. The magnitude of the dipole moment was experimentally determined to be 1.95(3) × 10(-30) C m (0.584(8) D) for the 0(+) states and 1.92(5) × 10(-30) C m (0.576(14) D) for the 0(-) states. 相似文献
928.
Gyula Bényei István Jalsovszky Dietrich Demus Krishna Prasad Shankar Rao Anikó Vajda 《Liquid crystals》2013,40(6):689-696
The synthesis and phase behaviour of the first cuneane derivatives having liquid crystalline properties are reported. This new class of liquid crystalline materials is the homologous series of bis[4‐(n‐alkoxyphenyl)]cuneane‐2,6‐dicarboxylates. They were synthesized by two methods: either by isomerization of the previously prepared bis[4‐(n‐alkoxyphenyl)]cubane‐1,4‐dicarboxylates or by direct esterification of the cuneane‐2,6‐dicarboxylic acid. Enantiotropic nematic phases were observed for the first four homologues. The higher homologues exhibited enantiotropic smectic A phases. The bis[4‐(n‐octylphenyl]cuneane‐2,6‐dicarboxylate exhibited the SmA phase at a lower temperature than its octyloxy analogue. The mesophases were investigated and established by polarizing optical microscopy, differential scanning calorimetry and X‐ray diffraction. Quantum chemical calculations suggest elongated structure for these new liquid crystalline compounds. 相似文献
929.
Junfang Zhao Justin Kai-Chi Lau Josipa Grzetic Udo H. Verkerk Jos Oomens K. W. Michael Siu Alan C. Hopkinson 《Journal of the American Society for Mass Spectrometry》2013,24(12):1957-1968
Infrared multiple-photon dissociation (IRMPD) spectroscopy and DFT calculations have been used to probe the most stable structures of a 3 * and a 4 * ions derived from both protonated pentaglycine (denoted G5) and pentaalanine (A5). The a 3 * and a 4 * ions derived from protonated A5 feature a CHR=N-CHR’- group at the N-terminus and an oxazolone ring at the C-terminus, as proposed previously [J. Am. Soc. Mass Spectrom. 19, 1788–1798 (2008)]. The isomeric a 4 * ion derived from A5 with a 3,5-dihydro-4H-imidazol-4-one ring structure was calculated to have a slightly better energy than the oxazolone, but the barrier to its formation is higher and there was no evidence of this ion in the IRMPD spectrum. By contrast, the a 4 * and [a 4 – H2O]+ (denoted a 4 0 ) ions from G5 gave strikingly similar IRMPD spectra and both have the 3,5-dihydro-4H-imidazol-4-one ring structure similar to that recently reported for the [GGGG + H – H2O]+ ion [Int. J. Mass Spectrom. 316–318, 268–272 (2012)]. In the absence of a solvent molecule, the pathway to the oxazolone is calculated to be lower than those to thermodynamically more stable products, the a 4 0 and the a 4 * with the 3,5-dihydro-4H-imidazol-4-one ring structure. Incorporation of one water molecule is sufficient to reduce the barrier to formation of the a 4 0 of G5 to below that for formation of the oxazolone. On the equivalent potential energy surface for protonated A5 the barrier to formation of the a 4 0 ion is 12.3 kcal mol–1 higher than that for oxazolone formation and the a 4 0 ion is not observed experimentally. Figure
? 相似文献
930.
Matthias Golecki Jochen Lach Alexander Jeremies Frank Lungwitz Dr. Michael Fronk Prof. Dr. Georgeta Salvan Prof. Dr. Dietrich R. T. Zahn Jaena Park Dr. Yulia Krupskaya Dr. Vladislav Kataev Prof. Dr. Rüdiger Klingeler Prof. Dr. Bernd Büchner Benjamin Mahns Prof. Dr. Martin Knupfer Dr. Pablo F. Siles Dr. Daniel Grimm Prof. Dr. Oliver G. Schmidt Andreas Reis Prof. Dr. Werner R. Thiel Daniel Breite Prof. Dr. Bernd Abel Prof. Dr. Berthold Kersting 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(24):7787-7801
A new strategy for the fixation of redox‐active dinickel(II) complexes with high‐spin ground states to gold surfaces was developed. The dinickel(II) complex [Ni2L(Cl)]ClO4 ( 1 ClO4), in which L2? represents a 24‐membered macrocyclic hexaaza‐dithiophenolate ligand, reacts with ambidentate 4‐(diphenylphosphino)benzoate (dppba) to form the carboxylato‐bridged complex [Ni2L(dppba)]+, which can be isolated as an air‐stable perchlorate [Ni2L(dppba)]ClO4 ( 2 ClO4) or tetraphenylborate [Ni2L(dppba)]BPh4 ( 2 BPh4) salt. The auration of 2 ClO4 was probed on a molecular level, by reaction with AuCl, which leads to the monoaurated NiII2AuI complex [NiII2L(dppba)AuICl]ClO4 ( 3 ClO4). Metathesis of 3 ClO4 with NaBPh4 produces [NiII2L(dppba)AuIPh]BPh4 ( 4 BPh4), in which the Cl? is replaced by a Ph? group. The complexes were fully characterized by ESI mass spectrometry, IR and UV/Vis spectroscopy, X‐ray crystallography ( 2 BPh4 and 4 BPh4), cyclic voltammetry, SQUID magnetometry and HF‐ESR spectroscopy. Temperature‐dependent magnetic susceptibility measurements reveal a ferromagnetic coupling J=+15.9 and +17.9 cm?1 between the two NiII ions in 2 ClO4 and 4 BPh4 (H=?2 JS1S2). HF‐ESR measurements yield a negative axial magnetic anisotropy (D<0), which implies a bistable (easy axis) magnetic ground state. The binding of the [Ni2L(dppba)]ClO4 complex to gold was ascertained by four complementary surface analytical methods: contact angle measurements, atomic‐force microscopy, X‐ray photoelectron spectroscopy, and spectroscopic ellipsometry. The results indicate that the complexes are attached to the Au surface through coordinative Au? P bonds in a monolayer. 相似文献