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991.
We explore the nature of intrinsic localized modes (ILMs) in a curved Fermi-Pasta-Ulam (FPU) chain and the effects of geometry
and second-neighbor interaction on the localization and movability properties of such modes. We determine analytically the
structure of the localized modes induced by an isotopic light-mass impurity in this chain. We further demonstrate that a nonlinear
impurity mode may be treated as a bound state of an ILM with the impurity.
相似文献
992.
The excited state absorption upconversion of Pr(0.5)Yb(3):ZBLAN glass material, under two-color excitation of the 960 nm semiconductor
laser and the Xe lamp light simultaneously, is reported in this article. It was found that the upconversion emission spectra
of 480.1, 519.0, 601.9 and 631.8 nm coincide with the common emission spectra. Meanwhile, the upconversion-excitation spectrum
has three obvious peaks under two-color excitation, and they respectively correspond to the 856.0 nm upconversion excitation
transition [1G4(Pr3+)→1I6(Pr3+) and 1G4(Pr3+)→3P1(Pr3+)], the 789.0 nm upconversion excitation transition 1G4(Pr3+)→3P2(Pr3+), and the 803.7 nm upconversion excitation transition 3H6(Pr3+)→1D2(Pr3+). The upconversion excitation transition 1G4(Pr3+)→1I6(Pr3+) is strong because its oscillator strength f = 23.040×10−6 is large, which results in a large peak appearing in the upconversion excitation spectrum. That is just the new interesting
two-color excitation upconversion luminescence phenomenon of Pr(0.5)Yb(3):ZBLAN induced by one laser and one continuous normal
light simultaneously. 相似文献
993.
994.
A New Route for Synthesis of Entecavir 总被引:3,自引:0,他引:3
Li Wei GUO Yuan Jing XIAO Li Ping YANG 《中国化学快报》2006,17(7):907-910
2-Amino-1,9-dihydro-9-[(1S,3R,4S)-4-hydroxy-3-(hydroxymethyl)-2-methylenecyclopen tyl]-6H-purin-6-one (entecavir, Scheme 1) is a novel carbocyclic 2-deoxyguanosine analog drug which has potent and selective anti hepatitis B virus (HBV) activity1-3. Entecavir is also effective against lamivudine-resistant YMDD mutants4. The US Food and Drug Administration (FDA) approved entecavir as a new preferred drug for the treatment of HBV after lamivudine in March, 2005. Scheme 1 The structure o… 相似文献
995.
Dr. Markus Staudt Dr. Adnan Cetin Prof. Lennart Bunch 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(10):e202102998
Anilines are key constituents in biologically active compounds and often obtained from transition metal-catalyzed coupling of an aryl halide with an amine. In this work, we report a transition metal-free method for the synthesis of meta-bromo- and meta-trifluoromethylanilines starting from 3-tribromomethylcyclopentanone or 3-(2-bromo-2-chloro-1,1,1-trifluoroethyl)cyclopentanone, respectively. The scope of the transformation is shown by application of primary, secondary and aromatic amines. The reaction proceeds in acceptable to high yields (20–81 %), and allows for the synthesis of anilines with substitution patterns otherwise difficult to access. 相似文献
996.
Matt Rammo Dr. Aleksander Trummal Dr. Merle Uudsemaa Juri Pahapill Katrin Petritsenko Dr. Meelis-Mait Sildoja Dr. Charles W. Stark Dr. Sigrid Selberg Prof. Ivo Leito Kirsti Palmi Dr. Jasper Adamson Prof. Aleksander Rebane 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(8):e202103707
Lipophilic fluorophores are widely implemented in nonlinear microscopy; however, few existing membrane-specific probes combine the high brightness of two-photon excited fluorescence (2PEF) with pH sensitivity. Herein we describe four novel two-photon excited fluorophores, based on a coumarin 151 core structure, where lipophilicity is induced by a covalently attached phosphazene moiety. Changing the environmental acidity using trifluoromethanesulfonic (triflic) acid leads to profound changes in the linear fluorescence and 2PEF characteristics, due to chromophores’ switching between neutral- and protonated forms. We characterize this dependence by measuring the two-photon absorption (2PA) spectra over the region λ2PA=550–1000 nm, observing 2PA cross sections of σ2PA=10–20 GM, with an associated 2PEF brightness of 10–13 GM, in neutral solutions of both acetonitrile and n-octanol. Although quantum chemical modelling and NMR measurements show that, at high chromophore concentrations, protonation may be accompanied by a dimerization process, these dimers likely do not form at the lower concentrations used in optical spectroscopy. 相似文献
997.
998.
New triazole-derivatives were synthesized and characterized (spectral, analytical and conformational). After that, the new derivatives were coordinated with VO (II) atom to prepare new series of complexes. Distorted octahedral and square-pyramidal geometries, were the geometries suggested based on UV- Vis and ESR spectra. A neutral poly-dentate mode of bonding was proposed by 1:1 (M:L), for all complexes. TGA study supports the molecular formula of VO (II) complexes as well as, mass spectral-analysis that executed for examples. The isotropic, anisotropic, molecular orbital and Hamiltonian parameters were estimated upon ESR spectra, for selected complexes. XRD patterns were executed for three complexes, two among appeared with particulate-sizes in nanometer-range. Conformational study was executed for all synthesizes applying RTD-B3LYP-FC method. Essential physical parameters were estimated and discussed. MOE-docking that considered a bright part, was performed over all compounds towards 3s7s and 5jm5, as functional tumor proteins. The docking interaction parameters, introduced strongly some synthesizes to be anti-tumor agents. 相似文献
999.
ABSTRACT The controlled laser air-force detection (CLAFD) technique was developed to explore the feasibility of multi-mechanical property detection of polyurethane by single excitation mode. The adhesiveness, elastic modulus, hardness, resilience, and cohesiveness of polyurethane were predicted by the global variable partial least squares regression (Gv-PLSR) algorithm. Different preprocessing methods were used to preprocess the original laser data. The interval partial least squares regression (I-PLSR) algorithm was used to decrease the influences of the multicollinearity of the global laser variable and increase the stability of the multi-mechanical property prediction models. To further improve the prediction accuracy of the modeling of I-PLSR algorithm, the synergy interval PLSR (Si-PLSR) algorithm was used to combine the intervals with the higher evaluation index root-mean-square error of cross-validation (RMSECV) to predict the multi-properties. The results demonstrated that as a novel mechanical property detection technique, the CLAFD technique predicts in an efficient way. A suitable preprocessing method for the original laser data could greatly improve the effectiveness of prediction. The I-PLSR algorithm was used to improve the model’s stability significantly. Nevertheless, the prediction accuracy decreased. Comparing the I-PLSR algorithm with the Si-PLSR algorithm, the prediction accuracy and the modal stability were optimized by the latter. However, the accuracy was still lower than the Gv-PLSR algorithm. Therefore, the Gv-PLSR was the best algorithm to establish the multi-mechanical properties prediction model. This study provided a new comprehensive, nondestructive, and cross-contamination-free method to evaluate the comprehensive mechanical properties (adhesiveness, elastic modulus, hardness, resilience, and cohesiveness) of materials efficiently, especially for the soft materials such as biomaterial and food material. 相似文献
1000.
As very light fermions, electrons are governed by antisymmetric wave functions that lead to exchange integrals in the evaluation of the energy. Here we use the localized representation of orbitals to decompose the electronic energy in a fashion that isolates the enigmatic exchange contributions and characterizes their distinctive control over electron distributions. The key to this completely general analysis is considering the electrons in groups of three, drawing attention to the curvatures of pair potentials, rather than just their amplitudes and slopes. We show that a positive curvature at short distances is essential for the mutual distancing of electrons and a negative curvature at longer distances is essential to account for the influence of lone pairs on bond torsion. Neither curvature is available in the absence of the exchange contributions. Thus, although exchange energies are much shorter range than Coulomb energies, their influence on molecular geometry is profound and readily understood. 相似文献