全文获取类型
收费全文 | 2298篇 |
免费 | 87篇 |
国内免费 | 9篇 |
专业分类
化学 | 1542篇 |
晶体学 | 13篇 |
力学 | 77篇 |
数学 | 334篇 |
物理学 | 428篇 |
出版年
2023年 | 19篇 |
2022年 | 50篇 |
2021年 | 51篇 |
2020年 | 59篇 |
2019年 | 71篇 |
2018年 | 51篇 |
2017年 | 37篇 |
2016年 | 100篇 |
2015年 | 68篇 |
2014年 | 79篇 |
2013年 | 144篇 |
2012年 | 160篇 |
2011年 | 167篇 |
2010年 | 104篇 |
2009年 | 86篇 |
2008年 | 147篇 |
2007年 | 129篇 |
2006年 | 105篇 |
2005年 | 103篇 |
2004年 | 100篇 |
2003年 | 71篇 |
2002年 | 87篇 |
2001年 | 29篇 |
2000年 | 32篇 |
1999年 | 19篇 |
1998年 | 24篇 |
1997年 | 18篇 |
1996年 | 16篇 |
1995年 | 13篇 |
1994年 | 9篇 |
1993年 | 11篇 |
1992年 | 11篇 |
1991年 | 16篇 |
1990年 | 8篇 |
1989年 | 13篇 |
1988年 | 7篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 16篇 |
1983年 | 6篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 16篇 |
1979年 | 15篇 |
1978年 | 19篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1975年 | 4篇 |
1974年 | 9篇 |
1973年 | 8篇 |
排序方式: 共有2394条查询结果,搜索用时 15 毫秒
61.
Denis Mashkovtsev Wataru Mizukami Jacek Korchowiec Anna Stachowicz-Kuśnierz Yuriko Aoki 《Journal of computational chemistry》2020,41(25):2203-2212
The elongation method with intermediate mechanical and electrostatic embedding (ELG-IMEE) is proposed. The electrostatic embedding uses atomic charges generated by a charge sensitivity analysis (CSA) method and parameterized for three different population analyses, namely, the Merz–Singh–Kollman scheme, the charge model 5, and the atomic polar tensor. The obtained CSA models were tested on two model systems. Test calculations show that the electrostatic embedding provides several times of decrease in the difference of energies of testing and reference calculations in comparison with the conventional elongation approach (ELG). The mechanical embedding is implemented in a combination of the conventional elongation method and the ONIOM approach. Moreover, it was demonstrated that the geometry optimization with the ELG-IMEE reduces the errors in the optimized structures by about one order in root-mean-square deviation, when compared to ELG. 相似文献
62.
Rosane Bassi Soares Denis Honorato Costa Walter Miyakawa Maria Goretti Temoteo Delgado Aguinaldo Silva Garcez Tania Mateus Yoshimura Martha Simões Ribeiro Silvia Cristina Nunez 《Photochemistry and photobiology》2020,96(3):618-624
Ventilator-associated pneumonia (VAP) is an infection that arises after endotracheal intubation affecting patients under intensive care. The presence of the endotracheal tube (ETT) is a risk factor since it is colonized by multispecies biofilm. Antimicrobial photodynamic therapy (aPDT) could be a strategy to decontaminate ETTs. We verify if methylene blue (MB) associated with external illumination of the ETT could be an alternative to destroy biofilm. We performed an in vitro and ex vivo study. In vitro study was performed with P. aeruginosa biofilm grew over ETT for 7 days. After treatment, the surviving cells were cultured for 3 days and the biofilm was analyzed by crystal violet absorbance. Ex vivo study employed ETT obtained from extubated patients. aPDT was performed with MB (100 µm ) and red LED (λ = 640±20 nm). We quantified the biofilm thickness and used scanning electron microscopy and fluorescence technique to verify morphological and functional changes after aPDT. Our results showed that bacteria remain susceptible to aPDT after sequential treatments. We also attested that aPDT can reduce biofilm thickness, disrupt biofilm attachment from ETT surface and kill microbial cells. These data suggest that aPDT should be investigated to decrease VAP incidence via ETT decontamination. 相似文献
63.
Aleksei S. Pronin Spartak S. Yarovoy Yakov M. Gayfulin Aleksey A. Ryadun Konstantin A. Brylev Denis G. Samsonenko Ilia V. Eltsov Yuri V. Mironov 《Molecules (Basel, Switzerland)》2020,25(24)
Compounds based on new cyanide cluster anions [{Mo6I8}(CN)6]2–, trans-[{Mo6I8}(CN)4(MeO)2]2– and trans-[{W6I8}(CN)2(MeO)4]2− were synthesized using mechanochemical or solvothermal synthesis. The crystal and electronic structures as well as spectroscopic properties of the anions were investigated. It was found that the new compounds exhibit red luminescence upon excitation by UV light in the solid state and solutions, as other cluster complexes based on {Mo6I8}4+ and {W6I8}4+ cores do. The compounds can be recrystallized from aqueous methanol solutions; besides this, it was shown using NMR and UV-Vis spectroscopy that anions did not undergo hydrolysis in the solutions for a long time. These facts indicate that hydrolytic stabilization of {Mo6I8} and {W6I8} cluster cores can be achieved by coordination of cyanide ligands. 相似文献
64.
Mikhail V. Vener Andrei V. Churakov Alexander P. Voronin Olga D. Parashchuk Sergei V. Artobolevskii Oleg A. Alatortsev Denis E. Makhrov Alexander G. Medvedev Aleksander Filarowski 《Molecules (Basel, Switzerland)》2022,27(3)
Two new peroxosolvates of drug-like compounds were synthesized and studied by a combination of X-ray crystallographic, Raman spectroscopic methods, and periodic DFT computations. The enthalpies of H-bonds formed by hydrogen peroxide (H2O2) as a donor and an acceptor of protons were compared with the enthalpies of analogous H-bonds formed by water (H2O) in isomorphic (isostructural) hydrates. The enthalpies of H-bonds formed by H2O2 as a proton donor turned out to be higher than the values of the corresponding H-bonds formed by H2O. In the case of H2O2 as a proton acceptor in H-bonds, the ratio appeared reversed. The neutral O∙∙∙H-O/O∙∙∙H-N bonds formed by the lone electron pair of the oxygen atom of water were the strongest H-bonds in the considered crystals. In the paper, it was found out that the low-frequency Raman spectra of isomorphous crystalline hydrate and peroxosolvate of N-(5-Nitro-2-furfurylidene)-1-aminohydantoin are similar. As for the isostructural hydrate and peroxosolvate of the salt of protonated 2-amino-nicotinic acid and maleic acid monoanion, the Raman spectra are different. 相似文献
65.
66.
Svetlana I. Dorovskikh Denis E. Tryakhov Darya D. Klyamer Alexander S. Sukhikh Irina V. Mirzaeva Natalia B. Morozova Tamara V. Basova 《Molecules (Basel, Switzerland)》2022,27(7)
To search for new suitable Pd precursors for MOCVD/ALD processes, the extended series of fluorinated palladium complexes [Pd(CH3CXCHCO(R))2] with β-diketone [tfa−1,1,1-trifluoro-2,4-pentanedionato (1); pfpa−5,5,6,6,6-pentafluoro-2,4-hexanedionato (3); hfba−5,5,6,6,7,7,7-heptafluoro-2,4-heptanedionato (5)] and β-iminoketone [i-tfa−1,1,1-trifluoro-2-imino-4-pentanonato (2); i-pfpa−5,5,6,6,6-pentafluoro-2-imino-4-hexanonato (4); i-hfba-5,5,6,6,7,7,7-heptafluoro-2-imino-4-heptanonato (6)] ligands were synthesized with 70–80% yields and characterized by a set of experimental (SXRD, XRD, IR, NMR spectroscopy, TG) and theoretical (DFT, Hirshfeld surface analysis) methods. Solutions of Pd β-diketonates contained both cis and trans isomers, while only trans isomers were detected in the solutions of Pd β-iminoketonates. The molecules 2–6 and new polymorphs of complexes 3 and 5 were arranged preferentially in stacks, and the distance between molecules in the stack generally increased with elongation of the fluorine chain in ligands. The H…F contacts were the main ones involved in the formation of packages of molecules 1–2, and C…F, F…F, NH…F contacts appeared in the structures of complexes 4–6. The stability of complexes and their polymorphs in the crystal phases were estimated from DFT calculations. The TG data showed that the volatility differences between Pd β-iminoketonates and Pd β-diketonates were minimized with the elongation of the fluorine chain in the ligands. 相似文献
67.
The optimum performance of an optical oxygen sensor based on polysulfone (PSF)/[Ru(II)-Tris(4,7-diphenyl-1,10-phenanthroline)] octylsulfonate (Ru(dpp)OS) was checked by carefully tuning the parameters affecting the membrane preparation. In particular, membranes having thickness ranging between 0.2 and 8.0 μm with various luminophore concentrations were prepared by dip-coating and tested. The membrane thickness was controlled by tuning the solution viscosity, and was measured both by secondary ion mass spectrometry (SIMS) and by visible spectroscopy (Vis). Luminescence-quenching-based calibration was a single value of the Stern-Volmer constant (K′SV) for membranes containing up to 20 mmol Ru(dpp) g−1 PSF (1.35 μm average thickness). The K′SV value decreased for larger concentration. The highest sensitivity was obtained with membrane thickness around 1.6 μm, having a response time close to 1 s. Thicker membranes exhibited an emission saturation effect and were characterized by longer response time. The K′SV behavior was interpreted on the basis of a mathematical approach accounting for the contribution of luminescence lifetime (τ0), oxygen diffusion coefficient (DO2) and oxygen solubility inside the membrane (sO2) establishing the role of all of them and allowing their experimental determination. Moreover, a simple experimental way to estimate K′SV without needing calibration was proposed. It was based either on the light emission asymmetry or on the percent variation of light emission on passing from pure nitrogen to pure oxygen. 相似文献
68.
Bernard Lavielle Bertrand Thomas Eric Gilabert Gregory Canchel Denis Horlait Sylvain Topin Fabien Pointurier Christophe Moulin 《Journal of mass spectrometry : JMS》2016,51(10):908-913
A double focusing sector field mass filter used in Nier–Johnson geometry has been built in order to perform Kr isotope enrichment for 81Kr and 85Kr isotopes. The principle consists in implanting Kr+ ions accelerated at 7 keV in Al foils after separation using the magnetic sector. A specific ion source has been designed capable of generating high Kr+ ion beams (>0.5 μA) to transfer into the collecting Al foils in 3 to 5 h significant fractions of large Kr samples (1015 to 1016 atoms) initially introduced in the instrument. Implanted Kr isotopes can be further selectively released from the Al foil by surface ablation using an infrared laser beam. Implantation yields and enrichment factors are measured using a conventional mass spectrometer. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
69.
Mirela M. Barsan Ian S. Butler Jessica Fitzpatrick Denis F. R. Gilson 《Journal of Raman spectroscopy : JRS》2011,42(9):1820-1824
The pressure dependences of the peaks observed in the micro‐Raman spectra of Prussian blue (Fe4[Fe(CN)6]3), potassium ferricyanide (K3[Fe(CN)6]), and sodium nitroprusside (Na2[Fe(CN)5(NO)]·2H2O) have been measured up to 5.0 GPa. The vibrational modes of Prussian blue appearing at 201 and 365 cm−1 show negative dν/dP values and Grüneisen parameters and are assigned to the transverse bending modes of the Fe C N Fe linkage which can contribute to a negative thermal expansion behavior. A phase transition occurring between 2.0 and 2.8 GPa in potassium ferricyanide is shown by changes in the spectral region 150–700 cm−1. In the spectra of the nitroprusside ion, there are strong interactions between the FeN stretching mode and the FeNO bending and the axial CN stretching modes. The pressure dependence of the NO stretching vibration is positive, 5.6 cm−1 GPa−1, in contrast to the negative behavior in the iron(II)‐meso‐tetraphenyl porphyrinate complex. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
70.
Bi W Pagneux V Lafarge D Aurégan Y 《The Journal of the Acoustical Society of America》2007,122(1):280-290
An efficient method is proposed for modeling time harmonic acoustic propagation in a nonuniform lined duct without flow. The lining impedance is axially segmented uniform, but varies circumferentially. The sound pressure is expanded in term of rigid duct modes and an additional function that carries the information about the impedance boundary. The rigid duct modes and the additional function are known a priori so that calculations of the true liner modes, which are difficult, are avoided. By matching the pressure and axial velocity at the interface between different uniform segments, scattering matrices are obtained for each individual segment; these are then combined to construct a global scattering matrix for multiple segments. The present method is an improvement of the multimodal propagation method, developed in a previous paper [Bi et al., J. Sound Vib. 289, 1091-1111 (2006)]. The radial rate of convergence is improved from O(n(-2)), where n is the radial mode indices, to O(n(-4)). It is numerically shown that using the present method, acoustic propagation in the nonuniform lined intake of an aeroengine can be calculated by a personal computer for dimensionless frequency K up to 80, approaching the third blade passing frequency of turbofan noise. 相似文献