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991.
The relativistic HALA effect has been shown to depend on the spatial deformation of the lone electron pairs of a heavy atom, as demonstrated for alkyl and alkene phosphine tellurides. It was found that HALA effect on phosphorous nuclear magnetic resonance shielding constant is strongly dependent on the spatial arrangements of light substituents on phosphorus, resulting in the deformation of the lone electron pairs of tellurium. 相似文献
992.
Previously unknown manifestation of heavy atom effect on the NMR chemical shifts of β- and γ-protons initiated by the relativistic effects of the tellurium and selenium atoms has been investigated in the representative series of selenium- and tellurium-containing compounds. To approve the four-component density functional approach to be the appropriate tool for the investigation of the heavy atom on light atom effect (HALA), the benchmark calculations of the proton chemical shifts have been performed at the CCSD level using comprehensively chosen locally dense basis set with taking into account solvent, vibrational, and relativistic corrections. A good agreement with the experimental data was achieved. The magnitudes of the relativistic HALA corrections to β- and γ-proton chemical shifts were found to vary in a wide range, namely from −3.08 ppm for the γ-proton of methyltelluraldehyde to 14.51 ppm for β-proton in benzotelluraldehyde. 相似文献
993.
Rodica Mariana Ion Irina Dumitriu Radu Claudiu Fierascu Mihaela-Lucia Ion Simona Florentina Pop Constantin Radovici Raluca Ioana Bunghez V. I. R. Niculescu 《Journal of Thermal Analysis and Calorimetry》2011,104(2):487-493
The selected sample for this study represents a piece of pavement ceramics from a private collection. The ceramic (approximately
XVIIIth century) comes from Campania region, Naples province. A chemical, mineralogical and morphological characterization
of a Campagna ceramic piece received from a particular collection has been performed. Inductively coupled plasma-atomic emission
spectroscopy—(ICP-AES) was used for the determination of Al2O3, CaO, Fe2O3, K2O, MgO, MnO, Na2O, and TiO2 as major constituents and Cu, Cr, Ni, Pb, and Zn as minor and trace selected elements. There is a very important characterization
method used for the control of the reaction process and of the properties of the materials obtained. Physical and mineralogical
analyses were made by using the thermal behavior (thermogravimetric analysis (TG) and differential thermal analysis (DTG))
and X-ray diffraction spectrometry for the mineralogical composition. The results of these analyses allow the establishment
of conclusions about several aspects of their manufacture, the origin of the raw materials and their provenance (local or
imported). They provide information supporting certain archeological hypothesis. The performed analysis revealed some very
interesting characteristics: lower amount of silica and increased concentration of alumina, the presence of calcium in relatively
low concentration (Ca-poor ceramic) and a mineralogical composition. 相似文献
994.
Sergei M. Kobelev Alexei D. Averin Alexei K. Buryak Franck Denat Roger Guilard Irina P. Beletskaya 《Tetrahedron letters》2012,53(2):210-213
Three approaches to three types of cyclen-based macrotricycles have been elaborated starting from trans-bis(3-bromobenzyl)cyclen. The macrotricycles were synthesized via Pd-catalyzed amination. The first approach employed consecutive macrocyclization and benzylation steps giving a cage-like tricycle. In the second, cyclen amino groups were Boc-protected prior to formation of the second and the third rings. In the third method, macrotricycles were synthesized according to a one-step procedure using diazacrown ethers. 相似文献
995.
Irina P. Beletskaya Valentine G. Nenajdenko 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(15):4828-4839
The Markovnikov rule, known to every student of organic chemistry, was formulated 150 years ago, in 1869. During its long history (almost as long as the history of organic chemistry itself), attitudes towards this famous statement of chemical reactivity have evolved from indifference up to the 1930s, through common acceptance as a useful educational paradigm with marginal use in research up to the 1990s, to its vigorous relaunch as an important designation of regioselectivity in the last few decades. The unexpected new popularity of the classical rule is accounted for by the rapid expansion in catalytic addition reactions and their critical importance as highly effective atom‐economical, regioselective methods in modern organic synthesis. A historical outline of the life and achievements of Vladimir Markovnikov is included to reveal the very wide scope of his interests as well as his prophetic predictions on structure, reactivity, selectivity, stereochemistry, and other key issues of organic chemistry. 相似文献
996.
Yury Yu. Rusakov Irina L. Rusakova Leonid B. Krivdin 《Magnetic resonance in chemistry : MRC》2015,53(7):485-492
The main factors affecting the accuracy and computational cost of the Second‐order Möller‐Plesset perturbation theory (MP2) calculation of 77Se NMR chemical shifts (methods and basis sets, relativistic corrections, and solvent effects) are addressed with a special emphasis on relativistic effects. For the latter, paramagnetic contribution (390–466 ppm) dominates over diamagnetic term (192–198 ppm) resulting in a total shielding relativistic correction of about 230–260 ppm (some 15% of the total values of selenium absolute shielding constants). Diamagnetic term is practically constant, while paramagnetic contribution spans over 70–80 ppm. In the 77Se NMR chemical shifts scale, relativistic corrections are about 20–30 ppm (some 5% of the total values of selenium chemical shifts). Solvent effects evaluated within the polarizable continuum solvation model are of the same order of magnitude as relativistic corrections (about 5%). For the practical calculations of 77Se NMR chemical shifts of the medium‐sized organoselenium compounds, the most efficient computational protocols employing relativistic Dyall's basis sets and taking into account relativistic and solvent corrections are suggested. The best result is characterized by a mean absolute error of 17 ppm for the span of 77Se NMR chemical shifts reaching 2500 ppm resulting in a mean absolute percentage error of 0.7%. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
997.
998.
Irina L. Rusakova Yury Yu. Rusakov Leonid B. Krivdin 《Magnetic resonance in chemistry : MRC》2014,52(8):413-421
The computational study of the one‐bond 29Si–13C spin–spin coupling constants has been performed at the second‐order polarization propagator approximation (SOPPA) level in the series of 60 diverse silanes with a special focus on the main factors affecting the accuracy of the calculation including the level of theory, the quality of the basis set, and the contribution of solvent and relativistic effects. Among three SOPPA‐based methods, SOPPA(MP2), SOPPA(CC2), and SOPPA(CCSD), the best result was achieved with SOPPA(CCSD) when used in combination with Sauer's basis set aug‐cc‐pVTZ‐J characterized by the mean absolute error of calculated coupling constants against the experiment of ca 2 Hz in the range of ca 200 Hz. The SOPPA(CCSD)/aug‐cc‐pVTZ‐J method is recommended as the most accurate and effective computational scheme for the calculation of 1J(Si,C). The slightly less accurate but essentially more economical SOPPA(MP2)/aug‐cc‐pVTZ‐J and/or SOPPA(CC2)/aug‐cc‐pVTZ‐J methods are recommended for larger molecular systems. It was shown that solvent and relativistic corrections do not play a major role in the computation of the total values of 1J(Si,C); however, taking them into account noticeably improves agreement with the experiment. The rovibrational corrections are estimated to be of about 1 Hz or 1–1.5% of the total value of 1J(Si,C). Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
999.
Simona Luiza Druţă-Romaniuc Jun-ichi Inoguchi Marian Ioan Munteanu Ana Irina Nistor 《Journal of Nonlinear Mathematical Physics》2013,20(3):428-447
In this paper we classify the magnetic trajectories corresponding to contact magnetic fields in Sasakian manifolds of arbitrary dimension. Moreover, when the ambient is a Sasakian space form, we prove that the codimension of the curve may be reduced to 2. This means that the magnetic curve lies on a 3-dimensional Sasakian space form, embedded as a totally geodesic submanifold of the Sasakian space form of dimension (2n+1). 相似文献
1000.