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71.
Laurent Griffe Dr. Mary Poupot Dr. Patrice Marchand Dr. Alexandrine Maraval Dr. Cédric‐Olivier Turrin Dr. Olivier Rolland Pascal Métivier Dr. Gérard Bacquet Dr. Jean‐Jacques Fournié Dr. Anne‐Marie Caminade Dr. Rémy Poupot Dr. Jean‐Pierre Majoral Dr. 《Angewandte Chemie (International ed. in English)》2007,46(14):2334-2334
72.
Infrared and Raman spectra have been obtained for benzyl fluoride and a vibrational assignment has been made. The spectra indicate the presence of a large number of conformers that differ only in the orientation of the C-F bond, as a result of free or nearly free internal rotation. 相似文献
73.
A simple rapid, accurate, and reliable method of simultaneous determination of arsenic, germanium, phosphorus, and silicon is reported. The method involves first, the determination of germanium as its phenlfluorone complex and its selective extraction with isoamyl alcohol. Phosphorus is next determined as its heteropoly blue after selective extraction of phosphomolybdic acid by isobutyl acetate at pH 1.0-0.8 and its direct reduction in this solvent. Silicon is then determined after its extraction as silicomolybdic acid by isooctyl alcohol at pH < 0.4 and direct reduction in the solvent phase. Finally, arsenic is determined in the remaining aqueous phase after reduction to its heteropoly blue. 相似文献
74.
Linder DP Rodgers KR Banister J Wyllie GR Ellison MK Scheidt WR 《Journal of the American Chemical Society》2004,126(43):14136-14148
Recent years have seen dramatic growth in our understanding of the biological roles of nitric oxide (NO). Yet, the fundamental underpinnings of its reactivities with transition metal centers in proteins and enzymes, the stabilities of their structures, and the relationships between structure and reactivity remains, to a significant extent, elusive. This is especially true for the so-called ferric heme nitrosyls ([FeNO](6) in the Enemark-Feltham scheme). The Fe-CO and C-O bond strengths in the isoelectronic ferrous carbonyl complexes are widely recognized to be inversely correlated and sensitive to structural, environmental, and electronic factors. On the other hand, the Fe-NO and N-O bonds in [FeNO](6) heme complexes exhibit seemingly inconsistent behavior in response to varying structure and environment. This report contains resonance Raman and density functional theory results that suggest a new model for FeNO bonding in five-coordinate [FeNO](6) complexes. On the basis of resonance Raman and FTIR data, a direct correlation between the nu(Fe)(-)(NO) and nu(N)(-)(O) frequencies of [Fe(OEP)NO](ClO(4)) and [Fe(OEP)NO](ClO(4)).CHCl(3) (two crystal forms of the same complex) has been established. Density functional theory calculations show that the relationship between Fe-NO and N-O bond strengths is responsive to FeNO electron density in three molecular orbitals. The highest energy orbital of the three is sigma-antibonding with respect to the entire FeNO unit. The other two comprise a lower-energy, degenerate, or nearly degenerate pair that is pi-bonding with respect to Fe-NO and pi-antibonding with respect to N-O. The relative sensitivities of the electron density distributions in these orbitals are shown to be consistent with all published indicators of Fe-N-O bond strengths and angles, including the examples reported here. 相似文献
75.
This study was designed to provide more detailed information on the subcellular sites of binding of the porphycene, termed 9-capronyloxytetrakis (methoxyethyl) porphycene (CPO), with a fluorescence resonance energy transfer (FRET) technique. The proximity of CPO to two fluorescent probes was determined: nonyl acridine orange (NAO), a dye with specific affinity for the mitochondrial lipid cardiolipin, and dihexa-oxacarbocyanine iodide (DiOC6), an agent that labels the endoplasmic reticulum (ER). FRET spectra indicated energy transfer between DiOC6 and CPO but no significant transfer between NAO and CPO. These results confirm data obtained by fluorescence microscopy, suggesting a similar pattern of subcellular localization by CPO and DiOC6 but not by CPO and NAO. However, when cells containing CPO were irradiated and then loaded with NAO, FRET between the two fluorophores was observed. Hence, a relocalization of CPO can occur during irradiation. These data provide an explanation for recent studies on CPO-catalyzed photodamage to both ER and mitochondrial Bcl-2. 相似文献
76.
The preparation of furo[3,2-b]indoles via Dieckmann cyclization is described. The precursor diesters were obtained from 3-hydroxy-1H-indole-2-carboxylic acid esters and methyl or ethyl bromoacetate. Reactions of the furo[3,2-b]indole enolic esters prepared are discussed. 相似文献
77.
Rai BK Durbin SM Prohofsky EW Sage JT Ellison MK Roth A Scheidt WR Sturhahn W Alp EE 《Journal of the American Chemical Society》2003,125(23):6927-6936
Detailed Fe vibrational spectra have been obtained for the heme model complex [Fe(TPP)(CO)(1-MeIm)] using a new, highly selective and quantitative technique, Nuclear Resonance Vibrational Spectroscopy (NRVS). This spectroscopy measures the complete vibrational density of states for iron atoms, from which normal modes can be calculated via refinement of the force constants. These data and mode assignments can reveal previously undetected vibrations and are useful for validating predictions based on optical spectroscopies and density functional theory, for example. Vibrational modes of the iron porphyrin-imidazole compound [Fe(TPP)(CO)(1-MeIm)] have been determined by refining normal mode calculations to NRVS data obtained at an X-ray synchrotron source. Iron dynamics of this compound, which serves as a useful model for the active site in the six-coordinate heme protein, carbonmonoxy-myoglobin, are discussed in relation to recently determined dynamics of a five-coordinate deoxy-myoglobin model, [Fe(TPP)(2-MeHIm)]. For the first time in a six-coordinate heme system, the iron-imidazole stretch mode has been observed, at 226 cm(-)(1). The heme in-plane modes with large contributions from the nu(42), nu(49), nu(50), and nu(53) modes of the core porphyrin are identified. In general, the iron modes can be attributed to coupling with the porphyrin core, the CO ligand, the imidazole ring, and/or the phenyl rings. Other significant findings are the observation that the porphyrin ring peripheral substituents are strongly coupled to the iron doming mode and that the Fe-C-O tilting and bending modes are related by a negative interaction force constant. 相似文献
78.
Noel V. Stanton Tracy Fritsch Ciaran Geraghty Mary Frances Verostek Bruce Weiner Patrick J. Parsons 《Accreditation and quality assurance》2006,11(11):590-592
Following implementation of the CLIA ‘88 laboratory regulations, the primary role of proficiency testing (external quality assessment, PT) in the U.S. has been widely viewed as one of assuring regulatory compliance. PT can also be an effective tool for detecting widespread analytical problems, subject to limitations based on the method of PT assigned value determination. A recent case study describes the role of two PT programs in detecting and resolving a calibration bias in the LeadCare blood lead analyzer, and illustrates the limitations of peer-group target determination in fulfilling that PT role. 相似文献
79.
The spectral characteristics and the quantum yield of the fluorescence from the second excited singlet state S2 of the aromatic thioketone molecules xanthione (XS) and thioxanthione (TXS) have been determined in solution at room temperature and 77 K. In 3-methylpentane, the measured quantum yields are φf (295 K) = 5.1 × 10?3 and φf(77 K) = 1.0 × 10?2 for XS, and φf (295 K) = 1.5 × 10?3 and φf (77 K) = 2.5 × 10?3 for TXS. Using the Strickler-Berg expression for the radiative lifetime, the decay rate of S2 is derived. It is concluded that internal conversion S2 ? S1 is the dominating deactivation channel of S2 with k77 Knr(S2 ? S1) = 1.0 × 1010 s?1 for XS and k77 Knr (S2→S1) = 2.2 × 1010 s?1 for TXS. Between 295 and 77 K, φf increases by a factor of about 2 following an Arrhenius type expression. This temperature dependence of φf is considered to be intramolecular in nature and is attributed to a temperature sensitive rate constant knr(S2?S1) with an activation energy of 190 ± 20 cm?1 and a frequency factor k′nr = 3 × 1010 s?1 for the XS molecule in 3-methylpentane. 相似文献
80.