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101.
Calculated energy profiles for the reactions of neutral Nb(2) and Nb(3) metal clusters with CO, D(2), N(2), and O(2) are presented. In each reaction path, both a physisorption energy minimum, where the reactant remains intact, and a chemisorption energy minimum, where the reactant has dissociated, are calculated and linked by saddle points. We calculate branching ratios for the forward (dissociative) and reverse reactions which we compare with the experimental kinetic data. It is found that a combination of average thermal energies and barrier heights leads to wide variation in branching ratios which compares favourably to previously determined experimental reaction rates. 相似文献
102.
A simple method for the speciation analysis of bio-accessible arsenic (As) in rice was developed using a continuous on-line leaching method to release the bio-accessible fraction. The continuous on-line leaching method has several advantages over commonly used batch methods including quicker and easier sample preparation, reduced risk of contamination and access to real time leaching data. The bio-accessibility of As in the samples was monitored using inductively coupled plasma mass spectrometry (ICP-MS). Results from a certified reference material as well as cooked and uncooked white rice showed that the majority of As was leached by saliva. Results obtained using the continuous on-line leaching method were comparable to those obtained using a batch method. Speciation analysis of the saliva leachate was performed using ion exchange chromatography coupled to ICP-MS. The four most toxic forms of As (As(III), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA) and As(V)) were clearly separated within 5 min in a single chromatographic run. Over 92% of bio-accessible As in the certified reference material and uncooked white rice sample was in the form of DMA and As(V), whereas it was present as DMA and As(III) in the cooked white rice. 相似文献
103.
Ekaterina A. Martynova Vladislav A. Voloshkin Sbastien G. Guillet Francis Bru Marek Beli Kristof Van Hecke Catherine S. J. Cazin Steven P. Nolan 《Chemical science》2022,13(23):6852
We present the use of gold sensitizers [Au(SIPr)(Cbz)] (PhotAu 1) and [Au(IPr)(Cbz)] (PhotAu 2) as attractive alternatives to state-of-the-art iridium-based systems. These novel photocatalysts are deployed in [2 + 2] cycloadditions of diallyl ethers and N-tosylamides. The reactions proceed in short reaction times and in environmentally friendly solvents. [Au(SIPr)Cbz] and [Au(IPr)(Cbz)] have higher triplet energy (ET) values (66.6 and 66.3 kcal mol−1, respectively) compared to commonly used iridium photosensitizers. These ET values permit the use of these gold complexes as sensitizers enabling energy transfer catalysis involving unprotected indole derivatives, a substrate class previously inaccessible with state-of-the-art Ir photocatalysts. The photosynthesis of unprotected tetracyclic spiroindolines via intramolecular [2 + 2] cycloaddition using our simple mononuclear gold sensitizer is readily achieved. Mechanistic studies support the involvement of triplet–triplet energy transfer (TTEnT) for both [2 + 2] photocycloadditions.We present the use of gold sensitizers [Au(SIPr)(Cbz)] (PhotAu 1) and [Au(IPr)(Cbz)] (PhotAu 2) as attractive alternatives to state-of-the-art iridium-based systems. 相似文献
104.
Nikolaos V. Tzouras Marina Saab Wim Janssens Thibault Cauwenbergh Prof. Dr. Kristof Van Hecke Dr. Fady Nahra Prof. Dr. Steven P. Nolan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(24):5541-5551
The discovery of sustainable and scalable synthetic protocols leading to gold–aryl compounds bearing N-heterocyclic carbene (NHC) ligands sparked an investigation of their reactivity and potential utility as organometallic synthons. The use of a mild base and green solvents provide access to these compounds, starting from widely available boronic acids and various [Au(NHC)Cl] complexes, with reactions taking place under air, at room temperature and leading to high yields with unprecedented ease. One compound, (N,N′-bis[2,6-(di-isopropyl)phenyl]imidazol-2-ylidene)(4-methoxyphenyl)gold, ([Au(IPr)(4-MeOC6H4)]), was synthesized on a multigram scale and used to gauge the reactivity of this class of compounds towards C−H/N−H bonds and with various acids, revealing simple pathways to gold–based species that possess attractive properties as materials, reagents and/or catalysts. 相似文献
105.
The molecular geometry, the three dimensional arrangement of atoms in space, is a major factor determining the properties and reactivity of molecules, biomolecules and macromolecules. Computation of stable molecular conformations can be done by locating minima on the potential energy surface (PES). This is a very challenging global optimization problem because of extremely large numbers of shallow local minima and complicated landscape of PES. This paper illustrates the mathematical and computational challenges on one important instance of the problem, computation of molecular geometry of oligopeptides, and proposes the use of the Extended Cutting Angle Method (ECAM) to solve this problem. 相似文献
106.
G.B. Hagemann J.D. Garrett B. Herskind J. Kownacki B.M. Nyakó P.L. Nolan J.F. Sharpey-Schafer P.O. Tjøm 《Nuclear Physics A》1984,424(2):365-382
155Ho and 157Ho have been populated in the reactions 141Pr(18O,4n) and 146Nd(15N, 4n) at 85 and 74 MeV, respectively. In both nuclei bands built on the ?[523] configuration were established to spin values considerably above the first backbend. A signature dependence in the excitation energies as well as in the ratio of M1 to E2 transition rates is observed below, but not above, the backbend in both nuclei. In 157Ho lifetimes were measured with the recoil-distance method. The ΔI = 2; E2 transition probabilities obtained show very little variation with either signature or spin and no irregularity at the backbend. The signature dependence and strong rise in the ratio B(M1)/B(E2) observed at the backbend in 157Ho therefore must be caused by the B(M1) values. A signature dependence in the B(E2, I → I ?1)/B(E2, I → I ?2) ratios also found in 157Ho below the backbend is mainly the result of signature dependence in the ΔI = 1 ; E2 transition rates. Qualitatively, most of the features observed can be explained by nonaxial deformations, which change from large negative to slightly positive values of γ at the backbend. 相似文献
107.
R. Wadsworth P. Regan S. M. Mullins G. J. Gyapong D. L. Watson P. J. Nolan M. J. Godfrey I. Jenkins Y. J. He B. J. Varley J. Simpso W. Gelletly 《Zeitschrift für Physik A Hadrons and Nuclei》1989,333(4):411-412
The states in the yrast band of132 Sm have been identified for the first time up to Jπ=16+. The yrast band of130Nd has also been extended from Jπ=16+ to 24+. The energy of the first 2+ state in132Sm indicates that the quadrupole deformation ε2 ~ 0.3 and is still increasing as the neutron number N decreases across the samarium isotopes. The results for130Nd allow the (h2/11)2 proton crossing frequency to be determined as ω=0.325 ± 0.005 MeV/?. This result is compared with cranked shell model predictions. 相似文献
108.
109.
Kieran G. O'Grady 《Inventiones Mathematicae》1992,107(1):351-395
Oblatum 1-X-1990 & 23-IV-1991 相似文献
110.
R. Wadsworth P. Regan S. M. Mullins G. J. Gyapong D. L. Watson P. J. Nolan M. J. Godfrey I. Jenkins Y. J. He B. J. Varley W. Gelletly J. Simpson 《Zeitschrift für Physik A Hadrons and Nuclei》1989,333(4):409-410
A rotational band of nine γ-rays has been observed in133Sm. The moment of inertia of the band indicates that it has a higher deformation than expected for states in nuclei in this region. The properties are such that it can be interpreted as being due to the odd neutron occupying the ν i2/13 nn intruder orbital. This is the first evidence for the occupation of this orbital in nuclei with neutron number N<73. 相似文献