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101.
Frontispiece: Matrix‐Free DNP‐Enhanced NMR Spectroscopy of Liposomes Using a Lipid‐Anchored Biradical 下载免费PDF全文
102.
Dynamic Analysis of Prestressed Cables with Uncertain Pretension 总被引:2,自引:0,他引:2
This paper deals with finite element dynamic analysis of prestressed cables with uncertain pretension subjected to deterministic excitations. The theoretical model addressed for cable modeling is a two-dimensional finite-strain beam theory, which allows us to eliminate any restriction on the magnitude of displacements and rotations. The dynamic problem is formulated by referring the motion to the inertial frame, which leads to a simple uncoupled quadratic form for the kinetic energy. The effect of the externally applied stochastic pretension is approximately described by means of an uncertain axial component of stress resultant, which is assumed constant along the cable in its dead load configuration. The so-called improved perturbation approach is employed to solve this stochastic problem, obtaining two coupled systems of nonlinear deterministic ordinary differential equations, governing the mean value and deviation of response. An efficient and accurate iterative procedure is proposed to obtain the solution of these equations. In order to investigate the influence of random pretension on structural response, few numerical applications are presented and results are discussed. 相似文献
103.
Paola Riente Alba MatasAdams Josep Albero Emilio Palomares Miquel A. Perics 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(36):9767-9770
The development of enantioselective catalytic processes that make use of sunlight as the energy source and nontoxic, affordable materials as catalysts represents one of the new and rapidly evolving areas in chemical research. The direct asymmetric α‐alkylation of aldehydes with α‐bromocarbonyl compounds can be successfully achieved by combining bismuth‐based materials as low‐band‐gap photocatalysts with the second‐generation MacMillan imidazolidinone as the chiral catalyst and simulated sunlight as a low‐cost and clean energy source. This reaction also proceeded with high efficiency when the reaction vial was exposed to the morning sunlight on a clear September day in Tarragona, Spain. 相似文献
104.
Alba Espargar Salom Llabrs Sven J. Saupe Carles Curutchet F. Javier Luque Raimon Sabat 《Angewandte Chemie (International ed. in English)》2020,59(21):8104-8107
Amyloids are characterized by their capacity to bind Congo red (CR), one of the most used amyloid‐specific dyes. The structural features of CR binding were unknown for years, mainly because of the lack of amyloid structures solved at high resolution. In the last few years, solid‐state NMR spectroscopy enabled the determination of the structural features of amyloids, such as the HET‐s prion forming domain (HET‐s PFD), which also has recently been used to determine the amyloid–CR interface at atomic resolution. Herein, we combine spectroscopic data with molecular docking, molecular dynamics, and excitonic quantum/molecular mechanics calculations to examine and rationalize CR binding to amyloids. In contrast to a previous assumption on the binding mode, our results suggest that CR binding to the HET‐s PFD involves a cooperative process entailing the formation of a complex with 1:1 stoichiometry. This provides a molecular basis to explain the bathochromic shift in the maximal absorbance wavelength when CR is bound to amyloids. 相似文献
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107.
Rodríguez Cáceres MI Durán Merás I Ornelas Soto NE López de Alba PL López Martinez L 《Analytical and bioanalytical chemistry》2008,391(4):1119-1127
This paper shows the potential of excitation–emission fluorescence spectroscopy and several second-order methods, such as
parallel factor analysis (PARAFAC), multiway partial least-squares (N-PLS) or bilinear least-squares (BLLS), as a multicalibration
technique for the analysis of leucovorin (LV) and irinotecan (CPT-11). Although CPT-11 presents native fluorescence, leucovorin
has little native fluorescence; however, under irradiation with short-wavelength UV light in the presence of traces of hydrogen
peroxide, leucovorin was converted into a highly fluorescent compound. This reaction has been used for the sensitive and selective
determination of both compounds. The convenience of analysing the total luminescence spectrum information when using multivariate
calibration methods on fluorescence data is demonstrated. Direct determination of mixtures of both drugs in urine was accomplished
on the basis of excitation–emission matrices (EEMs) and the three-way multivariate methods. 相似文献
108.
Thillaye du Boullay O Alba A Oukhatar F Martin-Vaca B Bourissou D 《Organic letters》2008,10(20):4669-4672
The preparation of the (1-naphthyl)(trifluoromethyl) O-carboxy-anhydride 1 and its use as a chiral derivatizing agent with several alpha-chiral primary amines are reported. The very large Delta delta(RS) values observed in (1)H NMR have been correlated with a marked preference of the corresponding alpha-hydroxy-amides for the eclipsed conformation. In comparison, the related O-methylated amides are shown to adopt staggered conformations, which substantiates the critical role of intramolecular hydrogen bonding in maximizing the anisotropic effect. 相似文献
109.
Estévez RE Paradas M Millan A Jiménez T Robles R Cuerva JM Oltra JE 《The Journal of organic chemistry》2008,73(4):1616-1619
We describe the first Ti-catalyzed Reformatsky-type coupling between alpha-halo ketones and aldehydes. The reaction affords beta-hydroxy ketones under mild, neutral conditions compatible with ketones and other electrophiles. The catalytic cycle possibly proceeds via bis(cyclopentadienyl)titanium enolates. 相似文献
110.
Rodrigues CM Rinaldo D dos Santos LC Montoro P Piacente S Pizza C Hiruma-Lima CA Brito AR Vilegas W 《Rapid communications in mass spectrometry : RCM》2007,21(12):1907-1914
Direct flow injection electrospray ionization ion trap tandem mass spectrometry (ESI-IT-MS/MS) was used to investigate the polyphenolic compounds present in an infusion from the barks of Hancornia speciosa Gom. (Apocynaceae), a native Brazilian plant popularly known as 'mangabeira', used as a source of nutrition and against gastric disorders. After a simple sample filtration pretreatment the characteristic fingerprint of the infusion was performed in negative ion ESI mode in a few minutes. At low capillary-voltage activation, the deprotonated molecules ([M--H]-) were observed and using collision-induced dissociation the product ion spectra showed the presence of a homologous series of B-type proanthocyanidins, as well as another series containing their respective C-glycosylated derivatives, with a degree of polymerization from 1 up to 6 units of interlinked catechins. Therefore, direct flow injection allowed us to identify the key compounds without preparative isolation of the components. 相似文献