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101.
Selected natural products have long been considered as desirable targets for total synthesis due to their unique biological properties and their challenging structural complexity. Laboratory synthesis of natural compounds usually relies on target-oriented synthesis, involving the production, isolation and purification of successive intermediates, requiring multiple steps to arrive to the final product. A far more economical approach using common synthetic scaffolds that can be readily transformed through biomimetic-like pathways to a range of structurally diverse natural products has been evolved in the last decade, leading synthesis to new directions. This tutorial review critically presents the hallmarks in this field. 相似文献
102.
Siskos AP Baerga-Ortiz A Bali S Stein V Mamdani H Spiteller D Popovic B Spencer JB Staunton J Weissman KJ Leadlay PF 《Chemistry & biology》2005,12(10):1145-1153
A system is reported for the recombinant expression of individual ketoreductase (KR) domains from modular polyketide synthases (PKSs) and scrutiny of their intrinsic specificity and stereospecificity toward surrogate diketide substrates. The eryKR(1) and the tylKR(1) domains, derived from the first extension module of the erythromycin PKS and the tylosin PKS, respectively, both catalyzed reduction of (2R, S)-2-methyl-3-oxopentanoic acid N-acetylcysteamine thioester, with complete stereoselectivity and stereospecificity, even though the substrate is not tethered to an acyl carrier protein or an intact PKS multienzyme. In contrast, and to varying degrees, the isolated enzymes eryKR(2), eryKR(5), and eryKR(6) exercised poorer control over substrate selection and the stereochemical course of ketoreduction. These data, together with modeling of diketide binding to KR(1) and KR(2), demonstrate the fine energetic balance between alternative modes of presentation of ketoacylthioester substrates to KR active sites. 相似文献
103.
Alexandros Eskenazis 《Archiv der Mathematik》2014,103(1):85-92
In this paper we introduce a class of functions contained in the disc algebra \({\mathcal{A}(D)}\) . We study functions \({f \in \mathcal{A}(D)}\) which have the property that the continuous periodic function \({u = {\rm Re}f|_{\mathbb{T}}}\) , where \({\mathbb{T}}\) is the unit circle, is nowhere differentiable. We prove that this class is non-empty and instead, generically, every function \({f \in \mathcal{A}(D)}\) has the above property. Afterwards, we strengthen this result by proving that, generically, for every function \({f \in \mathcal{A}(D)}\) , both continuous periodic functions \({u = {\rm Re}f|_\mathbb{T}}\) and \({\tilde{u} = {\rm Im}f|_\mathbb{T}}\) are nowhere differentiable. We avoid any use of the Weierstrass function and we mainly use Baire’s Category Theorem. 相似文献
104.
Microwave-assisted synthesis of 2-oxazolines from carboxylic acids using the open vessel technique is described. This efficient method involves direct condensation of carboxylic acids with excess 2-amino-2-methyl-1-propanol at 170 °C to give the corresponding 2-oxazolines in moderate to excellent yields. 相似文献
105.
Anna L. Bowman Alexandros Makriyannis 《Journal of computer-aided molecular design》2009,23(11):799-806
Monoacylglycerol lipase (MGL) is primarily responsible for the hydrolysis of 2-arachidonoylglycerol (2-AG), an endocannabinoid
with full agonist activity at both cannabinoid receptors. Increased tissue 2-AG levels consequent to MGL inhibition are considered
therapeutic against pain, inflammation, and neurodegenerative disorders. However, the lack of MGL structural information has
hindered the development of MGL-selective inhibitors. Here, we detail a fully refined homology model of MGL which preferentially
identifies MGL inhibitors over druglike noninhibitors. We include for the first time insight into the active-site geometry
and potential hydrogen-bonding interactions along with molecular dynamics simulations describing the opening and closing of
the MGL helical-domain lid. Docked poses of both the natural substrate and known inhibitors are detailed. A comparison of
the MGL active-site to that of the other principal endocannabinoid metabolizing enzyme, fatty acid amide hydrolase, demonstrates
key differences which provide crucial insight toward the design of selective MGL inhibitors as potential drugs. 相似文献
106.
Mercier RW Pei Y Pandarinathan L Janero DR Zhang J Makriyannis A 《Chemistry & biology》2010,17(10):1132-1142
The human cannabinoid 2 GPCR (hCB2) is a prime therapeutic target. To define potential cysteine-related binding motifs critical to hCB2-ligand interaction, a library of hCB2 cysteine-substitution mutants and a novel, high-affinity biarylpyrazole hCB2 antagonist/inverse agonist (AM1336) functionalized to serve as a covalent affinity probe to target cysteine residues within (or in the microenvironment of) its hCB2 binding pocket were generated. The data provide direct experimental demonstration that both hCB2 TMH7 cysteines [i.e., C7.38(284) and C7.42(288)] are critical to optimal hCB2-AM1336 binding interaction and AM1336 pharmacological activity in a cell-based functional assay (cAMP formation). Elongating the AM1336 aliphatic side chain generated another novel?hCB2 inverse agonist that binds covalently and selectively to C7.42(288) only. Identification of specific cysteine residues critical to hCB2 ligand interaction and function informs the structure-based design of hCB2-targeted medicines. 相似文献
107.
Canted ferromagnets present a important class of molecular magnets. In these materials the uncompensated magnetisation, created by the DzyaloshinskyMoriya interaction, has the particular property of being compatible with the symmetry of the underlying antiferromagnetic Hamiltonian. If the ordering transition is continuous, Landau theory and simple symmetry arguments about the crystal structure can be used to determine whether such parasitic ferromagnetism is possible, and therefore to aid the systematic search for new molecular ferromagnets. 相似文献
108.
This paper describes a new multilevel procedure that can solve the discrete Navier–Stokes system arising from finite volume discretizations on composite grids, which may consist of more than one level. SIMPLE is used and tested as the smoother, but the multilevel procedure is such that it does not exclude the use of other smoothers. Local refinement is guided by a criterion based on an estimate of the truncation error. The numerical experiments presented test not only the behaviour of the multilevel algebraic solver, but also the efficiency of local refinement based on this particular criterion. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
109.
Patrick Hoffmann Ricardo P. Mikalo Alexandros Yfantis David R. Batchelor Guenter Appel Dimitrios Yfantis Dieter Schmeißer 《Mikrochimica acta》2001,136(3-4):109-113
Synchrotron radiation based spectro-microscopy is shown to be an exciting tool for elemental analysis in the field of heterogeneous
interfaces, thin films, and device technology. Results are reported, taken with a spectrometer that enables the combination
of a photoemission electron microscope (PEEM) with photoelectron spectroscopies (XPS, UPS) operated at a high brilliance undulator
beam line at BESSY.
The properties of mc-Si (multi crystalline silicon) are of interest because of their applications in low priced photovoltaic
devices. An example of how to analyze the surface potentials of such surfaces without removing the native oxide is given.
Tin nano-scale particles are shown to be the decisive factor affecting the corrosion prevention of passivated tinplate surfaces. 相似文献
110.
Aspirin triggers the biosynthesis of oxygenated metabolites from arachidonic, eicosapentaenoic, and docosahexaenoic (DHA) acids. In a preceding issue, Serhan et?al. (2011) describe a novel aspirin-triggered DHA pathway for the biosynthesis of a potent anti-inflammatory and proresolving molecule. 相似文献