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21.
Switching between three different adsorbed states was achieved using potential control to separately induce electrochemical behaviour associated with changes in binding and orientation of the thiophene and pyridine moieties of 2-(2'-thienyl)pyridine adsorbed to Au(111) in neutral and basic solution. 相似文献
22.
Edoardo Apr Emily A. Carter Alessandro Fortunelli 《International journal of quantum chemistry》2005,101(2):230-230
Density Functional Theory (DFT) and direct ab initio molecular dynamics (MD) calculations were applied to the hydrogen molecule trapped in a water cluster composed of 12 water molecules (H2O)12. The static DFT calculation showed that the H2 molecule is trapped in the center of mass of (H2O)12. The vibrational frequency of the H–H stretching mode of the H2 molecule trapped in the water cluster was blueshifted from that in vacuo. On the other hand, the vibrational frequency of H2 in water‐hydrogen 1:1 complex (H2O–H2) was redshifted. A direct ab initio MD calculation of H2(H2O)12 at 50 K indicated that the H2 molecule is rotated freely around the center of mass of the water cluster. The origin of the spectral shift of H2 in water ice is discussed on the basis of the theoretical results. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
23.
A novel stationary phase for micro ion chromatography has been prepared by coating a porous poly(butyl methacrylate-co-ethylene dimethacrylate-co-2-acrylamido-2-methyl-1-propanesulfonic acid) monolith with quaternary amine-functionalized latex particles via simple electrostatic binding. This stationary phase enabled the separation of saccharides in the mobile phase with a high-pH value consisting of aqueous ammonia solution in anion-exchange mode using evaporative light scattering for detection. Effects of both porous properties of the monolithic stationary phase and chromatographic conditions on the separation ability were studied. Under optimized conditions, an efficient separation of seven saccharides was achieved in less than 10 min. The stationary phase also enables the separation of saccharides obtained by the enzymatic hydrolysis of corn starch. 相似文献
24.
Bluhm ME Kim SS Dertz EA Raymond KN 《Journal of the American Chemical Society》2002,124(11):2436-2437
Most species of bacteria employ siderophores to acquire iron. The chirality of the ferric siderophore complex plays an important role in cell recognition, uptake, and utilization. Corynebactin, isolated from Gram-positive bacteria, is structurally similar to enterobactin, a well known siderophore isolated from Gram-negative bacteria, but contains L-theronine instead of L-serine in the trilactone backbone. Corynebactin also contains a glycine spacer unit in each of the chelating arms. A hybrid analogue (serine-corynebactin) has been synthesized. The chirality and relative conformational stability of the three ferric complexes of enterobactin, corynebactin, and the hybrid has been investigated. In contrast to enterobactin, corynebactin assumes a Lambda configuration. However, the ferric serine-corynebactin hybrid forms a racemic mixture, only slightly favoring the Lambda conformation. 相似文献
25.
Bernd Hartke Douglas A. Gibson Emily A. Carter 《International journal of quantum chemistry》1993,45(1):59-70
This is the first application of a rigorous, established multiple time-step method to ab initio molecular dynamics. The resulting algorithm is conceptually simple and easy to implement, but very effective. It translates the large mass differences present in ab initio molecular dynamics into substantial savings in computer time while retaining high accuracy. This transforms ab initio molecular dynamics from a desirable but prohibitively expensive possibility into a viable method, at least for short-time phenomena in small systems or for otherwise inaccessibly complicated potential energy surfaces. © 1993 John Wiley & Sons, Inc. 相似文献
26.
Gray TG Rudzinski CM Meyer EE Holm RH Nocera DG 《Journal of the American Chemical Society》2003,125(16):4755-4770
The electronic, vibrational, and excited-state properties of hexanuclear rhenium(III) chalcogenide clusters based on the [Re(6)(mu(3)-Q)(8)](2+) (Q = S, Se) core have been investigated by spectroscopic and theoretical methods. Ultraviolet or visible excitation of [Re(6)Q(8)](2+) clusters produces luminescence with ranges in maxima of 12 500-15 100 cm(-)(1), emission quantum yields of 1-24%, and emission lifetimes of 2.6-22.4 microseconds. Nonradiative decay rate constants and the luminescence maxima follow the trend predicted by the energy gap law (EGL). Examination of 24 clusters in solution and 14 in the solid phase establish that exocluster ligands engender the observed EGL behavior; clusters with oxygen- or nitrogen-based apical ligands achieve maximal quantum yields and the longest lifetimes. The excited-state decay mechanism was investigated by applying nonradiative decay models to temperature-dependent emission experiments. Solid-state Raman spectra were recorded to identify vibrational contributions to excited-state deactivation; spectral assignments were enabled by normal coordinate analysis afforded from Hartree-Fock and DFT calculations. Excited-state decay is interpreted with a model where normal modes largely centered on the [Re(6)Q(8)](2+) core induce nonradiative relaxation. Hartree-Fock and DFT calculations of the electronic structure of the hexarhenium family of compounds support such a model. These experimental and theoretical studies of [Re(6)Q(8)](2+) luminescence provide a framework for elaborating a variety of luminescence-based applications of the largest series of isoelectronic clusters yet discovered. 相似文献
27.
Tryptanthrin is a natural product with numerous important pharmacological properties. Tryptanthrin and its analogs are commonly prepared by condensation of isatoic anhydride and isatin. In this Letter we investigate the formation of tryptanthrin derivatives upon Oxone-induced oxidative dimerization of indole-3-carbaldehydes. 相似文献
28.
Andreas Dorian Emily J. Landgreen Hayley R. Petras Prof. James J. Shepherd Prof. Florence J. Williams 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(42):10839-10843
The facile production of ArCF2X and ArCX3 from ArCF3 using catalytic iron(III)halides is reported, which constitutes the first iron-catalyzed halogen exchange for non-aromatic C−F bonds. Theoretical calculations suggest direct activation of C−F bonds by iron coordination. ArCX3 and ArCF2X products of the reaction are synthetically valuable due to their diversification potential. In particular, chloro- and bromodifluoromethyl arenes (ArCF2Cl, ArCF2Br respectively) provide access to a myriad of difluoromethyl arene derivatives (ArCF2R). To optimize for mono-halogen exchange, a statistical method called Design of Experiments was used. Optimized parameters were successfully applied to electron rich and electron deficient aromatic substrates, and to the late stage diversification of flufenoxuron, a commercial insecticide. These methods are highly practical, being run at convenient temperatures and using inexpensive common reagents. 相似文献
29.
Marie-Claire Giel Dr. Christopher J. Smedley Emily R. R. Mackie Taijie Guo Prof. Dr. Jiajia Dong Dr. Tatiana P. Soares da Costa Prof. Dr. John E. Moses 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(3):1197-1202
The boom in growth of 1,4-disubstituted triazole products, in particular, since the early 2000’s, can be largely attributed to the birth of click chemistry and the discovery of the CuI-catalyzed azide–alkyne cycloaddition (CuAAC). Yet the synthesis of relatively simple, albeit important, 1-substituted-1,2,3-triazoles has been surprisingly more challenging. Reported here is a straightforward and scalable click-inspired protocol for the synthesis of 1-substituted-1,2,3-triazoles from organic azides and the bench stable acetylene surrogate ethenesulfonyl fluoride (ESF). The new transformation tolerates a wide selection of substrates and proceeds smoothly under metal-free conditions to give the products in excellent yield. Under controlled acidic conditions, the 1-substituted-1,2,3-triazole products undergo a Michael addition reaction with a second equivalent of ESF to give the unprecedented 1-substituted triazolium sulfonyl fluoride salts. 相似文献
30.
Dr. Samantha A. Orr Dr. Emily C. Border Prof. Philip C. Andrews Dr. Victoria L. Blair 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(51):11876-11882
By exploring lithium–bromide exchange reactivity of aromatic Schiff's bases with tert-butyllithium (tBuLi), we have revealed unprecedented competitive intermolecular and intramolecular cascade annulation pathways, leading to valuable compounds, such as iso-indolinones and N-substituted anthracene derivatives. A series of reaction parameters were probed, including solvent, stoichiometry, sterics and organolithium reagent choice, in order to understand the influences that limit such ring-closing pathways. With two viable reactivity options for the organolithium on the imine; namely, nucleophilic addition or lithium–bromide exchange, a surprising competitive nature was observed, where nucleophilic addition dominated, even under cryogenic conditions. Considering the most commonly used solvents for lithium–bromide exchange, tetrahydrofuran (THF) and diethyl ether (Et2O), contrasting reactivity outcomes were revealed with nucleophilic addition promoted in THF, while Et2O yielded almost double the conversion of cyclic products than in THF. 相似文献