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991.
Yong Tang Jinfeng Zhuge Jihua Gou Ruey‐Hung Chen Christopher Ibeh Yuan Hu 《先进技术聚合物》2011,22(10):1403-1413
In this study, a hybrid nanopaper consisting of carbon nanofiber (CNF) and polyhedral oligomeric silsequioxane (POSS) or cloisite Na+ clay, has been fabricated through the papermaking process. The hybrid nanopaper was then coated on the surface of glass fiber (GF) reinforced polymer matrix composites through resin transfer molding (RTM) process. The morphologies of the hybrid nanopaper and resulting nanocomposites were characterized with scanning electron microscopy (SEM). It can be seen that the nanopaper had a porous structure with highly entangled carbon nanofibers and the polyester resin completely penetrated the nanopaper throughout the thickness. The thermal decomposition behavior of the hybrid nanopapers and nanocomposites was studied with the real‐time thermogravimetric analysis/ flourier transform infrared spectrometry (TGA/FTIR). The test results indicate that the addition of pristine nanoclay increased the thermal stability of the nanopaper, whereas the POSS particles decreased the thermal stability of the nanopaper. The fire retardant performance of composite laminates coated with the hybrid nanopaper was evaluated with cone calorimeter tests using a radiated heat flux of 50 kW/m2. The cone calorimeter test results indicate that the peak heat release rate (PHRR) decreased dramatically in composite laminates coated with the CNF‐clay nanopaper. However, the PHRRs of the CNF‐POSS nanopaper coated composite laminates increased. The formation of compact char materials was observed on the surface of the residues of the CNF‐clay nanopaper after cone calorimeter test. The flame retardant mechanisms of the hybrid nanopaper in the composite laminates are discussed. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
992.
A novel amperometric sensor based on the incorporation of multiwalled carbon nanotubes (MWCNT) into a poly(methylene blue) (PMB) film immobilized on carbon composite electrodes is described. Cyclic voltammetry indicated that at a surface covered by a MWCNT/PMB layer the cathodic reduction of hydrogen peroxide is facilitated and occurs already at 0.0 V versus SCE. The effect of the order of deposition of PMB and MWCNT, as well as its loading, on electrochemical behaviour was evaluated by cyclic voltammetry and electrochemical impedance spectroscopy. The influence of the various immobilised platforms on the electrocatalytic performance towards hydrogen peroxide was also examined. 相似文献
993.
The mobilities of electrosprayed proteins and protein multimers with molecular weights ranging from 12.4 kDa (cytochrome C
monomers) to 154 kDa (nonspecific concanavalin A hexamers) were measured in dry air by a planar differential mobility analyzer
(DMA) coupled to a time-of-flight mass spectrometer (TOF-MS). The DMA determines true mobility at atmospheric pressure, without
perturbing ion structure from that delivered by the electrospray. A nondenaturing aqueous 20 mM triethylammonium formate buffer
yields compact ions with low charge states, moderating polarization effects on ion mobility. Conversion of mobilities into
cross-sections involves a reduction factor ξ for the actual mobility relative to that associated with elastic specular collisions with smooth surfaces. ξ is known to be 1.36 in air from Millikan’s oil drop experiments. A similar enhancement effect ascribed to atomic-scale surface
roughness has been found in numerical simulations. Adopting Millikan’s value ξ = 1.36 and assuming a spherical geometry yields a gas-phase protein density ρ
p = 0.949 ± 0.053 g cm−3 for all our protein data. This is substantially higher than the 0.67 g cm−3 found in recent low-resolution DMA measurements of singly charged proteins. DMA-MS can distinguish nonspecific protein aggregates
formed during the electrospray process from those formed preferentially in solution. The observed charge versus diameter relation
is compatible with a protein charge reduction mechanism based on the evaporation of triethylammonium ions from electrosprayed
drops. 相似文献
994.
Moss CL Chung TW Wyer JA Nielsen SB Hvelplund P Tureček F 《Journal of the American Society for Mass Spectrometry》2011,22(4):731-751
Electron transfer and capture mass spectra of a series of doubly charged ions that were phosphorylated pentapeptides of a
tryptic type (pS,A,A,A,R) showed conspicuous differences in dissociations of charge-reduced ions. Electron transfer from both
gaseous cesium atoms at 100 keV kinetic energies and fluoranthene anion radicals in an ion trap resulted in the loss of a
hydrogen atom, ammonia, and backbone cleavages forming complete series of sequence z ions. Elimination of phosphoric acid was negligible. In contrast, capture of low-energy electrons by doubly charged ions
in a Penning ion trap induced loss of a hydrogen atom followed by elimination of phosphoric acid as the dominant dissociation
channel. Backbone dissociations of charge-reduced ions also occurred but were accompanied by extensive fragmentation of the
primary products. z-Ions that were terminated with a deaminated phosphoserine radical competitively eliminated phosphoric acid and H2PO4 radicals. A mechanism is proposed for this novel dissociation on the basis of a computational analysis of reaction pathways
and transition states. Electronic structure theory calculations in combination with extensive molecular dynamics mapping of
the potential energy surface provided structures for the precursor phosphopeptide dications. Electron attachment produces
a multitude of low lying electronic states in charge-reduced ions that determine their reactivity in backbone dissociations
and H- atom loss. The predominant loss of H atoms in ECD is explained by a distortion of the Rydberg orbital space by the
strong dipolar field of the peptide dication framework. The dipolar field steers the incoming electron to preferentially attach
to the positively charged arginine side chain to form guanidinium radicals and trigger their dissociations. 相似文献
995.
Sundberg TB Darricarrere N Cirone P Li X McDonald L Mei X Westlake CJ Slusarski DC Beynon RJ Crews CM 《Chemistry & biology》2011,18(10):1300-1311
Identification of methionine aminopeptidase-2 (MetAP-2) as the molecular target of the antiangiogenic compound TNP-470 has sparked interest in N-terminal Met excision's (NME) role in endothelial cell biology. In this regard, we recently demonstrated that MetAP-2 inhibition suppresses Wnt planar cell polarity (PCP) signaling and that endothelial cells depend on this pathway for normal function. Despite this advance, the substrate(s) whose activity is altered upon MetAP-2 inhibition, resulting in loss of Wnt PCP signaling, is not known. Here we identify the small G protein Rab37 as a MetAP-2-specific substrate that accumulates in the presence of TNP-470. A functional role for aberrant Rab37 accumulation in TNP-470's mode of action is demonstrated using a Rab37 point mutant that is resistant to NME, because expression of this mutant phenocopies the effects of MetAP-2 inhibition on Wnt PCP signaling-dependent processes. 相似文献
996.
Wright AD McCluskey A Robertson MJ MacGregor KA Gordon CP Guenther J 《Organic & biomolecular chemistry》2011,9(2):400-407
In an investigation into their potential ecological role(s), a group of mainly diterpene isonitriles, nine in total, isolated from the tropical marine sponge Cymbastela hooperi, and the sesquiterpene axisonitrile-3, isolated from the tropical marine sponge Acanthella kletra, were evaluated in a series of bioassays including anti-fouling, anti-algal, anti-photosynthetic, anti-bacterial (Gram +ve and -ve), anti-fungal, and anti-tubercular. The results of these assays showed that all of the tested compounds, with the exception of diterpene 9, were active in at least two of the applied test systems, with axisonitrile-3 (10) and diterpene isonitrile 1 being the two most active compounds overall, closely followed by diterpene isonitrile 3. Based on the results of the photosynthetic study a molecular modelling investigation was undertaken with all of the compounds used in that study. The results showed a positive correlation between reduction in photosynthetic activity and the interaction of the modelled compounds with a potential enzyme active site. 相似文献
997.
Campbell CD Collett CJ Thomson JE Slawin AM Smith AD 《Organic & biomolecular chemistry》2011,9(11):4205-4218
The O- to C-carboxyl transfer of oxazolyl carbonates promoted by triazolinylidenes, generated in situ with NEt(3), shows a markedly different rate and chemoselectivity profile to the same reaction promoted by triazolinylidenes generated using KHMDS. The mechanism of these pathways has been probed through extensive crossover studies to understand this process. The use of NEt(3) as a base allows domino multi-step reaction sequences to be developed, although chiral NHCs only generate modest levels of asymmetric induction (<15% ee) in these domino reaction processes. 相似文献
998.
The 1-hydroxy-1-methyl-6,6-diphenyl-5-hexenyl radical (4a) and the 1-hydroxy-1-methyl-7,7-diphenyl-6-heptenyl radical (4b) were prepared from the corresponding PTOC esters (anhydrides of a carboxylic acid and N-hydroxypyridine-2-thione). The key step in the synthetic method for the precursors was a coupling reaction of the respective carboxylic acids with the thiohydroxamic acid, which was conducted for ca. 5 min and followed rapidly by chromatography. Rate constants for cyclizations of radicals 4a and 4b in acetonitrile and in THF were measured directly between -30 and 60 °C by laser flash photolysis methods. The Arrhenius functions in acetonitrile are log k = 9.9-2.6/2.303RT and log k = 8.9-4.4/2.303RT (kcal mol(-1)) for 4a and 4b, respectively. Rate constants for cyclizations at room temperature of 9 × 10(7) s(-1) and 4 × 10(5) s(-1) are somewhat larger than the rate constants for cyclizations of analogous alkyl radicals. Crude rate constants at room temperature for H-atom trapping of 4a by thiophenol and 4b by t-butylthiol were k(T) = 1.2 × 10(9) M(-1) s(-1) and k(T) = 2 × 10(7) M(-1) s(-1), respectively, which are modestly larger than rate constants for reactions of alkyl radicals with the same trapping agents. 相似文献
999.
Paradise CL Sarkar PR Razzak M De Brabander JK 《Organic & biomolecular chemistry》2011,9(11):4017-4020
Amino acid-derived propargylic amides are cyclised in a one-pot, Au(III)-catalysed operation to yield 5-bromomethyl oxazoles. These compounds are further elaborated to bis-heterocycles, dipeptide mimics and more. 相似文献
1000.
Mbatia HW Ulloa OA Kennedy DP Incarvito CD Burdette SC 《Organic & biomolecular chemistry》2011,9(8):2987-2991
A highly crystalline iodinating reagent, {[K·18-C-6]ICl(2)}(n), was synthesized in high yield (93%). The trihalide is supported by an 18-crown-6 macrocycle and forms a coordination polymer in the solid state. This reagent iodinates anilines and phenols efficiently under mild conditions. Controlled mono-iodination with anilines was easily achieved while poly-iodination was observed with phenols. 相似文献