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81.
Two recent experiments for adsorbed acrylonitrile on the Si(001) surface reported different adsorption structures at 110 and 300 K. We investigate the reaction of acrylonitrile on Si(001) by first-principles density-functional calculations. We find that the so-called [4+2] structure in which acrylonitrile resides between two dimer rows is not only thermodynamically favored over other structural models but also easily formed via a precursor where the N atom of acrylonitrile is attached to the down atom of the Si dimer. The additional initial-state theory calculation for the C 1s core levels of adsorbed acrylonitrile provides an interpretation for the observed low- and room-temperature adsorption configurations in terms of the precursor and [4+2] structures, respectively. 相似文献
82.
83.
Enantioseparations of (R)- and (S)-6-O-desmethylnaproxens as O-ethoxycarbonyl/(R)-(+)-1-phenylethylamides and (R)- and (S)-naproxens as (R)-(+)-1-phenylethylamides were achieved by achiral gas chromatography in a single run within 11 min. The characteristic mass spectral patterns facilitated easier peak identification. The method for determinations of (R)-naproxen (1.0 to 50 ng) and (S)-naproxen (100 to 2000 ng) was linear with acceptable repeatability and accuracy. The enantiomeric composition ratios between (R)- and (S)-6-O-desmethylnaproxens and between (R)- and (S)-naproxens in urine sample collected six hours after oral administration of (S)-naproxen tablets were measured to be 2.2 (± 0.2):97.8 (± 0.2) and 2.1 (± 0.1):97.9 (± 0.1), respectively. 相似文献
84.
Temperature-dependent intermolecular force measurement of poly(N-isopropylacrylamide) grafted surface with protein 总被引:1,自引:0,他引:1
We have investigated the temperature dependence of the intermolecular force between poly(N-isopropylacrylamide) (PNiPAM) grafted surface and bovine serum albumin (BSA) in phosphate buffer (pH 7.4) using atomic force microscopy at the nanonewton scale. These observations show that the interaction force is nearly zero below the phase transition temperature of PNiPAM and that it increases steeply during the phase transition. Since the PNiPAM chains are grafted onto the aminosilane (gamma-aminopropyltriethoxysilane)-treated silicon wafer, we measured the force-distance curve of BSA-immobilized tips for the bare and the aminosilane-treated silicon wafer. These surfaces show no temperature dependence and their values are different from those of the PNiPAM-grafted surfaces at 30 degrees C. The results indicate that the measured adhesion force is between the PNiPAM-grafted surface and the BSA-immobilized tip. Our studies on the intermolecular force between other surfaces (CH(3)- and COOH-terminated self-assembled monolayers) and the BSA-immobilized tip indicate that the variation in the intermolecular force between the PNiPAM surface and BSA with temperature can be attributed to the changes in the properties of the PNiPAM chains. From consideration of the PNiPAM phase transition mechanism, it is speculated that the intermolecular force between the PNiPAM-grafted surface and BSA would be affected by changes in the arrangement of the bound water molecules around the PNiPAM chain and by changes in the conformation (i.e., in the chain mobility) of the PNiPAM chain during the phase transition. 相似文献
85.
Two ligand exchange chiral stationary phases (CSPs) based on (S)-leucinol derivative, sodium N-((S)-1-hydroxymethyl-3-methylbutyl)-N-undecylaminoacetate, and (R)-phenylglycinol derivative, sodium N-((R)-2-hydroxy-1-phenylethyl)-N-undecylaminoacetate, covalently bonded to silica gel have been successfully applied in the resolution of nine -hydroxycarboxylic acids. The latter was more effective than the former, the separation factors () being 1.05 to 2.12 while the resolution factors (RS) varying from 0.18 to 5.29 on the latter. The chromatographic resolution behaviors were dependent on the type and the content of organic modifier and the content of CuSO4 in aqueous mobile phase and the column temperature. A possible chiral recognition mechanism was also proposed based on the chromatographic resolution behaviors. 相似文献
86.
1-(p-Substituted phenyl)-2-vinylcyclopropanes such as 1-phenyl-2-vinylcyclopropane (Ia), 1-(p-chlorophenyl)-2-vinylcyclopropane (Ib), 1-(p-anisyl)-2-vinylcyclopropane (Ic), and 1-(p-tolyl)-2-vinylcyclopropane (Id) were prepared and polymerized radically, cationically and with Ziegler–Natta catalysts. Ia and Ib polymerized exclusively in 1,5-fashion with radical initiators. However, Ic and Id polymerized in 1,5-fashion only with Ziegler–Natta catalysts. All polymers were soluble in ordinary organic solvent and solution-cast films were clear and flexible, showing Tg values in the range of 39–71°C. Spectral data indicated that the double bonds of the polymer chains were in trans form in all cases. The difference between the polymerizabilities of different monomers are interpreted in terms of electronic properties of substituents. 相似文献
87.
Evan M. Sherbrook Hoimin Jung Dasol Cho My-Hyun Baik Tehshik P. Yoon 《Chemical science》2020,11(3):856
Catalysis is central to contemporary synthetic chemistry. There has been a recent recognition that the rates of photochemical reactions can be profoundly impacted by the use of Lewis acid catalysts and co-catalysts. Herein, we show that Brønsted acids can also modulate the reactivity of excited-state organic reactions. Brønsted acids dramatically increase the rate of Ru(bpy)32+-sensitized [2 + 2] photocycloadditions between C-cinnamoyl imidazoles and a range of electron-rich alkene reaction partners. A combination of experimental and computational studies supports a mechanism in which the Brønsted acid co-catalyst accelerates triplet energy transfer from the excited-state [Ru*(bpy)3]2+ chromophore to the Brønsted acid activated C-cinnamoyl imidazole. Computational evidence further suggests the importance of driving force as well as geometrical reorganization, in which the protonation of the imidazole decreases the reorganization penalty during the energy transfer event.Brønsted acids can catalyze triplet energy transfer reactions, and DFT computations suggest the unexpected importance of reorganization energy for catalysis. 相似文献
88.
[reaction: see text] Silver salts in the presence of a chelating ligand efficiently catalyze the stereospecific imination of sulfoxides and sulfides with sulfonylamides and PhI(OAc)(2) to afford sulfoximines and sulfilimines, respectively, in good yields. 相似文献
89.
Polyelectrolyte multilayer thin films were prepared via the alternate deposition of poly(allylamine hydrochloride) (PAH) and a blend of poly(acrylic acid) (PAA) and poly(styrenesulfonate) (PSS). When the pH of the blend solution was 3.5, the presence of PAA in this solution significantly increased the total film thickness. With only 10 wt % PAA in the blend adsorption solution, a large increase in film thickness was observed (92 nm cf. 18 nm). It was also demonstrated that the total amount of PSS adsorbed was enhanced by the presence of PAA in the blend solution, showing that the blend solution composition influenced that of the multilayer films. Thin films prepared with nanoblended layers also showed improved pH stability, because they exhibited reduced film rearrangement upon exposure to acidic conditions (pH = 2.5). 相似文献
90.
Homogeneous fluorescent derivatization of large proteins 总被引:1,自引:0,他引:1
A method of homogeneously derivatizing large proteins for highly sensitive analysis is described. Homogeneity of the derivative was realized by tagging all the free amino groups of proteins. With this method, alpha-chymotrypsinogen A, ovalbumin and bovine serum albumin were derivatized with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC). Prior to the derivatization, all the proteins were reduced and alkylated. After reacting the resulting unfolded proteins with excessive amounts of AQC, the samples were analyzed with matrix assisted laser desorption ionization-time of flight-mass spectrometry (MALDI-TOF-MS) to determine the derivatization degree. The results indicated that all three proteins had been, or had almost been, fully derivatized. HPLC and CE were used for characterizing these protein derivatives. Under the optimized fluorescence detection conditions, the detectability of the tagged proteins was 2400-6200 times better than that detected at UV 280 nm, 170-300 times better than detected at UV 214 nm, and 150-420 times better than measured with their native fluorescence. 相似文献