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941.
Bench BJ Johnson R Hamilton C Gooch J Wright JR 《Journal of colloid and interface science》2004,270(2):315-320
It has been shown in preliminary studies that the antibacterial protein avidin self-associates with the boric acid gel polymer, and avidin-coated gel particles in the micrometer and submicrometer size ranges are of interest for boron neutron-capture therapy (BNCT), which is neutron-induced fission of boron-10 to produce intense alpha radiation for tumor destruction. The gel particles carry large amounts of boron-10 and are theoretically able effect a meaningful tissue dosing through BNCT. A gross precipitation of gel particles occurs within 46 min of mixing when the avidin/colloid ratio is about 0.34 g avidin/g colloid. This is a minimum time if gel and avidin concentrations are in the low microgram/milliliter range, but at higher proportions of avidin the time delay to precipitation increases significantly; i.e., the colloid surface becomes blocked, inhibiting lattice formation. The avidin-coated gel particles eventually cross-link, forming a solid matrix and precipitating on a timescale measured on the order of an hour. At shorter exposure times rapid agglutination-like reactions were observed with biotinylated bovine albumin, suggesting that two-stage pretargeting of specific tissues should be possible with biotinylated antitumor antibodies. However, for BNCT to be practical, avidin's interaction with the gel needs to be strengthened, and all aryl-B(OH)(2) groups on the particle surfaces must be blocked, or else the particles will interact strongly and nonspecifically with each other and with the carbohydrate groups present on most cell surfaces. Glyceric acid delays the precipitation of the particle suspensions while most simple and complex carbohydrates accelerate it. 相似文献
942.
Rebecca F. Deprez-Poulain Julie Charton Virginie Leroux Benoit P. Deprez 《Tetrahedron letters》2007,48(46):8157-8162
We report here the convenient synthesis of 4H-1,2,4-triazole-3-thiols using di-2-pyridyl-thionocarbonate as the thiocarbonyl transfer reagent. This method is suitable for microplate parallel synthesis and produces samples in screening-ready condition. It uses two large sets of building-blocks: amines and hydrazides. 相似文献
943.
[reaction: see text] Silver(I) acetylides allow one-step alkynylation of adamantyl iodide in yields ranging from 25 to 68%. 相似文献
944.
Yates BJ Temsamani KR Ceylan O Oztemiz S Gbatu TP Larue RA Tamer U Mark HB 《Talanta》2002,58(4):739-745
Exploitation of the physical, chemical and electrically conductive properties of poly(3-dodecylthiophene) (P3DDT) for the preconcentration and release in solid phase microextraction (SPME) of organometallic arsenobetaine (AsB) from aqueous media was investigated. Hydrophobic interactions between this neutral arsenic species and an undoped polythiophene (no applied potential) with n-substituted alkyl groups (n=12) in the three position were used for the diffusion-controlled preconcentration. After absorption into the polymer matrix, the chemical properties of this conductive polymer were changed by applying an external potential. This potential provides a sufficient driving force for desorption of the analyte from the extraction phase into an aqueous solution for subsequent analysis. The applied positive potential oxidizes the polymer to its charged hydrophilic state, which releases the neutral analyte. The concentration and speciation of the analyte from the sample matrix was analyzed by HPLC coupled to an ICP-MS. The diffusion-controlled uptake was fast (equilibrium attained within minutes) and did not require pretreatment of the analyte. The electrochemically-controlled release of the analyte is also very rapid (within minutes). This conducting polymer film system, therefore, can offer analytical applications for the convenient preconcentration and subsequent analysis of neutral environmental species. 相似文献
945.
Li Z Sansom R Bonella S Coker DF Mullin AS 《The journal of physical chemistry. A》2005,109(34):7657-7666
Classical trajectory calculations were performed to simulate state-resolved energy transfer experiments of highly vibrationally excited pyrazine (E(vib) = 37,900 cm(-1)) and CO(2), which were conducted using a high-resolution transient infrared absorption spectrometer. The goal here is to use classical trajectories to simulate the supercollision energy transfer pathway wherein large amounts of energy are transferred in single collisions in order to compare with experimental results. In the trajectory calculations, Newton's laws of motion are used for the molecular motion, isolated molecules are treated as collections of harmonic oscillators, and intermolecular potentials are formed by pairwise Lennard-Jones potentials. The calculations qualitatively reproduce the observed energy partitioning in the scattered CO(2) molecules and show that the relative partitioning between bath rotation and translation is dependent on the moment of inertia of the bath molecule. The simulations show that the low-frequency modes of the vibrationally excited pyrazine contribute most to the strong collisions. The majority of collisions lead to small DeltaE values and primarily involve single encounters between the energy donor and acceptor. The large DeltaE exchanges result from both single impulsive encounters and chattering collisions that involve multiple encounters. 相似文献
946.
Newby JJ Serafin MM Peebles RA Peebles SA 《The journal of physical chemistry. A》2005,109(24):5316-5322
The rotational spectra for five isotopomers of the 1:1 weakly bound complex formed between dimethyl ether (DME) and acetylene (HCCH) have been measured by Fourier transform microwave spectroscopy. The experimental rotational constants, planar moments, and dipole moment components are consistent with a floppy complex possessing an effective C2v structure in which the hydrogen atom of acetylene is hydrogen bonded to the oxygen atom of dimethyl ether with an intermolecular H...O separation of 2.08(3) A. Experimental rotational constants for the normal isotopic species are A = 10382.5(17) MHz, B = 1535.7187(18) MHz, and C = 1328.3990(17) MHz and the dipole moment components are mua= mutotal = 1.91(10) D. Ab initio calculations at the MP2/6-311++G(2d,2p) level indicate that the energy barrier for motion of the HCCH subunit between the lone pairs of the DME, via a C2v intermediate structure, is very low (approximately 0.29 kJ mol(-1)). Inclusion of basis set superposition error and zero point energy corrections to the energies of four stationary points located on the potential energy surface shows that the relative stabilities are particularly sensitive to these corrections. The ab initio optimizations give rotational constants for the C2v structure of A = 10066 MHz, B = 1496 MHz, and C = 1324 MHz, and a dipole moment of mua= mu(total) = 2.12 D, in reasonable agreement with the experimentally determined values. The structural parameters and energetics of the DME-HCCH complex will be discussed and compared to similar complexes such as H2O-HCCH. 相似文献
947.
Briseno AL Aizenberg J Han YJ Penkala RA Moon H Lovinger AJ Kloc C Bao Z 《Journal of the American Chemical Society》2005,127(35):12164-12165
This work demonstrates a method for inducing site-specific nucleation and subsequent growth of large oriented organic semiconductor single crystals using micropatterned self-assembled monolayers (SAMs). We demonstrate growth of oriented, patterned, and large organic semiconductor single crystals for potential use in organic electronic devices. The control over multiple parameters in a single system has not yet been reported. The ability to control various aspects of crystal growth in one system provides a powerful technique for the bottom-up fabrication of organic single-crystal semiconductor devices. 相似文献
948.
High-speed gas chromatographic (GC) separation of residual solvents in pharmaceutical preparations, using a flow-modulation technique, is described. These volatile compounds are separated on a series-coupled (tandem) column ensemble consisting of a polyethylene glycol column and a trifluoropropylmethyl/dimethylpolysiloxane column. This column ensemble is operated in stop-flow mode to enhance, or "tune", the separation. A valve between the junction point of the tandem column ensemble and a source of carrier gas at a pressure above the GC inlet pressure is opened for intervals of 2-8 s. This stops or slightly reverses the flow of carrier gas in the first column. Stop-flow pulses are used to increase the separation of target analytes that overlap in the total ensemble chromatogram, compared to non-stop-flow, or conventional, operation. All 36 target compounds, based on ICH Classes I and II residual solvent lists, are resolved in 12 min using the stop-flow technique and a single chromatographic analysis. 相似文献
949.
Rebecca E. Conner Michael A. Babich Thomas P. Coohill 《Photochemistry and photobiology》1987,46(4):495-499
African green monkey kidney cells (CV-1P) were exposed to low fluences of 254 nm germicidal radiation and then infected with Herpes simplex virus, type I. The result of this treatment was an increase in viral plaque development rate, the large plaque effect (LPE). A measurement of the kinetics of plaque development suggested that a large portion of the effect could be due to events occurring in those cells that are adjacent to the initially infected cell. An infectious center assay was employed in order to isolate the effects of ultraviolet radiation (UV) on the initially infected cells from those effects on the adjacent cells that became infected as the plaque spread radially outward. Plaque development began earlier in UV irradiated cells and progressed at a uniformly accelerated rate compared to untreated cells. Results indicate that although the initially infected cell contributes to the LPE, the major effect is due to events that occur in the adjacent cells. Each round of viral replication appears to contribute equally to the LPE. The virally induced rate of fusion of the initially infected cell with its immediate neighbors is not affected by UV. 相似文献
950.
ABSTRACT The synthesis and characterisation of two homologous series of non-symmetric dimers are reported, the 1-(4-methoxybiphenyl-4?-yl)-6-(4-alkylanilinebenzylidene-4?-oxy)hexanes (MeOB6O.m, m = 1–10) and 1-(4-methoxybiphenyl-4?-yl)-6-(4-alkyloxyanilinebenzylidene-4?-oxy)hexanes (MeOB6O.Om, m = 1–9). All 10 members of the MeOB6O.m series exhibit the conventional nematic phase. At lower temperatures, the members with m = 1–7 formed the twist-bend nematic phase, NTB, whereas for m = 8–10 smectic behaviour replaced the NTB phase. All nine members of the MeOB6O.Om series also show the conventional nematic phase and for m = 1–3, a strongly monotropic NTB phase is also observed. The alkyloxy terminated dimers show the higher values of TNI and TNTB N . For both series, the values of TNI and TNTB N show a modest alternation and in the same sense as m is increased. These observations suggest that the spatial uniformity of molecular curvature is important in driving the formation of the NTB phase. The observation of smectic behaviour is attributed to the molecular inhomogeneity arising from the long terminal alkyl chain driving microphase separation. The transitional behaviour of these series is compared to those of the corresponding cyanobiphenyl-based series and overarching observations discussed. 相似文献