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11.
A kinetic spectrophotometric method for the determination of molybdenum is based on its catalytic effect on the oxidation
of pyrogallol red with hydrogen peroxide. The decrease of the absorbance of pyrogallol red in the presence of hydrogen peroxide
with time from 0.5 to 4.5 min is proportional to the concentration of Mo(VI) over the range 0.010–0.500 μg/mL. The limit of
detection is 0.008 μg Mo/mL. The precision and the effect of the presence of more than forty ions on the molybdenum determination
are reported. Probable interferences are completely removed by a cation exchange resin. The procedure was successfully applied
to the determination of molybdenum in plant materials and steels.
Received: 28 April 1997 / Revised: 16 June 1997 / Accepted: 18 June 1997 相似文献
12.
A flow injection gas-phase molecular absorption spectrophotometric method is described for the determination of sulphite in aqueous solution. The sulphite solution, 200 microl, is introduced into a stream of distilled water. The carrier stream containing a sulphite zone is reacted, in the first mixing coil, with a stream of sulphuric acid (1 M). The evolved sulphur dioxide is purged to the segments of nitrogen flow through the second mixing coil. The gaseous phase is separated from the liquid stream by the use of a purpose built gas-liquid separator and then is swept into a purpose built flow-through cell. The absorbance of the gaseous phase is measured at 200 nm using a UV/VIS spectrophotometer. Up to 440 microg of sulphite is determined. The limit of detection is 0.8 microg and the R.D.S. for the determination of 70 and 220 microg of sulphite are 1.02 and 0.76%, respectively. Up to 40 samples h(-1) can be analyzed. The effect of several anions and cations on the determination of sulphite was studied and the results showed that the method is relatively free from interferences. The proposed method was applied to the determination of sulphite in a synthetic sample, water sample and lemon juice. 相似文献
13.
Spectroscopical Properties of Di(phthalocyaninato)metalates(III) of the Rare Earth Elements. Part 2: The Multinuclear (1H, 13C, 15N, 17O, and 31P) NMR Spectra and Determination of Complex Bound Water The 1H, 13C, 15N, 17O and 31P NMR spectra of (PNP)[Ln(Pc2?)2] and (TDOA)[Ln(Pc2?)2] (Ln = La …? (—Pm) …? Lu); PNP: di(triphenylphosphine)-iminium; TDOA: Tri(n-dodecyl)n-octylammonium dissolved in CD2Cl2 are reported. With the exception of the nitrogen atoms of the cations all light atoms of both homologues complex salt rows have been detected and assigned. Proof of the presence of additional water contained in the (solid) complex salts has been given unambigously. The otherwise strong Fermi contact interactions diminuish rapidly with growing distance from the paramagnetic centre favouring dipolar (pseudo-contact) interactions. As a consequence the mostly element independent paramagnetic shifts of the atoms situated on the periphery of the anion as well as those of the cations and water are determined by the distance factor. Therefore a first glance of the structure of the ion-pair present in solution emerges, in which the water molecule seems to play an important role. 相似文献
14.
The title complexes, the Re(O)L(2)(Solv)(+) complexes (L = hoz, 2-(2'-hydroxyphenyl)-2-oxazoline(-) or thoz, 2-(2'-hydroxyphenyl)-2-thiazoline(-); Solv = H(2)O or CH(3)CN), are effective catalysts for the following fundamental oxo transfer reaction between closed shell molecules: XO + Y --> X + YO. Among suitable oxygen acceptors (Y's) are organic thioethers and phosphines, and among suitable oxo donors (XO's) are pyridine N-oxide (PyO), t-BuOOH, and inorganic oxyanions. One of the remarkable features of these catalysts is their high kinetic competency in effecting perchlorate reduction by pure atom transfer. Oxo transfer to rhenium(V) proceeds cleanly to afford the cationic dioxorhenium(VII) complex Re(O)(2)L(2)(+) in a two-step mechanism, rapid substrate (XO) coordination to give the precursor adduct cis-Re(V)(O)(OX)L(2)(+) followed by oxygen atom transfer (OAT) as the rate determining step. Electronic variations with PyO derivatives demonstrated that electron-withdrawing substituents accelerate the rate of Re(VII)(O)(2)L(2)(+) formation from the precursor adduct cis-Re(V)(O)(OX)L(2)(+). The activation parameters for OAT with picoline N-oxide and chlorate have been measured; the entropic barrier to oxo transfer is essentially zero. The potential energy surface for the reaction of Re(O)(hoz)(2)(OH(2))(+) with PyO was defined, and all pertinent intermediates and transition states along the reaction pathway were located by density functional theory (DFT) calculations (B3LYP/6-31G). In the second half of the catalytic cycle, Re(O)(2)L(2)(+) reacts with oxygen acceptors (Y's) in second-order reactions with associative transition states. The rate of OAT to substrates spans a remarkable range of 0.1-10(6) L mol(-)(1) s(-)(1), and the substrate reactivity order is Ph(3)P > dialkyl sulfides > alkyl aryl sulfides > Ph(2)S approximately DMSO, which demonstrates electrophilic oxo transfer. Competing deactivation and inhibitory pathways as well as their relevant kinetics are also reported. 相似文献
15.
Chakravarthi Simhadri Liting Bi Mathieu L. Lepage Mahdi Takaffoli Zhipeng Pei Stefania F. Musolino Abbas S. Milani Gino A. DiLabio Jeremy E. Wulff 《Chemical science》2021,12(11):4147
Motivated by a desire to develop flexible covalent adhesives that afford some of the same malleability in the adhesive layer as traditional polymer-based adhesives, we designed and synthesized two flexible, highly fluorinated bis-diazirines. Both molecules are shown to function as effective crosslinkers for polymer materials, and to act as strong adhesives when painted between two polymer objects of low surface energy, prior to thermal activation. Data obtained from lap-shear experiments suggests that greater molecular flexibility is correlated with improved mechanical compliance in the adhesive layer.Flexible, highly fluorinated covalent adhesives are synthesized, and are shown to afford comparable C–H insertion efficiency and adhesion strength relative to a rigid analogue, while providing improved mechanical compliance in the adhesion layer. 相似文献
16.
Ison EA Trivedi ER Corbin RA Abu-Omar MM 《Journal of the American Chemical Society》2005,127(44):15374-15375
The rhenium oxo complex [Re(O)(hoz)2][TFPB], 1 (where hoz = 2-(2'-hydroxyphenyl)-2-oxazoline(-) and TFPB = tetrakis(pentafluorophenyl)borate) catalyzes the hydrosilation of aldehydes and ketones under ambient temperature and atmosphere. The major organic product is the protected alcohol as silyl ether. Isolated yields range from 86 to 57%. The reaction requires low catalyst loading (0.1 mol %) and proceeds smoothly in CH2Cl2 as well as neat without solvent. In the latter condition, the catalyst precipitates at the end of reaction, allowing easy separation and catalyst recycling. Re(O)(hoz)(H), 3, was prepared, and its involvement in an ionic hydrosilation mechanism was evaluated. Complex 3 was found to be less hydridic than Et3SiH, refuting its participation in catalysis. A viable mechanism that is consistent with experimental findings, rate measurements, and kinetic isotope effects (Et3SiH/Et3SiD = 1.3 and benzaldehyde-H/benzaldehyde-D = 1.0) is proposed. Organosilane is activated via eta2-coordination to rhenium, and the organic carbonyl adds across the coordinated Si-H bond [2 + 2] to afford the organic reduction product. 相似文献
17.
The linear 3D piezoelasticity theory in conjunction with the versatile transfer matrix approach and the wave equation for the internal acoustic domain are employed for active non-stationary vibroacoustic response control of an arbitrarily thick, tri-laminate, fluid-filled, simply supported, piezocomposite cylindrical tank, excited by arbitrary (non-axisymmetric) time-dependent on-surface mechanical loads. The smart structure is composed of a supporting core layer of functionally graded orthotropic material perfectly bonded to inner and outer spatially distributed radially polarized functionally graded piezoceramic sensor and uniform force actuator (FGPM) layers. Active vibration damping is implemented by transferring the accumulated voltage on the sensor layer to the piezoelectric actuator layer in context of proportional and derivative control laws. Durbin's numerical inverse Laplace transform scheme is utilized to calculate the time response histories of the relevant interface displacement/stress components, center-point acoustic pressure, and actuator voltage, for selected loading configurations (i.e., concentrated step, impulse, and moving external loads). Numerical simulations demonstrate the effectiveness of the adopted distributed sensing/actuation configuration together with the active damping control strategy in suppressing the vibroacoustic response of a three-layered (Ba2NaNb5O15/Al/PZT4) water-filled piezoelastic cylindrical tank. Limiting cases are considered and the validity of results is established by comparison with the available data as well as with the aid of a commercial finite element package. 相似文献
18.
Nader Mansoori Oghaz Behzad Haghighi Mohammad Mehdi Alavianmehr Ebrahim Ghiamati 《Journal of solution chemistry》2013,42(3):544-554
A robust and efficient procedure is presented for calculating the solubility parameter. An analytical equation for internal pressure is proposed. Through a simple relation reported by Verdier and Andersen (fluid phase equilibrium 231: 125–137, 2005), one can easily find the solubility parameter via our analytical equation for the internal pressure. Also, the radial distribution function (RDF) of a Lennard–Jones LJ (12, 6) fluid, proposed by Xu and Hu (fluid phase equilibrium 30: 221–228, 1986), has been employed to calculate the internal pressure of normal alkanes from methane to decane. Their solubility parameters were evaluated according to the calculated values of the internal pressure. A comparison between the experimental and the estimated values demonstrated a very good agreement between them. 相似文献
19.
A facile, one-pot synthesis of new phenanthridine derivatives by a three-component reaction between phenantridine, dialkyl acetylenedicarboxylates(DAADs), and aromatic aldehydes is described. The reaction is characterized by mild conditions, high selectivity, and tolerance to various functional groups. 相似文献
20.
Structural Chemistry - In this work, the hydrogenation of acetylene on the Pd2/g-C3N4 catalyst is investigated by the density functional theory (DFT) and quantum theory of atoms in molecules... 相似文献