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101.
用量子化学从头算方法(HF/6-31G)和密度泛函理论(DFT)的B3LYP方法,以6-31G标准基组加一个极化函数,对(ClAlNH)n(n=1-10)簇合物的几何构型,电子结构和红外光谱进行了优化,并讨论了聚合反应(ClAlNH)m→(ClAlNH)n的热力学效应,结果表明,(ClAlNH)n系列簇合物的基态稳定结构为Cs(n=1),D2h(n=2),D3h(n=3),Td(n=4),Cs(n=5),D3d(n=6),Cs(n=7),S4(n=8),D3h(n=9),C2h(n=10,n=2,4,6,8,10等偶数对应的(ClAlNH)n簇化合物的结构比n等于奇数量更稳定。 相似文献
102.
A new optical CO2 sensor based on the luminescence intensity change of the europium(III) complex tris(thenoyltrifluoroacetonato) europium(III) dihydrate ([Eu(tta)3]) caused by the absorption change of various pH indicators—thymol blue, phenol red, or cresol red—with CO2 was developed and its CO2 sensing properties were investigated. For all the CO2 sensors using pH indicators the observed luminescence intensity from [Eu(tta)3] at 613 nm increased with increasing CO2 concentration. The linear calibration method based on the plot of (I100–I0)/(I–I0) versus the inverse of CO2 concentration was suggested, where I0 and I100 were luminescence intensities at 613 nm of the CO2 sensor film in 100% nitrogen and 100% gaseous CO2. In all cases the plots showed good linearity and the correlation factors of the plots, r2, were 0.991 for thymol blue, 0.990 for phenol red, and 0.998 for cresol red. The slopes of the plots (A/B) for thymol blue, phenol red, and cresol red were 2.2, 5.2, and 9.0%, respectively. The response times of the CO2 sensor film were 4.0 s for thymol blue, 4.4 s for phenol red, and 8.8 s for cresol red for switching from nitrogen to CO2, and the recovery times of films were 36 s for thymol blue, 39.2 s for phenol red, and 56.6 s for cresol red for switching from CO2 to nitrogen. The signal changes were fully reversible and hysteresis was not observed during the measurements. The highly sensitive CO2 sensor was developed using thymol blue as an indicator for the CO2-sensing probe. 相似文献
103.
Beate Hager Bettina Schwarzinger Heinz Falk 《Monatshefte für Chemie / Chemical Monthly》2006,137(2):163-168
Summary. Two model compounds for the green fluorescent protein chromophore were prepared. One of them incorporates the natural 4-hydroxybenzylidene
group of the natural tyrosin derived chromophore, the other one bears a methyl group instead of the hydroxy group. Whereas
the photochemically prepared (E)-diastereomer of the first compound very effectively reverted thermally (room temperature) to the thermodynamically stable
(Z)-diastereomer, the (E)-diastereomer of the second derivative proved to be stable even at elevated temperatures for more than a day. This finding
can be rationalized by constructing the appropriate resonance structures showing that only in the first case an effective
delocalization enables partial single bond character of the benzylidene double bond. From the standpoint of chemical etiology,
only Nature’s choice of the tyrosin derived chromophore of the green fluorescent protein provides an efficient radiationless
thermal relaxation channel for the unwanted photo-diastereomerization product formed after excitation besides the dominating
fluorescence channel of its chromophore. 相似文献
104.
Michael A. Collins 《Theoretical chemistry accounts》2002,108(6):313-324
This paper reviews the construction of molecular potential-energy surfaces by an interpolation method which has been developed
over the last several years. The method uses ab initio quantum chemistry calculations of the molecular electronic energy in
an automated procedure to construct global potential- energy surfaces which can be used to simulate chemical reactions with
either classical or quantum dynamics. The methodology is explained and several applications are presented to illustrate the
approach.
Received: 22 February 2002 / Accepted: 2 May 2002 / Published online: 6 November 2002
Correspondence to: M. A. Collins e-mail: collins@rsc.anu.edu.au
Acknowledgements. The methods described in this overview are the result of collaborations with former members of my group, in particular with
Josef Ischtwan, Meredith Jordon, Keiran Thompson and Ryan Bettens. I am also indebted for inspiration gained from many discussions
with my colleagues Leo Radom and Donghui Zhang (National University of Singapore). This work has been supported by the Supercomputer
Facility of the Australian National University and the Australian Partnership for Advanced Computing. 相似文献
105.
Verardo G Pagani E Geatti P Martinuzzi P 《Analytical and bioanalytical chemistry》2003,376(5):659-667
The composition of the surface waxes of three apple ( Malus domestica L.) cultivars ("Florina", "Golden B" and "Ozark Gold") has been studied by means of spectroscopic and GC–MS analysis of the class-fractionated mixture of components. Odd n -alkanes, mainly C27 and C29 molecules, are prevalent in the saturated fraction. Small concentrations of alkenes were also found; the C28:1 component is strongly (72%) in excess over the other 1-alkenes. Straight-chain esters (mainly of palmitic acid) of saturated primary alcohols (C18–C30) were also detected; whereas the acyl moiety is made up essentially of an even number of carbons, the alcohol counterpart does not exhibit this characteristic. Aldehydes are present (C20–C30) with the homologue patterns C26–C30 most strongly represented. Straight-chain free secondary alcohols characterize the waxes of "Florina" and "Ozark Gold"; the hydroxy function is located far from the extremity of the carbon framework. Outstanding is the presence of three alcohols with 29 carbon centres. These alcohols are accompanied by free straight-chain primary alcohols, mainly with even-numbered carbon chains in the range C26–C30. Free fatty acids are present; all of have a framework of even-numbered carbon chains mainly in the range C16–C20. C18:1 (oleic acid) is well represented. 相似文献
106.
107.
A.I. Baranov L. Kloo R.A. Lunin B.A. Popovkin 《Journal of solid state chemistry》2004,177(10):3616-3625
A systematic search for mixed low-valence, nickel-tin chalcogenides performed by establishing phase relations in the parts of Ni-Sn-Se and Ni-Sn-Te ternary systems resulted in the discovery of two new compounds, Ni5.62SnSe2 and Ni5.78SnTe2. Single crystals of both compounds were prepared by chemical transport with iodine and crystal structures were determined by single crystal X-ray investigation. The ED patterns for Ni5.78SnTe2 showed the presence of satellite reflections, which indicate a modulated structure with q≈0.4a*. Average crystal structures of both compounds were determined to be of tetragonal symmetry (Sp.gr. I4/mmm, Z=2) with a=3.6890(8) Å, c=18.648(3) Å, Rw=0.0716 and a=3.7680(5) Å, c=19.419(4) Å, Rw=0.0832, correspondingly, and are isostructural to known Ni5.72SbSe2 and Ni5.66SbTe2. Measurements were carried out for both compounds with respect to thermal, electrical and magnetic properties. Ab initio band structure calculations were also performed to take a first glance into the electronic structure of such type compounds. The anisotropy of their band structure was found. Physical property measurements showed both compounds to be the anisotropic metallic conductors and paramagnetics. Calculated difference charge density maps revealed pairwise covalent and multicenter metallic nature of the d-metal—chalcogen and d-metal—p-metal interactions, respectively. 相似文献
108.
《Journal of separation science》2003,26(11):1057-1062
The use of glass fiber as a support material for a surface compound serving to generate gaseous standard mixtures of ethene is described. The technique is based on the process of thermal decomposition of the surface compound in a desorber connected on‐line via a multi‐port valve to the calibrated device. The surface compound undergoes thermal decomposition at 245°C, yielding known amounts of ethene. The method enables on‐line preparation of a standard mixture immediately before the calibration step. Consequently, it can be also applied for the generation of standard mixtures containing volatile, malodorous, unstable, and toxic compounds. 相似文献
109.
Using well-cycled, thin composite graphite electrodes we analyze carefully the limitations of potentiostatic and galvanostatic intermittent titration techniques (PITT and GITT, respectively) for determination of the differential (incremental) intercalation capacitance, Cdif, and the chemical diffusion coefficient, D, of Li ions in these ion-insertion electrodes (IIEs). We demonstrate the superiority of the GITT over PITT to determine these quantities as the former technique allows for a more accurate determination of Cdif and hence D which closely approach to the spinodal domain related to the first-order phase transition during ion-insertion. We show that GITT is also more effective in eliminating the parasitic contributions of background currents to the total measured response. A pronounced difference in the initial, intrinsic kinetics of formation of a new phase in the bulk of the old one has been observed depending on the direction of titration (phases less saturated with Li are formed faster during deintercalation than the Li-rich phases in the course of intercalation). 相似文献
110.
An optical CO2 sensor based on the overlay of the CO2 induced absorbance change of pH indicator dye α-naphtholphthalein in poly(isobutyl methacrylate) (polyIBM) layer with the fluorescence of tetraphenylporphyrin (TPP) in polystyrene layer is developed. The observed luminescence intensity from TPP at 655 nm increased with increasing the CO2 concentration. The ratio I100/I0 value of the sensing film consisting of α-naphtholphthalein in polyIBM and TPP in polystyrene layer, where I0 and I100 represent the detected luminescence intensities from a layer exposed to argon and CO2 saturated conditions, respectively, that the sensitivity of the sensor, is estimated to be 192. The response and recovery times of the sensing film are less than 6.0 s for switching from argon to CO2, and for switching from CO2 to argon. The signal changes are fully reversible and no hysterisis is observed during the measurements. The highly sensitive optical CO2 sensor based on fluorescence intensity changes of TPP due to the absorption change of α-naphtholphthalein in polyIBM layer with CO2 is achieved. 相似文献