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151.
Nikolay Tyutyulkov Ivo Kanev Oskar Polansky Jürgen Fabian 《Theoretical chemistry accounts》1977,46(3):191-203
The analysis of experimental data for singlet transitions (E
n) of even polyenes (I), cations (II) and anions (III) of odd polyenes show that for infinite chains E
(I)/E
(II)=E
(I)/E
(III) = 2:1. It is shown that the energy gap is equal for the three systems. In cases (II) and (III) there is a level (NBMO) in the gap which is vacant in (II) and occupied in (III). That is why the first optical transition in (II) and (III) depends on the semiwidth of the gap. 相似文献
152.
我们利用Born-Mayer-Huggins相互作用势函数对(KF)N(N=108,256,500和864)团簇进行了分子动力学(MD)模拟。为了避免周期性边界条件对相变、成核和重结晶的干扰作用,对体系采用了自由边界。基于MD模拟结果,对团簇的熔化温度、熔化焓、扩散系数、成核速率、固液界面自由能、临界核大小等进行了计算和讨论。在对(KF)864双晶团簇的热退火模拟中,观察到了固态的重结晶和晶粒的生长。经典的成核理论成功地解释了(KF)864双晶团簇的重结晶MD模拟结果。 相似文献
153.
Preparation, 19F NMR Spectroscopic Evidence and Study of the Formation of Metal-Mixed Cluster Anions [(Mo6?nWnCl )F ]2?, n = 0?6 The complete system of metal-mixed octahedral cluster ions [(Mo6?nWnCl)F]2?, n = 0?6, is prepared by tempering Mo powder with WCl6 at 600°C. A mixture containing inclusively the geometric isomers (n = 2, 3, 4) all ten possible species is transferred into the tetra-n-butylammonium salts (TBA)2[(Mo6?nWnCl)F]. In the 19F nmr spectrum the 24 expected signals are observed, assigned on the basis of their chemical shifts, multiplicities and intensities, and confirmed by a 2D-19F-19F COSY spectrum. From the integrated intensities the distribution of the different components is derived revealing a non-statistical formation, in that isomers with Mo…?Mo or W…?W atoms in trans-positions in comparision to those with mixed Mo…?W axes are favoured, and that especially the homoleptic compounds Mo6 and W6 are present to an over-average extent. Evaluation of 19F chemical shifts reveals that F bound to W which is in antipodal position to Mo resonates at higher field compared to F bound to W in a W…?W arrangement, caused by an increased shielding, which is synonymous to a positive antipodal-effect by Mo. Vice versa F bound to Mo with an antipodal W resonates at lower field compared with F bound to Mo in an Mo…?Mo arrangement caused by an increased deshielding and synonymous a negative antipodal-effect by W. The chemical shifts, resulting from antipodal-effects, are different for the compounds within the [(Mo6?nWnCl)F]2? - system. The difference of the antipodal effect of successive substitution products results in characteristic values designated as antipodal shift constants, depending on the kind of substituents, which is valid for other cluster systems, too. 相似文献
154.
A combined method for determination of the standard enthalpies of formation of nitroform and its salts was proposed. The enthalpies
of dissolution of nitroform and its ammonium, hydrazinium, guanidinium, and potassium salts in water were measured. The enthalpy
of combustion of hydrazinium salt of nitroform was determined by a combustion calorimetry, and its standard enthalpy of formation
was calculated. The enthalpy of formation of trinitromethyl anion in indefinitely diluted aqueous solution −24.94±0.79 kJ
mol−1, was calculated on the basic of the data obtained for enthalpies of formation and dissolution of ammonium and hydrazinium
salts of nitroform. Standard enthalpies of formation of nitroform and its salts were calculated.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2451–2454, December, 1998. 相似文献
155.
H. N. Altshuler L. P. Abramova N. V. Malyshenko G. Yu. Shkurenko E. V. Ostapova 《Russian Chemical Bulletin》2005,54(8):1978-1981
The ion-exchange equilibrium in network polymers obtained from cis-2,8,14,20-tetraphenyl-4,6,10,12,16,18,22,24-octahydroxycalix[4]arene by template synthesis on cations Na+, K+, and Ba2+ as matrices was studied. The selectivity coefficients of ion exchanges Ba2+-H+, Na+-H+, K+-H+, Na+-K+, and Na+-NH4
+ were determined. The template synthesis enhanced the affinity of the polymers to matrix-forming cations by 6–8 kJ mol−1.
__________
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1919–1922, August, 2005. 相似文献
156.
Isao Hasegawa 《Journal of Sol-Gel Science and Technology》1994,2(1-3):127-130
29Si NMR peaks due to species with the double four-membered ring siloxane backbone composed of both Si(O–)4/2 and CH3Si(O–)3/2 units, (CH3)
n
Si8O
20 – n
/(8 – n) –
(n=1–3), formed by co-hydrolysis of tetraethoxysilane and methyltriethoxysilane in the presence of tetramethylammonium ions in methanol have been assigned. It has been found that 29Si NMR peaks due to Si(OSi)3(O–) units shift to lower frequencies by replacement of the adjacent Si(O–)4/2 units by CH3Si(O–)3/2 units, in other words, with increasing m value in Si[OSi(O–)3]3 – m
[OSi(CH3) (O–)2]
m
(O–) (m=0–2). Peaks from CH3
Si(OSi)3 units in the species have also appeared as separated due to the kind of neighbor structural units. On the basis of the assignments, positions of CH3Si(O–)3/2 units in the cubic octameric siloxane framework of (CH3)
n
Si8O
20 – n
/(8 – n) –
(n=2, 3), for both of which three isomers are present, have been estimated. 相似文献
157.
Changmei Sun Rongjun Qu Qiang Xu Chunnuan Ji Yanzhi Sun 《European Polymer Journal》2007,43(4):1501-1509
Two novel chelating resins were prepared by anchoring ethylenediamine to crosslinked polystyrene via a spacer containing sulfide. Their structures were characterized by Fourier transform-infrared spectra (FTIR) and scanning electron microscopy (SEM). Porous structure parameters of the resins were measured by ASAP 2020 using BET and BJH methods. Their adsorption capacities for several heavy metal ions especially Hg2+ were investigated. The results showed that for the two resins, the more N contents did not mean the better adsorption capacity and the saturated adsorption capacity of poly(2-ethylenediamidomercaptomethylstyrene) (PSM-EDA) for Hg2+ could reach to 3.0 mmol/g at room temperature. Isothermal adsorptions of the resins for Hg2+ could be described by Langmuir formula. The adsorption mechanism of the resins for Hg2+, Cu2+ and Ag+ was confirmed by X-ray photoelectron spectroscopy (XPS) and FTIR. 相似文献
158.
Sridharan RajagopalMichael E Brooks Thach-Mien NguyenMichael Novak 《Tetrahedron》2003,59(40):8003-8010
We report the synthesis of N-acetoxy-N-(1-methyl-5H-pyrido[4,5-b]indol-3-yl)acetamide, 7, its N-pivaloyloxy analogue, 9, and improved synthesis of indole-2-acetonitrile, 3 (70% in five steps from indole-2-carboxylic acid), the carcinogenic amine Trp-P-2, 4 (40% from 3), and the nitro compound, 5 (40% from 4 by oxidation with H2O2 using Mo(CO)6 catalyst). In aqueous solution at neutral pH, 7 primarily undergoes C-O bond cleavage to yield the hydroxamic acid, 8, but under the same conditions the sterically hindered 9 decomposes predominately by N-O bond cleavage with a pH independent rate constant that is 7.5-fold smaller than that for 7. In the pH range 0.5-7.0 three different processes for the decomposition of 9 were detected by kinetics. Only the process that dominates at neutral pH generates a nitrenium species that can be trapped by N3−. 相似文献
159.
钾(Ⅰ)(苯并-15-冠-5)新型配合物的合成及性质 总被引:1,自引:0,他引:1
在非水溶剂中合成并-15-冠-5与碘化钾,硫氰化钾及苦味酸钾形成的三种新型固体配合物,并进行了有关物理,化学性质表征,结果表明,钾(Ⅰ)离子不仅易苯并-15-冠-5天成常见的1:2夹心式配合物,而且还能生成稳定的1:1型固体配合物。 相似文献
160.
B. G. Bazarov R. F. Klevtsova A. E. Sarapulova K. N. Fedorov L. A. Glinskaya Zh. G. Bazarova 《Journal of Structural Chemistry》2005,46(4):756-760
Single crystals of triple molybdate of composition 5:1:3 K5Pb0.5Hf1.5(MoO4)6 have been grown and their crystal structure has been solved from X-ray diffraction data (an automated diffractometer X8 APEX, MoK α -radiation, 2173 F(hkl), R = 0.0321). Trigonal unit cell parameters are: a = b = 10.739(2) Å, c = 37.933(9) Å; V = 3789(1) Å3, Z = 6, ρcalc = 4.014 g/cm3, space group \(R\bar 3\). Three-dimensional mixed framework of the structure is formed by two types of MoO4 tetrahedra and Pb and Hf octahedra linking via common O-vertices. Potassium atoms of three types occupy large vacancies in the framework. 相似文献