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101.
《Electroanalysis》2004,16(12):1051-1058
The voltammetric behavior of α‐ketoglutarate (α‐KG) at the hanging mercury drop electrode (HMDE) has been investigated in acetate buffer solution. Under the optimum experimental conditions (pH 4.5, 0.2 M NaAc‐HAc buffer solution), a sensitive reductive wave of α‐KG was obtained by linear scan voltammetry (LSV) and the peak potential was ?1.18 V (vs. SCE), which was an irreversible adsorption wave. The kinetic parameters of the electrode process were α=0.3 and ks=0.72 1/s. There was a linear relationship between peak current ip, α‐KG and α‐KG concentration in the range of 2×10?6–8×10?4 M α‐KG. The detection limit was 8×10?7 M and the relative standard deviation was 2.0% (Cα‐KG=8×10?4 M, n=10). Applications of the reductive wave of α‐KG for practical analysis were addressed as follows: (1) It can be used for the quantitative analysis of α‐KG in biological samples and the results agree well with those obtained from the established ultraviolet spectrophotometric method. (2) Utilizing the complexing effect between α‐KG and aluminum, a linear relationship holds between the decrease of peak current of α‐KG Δip and the added Al concentration Cequation/tex2gif-inf-5.gif in the range of 5.0×10?6–2.5×10?4 M. The detection limit was 2.2×10?6 M and the relative standard deviation was 3.1% (Cequation/tex2gif-inf-6.gif=4×10?5 M, n=10). It was successfully applied to the detection of aluminum in water and synthetic biological samples with satisfactory results, which were consistent with those of ICP‐AES. (3) It was also applied to study the effect of AlIII on the glutamate dehydrogenase (GDH) activity in the catalytically reaction of α‐KG+NH +NADH?L ‐glutamate+NAD++H2O by differential pulse polarography (DPP) technique. By monitoring DPP reductive currents of NAD+ and α‐KG, an elementary important result was found that Al could greatly affect the activity of GDH. This study could be attributed to intrinsic understanding of the aluminum's toxicity in enzyme reaction processes. 相似文献
102.
103.
Shengzhao Zhang Minghui Ye Yufei Zhang Yongchao Tang Xiaoqing Liu Cheng Chao Li 《Advanced functional materials》2023,33(22):2208230
Despite the merits of high specific capacity, low cost, and high safety, the practical application of aqueous Zn metal batteries (AZMBs) is plagued by the dendritic growth and corrosion reaction of Zn metal anodes. To solve these issues, a Zn3(PO4)2·4H2O protective layer is in-situ constructed on Zn foil (Zn@ZnPO) by a simple hydrothermal method, avoiding the traditional slurry-casting process. The insulating and conformable ZnPO layer improves the wettability of Zn@ZnPO and aqueous electrolyte via decreasing the contact angle to 11.7o. Compared with bare Zn, the Zn@ZnPO possesses a lower desolvation activation energy of 35.25 kJ mol-1, indicating that the ZnPO fasters the desolvation of hydrated Zn2+ ions and thereby ameliorates their transport dynamics. Micro-morphology and structural characterization show that there are no dendrites forming on the post-cycling Zn@ZnPO anodes, and the interfacial ZnPO layer remains almost identical before and after cycles. It can be explained that the electrochemically stable ZnPO layer acts as an ionic modulator to enable the homogeneous distribution of Zn2+ ions, inhibiting the growth of Zn dendrites. Benefiting from these advantages, the Zn@ZnPO based symmetric and full cells deliver highly reversible Zn plating/stripping behavior and long cycling lifespans. 相似文献
104.
Kehayias JJ 《Analytical and bioanalytical chemistry》2004,379(2):188-191
Body composition has become the main outcome of many nutritional intervention studies including osteoporosis, malnutrition, obesity, AIDS, and aging. Traditional indirect body composition methods developed with healthy young adults do not apply to the elderly or diseased. Fast neutron activation (for N and P) and neutron inelastic scattering (for C and O) are used to assess in vivo elements characteristic of specific body compartments. Non-bone phosphorus for muscle is measured by the 31P(n,)28Al reaction, and nitrogen for protein via the 14N(n,2n)13N fast neutron reaction. Inelastic neutron scattering is used to measure total body carbon and oxygen. Body fat is derived from carbon after correcting for contributions from protein, bone, and glycogen. Carbon-to-oxygen ratio (C/O) is used to measure the distribution of fat and lean tissue in the body and to monitor small changes of lean mass. A sealed, D–T neutron generator is used for the production of fast neutrons. Carbon and oxygen mass and their ratio are measured in vivo at a radiation exposure of less than 0.06 mSv. Gamma-ray spectra are collected using large BGO detectors and analyzed for the 4.43 MeV state of carbon and 6.13 MeV state of oxygen, simultaneously with the irradiation. P and N analysis by delayed fast neutron activation is performed by transferring the patient to a shielded room equipped with an array of NaI(Tl) detectors. A combination of measurements makes possible the assessment of the quality of fat-free mass. The neutron generator system is used to evaluate the efficacy of new treatments, to study mechanisms of lean tissue depletion with aging, and to investigate methods for preserving function and quality of life in the elderly. It is also used as a reference method for the validation of portable instruments of nutritional assessment. 相似文献
105.
Rosario De Lisi Mario Goffredi Vincenzo Turco Liveri 《Journal of solution chemistry》1981,10(5):351-356
The conductances of dilute aqueous solutions of KCl, KBr, and KI have been measured over the temperature range 2 to 8°C and have been analyzed by the Fuoss-Hsia equation. The ionic Walden products at infinite dilution have been discussed in terms of local viscosity. The temperature dependence of these products suggest that near the temperature of maximum density of water, the structure-breaking ability of these ions changes in a regular way. 相似文献
106.
Wet oxidation of BPL porous carbon by H2O2 and HNO3 changes the pore structure and also increases the concentration of surface oxides. KOH uptake is increased by oxidation and is seen to be dependent on KOH concentration and to a lesser extent on inert electrolyte concentration. Enthalpy of immersion measurements have allowed the estimation of the enthalpy of hydration of the surface oxides and the enthalpy of neutralization of the easily accessible acid oxides. 相似文献
107.
Barral L. Cano J. López J. López-Bueno I. Nogueira P. Ramírez C. Abad M. J. 《Journal of Thermal Analysis and Calorimetry》1999,55(1):37-45
A study of an epoxy-cycloaliphatic amine system has been realized using a thermogravimetric technique (TG). Isothermal and
non-isothermal (dynamic) methods were employed to determine the kinetic data of this system.
Five methods were used for determining the activation energies of this system in the dynamic heating experiments. In two of
them (Flynn-Wall-Ozawa, and Kissinger) it is not necessary to have a prior knowledge of the reaction mechanism of the degradation
behaviour for this system. In the other ones (Coats and Redfern, Horowitz and Metzger, and Van Krevelen et al.) it is necessary
to know this reaction mechanism, besides Criado et al. method was used for determining it.
The results have shown that good agreement between the activation energies obtained from all methods can be achieved if it
is assumed that the degradation behaviour of this system is of sigmoidal-rate type.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
108.
Rosenberg Edward Freeman William Carlos Zinnia Hardcastle Kenneth Yong Jin Yoo Milone Luciano Gobetto Roberto 《Journal of Cluster Science》1992,3(4):439-457
The general relationships between trinuclear cluster reactivity and the ligand dynamical processes in these systems are explored. Three specific mechanistic studies are presented: (1) the rate and stereochemistry of ligand addition to 3-imidoyl complexes, (2) the factors influencing the rate of carbon-hydrogen bond activation in 3-alkyne complexes, and (3) the origin of anomalously large kinetic deuterium isotope effect in metal to ligand and ligand to metal hydrogen transfer in trinuclear and binuclear complexes. In all three cases, the current state of the mechanistic studies are summarized and the possible rate of specific ligand dynamical processes in controlling the mechanism are put forth. 相似文献
109.
Takaya Matsumoto 《Catalysis Surveys from Asia》2007,11(1-2):31-48
In this article, two kinds of our transition metal-catalyzed olefin arylations are summarized and discussed. The first one
is Ir-catalyzed novel anti-Markovnikov hydroarylation of olefins with benzene. Using this reaction catalyzed by [Ir(μ-acac-O,O′,C3)(acac-O,O′)(acac-C3)]2 (acac = acetylacetonato), 1, straight-chain alkylarenes, which were not obtainable by the conventional Friedel-Crafts aromatic alkylation with olefins,
were able to be successfully synthesized directly from arenes and olefins with the higher selectivity than that of branched
alkylarenes. This is the first efficient catalyst which shows the desirable high regioselectivity. The reaction of benzene
with propylene gave n-propylbenzene and cumene in 61% and 39% selectivities, respectively, and the reaction of benzene and styrene afforded 1,2-diphenylethane
in 98% selectivity. The reaction of alkylarene and olefin showed meta and para orientations. A wide range of olefins and arenes
can be employed for the synthesis of alkylarenes. The mechanism of the reaction involves C–H bond activation of benzene by
Ir center to form Ir–phenyl species. The second reaction is Rh-catalyzed oxidative arylation of ethylene with benzene to directly
produce styrene, namely one-step synthesis of styrene. The reaction of benzene with ethylene catalyzed by Rh(ppy)2(OAc) (ppyH = 2-phenylpyridine, OAc = acetate), 3 with Cu oxidizing agent gave styrene and vinyl acetate in 77% and 23% selectivities, respectively, in contrast to those by
Pd(OAc)2, 47% of styrene and 53% of vinyl acetate. The mechanism of the reaction involves Rh-mediated C–H bond activation of benzene,
which appears to be a rate-determining step. Furthermore, Rh complexes in a Rh(I) oxidation state at the beginning of the
reaction work as catalysts for the reaction by addition of acacH and O2 without any oxidizing agent, like Cu salt. 相似文献
110.
水煤气变换反应的微观动力学分析──Cu基催化剂上H_2S中毒失活原因的 Monte Carlo 模拟研究 总被引:1,自引:0,他引:1
用BOCMP方法及MonteCarlo模拟技术,对H2S导致Cu基催化剂失活的原因进行了计算分析。研究结果表明,当原料气中存在H2S时,WGS反应的活化能明显高于无H2S时的活化能,随着表面H2S浓度的增大(θ=0,0.10,0.25),反应的活化能也逐渐变大(其大小比为1∶1.34∶3.3),究其原因可归结为H2S的存在使得反应物分子的吸附热减小,从而使H2O的解离吸附(WGS反应的速控步骤)活化能增大。 相似文献