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811.
A rigorous experimental and numerical assessment is made of the benefits and limits of miniaturization in the Kolsky bar system.
The primary issues that arise in very high strain rate testing (stress equilibration, inertial effects, wave dispersion, friction,
and controllability of deformations) are addressed through experiments coupled with explicit finite element analyses. A miniaturized
Kolsky bar system that includes the input bar is developed, together with the use of the laser occlusive radius detector to
obtain local measurements of specimen strain during the very high rate deformations. It is demonstrated that this miniaturized
Kolsky bar system can be used to provide fully validated results, including the explicit determination of equilibration, over
a very wide range of strain rates (1×103 to 5×104 s−1). The desired high strain rate can be achieved even at low accumulated strains, and the total strain developed can be controlled
very effectively. Specific conditions are developed for determining the range of utility of the technique for a given material.
The technique is applied to the characterization of 6061-T651 aluminum, and the results are compared with the results obtained
using a conventional Kolsky bar. 相似文献
812.
813.
814.
采用电化学阳极氧化技术,以含有NH4F和H2O的甘油溶液为电解液,在宽氧化电压范围(20~100V)下于纯钛表面制备了结构高度有序的TiO2纳米管阵列。利用扫描电子显微镜(SEM)考察了阳极氧化工艺(氧化电压、NH4F浓度、环境温度、水分含量等因素)及退火处理对纳米管形貌的影响;采用X射线衍射分析(XRD)表征了不同氧化电压和退火前后TiO2纳米管阵列的物相;并从电流-时间曲线出发简要地分析了纳米管阵列的形成机理。结果表明,纳米管的内外径和管长随氧化电压的增大而增大;NH4F浓度和环境温度对纳米管形貌有一定的影响;水分含量的多寡决定了能否在高电压下自组装形成纳米管阵列;TiO2纳米管阵列具有良好的热稳定性,管状形貌可以保持到700℃;直接制备的TiO2纳米管阵列均为无定型结构,经450℃退火处理后,无定型的TiO2纳米管转变为锐钛矿相,而600℃退火处理后,部分锐钛矿相转变为金红石相。 相似文献
815.
<正>The chemokine CXCR4 receptor is over-expressed in a wide variety of tumors.In this study,AMD3100,which was a prototype non-peptide antagonist of CXCR4 receptor,was labeled with ~(99m)Tc.~(99m)Tc-AMD3100 was verified by thin layer radio chromatography(TLRC).The tumor-localizing properties of ~(99m)Tc-AMD3100 were evaluated and proved in mice bearing Hep-G2 tumor xenograft.~(99m)Tc-AMD3100 was a promising,novel receptor-specific radiopharmaceutical with potential application in the imaging of human tumors. 相似文献
816.
<正>Chelate tetra(acetylacetonato) tin(Ⅳ) was prepared and used as catalyst for polytrimethylene terephthalate synthesis.It exhibited higher catalytic activity than tetrabutyl titanate,butyltinhydroxide oxide and dibutyltin oxide.Decrease in reaction time, content of terminal carboxyl group,color intensity and increase in intrinsic viscosity were observed.The unique molecular structure can be considered as factor remarkably improving the catalytic activity of tetra(acetylacetonato) tin(Ⅳ). 相似文献
817.
Yang J Tveten EZ Chen D Holmen A 《Langmuir : the ACS journal of surfaces and colloids》2010,26(21):16558-16567
Co/γ-Al(2)O(3) catalysts with particle sizes in the range of 4-15 nm were investigated by isothermal hydrogenation (IH), temperature programmed hydrogenation (TPH), and steady-state isotopic transient kinetic analysis (SSITKA). Kinetic isotope effect experiments were used to probe possible mechanisms on Co/γ-Al(2)O(3) with different particle size. It was found that CO dissociated on Co/γ-Al(2)O(3) catalysts at 210 °C. The total amount of CO(2) formed following the dissociation depends on the cobalt crystal size. O-Co binding energy was found to be highly dependent on the Co metal particle size, whereas similar C-Co binding energy was found on catalysts with different Co particle size. Very strongly bonded carbon and oxygen surface species increased with decreasing particle size and acted as site blocking species in the methanation reaction. SSITKA experiments showed that the intrinsic activity (1/τ(CH(x))) remained constant as the particle size increased from 4 to 15 nm. The number of surface intermediates (N(CH(x))) increased with increasing particle size. The apparent activation energies were found similar for these catalysts, about 85 kJ/mol. D(2)-H(2) switches further confirmed that the particle size did not change the kinetically relevant steps in the reaction. The reactivity of the active sites on the 4 nm particles was the same as those on the 8, 11, and 15 nm particles, and only the number of total available surface active sites was less on the 4 nm particles than on the others. 相似文献
818.
Xinsheng Xu Lixia Jia Lei Shi Xuehan Ji Zhifeng Cui 《Research on Chemical Intermediates》2010,36(3):269-275
Chemically induced dynamic electron polarization (CIDEP) is one of the important research fields of dynamic spin chemistry.
In the present work, with ethylene glycol, 1,2-propanol and their mixtures with different ratios in volume as solvents and
duroquinone as photosensitive molecule, the influence of solvent viscosity on the CIDEP of photolyzed duroquinone radicals
has been studied experimentally. In each solvent, duroquinone neutral radicals are observed. Duroquinone neutral radicals
are generated through hydrogen transfer reaction from hydrogen-donor solvent molecules to excited duroquinone triplet. The
CIDEP mechanism is mainly triplet mechanism. The CIDEP intensity of duroquinone neutral radicals decreases with the increase
in the solvent viscosity, and the variation was rapid in low-viscosity range and slow in high-viscosity range. 相似文献
819.
Wen Wang Jian-Cun Rao Hua Ke Ming Feng Rui-Lin Xia Qing-Chang Meng De-Chang Jia Yu Zhou 《Journal of Sol-Gel Science and Technology》2010,56(1):87-92
We report the independent invention of perovskite ferroelectric nanowires strontium bismuth tantalate (SrBi2Ta2O9, SBT). Electrophoretic sol–gel techniques have been used successfully. The morphology and structures are analyzed via SEM,
TEM and XRD. SBT nanowires and nanoparticles filled template revealed 30 and 40 μm long, respectively. SBT are proved to be
a single phase of orthorhombic perovskite structure. As it indicated, SBT nanowires has been crystallized at 700 °C. To minimize
surface polarity, SBT nanowires oriented preferentially along the growing axis (c axis) by translation and rotation of atomic clusters of SBT. 相似文献
820.
Hongtao Cui Yanyan Jia Wanzhong Ren Wenhua Wang 《Journal of Sol-Gel Science and Technology》2010,55(1):36-40
Nearly monodispersed cobalt ferrite nanoparticles were synthesized by a low temperature sol–gel route using propylene oxide
as a gelation agent. The nanoparticles were obtained by the reaction of FeCl2 and CoCl2 in ethanol solution with propylene oxide to form the sol, followed by the boiling of the sol solution. The unique chemistry
of this procedure allows the formation of highly homogeneous gel intermediate, resulting in the great reducing of crystallization
temperature of ferrites to less than 100 °C without postannealing step. This guarantees the preparation of well defined and
non-aggregated ferrite nanoparticles on an ultra-large scale of about 75 g in a single reaction. This large scale synthesis
strategy offers important advantages over other conventional routes for the preparation of CoFe2O4 nanoparticles, showing the promising application of this route in the industrial production. 相似文献