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41.
The thread whirling is an efficient and precise machining process for manufacturing of screws. The shaping motion of whirling is complex and difficult to model. In this paper, a novel model basing on equivalent cutting volume is proposed. The cutting force and the chip morphology are investigated to validate the model. The simulation of cutting force is in good agreement with the experimental results with error less than 16.5%. A chip with saw-toothed edges is obtained from simulation and for experimental verification. A case study on the effect of the tool edge geometry on cutting forces is also presented. The simulation results show that the tool edge geometry greatly influences the cutting forces. The tool with round edge is a good choice for reducing the cutting forces. The ratio of ac/Re holds the balance in selecting the parameter of cutting conditions. The model is applicable for the simulation of whirling process and can be used for parameter optimisation of the cutting tool edge. 相似文献
42.
Dr. Lisa C. Kühnel Dr. Bettina M. Nestl Prof. Dr. Bernhard Hauer 《Chembiochem : a European journal of chemical biology》2017,18(22):2222-2225
Squalene–hopene cyclases (SHCs) catalyze the polycyclization of squalene into a mixture of hopene and hopanol. Recently, amino-acid residues lining the catalytic cavity of the SHC from Alicyclobacillus acidocaldarius were replaced by small and large hydrophobic amino acids. The alteration of leucine 607 to phenylalanine resulted in increased enzymatic activity towards the formation of an intermolecular farnesyl–farnesyl ether product from farnesol. Furthermore, the addition of small-chain alcohols acting as nucleophiles led to the formation of non-natural ether-linked terpenoids and, thus, to significant alteration of the product pattern relative to that obtained with the wild type. It is proposed that the mutation of leucine at position 607 may facilitate premature quenching of the intermediate by small alcohol nucleophiles. This mutagenesis-based study opens the field for further intermolecular bond-forming reactions and the generation of non-natural products. 相似文献
43.
The purpose of this study was to develop regression equations to predict manual arm strength for a wide variety of hand locations within the reach envelope. Maximum voluntary manual arm strength was determined from 71 female participants in six exertion directions (superior, inferior, anterior, posterior, medial and lateral), in a total of 28 hand locations. Forces ranged from 51.3 to 164.4 N, and had a pooled coefficient of variation of 29.9%. Across all 168 combinations of hand locations and exertion directions, the multivariate regression equations explained 92.5% of the variance and had a root mean square error (RMSE) of only 6.4 N, using only the anterior, lateral and vertical location of the hand relative to the active shoulder joint as inputs. These equations provide a proof-of-principle for our novel regression approach, and represent a first step towards a more comprehensive equation to estimate maximum acceptable forces for occupational tasks. 相似文献
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Zero-valent iron nanoparticles rapidly aggregate. One of the reasons is magnetic forces among the nanoparticles. Magnetic field around particles is caused by composition of the particles. Their core is formed from zero-valent iron, and shell is a layer of magnetite. The magnetic forces contribute to attractive forces among the nanoparticles and that leads to increasing of aggregation of the nanoparticles. This effect is undesirable for decreasing of remediation properties of iron particles and limited transport possibilities. The aggregation of iron nanoparticles was established for consequent processes: Brownian motion, sedimentation, velocity gradient of fluid around particles and electrostatic forces. In our previous work, an introduction of influence of magnetic forces among particles on the aggregation was presented. These forces have significant impact on the rate of aggregation. In this article, a numerical computation of magnetic forces between an aggregate and a nanoparticle and between two aggregates is shown. It is done for random position of nanoparticles in an aggregate and random or arranged directions of magnetic polarizations and for structured aggregates with arranged vectors of polarizations. Statistical computation by Monte Carlo is done, and range of dominant area of magnetic forces around particles is assessed. 相似文献
46.
钢纤维混凝土密肋复合楼盖将材料的复合与结构的复合有机的结合,具有良好的受力及保温隔热等性能。通过利用非线性有限元方法,对钢纤维密肋复合楼盖结构体系的受力性能进行了全过程分析,并通过改变钢纤维含量进行参数讨论。建模过程中钢纤维的作用主要通过修改混凝土的本构关系及弹性模量等参数来体现,同时不考虑钢纤维与混凝土间的粘结与滑移... 相似文献
47.
Behzad D. Manshadi Anastasios P. Vassilopoulos Julia de Castro Thomas Keller 《Canadian Metallurgical Quarterly》2011,15(5):833-840
Glass-fiber-reinforced polymer (GFRP) cell-core sandwiches are composed of outer GFRP face sheets, a foam core, and a grid of GFRP webs integrated into the core to reinforce the shear load capacity. One of the critical failure modes of cell-core sandwich structures is shear wrinkling, a local buckling failure in the sandwich webs because of shear loading. The shear wrinkling behavior of GFRP laminates with different laminate sequences, stabilized by a polyurethane foam core, was experimentally and numerically investigated. Shear wrinkling was simulated by a biaxial compression–tension setup. The results show that an increasing transverse tension load significantly decreases the wrinkling load. The decreasing effect of tension is explained by the lateral contraction because of Poisson’s effect, which causes an increase in the initial imperfections and subsequent accelerated bending. 相似文献
48.
Jun Wang Zhiqiang Qiao Jinpeng Shen Rui Li Yuntao Yang Guangcheng Yang 《Propellants, Explosives, Pyrotechnics》2015,40(4):514-517
Three‐dimensional nanostructured porous Co3O4 was synthesized on a silicon substrate via a hydrothermal route in conjunction with annealing treatment. The structure and morphology of the obtained Co3O4 samples were systemically examined using field‐emission scanning electron microscopy and X‐ray diffraction. The Co3O4 structures were composed of nanosheets forming a pore‐network architecture that promoted Al penetration into its inner regions during deposition resulting in enhanced interfacial contact area, which significantly improve metastable intermolecular composites (MICs) burning rate and the release of energy. The successfully Co3O4 was used to synthesize Al/Co3O4 based MICs by integration with nano‐Al deposited via thermal evaporation. The heat of reaction of Al/Co3O4, particularly the exothermic reaction before Al melting, was greatly enhanced by the Co3O4 nanostructures. The Al/Co3O4 based MICs were fabricated on a silicon substrate, which is very convenient for integrating MICs with silicon‐based microelectromechanical systems to achieve functional nanoenergetics‐on‐a‐chip. 相似文献
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