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1.
《Soils and Foundations》2022,62(2):101106
This study investigates three aspects of the dynamic response of earth-core rockfill dams (ECRDs) under earthquake loadings, including induced shear strain, increased fundamental period, and shear modulus reduction. A database of the recorded ground motions of ECRD cases in Japan is analyzed to carry out this study. The required response parameters as mentioned above are extracted by analyzing the acceleration time histories recorded at the dams’ crests and foundations. Subsequently, statistical analyses are performed to achieve the objectives of this study. A graph is developed describing the change in the dam’s fundamental period with the induced shear strain, and it is observed that the increase of the dam’s period is dependent on the increase in the shear strain levels. A relationship is established to estimate the anticipated levels of shear strain from the intensity measure (IM) of the earthquake signals. In the proposed predictive relationship, a new IM is used that can adequately characterize the severity of an earthquake. Finally, a curve and a range are suggested for the average shear modulus degradation of the ECRD’s core materials. The presented empirical graphs and relationships in this study are valuable tools to obtain an appropriate perception of dams’ nonlinear behaviour under strong earthquake excitations.  相似文献   
2.
《Soils and Foundations》2022,62(3):101159
Suffusion erosion, characterized as the selective detachment and transportation of finer particles by seepage flow, is hazardous to the stability and serviceability of geotechnical structures. The removal of finer particles deteriorates the structure and fabric of the soil, leading to the degradation of its mechanical properties. Studies into the effects of suffusion on mechanical behavior have so far produced disparate results depending on the pre-erosion relative density of the specimens tested. To investigate this issue, small cyclic and monotonic loading tests were performed on intact and eroded gap-graded silty sand specimens in three dispersed density states, using a triaxial cell modified for the purpose of erosion. The variation of Young's modulus showed an inverse relationship with the pre-erosion density of the specimen, as the small strain stiffness decreased in the dense cases and increased in the loose cases. Conversely, Poisson's ratio increased in value as suffusion progressed regardless of the initial density of the specimens. In the contractive phase of monotonic loading, the densification of the coarse soil skeleton by the downward seepage flow resulted in a decrease in contractiveness and an increase in secant stiffness. In the dilative phase, the increase in porosity by the erosion of finer particles reduced the dilatancy and peak strength of the specimens. The results suggest that the pre-suffusion density determines the primary locus of affected mechanical behavior in triaxial compression, which shifts from the contractive phase to the dilative phase with the increase in pre-suffusion density. The critical state strength, inferred using stress–dilatancy theory, was largely unaffected by the erosion of finer particles. As the results indicate, pre-erosion density may be of practical significance in assessing the vulnerability to deterioration and collapse of geotechnical formations and structures subjected to suffusion erosion.  相似文献   
3.
《Soils and Foundations》2022,62(6):101246
This study analyzed the effect of different treatment methods in enzyme-induced carbonate precipitation (EICP) on the mechanical properties of soil. Soybean crude urease was used to catalyze the precipitation of calcium carbonate (CaCO3). A multiple-phase method was proposed and further compared with commonly practiced EICP treatment methods (including the one-phase method, two-phase method, and premix-and-compact method) from the aspects of chemical conversion efficiency, CaCO3 precipitation distribution, permeability, and unconfined compressive strength. Based on the findings, the characteristics of each method were further discussed and summarized. Although the enzymatic CaCO3 precipitation generated from all the treatment methods could potentiate the soil strength to a great or less degree, using the proposed multiple-phase method could bring about a high chemical conversion efficiency, uniform distribution of CaCO3 as well as preferable permeability retention. In addition, the multiple-phase method could significantly improve the efficiency of urease usage.  相似文献   
4.
To investigate the influence of the addition of Pr–Ga alloys on magnetic properties and morphology of materials, the hot-deformed PrNd-Fe-B magnets were prepared by the addition of Pr–Ga alloys using a dual-alloys diffusion. The room-temperature coercivity of the hot-deformed PrNd-Fe-B magnets increases substantially from 1.68 to 2.34 T, while the remanence decreases from 1.42 to 1.24 T, by the addition of 5 wt% Pr–Ga alloys. Moreover, the thermal stability of coercivity improves from ?0.46%/oC to ?0.42%/oC. Two types of grain boundary phases (PrNd-rich and PrNd-Ga-rich) are generated at grain boundaries by microstructural analysis, resulting in the decrease of Fe element concentration from more than 60% to about 10% at grain boundaries. The decrease of ferromagnetic element concentration at grain boundaries and the refinement of grain are considered to be the main reasons for the improvement of coercivity and thermal stability.  相似文献   
5.
New energy vehicles and offshore wind power industries have a high demand for sintered Nd–Fe–B magnets with high intrinsic coercivity and high corrosion resistance. In this study, the magnetic properties, anticorrosion properties, and microstructure of Nd–Fe–B sintered magnets with the intergranular addition of low-melting-point eutectic Tb68Ni32 alloy powders were investigated. The aim is to determine if the addition of Tb68Ni32 can improve these properties. A low melting-point eutectic alloy Tb68Ni32 powders was prepared as a grain boundary additive and blended with the master alloy powders prior to sintering. The coercivity of the resultant magnets gradually increases from 1468 to 2151 kA/m by adding increasing amounts of Tb68Ni32. At the same time, the remanence first increases and then slightly decreases. After studying the microstructure and elemental composition of the Tb68Ni32 added magnets, it is found that the significant increase in coercivity and the negligible reduction in remanence is due to densification, improved grain orientation, a uniform and continuous boundary phase distribution, as well as the generation of a (Nd,Pr,Tb)2Fe14B “core–shell” structure surrounding the main-phase grain. Moreover, the corrosion resistance of the magnet is greatly improved owing to the enhancement of electrochemical stability, as well as the optimization of the distribution and morphology of the intergranular phase.  相似文献   
6.
To upgrade the electric properties of lead-free piezoceramics, (1–x)(Ba0.98Ca0.02Ti0.94Sn0.04Zr0.02)O3-xY2O3 (abbreviated as (1–x)BCTSZ-xY, x = 0 mol%, 0.02 mol%, 0.04 mol%, 0.06 mol%, 0.08 mol% and 0.1 mol%) ceramics were successfully synthesized by traditional solid-state sintering method. The phase structure and microstructure of ceramics were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and piezoresponse force microscopyeramics (PFM). The electric properties of ceramics were researched through piezoelectric, dielectric and ferroelectric test instruments. The results show that all samples have pure perovskite structure and favorable electric properties. The optimal electric properties which especially include superior ferroelectric properties are gained when Y2O3 content is 0.06 mol% (d33 = 419 pC/N, kp = 52%, Tc = 89.5 °C, εr = 26900, tanδ = 2.86%, Pr = 14.41 μC/cm2, Ec = 1.8 kV/cm). Moreover, the temperature-dependent dielectricity of samples shows apparent relaxor behavior under different frequencies. The Curie–Weiss law further proves that all samples are typical relaxor ferroelectrics, and the relaxor degree of samples decreases with increase of Y2O3 content. In conclusion, Y2O3 plays a significant role in enhancing electric properties of BCTSZ ceramics.  相似文献   
7.
Low cost and high abundance rare earth elements Y and Ce have attracted tremendous interests of the industrial and scientific societies for fabricating the highly cost-performance efficient rare earth permanent magnets. However, the effect of separate replacement of Nd by Y or Ce on the performances of NdFeB-type magnet under the same atomic ratio and preparation conditions is still unclear. In this work, we systematically investigated the magnetic properties, thermal stabilities and service performances of (Nd0.8Y0.2)13.80FebalAl0.24Cu0.1B6.04 (atomic fraction, denoted as 20Y) and (Nd0.8Ce0.2)13.80FebalAl0.24Cu0.1B6.04 (atomic fraction, denoted as 20Ce) magnets. The results demonstrate that the μ0Mr, μ0Hc and (BH)max of 20Y magnet are respectively 1.325 T, 1.173 T and 343.467 kJ/m3, which are comprehensively higher than those of 20Ce magnet (μ0Mr = 1.310 T, μ0Hc = 0.948 T, (BH)max = 321.105 kJ/m3). Moreover, the 20Y magnet has higher thermal stability compared with 20Ce magnet which is favorable for the magnetic performances at elevated temperatures. The investigation of microstructure and elemental distribution indicates that the excellent magnetic performances of NdY-Fe-B magnet can be attributed not only to the preferable intrinsic properties 4πMs, Ha and Tc of Y2Fe14B, but also to the in-situ core–shell structure of the 2:14:1 matrix phase grain with Y-rich core and Nd-rich shell, along with the thicker grain boundary layer between the adjacent matrix phase grains in NdY-Fe-B magnet. Furthermore, the 20Y magnet exhibits better mechanical property and higher corrosion resistance than 20Ce magnet, which are helpful for prolonging the service life of the magnet in practical application.  相似文献   
8.
丁琴  陶明  李响 《黄金科学技术》2022,30(2):243-253
混凝土是巷道支护过程中的重要建筑材料,然而混凝土在巷道施工中常常出现质量问题,为了不影响正常生产,需要对其进行修补。地聚合物混凝土凝结时间快,早期强度高,界面结合能力强,耐高温性和抗冻性强,耐腐蚀性良好,具有用作修补材料的潜力。以粉煤灰和矿粉为原料,Na2SiO3溶液和NaOH为碱激发剂制备地聚合物胶砂,研究不同的碱激发剂模数(1.0、1.2、1.4)和掺量(10%、15%、20%)对不同龄期胶砂力学性能的影响。结果表明:当碱激发剂模数为1.2,碱掺量为15%时,胶砂强度达到最大值。设计正交试验,研究了不同水胶比(0.45、0.50、0.55)、粉煤灰掺量(30%、50%、70%)和砂率(30%、35%、40%)对不同龄期地聚合物混凝土的工作性能和力学性能的影响。结果表明:粉煤灰掺量对抗压强度影响最为显著,水胶比次之,而砂率对强度发展几乎没有影响。最优的配合比为水胶比为0.50,粉煤灰掺量为50%,砂率为35%。  相似文献   
9.
胡波  刘伟  杨仲田 《辐射防护》2022,42(4):345-353
为了研究γ辐射和热同时作用对膨润土的影响,以高庙子改性钠基膨润土为研究对象,开展了90℃热作用下、不同剂量率和不同累积剂量的γ辐射老化试验。结果表明:γ辐射和90℃热同时作用引起了膨润土物理化学性质和微观结构的变化。在老化作用后,膨润土的吸水率、pH值、阳离子交换容量、层荷以及蒙脱石001晶面方向的微晶尺寸均减小,比参考样分别降低了(最大减幅)18.4%、7.8%、3.4%、2.9%和15.6%,且表现出剂量率效应;老化作用对膨润土的矿物成分及含量影响较小。在高放废物地质处置的工程屏障设计和安全评价中,应考虑膨润土性质变化的影响因素。  相似文献   
10.
随着对氡气危害认识的加深,花岗岩作为生产、生活上接触较多的天然辐射来源,其氡析出特征对人居环境的辐射影响得到广泛关注。本文从岩石的原生特性和次生变化两方面对花岗岩的氡析出进行文献综述,发现花岗岩氡析出与岩石化学成分、矿物成分和成因类型等原生特性以及次生风化和蚀变导致的放射性核素分布、矿物颗粒大小以及岩石微裂隙等因素密切相关。研究表明,铀镭活度与花岗岩氡析出表现出线性相关,但受铀赋存矿物类型的影响,矿物成分的具体影响还需进一步研究,可能与其构造背景或者物质来源有关。岩石次生变化对花岗岩氡析出的影响主要表现为风化和蚀变使得放射性核素迁移到颗粒表面和岩石裂隙等有利于氡析出的位置,而颗粒变小比表面积增大以及岩石内表面积和孔隙率增加使得铀镭发生富集和逃逸,从而最终促进岩石氡的析出。岩石原生特性和次生变化对花岗岩的氡析出起着重要的影响作用,铀镭活度可以作为花岗岩氡析出率潜力的预测指标,而对于矿物成分和岩石的次生变化则是研究花岗岩氡析出的重要潜在因素。故此,未来需要系统研究并定量描述岩石化学、矿物成分和次生变化,并据此建立合理有效的岩石氡析出模型,帮助更全面地掌握岩石中氡析出规律,为地下工程及人居环境的氡防护提供理论依据。  相似文献   
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