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971.
镁合金是实际应用中最轻的金属结构材料,在航天航空、轨道交通、汽车、3C(computer,communication,consumer electronics)产品等领域具有广阔的应用前景。但镁合金材料强度偏低,尤其是高温强度,其抗蠕变性较差;镁合金铸件容易形成缩松和热裂纹,成品率低,镁合金变形件塑性加工条件控制困难,导致组织与力学性能不稳定。介绍了高性能镁合金材料(非稀土镁合金、含稀土镁合金、镁锂合金)及其成形技术(重力铸造、低压铸造、压铸、挤压铸造、半固态成形、塑性成形)的开发现状,综述了其在航天航空领域的应用状况,并展望了今后的发展趋势。 相似文献
972.
王智平 《华北航天工业学院学报》2008,(1):12-14
本文通过查阅国内外几十种板栅合金配方,结合笔者的工作经验,在经过多次试验分析论证的基础上,找出了降低蓄电池水损耗的可行办法。采用本试验合金铸板,延长电池的使用寿命,达到了免维护电池的要求,每年可为生产企业增加可观的经济效益。 相似文献
973.
介绍了低成本、高稳定的固态电压标准器的研制 ,该标准器可取代 0 .0 0 0 5级以下的标准电池 ,具有较高的应用和推广价值。 相似文献
974.
介绍了对LC9板材孔壁采用冷挤压工艺前后的疲劳寿命对比试验情况;论述了孔壁冷挤压强化对疲劳寿命的影响。 相似文献
975.
Surface integrity and fatigue behavior when turning γ-TiAl alloy with optimized PVD-coated carbide inserts 总被引:2,自引:0,他引:2
This paper presents a comprehensive investigation on the effects of tool and turning parameters on surface integrity and fatigue behavior in turning c-Ti Al alloy. The wear of inserts surface, cutting forces, and surface roughness were studied to optimize PVD-coated carbide inserts.Surface topography, residual stresses, microhardness, and microstructure were analyzed to characterize the surfaces layer under different turning parameters. Surface integrity and fatigue life tests of c-Ti Al alloy were conducted under turning and turning-polishing processes. The results show that compared to CNMG120412-MF4, CNMG120408-SM is more suitable because it obtained low cutting force, surface roughness, and tool wear. With increasing the cutting speed and depth, the depths of the compressive residual stress layer, hardening layer, and plastic deformation layer increased. For turning and turning-polishing specimens, the compressive residual stress was relaxed by less than 20%–30% after 10~7 cycles. The fatigue life of a turning-polishing specimen with R_a= 0.15 mm has increased 3 times from that of a turning specimen with R_a= 0.43 mm. 相似文献
976.
P.H. Krisko M. Horstman M.L. Fudge 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(7):1138-1146
In this paper we revisit the 1995 Kaman database of the SOCIT4 fragment characteristics with added analysis of a subset of the cataloged fragments from the test. This database was compiled from the last of a series of four hypervelocity impact tests conducted under a U.S. Department of Defense program in 1991–1992. This test targeted a flight-ready, U.S. Transit navigation satellite, yielding collision fragments in the size regime of sub-millimeter through tens of centimeters. Results in this database were used in the 1998 NASA Standard Breakup Model to represent characteristic length (size) and area-to-mass distributions of fragments smaller than 10 cm. 相似文献
977.
The Hopkinson pressure bar tests for base metal and friction stir jointing(FSJ) jointed region of 7022 a- luminum alloy are carried out at different temperatures and strain rates. The temperature is 30--400 ℃ and the strain rate is 1 200-5 000 s 1. High strain rate for base metal and FSJ jointed region of 7022 aluminum alloy are studied. The corresponding stress-strain curves are obtained. The results show that the flow stresses of base metal and FSJ jointed region of 7022 aluminum alloy decline with the increase of temperature and increase with the in- crease of strain rate. Furthermore, the constitutive equation for base metal and FSJ jointed region of 7022 alumi- num alloy at high temperature and high strain rate is obtained based on Johnson-Cook model. 相似文献
978.
Although the physical organization of spatialinformation clearly influences how it is recognized,recalled, and mentally transformed, few studies haveexplored how different levels of organizationinteract. This study focused on 4- and 6-year-oldchildren's memory for spatial configurations andexamined the relative influence of two levels oforganization: symmetry (vertical, horizontal, or none)and codability (verbal or nonverbal). We predictedthat the influence of symmetry would be lesspronounced among the older children for whom thepatterns were more codable. The results partiallysupported this prediction: Older children'sreconstructions were accurate regardless of patternsymmetry; younger children's reconstructions ofvertically-symmetric patterns were more accurate thantheir reconstructions of horizontally-symmetric andasymmetric patterns. Taken together, the resultsrevealed an interaction between age and symmetry onthe accuracy of children's reconstructions, suggestingthat younger children were more sensitive than olderchildren to differences in pattern symmetry. Thus,different levels of organization may influencechildren's ability to recall spatial information andthe relative influence of these levels may changeduring development. 相似文献
979.
980.