全文获取类型
收费全文 | 1399篇 |
免费 | 159篇 |
国内免费 | 114篇 |
专业分类
电工技术 | 45篇 |
综合类 | 118篇 |
化学工业 | 89篇 |
金属工艺 | 157篇 |
机械仪表 | 177篇 |
建筑科学 | 351篇 |
矿业工程 | 37篇 |
能源动力 | 34篇 |
轻工业 | 12篇 |
水利工程 | 34篇 |
石油天然气 | 47篇 |
武器工业 | 10篇 |
无线电 | 29篇 |
一般工业技术 | 427篇 |
冶金工业 | 43篇 |
原子能技术 | 25篇 |
自动化技术 | 37篇 |
出版年
2024年 | 4篇 |
2023年 | 13篇 |
2022年 | 33篇 |
2021年 | 38篇 |
2020年 | 48篇 |
2019年 | 55篇 |
2018年 | 44篇 |
2017年 | 62篇 |
2016年 | 52篇 |
2015年 | 68篇 |
2014年 | 56篇 |
2013年 | 83篇 |
2012年 | 81篇 |
2011年 | 84篇 |
2010年 | 80篇 |
2009年 | 87篇 |
2008年 | 98篇 |
2007年 | 96篇 |
2006年 | 76篇 |
2005年 | 62篇 |
2004年 | 59篇 |
2003年 | 54篇 |
2002年 | 38篇 |
2001年 | 42篇 |
2000年 | 32篇 |
1999年 | 31篇 |
1998年 | 25篇 |
1997年 | 20篇 |
1996年 | 21篇 |
1995年 | 17篇 |
1994年 | 10篇 |
1993年 | 19篇 |
1992年 | 15篇 |
1991年 | 14篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 10篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1980年 | 3篇 |
1979年 | 2篇 |
排序方式: 共有1672条查询结果,搜索用时 15 毫秒
81.
82.
海上稠油热采开发过程中,通常采用蒸汽吞吐的方式进行原油开采。为满足稠油热采长效密封要求,研制了HPHT-215型热采防砂封隔器。封隔器胶筒采用特制的氟硅基复合材料+玻璃纤维网结构,并开展了材料性能评价测试。通过有限元分析和室内胶筒组合测试,对胶筒材料和组合结构进行了评价优化。室内全尺寸整机测试表明:封隔器能够满足耐温350 ℃、耐压21 MPa密封性能要求,并开展了高低温多轮次密封性能评价测试。该型热采防砂封隔器的研制成功,为海上稠油蒸汽吞吐多轮次开发提供了保障,具有广泛的应用前景。 相似文献
83.
针对焊缝和母材蠕变性能不相同的带焊缝CT试样,提出了一个等效均质材料模型,建立了焊缝中心裂纹、焊缝界面裂纹和非对称焊缝裂纹情况下由试验数据确定C*参量的修正式。采用ABAQUS软件进行了带焊缝CT试样C*参量的有限元分析。有限元数值解与修正式的预测值比较表明:与均质材料CT试样相比,低匹配焊缝会导致CT试样的hw因子增大,高匹配焊缝会导致hw因子值降低,采用ASTM E1457提供的公式在低匹配情况下会过低估算C*参量,在高匹配情况下会过高估算C*参量。无论是低匹配(M<1)焊缝还是高匹配(M >1)焊缝,修正后CT试样的C*参量计算式都可给出与有限元解非常接近的估算结果,可用于焊缝蠕变裂纹行为预测。 相似文献
84.
A full-scale, self-consistent, non-linear, large-signal model of double-drift hetero-structure IMPATT diode with general doping profile is derived. This newly developed model, for the first time, has been used to analyze the large-signal characteristics of hexagonal SiC-based double-drift IMPATT diode. Considering the fabrication feasibility, the authors have studied the large-signal characteristics of Si/SiC-based hetero-structure devices. Under small-voltage modulation (~ 2%, i.e. small-signal conditions) results are in good agreement with calculations done using a linearised small-signal model. The large-signal values of the diode's negative conductance (5 × 106S/m2), susceptance (10.4 × 107 S/m2}), average breakdown voltage (207.6 V), and power generating efficiency (15%, RF power: 25.0 W at 94 GHz) are obtained as a function of oscillation amplitude (50% of DC breakdown voltage) for a fixed average current density. The large-signal calculations exhibit power and efficiency saturation for large-signal (> 50%) voltage modulation and thereafter decrease gradually with further increasing voltage-modulation. This generalized large-signal formulation is applicable for all types of IMPATT structures with distributed and narrow avalanche zones. The simulator is made more realistic by incorporating the space-charge effects, realistic field and temperature dependent material parameters in Si and SiC. The electric field snap-shots and the large-signal impedance and admittance of the diode with current excitation are expressed in closed loop form. This study will act as a guide for researchers to fabricate a high-power Si/SiC-based IMPATT for possible application in high-power MM-wave communication systems. 相似文献
85.
本文建立了一个测定动态弹塑性断裂韧性JId的方法。该方法利用改进的Hopkinson压杆加载Charpy冲击试样,利用压杆上应变片记录的入射应力波和反射应力波,由一维应力波理论得到试样所受的载荷和加载点位移。在建立的裂纹尖端张开位移COD和裂纹扩展量Δa的关系中,令Δa=0,可得到裂纹起裂时的临界(COD)c从而确定裂纹的动态起裂点。与其它方法相比,本文的方法不需要昂贵的仪器来测试动态断裂参数;不需将应变片贴在试样上确定起裂时间,所以该方法可在较高或较低的温度下使用;在动态弹塑性断裂韧性JId的计算中,考虑了材料的动态应力—应变行为,使测得的JId值能更好地反映材料在应力波载荷作用下的动态断裂性能。 相似文献
86.
The microstructure of a composite coating system, which was composed of an inner layer of Fe-Cr-Al and an outer layer of aluminum, was studied after it was respectively oxidized and sulfurdized at elevated temperatures. Apart from the Al2O3 scale formed on the surface, the microstructure of the composite coatings exposed at 900℃ in air for 4h was a three-layer structure. The first layer consisted of a solid solution of Cr and Fe in α aluminum and an intermetallic compound FeAl3, while the second layer was a single phase of the aluminide and the third layer still remained the same appearance as the original Fe-Cr-Al coating.The microstructural observation of the specimen tested at 850-900 ℃ at low oxygen pressure and high sulfur pressure for 576h revealed that the surface coatings of the specimen had transformed into a duplex structure containing an outer layer and a thicker aluminide layer beneath. X-ray diffraction results showed that the out layer was composed of Al2S3 and Al2O3 and that AlCrFe2 was the main phase composition of the aluminide layer, with a few of Al2S3 and Al2O3 accompanied. 相似文献
87.
辛雁清 《中国水能及电气化》2015,(7)
世界各国混凝土抗压强度的试验标准各不相同,同样的混凝土,得出的抗压强度试验值不同。在国际技术交流中,为保持使用数据的一致性,必须研究混凝土圆柱体试件与立方体试件所测得的抗压强度值的关系。本文介绍了混凝土圆柱体试件与立方体试件的强度比的影响因素、转换系数与转换公式,供同行遇到类似问题时参考。 相似文献
88.
结合工程实例,从试验检测的角度,分析了普通混凝土配合比设计、试件取样及其现场强度检测方法取舍等方面存在的问题与所应采取的基本措施. 相似文献
89.
Yui Tanaka Tadao Nakagomi Itaru Suzuki Kou Matoba Keiji Murayama 《Welding International》2013,27(6):422-430
We conducted the welding experiment using three kinds of test piece, actual size, diaphragm and butt joint. Then, we examined the influence on strength, cooling time and carbon equivalent of weld metal by welding conditions on the different test pieces. We calculated an estimate of cooling time and chemical components. Consequently, we concluded that the strength of weld metal can be estimated by heat input, interpass temperature, carbon equivarent of welding wire and shape of test piece. 相似文献
90.
Charpy impact tests were conducted at different temperatures and loading rates. Temperature dependences of the crack initiation
and propagation energies were determined for carbon steel 45, steels St. 3 and 15Kh2NMFA from the load-time curves obtained
with due account of the impact test results. The effect of the loading rate on the temperature dependence of the impact toughness
was analyzed within the range from 1 to 4.4 m/s.
__________
Translated from Problemy Prochnosti, No. 1, pp. 29–34, January–February, 2009. 相似文献