全文获取类型
收费全文 | 389784篇 |
免费 | 26332篇 |
国内免费 | 19215篇 |
专业分类
电工技术 | 22950篇 |
技术理论 | 69篇 |
综合类 | 47997篇 |
化学工业 | 46744篇 |
金属工艺 | 16638篇 |
机械仪表 | 19154篇 |
建筑科学 | 47963篇 |
矿业工程 | 18741篇 |
能源动力 | 12090篇 |
轻工业 | 23886篇 |
水利工程 | 17367篇 |
石油天然气 | 18501篇 |
武器工业 | 3413篇 |
无线电 | 25151篇 |
一般工业技术 | 34125篇 |
冶金工业 | 21678篇 |
原子能技术 | 4914篇 |
自动化技术 | 53950篇 |
出版年
2024年 | 1024篇 |
2023年 | 3087篇 |
2022年 | 6198篇 |
2021年 | 7429篇 |
2020年 | 8105篇 |
2019年 | 6653篇 |
2018年 | 6433篇 |
2017年 | 7596篇 |
2016年 | 9514篇 |
2015年 | 11038篇 |
2014年 | 20836篇 |
2013年 | 19912篇 |
2012年 | 23876篇 |
2011年 | 26182篇 |
2010年 | 21227篇 |
2009年 | 23122篇 |
2008年 | 21710篇 |
2007年 | 27233篇 |
2006年 | 25847篇 |
2005年 | 22397篇 |
2004年 | 19165篇 |
2003年 | 17507篇 |
2002年 | 15081篇 |
2001年 | 12394篇 |
2000年 | 11223篇 |
1999年 | 9381篇 |
1998年 | 7298篇 |
1997年 | 6450篇 |
1996年 | 6213篇 |
1995年 | 5630篇 |
1994年 | 5029篇 |
1993年 | 3470篇 |
1992年 | 3221篇 |
1991年 | 2289篇 |
1990年 | 1887篇 |
1989年 | 1653篇 |
1988年 | 1405篇 |
1987年 | 925篇 |
1986年 | 645篇 |
1985年 | 702篇 |
1984年 | 732篇 |
1983年 | 650篇 |
1982年 | 537篇 |
1981年 | 547篇 |
1980年 | 391篇 |
1979年 | 225篇 |
1978年 | 177篇 |
1977年 | 137篇 |
1976年 | 98篇 |
1975年 | 112篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
71.
《Intermetallics》2015
Drop-tube processing was used to rapidly solidify droplets of Ni64.7Fe10Si25.3 and Ni59.7Fe15Si25.3 alloys. In the larger droplets, and therefore at low cooling rates, only two phases, γ-Ni31Si12 and β1-Ni3Si were observed. Conversely, in the smaller droplets, and therefore at higher cooling rates, the metastable phase Ni25Si9 was also observed. The critical cooling rate for the formation of Ni25Si9 was estimated as 5 × 103 K s−1. SEM and TEM analysis reveals three typical microstructures: (I) a regular structure, comprising single-phase γ-Ni31Si12 and a eutectic structure between γ-Ni31Si12 and β1-Ni3Si; (II) a refined lamellar structure with a lamellar spacing <50 nm comprising γ-Ni31Si12 and β1-Ni3Si; (III) an anomalous structure with a matrix of Ni25Si9 and only a very small proportion of a second, and as yet unidentified, phase. These results indicate that there is an extended stability field for Ni25Si9 in the Ni-rich part of the Ni–Fe–Si ternary system in comparison to the Ni–Si binary system. With an increase of cooling rate, an increasing fraction of small droplets experience high undercoolings and, therefore, can be undercooled into the Ni25Si9 stability field forming droplets consisting of only the anomalous structure (III). The Fe atoms are found to occupy different substitutional sites in different phase, i.e. Fe substitutes for Ni in the γ phase and Si in the L12 (β1) phase respectively. 相似文献
72.
Static stresses analysis of carbon nano-tube reinforced composite (CNTRC) cylinder made of poly-vinylidene fluoride (PVDF) is investigated in this study. Non-axisymmetric thermo-mechanical loads are applied on cylinder in presence of uniform longitudinal magnetic field and radial electric field. The surrounded elastic medium is modeled by Pasternak foundation because of its advantages to the Winkler type. Distribution of radial, circumferential and effective stresses, temperature field and electric displacements in CNTRC cylinder are determined based on Mori–Tanaka theory. The detailed parametric study is conducted, focusing on the remarkable effects of magnetic field intensity, elastic medium, angle orientation and volume fraction of carbon nano-tubes (CNTs) on distribution of effective stress. Results demonstrated that fatigue life of CNTRC cylinder will be significantly dependent on magnetic intensity, angle orientation and volume fraction of CNTs. Results of this research can be used for optimum design of thick-walled cylinders under multi-physical fields. 相似文献
73.
A metal matrix composite has been obtained by a novel synthesis route, reacting Al3Ti and graphite at 1000 °C for about 1 min after ball-milling and compaction. The resulting composite is made of an aluminium matrix reinforced by nanometer sized TiC particles (average diameter 70 nm). The average TiC/Al ratio is 34.6 wt.% (22.3 vol.%). The microstructure consists of an intimate mixture of two domains, an unreinforced domain made of the Al solid solution with a low TiC reinforcement content, and a reinforced domain. This composite exhibits uncommon mechanical properties with regard to previous micrometer sized Al–TiC composites and to its high reinforcement volume fraction, with a Young’s modulus of ∼110 GPa, an ultimate tensile strength of about 500 MPa and a maximum elongation of 6%. 相似文献
74.
This paper deals with the investigation of the effect of hygrothermal conditions on the bending of nanoplates using Levy type solution model employing the state-space concept. The nanoplates are assumed to be subjected to a hygrothermal environment. The two-unknown function plate theory is used to derive the governing differential equations on the basis of Eringen's nonlocal elasticity theory. The governing equations contain the small scale effect as well as hygrothermal and mechanical effects. These equations are converted into a set of first-order linear ordinary differential equations with constant coefficients. Analytical solution of bending response for nanoplates under combinations of simply supported, clamped and free boundary conditions is obtained. Comparison of the results with those being in the open literature is made. The influences played by small scale parameter, temperature rise, the degree of moisture concentration, boundary conditions, plate aspect ratio and side-to-thickness ratio are studied. 相似文献
75.
Risk allocation decisions are of critical importance in project management. The present study proposes an explanation for how risk allocation in a contract motivates a contractor to cooperate with a project owner. Theories of risk allocation and trust were used to motivate the research. Using a survey methodology, we collected data concerning 124 construction projects in China. We found that risk allocation influenced the contractor’s role behavior through the contractor’s feeling of being trusted but not the contractor’s trust in the owner. Feeling of being trusted partially mediated the effect of risk allocation on the contractor’s in-role (i.e., contractual) behavior and fully mediated the effect on extra-role behavior. The study introduces a social and psychological view of the impacts of risk allocation to the project and engineering management literature. We contribute to theory by arguing and demonstrating the mediating effect of trust on the relationship between risk allocation and contractor behavior. From a practical standpoint, we conclude that contractual risk allocation has a significant impact on building a trusting relationship between owners and contractors and that contractors who feel trusted perform both contractually mandated actions and actions external to the contract more diligently, resulting in the likelihood of improved outcomes for both parties. 相似文献
76.
77.
78.
基于承包商预期收益不变的不平衡报价模型 总被引:1,自引:0,他引:1
在招标实践中,通常采用最低价中标原则,使得投标人不得不压低其投标价格。基于承包商预期收益不变的不平衡报价模型,是在“工程量清单报价”的条件下,考虑到施工中工程量的变化及施工顺序的影响,体现了资金的时间价值,在保持承包商预期收益不变的前提下,通过调整各分项工程的单价,来降低工程报价,以增加中标机会而建立的。所建立的模型简单,易于操作,并配以具体的工程实例,通过计算机求得其最优解,可供承包商投标报价时参考。 相似文献
79.
80.
大同市节水型社会建设的探讨 总被引:1,自引:0,他引:1
大同市是全国108个比较严重缺水城市之一,人均水资源量不足全国的1/10(全国人均水资源量2231m^3),稍超过全省的1/2(全省人均水资源量388m^3),市中心城区工农业及城市生活用水近20年来靠超采地下水来支撑。文中就大同市水资源供需不平衡的现状,提出大同市节水型社会建设的必要性,及今后水资源开源和节流的措施。 相似文献