全文获取类型
收费全文 | 342941篇 |
免费 | 28833篇 |
国内免费 | 18464篇 |
专业分类
电工技术 | 22022篇 |
技术理论 | 56篇 |
综合类 | 44900篇 |
化学工业 | 37424篇 |
金属工艺 | 13127篇 |
机械仪表 | 20473篇 |
建筑科学 | 45496篇 |
矿业工程 | 20028篇 |
能源动力 | 11836篇 |
轻工业 | 18548篇 |
水利工程 | 16634篇 |
石油天然气 | 18852篇 |
武器工业 | 3613篇 |
无线电 | 22261篇 |
一般工业技术 | 26571篇 |
冶金工业 | 19289篇 |
原子能技术 | 3701篇 |
自动化技术 | 45407篇 |
出版年
2024年 | 1121篇 |
2023年 | 3612篇 |
2022年 | 6692篇 |
2021年 | 8187篇 |
2020年 | 8809篇 |
2019年 | 7403篇 |
2018年 | 7120篇 |
2017年 | 8514篇 |
2016年 | 9879篇 |
2015年 | 10882篇 |
2014年 | 19505篇 |
2013年 | 18574篇 |
2012年 | 23275篇 |
2011年 | 24767篇 |
2010年 | 19374篇 |
2009年 | 19963篇 |
2008年 | 18645篇 |
2007年 | 23962篇 |
2006年 | 22732篇 |
2005年 | 19779篇 |
2004年 | 16907篇 |
2003年 | 14920篇 |
2002年 | 12448篇 |
2001年 | 10515篇 |
2000年 | 8903篇 |
1999年 | 7330篇 |
1998年 | 5629篇 |
1997年 | 4918篇 |
1996年 | 4407篇 |
1995年 | 3803篇 |
1994年 | 3383篇 |
1993年 | 2469篇 |
1992年 | 2194篇 |
1991年 | 1654篇 |
1990年 | 1427篇 |
1989年 | 1280篇 |
1988年 | 996篇 |
1987年 | 684篇 |
1986年 | 542篇 |
1985年 | 453篇 |
1984年 | 404篇 |
1983年 | 300篇 |
1982年 | 280篇 |
1981年 | 221篇 |
1980年 | 178篇 |
1979年 | 156篇 |
1978年 | 89篇 |
1977年 | 96篇 |
1976年 | 65篇 |
1959年 | 66篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
《Calphad》2020
This publication contains the thermodynamic results received by the drop calorimetry method. The experiments were conducted for four different cross sections, at the temperature of 1080 K. The investigated alloys were as follows: (Ga0.75Li0.25)1-xGex, (Ge0.50Li0.50)1-xGax, (Ga0.50Li0.50)1-xGex, (Ga0.25Li0.75)1-xGex. The mixing enthalpy changes measured for all four cross sections of the Ga-Ge-Li system are characterized by negative deviations from the ideal solutions. The Muggianu model with the ternary interaction parameters was applied to elaborate the experimental data of the mixing enthalpy change with the use of the optimized thermodynamic parameters of the binary systems available in the literature. 相似文献
82.
This paper presents an analytical solution to the non-uniform pressure on thick-walled cylinder. The formulation is based on the linear elasticity theory (plain strain) and stress function method. As an example, the proposed solution is used to model the stress distribution due to non-uniform steel reinforcement corrosion in concrete. The model is formulated considering different scenarios of corrosion pressure distribution. It is validated against the finite element model for different cases of non-uniform pressure distributions. The results show that the corrosion-induced cracks are likely to start just beyond the anodic zone. This is confirmed by the experimental tests on concrete cylinder exposed to non-uniform accelerated corrosion of steel reinforcement. The model can be effectively used to calculate the distribution of corrosion-induced stresses in concrete. 相似文献
83.
通过分析A公司在研发项目范围管理中所存在问题,提出研发项目范围管理的方法及其在C产品的应用实例,通过运用研发项目范围管理的工具和方法,改善产品开发流程,从而缩短新产品开发周期,提高响应市场的速度,并提高企业研发项目的管理能力。 相似文献
85.
Social media-based screening is a well-known practice to both recruiters and job seekers. Little is known, however, about how job seekers present themselves on social media, i.e. ‘self-disclosure’, for employment purposes. This study builds on the theories of hyperpersonal computer-mediated communication, self-efficacy and social exchange to examine job seekers’ professional online image concerns, social media self-efficacy, and perceptions of social media effectiveness in the job search as predictors of inappropriate and career-oriented self-disclosures on these media. Findings from a sample of 3374 Italian respondents showed that career-oriented self-disclosure was predicted by all three factors, whereas inappropriate self-disclosure was only predicted by social media self-efficacy. Furthermore, the relationship between professional online image concerns and inappropriate self-disclosure was moderated by age, education and work experience, but not by gender. Theoretical and practical implications are discussed, and directions for future research are suggested. 相似文献
86.
《International Journal of Hydrogen Energy》2021,46(58):30061-30078
A uniform solid product layer normally assumed in the shrinking-core model cannot predict the kinetic transition behavior of the H2 adsorption reactions. In this study, the concept of a uniform solid product layer has been replaced by that of the inward growth of solid products on the solid surface. A rate equation is established to calculate the inward growth of the solid product and was implemented into the shrinking-core model to calculate the H2 adsorption kinetics for various shapes of Mg-based materials. The prediction accuracy of the developed model is verified from the detailed experimental data. To account for the external gas diffusion around the particle and the intraparticle gas diffusion, an analytical equation is derived using the Thiele modulus method. This model can be used to analyze various kinetic aspects and to analyze the effect of change in the particle microstructure on intraparticle diffusion. 相似文献
87.
Non-convex of an optimal power dispatch problem makes it difficult to guarantee the global optimum. This paper presents a convex relaxation approach, called the Moment Semidefinite Programming (MSDP) method, to facilitate the search for deterministic global optimal solutions. The method employs a sequence of moments, which can linearize polynomial functions and construct positive semidefinite moment matrices, to form an SDP convex relaxation for power dispatch problems. In particular, the rank of the moment matrix is used as a sufficient condition to ensure the global optimality. The same condition can also be leveraged to estimate the number of global optimal solution(s). This method is effectively applied to {0,1}-economic dispatch (ED) problems and optimal power flow (OPF) problems. Simulation results showed that the MSDP method is capable of solving {0,1}-ED problems with integer values directly, and is able to identify if more than one global optimal solutions exist. In additional, the method can obtain rank-1 moment matrices for OPF’s counterexamples of existing SDP method, this ensures the global solution and overcomes the problem that existing SDP method cannot meet the rank-1 condition sometimes. 相似文献
88.
Salman M.A. Salman 《国际水资源开发杂志》2015,31(1):4-16
The United Nations Watercourses Convention entered into force on 17 August 2014, following a long and complex journey that dates back to 1970 when the UN referred the matter to its legal arm, the International Law Commission. This article follows the Convention through that long and turbulent road, examines its main provisions and analyses the reasons for the delay of its entry into force. It concludes by answering the question of why entry into force of the Convention should indeed matter. 相似文献
89.
90.
The effect of charge on the dihydrogen storage capacity of Sc2–C6H6 has been investigated at B3LYP-D3/6-311G(d,p) level. The neutral system Sc2–C6H6 can store 8H2 with gravimetric density of 8.76 wt %, and one H2 dissociates and bonds atomically on the scandium atom. The adsorption of 8H2 on Sc2–C6H6 is energetically favorable below 155 K. The atom-centered density matrix propagation (ADMP) molecular dynamics simulations show that Sc2–C6H6 can adsorb 3H2 within 1000 fs at 300K. Compared with Sc2–C6H6, the charged systems can adsorb more hydrogen molecules with higher gravimetric density, and all the H2 are adsorbed in the molecular form. The gravimetric densities of Sc2–C6H6+ and Sc2–C6H62+ are 9.75 and 10.71 wt%. Moreover, the maximum adsorption of charged systems are favorable in wider temperature range. Most importantly, the ADMP-MD simulations indicate that Sc2–C6H62+ can adsorb 6 hydrogen molecules within 1000 fs at 300K. It can be found that the gravimetric density (6.72 wt%) of Sc2–C6H62+ still exceeds the target of US Department of Energy (DOE) under ambient conditions. 相似文献