全文获取类型
收费全文 | 26470篇 |
免费 | 4182篇 |
国内免费 | 2714篇 |
专业分类
电工技术 | 1269篇 |
技术理论 | 1篇 |
综合类 | 2046篇 |
化学工业 | 2161篇 |
金属工艺 | 840篇 |
机械仪表 | 1173篇 |
建筑科学 | 4307篇 |
矿业工程 | 1973篇 |
能源动力 | 701篇 |
轻工业 | 725篇 |
水利工程 | 864篇 |
石油天然气 | 1854篇 |
武器工业 | 112篇 |
无线电 | 1758篇 |
一般工业技术 | 2302篇 |
冶金工业 | 2446篇 |
原子能技术 | 135篇 |
自动化技术 | 8699篇 |
出版年
2024年 | 417篇 |
2023年 | 1294篇 |
2022年 | 2240篇 |
2021年 | 2146篇 |
2020年 | 1825篇 |
2019年 | 1284篇 |
2018年 | 844篇 |
2017年 | 842篇 |
2016年 | 793篇 |
2015年 | 862篇 |
2014年 | 1408篇 |
2013年 | 1496篇 |
2012年 | 1431篇 |
2011年 | 1725篇 |
2010年 | 1365篇 |
2009年 | 1441篇 |
2008年 | 1280篇 |
2007年 | 1467篇 |
2006年 | 1369篇 |
2005年 | 1239篇 |
2004年 | 931篇 |
2003年 | 858篇 |
2002年 | 723篇 |
2001年 | 569篇 |
2000年 | 526篇 |
1999年 | 476篇 |
1998年 | 508篇 |
1997年 | 311篇 |
1996年 | 262篇 |
1995年 | 180篇 |
1994年 | 181篇 |
1993年 | 140篇 |
1992年 | 133篇 |
1991年 | 121篇 |
1990年 | 118篇 |
1989年 | 67篇 |
1988年 | 64篇 |
1987年 | 49篇 |
1986年 | 68篇 |
1985年 | 78篇 |
1984年 | 51篇 |
1983年 | 47篇 |
1982年 | 31篇 |
1981年 | 17篇 |
1980年 | 23篇 |
1979年 | 17篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1975年 | 5篇 |
1959年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
高边坡深孔预裂爆破是一项对施工质量、安全要求极高的爆破技术, 必须进行科学的爆破技术设计,确定合理的爆破参数;高度重视爆破钻孔工艺、装药工艺、网络工艺以及边坡稳定性地质分析.在洞巴水电站中不允许采用超欠平衡的开挖方法进行施工,利用设计台阶高度,采用深孔预裂爆破对溢洪道高边坡的稳定及开挖平整度进行有效控制,取得良好效果. 相似文献
82.
A finite-difference Total Variation Diminishing (TVD) numerical simulation model for coupling the Reynolds Averaged Navier-Stokes (RANS) equations, pressure-relative continuity equation and various k-ε turbulence models was developed to solve the incompressible flow based on the pseudo-compressibility method. The hyperbolicity of all these equations was studied and the discretization of the fully coupling equations with all the primal variables and source terms were made in this article. Numerical simulation for modeling the flow around a ground-mounted square rib was implemented and validated by comparing with the published wind tunnel experimental data. It is shown that such a numerical simulation method with a proper turbulence model has a very good accuracy to simulate the flow around a surface-mounted rib. It is concluded that the Renormalization Group (RNG) and Chen-Kim k-ε turbulence models have much better ability to predict the characteristics of the vortex structure and flow separation than the standard k-ε model. 相似文献
83.
The reliability of a system is the probability that the system will perform its intended mission under given conditions. This
paper provides an overview of the approaches to reliability modelling and identifies their strengths and weaknesses. The models
discussed include structure models, simple stochastic models and decomposable stochastic models. Ignoring time-dependence,
structure models give reliability as a function of the topological structure of the system. Simple stochastic models make
direct use of the properties of underlying stochastic processes, while decomposable models consider more complex systems and
analyse them through subsystems. Petri nets and dataflow graphs facilitate the analysis of complex systems by providing a
convenient framework for reliability analysis. 相似文献
84.
The mirror effect for word frequency refers to the finding that low-frequency words have higher hit rates and lower false alarm rates than high-frequency words. This result is typically interpreted in terms of conventional signal detection theory (SDT), in which case it indicates that the order of the underlying old item distributions mirrors the order of the new item distributions. However, when viewed in terms of a mixture version of SDT, the order of hits and false alarms does not necessarily imply the same order in the underlying distributions because of possible effects of mixing. A reversal in underlying distributions did not appear for fits of mixture SDT models to data from 4 experiments. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
85.
This paper compares state-space and input–output realizations for nonlinear discrete-time dynamic models. For linear models, these two realizations are essentially equivalent and their structures are closely related, but these statements do not hold for nonlinear models. We illustrate this point with simple, realistic examples for which only one of the two realizations exists or for which both exist but their structures are profoundly different. Overall, the main point of this paper is the importance of the choice of realization in the development of nonlinear dynamic models. 相似文献
86.
87.
地下连续墙在太钢老厂改造工程中的应用 总被引:1,自引:1,他引:0
结合某深基坑支护施工实例 ,介绍了采用多头潜水钻成槽机进行地下连续墙施工的基本原理、工艺流程及注意事项。指出该方案对于在老厂区改造工程狭窄场地条件下 ,解决深基坑施工保护附近建 (构 )筑物安全具有独特的优势 相似文献
88.
阐述了时空效应规律在软土深基坑工程中的运用情况,实践证明,运用时空效应规律,能可靠而合理地利用土体自身在基坑开挖过程中控制土体位移的潜力而达到保护环境的目的。 相似文献
89.
Withdrawal from an escalating-dose, bingelike regimen of cocaine administration in rats produced significantly depressed levels of locomotor activity during the nocturnal portion of the day-night cycle. This effect was observed during the first 48 hrs of testing. Extracellular single-unit recordings of ventral tegmental area (VTA) dopamine (DA) neurons revealed no differences between saline- and cocaine-treated rats with respect to basal firing rates. However, significantly fewer spontaneously active VTA DA neurons were encountered in rats withdrawn from binge cocaine. As with the nocturnal hypoactivity, this effect was observed only during the first 48 hrs of withdrawal. These findings suggest that short-term DA neuron dysfunction during cocaine withdrawal temporally corresponds to behavioral disruptions that are similar to those described in human addicts. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
90.
Argyris G. Kagiannas Thanassis Didis Dimitris Th. Askounis John Psarras 《国际能源研究杂志》2003,27(2):173-186
The needs that an energy supply system must meet are constantly changing, due to technological, social and political reasons. Effective energy planning is a dynamic process that is repeated periodically and adjusts to changing conditions. Energy decision makers and planners are no longer able to rely on inductive decision making since they have to investigate the effect of various decision parameters and possible future changes. To help in this process, models have been developed where estimates of future load growth, candidate power plants, fuels and other key factors can be introduced, from which the planners can evaluate decision parameters and the available alternatives. The paper presents the different methodologies and practices that are used by 11 energy models for energy demand forecasting, supply side management and generation expansion planning, demand side management and integrated resource planning. The paper concludes to the presentation of a strategic appraisal of the examined energy models appropriate for energy planning in Mozambique. Three models are proposed for conducting demand forecasting, generation expansion planning and demand side management. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献