全文获取类型
收费全文 | 6118篇 |
免费 | 724篇 |
国内免费 | 362篇 |
学科分类
工业技术 | 7204篇 |
出版年
2024年 | 24篇 |
2023年 | 132篇 |
2022年 | 263篇 |
2021年 | 300篇 |
2020年 | 270篇 |
2019年 | 176篇 |
2018年 | 162篇 |
2017年 | 191篇 |
2016年 | 195篇 |
2015年 | 215篇 |
2014年 | 566篇 |
2013年 | 374篇 |
2012年 | 429篇 |
2011年 | 565篇 |
2010年 | 409篇 |
2009年 | 446篇 |
2008年 | 392篇 |
2007年 | 451篇 |
2006年 | 402篇 |
2005年 | 294篇 |
2004年 | 230篇 |
2003年 | 209篇 |
2002年 | 143篇 |
2001年 | 132篇 |
2000年 | 68篇 |
1999年 | 48篇 |
1998年 | 25篇 |
1997年 | 19篇 |
1996年 | 8篇 |
1995年 | 9篇 |
1994年 | 3篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 11篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1982年 | 1篇 |
1979年 | 1篇 |
1972年 | 1篇 |
1966年 | 1篇 |
1965年 | 3篇 |
排序方式: 共有7204条查询结果,搜索用时 15 毫秒
1.
2.
3.
价值观的传播是一个缓慢的过程,在当前工业文明向生态文明过渡的时期,如何有效地提升民众的生态意识是值得探讨的问题。以生态审美意识传播为切入点,通过了解国内外主流的室内环境生态评估指标体系的前后变化,总结当前室内环境生态评估的变化趋势及其主要特征;从指标体系的变化中分析生态审美价值观的渗透方式,探讨当代室内环境生态评估对生态审美价值观传播的促进作用。最后,通过实验设定针对室内传统营造技艺应用的评估工具,并且在评估工具的使用过程中展示传播的模式与效用,通过评估反馈再一次验证室内环境生态评估对生态审美价值观的正向传播作用。 相似文献
4.
5.
介绍了我国流域生态需水研究现状,在对流域生态环境需水计算的前提条件进行阐述的基础上,根据生态需水的水文学原理以及生态系统学原理,从8个方面提出了流域生态环境需水的计算方法,以确定整个流域的生态环境需水量,从而合理量化生态需水总量,达到水资源优化配置的目的. 相似文献
6.
上海市水环境生态安全评价 总被引:3,自引:0,他引:3
从“状态—压力—响应”指标框架体系出发,针对上海市水环境生态系统的现状特点,从时间变化和空间对比分析角度分别建立了上海市水环境生态安全评价指标体系;利用标准化和变异系数法确定各指标的标准化值和权重,采用综合指数评价法得到安全评价的综合指数值。在此基础上采用等级划分法,建立起综合指数值与生态安全评判的等级关系。各指标层的变化趋势揭示了上海市水环境生态安全的现状和发展趋势,即中心城区的水环境生态安全等级普遍低于郊区;在年际变化上,状态指标层评价值呈下降趋势,需要持续保护水环境生态系统;而压力和响应指标层评价值不断上升,保证了总体的良性发展趋势。 相似文献
7.
McWayne Christine M.; Fantuzzo John W.; McDermott Paul A. 《Canadian Metallurgical Quarterly》2004,40(4):633
The present concurrent study combined developmental and ecological considerations to examine the unique contribution of multiple preschool competencies to an indicator of early academic success. Participants included 195 Head Start children from 32 classrooms representative of a large, urban Head Start program. Dimensional (variable-centered) analyses revealed 3 distinct classroom competency dimensions (i.e., General Classroom Competencies, Specific Approaches to Learning, and Interpersonal Classroom Behavioral Problems). The first 2 of these dimensions were found to be uniquely associated with early academic success. Findings from typological (person-centered) analyses supported the dimensional findings. Typological analyses revealed 7 profiles of classroom competency distinguished by high scores on the dimensions of General Competencies and Approaches to Learning, and these profiles were found to relate differentially to the indicator of early academic success. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
8.
9.
10.
Modelling the effects of dam removal on migratory walleye (Sander vitreus) early life‐history stages
Many dams in the USA have outlived their intended purpose and an increasing number are being considered for removal. Yet, quantitative studies of the potential physical, biological and ecological responses are needed to assess dam removal decisions. In this paper, the responses of migratory walleye (Sander vitreus) to increased spawning habitat availability as a result of dam removal was studied by comparing scenarios with and without a high‐head dam in the Sandusky River (Ohio), a major tributary to Lake Erie. A conceptual, ecological model was proposed to define the relationship between hydrodynamics and walleye spawning, egg hatching, larval drift and survival. A mathematical, ecological model of the early life‐history stages was then developed and coupled with time series of depth and velocity predictions over the spawning grounds from a 1‐D hydrodynamic model. Model simulations were run for 1984–1993 for both the with‐ and without‐dam scenarios to assess the potential benefit of dam removal. The simulation results demonstrated that velocity, depth and water temperature are major factors influencing adult walleye spawning success. Without the dam, 10 times the amount of spawning habitat would be available for walleye to spawn. This increase in spawning habitat area resulted in up to five times the total egg deposition and seven times the larval output to the nursing grounds, based on the assumption that 5% of the walleye population of Lake Erie migrated up the Sandusky River to spawn. We concluded that the spawning habitat in the current condition (with the dam) is limiting and additional spawning habitat upstream could significantly increase the number of larval walleye drifting to Lake Erie. The model sensitivity analysis showed that the number of walleye migrating up the river in spring is the dominant factor for larval recruitment to the lake. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献