全文获取类型
收费全文 | 16277篇 |
免费 | 1458篇 |
国内免费 | 635篇 |
学科分类
工业技术 | 18370篇 |
出版年
2024年 | 77篇 |
2023年 | 254篇 |
2022年 | 400篇 |
2021年 | 497篇 |
2020年 | 515篇 |
2019年 | 419篇 |
2018年 | 447篇 |
2017年 | 501篇 |
2016年 | 604篇 |
2015年 | 612篇 |
2014年 | 974篇 |
2013年 | 967篇 |
2012年 | 948篇 |
2011年 | 1207篇 |
2010年 | 886篇 |
2009年 | 997篇 |
2008年 | 868篇 |
2007年 | 1009篇 |
2006年 | 931篇 |
2005年 | 845篇 |
2004年 | 737篇 |
2003年 | 637篇 |
2002年 | 566篇 |
2001年 | 491篇 |
2000年 | 357篇 |
1999年 | 307篇 |
1998年 | 228篇 |
1997年 | 213篇 |
1996年 | 187篇 |
1995年 | 137篇 |
1994年 | 112篇 |
1993年 | 81篇 |
1992年 | 46篇 |
1991年 | 36篇 |
1990年 | 38篇 |
1989年 | 26篇 |
1988年 | 23篇 |
1987年 | 18篇 |
1986年 | 13篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 14篇 |
1982年 | 11篇 |
1980年 | 11篇 |
1966年 | 10篇 |
1965年 | 12篇 |
1964年 | 11篇 |
1963年 | 8篇 |
1959年 | 8篇 |
1957年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
81.
一种基于满意度方法的建筑工程索赔决策模型 总被引:2,自引:0,他引:2
本文在对索赔问题进行全面系统分析基础上,提出一种索赔主体对索赔事件的不确定性分析模型和决策满意度模型,并进一步讨论了索赔主体优选索赔方案作为索赔报告提出的方法。 相似文献
82.
The search for good lineal, or depth-first, spanning trees is an important aspect in the implementation of a wide assortment of graph algorithms. We consider the complexity of findingoptimal lineal spanning trees under various notions of optimality. In particular, we show that several natural problems, such as constructing a shortest or a tallest lineal tree, are NP-hard. We also address the issue of polynomial-time, near-optimization strategies for these difficult problems, showing that efficient absolute approximation algorithms cannot exist unlessP = NP.This author's research was supported in part by the Sandia University Research Program and by the National Science Foundation under Grant M IP-8603879.This author's research was supported in part by the National Science Foundation under Grants ECS-8403859 and MIP-8603879. 相似文献
83.
84.
Behaviors and emotions during specific visits may reveal the interpersonal processes of mother-daughter ties, yet most research uses global assessments of these ties. Forty-eight mother-daughter pairs participated in audiotaped conversations and completed surveys. All mothers were over age 70 and in good health. Daughters tended to take a central role in structuring the conversations. Conversations were characterized by high levels of felt and expressed positive emotions and behaviors for mothers and daughters. Nevertheless, mothers reported more positive and fewer negative emotions, whereas daughters expressed more positive behaviors than did mothers. Mothers' positive feelings and behaviors were associated with daughters'. Finally, mothers' and daughters' emotions and behaviors were associated with their destructive responses to being upset with each other, providing support for the ambivalence perspective of parent-offspring relationships. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
85.
The purpose of this study was to examine predictors and consequences of spouses' involvement in each others' strategies for pursuing important personal goals called life tasks. Husbands and wives within 39 short- and long-term marriages described five life tasks and provided appraisals of whether each was shared with their spouse. Participants later completed 14 consecutive diary entries recording daily life task pursuit strategies, the extent of spouse involvement in each, and measures of positive and negative affect. Results indicated that interdependence in life task appraisals prospectively predicted greater spouse involvement, and greater spouse involvement was associated with more positive affect for that day. Life task appraisals may provide avenues for understanding couples' strategies for dealing with goals or stressors and how those strategies affect mood. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
86.
87.
The environmental and socio‐economic impacts of biomass utilization by co‐firing with brown coal in an existing thermoelectric unit in Greece or through its pure combustion in a new plant were studied and evaluated in this work. The 125 MWe lignite‐fired power plant in Ptolemais Power Station (Western Macedonia) was used as reference system. The environmental benefits of the alternative biomass exploitation options were quantified based on the life cycle assessment methodology, as established by SETAC, while the BIOSEM technique was used to carry out socio‐economic calculations. The obtained results showed clear environmental benefits of both biomass utilization alternatives in comparison with the reference system. In addition, co‐firing biomass with lignite in an existing unit outperforms the combustion of biomass exclusively in a new plant, since it exhibits a better environmental performance and it is a low risk investment with immediate benefits. A biomass combustion unit requires a considerably higher capital investment and its benefits are more evident in the long run. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
88.
A model for building integrated photovoltaic systems has been developed and implemented in a dynamic simulation tool. This tool takes into account the thermal interactions between the PV collector and the building. The influence of the type of integration upon the PV collector efficiency has been evaluated and hybrid PV/air collectors have been studied. An overall efficiency is defined, including the production of electricity and heat. A case study has been performed on two different typical buildings. In the case of a multi-crystalline silicon PV collector integrated on the roof of a single family house located in Paris, the efficiency of unventilated PV modules fixed on the roof is 14%. If the PV collector is used to preheat the ventilation air, the efficiency reaches 20%. A proper building integration also improves the environmental balance of PV technologies over their life cycle. 相似文献
89.
让住户满意的物业管理职能研究 总被引:1,自引:0,他引:1
从使住户满意的角度研究了物业管理中的计划、组织、领导、控制和创新五项职能,以指导物业管理企业提高管理水平和服务质量. 相似文献
90.
A series of polyesters was prepared to evaluate hydrolytic stability as a function of cyclohexyl dibasic acid content. The
three cyclohexyl dibasic acids: 1,2; 1,3; and 1,4 were formulated into polyesters with two glycols. The proportion of cis
and trans isomers was evaluated via 1H NMR. The hydrolytic stability of short chain polyesters was evaluated in an acetone/water mixture which solubilized the
polyesters to mimic oligoester behavior within a thermosetting polyester coating environment. The rate of hydrolysis was monitored
by acid titration and corroborated by GPC. Surprisingly, 1,2-cylohexyl diacid-based polyesters were robust, and 1,3-cyclohexyl
diacid-based polyesters were the most susceptible to hydrolysis. Evidently, a 1,2-anchimeric effect for cyclohexyl dibasic
acid polyesters was not an important consideration, while the 1,3-cyclohexyl ester interaction was. Consequently, an anomeric
effect was proposed.
Presented at the 81st Annual Meeting of the Federation of Societies for Coatings Technology, November 12–14, 2003, in Philadelphia,
PA. 相似文献