全文获取类型
收费全文 | 1881篇 |
免费 | 158篇 |
国内免费 | 50篇 |
专业分类
电工技术 | 75篇 |
综合类 | 312篇 |
化学工业 | 134篇 |
金属工艺 | 35篇 |
机械仪表 | 108篇 |
建筑科学 | 341篇 |
矿业工程 | 71篇 |
能源动力 | 36篇 |
轻工业 | 158篇 |
水利工程 | 105篇 |
石油天然气 | 117篇 |
武器工业 | 7篇 |
无线电 | 75篇 |
一般工业技术 | 146篇 |
冶金工业 | 114篇 |
原子能技术 | 104篇 |
自动化技术 | 151篇 |
出版年
2024年 | 7篇 |
2023年 | 29篇 |
2022年 | 41篇 |
2021年 | 69篇 |
2020年 | 76篇 |
2019年 | 45篇 |
2018年 | 48篇 |
2017年 | 46篇 |
2016年 | 69篇 |
2015年 | 78篇 |
2014年 | 149篇 |
2013年 | 216篇 |
2012年 | 147篇 |
2011年 | 128篇 |
2010年 | 130篇 |
2009年 | 99篇 |
2008年 | 87篇 |
2007年 | 89篇 |
2006年 | 91篇 |
2005年 | 65篇 |
2004年 | 61篇 |
2003年 | 60篇 |
2002年 | 32篇 |
2001年 | 39篇 |
2000年 | 32篇 |
1999年 | 23篇 |
1998年 | 18篇 |
1997年 | 12篇 |
1996年 | 14篇 |
1995年 | 9篇 |
1994年 | 13篇 |
1993年 | 4篇 |
1992年 | 13篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1971年 | 2篇 |
1966年 | 2篇 |
1962年 | 1篇 |
1961年 | 2篇 |
1960年 | 8篇 |
1956年 | 2篇 |
1955年 | 1篇 |
排序方式: 共有2089条查询结果,搜索用时 312 毫秒
71.
Competitiveness and an Emerging Sector: The Russian Software Industry and its Global Linkages 总被引:1,自引:0,他引:1
This paper analyzes the Russian software industry in the context of trade in information technology services. We assess Russia's underlying sources of competitive edge in software, such as its scientific establishments, education system, diaspora and low costs, and identify the institutional impediments to growth. A survey reveals that foreign outsourcing contracts, a high value-added niche and high education levels characterize Russia's small, privately held software firms. A comparison with the Indian software industry underscores the structural differences in outsourcing relationships developed by the two countries and emphasizes that national advantages are complex amalgamations of many factors and need to be overtly marketed. Beyond the resources that give comparative and competitive advantage to a transitioning economy, a critical role is played by powerful industry organizations and by non-market state institutions that can level the economic field and inject credibility into market structures. 相似文献
72.
针对挤扩多级支盘桩相对于普通等截面直孔灌注桩具有较高承载力和较低沉降量的特性,采用自平衡静载荷试验方法,对浙江湖州市某工程同一场地中的挤扩多支盘桩与普通等截面直孔灌注桩进行极限承载力的对比试验研究.工程试验结果表明,在同等工程地质条件下挤扩多支盘桩与普通直孔灌注桩相比,其极限抗压承载力和极限抗拔承栽力都较大提高,每立方米混凝土的抗压承载力提高达75.3%以上,而混凝土的用量却少41.9%;单方极限抗拔承载力提高118.9%以上,而挤扩多支盘桩的混凝土用量比等少44.1%以上,且沉降曲线较缓,因此能获得较好的经济效益.该工程试验对这种新型桩的承载理论研究和类似工程实践具有客观的参考价值和借鉴意义. 相似文献
73.
Comparative optimism has been studied extensively in adults and is a significant component of social- cognitive models about health. In contrast, little is known about comparative optimism in children or about the wider social- cognitive processes that underpin their health-related behavior. This study investigated comparative optimism for health- and nonhealth-related topics in 101 children 8 or 9 years of age, the youngest ages that have been investigated so far. Children were shown to be unrealistically optimistic for health and nonhealth events. The implications of these findings for understanding comparative optimism in children are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
74.
Safety-critical systems typically operate in unpredictable environments. Requirements for safety and reliability are in conflict with those for real-time responsiveness. Due to unpredictable environmental needs there is no static trade-off between measures to accommodate the conflicting objectives. Instead every feature or operating system service has to be adaptive. Finally, for any design problem, there cannot be any closed-form (formal) approach taking care at the same time of (external) time constraints or deadlines, and synchronization requirements in distributed design. The reason is that these two aspects are causally independent. - In this situation we worked out a heuristic experimental, performance-driven and performance-based methodology that allows in an educated way to start with a coarse system model, with accurate logical expectations regarding its behavior. Through experiments these expectations are validated. If they are found to successfully stand the tests extended expectations and model features are generated for refining the previous design as well as its performance criteria. The refinement is done in such a way that the previous experimental configurations are extreme model cases or data profiles which both logically and experimentally are to reproduce the behavior of the previous modeling step. Thus the novel performance aspects or tendencies could then unambiguously be attributed to the influences of the refined model features. We termed this methodology Incremental Experimentation. As a general methodology it relies on a principle of comparative performance studies rather than on realistic data for narrow application ranges. The paper describes how we applied a 5-step design and refinement procedure for developing, analyzing, and evaluating our distributed operating system MELODY that exhibits novel services for supporting real-time and safety-critical applications in unpredictable environments. Experimental set-ups and theme-related findings are discussed in particular. 相似文献
75.
蔡卫红 《长沙通信职业技术学院学报》2004,3(4):31-34
文章从全球3G三大主流技术标准各自特点入手,分析了各技术标准的优点及劣势,并就我国国情现状简要分析了中国各电信运营商今后对3G的选择。 相似文献
76.
扭轮摩擦传动静力学分析 总被引:3,自引:1,他引:3
讨论了扭轮摩擦传动机构稳定运行的力学条件,扭轮所受驱动力和扭轮轴线之间的夹角.驱动力矩机构轴向栽荷与扭轮和传动轴间正压力的关系.通过分析得出了驱动力矩、扭轮所受的来自于传动轴圆周切向驱动力主要取决于扭轮与传动轴间的正压力,扭轮所受驱动力的方向和扭轮轴轴线的夹角随着扭轮与传动轴间正压力和传动轴的轴向栽荷的变化而变化的结论. 相似文献
77.
蛋白质结构预测方法的研究进展 总被引:11,自引:0,他引:11
殷志祥 《计算机工程与应用》2004,40(20):54-57
目前,在蛋白质结构预测方面,人们努力发展新的方法,该文主要介绍了蛋白质结构预测的方法和进展。详细地综述了几种方法,并简单地介绍了蛋白质结构预测的几个不同阶段,并提出了在蛋白质结构预测方面存在的一些困难。 相似文献
78.
结合某70 m高混凝土双曲薄拱坝排沙孔进口检修闸门更换的方案比选,详细对比了放空水库方案与水下更换方案的优缺点。对比发现,两方案均不可行。放空水库方案主要是因为非技术方面的原因无法采用,水下浮体门封堵方案则存在一系列风险和限制条件,不适宜在本工程中采用。因此,下一步应加强水下修补技术的研究。 相似文献
79.
空气质量中二氧化硫、二氧化氮、可吸入颗粒物三种污染因子用连续采样-实验室分析法与空气质量自动监测系统两种方法进行比对实验并进行原因分析。 相似文献
80.
Using detailed micro-level survey data for three advanced European welfare-state economies (Germany, Netherlands and UK), our analyses suggest a fairly common hierarchy to homeownership, according to partnership status, exists. In all three countries, a variety of interrelated factors appear to encourage greater propensities for homeownership amongst co-residential households (married/cohabiting), as compared to single-person households. However, important macro-contextual differences do appear to play a significant role in mediating the magnitude of difference within this hierarchy. For instance, in Germany the importance of marriage as a predictor of homeownership is found to be particularly strong, with married couples having far higher propensities for homeownership, even when compared to non-married cohabiters. In the Netherlands and UK, where an emphasis on traditional family and marriage is less pronounced, and where homeownership is generally more popular and accessible, the differentiation between married/unmarried partners is greatly reduced. Furthermore, we find no evidence to suggest that living-apart-together partners are more/less likely to own their home than singles. 相似文献