全文获取类型
收费全文 | 1543篇 |
免费 | 91篇 |
国内免费 | 130篇 |
专业分类
电工技术 | 106篇 |
技术理论 | 1篇 |
综合类 | 247篇 |
化学工业 | 70篇 |
金属工艺 | 17篇 |
机械仪表 | 65篇 |
建筑科学 | 121篇 |
矿业工程 | 128篇 |
能源动力 | 28篇 |
轻工业 | 46篇 |
水利工程 | 28篇 |
石油天然气 | 23篇 |
武器工业 | 10篇 |
无线电 | 159篇 |
一般工业技术 | 125篇 |
冶金工业 | 119篇 |
原子能技术 | 3篇 |
自动化技术 | 468篇 |
出版年
2023年 | 18篇 |
2022年 | 17篇 |
2021年 | 27篇 |
2020年 | 26篇 |
2019年 | 22篇 |
2018年 | 22篇 |
2017年 | 34篇 |
2016年 | 41篇 |
2015年 | 36篇 |
2014年 | 72篇 |
2013年 | 94篇 |
2012年 | 94篇 |
2011年 | 147篇 |
2010年 | 124篇 |
2009年 | 102篇 |
2008年 | 86篇 |
2007年 | 130篇 |
2006年 | 84篇 |
2005年 | 108篇 |
2004年 | 96篇 |
2003年 | 64篇 |
2002年 | 56篇 |
2001年 | 46篇 |
2000年 | 37篇 |
1999年 | 29篇 |
1998年 | 15篇 |
1997年 | 16篇 |
1996年 | 15篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 9篇 |
1992年 | 7篇 |
1991年 | 10篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1988年 | 10篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1974年 | 2篇 |
1966年 | 2篇 |
1962年 | 2篇 |
1958年 | 1篇 |
排序方式: 共有1764条查询结果,搜索用时 187 毫秒
71.
长三角城市群的空间组织特征与规划取向探讨——基于企业联系的实证研究 总被引:1,自引:0,他引:1
在“流动空间”及“全球城市区域”等理论概念的指引下,运用城市网络研究方法,对长三角各县市单元以企业分支机构空间数据为支撑的网络联系进行定量分析,从而获得对长三角城市群内部空间组织特征与演变趋势的认知.研究表明,自2001年以来,长三角城市群的空间组织关系呈现出不断强化的网络化特征.在演变进程中,上海在长三角城市群中的核心地位得到了巩固,网络能力不断提升;以上海为中心的跨省域近域都市圈也已形成且不断发育;而南京、杭州作为省会城市在其各自省域范围内的中心功能和核心功能腹地亦很显见.在省会以下层面的地级城市则越来越多地表现出专业化节点的功能特征,其本级城市和直接腹地空间则受到了多个强中心的辐射而同时融入了不同都市圈;总体而言,在市场经济的自组织作用力下,长三角区域空间的网络化格局日趋显著.文章最后基于实证研究的结论,对我国城市群发展规划的要义、趋势和取向做若干探讨. 相似文献
72.
Abdullah Yesil Shahram Minaei 《International Journal of Circuit Theory and Applications》2020,48(11):2023-2038
In this paper, two new complementary metal oxide semiconductor (CMOS) realizations for second-generation voltage conveyor (VCII) are presented. The first proposed VCII has a very simple structure employing only six transistors. The second proposed VCII employs 11 transistors, and none of the transistors at both proposed circuits suffer from the body effect. Small-signal analysis, parasitic elements, and input-referred noise of the proposed VCIIs are given. Moreover, a new active element called voltage controlled second-generation voltage conveyor (VC-VCII) is proposed as dual element of current controlled second-generation current conveyor (CCCII) active element. Its parasitic resistance at the Y terminal can be controlled electronically. Two presented CMOS structures of VCII are worked as VC-VCII with slight modification. Proposed circuits are simulated in Cadence Analog environment using TSMC 0.18-μm process parameters with ±0.9-V supply voltages. Both CMOS structures occupy a small chip area of 276.8 and 271 μm2, respectively. The bandwidth of the current follower stage of the proposed VCIIs is found as 794 MHz, whereas the bandwidth of the voltage follower stage for the first and second proposed VCIIs is found as 2.57 and 1.92 GHz, respectively. As an application example, voltage-mode first-order low-pass filter has been given with its tunable gain by using VC-VCII. 相似文献
73.
Many Dutch ecosystems, whether terrestrial, aquatic or sediment-based, are diffusely polluted by mixtures of contaminants, whose concentrations often exceed regulatory Safe Values or other generic quality criteria. This situation has unclear consequences, especially when local authorities are confronted with such pollution. Water managers are frequently in doubt whether their water systems satisfy the criteria for ‘Good Ecological Status’ as defined in the EU's Water Framework Directive. In case of soils, soil users may wonder whether the soil is ‘fit for use’. In case of nature conservation, the problem is that protected species might suffer from toxic stress. Official regulations in these cases call for appropriate action, but it is unclear whether the diffuse exposure causes adverse effects, and what the action should be. This paper proposes and discusses a site-oriented approach in the risk assessment of diffusely contaminated sites that can be used in addition to the compound-oriented policies from which the abovementioned generic quality criteria were derived. The site-oriented approach can be of help in reducing site-specific risks of diffuse contamination.Reflecting on the results of a large Dutch research effort in systems-oriented ecotoxicological effects, the conclusion is drawn that exposure and effects of diffuse pollution are site-specific in kind and magnitude, determined by the local combination of source-pathway-receptor issues, and often not clearly detectable (though often present). To assist in risk management, higher-tier methods can address various aspects, like addressing local mixture composition, bioavailability, and sensitivity of local species groups. Higher-tier risk assessment methods have as yet been developed mainly for cases of serious contamination, like for pesticide management and Risk-Based Land Management. For diffuse pollution, site-specific information can also be used to obtain site-specific exposure and impact information, while practical and ecology-based approaches can be introduced to obtain an integrated overview of the meaning of site contamination and to derive options for managing and reducing the local risks. These issues are discussed against the background of current major policy shifts, in The Netherlands and elsewhere, from a pollutant-oriented assessment to an additional ecological and site-oriented assessment. The latter is most clearly represented in the Good Ecological Status aim of the EU-Water Framework Directive. The paper assesses, integrates and discusses the results of the Dutch research effort in this policy context. 相似文献
74.
文章阐述了白云鄂博铁矿富钾板岩的几种综合利用的途径,分别探讨了碳酸钠、石灰石烧结法和湿法的酸碱分离方法,以此达到富钾板岩综合利用的目的. 相似文献
75.
本文在深入分析河北省迁安市城市建设和工业快速发展对水资源需求增大现状的基础上,提出该市保护与合理开发利用水资源的若干对策建议:一是依靠科技进步,大力提高水资源利用率,全面建设节水型社会;二是强化政府职能,发挥企业治理水资源污染的积极性和主动性,全面建设环境友好型社会;三是建设生态防洪工程,构建和谐迁安。 相似文献
76.
77.
传统舞台吊杆控制系统多采用匀速控制,存在吊杆定位误差大,零速停靠不易实现等缺点.该文介绍了舞台吊杆变速控制方案,重点介绍了变速算法的应用与实现,实验结果表明,该算法可以使吊杆实现零速制动,减小定位误差. 相似文献
78.
79.
HU Zhi-qin 《数字社区&智能家居》2008,(11)
克鲁斯卡尔(Kruskal)算法是实现图的最小生成树最常用的算法。本文主要介绍克鲁斯卡尔(Kruskal)算法的实现方法,并对克鲁斯卡尔(Kruskal)算法的效率进行分析。 相似文献
80.
In this paper, we address the identification problem of p-inputs q-outputs MA models, corrupted by a white noise with unknown covariance matrix, in the case where p<q. Under certain additional conditions, we show that the generating function of the MA model is identifiable (up to a p×p constant orthogonal matrix) from the autocovariance function of the observation. Our results extend those already obtained in Desbouvries et al. [5] and Desbouvries and Loubaton [6]. 相似文献