全文获取类型
收费全文 | 36305篇 |
免费 | 3784篇 |
国内免费 | 1525篇 |
专业分类
电工技术 | 2062篇 |
技术理论 | 13篇 |
综合类 | 4043篇 |
化学工业 | 1947篇 |
金属工艺 | 443篇 |
机械仪表 | 730篇 |
建筑科学 | 14088篇 |
矿业工程 | 2858篇 |
能源动力 | 891篇 |
轻工业 | 768篇 |
水利工程 | 2973篇 |
石油天然气 | 3572篇 |
武器工业 | 164篇 |
无线电 | 1779篇 |
一般工业技术 | 1239篇 |
冶金工业 | 1110篇 |
原子能技术 | 166篇 |
自动化技术 | 2768篇 |
出版年
2024年 | 172篇 |
2023年 | 519篇 |
2022年 | 1041篇 |
2021年 | 1222篇 |
2020年 | 1339篇 |
2019年 | 1098篇 |
2018年 | 898篇 |
2017年 | 1278篇 |
2016年 | 1306篇 |
2015年 | 1354篇 |
2014年 | 2717篇 |
2013年 | 2264篇 |
2012年 | 2687篇 |
2011年 | 2901篇 |
2010年 | 2389篇 |
2009年 | 2246篇 |
2008年 | 2221篇 |
2007年 | 2384篇 |
2006年 | 2251篇 |
2005年 | 1796篇 |
2004年 | 1432篇 |
2003年 | 1252篇 |
2002年 | 1063篇 |
2001年 | 917篇 |
2000年 | 675篇 |
1999年 | 479篇 |
1998年 | 338篇 |
1997年 | 265篇 |
1996年 | 179篇 |
1995年 | 189篇 |
1994年 | 145篇 |
1993年 | 112篇 |
1992年 | 110篇 |
1991年 | 57篇 |
1990年 | 64篇 |
1989年 | 46篇 |
1988年 | 34篇 |
1987年 | 16篇 |
1986年 | 28篇 |
1985年 | 25篇 |
1984年 | 18篇 |
1983年 | 18篇 |
1982年 | 12篇 |
1981年 | 25篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1964年 | 2篇 |
1961年 | 3篇 |
1959年 | 3篇 |
1956年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
In this age of public skepticism about science, sustainability science offers a way to increase the application of science in planning and policy. This paper explores the relationship between science and society and the emergence of sustainability science. A comparison of the theory and practice of sustainability science and planning reveals the potential for a natural partnership. Based on the analysis, I suggest ways that planning may bridge the gap and build on the opportunity to strengthen its purpose and impact. 相似文献
992.
Soil sealing footprint as an indicator of dispersed urban growth: a multivariate statistics approach
The present study introduces a set of indicators derived from high-resolution land-use maps with the aim to illustrate the spatial distribution, intensity, and diversity of sealed soils in a Mediterranean region (Rome, Italy) shifting from a mono-centric spatial organization toward a dispersed urban agglomeration. A multivariate approach provides a comprehensive assessment of Rome ‘sealing footprint’, classifying local districts according to different imperviousness profiles. Results illustrate the rearrangement of the land-use structure determined by suburbanization with higher soil consumption and lower land-use efficiency. The approach is considered a promising tool to inform policies for a spatially balanced and land-saving urban development. 相似文献
993.
The fine granular area (FGA) plays a crucial role in the VHCF regime. However, so far, the uniform understanding or conclusion about the formation mechanism of FGA has not been drawn. In view of the significance of FGA, the current studies on FGA, i.e., the FGA size, the stress intensity factor range at the periphery of FGA, the crack initiation and growth process in FGA, and the formation mechanisms of FGA, are reviewed in the present paper. The role of internal hydrogen in the VHCF regime is further discussed. In the end, two important definite conclusions are drawn based on the present investigations. 相似文献
994.
As redevelopment and gentrification strategies globally continue to be aimed at attracting wealthier residents and consumers in an effort to drive economic growth, concerns for and interventions in the interests of social equity appear decreasingly relevant. Government, private sector and community organisations have of course worked together in different times and places to implement programs that are more rather than less inclusive – the variations always depending on the spatial politics of the context. This paper examines contemporary discourses and practices of place-making in Melbourne, and asks whether ways of thinking about urban redevelopment as place-making in this time and place are likely to enable the inclusion of social equity in these urban “improvements”. 相似文献
995.
《Journal of Nuclear Science and Technology》2013,50(12):934-942
Distribution coefficients K ds of several radionuclides on suspended particulate matter (SPM) have been determined with laboratory batch experiments using samples collected in the Kinki district, Japan. Most SPM in coastal water was retained on the initial filter of four sequential filtering stages (20, 5, 1 and 0.45 μm pore size), maximum K d also being found for the SPM retained in this first stage. When the filtrations were not performed in series, however, but were conducted from the same tracer solution in parallel, the K d values were identical for the smaller filter sizes (5, 1 and 0.45 μm) and were greater, by ca. 150% than those derived from the 20 μm filter. The degree of association of the radionuclides with SPM was 85Sr<137Cs<65Zn<54Mn<60Co. The particulate radioactivity fraction of the SPM in coastal water was estimated at most 0.1 for radionuclides with K d of ca. 5 X 104 ml/g, i.e. which are highly associated with the SPM (2 mg/l). The scavenging effect by SPM seemed to be, however, considerable, the settling velocity being estimated at ca. 25 cm/day for particles of the Stoke's diameter of 30 μm. 相似文献
996.
以小煤矿严重破坏区复采综放工作面3起火灾事故为案例,分析火灾原因,提出了复采工作面穿越小煤矿破坏区特殊支护、消火道防灭火等防治小煤矿自然发火技术,结合工作面破坏区灌浆超前防治、局部均压、注氮等防灭火措施,有效地消除了火灾事故,确保工作面顺利回采。 相似文献
997.
黄骅坳陷埕海地区奥陶系天然气地球化学特征较为特殊,具有非烃含量高、稳定同位素重的特征。通过同位素特征,进一步结合地质、地化资料综合分析,对埕海地区奥陶系天然气的成因类型和气源进行探讨。认为埕海地区奥陶系天然气为煤成气,主力气源岩为石炭-二叠系烃源岩。 相似文献
998.
对移动警务安全接入平台中的终端设备的安全防护问题进行了研究,提出并研制了一种基于动态策略的移动警务终端安全管控系统,整个系统由客户端、前置服务端和内网服务端组成,前置服务端和内网服务端分别部署在前置区和公安内网,客户端部署在移动终端设备上,确保在移动接入区和公安内网区有效进行物理隔离的前提下,将系统制定的各种安全策略规则下发到客户端执行,规范用户对移动终端的本地软硬件资源和网络资源的使用,实现安全威胁检测、防护及预警,对移动终端用户的违规访问、操作行为进行全面监测和上报,实现终端设备安全和行为的统一管理. 相似文献
999.
In this paper, a compact asymmetric coplanar waveguide (CPW) feed with split-ring resonator (SRR) is proposed to resonate at dual-band operations for wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX) applications. The asymmetric CPW-fed SRR patch (ACSP) antenna consists of a meander line, square-shaped split ring, and CPW ground plane. The proposed ACSP antenna resonates at two operating frequencies, namely, 2.48 GHz (2.4–2.74 GHz) and 3.49 GHz (3.25–3.64 GHz) with reflection coefficients (S11) of −16.65 dB and −32.67 dB, respectively. The measured results agree closely with the simulation results of the proposed antenna. 相似文献
1000.
无线体域网中传输的是与生命高度相关的敏感数据,身份认证是信息安全保护的第一道防线。现有的基于人体生物信息的身份认证方案存在信息难提取、偶然性大和误差性大的问题,基于传统密码学的认证方案需较大计算资源和能量消耗,并不适用于无线体域网环境。为此,在动态口令和非对称加密机制基础上,提出一种适用于无线体域网的动态口令双向认证轻量协议,并对其进行形式化分析。通过理论证明、SVO逻辑推理及SPIN模型检测得出:该协议满足双向认证,且能够抵御重放攻击、伪装攻击、拒绝服务器攻击和口令离线攻击,具有较高安全性。 相似文献