全文获取类型
收费全文 | 27600篇 |
免费 | 2901篇 |
国内免费 | 1469篇 |
专业分类
电工技术 | 1688篇 |
技术理论 | 5篇 |
综合类 | 3018篇 |
化学工业 | 2073篇 |
金属工艺 | 442篇 |
机械仪表 | 730篇 |
建筑科学 | 6430篇 |
矿业工程 | 3038篇 |
能源动力 | 978篇 |
轻工业 | 796篇 |
水利工程 | 2837篇 |
石油天然气 | 3307篇 |
武器工业 | 160篇 |
无线电 | 1650篇 |
一般工业技术 | 1319篇 |
冶金工业 | 1034篇 |
原子能技术 | 167篇 |
自动化技术 | 2298篇 |
出版年
2024年 | 84篇 |
2023年 | 353篇 |
2022年 | 722篇 |
2021年 | 835篇 |
2020年 | 985篇 |
2019年 | 750篇 |
2018年 | 711篇 |
2017年 | 914篇 |
2016年 | 988篇 |
2015年 | 1044篇 |
2014年 | 1881篇 |
2013年 | 1565篇 |
2012年 | 2032篇 |
2011年 | 2147篇 |
2010年 | 1741篇 |
2009年 | 1706篇 |
2008年 | 1643篇 |
2007年 | 1931篇 |
2006年 | 1892篇 |
2005年 | 1563篇 |
2004年 | 1256篇 |
2003年 | 1099篇 |
2002年 | 887篇 |
2001年 | 742篇 |
2000年 | 582篇 |
1999年 | 442篇 |
1998年 | 314篇 |
1997年 | 217篇 |
1996年 | 162篇 |
1995年 | 170篇 |
1994年 | 122篇 |
1993年 | 95篇 |
1992年 | 83篇 |
1991年 | 47篇 |
1990年 | 54篇 |
1989年 | 36篇 |
1988年 | 29篇 |
1987年 | 12篇 |
1986年 | 24篇 |
1985年 | 23篇 |
1984年 | 17篇 |
1983年 | 16篇 |
1982年 | 10篇 |
1981年 | 22篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1960年 | 1篇 |
1959年 | 3篇 |
1956年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
The problem of managing water scarcity by resorting to complex interconnected multi-source water systems needs to utilize
management optimization techniques analyzing aspects of water quantity and quality in a common strategy. In the southern regions
of Mediterranean Europe, the greater part of water resources for supply systems are derived from artificial reservoirs and
water systems can become quite complex since they interconnect several sources and demand centers, as indeed occurs in the
Region of Sardinia (Italy). A simplified approach to the requirement to insert water quality aspects in the mathematical optimization
model can be achieved by examining the trophic conditions of reservoirs. Trophic State Indexes (TSI) based on Carlson’s (1977) make it possible to insert quality constraints in the water management optimization model also considering complex multi-reservoir
and multi-user systems. Model formalization and implementation by the optimization toolkit WARGI (Water Resource system optimization
aided by Graphical Interface) (Sechi and Zuddas 2000; Manca et al. 2004; Salis et al. 2005) is illustrated in this paper. The usefulness of a mixed quantity–quality optimization approach has been confirmed by WARGI
application to a real multi-reservoir water resources system in southern Sardinia. The optimization model remains computationally
efficient dealing with this complex multi-reservoir system and the obtained results can be seen as a reference target in a
subsequent simulation phase. 相似文献
94.
丽水市矿产资源产业必须走可持续发展之路 总被引:1,自引:0,他引:1
丽水市的优势自然资源之一是矿产资源。本文对丽水市境内的矿产资源的优势及开发现状进行了详尽分析。在此基础上提出如何开发利用好这一资源 ,走可持续发展道路的具体措施 相似文献
95.
介绍了阳泉市煤矿采空区对公路建设所造成的危害,对其上覆岩层变形破坏的地质因素及其破坏机理作了分析,指出应该采取各种措施减少对公路的破坏。 相似文献
96.
Withdrawal from an escalating-dose, bingelike regimen of cocaine administration in rats produced significantly depressed levels of locomotor activity during the nocturnal portion of the day-night cycle. This effect was observed during the first 48 hrs of testing. Extracellular single-unit recordings of ventral tegmental area (VTA) dopamine (DA) neurons revealed no differences between saline- and cocaine-treated rats with respect to basal firing rates. However, significantly fewer spontaneously active VTA DA neurons were encountered in rats withdrawn from binge cocaine. As with the nocturnal hypoactivity, this effect was observed only during the first 48 hrs of withdrawal. These findings suggest that short-term DA neuron dysfunction during cocaine withdrawal temporally corresponds to behavioral disruptions that are similar to those described in human addicts. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
97.
98.
鄂尔多斯盆地姬塬-堡子湾地区长4+5油层成岩作用与储层评价 总被引:4,自引:4,他引:0
利用岩石铸体薄片鉴定、X射线衍射分析、扫描电镜分析等测试手段,对鄂尔多斯盆地姬塬一堡子湾地区延长组长4+5油层储集岩的岩石学特征、成岩作用和物性特征进行了分析。结果表明,该储集岩为细粒的长石砂岩和岩屑长石砂岩,颗粒呈次棱角状,成分成熟度普遍较低,结构成熟度中等一较好;经历了压实、胶结、压溶和溶解等一系列成岩作用;储集岩具有低孔、低渗的特点。在以上研究基础上,结合压汞分析、孔隙组合分析,对储层进行综合评价认为,长4+5储层可分为4类,研究区以Ⅱ、Ⅲ类(中等一差)储层为主。 相似文献
99.
在分析铁路通信资源结构的基础上,利用地理信息系统技术、数据库技术和客户/服务器(C/S)模式,为铁通(ChinaTietong)各级分公司和运营部门提供一套较为完善的资源管理信息系统。文中分析了铁通资源的结构与资源之间的关联,介绍了系统功能、物理结构及体系结构,详细分析了数据库设计、地理信息系统和系统安全性所采用的关键技术。这套系统的应用对铁通网络管理的现代化将起到重要的推动作用。 相似文献
100.
V.J. Logeeswaran F.E.H. Tay M.L. Chan F.S. Chau Y.C. Liang 《Analog Integrated Circuits and Signal Processing》2003,37(1):17-33
In this paper, the response to the first harmonic component (2f) of the electrostatic force in single terminal driven electrostatic comb-drive and parallel-plate drive was used as a signal to extract device parameters, namely, the Q-factor and resonant frequency instead of the fundamental (1f) resonance response. It is shown that the difficulty in motional measurement due to electrical cross-talk (parasitics) using 1f measurement can be overcome with a higher signal-to-noise ratio of the 2f signal. Both atmospheric (low-Q) and reduced pressure environment were investigated using off-chip electronics and lock-in amplifier. The measurements were done on the electrostatic comb-drive and capacitive parallel plate sensing plates that form the two core modules of a yaw rate sensor (dual-axis resonator). The effects of AC and DC bias voltages on the measured response have been investigated. Experimental amplitude and phase response data have been analysed using the Lorentzian curve-fit, Resonance Curve Area (RCA) method, the half-power bandwidth method (3 dB) and the Nyquist plot for data fitting and determination of the Q-factor and resonance frequency. 相似文献