全文获取类型
收费全文 | 2211篇 |
免费 | 434篇 |
国内免费 | 700篇 |
专业分类
测绘学 | 158篇 |
大气科学 | 614篇 |
地球物理 | 494篇 |
地质学 | 1326篇 |
海洋学 | 410篇 |
天文学 | 34篇 |
综合类 | 123篇 |
自然地理 | 186篇 |
出版年
2024年 | 8篇 |
2023年 | 26篇 |
2022年 | 59篇 |
2021年 | 72篇 |
2020年 | 81篇 |
2019年 | 85篇 |
2018年 | 58篇 |
2017年 | 76篇 |
2016年 | 83篇 |
2015年 | 111篇 |
2014年 | 122篇 |
2013年 | 114篇 |
2012年 | 133篇 |
2011年 | 163篇 |
2010年 | 132篇 |
2009年 | 162篇 |
2008年 | 152篇 |
2007年 | 151篇 |
2006年 | 179篇 |
2005年 | 145篇 |
2004年 | 143篇 |
2003年 | 124篇 |
2002年 | 122篇 |
2001年 | 81篇 |
2000年 | 101篇 |
1999年 | 107篇 |
1998年 | 101篇 |
1997年 | 98篇 |
1996年 | 74篇 |
1995年 | 72篇 |
1994年 | 44篇 |
1993年 | 65篇 |
1992年 | 20篇 |
1991年 | 30篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1980年 | 3篇 |
1979年 | 1篇 |
排序方式: 共有3345条查询结果,搜索用时 171 毫秒
991.
吉长东 《测绘与空间地理信息》2011,(6):25-26
"指导学生撰写毕业设计(论文)是实现培养目标的重要教学环节,具有不可替代的作用,‘决不能降低要求,更不能放任自流’"[1]。毕业设计(论文)一般经过选题、过程控制和答辩等几个环节,文章结合我院测绘工程专业多年毕业设计(论文)实际,着手研究选题环节的质量控制,对提高毕业设计(论文)的质量,适应我校应用创新型学生培养方案,... 相似文献
992.
Simulated Spatiotemporal Response of Ocean Heat Transport to Freshwater Enhancement in North Atlantic and Associated Mechanisms
下载免费PDF全文
![点击此处可从《Acta Meteorologica Sinica》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The Atlantic Meridional Overturning Circulation(AMOC)transports a large amount of heat to northern high latitudes,playing an important role in the global climate change.Investigation of the freshwater perturbation in North Atlantic(NA)has become one of the hot topics in the recent years.In this study,the mechanism and pathway of meridional ocean heat transport(OHT)under the enhanced freshwater input to the northern high latitudes in the Atlantic are investigated by an ocean-sea ice-atmosphere coupled model.The results show that the anomalous OHT in the freshwater experiment(FW)is dominated by the meridional circulation kinetic and ocean thermal processes.In the FW,OHT drops down during the period of weakened AMOC while the upper tropical ocean turns warmer due to the retained NA warm currents.Conversely,OHT recovers as the AMOC recovers,and the mechanism can be generalized as:1)increased ocean heat content in the tropical Southern Ocean during the early integration provides the thermal condition for the recovery of OHT in NA;2)the OHT from the Southern Ocean enters the NA through the equator alongthe deep Ekman layer;3)in NA,the recovery of OHT appears mainly along the isopycnic layers of 24.70-25.77 below the mixing layer.It is then transported into the mixing layer from the "outcropping points"innorthern high latitudes,and finally released to the atmosphere by the ocean-atmosphere heat exchange. 相似文献
993.
In this paper, the seismic response reduction performance of magnetorheological (MR) damper is experimentally investigated for a suspension bridge. First, the force–displacement and force–velocity curves under a range of excitation frequencies, amplitudes and currents are obtained by mechanical behavior test of the RD1097 type MR damper. Then a new non-linear hysteretic model is proposed to model the mechanical behavior of the MR damper and the model parameters are identified from test data. An experimental method, as well as a set of testing setups with the MR damper for longitudinal seismic response reduction of a SDOF generalized system representing the fundamental longitudinal mode of suspension bridge, is developed. Finally, the seismic response reduction experiment subject to three kinds of earthquake excitations, including the Pingsheng Bridge earthquake wave, the El-Centro wave and the Taft wave, is carried out, and nine control cases, including uncontrolled, six passive control schemes with different input currents and two semi-active Bang–Bang control schemes, are tested. The results verify that the seismic response reduction experimental method is feasible and the good performance of seismic longitudinal response reduction of the suspension bridge can be achieved by MR damper. It is also shown that the passive control with optimum input current outperforms the semi-active Bang–Bang controls. 相似文献
994.
150年来地下铁道得到了广泛的发展,近20年来我国的地下铁道更是得到了迅猛的发展.在地下铁道给城市居民的工作和生活带来方便的同时,其引发的振动与噪音也给城市建设和居民生活带来了危害.本文从振动产生、振动传播和振动作用三个阶段论述了地铁振源及其传播的规律;传播特性与振源频率、振源与轨道距离、振动频率,以及列车运行速度、隧道埋深、地质条件、建筑物结构等有关;振动传播影响因素包括:土壤类型、钢轨类型、轨道类型、建筑物质量类型、建筑物材料等;地铁振动的危害是多方面的,噪声干扰人们的日常生活,振动对建筑物的安全性、使用寿命造成影响,同时还影响精密仪表测量等.本文提出了在规划设计阶段、施工阶段的振动控制措施,以期减小其危害. 相似文献
995.
Conflicting sorption coefficients for ortho‐phenylphenol (OPP) have been reported in the literatures, which resulted in the conflicting assessments on OPP mobility in soil. To ascertain the sorption coefficient of OPP, batch experiments were performed based on OECD guideline 106, using three types of soils. Headspace solid‐phase microextraction (HS‐SPME) and GC‐MS were applied to the determination of OPP concentration in the liquid phase. The sorption isotherms obtained for all three soils under equilibrium conditions were described well, assuming linear sorption. The organic carbon normalized distribution coefficients (Koc) ranged from 894 to 1703 L kg?1, which suggested that OPP is moderately mobile in soil. The results also showed that the Koc value of OPP can be predicted precisely from Kow, whereas it was underestimated by one order of magnitude when water solubility is used. 相似文献
996.
Masayuki Sakakibara Yuko Ohmori Nguyen Thi Hoang Ha Sakae Sano Koichiro Sera 《洁净——土壤、空气、水》2011,39(8):735-741
Phytoremediation is an environmental remediation technique that takes advantage of plant physiology and metabolism. The unique property of heavy metal hyperaccumulation by the macrophyte Eleocharis acicularis is of great significance in the phytoremediation of water and sediments contaminated by heavy metals at mine sites. In this study, a field cultivation experiment was performed to examine the applicability of E. acicularis to the remediation of water contaminated by heavy metals. The highest concentrations of heavy metals in the shoots of E. acicularis were 20 200 mg Cu/kg, 14 200 mg Zn/kg, 1740 mg As/kg, 894 mg Pb/kg, and 239 mg Cd/kg. The concentrations of Cu, Zn, As, Cd, and Pb in the shoots correlate with their concentrations in the soil in a log‐linear fashion. The bioconcentration factor for these elements decreases log‐linearly with increasing concentration in the soil. The results indicate the ability of E. acicularis to hyperaccumulate Cu, Zn, As, and Cd under natural conditions, making it a good candidate species for the phytoremediation of water contaminated by heavy metals. 相似文献
997.
998.
为监测岩土层含水量的变化,预警地质灾害,中国地质科学院探矿工艺研究所研制了HS-Ⅱ型自动监测仪.本文介绍监测仪的电容式水分传感技术、构成、原理和施工方法及其应用实验.监测仪对实验区进行的多点分层测试表明,该仪器监测数据可靠,工作正常,符合自动化和实时化的监测技术要求. 相似文献
999.
1000.