全文获取类型
收费全文 | 20069篇 |
免费 | 3312篇 |
国内免费 | 4149篇 |
专业分类
测绘学 | 3871篇 |
大气科学 | 2999篇 |
地球物理 | 3288篇 |
地质学 | 9579篇 |
海洋学 | 2562篇 |
天文学 | 670篇 |
综合类 | 1747篇 |
自然地理 | 2814篇 |
出版年
2024年 | 74篇 |
2023年 | 242篇 |
2022年 | 574篇 |
2021年 | 725篇 |
2020年 | 757篇 |
2019年 | 907篇 |
2018年 | 646篇 |
2017年 | 791篇 |
2016年 | 780篇 |
2015年 | 912篇 |
2014年 | 1152篇 |
2013年 | 1188篇 |
2012年 | 1214篇 |
2011年 | 1376篇 |
2010年 | 1076篇 |
2009年 | 1224篇 |
2008年 | 1281篇 |
2007年 | 1431篇 |
2006年 | 1391篇 |
2005年 | 1286篇 |
2004年 | 1195篇 |
2003年 | 987篇 |
2002年 | 960篇 |
2001年 | 749篇 |
2000年 | 744篇 |
1999年 | 607篇 |
1998年 | 580篇 |
1997年 | 491篇 |
1996年 | 424篇 |
1995年 | 366篇 |
1994年 | 348篇 |
1993年 | 255篇 |
1992年 | 207篇 |
1991年 | 148篇 |
1990年 | 121篇 |
1989年 | 106篇 |
1988年 | 75篇 |
1987年 | 46篇 |
1986年 | 31篇 |
1985年 | 20篇 |
1984年 | 16篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 2篇 |
1954年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
941.
942.
943.
944.
945.
WANG Luyao LIU Kai MA Yan ZHANG Yaoyao TONG Jue JIA Wuhui ZHANG Shouchuan SUN Junliang 《《地质学报》英文版》2024,98(3):801-818
Geothermal resources are increasingly gaining attention as a competitive, clean energy source to address the energy crisis and mitigate climate change. The Wugongshan area, situated in the southeast coast geothermal belt of China, is a typical geothermal anomaly and contains abundant medium- and low-temperature geothermal resources. This study employed hydrogeochemical and isotopic techniques to explore the cyclic evolution of geothermal water in the western Wugongshan region, encompassing the recharge origin, water–rock interaction mechanisms, and residence time. The results show that the geothermal water in the western region of Wugongshan is weakly alkaline, with low enthalpy and mineralization levels. The hydrochemistry of geothermal waters is dominated by Na-HCO3 and Na-SO4, while the hydrochemistry types of cold springs are all Na-HCO3. The hydrochemistry types of surface waters and rain waters are Na-HCO3 or Ca-HCO3. The δD and δ18O values reveal that the geothermal waters are recharged by atmospheric precipitation at an altitude between 550.0 and 1218.6 m. Molar ratios of major solutes and isotopic compositions of 87Sr/86Sr underscore the significant role of silicate weathering, dissolution, and cation exchange in controlling geothermal water chemistry. Additionally, geothermal waters experienced varying degrees of mixing with cold water during their ascent. The δ13C values suggest that the primary sources of carbon in the geothermal waters were biogenic and organic. The δ34S value suggests that the sulfates in geothermal water originate from sulfide minerals in the surrounding rock. Age dating using 3H and 14C isotopes suggests that geothermal waters have a residence time exceeding 1 kaBP and undergo a long-distance cycling process. 相似文献
946.
947.
珠江口盆地珠一坳陷在中始新世裂陷期文昌组沉积早、晚期之间存在明显的构造转换,该构造事件对古近系源?汇体系的形成和演变有重大影响.基于研究区地震、钻井、测井等资料的综合分析,本文认为构造转换控制了裂陷期源?汇体系的盆山地貌、物源供给、搬运方向及沉积样式等基本要素,并影响深层古近系储层条件.而且在构造转换的制约下,研究区发... 相似文献
948.
利用NCEP FNL分析资料及南京多普勒雷达观测,借助WRF模式,对2017年8月19日发生在长江中下游地区的一次中尺度对流系统(MCS)进行模拟和诊断分析。此次MCS组织模态PS(Parallel Stratiform)型和TS(Trailing Stratiform)型共存,开始为带状结构,最后演变为强弓状飑线。气旋切变和低空急流是此次过程的重要影响系统,而午后强烈发展的地面锋触发了此次强对流。在垂直风切变和冷池共同作用下,西侧初始对流发展为PS型模态,东侧发展为TS型模态。由于PS型模态的中低层垂直风切变发生转向,导致其消散。TS型模态附近冷池和垂直风切变相配合,且在后向入流(Rear Inflow Jets,RIJ)作用下发展成为强弓状飑线;RIJ受中低层涡旋对影响而发展增强,其中气旋式涡旋主要由涡度方程中拉伸项决定,而反气旋式涡旋则主要由倾侧项决定。 相似文献
949.
试样经碱熔,盐酸提取的钛,在以盐酸、硫酸、磷酸组成的强酸性溶液体系中,利用铝片的强还原性,还原四价钛为三价钛。再用三价铁氧化三价钛为四价钛,过量的三价铁离子与硫氢酸根离子生成血红色络合物,根据此原理测定高含量钛。实验证明,溶液在此强酸性体系中,隔绝空气和控制时间的条件下,其含量范围在0.13%~100%内,测定结果准确度高。 相似文献
950.
Revisiting Peruvian anchovy (Engraulis ringens) trophodynamics provides a new vision of the Humboldt Current system 总被引:6,自引:4,他引:2
The Peruvian anchovy or anchoveta (Engraulis ringens) forages on plankton and is a main prey for marine mammals, seabirds, fish, and fishers, and is therefore a key element of the food web in the Humboldt Current system (HCS). Here, we present results from the analysis of 21,203 anchoveta stomach contents sampled during 23 acoustic surveys over the period 1996–2003. Prey items were identified to the genus level, and the relative dietary importance of different prey was assessed by determination of their carbon content. Variability in stomach fullness was examined relative to the diel cycle, the distance from the coast, sea surface temperature, and latitude, using generalized additive models (GAMs). Whereas phytoplankton largely dominated anchoveta diets in terms of numerical abundance and comprised >99% of ingested prey items, the carbon content of prey items indicated that zooplankton was by far the most important dietary component, with euphausiids contributing 67.5% of dietary carbon followed by copepods (26.3%). Stomach fullness data showed that anchoveta feed mainly during daytime between 07h00 and 18h00, although night-time feeding also made a substantial contribution to total food consumption. Stomach fullness also varied with latitude, distance from the coast, and temperature, but with substantial variability indicating a high degree of plasticity in anchoveta feeding behaviour. The results suggest an ecological role for anchoveta that challenges current understanding of its position in the foodweb, the functioning of the HCS, and trophic models of the HCS. 相似文献