全文获取类型
收费全文 | 7024篇 |
免费 | 1596篇 |
国内免费 | 2567篇 |
专业分类
测绘学 | 1166篇 |
大气科学 | 1167篇 |
地球物理 | 1434篇 |
地质学 | 4611篇 |
海洋学 | 1194篇 |
天文学 | 104篇 |
综合类 | 525篇 |
自然地理 | 986篇 |
出版年
2024年 | 85篇 |
2023年 | 249篇 |
2022年 | 472篇 |
2021年 | 534篇 |
2020年 | 437篇 |
2019年 | 488篇 |
2018年 | 450篇 |
2017年 | 438篇 |
2016年 | 407篇 |
2015年 | 476篇 |
2014年 | 497篇 |
2013年 | 519篇 |
2012年 | 630篇 |
2011年 | 629篇 |
2010年 | 623篇 |
2009年 | 565篇 |
2008年 | 507篇 |
2007年 | 506篇 |
2006年 | 499篇 |
2005年 | 399篇 |
2004年 | 298篇 |
2003年 | 243篇 |
2002年 | 273篇 |
2001年 | 252篇 |
2000年 | 218篇 |
1999年 | 100篇 |
1998年 | 34篇 |
1997年 | 43篇 |
1996年 | 44篇 |
1995年 | 36篇 |
1994年 | 28篇 |
1993年 | 37篇 |
1992年 | 35篇 |
1991年 | 15篇 |
1990年 | 10篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1979年 | 7篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1974年 | 9篇 |
1965年 | 4篇 |
1957年 | 4篇 |
1954年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
Roseanna J. Mayfield Peter G. Langdon C. Patrick Doncaster John A. Dearing Rong Wang Gaute Velle Kimberley L. Davies Stephen J. Brooks 《第四纪科学杂志》2021,36(3):360-376
Much is known about how climate change impacts ecosystem richness and turnover, but we have less understanding of its influence on ecosystem structures. Here, we use ecological metrics (beta diversity, compositional disorder and network skewness) to quantify the community structural responses of temperature-sensitive chironomids (Diptera: Chironomidae) during the Late Glacial (14 700–11 700 cal a bp ) and Holocene (11 700 cal a bp to present). Analyses demonstrate high turnover (beta diversity) of chironomid composition across both epochs; however, structural metrics stayed relatively intact. Compositional disorder and skewness show greatest structural change in the Younger Dryas, following the rapid, high-magnitude climate change at the Bølling–Allerød to Younger Dryas transition. There were fewer climate-related structural changes across the early to mid–late Holocene, where climate change was more gradual and lower in magnitude. The reduced impact on structural metrics could be due to greater functional resilience provided by the wider chironomid community, or to the replacement of same functional-type taxa in the network structure. These results provide insight into how future rapid climate change may alter chironomid communities and could suggest that while turnover may remain high under a rapidly warming climate, community structural dynamics retain some resilience. 相似文献
202.
204.
西藏当雄九子拉地区石炭系诺错组地层序列中,首次发现了一套非正常沉积的粉砂岩和灰岩的组合.岩系中可识别出非正常的沉积构造,即微同沉积断裂、火焰状构造、同生变形构造及振动液化泄水构造等,这一软沉积变形构造具震积岩的识别标志特征,代表灾变事件震积的地质记录.在剖面结构上大致显示为7个单元的震积序列,自下而上由下伏弱震层(A)—液化脉(B)—震褶岩(C)—震裂岩(D)—阶梯状微断层(E)—火焰状构造(F)—上覆未震层(G)的渐变过程及震积作用逐渐减弱的趋势呈不同形式的组合出现,有ABG、ACDG、AEG、ABCG和ABFG等组合.本研究分析认为晚古生代诺错组早期存在一个强烈的构造活动时期,结合震积岩的分布及区域地质背景研究表明,九子拉北侧一带可能为近东西向同生断裂带,该断裂带的强烈构造活动是本区诺错组震积作用的直接诱发因素.从而佐证了九子拉地区正处于构造转换阶段.本研究对分析晚古生代的构造演化、沉积盆地类型奠定了基础,同时保存完好的震积事件地层记录对推断古断裂、古环境也具有较大意义. 相似文献
205.
陇中盆地及周边地区是青藏高原向北东方向扩展的最前缘部位,其地貌演化过程的研究对于深入理解高原的隆升与扩展过程具有重要意义。鉴于夷平面在探讨高原隆升年代、幅度和过程方面的可靠性,首先总结陇中盆地及周边地区夷平面相关研究的前期成果,并结合最新年代数据,确定了不同区域主夷平面的发育和解体年代;再利用古河道拟合等方法定量评估了相关夷平面的隆升量;最后探讨了主夷平面的性质及其隆升过程。研究发现,陇中盆地及周边的地区的高海拔低起伏地貌面是被抬高的先存夷平面;不同区域主夷平面的发育与解体时间整体同步,它们自晚渐新世开始发育,并于晚中新世8~6 Ma左右解体;模拟结果表明,美武高原主夷平面自晚中新世以来相对陇中盆地隆升了约1 400~1 600 m,并且早更新世以来的隆升速率明显大于晚中新世-早更新世时期。 相似文献
206.
The Enhanced Geothermal System (EGS) is an artificial geothermal system that aims to economically extract heat from hot dry rock (HDR) through the creation of an artificial geothermal reservoir. Chemical stimulation is thought to be an effective method to create fracture networks and open existing fractures in hot dry rocks by injecting chemical agents into the reservoir to dissolve the minerals. Granite is a common type of hot dry rock. In this paper, a series of chemical stimulation experiments were implemented using acid and alkaline agents under high temperature and pressure conditions that mimic the environment of formation. Granite rock samples used in the experiments are collected from the potential EGS reservoir in the Matouying area, Hebei, China. Laboratory experimental results show that the corrosion ratio per unit area of rock is 3.2% in static acid chemical experiments and 0.51% in static alkaline chemical experiments. The permeability of the core is increased by 1.62 times in dynamic acid chemical experiments and 2.45 times in dynamic alkaline chemical experiments. A scanning electron microscope analysis of the core illustrates that secondary minerals, such as chlorite, spherical silica, and montmorillonite, were formed, due to acid-rock interaction with plagioclase being precipitated by alkaline-rock interactions. Masking agents in alkaline chemical agents can slightly reduce the degree of plagioclase formation. A chemical simulation model was built using TOUGHREACT, the mineral dissolution and associated ion concentration variation being reproduced by this reactive transport model. 相似文献
207.
208.
ZHANG Chenglong QIN Y YANG Yicheng FENG Zuohai LIU Xijun LI Saisai WAN Lei WANG Chunzeng 《《地质学报》英文版》2021,95(3):740-749
It is unclear whether the South China blocks have an affinity with continental Gondwana due to a lack of direct Pan-African magmatic and metamorphic features. In this study, we conducted U-Pb geochronological and Lu-Hf isotopic analyses for detrital zircons from a sandstone of the Chang’an Formation of the Nanhua Group in the Longsheng region of northern Guangxi, with the aim of constraining the timing of sedimentation and information as to its source, as well as seeking evidence for Pan-African events in the South China blocks. The results show that the ages of detrital zircons peaked at 654.7 ± 6.2 Ma, 773.2 ± 4.1 Ma and 821.9 ± 6.5 Ma, with some at 920–870 Ma; the youngest age indicates the existence of the Pan-African thermal event. The εHf(t) and TDM2 values demonstrate that the study area has experienced three stages of crustal growth at 3.0–2.4 Ga, 2.1–1.5 Ga and 1.3–0.9 Ga. With intensively distributed Neoproterozoic mafic-ultramafic and granitic plutons emplaced at 830–810 Ma along the southwestern section of the Jiangnan Orogenic Belt and positive εHf(t) values from a large group of zircon grains, it is proposed that the sediments of the Chang’an Formation (of Nanhua Group) were largely sourced from the southeastern margin of the Yangtze block. Comparison with the zircon age spectra of the Cathaysian block shows that about 79% of the Pan-African aged detrital zircon grains that have TDM2 = 1352–1031 Ma and εHf(t) = 3.68–8.79, were sourced from the recycled Grenvillian crust of the Cathaysian block, suggesting that the Cathaysian block had a close connection with Gondwana. 相似文献
209.