全文获取类型
| 收费全文 | 2592篇 |
| 免费 | 802篇 |
| 国内免费 | 555篇 |
专业分类
| 测绘学 | 186篇 |
| 大气科学 | 573篇 |
| 地球物理 | 578篇 |
| 地质学 | 1404篇 |
| 海洋学 | 457篇 |
| 天文学 | 75篇 |
| 综合类 | 309篇 |
| 自然地理 | 367篇 |
出版年
| 2025年 | 2篇 |
| 2024年 | 64篇 |
| 2023年 | 98篇 |
| 2022年 | 152篇 |
| 2021年 | 183篇 |
| 2020年 | 164篇 |
| 2019年 | 156篇 |
| 2018年 | 166篇 |
| 2017年 | 150篇 |
| 2016年 | 190篇 |
| 2015年 | 153篇 |
| 2014年 | 211篇 |
| 2013年 | 148篇 |
| 2012年 | 139篇 |
| 2011年 | 143篇 |
| 2010年 | 159篇 |
| 2009年 | 142篇 |
| 2008年 | 118篇 |
| 2007年 | 104篇 |
| 2006年 | 109篇 |
| 2005年 | 78篇 |
| 2004年 | 73篇 |
| 2003年 | 107篇 |
| 2002年 | 160篇 |
| 2001年 | 115篇 |
| 2000年 | 79篇 |
| 1999年 | 88篇 |
| 1998年 | 79篇 |
| 1997年 | 85篇 |
| 1996年 | 56篇 |
| 1995年 | 51篇 |
| 1994年 | 39篇 |
| 1993年 | 47篇 |
| 1992年 | 28篇 |
| 1991年 | 17篇 |
| 1990年 | 16篇 |
| 1989年 | 11篇 |
| 1988年 | 16篇 |
| 1987年 | 10篇 |
| 1986年 | 8篇 |
| 1985年 | 9篇 |
| 1984年 | 8篇 |
| 1983年 | 5篇 |
| 1982年 | 2篇 |
| 1981年 | 3篇 |
| 1980年 | 3篇 |
| 1977年 | 1篇 |
| 1975年 | 1篇 |
| 1958年 | 2篇 |
| 1957年 | 1篇 |
排序方式： 共有3949条查询结果，搜索用时 15 毫秒
991.
The end-Guadalupian extinction is an important biotic event in the Phanerozoic with an ecological impact comparable to the ‘big five’ extinctions. However, the age, pattern, and mechanism of this extinction are all under debate. The bivalves of the Alatoconchidae family attained body volumes up to 10,000 cm3 and had a wide distribution in the low latitude Palaeotethys and Panthalassa. These giant clams originated in the early Kungurian and went extinct in the Late Guadalupian. Therefore, they are the typical victims of the end-Guadalupian extinction and are major index fossils for the understanding of this event. Although extraction of these giant bivalves from the host-resistant limestone is hard, plenty of new-found transverse sections on outcrops are available for morphological reconstruction and volume estimation. The measurement from the representative fossil localities in South China indicates the clams achieved a substantial volume increase during the Wordian and sustained the giant size to the late Capitanian, till their abrupt disappearance. The giant clams originated under atmospheric hyperoxia and warm climate after the Late Palaeozoic Ice Age. Their body volume increase was roughly parallel to the seawater warming. The accompanied high seawater carbonate saturation and Mg/Ca ratio are beneficial to their biomineralization of the large shells with aragonite or high-Mg calcite components. On the contrary, these giant bivalves were probably killed by the major or rapid changes of those environmental factors that once facilitated their success, such as drastic fluctuation of seawater temperature, sudden ocean acidification, and marine anoxia. 相似文献
992.
Fan Yang Fei Xue M. Santosh Zesheng Qian Cun Zhang Jiarun Tu 《Geological Journal》2021,56(6):3207-3224
Numerous granitoid suites exposed in the Qilian orogen, NE Tibetan Plateau preserve important records of the tectonic evolution of this orogen. Here we present zircon U–Pb, zircon rare earth elements (REEs), and whole-rock geochemical and Sr–Nd–Hf isotopic data on Niuxinshan granitoids in the North Qilian orogen, with a view to constrain their petrogenesis and timing of emplacement, as well as to gain new insights into the Early Palaeozoic tectonic evolution of the Qilian orogen. Zircon U–Pb data show multiple concordant ages of ~517, 455–425, 397–389, and 351–319 Ma for syenogranite, and ages of ~758 and 724 Ma together with some scattered Early Mesozoic discordant ages for porphyritic granite, suggesting episodic magmatism from Neoproterozoic to Early Mesozoic. Zircon ∑REEs range from 276.43 to 4,582.32 ppm, and are characterized by depletion of light REEs (LREEs) and enrichment heavy REEs (HREEs) with negative Eu anomalies, indicating a mixture of magmatic and hydrothermal zircons. Whole-rock geochemical data show similar variation of LREEs, large-ion lithophile elements (LILEs), HREEs, and high-field-strength elements (HFSEs) with zircon REEs, with Eu, Ba, P, and Ti negative anomalies and Rb, U, and Pb positive anomalies. Based on their formation ages, two groups of granitoids are identified. Group I rocks (Early Palaeozoic) are represented by I-type granites whereas Group II rocks (Early Mesozoic) are of S-type. Whole-rock Sr–Nd–Hf isotopes display (87Sr/86Sr)i ratios of 0.707085–0.709591, εNd(t) values of −5.3 to −2.3, εHf(t) values of −2.2 to 0, and two-stage model (Nd and Hf) ages of 1.6–1.4 Ga for Group I rocks, and of 0.728156–0.734113, −9.4 to −9.3, −10.6 to −6.9, and 2.1–1.9 Ga for Group II rocks. Accordingly, we infer that the magma for Group I was sourced from the partial melting of basaltic protoliths in the mafic lower crust and underwent fractional crystallization. Group II was derived from metasedimentary protoliths through reworking of ancient Palaeoproterozoic crustal components. Integrating the results from this study with those from previous studies on Niuxinshan granitoids, we argue that the southward subduction model of the North Qilian Ocean beneath the Qilian Block during the Early Palaeozoic might be a more reasonable scenario. However, the Early Mesozoic magmatic event reported here remains equivocal in the North Qilian orogen. 相似文献
993.
Xue Miao Daoliang Chu Jinnan Tong Michael J. Benton Jianxin Yu Liang Luo Wenchao Shu Yuyang Wu 《Geological Journal》2021,56(12):6176-6188
The Permian–Triassic mass extinction was the largest biotic extinction event in the Phanerozoic and affected both marine and continental life. Marine Permian–Triassic transitional sequences can be correlated in many regions, but this has proved difficult for continental successions. A growing number of studies show that spinicaudatans are some of the most common fossils in continental strata and can be used as index fossils for continental stratigraphic division and correlation. Here we document the morphology and biostratigraphic significance of Euestheria gutta based on well-preserved fossils from southwestern China. It shows strong intraspecific morphological variation, while the most important feature is the strongly convex larval valve and significant finely pitted to weakly reticulated ornamentation on the growth bands. Evidence from palaeobotany, charcoal, and organic carbon isotopes indicated that the continental mass extinction in southwestern China was marked by the catastrophic loss of tropical rainforest vegetation, enhanced wildfire and a negative carbon isotope excursion (CIE) during the P–Tr transition. Meanwhile, abundant E. gutta first appeared at the onset of the negative CIE and just above the horizon of the loss of macroflora. Based on the global geographic distribution of E. gutta and temporal correlation, we conclude that this species existed from the latest Permian to the earliest Triassic, and the occurrence of E. gutta could be used as an index fossil of the continental mass extinction interval or P–Tr transitional beds. 相似文献
994.
Guoqiang Xue Nannan Zhou Ruiting Wang Hongtao Liu Wenbo Guo 《Geological Journal》2021,56(6):3314-3321
The Fengtai Pb–Zn metallogenic deposits located in China's western region have good minerogenetic conditions and exploration potential. However, the Fengtai mining area passed through complex orogenic process zones, such as subduction, collision, and integration between the Yangtze Plate and the North China Plate. Existing geological research and drilling results showed that the ore bodies of large-scale Pb–Zn deposits in the ore-gathering area were steeply inclined, and the detection depths of the majority of the metal deposits were generally less than 300 m. Deep ore-controlling structures at approximately 500–1,000 m are not well understood. Therefore, high-precision and large-depth geophysical detection techniques are necessary to achieve the required accurate detection results. This study revealed that the resistivity values of the ore and host rocks were quite different, which is essential for effective and efficient geophysical prospecting. Based on the petrophysical result, the grounded-wire transient electromagnetic method system has been found to be one of the better choices for the deep prospecting of the metal deposits and was applied to detect Pb–Zn deposits in the Bafangshan-Erlihe area. First, the grounded-wire transient electromagnetic method's effectiveness was verified using results from survey line 1 at a known ore deposit verified by the drilling result. Then, the technique was used to identify deposits in an unexplored area. A deep anticline and ore body were successfully imaged. Most lead-zinc ore bodies are controlled by the hinge and two wings of the tight anticline, and distributed in the contact zone between limestone and phyllite. The results provide a critical basis for deep prospecting and drilling design. 相似文献
995.
事件沉积是地质学研究热点之一.黔南独山地区早泥盆世丹林组沉积时期事件沉积记录为华南板块海西早期构造演化再研究提供了新的线索.通过路线调查、剖面实测、岩相解析、实验测试查明丹林组存在砂岩液化、自形-半自形独居石及金红石、团块状黄铁矿、锑异常层等事件沉积记录.经研究本文认为,上述现象是由于黔南独山地区早泥盆世丹林组沉积时期可能存在潜火山活动引起,该潜火山活动导致了同时期的热事件沉积,并表明事件沉积环境为热水盆地.分布于独山地区的锑、铅、锌、铁、金矿化均赋存于泥盆系地层之中,且具有显著的层控特点;故而该地区的多金属矿化很可能与华南板块海西早期的构造-岩浆活动热事件启动密切相关. 相似文献
996.
997.
Growth and energy budget of marine amphipod juvenile Eogammarus possjeticus at different temperatures(20°C,24°C, 26°C, 28°C, 30°C, 32°C and 34°C) were investigated in this study. The results showed that the cumulative mortality rate increased significantly with rising temperature(p0.01), and exceeded 50% after 24 h when temperature was above 30°C. With the temperature increasing from 20°C to 26°C, the ingestion rate and absorption rate increased, but decreased significantly above 28°C(p0.01), indicating a decline in feeding ability at high temperatures. The specific growth rate increased with rising temperature, but decreased significantly(p0.01) after reaching the maximum value at 24°C. Similarly, the oxygen consumption and ammonia emission rates also showed a trend of first increase and then decrease. However, the O:N ratio decreased first and then increased with rising temperature, indicating that the energy demand of E. possjeticus juvenile transferred from metabolism of carbohydrate and lipid to protein. In the energy distribution of amphipods, the proportion of each energy is different. With rising temperature, the ratio of the energy deposited for growth accounted for ingested gross energy showing a trend of decrease, while the energy lost to respiration, ammonia excretion, and feces accounted for ingested gross energy being showed a trend of increase. It seemed that rising temperature increased the metabolism and energy consumption of the amphipods and, meanwhile, decreased the energy used for growth, which may be an important reason for the slow growth and small body size of the amphipods during the summer high-temperature period. 相似文献
998.
为探索深海孔隙水中稀土元素的生物地球化学循环过程,对太平洋菲律宾海九州-帕劳海脊东、西两侧的两个钻孔沉积物进行了高精度的孔隙水采样工作,分析了主、微量元素和稀土元素的地球化学特征,并对稀土元素的浓度、配分模式以及分馏特征进行了详细的讨论。结果表明：这两个钻孔沉积物均处于氧化环境,表现出海水-沉积物界面和浅层孔隙水（2.5～20 cm）中相对富集轻稀土和中稀土,而中层（25～60 cm）和深层沉积物（＞65 cm）孔隙水中则相对富集重稀土元素的特征。初步推断有机质和锰（氢）氧化物的分解和吸附作用是造成孔隙水中稀土元素分馏的主要因素。相比于九州-帕劳海脊的东、西两侧海域,孔隙水中的稀土元素浓度和分馏程度存在一定的差异,周围环境中的矿物组成和锰（氢）氧化物等是其主要的控制因素,但是研究区域深海孔隙流体并不能为海洋贡献稀土元素。 相似文献
999.
Zengxue Li Qingbo Zeng Meng Xu Dongdong Wang Guangzeng Song Pingli Wang Xiaojing Li Xue Zheng 《海洋学报(英文版)》2021,40(2):95-106
In the present study, the coal-rock organic facies of Oligocene Yacheng Formation of the marginal basin in the South China Sea were classified and divided. In addition, through the correlations of the large-scale coal-bearing basins between the epicontinental sea and the South China Sea, it was concluded that the coal forming activities in the South China Sea presented particularity and complexity. Furthermore, the coal forming mechanisms also presented distinctiveness. The marginal basins in th... 相似文献
1000.