全文获取类型
| 收费全文 | 2218篇 |
| 免费 | 138篇 |
| 国内免费 | 116篇 |
专业分类
| 测绘学 | 43篇 |
| 大气科学 | 74篇 |
| 地球物理 | 347篇 |
| 地质学 | 869篇 |
| 海洋学 | 533篇 |
| 天文学 | 16篇 |
| 综合类 | 46篇 |
| 自然地理 | 544篇 |
出版年
| 2024年 | 7篇 |
| 2023年 | 10篇 |
| 2022年 | 29篇 |
| 2021年 | 43篇 |
| 2020年 | 49篇 |
| 2019年 | 74篇 |
| 2018年 | 61篇 |
| 2017年 | 87篇 |
| 2016年 | 102篇 |
| 2015年 | 49篇 |
| 2014年 | 77篇 |
| 2013年 | 362篇 |
| 2012年 | 80篇 |
| 2011年 | 84篇 |
| 2010年 | 94篇 |
| 2009年 | 104篇 |
| 2008年 | 148篇 |
| 2007年 | 121篇 |
| 2006年 | 115篇 |
| 2005年 | 89篇 |
| 2004年 | 71篇 |
| 2003年 | 67篇 |
| 2002年 | 72篇 |
| 2001年 | 52篇 |
| 2000年 | 63篇 |
| 1999年 | 48篇 |
| 1998年 | 36篇 |
| 1997年 | 36篇 |
| 1996年 | 37篇 |
| 1995年 | 29篇 |
| 1994年 | 36篇 |
| 1993年 | 21篇 |
| 1992年 | 13篇 |
| 1991年 | 15篇 |
| 1990年 | 8篇 |
| 1989年 | 8篇 |
| 1988年 | 6篇 |
| 1987年 | 6篇 |
| 1986年 | 8篇 |
| 1985年 | 16篇 |
| 1984年 | 15篇 |
| 1983年 | 6篇 |
| 1982年 | 6篇 |
| 1981年 | 6篇 |
| 1980年 | 1篇 |
| 1979年 | 2篇 |
| 1978年 | 2篇 |
| 1954年 | 1篇 |
排序方式： 共有2472条查询结果，搜索用时 15 毫秒
91.
《Geoforum》2016
Pinole is a heritage foodstuff whose analysis provides the lens to understand the plight of Mexican farmers and the role translocal actors play in the articulation of global food heritage. To preserve and sell pinole, the pinole project was created from two groups of Mexicans born in Ozolco - a small rural village - and who now reside on either side of the Mexican and US border. By analysing members’ discourses, this article demonstrates how pinole is essentialised or commodified, and how it provides the platform for actors to formulate a variety of identities according to their socio-economic and geographical contexts. Bridging the literatures on food-studies and place-making, the multifunctionality of pinole transpires as inherently linked to the emergence of differing notions of place embedded in Ozolco. Exploring members’ varying priorities, from perpetuating rural lifestyles to preserving their hometown and its native blue corn, the project epitomises the struggle of farmers with Mexico’s migration drain and their efforts to economically engage with global markets of corn by circulating an added-value corn product within translocal networks as well as re-appropriate corn’s socio-cultural meaning. 相似文献
92.
We present a structural analysis of serpentine-bearing faults and shear zones in the Koniambo Massif, one of the klippes of the Peridotite Nappe of New Caledonia. Three structural levels are recognized. The upper level is characterized by a dense network of fractures. Antigorite and polygonal serpentine form slickenfibers along fault planes with distinct kinematics. As a result, the upper level keeps the record of at least two deformation events, the first associated with the growth of antigorite (WNW-ESE extension), the second with the growth of polygonal serpentine (NW–SE compression). The lower level coincides with the ‘serpentine sole’ of the nappe, which consists of massive tectonic breccias overlying a layer of mylonitic serpentinites. The sole records pervasive tangential shear with top-to-SW kinematics and represents a décollement at the base of the nappe. The intermediate level is characterized by the presence of several meters-thick conjugate shear zones accommodating NE–SW shortening. Like the sole, these shear zones involve polygonal serpentine and magnesite as the main syn-kinematic mineral phases. The shear zones likely root into the basal décollement, either along its roof or, occasionally, around its base. Compared to top-to-SW shearing along the sole, the two deformation events recorded in the upper level are older.The three structural levels correlate well with previously recognized spatial variations in the degree of serpentinization. It is therefore tempting to consider that the intensity of serpentinization played a major role in the way deformation has been distributed across the Peridotite Nappe. However, even the least altered peridotites, in the upper level, contain so much serpentine that, according to theoretical and experimental work, they should be nearly as weak as pure serpentinite. Hence, no strong vertical gradient in strength due to variations in the degree of serpentinization is expected within the exposed part of the nappe. Our proposal is that strain localization along the serpentine sole results from the juxtaposition of the nappe, made of weak serpentinized peridotites, against the strong mafic rocks of its substratum. This interpretation is at odds with the intuitive view that would consider the nappe, made of peridotites, as stronger than its basement. 相似文献
93.
A new genus Barbderma gen. nov. with a new species, Barbderma oblonguata sp. nov., and a new species, Sinoprotodiplatys ellipsoideuata sp. nov., of the family Protodiplatyidae are described from the Lower Cretaceous Yixian Formation at the Huangbanjigou Village, Beipiao City, Liaoning Province, China. Both new species are assigned to Protodiplatyidae mainly based on their diagnostic characters of antenna, pronotum, tegmina, tarsi and the distinct long, slender, multi-segmented cerci. These findings of fossil Protodiplatyidae provide more evidence to confirm the existence of these basal earwigs in the Early Cretaceous. Key diagnostic characters for genera of Protodiplatyidae are compared to highlight the generic variations and similarities. Evolutionary trend of cerci morphology suggests that it is likely that the cerci were evolved from long, slender and segmented to the stout terminal forceps without segmentation. 相似文献
94.
Diverse new material of mantises found in the Cretaceous amber-bearing deposits from Lebanon (Barremian), Spain (Albian), and Myanmar (Albian–Cenomanian) are described and figured. The Lebanese and Spanish forms are nymphs; while the one from Myanmar is an adult specimen. The Lebanese nymph corresponds to a new specimen of Burmantis lebanensis Grimaldi, 2003 while the adult Burmese (Myanmar) specimen belongs to the new species Burmantis zherikhini. The Spanish specimen represents a new genus and species and is established as Aragonimantis aenigma, but is considered family incertae sedis. The Spanish specimen is the first record of Mesozoic mantises from western-European amber deposits. A revised phylogenetic hypothesis for Cretaceous mantises is proposed. 相似文献
95.
Two new species, Cretohypna puncta sp. nov. and Cretohypna robusta sp. nov., of Glaphyridae are described and illustrated. These fossils were collected from the Jehol Biota, Lower Cretaceous Yixian Formation of Liutiaogou Village in Ningcheng, Inner Mongolia, China. Up to date, 18 fossil species in 6 genera of Glaphyridae have been reported, among which ten species are from China. Respective keys to the Mesozoic genera of Glaphyridae and to species of Cretohypna Yan, Nikolajev & Ren, 2012 are provided. This is the first report of spiracles in fossil Glaphyridae leading to a hypothesis that the character of the 7th abdominal spiracles present in pleural membrane is a plesiomorphy for Glaphyridae. 相似文献
96.
Specimens of the Venicoridae (Heteroptera) occur in the Lower Cretaceous Yixian Formation in northeastern China. We describe a new genus and two new species Halonatusivena shii gen. et sp. nov. and Halonatusivena nervosus sp. nov. from this formation. The veins of the membrane are distinctive; the edges of veins are not simple but resemble an irregular stain, with a reduced vasiform structure previously unknown in the Heteroptera. Remarkably, the antennae of one of the specimens of Halonatusivena shii exhibit morphological abnormality. An identification key for the known species of the Venicoridae is provided. 相似文献
97.
当前我国正处经济增速减缓的新常态,供给侧结构性改革应运而生。我国乃至世界的矿业更是处于发展的严冬之季,产能严重过剩,大宗商品价格持续走低。在当前形势下,我们要用新常态眼光看待矿业未来发展之路,因地制宜,着力加强供给侧改革,刻不容缓。 相似文献
98.
C. Klootwijk 《Australian Journal of Earth Sciences》2016,63(5):513-549
Structural, magnetic and gravity trends of the southern New England Orogen (SNEO) indicate four oroclinal structures, none conclusively confirmed paleomagnetically. Curved structures of the Tamworth Belt (TB)—a continental forearc exposed across six tectono-stratigraphic blocks with interlinked Carboniferous stratigraphies and extensive ignimbritic rocks known to retain primary magnetisations despite prevalent overprinting—are prospective to oroclinal testing through comparison of Carboniferous pole paths for individual blocks. Pole paths (a) have been established for the Rocky Creek and Werrie blocks (northwestern/western TB), (b) are described herein for the Rouchel Block (southwestern TB), and (c) are forthcoming for the Gresford and Myall blocks (southern/southeastern TB). The Rouchel path derives from detailed paleomagnetic, rock magnetic and magnetic fabric studies. Thermal, alternating field and liquid nitrogen demagnetisations show a low-temperature overprint, attributed to late Oligocene weathering, and high-temperature (HT) primary and overprint components in both magnetite and hematite carriers, showing slight, systematic, directional differences with hematite providing the better cleaned site poles. Seven primary mean-site poles of Tournaisian and mainly Visean age and three overprint poles show six positive fold tests, five at 95% or higher confidence levels. Two dispersed groupings of intermediate (IT) and HT overprint site poles of Permian and Permo-Triassic age are attributed to early and late phases in oroclinal evolution of the SNEO. HT and IT/HT overprint site poles of mid-Carboniferous age are attributed to Variscan Australia–Asia convergence. Individual pole paths for the Rocky Creek, Werrie and Rouchel blocks show no noticeable rotation between them, indicating primary curvature for the southwestern TB. Their integrated SNEO pole path establishes a reference frame for determining rotations of the southern and southeastern TB. 相似文献
99.
The monitoring of sulfur species in crater lakes has proven to be useful for forecasting episodes of volcanic unrest in certain active volcanoes, including Poás, Costa Rica; Kusatsu-Shirane, Japan; and Mt. Ruapehu, New Zealand. In this study, we have improved the current geochemical monitoring of El Chichón volcano through the setting of optimal high-performance liquid chromatography conditions (HPLC) for the analysis of S2−, SO32−, S2O32−, S4O62− and SO42− using a common chromatographic system. The procedure was applied to the analysis of lake samples taken in March, July and October of 2014 and April of 2015. The results were promising, since nearly all species were detected (with the exception of S2O32−) in measurable amounts, including S2− (<0.85–5.05 mg/L), SO32− (<2.77–26.1 mg/L), S4O62− (108.27–303.82 mg/L) and SO42− (489.58–676.26 mg/L). The spatial distribution of these species along the lakeshore showed zones of increased concentrations to the east and southeast of the lake, which provides information on the distribution of faults or cracks that feed hydrothermal fluids to the lake. This method thus provides additional information linked to the volcanic and hydrothermal activity of the volcano. 相似文献
100.
The 19 September 1985 (Mw8.1) earthquake, located on the Michoacán coast, Mexico, generated great damage in Mexico City, more than 300 km away from the epicentral area. Other important cities near the coast and in central Mexico also suffered severe damage. Thirty years after this important event, the National Autonomous University of Mexico (UNAM), the Centro de Investigación Científica y de Educación Superior de Ensenada, Baja California (CICESE) and other institutions organized a conference to discuss the scientific advances, particularly in seismology, that had taken place in Mexico since then. 相似文献