全文获取类型
收费全文 | 28946篇 |
免费 | 352篇 |
国内免费 | 967篇 |
专业分类
测绘学 | 1517篇 |
大气科学 | 2345篇 |
地球物理 | 5565篇 |
地质学 | 13196篇 |
海洋学 | 1347篇 |
天文学 | 2481篇 |
综合类 | 2175篇 |
自然地理 | 1639篇 |
出版年
2022年 | 28篇 |
2021年 | 63篇 |
2020年 | 68篇 |
2019年 | 90篇 |
2018年 | 4849篇 |
2017年 | 4132篇 |
2016年 | 2703篇 |
2015年 | 366篇 |
2014年 | 263篇 |
2013年 | 282篇 |
2012年 | 1178篇 |
2011年 | 2942篇 |
2010年 | 2195篇 |
2009年 | 2534篇 |
2008年 | 2074篇 |
2007年 | 2508篇 |
2006年 | 228篇 |
2005年 | 366篇 |
2004年 | 582篇 |
2003年 | 565篇 |
2002年 | 400篇 |
2001年 | 127篇 |
2000年 | 139篇 |
1999年 | 86篇 |
1998年 | 111篇 |
1997年 | 68篇 |
1996年 | 65篇 |
1995年 | 61篇 |
1994年 | 55篇 |
1993年 | 63篇 |
1992年 | 46篇 |
1991年 | 39篇 |
1990年 | 40篇 |
1989年 | 41篇 |
1988年 | 47篇 |
1987年 | 50篇 |
1986年 | 47篇 |
1985年 | 57篇 |
1984年 | 67篇 |
1983年 | 51篇 |
1982年 | 57篇 |
1981年 | 67篇 |
1980年 | 67篇 |
1979年 | 46篇 |
1978年 | 44篇 |
1977年 | 37篇 |
1976年 | 38篇 |
1975年 | 32篇 |
1974年 | 33篇 |
1973年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Amr S. Elnashai 《地震工程与工程振动(英文版)》2007,6(2):99-109
Studying strong motion records and the spatial distribution of ground shaking is of great importance in understanding the underlying causes of damage in earthquakes. Many regions in the world are either not instrumented or are sparsely instrumented. As such, significant opportunities for motion-damage correlations are lost. Two recent and damaging earthquakes belong to the class of lost opportunities, namely the Kashmir (Pakistan) earthquake of October 2005 and the Yogyakarta (Indonesia) earthquake of May 2006. In this paper, an overview of the importance of supply and demand studies in earthquake-stricken regions is given, followed by two examples of investigative engineering seismology aimed at reconstructing the hazard from sparse data. The paper closes with a plea for responsible authorities to invest in seismic monitoring networks in the very near future. 相似文献
992.
In numerical simulation of wave scattering under oblique incident body waves using the finite element method, the free field motion at the incident lateral boundary induced by the background layered half-space complicates the computational area. In order to replace the complex frequency domain method, a time-domain method to calculate the free field motion of a layered half-space subjected to oblique incident body waves is developed in this paper. The new method decouples the equations of motion used in the finite element method and offers an interpolation formula of the free field motion. This formula is based on the fact that the apparent horizontal velocity of the free field motion is constant and can be calculated exactly. Both the theoretical analysis and numerical results demonstrate that the proposed method offers a high degree of accuracy. 相似文献
993.
MAO Hui MAO JieTai BI YanMeng LI ChengCai? & LIU XiaoYang Department of Atmospheric Sciences School of Physics Peking University Beijing China Shenzhen Meteorological Bureau Shenzhen China 《中国科学D辑(英文版)》2007,50(2):296-305
A Global Positioning System (GPS) receiver can generally track 5-7 rays from GPS satellites at any moment, and water vapor along these ray paths (slant-path water vapor, SWV) may be retrieved using the methods developed in recent years. This paper suggests two new parameters-absolute vertical SWV (VSWV) and relative VSWV derived from SWV, and their temporal and spatial figures can reflect the heterogeneous distribution and variation of water vapor field. This approach has been applied to the weather diagnoses in a severe storm event in Beijing during July 2004, and it is concluded that the temporal and spatial figures of absolute VSWV and relative VSWV can be useful in monitoring the evolution of water vapor field and be potential in better understanding the precipitation process. 相似文献
994.
Helium and argon isotopes of the Tertiary basic igneous rocks from Shandong Peninsula and implications for the magma origin 总被引:2,自引:0,他引:2
TANG HuaYun ZHENG JianPing? CHEN HongHan & YE XianRen State Key Laboratory of Geological Processes Mineral Resources Faculty of Earth Sciences China University of Geosciences Wuhan China Faculty of Earth Resources China University of Geosciences Wuhan China State Key Laboratory of Gas Geochemistry Institute of Geology Geophysics Chinese Academy of Sciences Lanzhou China 《中国科学D辑(英文版)》2007,50(7):1021-1032
Helium (He) and Argon (Ar) isotopic compositions of the Tertiary basic igneous rocks were determined by the high temperature melting extraction method. The selected samples for the studies included al-kaline basalts and diabases from the Jiyang basin,and the surrounding Shanwang and Qixia outcrops in the Shandong Peninsula,eastern China. The results show that the Paleogene basalts and diabases from the Jiyang basin yielded a wide range of P4 PHe abundance of (73.70-804.16)×10 P-8 Pcm P3 P STP·g P-1 P,with P3 PHe/ P4 PHe ratios of 0.374-2.959 Ra,which was lower than the MORB but evidently higher than the con-tinental crust value. The Neogene alkaline basalts from the Jiyang basin,Shanwang and Qixia outcrops have variable P4 PHe abundances ((42.34-286.72)×10-8 Pcm P3 P STP·g-1 P),and "continental crust-like" P3 PHe/ P4 PHe ratios (0.013-0.074 Ra). All of them contain atmospheric-like P40 PAr/ P36 PAr ratio (395.4-1312.7),reflecting the mantle sources with air components. Their low P3 PHe/ P4 PHe ratios are interpreted as the enrichment of the radiogenic P4 PHe mainly inherited from the mantle. He and Ar systematics show the mixing of MORB-type,air and a P4 PHe enriched member in the mantle source,suggesting that these igneous rocks originated from the depleted asthenospheric mantle mixed with an EMI component. Therefore,the present He and Ar isotopes do not support the viewpoints that the Cenozoic igneous rocks of Eastern North China were the products of mantle plume(s) activities. 相似文献
995.
XU QingHai LI YueCong YANG XiaoLan & ZHENG ZhenHua College of Resource Environment Hebei Normal University Shijiazhuang China Institute of Geology Geophysics Chinese Academy of Sciences Beijing China Hebei Institute of Geography Science Shijiazhuang China 《中国科学D辑(英文版)》2007,50(4):582-599
205 surface pollen samples from different communities in Northern China were analyzed to understand the quantitative relationship between pollen and its original vegetation. Pollen analysis and vegetation investigation show that the pollen assemblages differ a lot in different vegetation regions. Arboreal pollen account for more than 30% in temperate broad-deciduous forests region. In temperate steppe regions, herb pollen percentages are more than 90%, where Artemisia and Chenopodiaceae are domi- nant pollen types with Artemisia percentages more than 30%. In temperate desert, Chenopodiaceae pollen percentages are more than Artemisia, where ferns are rare. Cyperaceae pollen percentages are more than 20% in sub-alpine or cold meadows. The relations between pollen percentages and vegeta- tion cover indicate that most arboreal pollen shows a close relationship with parent plant covers, most shrubby pollen types have more or less correlations, but most herbs do not show clear correlations. For arboreal pollen types, Picea pollen shows the closest correlation with spruce trees coverage, then is Quercus and Carpinus. Betula, Larix and Juglans have also high correlation coefficients with their plants coverage, but Betula pollen is of overrepresented pollen type and more than 40% in birch forest, while Larix and Juglans pollen is underrepresented and pollen percentages are more than 10% in Larix or Juglans pure forests. Pinus is of overrepresented pollen type, and pollen percentages have some relations with plants cover. Pine forest might present when Pinus pollen percentages are more than 30%. The relations between Ulmus and Populus pollen percentages and vegetation cover are not close, where they are mixed with other arbors, they cannot be recorded easily, but if their pollen percentages are more than 1%, Ulmus or Populus trees should exist. For shrubby pollen types, the correlation be- tween Vitex pollen percentages and vegetation cover is the highest, then is Corylus, Tamariaceae and Nitraria, and their pollen percentages are less than 1% where original plant are absent. Caragana and Spiraea pollen percentages have some relations with vegetation cover. The relations between pollen percentages and vegetation cover are not clear for Rosaceae and Saxifragaceae. For herb pollen types, Cyperaceae pollen has the closest correlation with vegetation cover, where pollen percentages are more than 20% when Cyperaceae are constructive or dominant species in vegetation, and pollen per- centages are less than 5% where Cyperaceae are not constructive or dominant species (cover less than 30%). Artemisia and Chenopodiaceae pollen percentages mainly have close relations with ecological regions. The relations between pollen percentages and cover are not clear for Gramineae, Legumi- nosae and Compositae. 相似文献
996.
Comparison of 15 evaporation methods applied to a small mountain lake in the northeastern USA 总被引:7,自引:0,他引:7
Donald O. Rosenberry Thomas C. Winter Donald C. Buso Gene E. Likens 《Journal of Hydrology》2007,340(3-4):149-166
Few detailed evaporation studies exist for small lakes or reservoirs in mountainous settings. A detailed evaporation study was conducted at Mirror Lake, a 0.15 km2 lake in New Hampshire, northeastern USA, as part of a long-term investigation of lake hydrology. Evaporation was determined using 14 alternate evaporation methods during six open-water seasons and compared with values from the Bowen-ratio energy-budget (BREB) method, considered the standard. Values from the Priestley–Taylor, deBruin–Keijman, and Penman methods compared most favorably with BREB-determined values. Differences from BREB values averaged 0.19, 0.27, and 0.20 mm d−1, respectively, and results were within 20% of BREB values during more than 90% of the 37 monthly comparison periods. All three methods require measurement of net radiation, air temperature, change in heat stored in the lake, and vapor pressure, making them relatively data intensive. Several of the methods had substantial bias when compared with BREB values and were subsequently modified to eliminate bias. Methods that rely only on measurement of air temperature, or air temperature and solar radiation, were relatively cost-effective options for measuring evaporation at this small New England lake, outperforming some methods that require measurement of a greater number of variables. It is likely that the atmosphere above Mirror Lake was affected by occasional formation of separation eddies on the lee side of nearby high terrain, although those influences do not appear to be significant to measured evaporation from the lake when averaged over monthly periods. 相似文献
997.
998.
Adam Carter Benjamin van Wyk de Vries Karim Kelfoun Patrick Bachèlery Pierre Briole 《Bulletin of Volcanology》2007,69(7):741-756
A clear model of structures and associated stress fields of a volcano can provide a framework in which to study and monitor
activity. We propose a volcano-tectonic model for the dynamics of the summit of Piton de la Fournaise (La Reunion Island,
Indian Ocean). The summit contains two main pit crater structures (Dolomieu and Bory), two active rift zones, and a slumping
eastern sector, all of which contribute to the actual fracture system. Dolomieu has developed over 100 years by sudden large
collapse events and subsequent smaller drops that include terrace formation. Small intra-pit collapse scars and eruptive fissures
are located along the southern floor of Dolomieu. The western pit wall of Dolomieu has a superficial inward dipping normal
fault boundary connected to a deeper ring fault system. Outside Dolomieu, an oval extension zone containing sub-parallel pit-related
fractures extends to a maximum distance of 225 m from the pit. At the summit the main trend for eruptive fissures is N80°,
normal to the north–south rift zone. The terraced structure of Dolomieu has been reproduced by analogue models with a roof
to width ratio of approximately 1, suggesting an original magma chamber depth of about 1 km. Such a chamber may continue to
act as a storage location today. The east flank has a convex–concave profile and is bounded by strike-slip fractures that
define a gravity slump. This zone is bound to the north by strike-slip fractures that may delineate a shear zone. The southern
reciprocal shear zone is probably marked by an alignment of large scoria cones and is hidden by recent aa lavas. The slump
head intersects Dolomieu pit and may slide on a hydrothermally altered layer known to be located at a depth of around 300 m.
Our model has the summit activity controlled by the pit crater collapse structure, not the rifts. The rifts become important
on the mid-flanks of the cone, away from pit-related fractures. On the east flank the superficial structures are controlled
by the slump. We suggest that during pit subsidence intra-pit eruptions may occur. During tumescence, however, the pit system
may become blocked and a flank eruption is more likely. Intrusions along the rift may cause deformation that subsequently
increases the slump’s potential to deform. Conversely, slumping may influence the east flank stress distribution and locally
control intrusion direction. These predictions can be tested with monitoring data to validate the model and, eventually, improve
monitoring. 相似文献
999.
North Pacific sea ice cover, a predictor for the Western North Pacific typhoon frequency? 总被引:14,自引:0,他引:14
Fan Ke 《中国科学D辑(英文版)》2007,50(8):1251-1257
The relationship between the sea ice cover in the North Pacific and the typhoon frequency has been studied in this paper. It follows that the index for the sea ice cover in the North Pacific (ISA) both in December-January-February (DJF) and in March-April-May (MAM) is negatively correlated with annual typhoon number over the western North Pacific (TNWNP) during 1965―2004, with correlation coeffi-cients of -0.42 and -0.49 respectively (above 99% significant level). Large sea ice cover in the North Pacific tends to decrease TNWNP. Positive ISA (MAM) is associated with the tropical circulation and SST anomalies in the North Pacific, which may lead to unfavorable dynamic and thermal conditions for typhoon genesis over WNP from June to October (JJASO). The variability of the atmospheric circula-tion over the North Pacific, associated with the ISA anomaly in MAM is connected to the tropical at-mospheric circulation variability in MAM via the teleconnection wave train. Besides, as the tropical circulation has strong seasonal persistency from the MAM to JJASO, thus, the ISA in MAM-related variability of the tropical atmospheric circulation as well as the SST can affect the typhoon activity over the western North Pacific. 相似文献
1000.