全文获取类型
收费全文 | 25361篇 |
免费 | 2403篇 |
国内免费 | 2023篇 |
专业分类
测绘学 | 2020篇 |
大气科学 | 2601篇 |
地球物理 | 4917篇 |
地质学 | 12662篇 |
海洋学 | 1932篇 |
天文学 | 1573篇 |
综合类 | 2314篇 |
自然地理 | 1768篇 |
出版年
2025年 | 9篇 |
2024年 | 167篇 |
2023年 | 202篇 |
2022年 | 324篇 |
2021年 | 402篇 |
2020年 | 343篇 |
2019年 | 389篇 |
2018年 | 4136篇 |
2017年 | 3570篇 |
2016年 | 2470篇 |
2015年 | 570篇 |
2014年 | 569篇 |
2013年 | 482篇 |
2012年 | 1236篇 |
2011年 | 2648篇 |
2010年 | 2041篇 |
2009年 | 2233篇 |
2008年 | 1933篇 |
2007年 | 2299篇 |
2006年 | 401篇 |
2005年 | 441篇 |
2004年 | 522篇 |
2003年 | 507篇 |
2002年 | 388篇 |
2001年 | 215篇 |
2000年 | 218篇 |
1999年 | 190篇 |
1998年 | 147篇 |
1997年 | 108篇 |
1996年 | 91篇 |
1995年 | 82篇 |
1994年 | 81篇 |
1993年 | 72篇 |
1992年 | 57篇 |
1991年 | 48篇 |
1990年 | 29篇 |
1989年 | 15篇 |
1988年 | 26篇 |
1987年 | 20篇 |
1986年 | 15篇 |
1985年 | 11篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 23篇 |
1980年 | 19篇 |
1979年 | 4篇 |
1976年 | 8篇 |
1958年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
121.
122.
YUAN Xuyin DENG Xu SHEN Zhiyong GAO Yun 《中国地球化学学报》2007,26(4):384-393
The species of Cu, Pb, Zn, Cd and Cr in sediments of the Taihu Lake, China, have been analyzed using the sequential chemical extraction method. Variations in the chemical fractions of these metals and their geographic distributions have also been studied. For all five metals, the residual fraction is highest but the exchangeable fraction is lowest among all the fractions. Compared to other metals, Cd has the highest percentage in the exchangeable fraction, and Cr is associated mainly with the residual fraction. Cu in the organic fraction and Pb in the Fe-Mn fraction are the important species, whereas the lowest percentages are found for Cd in the organic fraction, Cu in the Fe-Mn oxide fraction and Pb in the carbonate fraction. With respect to spatial differences, the total contents in the non-residual fractions of the metals in bay sediments are found to be higher than those in other sediments. The fractions of Cd, Cu and Cr showed significant variations in different regions. The fractions of Pb and Zn, however, did not show significant variations in spatial distribution, suggesting different amounts and different paths of anthropogenic input for the metals. Comparisons of the metal speciation indicated that Cd might be the most bioavailable metal, followed by Pb. 相似文献
123.
Kryštof Verner Jiří Žák Jaroslava Pertoldová Josef Šrámek Jiří Sedlák Jakub Trubač Patricie Týcová 《International Journal of Earth Sciences》2009,98(3):517-532
The Plechy pluton, southwestern Bohemian Massif, represents a late-Variscan, complexly zoned intrusive center emplaced near
the crustal-scale Pfahl shear zone; the pluton thus provides an opportunity to examine the interplay among successive emplacement
of large magma batches, magmatic fabric acquisition, and the late-Variscan stress field associated with strike-slip shearing.
The magmatic history of the pluton started with the emplacement of the porphyritic Plechy and Haidmühler granites. Based on
gravity and structural data, we interpret that the Plechy and Haidmühler granites were emplaced as a deeply rooted, ∼NE–SW
elongated body; its gross shape and internal fabric (steep ∼NE–SW magmatic foliation) may have been controlled by the late-Variscan
stress field. The steep magmatic foliation changes into flat-lying foliation (particularly recorded by AMS) presumably as
a result of divergent flow. Magnetic lineations correspond to a sub-horizontal ∼NE–SW finite stretch associated with the divergent
flow. Subsequently, the Třístoličník granite, characterized by steep margin-parallel magmatic foliation, was emplaced as a
crescent-shaped body in the central part of the pluton. The otherwise inward-younging intrusive sequence was completed by
the emplacement of the outermost and the most evolved garnet-bearing granite (the Marginal granite) along the southeastern
margin of the pluton.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
124.
<正>El Nio is a remarkable climate phenomenon with a basinwide warming of sea surface temperatures(SST) in the easterncentral tropical Pacific. El Nio means The Little Boy, or Christ Child in Spanish, and on the contrary, a basinwide cooling of the tropical Pacific SST is called La Nia that means The Little Girl in Spanish. Always, a large-scale SST change in the tropical 相似文献
125.
Numerical simulation for the coupling effect of local atmospheric circulations over the area of Beijing,Tianjin and Hebei Province 总被引:8,自引:0,他引:8
ShuHua Liu ZhenXin Liu Ju Li YinChun Wang YanJun Ma Li Sheng HePing Liu FuMing Liang GuoJun Xin JianHua Wang 《中国科学D辑(英文版)》2009,52(3):382-392
Using the model system MM5.V3 and multi-layer grid nesting technique, we have done a multi-scale numerical simulation over
the area of Beijing, Tianjin and Hebei Province to analyze the temperature and wind field there and study its local circulations.
The results show a coupling effect of Urban Heat Island Circulation (UHIC), Mountain Valley Breeze (MVB) and Sea Land Breeze
(SLB) occurs in this area when the synoptic system is weak. The SLB can penetrate deep into the mainland for about 200 km
when it is blooming. MVB can extend to south and cover almost the whole plain area in Beijing. Both MVB and SLB are diurnal
periodical; meanwhile the phase of MVB drops behind that of SLB for about six hours. As a local circulation, the UHIC weakens
the two circulations above, and it also has a diurnal period. As a result, the coupling effect of circulations reveals not
only different features in spring-summer period and autumn-winter period in a year but also the difference between early morning
to noonday and afternoon to night in a day. We noted the diffusion of contamination over the area around Beijing, and found
the steady presence of a transport routine of contamination over North-China throughout the year caused by the Coupling Effect
mentioned above. This find is important for studying the environment pollution in this area.
Supported by Central Public Welfare Special Fund Program for the Institute and Higher Education (Grant No. IUMKY200701), Public
Welfare Special Fund Program (Meteorology) of China Scientific and Technological Ministry (Grant Nos. CYHY20080620, CYHY200706004),
Spread New Technology Program of China Meteorological Administration (Grant No. CMATG2007M15) and Urban Meteorology Scientific
Research Fund Program of the Institute of Beijing Urban Meteorology, China Meteorological Administration (Grant No. UMRF200702) 相似文献
126.
Iranian strong motion records as well as detailed conditions of their instrument sites and the characteristics of their causative seismic sources are compiled and processed. The dataset consists of 2286 three-component records from 461 Iranian earthquakes with at least two high-quality records having moment magnitude from 3.9 to 7.3. These records are about 20% of the Iranian database and are suitable for seismic hazard analysis and engineering applications. Perhaps for the first time in the literature, the distance to the surface projection of the fault is reported for a great number of records corresponding to earthquakes with M > 6.0. The raw accelerations are processed using the wavelet de-noising method. Having corrected and filtered these raw data, the pseudospectral accelerations are calculated for each of the three components of time series, separately. In addition to the ground motion parameters, a large and comprehensive list of metadata characterizing the recording conditions of each record is also developed. Moreover, careful revision of the characteristics of the earthquakes such as location, magnitude, style of faulting and fault rupture plane geometry, if available, is carried out using the best available information in a scientifically sound manner. Finally, we also focus on special ground motion records including records with peak ground acceleration (PGA) >300 cm/s2 and distances less than 30 km. These are “exceptional” records in the Iranian dataset and include less than 2% of the selected dataset. 相似文献
127.
Tao Chen Christoph Clauser Gabriele Marquart Karen Willbrand Thomas Hiller 《Hydrogeology Journal》2018,26(6):1903-1916
Upscaling permeability of grid blocks is crucial for groundwater models. A novel upscaling method for three-dimensional fractured porous rocks is presented. The objective of the study was to compare this method with the commonly used Oda upscaling method and the volume averaging method. First, the multiple boundary method and its computational framework were defined for three-dimensional stochastic fracture networks. Then, the different upscaling methods were compared for a set of rotated fractures, for tortuous fractures, and for two discrete fracture networks. The results computed by the multiple boundary method are comparable with those of the other two methods and fit best the analytical solution for a set of rotated fractures. The errors in flow rate of the equivalent fracture model decrease when using the multiple boundary method. Furthermore, the errors of the equivalent fracture models increase from well-connected fracture networks to poorly connected ones. Finally, the diagonal components of the equivalent permeability tensors tend to follow a normal or log-normal distribution for the well-connected fracture network model with infinite fracture size. By contrast, they exhibit a power-law distribution for the poorly connected fracture network with multiple scale fractures. The study demonstrates the accuracy and the flexibility of the multiple boundary upscaling concept. This makes it attractive for being incorporated into any existing flow-based upscaling procedures, which helps in reducing the uncertainty of groundwater models. 相似文献
128.
129.
ChenChen Fang YongQiang Xiong Yun Li QianYong Liang TongShan Wang YongXin Li 《中国科学:地球科学(英文版)》2016,59(2):362-370
On the basis of the results of simulation experiments, now we better understand the contribution of high carbon number hydrocarbons to diamondoid generation during thermal pyrolysis of crude oil and its sub-fractions(saturated, aromatic, resin, and asphalene fractions). However, little is known about the effect of volatile components in oil on diamondoid generation and diamondoid indices due to the lack of attention to these components in experiments. In this study, the effect of volatile components in oil on diamondoid generation and maturity indices was investigated by the pyrolysis simulation experiments on a normal crude oil from the HD23 well of the Tarim Basin and its residual oil after artificial volatilization, combined with quantitative analysis of diamondoids. The results indicate that the volatile components(≤n C12) in oil have an obvious contribution to the generation of adamantanes, which occurs mainly in the early stage of oil cracking(Easy Ro1.0%), and influences the variations in maturity indices of adamantanes; but they have no obvious effect on the generation and maturity indices of diamantanes. Therefore, some secondary alterations e.g., migration, gas washing, and biodegradation, which may result in the loss of light hydrocarbons in oil under actual geological conditions, could affect the identification of adamantanes generated during the late-stage cracking of crude oil, and further influence the practical application of adamantane indices. 相似文献
130.
André Francisco Pilon 《Environmental Geology》2009,57(2):337-345
For the diagnosis and prognosis of the problems of quality of life, a multidisciplinary ecosystemic approach encompasses four
dimensions of being-in-the-world, as donors and recipients: intimate, interactive, social and biophysical. Social, cultural
and environmental vulnerabilities are understood and dealt with, in different circumstances of space and time, as the conjugated
effect of all dimensions of being-in-the-world, as they induce the events (deficits and assets), cope with consequences (desired
or undesired) and contribute for change. Instead of fragmented and reduced representations of reality, diagnosis and prognosis
of cultural, educational, environmental and health problems considers the connections (assets) and ruptures (deficits) between
the different dimensions, providing a planning model to develop and evaluate research, teaching programmes, public policies
and field projects. The methodology is participatory, experiential and reflexive; heuristic-hermeneutic processes unveil cultural
and epistemic paradigms that orient subject-object relationships; giving people the opportunity to reflect on their own realities,
engage in new experiences and find new ways to live better in a better world. The proposal is a creative model for thought
and practice, providing many opportunities for discussion, debate and development of holistic projects integrating different
scientific domains (social sciences, psychology, education, philosophy, etc.).
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
相似文献
André Francisco PilonEmail: |