全文获取类型
收费全文 | 6669篇 |
免费 | 251篇 |
国内免费 | 26篇 |
专业分类
测绘学 | 205篇 |
大气科学 | 450篇 |
地球物理 | 2681篇 |
地质学 | 2110篇 |
海洋学 | 224篇 |
天文学 | 1039篇 |
综合类 | 33篇 |
自然地理 | 204篇 |
出版年
2022年 | 48篇 |
2021年 | 113篇 |
2020年 | 118篇 |
2019年 | 88篇 |
2018年 | 278篇 |
2017年 | 269篇 |
2016年 | 398篇 |
2015年 | 289篇 |
2014年 | 317篇 |
2013年 | 389篇 |
2012年 | 322篇 |
2011年 | 263篇 |
2010年 | 273篇 |
2009年 | 276篇 |
2008年 | 218篇 |
2007年 | 166篇 |
2006年 | 164篇 |
2005年 | 133篇 |
2004年 | 128篇 |
2003年 | 133篇 |
2002年 | 112篇 |
2001年 | 106篇 |
2000年 | 103篇 |
1999年 | 65篇 |
1998年 | 102篇 |
1997年 | 77篇 |
1996年 | 67篇 |
1995年 | 84篇 |
1994年 | 99篇 |
1993年 | 69篇 |
1992年 | 66篇 |
1991年 | 56篇 |
1990年 | 75篇 |
1989年 | 56篇 |
1988年 | 57篇 |
1987年 | 52篇 |
1986年 | 64篇 |
1985年 | 53篇 |
1984年 | 55篇 |
1983年 | 62篇 |
1982年 | 69篇 |
1981年 | 58篇 |
1980年 | 57篇 |
1979年 | 60篇 |
1978年 | 66篇 |
1977年 | 52篇 |
1975年 | 56篇 |
1973年 | 59篇 |
1972年 | 47篇 |
1971年 | 53篇 |
排序方式: 共有6946条查询结果,搜索用时 0 毫秒
991.
Z. Vencelides Z. Hrkal H. Nováková H. Prchalová 《Journal of Atmospheric Chemistry》2011,68(2):127-138
In harmony with requirements of Water Framework Directive the natural backgrounds of selected metals were established on the
territory of Czech Republic. This paper is intended to provide characteristics and results of testing methods focused on quantification
of the impacts of anthropogenic activities based on data of regional monitoring and their separation from acid atmospheric
deposition including an appropriate discussion regarding the natural backgrounds of relevant metals. The results indicate
that even in regions extremely affected by acid atmospheric deposition as is the territory of the Czech Republic this acid
deposition will not have direct impact on the quality of ground waters on a regional scale. Consequently, the proved changes
in quality of ground waters seem to have been caused by secondary processes, specifically by mobilization of metals in a rock
environment due to increased acidity. 相似文献
992.
Sánchez-Rodríguez A Sosa-Ferrera Z Santana-del Pino A Santana-Rodríguez JJ 《Marine pollution bulletin》2011,62(5):985-991
The presence of booster biocides in the aquatic environment has been associated with a risk to non-target species due to their proven toxicity. The aim of the present study was to determine the spatial and temporal distribution of common booster biocides in different harbours of the island of Gran Canaria (Spain) and evaluate, by means of a probabilistic risk assessment (PRA), the ecological risk posed by these compounds. With these objectives, a monitoring campaign was conducted between January 2008 and May 2009, collecting a total of 182 seawater samples. Four common booster biocides (TCMTB, diuron, Irgarol 1051 and dichlofluanid) were monitored. Diuron levels ranged between 2.3 and 203 ng/L and Irgarol 1051 between 2.4 and 146.5 ng/L. The ecological risk associated with these levels was always low, however, with probabilities of exceeding the 10th percentile of autotroph toxicity below 3.5%. 相似文献
993.
The Sultepec-Goleta area in southern Mexico hosts one of the major Eocene silicic volcanic centers that make up the Cenozoic
volcanic record of the north-central part of the Sierra Madre del Sur. This center is represented by a partially exhumed NNE-SSW
trending ignimbritic field that covers an area of ∼400 km2 with a preserved volume of ∼200 km3. A remarkable feature of volcanic center is the exposure of pyroclastic dike complexes up to 1 km wide that extend almost
continuously along the western and southern flanks of the volcanic field. The ignimbritic record comprises four units with
different textural features as well as variable proportions of the main components (i.e. phenocrysts, pumice and lithic clasts).
The most extensive unit is the basal Goleta Ignimbrite, of which the middle and upper members are richer in phenocrysts than
the lower member. It has a thickness that ranges from ∼200 m in the north to at least 600 m in the south of the volcanic center.
The overlying ignimbrite units (Cienega, Lobera and Potrero ignimbrites) are phenocryst-poor and are distributed in the northern
sector of the volcanic field. The semi-curvilinear trend of the pyroclastic dikes along the southern flank of the Goleta Range,
coupled with the greater thickness of the Goleta Ignimbrite encircled by the dikes, is indicative of the development of a
partial-collapse caldera. Based on spatial relationships as well as analogies in the nature and abundances of the components,
it has been recognized that the central and southern dike complexes fed the relatively phenocryst-rich Goleta Ignimbrite,
whereas the phenocryst-poor units of the northern sector were extruded through the pyroclastic conduits distributed around
Sultepec. We suggest that the stirring produced by the partial collapse of the magma chamber roof beneath the southern sector
of the study area triggered the tapping of phenocryst-rich portions of the zoned magma chamber, resulting in an increase of
phenocryst content in the upper members of the Goleta Ignimbrite. The presence of breccias and lithic-rich facies dominated
by wallrock fragments at the borders of the pyroclastic dikes, including those of the northern extra-caldera sector, indicate
that erosion of the conduit walls above the fragmentation level contributed to widening of the conduits and the construction
of wide dike complexes. 相似文献
994.
Teresa Grabowska Grzegorz Bojdys Miroslav Bielik Kristián Csicsay 《Acta Geophysica》2011,59(3):526-560
The paper presents 2D density and magnetic models of the crust and upper mantle along the DSS line profile of the CELEBRATION
2000 project that crosses the most important geological units in Central Europe. These are the Alps-Carpathians-Pannonian
(ALCAPA) region, the SE part of the Paleozoic Platform (PLZ), the Trans-European Suture Zone (TESZ) and a fragment of the
SW portion of the East European Craton (EEC). The density and magnetic models were constructed on the basis of a 2D model
of P-wave velocity converted into density model, geological data as well as geothermal data and the results of integrated geophysical
modelling for the lithosphere-asthenosphere boundary. 相似文献
995.
Germán Aguilar Rodrigo Riquelme Joseph Martinod José Darrozes Eric Maire 《地球表面变化过程与地形》2011,36(13):1736-1748
We quantify erosion rates in the higher sectors of the Huasco Valley, in the Main Cordillera of the semi‐arid Andes of Chile, using elevation differences between three successive geomorphic markers (pediments and paleo‐valleys) and the present day valley. Available Ar‐Ar ages of Neogene pediments are used to estimate mean erosion rates for the three periods (16 to 13 My, 13 to 8 My, and following 8 My). The landscape of the Huasco Valley is in a transient state, as indicated by well‐preserved pediment surfaces in interfluves, valleys deeply incised by fluvial and glacial erosion and scarped head‐valleys that represent the current knickzones. Higher erosion rates (45–75 m/My) are calculated for the more recent period (< 8 My) during which deep incision developed compared to previous periods (6–31 m/My). Quantitative data indicate that glaciers had a much higher erosional capability than fluvial activity in the higher sectors of the Main Cordillera. Comparison with erosion rates calculated in other drainage basins of the Chilean Andes suggests that the variability of erosion rates depends on the landscape's transient erosive state. The landscape's geomorphologic response to the uplift of the Main Cordillera results in the retreat of a knickzone, for which retreat velocity depends on precipitation rate pattern and glacial erosion intensity. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
996.
Mourad Essalhi Stanislas Sizaret Luc Barbanson Yan Chen France Lagroix François Demory José M. Nieto Reinaldo Sáez M. Ángeles Capitán 《Mineralium Deposita》2011,46(8):981-999
In the Rio Tinto district of the Iberian Pryrite Belt of South Spain, the weathering of massive sulfide bodies form iron caps,
i.e., true gossans and their subsequent alteration and re-sedimentation has resulted in iron terraces, i.e., displaced gossans.
To study the stucture and evolution of both types of gossans, magnetic investigations have been carried out with two foci:
(1) the characterisation and spatial distribution of magnetic fabrics in different mineralised settings, including massive
sulfides, gossans, and terraces, and (2) paleomagnetic dating. Hematite has been identified as the suceptibility carrier in
all sites and magnetic fabric investigation of four gossans reveals a vertical variation from top to bottom, with: (1) a horizontal
foliation refered to as “mature” fabric in the uppermost part of the primary gossans, (2) highly inclined or vertical foliation
interpreted as “immature” fabric between the uppermost and lowermost parts, and (3) a vertical foliation interpreted to be
inherited from Hercynian deformation in the lowermost part of the profiles. In terraces, a horizontal foliation dominates
and is interpreted to be a “sedimentary” fabric. Rock magnetic studies of gossan samples have identified goethite as the magnetic
remanence carrier for the low-temperature component, showing either a single direction close to the present Earth field (PEF)
direction or random directions. Maghemite, hematite, and occasionally magnetite are the remanence carriers for the stable
high-temperature component that is characterized by non PEF directions with both normal and reversed magnetic polarities.
No reliable conclusion can be yet be drawn on the timing of terrace magnetization due to the small number of samples. In gossans,
the polarity is reversed in the upper part and normal in the lower part. This vertical distribution with a negative reversal
test suggests remanence formation during two distinct periods. Remanence in the upper parts of the gossans is older than in
the lower parts, indicating that the alteration proceeded from top to bottom of the profiles. In the upper part, the older
age and the horizontal “mature” fabric is interpreted to be a high maturation stage of massive sulfides’ alteration. In the
lower part, the age is younger and the inherited “imature” vertical Hercynian fabric indicates a weak maturation stage. These
two distinct periods may reflect changes of paleoclimate, erosion, and/or tectonic motion. 相似文献
997.
Oswaldo Siga Leonardo Fadel Cury Ian McReath Ligia Maria de Almeida Leite Ribeiro Kei Sato Miguel Ângelo Stipp Basei Cláudia Regina Passarelli 《Gondwana Research》2011,19(1):260-274
The results of geological mapping, chemical analysis and radiometric dating of metabasic rocks of Betara Formation, and mapping and dating of those present in the Betara basement nucleus together with mylonitic granodiorite and syenogranite are reported here. U–Pb analysis of bulk zircon fractions from the metabasic rocks of the basement nucleus yielded a Statherian age of 1790 ± 22 Ma, while the metabasic rocks from the upper part of the Betara Formation yielded a Calymmian age between 1500 and 1450 Ma. This age is a minimum for the deposition of the Betara Formation. The older metabasic rocks are associated with post-tectonic, possibly anorogenic syenogranite, while the younger ones are gabbro or very porphyritic ankaramite whose REE patterns are consistent with crystallization from an N-MORB parent magma. The observations and data point to the probable events associated with extensional processes of the end of Paleoproterozoic and early Mesoproterozoic. Similar registers of Statherian (1.80–1.75 Ga) and Calymmian (1.50–1.45 Ga) extensional events are recorded in other parts of the South American and African continents. The Neoproterozoic witnessed the formation and junction of the tectonic slices which formed the Apiaí domain during the assemblage of western Gondwana. 相似文献
998.
999.
Comparison of quantitative petrographic, stable isotope and cathodoluminescence data for fingerprinting Czech marbles 总被引:1,自引:1,他引:0
Various marbles from both historic quarries and historical artefacts of the Czech Republic were examined in order to make determinations of their provenance. The methodology used was based upon a combination of petrographic image analysis (PIA) of thin sections, stable isotope geochemistry of carbonates, and cathodoluminescence. Multivariate statistical methods (i.e. cluster analysis and discriminant analysis) confirmed the geoscientific relevance of the marble’s different characteristics with a high degree of consistency as well as the enhanced significance of stable C and O isotopes in correlation with the petrographic data. The qualitative cathodoluminescence data provided a useful additional tool to help recognise the fingerprinting of marbles with similar petrographic and/or geochemical characteristics. 相似文献
1000.