全文获取类型
收费全文 | 9777篇 |
免费 | 372篇 |
国内免费 | 58篇 |
专业分类
测绘学 | 279篇 |
大气科学 | 855篇 |
地球物理 | 2497篇 |
地质学 | 3676篇 |
海洋学 | 682篇 |
天文学 | 1700篇 |
综合类 | 39篇 |
自然地理 | 479篇 |
出版年
2023年 | 45篇 |
2022年 | 67篇 |
2021年 | 171篇 |
2020年 | 195篇 |
2019年 | 166篇 |
2018年 | 401篇 |
2017年 | 417篇 |
2016年 | 548篇 |
2015年 | 410篇 |
2014年 | 494篇 |
2013年 | 676篇 |
2012年 | 536篇 |
2011年 | 577篇 |
2010年 | 490篇 |
2009年 | 604篇 |
2008年 | 448篇 |
2007年 | 338篇 |
2006年 | 361篇 |
2005年 | 293篇 |
2004年 | 282篇 |
2003年 | 244篇 |
2002年 | 225篇 |
2001年 | 178篇 |
2000年 | 158篇 |
1999年 | 140篇 |
1998年 | 135篇 |
1997年 | 157篇 |
1996年 | 95篇 |
1995年 | 97篇 |
1994年 | 95篇 |
1993年 | 65篇 |
1992年 | 65篇 |
1991年 | 52篇 |
1990年 | 78篇 |
1989年 | 40篇 |
1988年 | 46篇 |
1987年 | 56篇 |
1986年 | 37篇 |
1985年 | 54篇 |
1984年 | 51篇 |
1983年 | 51篇 |
1982年 | 46篇 |
1981年 | 47篇 |
1980年 | 32篇 |
1979年 | 40篇 |
1978年 | 34篇 |
1977年 | 30篇 |
1975年 | 28篇 |
1973年 | 26篇 |
1972年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
71.
Isabel Pérez Francisco Martín Romero Olivia Zamora Margarita Eugenia Gutiérrez-Ruiz 《Environmental Earth Sciences》2014,72(5):1521-1531
A total of 113 samples of waste and soil were collected from a site in the state of San Luis Potosi, Mexico, that was occupied for several years by the metallurgical industry. Specific magnetic susceptibility (MS), electrical conductivity (EC) and pH were determined, as well as the total and available concentrations of potentially toxic elements (PTEs) such as As, Cd, Cu, Fe, Pb and Zn, which may cause a health risk for humans, animals and ecosystems, and the concentrations of major ions in aqueous extracts of soils and wastes. The solid phases of the samples were also characterized. The results revealed that the soils and wastes exhibited elevated values of PTEs, MS and EC. For soils these values decreased with increasing distance from the waste storage sites. The MS values were elevated primarily due to the presence of Fe-oxyhydroxides, such as magnetite, hematite and goethite, which contain PTEs in their structure leading to a high correlation between the value of MS and the As, Cd, Fe and Pb contents (r = 0.57–0.91) as well as between the PTEs values (r = 0.68–0.92). The elevated EC values measured in the metallurgical wastes were the result of presence of the sulfate minerals of Ca, Mg and Fe. The pollution index, which indicates the levels of simultaneous toxicity from elements such as As, Cd and Pb, was determined, with extreme hazard zones corresponding to areas that exhibit high MS values (0.91 correlation). In conclusion, MS measurements can be used as an indirect indicator to evaluate the PTE contamination in metallurgical areas, and EC measurements can aid in the identification of pollution sources. 相似文献
72.
Mount Pinatubo volcano erupted in June 1991 in the main island of Luzon belonging to the Philippines archipelago. Huge economic
losses and population exodus have followed. This major crisis has been relayed with other crises due to rain-fed lahars which
have been supplied with eruption deposits. These lahars have occurred every year since 1991 during the rainy season. They
will probably last until 2005. After a brief presentation of the Philippine official response system to disasters, this paper
draws up a critical analysis of the different kinds of institutional and social responses deployed to manage the different
crisis and post-crisis phases of this event. Based on three viewpoints: from population, media and other actors, this analysis
attempts to point out the strengths and weaknesses of the official management system, especially by studying the efficiency
and the range of the solutions taken. So, it appears that the management of the June 1991 main crisis (eruption) was a success.
On the other hand, difficulties have occurred with lahars risk management. Indeed, these lahars have obliged the authorities
to protect and relocate thousands of people. In spite of persistent problems, the management system (monitoring/warning/evacuation)
of lahar crises improves year after year. Failures appear especially within the rehabilitation program (protection/rehousing).
Many direct (lack of means, preparedness, coordination, dialog, etc.) and indirect (politico-administrative, socio-economic,
cultural contexts) factors come together to lock the wheels of the institutional response system. They defer the socio-economic
start of this vital northern Philippines area.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
73.
C. P. Goff L. van Driel-Gesztelyi P. Démoulin J. L. Culhane S. A. Matthews L. K. Harra C. H. Mandrini K. L. Klein H. Kurokawa 《Solar physics》2007,240(2):283-299
A series of flares (GOES class M, M and C) and a CME were observed in close succession on 20 January 2004 in NOAA 10540. Radio
observations, which took the form of types II, III and N bursts, were associated with these events. We use the combined observations
from TRACE, EIT, Hα images from Kwasan, MDI magnetograms and GOES to understand the complex development of this event. Contrary
to a standard interpretation, we conclude that the first two impulsive flares are part of the CME launch process while the
following long-duration event flare represents simply the recovery phase. Observations show that the flare ribbons not only
separate but also shift along the magnetic inversion line so that magnetic reconnection progresses stepwise to neighboring
flux tubes. We conclude that “tether cutting” reconnection in the sheared arcade progressively transforms it to a twisted
flux tube, which becomes unstable, leading to a CME. We interpret the third flare, a long-duration event, as a combination
of the classical two-ribbon flare with the relaxation process following forced reconnection between the expanding CME structure
and neighboring magnetic fields.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
74.
There is an emerging requirement for processing global navigation satellite system (GNSS) signals indoor where the signal
is very weak and subjected to spatial fading. Typically, longer coherent integration intervals provide the additional processing
gain required for the detection and processing of such weak signals. However, the arbitrary physical motion of the handset
imputed by the user limits the effectiveness of longer coherent integration intervals due to the spatial decorrelation of
the multipath-faded GNSS signal. In this paper, limits of coherent integration due to spatial decorrelation are derived and
corroborated with experimental verification. A general result is that the processing gain resulting from direct coherent integration
saturates after the antenna has moved through a certain distance, which for typical indoor propagation, is about half a carrier
wavelength. However, a refined Doppler search coupled with a prolonged coherent integration interval extends this limit, which
is effectively a manifestation of selective diversity. 相似文献
75.
76.
Juan Porta Jorge Parapar Paula García Gracia Fernández Juan Touriño Ramón Doallo Francisco Ónega Inés Santé Pablo Díaz David Miranda Rafael Crecente 《Earth Science Informatics》2013,6(4):209-226
Land abandonment and stagnation of rural markets in the last few years have become one of the main concerns of rural administrations. The use of Web and GIS (Geographic Information System) technologies can help to mitigate the effects of these problems. This paper pro-poses a novel Web-GIS tool with spatial capabilities for the dynamization of rural land markets by encouraging the transfer of land from owners to farmers through the leasing of plots. The system, based on open source software, offers information about the properties, their environment and their owners. It uses standards for handling the geographic information and for communicating with external data sources. This system was used as the basis for the development of SITEGAL, the tool for the management of the Land Bank of Galicia (www.bantegal.com/sitegal). SITEGAL has been operational since 2007 obtaining benefits for both administration and users (farmers and land owners), and promoting the e-Government. 相似文献
77.
This study evaluates impacts from tropical cyclone (TC) landfalls on populated areas located along the Pacific Ocean coast of Mexico. The period of interest is from 1970 through 2010 and an international disaster database is used to identify the impact from the landfalling TCs. More than 30 landfall events occurred during the period; we examined the top 25 TCs based on rainfall accumulation, as well as the top 10 TC-related disasters based on the affected population. Each event resulted in affected population from 20 000 to more than 800 000. Strong winds and heavy rainfall, during periods of one to three days, are associated with property damage and loss of lives. Our results indicate that excessive rainfall accumulations and daily rates, over highly populated areas, are important elements associated with the occurrence of disasters. Six of the top 10 TC-related disasters occurred during El Niño and three during neutral conditions; however, looking at the top 25 events, 10 occurred during El Niño and 10 during neutral conditions. Three case studies that occurred during El Niño events (Liza in 1976, Pauline in 1997, and Lane in 2006) are documented in more detail as they affected areas with different population densities in the southern and northwestern coasts of Mexico. 相似文献
78.
Anne-Marie Lézine Augustin F.-C. Holl Judicaël Lebamba Annie Vincens Chimène Assi-Khaudjis Louis Février Émmanuelle Sultan 《Comptes Rendus Geoscience》2013,345(7-8):327-335
This paper discusses the relationship between patterns of human settlements and environmental change during the Holocene along the northwestern margins of the equatorial rain forest of central Africa. Palaeoenvironmental data from high-resolution sediment cores from lacustrine deposits, plant macro-remains from forest soils, and archaeological data are harnessed to discuss the differential impact of climate and/or humans on the central African rain forest. It is shown that climate change impacted the rain forest well before the widespread expansion of human settlements all over the study area. 相似文献
79.
Olivier J. Hardy Céline Born Katarina Budde Kasso Daïnou Gilles Dauby Jérôme Duminil Eben-Ezer B.K. Ewédjé Céline Gomez Myriam Heuertz Guillaume K. Koffi Andrew J. Lowe Claire Micheneau Dyana Ndiade-Bourobou Rosalía Piñeiro Valérie Poncet 《Comptes Rendus Geoscience》2013,345(7-8):284-296
The biogeographic history of the African rain forests has been contentious. Phylogeography, the study of the geographic distribution of genetic lineages within species, can highlight the signatures of historical events affecting the demography and distribution of species (i.e. population fragmentation or size changes, range expansion/contraction) and, thereby, the ecosystems they belong to. The accumulation of recent data for African rain forests now enables a first biogeographic synthesis for the region. In this review, we explain which phylogeographic patterns are expected under different scenarios of past demographic change, and we give an overview of the patterns detected in African rain forest trees to discuss whether they support alternative hypotheses regarding the history of the African rain forest cover. The major genetic discontinuities in the region support the role of refugia during climatic oscillations, though not necessarily following the classically proposed scenarios. We identify in particular a genetic split between the North and the South of the Lower Guinean region. Finally we provide some perspectives for future study. 相似文献
80.
16 lines of Pr ii possibly present in the solar photospheric spectrum have been studied. When including hyperfine structure in synthetic calculations, investigations of 9 lines result in an abundance A
Pr = 0.71 ± 0.08 in the log A
H = 12.00 scale. 相似文献