全文获取类型
收费全文 | 87784篇 |
免费 | 886篇 |
国内免费 | 1445篇 |
专业分类
测绘学 | 3034篇 |
大气科学 | 5847篇 |
地球物理 | 17049篇 |
地质学 | 34629篇 |
海洋学 | 6553篇 |
天文学 | 16949篇 |
综合类 | 2398篇 |
自然地理 | 3656篇 |
出版年
2022年 | 620篇 |
2021年 | 918篇 |
2020年 | 969篇 |
2019年 | 1063篇 |
2018年 | 6716篇 |
2017年 | 5846篇 |
2016年 | 4912篇 |
2015年 | 1370篇 |
2014年 | 2318篇 |
2013年 | 3517篇 |
2012年 | 3373篇 |
2011年 | 5414篇 |
2010年 | 4538篇 |
2009年 | 5263篇 |
2008年 | 4525篇 |
2007年 | 5122篇 |
2006年 | 2784篇 |
2005年 | 1947篇 |
2004年 | 1973篇 |
2003年 | 1938篇 |
2002年 | 1767篇 |
2001年 | 1467篇 |
2000年 | 1342篇 |
1999年 | 1049篇 |
1998年 | 1030篇 |
1997年 | 1042篇 |
1996年 | 867篇 |
1995年 | 842篇 |
1994年 | 802篇 |
1993年 | 668篇 |
1992年 | 647篇 |
1991年 | 676篇 |
1990年 | 711篇 |
1989年 | 631篇 |
1988年 | 601篇 |
1987年 | 689篇 |
1986年 | 542篇 |
1985年 | 729篇 |
1984年 | 772篇 |
1983年 | 759篇 |
1982年 | 687篇 |
1981年 | 593篇 |
1980年 | 624篇 |
1979年 | 500篇 |
1978年 | 528篇 |
1977年 | 479篇 |
1976年 | 430篇 |
1975年 | 417篇 |
1974年 | 440篇 |
1973年 | 497篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Dr. E. K. Walton 《International Journal of Earth Sciences》1960,50(1):63-77
Lower Palaeozoic successions in the Southern Uplands are much thicker than previously supposed and sedimentation may have lasted well into Ludlow times. Volcanic rocks are Arenig and Glenkiln in age and are often interbedded with greywackes and shales. Lapworth's concept of the structure as an anticlinorium and a synclinorium is rejected and it is suggested that the rocks have been folded into a series of compound monoclines which face north-westwards. These are probably cut by strike faults which bring up the older beds to the north.
Zusammenfassung Die altpaläozoischen Schichtfolgen in den Südlichen Hochlanden sind viel mächtiger, als bisher angenommen wurde, und die Ablagerung kann bis ins Ludlow gereicht haben. Vulkanite haben Arenig- und Glenkiln-Alter; sie wechsellagern oft mit Grauwacken und Tonschiefern.Lapworths Vorstellung, der tektonische Bau sei ein Antiklinorium und ein Synklinorium, wird bestritten. Es wird angenommen, daß die Gesteine zu zusammengesetzten Monoklinen gefaltet wurden, deren steile Flügel nordwestwärts weisen. Sie werden wahrscheinlich durch streichende Verwerfungen zerschnitten, die die älteren Schichten im Norden herausheben.相似文献
52.
Distribution of the trace elements Cr, Cu, Ni, Pb and Zn in surficial sediments of the river/sea environment in Danang –
Hoian area (Vietnam) was investigated to examine the degree of metal pollution caused by anthropogenic activities. Point sources
from domestic and industrial wastes are identified as dominant contributors of trace element accumulation. Surficial sediments
of Hoian River show extremely high total concentrations of Cu (Average Concentration 295 μg/g), Ni (AC 112 μg/g), Pb (AC 396 μg/g)
and Zn (AC 429 μg/g) that exceed assigned safety levels ER-M. Similarly, the sediments of Han River show high Pb (AC 188 μg/g)
and Zn (AC 282 μg/g) contents. In marine sediments of Thanhbinh beach Pb is also enriched (138 μg/g) above guideline levels.
In contrast the sediments of the Cude River are dominated by trace element concentrations close to background values.
Received: 17 December 1998 · Accepted: 6 May 1999 相似文献
53.
Reply to comment on ‘Up‐scaling potential impacts on water flows from agricultural water interventions: opportunities and trade‐offs in the Osman Sagar catchment,Musi sub‐basin,India’. Hydrological Processes 27: 3905–3921 by Bouma et al., 下载免费PDF全文
Kaushal K. Garg Suhas P. Wani Jennie Barron Louise Karlberg Johan Rockstrom 《水文研究》2014,28(8):3352-3355
54.
Chuanbo Zhou Shiwei Lu Nan Jiang Dingbang Zhang Zhihua Zhang Gaojian Miao 《Geotechnical and Geological Engineering》2016,34(3):847-866
In Daye Iron Mine, the open-pit mining has ended and the underground mining started in 2003. The present pit slopes are as high as 430 m and the slope angle is up to 43°. During the process of open-pit to underground mining, the high-steep pit slopes would be affected by both open-pit mining and underground mining, and its deformation characteristics would become more complex. So in this paper, the trinity method of numerical simulation, model experiment and field test was adopted to analyze the displacement and stress fields systematically. The results show that: (1) Prominent rebound deformation occurs near the slope foot, which is induced by the unloading in open-pit mining. When it is backfilled to 0 m level, the rebound deformation decreases, which indicate that backfilling mass can restrict the deformation and improve the slope stability; (2) Subsidence dominates the slope deformation in open-pit to underground mining and it increases with an increasing elevation of monitoring point; the maximum horizontal displacement occurs in the lower part of the slopes, because the backfilled part is squeezed by both the north slope and the south slope, and it has a lower elastic modulus than the previous orebody; (3) The stress and its variability near the slope foot are much larger than other places, indicating that the slope foot is most affected by stress redistribution and stress concentration may occur here; the stress at other stress monitoring points changes little, indicating that the influence of open-pit to underground mining is local; (4) The effect of underground mining on the deformation of the faults is not prominent; (5) Mining operations in near-ground part affect more on the variation of deformation and stress of pit slopes than that in deeper part. 相似文献
55.
B. I. Nazarov S. F. Abdullaev V. A. Maslov 《Izvestiya Atmospheric and Oceanic Physics》2010,46(4):475-481
We studied the temperature variations of the lower air layer caused by dust content using a dust storm in Dushanbe in November
2007 as an example. Quantitative estimates of air cooling and a decrease in the diurnal temperature difference due to a diminishing
horizontal visibility range are given. Observations of air temperature variations due to the dust content of the atmosphere
in an arid zone are presented. The critical value of aerosol concentration for toggling between the greenhouse and antigreenhouse
effects is determined. The long-term effect of dust aerosol on climate is analyzed. 相似文献
56.
This paper considers volcanogenic exhalation mineralization using data from 35 years of observation of fumarole activity during an earlier phase of the posteruptive activity of the Second Cone, which is one of the New Tolbachik volcanoes that were formed during the eruption at the North Vent of the Great Tolbachik Fissure Eruption (Kamchatka, 1975–1976). We describe the main types of mineral associations, identify the key mineral species and the secondary and accessory minerals, as well as the sequence of mineral generation. We provide a summary of minerals and compounds that have been identified in ejecta of fumaroles on the Second Cone. 相似文献
57.
I. S. Lykova I. V. Pekov N. N. Kononkova A. K. Shpachenko 《Geology of Ore Deposits》2010,52(8):837-842
Jinshanjiangite (acicular crystals up to 2 mm in length) and bafertisite (lamellar crystals up to 3 × 4 mm in size) have been found in alkali granite pegmatite of the Gremyakha-Vyrmes Complex, Kola Peninsula. Albite, microcline, quartz, arfvedsonite, zircon, and apatite are associated minerals. The dimensions of a monoclinic unit cell of jinshanjiangite and bafertisite are: a = 10.72(2), b=13.80(2), c = 20.94(6) Å, β = 97.0(5)° and a = 10.654(6), b = 13.724(6), c = 10.863(8) Å, β = 94.47(8)°, respectively. The typical compositions (electron microprobe data) of jinshanjiangite and bafertisite are: (Na0.57Ca0.44)Σ1.01(Ba0.57K0.44)Σ1.01 (Fe3.53Mn0.30Mg0.04Zn0.01)Σ3.88(Ti1.97Nb0.06Zr0.01)Σ2.04(Si3.97Al0.03O14)O2.00(OH2.25F0.73O0.02)Σ3.00 and (Ba1.98Na0.04K0.03)Σ2.05(Fe3.43Mn0.37Mg0.03)Σ3.83(Ti2.02Nb0.03)Σ2.05 (Si3.92Al0.08O14)(O1.84OH0.16)Σ2.00(OH2.39F1.61)Σ3.00, respectively. The minerals studied are the Fe-richest members of the bafertisite structural family. 相似文献
58.
Ohne Zusammenfassung 相似文献
59.
Louisiana’s Haynesville Shale is one of several unconventional gas plays that have been discovered in the U.S. in recent years
and promise to dramatically change the course of future domestic energy development. The Haynesville Shale is the deepest,
hottest, and highest pressured shale among the big four plays in the U.S. with drilling and completion cost ranging between
7 and7 and 10 million per well. The average Haynesville well has an initial production rate of 10 MMcfd and declines rapidly,
producing 80% of its expected recovery during the first 2 years of production. The purpose of this article is to describe
the productivity characteristics of Haynesville wells, project future production from the inventory of active wells, and assess
production potential based on drilling scenarios. We offer statistical analysis of the wells drilled to date and construct
type profiles to characterize the play. We estimate that the current inventory of Haynesville wells will produce 3 Tcf over
their lifecycles, and within the next 3 years, cumulative build-out in the region will range between 3 and 9 Tcf. To maintain
current gas production levels in the state, we estimate that about 550 shale gas wells per year will need to be brought online
over the next 3 years. 相似文献
60.
Jiawei Yang Chengyu Liu Rong Shu Feng Xie 《Journal of the Indian Society of Remote Sensing》2018,46(11):1749-1759
To prevent confusion between water and buildings in the extraction of urban surface water from hyperspectral data, we analyzed the spectra of shadows and water in hyperspectral images, and proposed an anti-shadow water extraction method. This method first uses the normalized difference vegetation index (NDVI) for initial water extraction, then uses the height of the reflectance peak at 588 nm to eliminate the shadow of buildings. The method was validated by two hyperspectral datacubes, which were obtained for Jiaxing City and Zhoushan City in Zhejiang Province, China. Compared to the common spectral indices used to extract a water body, such as the NDVI, normalized difference water index, hyperspectral difference water index, and index of water index, the proposed method could effectively eliminate the shadow of buildings. The commission error reduced from more than 40% to about 15%, and the Kappa coefficient was increased from 60 and 70% to over 80% for the two datacubes. This indicated that the proposed method can inhibit the shadow of buildings and does not have a regional dependence. 相似文献