全文获取类型
收费全文 | 67433篇 |
免费 | 942篇 |
国内免费 | 679篇 |
专业分类
测绘学 | 2192篇 |
大气科学 | 4961篇 |
地球物理 | 13643篇 |
地质学 | 23015篇 |
海洋学 | 5632篇 |
天文学 | 16009篇 |
综合类 | 239篇 |
自然地理 | 3363篇 |
出版年
2021年 | 561篇 |
2020年 | 589篇 |
2019年 | 707篇 |
2018年 | 1621篇 |
2017年 | 1518篇 |
2016年 | 1958篇 |
2015年 | 1129篇 |
2014年 | 1872篇 |
2013年 | 3369篇 |
2012年 | 2015篇 |
2011年 | 2624篇 |
2010年 | 2307篇 |
2009年 | 3071篇 |
2008年 | 2684篇 |
2007年 | 2686篇 |
2006年 | 2547篇 |
2005年 | 2009篇 |
2004年 | 1975篇 |
2003年 | 1871篇 |
2002年 | 1888篇 |
2001年 | 1692篇 |
2000年 | 1608篇 |
1999年 | 1405篇 |
1998年 | 1391篇 |
1997年 | 1387篇 |
1996年 | 1195篇 |
1995年 | 1098篇 |
1994年 | 1043篇 |
1993年 | 884篇 |
1992年 | 785篇 |
1991年 | 825篇 |
1990年 | 821篇 |
1989年 | 805篇 |
1988年 | 729篇 |
1987年 | 864篇 |
1986年 | 759篇 |
1985年 | 894篇 |
1984年 | 1059篇 |
1983年 | 938篇 |
1982年 | 934篇 |
1981年 | 805篇 |
1980年 | 737篇 |
1979年 | 707篇 |
1978年 | 713篇 |
1977年 | 631篇 |
1976年 | 574篇 |
1975年 | 575篇 |
1974年 | 575篇 |
1973年 | 631篇 |
1972年 | 427篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
261.
Summary This paper concerns the use of airborne or ground-based Doppler radars to observe precipitating systems over complex orography.
As nearly all of the previous experiments involving Doppler radars were conducted over flat surfaces over the continents or
the oceans, new techniques are needed firstly to separate ground clutter from meteorological signal and, in the case of airborne
Doppler observations, to deduce navigational errors. Secondly, it is necessary to take the atmospheric circulation induced
by orography into account in the three-dimensional wind field analysis. Variational techniques are presented to solve these
problems.
The proposed methods are tested with simulated ground-based and airborne Doppler radar observations for analytic flows over
analytic terrains and for numerically simulated wind and reflectivity fields for the Brig event (22 September 1993) of heavy
precipitation over the southern flank of the Alps (Cosma and Richard, 1998), and with actual airborne Doppler data relative
to weak snow showers over the Rocky Mountains on 12 March 1995.
Received March 22, 1999/Revised June 1, 1999 相似文献
262.
263.
264.
Di Baofeng Katsenis Loukas Stamatopoulos Constantine A. Panoskaltsis Vassilis P. 《Landslides》2021,18(6):2297-2307
Landslides - Earthquake-induced landslides involve excessive movement of slopes, usually along slip surfaces. This seismic movement of slopes may depend crucially on (a) the soil response along the... 相似文献
265.
The question of what lies ahead is of particular concern for Latin Americanists. The last decade has witnessed a serious erosion of both the popularity of their specialty, and an equally troublesome reduction in employment opportunities. This paper uses Association of American Geographers (AAG) data bases to document the age-gender structure of contemporary Latin Americanist geographers, and projects likely compositional changes through the end of the century. 相似文献
266.
This paper presents an integrated measurement technique based on DC methods (vertical electrical sounding, electrical resistivity tomography) which was used to identify faults and determine their geoelectric parameters in the western part of the Chuya basin. New information on the structure of the Chagan River valley located in the zone of the disastrous 27 September 2003 Chuya earthquake has been obtained from the results of these methods. Geoelectric cross-sections of the sedimentary sequence and the upper part of the basement were obtained from VES data, showing the block structure of the study area. Electrical resistivity tomography sections confirm the presence of a major fault between basement blocks of different heights and indicate the presence of faults bounding the valley on its right side and in the southwestern part. 相似文献
267.
David L. Finnegan Janet P. Kotra Diane M. Hermann William H. Zoller 《Bulletin of Volcanology》1989,51(2):83-87
A simple system was designed using7LiOH-impregnated filters to collect acidic gases from ambient air and from highly concentrated volcanic plumes or gas streams. These filters were developed for analysis using instrumental neutron activation analysis, but other analytical techniques could be used as well. The sampling system was designed to use a series of 1–3 M7LiOH-impregnated filters to collect high concentrations of acidic gases found in gas plumes of active volcanoes. The filters are quantitative for SO2 and the halide acids when sufficient base is present to neutralize the acidic species. Extremely high concentrations of SO2 may not be collected quantitatively since SO2 is a relatively weak Lewis acid compared to the halide acids. The acidic oxides of Sb, As, and Se were also collected quantitatively. A particle filter preceded the impregnated filters in order to remove particles from the fumes. This system has proven effective under difficult sampling conditions and, since it is portable and light weight, it could be used for many volcanological applications where high levels of acidic gaseous phase species need to be collected. 相似文献
268.
An ecotoxicological assessment is given to the state of small lakes in specially protected natural areas in Northwestern and Central European Russia, which suffer from aerotechnogenic acidification. The toxicity of water and bottom sediments is shown to increase with decreasing water pH. The most sensitive characteristics of aquatic organisms in different trophic groups are chosen, allowing the state of lakes to be monitored. 相似文献
269.
A. V. Mityukov A. M. Nikishin O. A. Almendinger S. N. Bolotov V. A. Lavrishchev N. K. Myasoedov E. V. Rubtsova 《Moscow University Geology Bulletin》2012,67(2):81-92
This work is based on the results of 2-D and 3-D surveys in the Tuapse Basin and field works in the Crimea-Caucasus region. Seven zones were outlined in the model of sedimentation starting from the eroded mountain structure of the Greater Caucasus down to deep water sediments of the Tuapse Basin. The slope and deep-water sediments of channels and fan complexes are characterized. Volume models of the sedimentation system in the Black Sea are shown for the first time. 相似文献
270.
Gabriella Sch?ll-Barna Attila Demény Gábor Serlegi Szilvia Fábián Pál Sümegi István Fórizs Bernadett Bajnóczi 《Journal of Paleolimnology》2012,47(1):87-100
Geochemical records of bivalve shells have been increasingly studied in the last decade to obtain information on climate conditions.
In this paper we present stable isotope compositions of living and prehistoric shells of freshwater mussels (Unionidae) and
their relationships with climate conditions in a shallow lake environment of Lake Balaton, West-Central Hungary. Physical
conditions and stable oxygen isotope compositions of lake water samples were monitored where living bivalves were collected.
Comparisons between seasonal variations in ambient temperature, water composition and within-shell isotopic variations indicate
that the shells of Unio pictorum do reflect local changes at high resolution and thus can be used to study past conditions. Additionally, shells covering
the last two decades were gathered at several locations along the lake in order to determine spatial and temporal variations
in the shells’ isotopic compositions as a function of weather conditions. As an application, prehistoric shells collected
in archaeological excavations were analysed in order to study past environmental variations. Climate variations during the
Late Copper Age (5460–4870 cal. yr BP) have been assumed on the basis of geomorphological and archaeozoological observations
at the site Balatonkeresztúr-Réti-dűlő (south of Lake Balaton), that suggested increasing humidity as a cause of changes in
settlement location and domestic livestock husbandry. Stable carbon and oxygen isotope compositions of prehistoric bivalve
shells were analyzed from excavations representing five archaeological subphases (Boleráz subphase, 5460–5310 cal. yr BP;
two transitional subphases around 5310 cal. yr BP; Early Classic subphase, 5310–5060 cal. yr BP; Late Classic subphase, 5040–4870 cal.
yr BP). The analyses revealed significant negative C and O isotope shifts in the transitional subphases relative to the earlier
and later subphases. The isotopic variations indicate that the local climate became relatively wet and possibly cold around
5310 cal. yr BP, then it returned to drier (and likely warmer) conditions during the Classic subphases. This interpretation
is in agreement with previous studies on climate changes related to the “5.3 ky event” in the European continental area and
the North Atlantic Region, indicating an Atlantic influence in the Carpathian Basin. 相似文献