首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2851篇
  免费   115篇
  国内免费   18篇
测绘学   106篇
大气科学   337篇
地球物理   593篇
地质学   856篇
海洋学   321篇
天文学   544篇
综合类   4篇
自然地理   223篇
  2023年   9篇
  2022年   10篇
  2021年   33篇
  2020年   43篇
  2019年   44篇
  2018年   82篇
  2017年   61篇
  2016年   112篇
  2015年   64篇
  2014年   87篇
  2013年   140篇
  2012年   123篇
  2011年   158篇
  2010年   130篇
  2009年   190篇
  2008年   173篇
  2007年   155篇
  2006年   132篇
  2005年   108篇
  2004年   116篇
  2003年   104篇
  2002年   97篇
  2001年   76篇
  2000年   83篇
  1999年   68篇
  1998年   84篇
  1997年   45篇
  1996年   44篇
  1995年   32篇
  1994年   23篇
  1993年   32篇
  1992年   22篇
  1991年   31篇
  1990年   13篇
  1989年   16篇
  1987年   15篇
  1986年   10篇
  1985年   18篇
  1984年   26篇
  1983年   19篇
  1982年   11篇
  1981年   6篇
  1980年   8篇
  1979年   8篇
  1978年   9篇
  1977年   10篇
  1976年   13篇
  1975年   13篇
  1973年   8篇
  1971年   7篇
排序方式: 共有2984条查询结果,搜索用时 15 毫秒
761.
762.

Foreword: Special Topic

Theory and simulation of solar system plasmas  相似文献   
763.
Twenty-five fans in NE Poland, formed under subaerial terminoglacial (previously called ice-contact) conditions, were investigated to model the dominant genetic processes involved. These fans show, as do other types, a proximal, a middle and a distal subenvironment. It is found, however, that the characteristics of these subenvironments as present in subaerial terminoglacial fans differ in several respects from those in fans formed under other climatic conditions. The present study deals with the middle and distal subenvironments. These appear to be much less complex than the proximal subenvironment in this type of fan. The middle terminoglacial fan comprises two sandy facies, characterized by unchannelized transport (mainly sheet floods) and stream flows. The distal terminoglacial fan is characterized by one (sandy/silty) facies, resulting from unchannelized currents and from settling in ephemeral ponds; braided streams play a secondary part in this fan subenvironment. The characteristics of the middle and distal fan subenvironments are described and illustrated, as is the facies from the distal subenvironment. Their vertical and lateral relationships are presented in a facies model.  相似文献   
764.
1Environmentalseting1.1IntroductionThecoastalwetlandsandestuariesofLouisianaareoneoftheworld'sgreatecosys-tems[1].Formilennia...  相似文献   
765.
766.
Summary The redistribution of kinetic energy in the 500mbar level is studied for 1966 as well as for 1967. The total kinetic energy is split up in three parts: a) the energy due to the mean flow, b) the energy due to eddies with a period of time longer than a month and c) the energy due to eddies with a period of time less than a month but longer than one day.The transport of these energies takes place in formally three different ways, namely by the mean flow, by longperiod and shortperiod eddies (or monthly and daily eddies).Both the transports in zonal and meridional direction are studied. As will be shown in section 2, this yields 16 transportterms. It turns out that for the 500mbar level in the region from 100°W to 30°E and from 30°N to 65°N and based on geostrophic approximated winds: a) the longperiod eddies are important, b) the role of the longperiod eddies as well as the role of the shortperiod eddies decreases with increasing latitude and c) the zonal transports and the divergence of those transports are mostly larger than the meridional transports, and the divergence of the meridional transports.
Untersuchungen der 500 mbar-Fläche in bezug auf die allgemeine Zirkulation,
Zusammenfassung Die Verteilung der kinetischen Energie im 500mb-Niveau wird für die Jahre 1966 und 1967 untersucht. Die gesamte kinetische Energie wird dabei in drei Teile zergliedert: a) die kinetische Energie der mittleren Strömung, b) die Energie aus länger als einen Monat andauernden Wirbeln und c) die Energie aus kürzer als einen Monat, aber länger als einen Tag andauernden Wirbelelementen.Der Transport dieser Energien erfolgt formal auf drei verschiedenen Wegen, nämlich durch die mittlere Strömung, durch lang- und kurzperiodige Wirbelelemente (Turbulenzelemente von Monatsdauer bzw. von Tagesdauer). Es werden die Transporte in zonaler und in meridionaler Richtung untersucht; daraus ergeben sich 16 Transportterme. Für die Region von 100°W bis 30°E und 30°N bis 65°N erweist sich unter Zugrundelegung geostrophisch approximierter Winde, a) daß langperiodige Wirbel von Bedeutung sind, b) daß die Bedeutung langperiodiger wie auch kurzperiodiger Wirbelelemente mit zunehmender geographischer Breite abnimmt und c) daß die zonalen Transporte und ihre Divergenz meistens größer sind als die meridionalen Transporte und die Divergenz meridionaler Transporte.


With 25 Figures  相似文献   
767.
Scandium, aluminium and iron contents of a considerable number of rocks, minerals and sediments for various origin are given. They have been obtained by instrumental neutron activation analysis.The concentrations of these elements in rocks and minerals are very variable. However the Fe/Sc and Al/Sc ratios for the finer particles of sediments from different origins are fairly constant. At a spec. surf. of 100 m2/g is found 0.2 to 0.3 × 104 for Fe/Sc and 0.60 to 0.95 × 104 for Al/Sc (mol).In the coarser sediments there is a considerable influence of particle size. Consequently when Sc-contents of sediments are compared for classification purposes, their spec. surf. or granulometric composition should be determined as well.  相似文献   
768.
O-H stretching vibrations in kaolinite,and related minerals   总被引:1,自引:0,他引:1  
The grades of ordering as represented by I.R. and X-ray spectra for platy kaolinite, fire clay mineral, ball clay, dickite, nacrite and tubular dehydrated halloysite samples of various origin, are related.Well ordered kaolinite, has four bands 3,693, 3,668, 3,652 and 3,620 cm–1. In less ordered kaolinite, fire clay mineral and ball clay these bands have shifted a little or of the middle two, which are the weakest, only one band may be left (between brackets): less ordered kaolinite: 3,695, 3,667, 3,652 (3,653) and 3,620 cm–1; fire clay mineral 3,696, 3,668, 3,653 (3,653) and 3,621 cm–1; ball clay 3,697, 3,652 and 3,621 cm–1.Dehydrated halloysite has 3,693–3,698, 3,668, 3,650–3,654 and 3,620–3,626 cm–1 bands. In the most disordered dehydrated halloysite samples (Martinsberg and Baia Mare) only two bands are left at 3,696 and 3,624 cm–1.Dickite has four bands: 3,708, 3,656, 3,627 and 3,622 cm–1. For the lesser ordered Mexico sample it is 3,701, 3,652, 3,627 and 3,621 cm–1. Nacrite also has four bands i.e.: 3,700, 3,650, 3,627 and 3,620 cm–1.There is, apart from orientation effects, a wide variation in the absolute and especially in the relative intensities of the I.R. bands and X-ray reflections for each of the mineral groups investigated here, but of various origin. The need of a nomenclature adapted to the level of our knowledge about this matter to day and comprising all these variations included those in morphology is emphasized.Quantitative analyses, the adjective meant in the sense of an accuracy of minimal 5%, constitute a difficult problem which is perhaps even wholly impossible to solve with the conventional methods of today.  相似文献   
769.
Summary In the present paper, we apply endoreversible thermodynamics in order to calculate the upper bound for the fraction of solar energy absorbed by the Earth, that can be converted into the mechanical energy present in the atmosphere. We assume the presence of six Hadley cells in the Earth's wind system and find an upper limit of 1.17%. For Mars we assume a single Hadley cell and find an upper limit of 0.87%.With 10 Figures  相似文献   
770.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号