全文获取类型
收费全文 | 46065篇 |
免费 | 899篇 |
国内免费 | 454篇 |
专业分类
测绘学 | 1445篇 |
大气科学 | 3522篇 |
地球物理 | 9750篇 |
地质学 | 15732篇 |
海洋学 | 3778篇 |
天文学 | 10721篇 |
综合类 | 196篇 |
自然地理 | 2274篇 |
出版年
2021年 | 402篇 |
2020年 | 426篇 |
2019年 | 486篇 |
2018年 | 1124篇 |
2017年 | 1047篇 |
2016年 | 1387篇 |
2015年 | 810篇 |
2014年 | 1340篇 |
2013年 | 2289篇 |
2012年 | 1446篇 |
2011年 | 1782篇 |
2010年 | 1680篇 |
2009年 | 2249篇 |
2008年 | 1942篇 |
2007年 | 1932篇 |
2006年 | 1802篇 |
2005年 | 1378篇 |
2004年 | 1380篇 |
2003年 | 1245篇 |
2002年 | 1294篇 |
2001年 | 1164篇 |
2000年 | 1082篇 |
1999年 | 955篇 |
1998年 | 961篇 |
1997年 | 940篇 |
1996年 | 780篇 |
1995年 | 716篇 |
1994年 | 677篇 |
1993年 | 588篇 |
1992年 | 507篇 |
1991年 | 520篇 |
1990年 | 503篇 |
1989年 | 521篇 |
1988年 | 461篇 |
1987年 | 542篇 |
1986年 | 489篇 |
1985年 | 571篇 |
1984年 | 698篇 |
1983年 | 618篇 |
1982年 | 596篇 |
1981年 | 539篇 |
1980年 | 478篇 |
1979年 | 471篇 |
1978年 | 486篇 |
1977年 | 415篇 |
1976年 | 368篇 |
1975年 | 391篇 |
1974年 | 359篇 |
1973年 | 398篇 |
1972年 | 284篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
I.IN~crIOXLocatedinthecoddlepatofTallmBasin,withanareaof33.76X104klnZ,theTaldirnakan~isinthehinterlandofEurasia.Blockedbythehighmountainsaround,vapourofoceancanhardlyreachthedesert.APartfromthis,asthedeSertisinthesinkingcompensationareaoftheascensionalaircurrentaamstheQinghal-XIZangPlateau,itSprecipitationisrareandtheevaporationcapacityisintensealltheyearround.Allthesecontributetotheformationsofthetypifydrydesertclimate.Theacidityindexofthedesertandthearoundregionisashighasmorethan50,w… 相似文献
142.
C. Christiansen F. Gertz M. J. C. Laima L. C. Lund-Hansen T. Vang C. Jürgensen 《Environmental Geology》1997,29(1-2):66-77
The yearly nutrient supply from land and atmosphere to the study area in SW Kattegat is 10 900 tons of N and 365 tons of
P. This is only few percent of the supply from adjacent marine areas, as the yearly transport through the study area is 218 000
tons of N and 18 250 tons of P. Yearly net deposition makes up 1340 tons of N (on average 2.5 g m–2 yr–1) and 477 ton of P (on average 0.9 g m–2 yr–1). Shallow-water parts of the study area have no net deposition because of frequent (>35% of the year) resuspension. Resuspension
frequency in deep water is <1% of the year. Resuspension rates, as averages for the study area, are 10–17 times higher than
net deposition rates. Because of resuspension, shallow-water sediments are coarse lag deposits with small amounts of organic
matter (1.1%) and nutrients (0.04% N and 0.02% P). Deep-water sediments, in contrast, are fine grained with high levels of
organic matter (11.7%) and nutrients (0.43% N and 0.15% P). Laboratory studies showed that resuspension changes the diffusive
sediment water fluxes of nutrients, oxygen consumption, and penetration into the sediment. Fluxes of dissolved reactive phosphate
from sediment to water after resuspension were negative in organic-rich sediments (13.2% organic matter) with low porosity
(56) and close to zero in coarse sediments with a low organic matter content (2.3%) and high porosity (73). Fluxes of inorganic
N after resuspension were reduced to 70% and 0–20% in relation to the rates before resuspension, respectively.
Received: 10 July 1995 · Accepted: 19 January 1996 相似文献
143.
Forward modeling of zero-offset data is performed in the frequency-space domain using a one-way extrapolation equation. The use of the frequency domain offers several advantages over conventional time domain methods. The greatest advantage of the frequency domain is that all time derivatives are evaluated exactly by a simple multiplication. Synthetic zero-offset sections are computed with a high degree of accuracy for arbitrary velocity and reflectivity structures. Examples are shown for realistic complicated models and compared with results from physical modeling. 相似文献
144.
145.
P. Nenovski 《Planetary and Space Science》1985,33(11):1313-1316
In the recent estimation by Maltsev and Lyatsky (1984) of the group velocity of surface waves on the inner boundary of the plasma sheet, the effect of the curvature of the field lines of the ambient magnetic field of the Earth on the spectrum has been assessed. The authors have not accounted for the fact, however, that the group velocity of the compressional surface magnetohydrodynamic waves itself is nonzero transverse to the magnetic field—a characteristic which has been omitted in the spectrum of Chen and Hasegawa (1974), being used by Maltsev and Lyatsky.This characteristic of compressional surface MHD waves is inherent for the spectrum , obtained by Nenovski (1978) in the cold plasma limit VA ? VS(VA is Alfvén velocity, and VS, sound velocity). A comment has been made on the restrictions, proceeding from the approximation, used by Maltsev and Lyatsky. The estimation of the velocities for movements of auroral riometer absorption bays have been reviewed. 相似文献
146.
147.
In this paper, the currently accepted correlation of the Early Pleistocene Ludhamian stage of England with the Tiglian‐A sub‐stage of the Netherlands is challenged. Recent investigations of Early Pleistocene marine North Sea deposits from a borehole near Noordwijk (the Netherlands) yielded evidence from molluscs, dinoflagellate cysts and sporomorphs for an alternation of warm‐temperate and arctic intervals within the Praetiglian and Tiglian stages. Marine equivalents of the terrestrial‐based pollen sub‐stages Tiglian A and B have been recognised in the upper part of the sequence. A Praetiglian age can be assigned to the lower part of the sequence on the basis of mollusc analysis. Within the Praetiglian, an alternation of warm and cold phases has been recognised from both the dinoflagellate cyst and molluscan records. Three cold phases within the Praetiglian are tentatively correlated with marine isotope stages (MIS) 96–100. The molluscan assemblages provide evidence for climate forcing of the sea level: highest sea levels are reached in the warm‐temperate intervals. Within the Praetiglian, an interval with an acme zone of the dinoflagellate cyst Impagidinium multiplexum, is correlated with the Ludhamian and tentatively linked to MIS 97 and/or MIS 96. The cold molluscan assemblages from the Noordwijk borehole include an acme zone of Megayoldia thraciaeformis, the first and only occurrence of this North Pacific bivalve in the North Sea Basin. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
148.
Erosion of man-made, forestry drainage channels occurs when the plough cuts through the surface peat layer into the underlying erodible mineral soil. A procedure is developed, based on hydraulic considerations, which will allow the drainage engineer to design stable drainage networks in upland forestry plantations. An example design chart is given for an erodible sandy loam type soil. 相似文献
149.
150.