全文获取类型
收费全文 | 20410篇 |
免费 | 4113篇 |
国内免费 | 5290篇 |
专业分类
测绘学 | 1407篇 |
大气科学 | 2161篇 |
地球物理 | 2650篇 |
地质学 | 14859篇 |
海洋学 | 2952篇 |
天文学 | 292篇 |
综合类 | 1441篇 |
自然地理 | 4051篇 |
出版年
2024年 | 100篇 |
2023年 | 280篇 |
2022年 | 714篇 |
2021年 | 903篇 |
2020年 | 821篇 |
2019年 | 1080篇 |
2018年 | 924篇 |
2017年 | 991篇 |
2016年 | 1046篇 |
2015年 | 1117篇 |
2014年 | 1304篇 |
2013年 | 1182篇 |
2012年 | 1394篇 |
2011年 | 1471篇 |
2010年 | 1218篇 |
2009年 | 1464篇 |
2008年 | 1234篇 |
2007年 | 1522篇 |
2006年 | 1454篇 |
2005年 | 1272篇 |
2004年 | 1149篇 |
2003年 | 1086篇 |
2002年 | 944篇 |
2001年 | 727篇 |
2000年 | 613篇 |
1999年 | 598篇 |
1998年 | 444篇 |
1997年 | 444篇 |
1996年 | 415篇 |
1995年 | 374篇 |
1994年 | 313篇 |
1993年 | 261篇 |
1992年 | 249篇 |
1991年 | 200篇 |
1990年 | 122篇 |
1989年 | 160篇 |
1988年 | 74篇 |
1987年 | 46篇 |
1986年 | 27篇 |
1985年 | 18篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1954年 | 3篇 |
1877年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
31.
Richard C. Preece Simon A. Parfitt G. Russell Coope Kirsty E. H. Penkman Philippe Ponel John E. Whittaker 《第四纪科学杂志》2009,24(6):557-580
Considerable debate surrounds the age of the Middle Pleistocene glacial succession in East Anglia following some recent stratigraphical reinterpretations. Resolution of the stratigraphy here is important since it not only concerns the glacial history of the region but also has a bearing on our understanding of the earliest human occupation of north‐western Europe. The orthodox consensus that all the tills were emplaced during the Anglian (Marine Isotope Stage (MIS) 12) has recently been challenged by a view assigning each major till to a different glacial stage, before, during and after MIS 12. Between Trimingham and Sidestrand on the north Norfolk coast, datable organic sediments occur immediately below and above the glacial succession. The oldest glacial deposit (Happisburgh Till) directly overlies the ‘Sidestrand Unio‐bed’, here defined as the Sidestrand Hall Member of the Cromer Forest‐bed Formation. Dating of these sediments therefore has a bearing on the maximum age of the glacial sequence. This paper reviews the palaeobotany and describes the faunal assemblages recovered from the Sidestrand Unio‐bed, which accumulated in a fluvial environment in a fully temperate climate with regional deciduous woodland. There are indications from the ostracods for weakly brackish conditions. Significant differences are apparent between the Sidestrand assemblages and those from West Runton, the type site of the Cromerian Stage. These differences do not result from contrasting facies or taphonomy but reflect warmer palaeotemperatures at Sidestrand and a much younger age. This conclusion is suggested by the higher proportion of thermophiles at Sidestrand and the occurrence of a water vole with unrooted molars (Arvicola) rather than its ancestor Mimomys savini with rooted molars. Amino acid racemisation data also indicate that Sidestrand is significantly younger than West Runton. These data further highlight the stratigraphical complexity of the ‘Cromerian Complex’ and support the conventional view that the Happisburgh Till was emplaced during the Anglian rather than the recently advanced view that it dates from MIS 16. Moreover, new evidence from the Trimingham lake bed (Sidestrand Cliff Formation) above the youngest glacial outwash sediments (Briton's Lane Formation) indicates that they also accumulated during a Middle Pleistocene interglacial – probably MIS 11. All of this evidence is consistent with a short chronology placing the glacial deposits within MIS 12, rather than invoking multiple episodes of glaciation envisaged in the ‘new glacial stratigraphy’ during MIS 16, 12, 10 and 6. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
32.
In this paper the tidal phenomena on the Earth are concisely specified, including solid tides, ocean tides and atmospheric tides due to the luni-solar tide-generating force, and the Earth pole tide due to the motion of the Earth's rotation axis (polar motion); as well as their effects on the Earth rotation. The outcomes of scientific researches of Chinese astronomers on these topics are described in some detail. These researches deal with the mechanisms responsible for tidal effects on the earth rotation, and on the measurements of the Earth rotation parameters. Finally, the effects discovered by Chinese researchers on the measurements of the period and change in period of pulsars are discussed. These effects are very small in magnitude but not negligible. 相似文献
33.
Afforestation has been suggested as a means of improving soil and water conservation in north‐western China, especially on the Loess Plateau. Understanding of the hydrological responses to afforestation will help us develop sustainable watershed management strategies. A study was conducted during the period of 1956 to 1980 to evaluate runoff responses to afforestation in a watershed on the Loess Plateau with an area of 1·15 km2, using a paired watershed approach. Deciduous trees, including locust (locusta L.), apricot (praecox L.) and elm (ulmus L.), were planted on about 80% of a treated watershed, while a natural grassland watershed remained unchanged. It was estimated that cumulative runoff yield in the treated watershed was reduced by 32% as a result of afforestation. A significant trend was also observed that shows annual runoff reduction increases with the age of the trees planted. Reduction in monthly runoff occurred mainly from June to September, which was ascribed to greater rainfall and utilization by trees during this period. Afforestation also resulted in reduction in the volume and peak flow of storm runoff events in the treated watershed with greater reduction in peak flow. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
34.
吴秋凤 《广东海洋大学学报》2003,23(5):94-98
在阐述西部大开发中科技主导地位的基础上 ,从科技应用成效二重性的视角 ,探讨了关注西部科技伦理的必要性 ,并初步提出了西部大开发战略的科技伦理调控机制 相似文献
35.
I.IN~crIOXLocatedinthecoddlepatofTallmBasin,withanareaof33.76X104klnZ,theTaldirnakan~isinthehinterlandofEurasia.Blockedbythehighmountainsaround,vapourofoceancanhardlyreachthedesert.APartfromthis,asthedeSertisinthesinkingcompensationareaoftheascensionalaircurrentaamstheQinghal-XIZangPlateau,itSprecipitationisrareandtheevaporationcapacityisintensealltheyearround.Allthesecontributetotheformationsofthetypifydrydesertclimate.Theacidityindexofthedesertandthearoundregionisashighasmorethan50,w… 相似文献
36.
文章阐述了地勘单位物业管理社会化的必然性和内函 ,提出发展地勘单位物业管理的基本内容和需要解决的问题 ,最终实现以业养业 ,自我发展。 相似文献
37.
S. Baes-Fischlmair W.W. Zeilinger J.-C. Vega-Beltran J.E. Beckman 《Astrophysics and Space Science》2003,284(2):735-738
It is assumed that the two-fold disc-wide symmetry of spirals is caused by density waves, but also the potential of a bar
component may have a significant influence on structural properties. The strength of the bar component appears to be anti-correlated
with the degree of symmetry of star-forming regions in the spiral arms (Rozas et al., 1998). We present new results of R and
Hα surface photometry of a sample of bright barred spirals. A photometric decompositon of the galaxy components is carried
out in order to make a more accurate measurement of the strength of the bar and its interrelation to gas and stars in the
disc.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
38.
Nikolay Sidorenkov 《Celestial Mechanics and Dynamical Astronomy》2003,87(1-2):27-38
Spectral analysis of the components of the relative atmospheric angular momentum vector is performed based on the series of these components for the 6 h intervals within the period of 1958–2000. These series have been computed in the Subbureau of the Atmospheric Angular Momentum of the International Earth Rotation Service using the NCEP/NCAR reanalysis of atmospheric observations. The basic harmonics of diurnal tides are determined. New results on the fortnight's and week's duration oscillations of the equatorial components of the atmospheric angular momentum are obtained. The zonal tides transformation mechanisms in the atmosphere are discussed. It is shown that the main mechanism of the zonal tides effect on the atmospheric variability is the amplitude modulation of daily oscillations of the relative atmospheric angular momentum. The effects of the atmospheric tides on the Earth rotation are discussed. 相似文献
39.
本文论述了保安地区火山岩的地质、岩石、副矿物、岩石化学、微量元素、稀土元素、稳定同位素、火山岩相及火山机构等特征。并对其演化规律、形成机制与成矿作用的关系,作了初步探讨。 相似文献
40.
FUZZY COMPREHENSIVE EVALUATION OF CONTAINER TRANSPORTATION MODES ALONG THE CHANGJIANG RIVER MAIN LINE AND ITS DELTA AREA 总被引:1,自引:0,他引:1
ZHANGShi-yu XIAOHan-liang 《中国地理科学(英文版)》2003,13(3):259-261
The Changjiang River (Yangtze) is one of the fastest growth areas of container transportation in Chi-na. Rail, road and water transportation have competed against each other for container transportation in the Chang-jiang River main line and its delta area. It is of significance to assess these different transportation modes scientifi-cally in order to organize container transportation efficiently in this area and make decision for integral plan and construction of transportation system in this area. This paper outlines application of fuzzy comprehensive evaluation to appraise different modes of typical direction of containers. Twelve assessment indexes were decided. Membership functions were formulated. Evaluation results indicated that road transportation was optimal mode in the Changjiang River delta area, however water transportation was the primary way in the Changjiang River main line. 相似文献