全文获取类型
收费全文 | 41030篇 |
免费 | 6786篇 |
国内免费 | 8829篇 |
专业分类
测绘学 | 3706篇 |
大气科学 | 5561篇 |
地球物理 | 7451篇 |
地质学 | 21247篇 |
海洋学 | 5523篇 |
天文学 | 3489篇 |
综合类 | 2742篇 |
自然地理 | 6926篇 |
出版年
2024年 | 190篇 |
2023年 | 528篇 |
2022年 | 1366篇 |
2021年 | 1583篇 |
2020年 | 1505篇 |
2019年 | 1919篇 |
2018年 | 1379篇 |
2017年 | 1610篇 |
2016年 | 1640篇 |
2015年 | 1830篇 |
2014年 | 2348篇 |
2013年 | 2400篇 |
2012年 | 2473篇 |
2011年 | 2618篇 |
2010年 | 2265篇 |
2009年 | 2795篇 |
2008年 | 2723篇 |
2007年 | 2834篇 |
2006年 | 2726篇 |
2005年 | 2569篇 |
2004年 | 2237篇 |
2003年 | 2132篇 |
2002年 | 1824篇 |
2001年 | 1628篇 |
2000年 | 1640篇 |
1999年 | 1436篇 |
1998年 | 1238篇 |
1997年 | 945篇 |
1996年 | 784篇 |
1995年 | 663篇 |
1994年 | 622篇 |
1993年 | 512篇 |
1992年 | 406篇 |
1991年 | 333篇 |
1990年 | 232篇 |
1989年 | 182篇 |
1988年 | 143篇 |
1987年 | 83篇 |
1986年 | 61篇 |
1985年 | 51篇 |
1984年 | 32篇 |
1983年 | 35篇 |
1982年 | 22篇 |
1981年 | 18篇 |
1980年 | 12篇 |
1979年 | 6篇 |
1978年 | 22篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1954年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 531 毫秒
271.
272.
273.
Takuya Itaki Masashi Ito Hisashi Narita Naokazu Ahagon Hideo Sakai 《Deep Sea Research Part I: Oceanographic Research Papers》2003,50(12):1507
The depth distributions of the radiolarian fauna in the Chukchi and Beaufort Seas, marginal seas of the western Arctic Ocean, were examined quantitatively in depth-stratified plankton tows from 4 or 5 intervals above 500 m and in surface sediments from various depths between 163 and 2907 m. The radiolarian assemblage from the water column in September 2000 was dominated by Amphimelissa setosa and followed by the Actinomma boreale/leptoderma group, Pseudodictyophimus gracilipes and Spongotrochus glacialis. These species are related to the Arctic Surface Water shallower than 150 m. This assemblage is similar to that in the Greenland Sea relating to the ice edge, but did not contain typical Pacific radiolarians in spite of the flow of water of Pacific origin in this region. The living depth of Ceratocyrtis historicosa was restricted to the relatively warm water between 300 and 500 m corresponding to the upper Arctic Intermediate Water (AIW) originating from the Atlantic Ocean. Radiolarian assemblages in the surface sediments are similar to those in the plankton tows, except for common Cycladophora davisiana in sediment samples below 500 m. C. davisiana is probably a deep-water species adapted to the lower AIW or the Canadian Basin Deep Water ventilated from the shelves. 相似文献
274.
本文给出了吉尼系数的一般计算公式 ,推导出正态分布的吉尼系数渐进无偏估计 ,并以实例对比了传统的吉尼系数的算法——万分法与本文中提出的估计方法。 相似文献
275.
西太平洋暖池变异及其对西太平洋次表层海温场的影响 总被引:9,自引:0,他引:9
应用热带太平洋上层XBT温度资料,分析研究了西太平洋暖池区(0°~16°N,125°~145°E)上层海洋的变化特征以及与西太平洋次表层海温场之间的关系.研究表明,西太平洋暖池区的垂向温度存在显著的年际变化,尤其在次表层(120~200m)的变化最为明显.西太平洋暖池区的次表层冷暖信号明显早于西太平洋次表层的海温异常.分析发现,西太平洋暖池区的海温异常是导致整个西太平洋次表层海温场变异的关键区,当西太平洋暖池区的次表层冷暖信号加强时,3~4个月后西太平洋海温场出现大范围的冷暖异常. 相似文献
276.
根据1988年7月调查资料讨论了台湾海峡中北部海域夏季上升流区各种形态磷的分布特征。结果表明,上升流中心区(即海坛岛东侧一带水域)具有低温、高盐、低溶解氧;DIp,TDP,PP,TP较高;DOP较低(0.27);及DIP/DOP比值(约为1)较高的特性。DOP是该海域磷的主要形态(占TP的49.2%),其含量分布及其形态转化与生物活动直接相关,是该海域生物生产力高的体现。 相似文献
277.
Rheological Properties and Incipient Motion of Cohesive Sediment in the Haihe Estuary of China 总被引:2,自引:1,他引:2
The Haihe cohesive sediment, which is typical in China, is studied systematically for its basic physical and incipientmotion properties. Following the requirements of dredging works in the Haihe Estuary, cohesive sediment samples weretaken from three locations. Laboratory experiments were conducted to determine the rheological properties of these sam-ples and to examine the incipient motion of the cohesive sediment. It is found that the cohesive sediment has an obviousyield stress τb, which increases with the mud density in a manner of an exponential function, and so does the viscosityparameter η. The cohesive sediment behaves like a Bingham fluid when its density is below 1.38 ~ 1.40 g/cm3, andwhen denser than these values, it may become a power-law fluid. The incipient motion experiment also revealed that theincipient velocity of the cohesive sediment increases with the density in an exponential manner. Therefore, the incipientmotion is primarily related to the density, which is different from the case for non-cohesive sediment in which the incipi-ent motion is correlated with the diameter of sand particles instead. The incipient motion occurs in two different ways de-pending on the concentration of mud in the bottom. For sufficiently fine particles and a concentration lower than1.20 g/cm3, the cohesive sediment appears as fluidized mud, and the incipient motion is in the form of instability of aninternal wave. For a higher concentration, the cohesive sediment appears as general quasi-solid-mud, and the incipientmotion can be described by a series of extended Shields curves each with a different porosity for newly deposited alluvial mud. 相似文献
278.
279.
冰心中的气候环境记录与全球变化研究 总被引:1,自引:0,他引:1
冰心是高分辨地记录全球变化的主要信息载体之一。本文总结了冰心中提取古气候和古环境信息的系列记录,包括同位素、微量气体、阴阳离子、微粒、生物和有机质等。着重讨论了由这些记录提取的古气候和古环境变化方面的研究进展,并提出了今后的研究重点。 相似文献
280.
H. Hummel C. Amiard-Triquet G. Bachelet M. Desprez J. Marchand B. Sylvand J.C. Amiard H. Rybarczyk R.H. Bogaards J. Sinke Y. De Wit L. De Wolf 《Journal of Sea Research》1996,35(4):315-321
Variation in the sensitivity to stress of Macoma balthica was measured in several French and Dutch estuaries. For adult and juvenile Macoma balthica exposed to copper under conditions of starvation, differences in mortality rate, condition, glycogen, burrowing rate and copper content were assessed. No significant differences were observed between adults and juveniles; the influence of treatment and origin was always evident. Animals from the most southern estuaries, Loire and Gironde, near to the species's southern limit of distribution, showed, in the field, the strongest deviations for the ecophysiological traits measured, and were in the experiments the most sensitive to stress. 相似文献