全文获取类型
收费全文 | 11089篇 |
免费 | 2416篇 |
国内免费 | 4442篇 |
专业分类
测绘学 | 912篇 |
大气科学 | 1092篇 |
地球物理 | 1970篇 |
地质学 | 11674篇 |
海洋学 | 890篇 |
天文学 | 163篇 |
综合类 | 773篇 |
自然地理 | 473篇 |
出版年
2024年 | 131篇 |
2023年 | 460篇 |
2022年 | 456篇 |
2021年 | 556篇 |
2020年 | 458篇 |
2019年 | 594篇 |
2018年 | 475篇 |
2017年 | 444篇 |
2016年 | 443篇 |
2015年 | 520篇 |
2014年 | 802篇 |
2013年 | 604篇 |
2012年 | 644篇 |
2011年 | 700篇 |
2010年 | 555篇 |
2009年 | 642篇 |
2008年 | 602篇 |
2007年 | 616篇 |
2006年 | 569篇 |
2005年 | 555篇 |
2004年 | 471篇 |
2003年 | 516篇 |
2002年 | 490篇 |
2001年 | 527篇 |
2000年 | 444篇 |
1999年 | 442篇 |
1998年 | 415篇 |
1997年 | 491篇 |
1996年 | 470篇 |
1995年 | 428篇 |
1994年 | 410篇 |
1993年 | 359篇 |
1992年 | 365篇 |
1991年 | 343篇 |
1990年 | 284篇 |
1989年 | 262篇 |
1988年 | 60篇 |
1987年 | 50篇 |
1986年 | 22篇 |
1985年 | 36篇 |
1984年 | 24篇 |
1983年 | 20篇 |
1982年 | 26篇 |
1981年 | 21篇 |
1980年 | 27篇 |
1979年 | 11篇 |
1954年 | 7篇 |
1951年 | 7篇 |
1950年 | 6篇 |
1948年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
71.
黄河利津水文站不同粒径悬浮颗粒物中有机碳含量的研究 总被引:1,自引:0,他引:1
估算不同粒径TSS中POC的入海日通量,对黄河利津水文站悬浮颗粒物(total suspended solid,TSS)样品,采用基于stokes原理的沉降法分为Ⅴ级,对分级后的样品测其有机碳(particulate organic carbon,POC)含量和粒度组成。在此基础上,用多元线性回归法对数据进一步处理,准确得到样品中不同粒径TSS中POC的含量。研究表明,黄河口淡水端水体TSS,<8μm的粘土和极细粉砂、8~16μm的细粉砂中,POC的含量为0.600%和0.400%左右;16~32μm的中粉砂中,POC的含量不足0.200%;而32~63μm的粗粉砂和>63μm砂中POC含量仅为0.050%和0.004%左右,80%以上的POC主要集中在<16μm的TSS中,而<32μm的TSS承载了95%以上的POC。 相似文献
72.
Starting from the widespread phenomena of porous bottoms in the near shore region, considering fully the diversity of bottom topography and wave number variation, and including the effect of evanescent modes, a general linear wave theory for water waves propagating over uneven porous bottoms in the near shore region is established by use of Green‘s scond identity. This theory can be reduced to a number of the most typical mild-slope equations curreutly in use and provide a reliable research basis for follow-up development of nonlinear water wave theory involving porous bottoms. 相似文献
73.
74.
热演化史研究是盆地模拟中的重要环节,通过其研究可以为烃源岩成熟度史、生烃史、排烃史模拟提供必要的参数,准确地评价盆地的油气资源。 相似文献
75.
76.
董胜 《中国海洋大学学报(自然科学版)》1997,(2)
针对海上矿石运输,介绍了一种完成定量任务并能使投资费用最少为目标的最优船队组建方法,同时对易变参数进行了灵敏度分析,使决策更加科学化 相似文献
77.
In this study, the impact of oceanic processes on the sensitivity of transient climate change is investigated using two sets of coupled experiments with and without tidal forcing, which are termed Exp_Tide and Exp_Control,respectively. After introducing tidal forcing, the transient climate response(TCR) decreases from 2.32 K to 1.90 K,and the surface air temperature warming at high latitudes decreases by 29%. Large ocean heat uptake efficiency and heat storage can explain the low TCR in Exp_Tide. Approximately 21% more heat is stored in the ocean in Exp_Tide(1.10×10~(24) J) than in Exp_Control(0.91×10~(24) J). Most of the large ocean warming occurs in the upper 1 000 m between 60°S and 60°N, primarily in the Atlantic and Southern Oceans. This ocean warming is closely related to the Atlantic Meridional Overturning Circulation(AMOC). The initial transport at mid-and high latitudes and the decline in the AMOC observed in Exp_Tide are both larger than those observed in Exp_Control. The spatial structures of AMOC are also different with and without tidal forcing in present experiments. The AMOC in Exp_Tide has a large northward extension. We also investigated the relationship between AMOC and TCR suggested by previous studies using the present experiments. 相似文献
78.
对增长曲线模型中回归矩阵的函数的线性估计进行了研究。在矩阵损失下 ,作者得到了线性估计在一切线性估计类中可容许的充要条件 相似文献
79.
The major and minor element contents in the sediment core H9 from the hydrothermal fields of the Okinawa Trough show a sharp change at the depth of 80 cm. The elements enriched in the upper 80 cm core are those enriched in the hydrothermal deposits and in the surface sediments recovered from the hydrothermal fields in the trough, which indicates the input of hydrothermal materials. Comparing with other hydrothermal sediments from Mid-ocean Ridges or the Lau Basin, the degree of the enrichment of elements iron, copper,cobalt, and nickel is relatively low. However, the enrichment of elements manganese, lead, arsenic, antimony and mercury is remarkable. The average contents of these elements in the upper 80 cm core sediments are three to six times those in the lower section, and 3~12 times those in the surface sediments which are not influenced by hydrothermal activities. Hydrothermal activities have contributed significant manganese, lead, arsenic, antimony and mercury to the sediments, and these elements are distinct indicators for the hydrothermal activity in the Okinawa Trough. The significant enrichment of these elements in Core H9 upward from the depth 80 cm indicates the start or the significant enhancing of the hydrothermal activity in this area at about 5 740 aB.P. The average accumulation rate of manganese during this period is about 40 461 μg/(cm2·ka), which is similar to the hydrothermal sediments in the Lau Basin or the East Pacific Rise. 相似文献
80.
本文应用向量随机过程分解模型对旋转谱作出物理解释;此外,还修改了线性振荡度的定义,导出了极化度、线性振荡度和旋转系数之间的关系式,并讨论了它们与总相干、同相相干、异相相干之间的关系。 相似文献