全文获取类型
收费全文 | 2835篇 |
免费 | 454篇 |
国内免费 | 780篇 |
专业分类
测绘学 | 21篇 |
大气科学 | 109篇 |
地球物理 | 318篇 |
地质学 | 621篇 |
海洋学 | 2484篇 |
天文学 | 1篇 |
综合类 | 212篇 |
自然地理 | 303篇 |
出版年
2024年 | 22篇 |
2023年 | 73篇 |
2022年 | 142篇 |
2021年 | 133篇 |
2020年 | 146篇 |
2019年 | 134篇 |
2018年 | 137篇 |
2017年 | 119篇 |
2016年 | 154篇 |
2015年 | 125篇 |
2014年 | 175篇 |
2013年 | 176篇 |
2012年 | 158篇 |
2011年 | 186篇 |
2010年 | 161篇 |
2009年 | 189篇 |
2008年 | 196篇 |
2007年 | 205篇 |
2006年 | 192篇 |
2005年 | 149篇 |
2004年 | 144篇 |
2003年 | 117篇 |
2002年 | 117篇 |
2001年 | 97篇 |
2000年 | 91篇 |
1999年 | 84篇 |
1998年 | 67篇 |
1997年 | 49篇 |
1996年 | 55篇 |
1995年 | 39篇 |
1994年 | 41篇 |
1993年 | 50篇 |
1992年 | 43篇 |
1991年 | 21篇 |
1990年 | 12篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 18篇 |
1984年 | 12篇 |
1983年 | 12篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1979年 | 1篇 |
排序方式: 共有4069条查询结果,搜索用时 15 毫秒
71.
辽东湾地区下第三系地震速度—岩性预测模型研究 总被引:9,自引:1,他引:9
地震速度-岩性预测模型由四个子模型组成:即(1)砂泥岩压实模型;(2)地震层速度转换模型;(3)速度校正模型;(4)砂岩指数转换模型。辽东湾地区的实际资料证明,上述四个子模型不但决定了岩性预测的具体方法,而且严格控制岩性预测的精度。 相似文献
72.
2002年2月—2004年11月对胶州湾异养细菌和大肠菌群进行长期调查发现,胶州湾异养细菌丰度在105—106cells/ml之间,其中河口区域和近岸区域数量较高,其它区域相对较低。从季节上来看,夏季、秋季细菌丰度较高(分别为7.4×105、7.2×105cells/ml),冬季和春季丰度较低(分别为4.1×105cells/ml、5.9×105cells/ml),且在一年内呈现出一定的规律性波动。从季节尺度上看异养细菌丰度与温度呈现很好的正相关性(R=0.54)。对大肠菌群的研究表明,河口区域的大肠菌群数量显著高于其它区域,并且河口区域大肠菌群常年处于严重超标状态(最高为1.1×106cells/L,超过国家前三类水质标准的100倍)。根据大肠菌群的数量状况可以将胶州湾分为三个区域,即严重污染区、中度污染区和轻度污染区。该区域划分与通过营养盐对胶州湾区域的划分(富营养区、中度营养区、贫营养区)结果一致。 相似文献
73.
Antonio Tovar-Snchez Sergio A. Saudo-Wilhelmy A. Russell Flegal 《Estuarine, Coastal and Shelf Science》2004,60(4):717-728
Despite the fact that Co is an essential trace element for the growth of marine phytoplankton, there is very limited information on the cycling of this trace metal in the marine environment. We report here the distribution of dissolved (<0.4 μm) and particulate (>0.4 μm) Co in surface waters of the Hudson River Estuary (HRE) and San Francisco Bay (SFB). Samples were collected during several cruises (from 1990 to 1995 in SFB and from 1995 to 1997 in the HRE) along the whole salinity gradient. Dissolved Co concentrations (mean±1 standard deviation) were nearly identical in magnitude in both estuaries despite differences in climate, hydrography, riverine-flow conditions and land-usage (HRE=0.91±0.61 nM; SFB=1.12±0.69 nM). Dissolved Co levels in each system showed non-conservative distributions when plotted as a function of salinity, with increasing concentrations downstream from the riverine end-members. Desorption from suspended particulates and sewage inputs, therefore, seems to be the major processes responsible for the non-conservative behavior of Co observed. Mass balance estimates also indicated that most of the estuarine Co is exported out of both estuaries, indicating that they and other estuarine systems are principal sources of this essential trace element to the open ocean. 相似文献
74.
本文根据1992年夏季对湄洲湾水质环境质量调查资料,对该海区海水中油的含量及分布特征进行了分析研究。结果表明:湄洲湾夏季表层海水油的含量为5-51μg/dm^3,平均值为19.8μg/dm^3。海水的混合系数较小,高潮和低潮时油含量分布的差异,除了与陆源污染源分布有关外,主要是由水文动力学条件所决定。 相似文献
75.
Effect of native and invasive cordgrass on Macoma petalum density, growth, and isotopic signatures 总被引:1,自引:0,他引:1
Ecosystem engineers can influence community and ecosystem dynamics by controlling resources, modifying the flow of energy or biomass, or changing physical characteristics of the habitat. Invasive hybrid cordgrass (Spartina alterniflora × Spartina foliosa) is an ecosystem engineer in salt marshes in San Francisco Bay, California, U.S.A. that raises intertidal elevations and may be either increasing C4 plant carbon input into food webs or tying up carbon in a form that is not usable by consumers. A manipulative experiment compared abundance, growth, and stable isotope (δ13C and δ15N) composition of the clam Macoma petalum (=M. balthica) among native marsh, hybrid Spartina, and mudflats in central San Francisco Bay. We found higher densities (individuals m−2) of M. petalum on mudflats compared to either native or hybrid Spartina (p < 0.001). Macoma petalum shell growth was significantly greater in mudflats than in either vegetation type in 2002 (p = 0.005) but not 2003. Differences in shell growth between native and hybrid Spartina were not significant. Stable isotope results showed differences between habitats in δ13C but not δ15N. Carbon signatures of M. petalum placed in Spartina were much more depleted than the isotopic signature of Spartina. Neither native nor hybrid Spartina appears to be a significant carbon source for M. petalum in San Francisco Bay, and we found no evidence that hybrid Spartina contributes carbon to M. petalum beyond what is provided by S. foliosa, despite the hybrid's much greater biomass. Our results show that loss of mudflat habitat, rather than increased input of C4 carbon, is the greatest effect of the invasion of hybrid Spartina on M. petalum. 相似文献
76.
Seasonal Variability of Near-Surface Heat Budget of Selected Oceanic Areas in the North Tropical Indian Ocean 总被引:1,自引:0,他引:1
The results obtained from an Ocean General Circulation Model (OGCM), the Modular Ocean Model 2.2, forced with the National
Center for Environmental Prediction/National Center for Atmospheric Research reanalysis data, and observational data have
been utilized to document the climatological seasonal cycle of the upper ocean response in the Tropical Indian Ocean. We address
the various roles played by the net surface heat flux and the local and remote ocean dynamics for the seasonal variation of
near-surface heat budget in the Tropical Indian Ocean. The investigation is based in seven selected boxes in the Arabian Sea,
Bay of Bengal and the Equatorial Indian Ocean. The changes of basin-wide heat budget of ocean process in the Arabian Sea and
the Western Equatorial Indian Ocean show an annual cycle, whereas those in the Bay of Bengal and the Eastern Equatorial Indian
Ocean show a semi-annual cycle. The time tendency of heat budget in the Arabian Sea depends on both the net surface heat flux
and ocean dynamics while on the other hand, that in the Bay of Bengal depends mainly on the net surface flux. However, it
has been found that the changes of heat budget are very different between western and eastern regional sea areas in the Arabian
Sea and the Bay of Bengal, respectively. This difference depends on seasonal variations of the different local wind forcing
and the different ocean dynamics associated with ocean eddies and Kelvin and Rossby waves in each regional sea areas. We also
discuss the comparison and the connection for the seasonal variation of near-surface heat budget among their regional sea
areas.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
77.
Since the Intermediate Oyashio Water (IOW) gradually accumulates in Sagami Bay, it can reasonably be supposed that the IOW
also flows out from Sagami Bay, even though it may be altered by mixing with other waters. We have occasionally observed a
water less than 34.2 psu with a potential density of 26.8 at the southeastern area off Izu Peninsula in July 1993 by the training
vessel Seisui-maru of Mie University. Observational data supplied by the Japan Meteorological Agency and the Kanagawa Prefectural
Fisheries Experimental Station show that the IOW of less than 34.1 psu was observed at northern stations of the line PT (KJ)
off the Boso Peninsula and to the east of Oshima in the late spring 1993. Based upon these observations, it is concluded that
the IOW flows out from Sagami Bay into the Shikoku Basin along southeastern area off the Izu Peninsula. The less saline water
(<34.2 psu) was also observed to the west of Miyake-jima during the same cruise, and the westward intrusion of IOW from south
of the Boso Peninsula to the Shikoku Basin through the gate area of the Kuroshio path over the Izu Ridge was detected. This
event indicated that the IOW branched south of the Boso Peninsula and flowed into Sagami Bay and/or into the gate area over
the Izu Ridge. The southward intrusion of IOW into the south of the Boso Peninsula is discussed in relation to the latitudinal
location of the main axes of the Kuroshio and the Oyashio.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
78.
79.
化学生态调控对鳌山湾氮磷营养盐的影响 总被引:2,自引:0,他引:2
鳌山湾,是一个营养类型特殊的海湾,湾中基本无径流输入,呈“C”字形,封闭性较强,水较浅,湾内主要有筏式扇贝养殖和底播贝类养殖,沿岸有滩涂池塘养殖.根据1996年11月至1998年5月的调查结果得知,鳌山湾海域为贫营养海域[1,2].为探讨贫营养海域进行化学生态调控的可能性,利用鳌山湾的封闭性,根据其水交换规律[3],于1999年6月首次对鳌山湾进行了全湾规模较大的化学生态调控试验,旨在有效提高鳌山湾的营养水平,为今后在贫营养海域合理发展海水养殖业提供科学依据,获得了十分理想的效果. 相似文献
80.
Ucan Osman N. Albora A. Muhittin Hisarli Z. Mümtaz 《Marine Geophysical Researches》2001,22(4):251-264
In this paper, residual and regional gravity and magnetic anomalies of Saros Bay are separated using wavelet method. Wavelet
is one of the modern, stochastic image approaches processing technique in electronics. The vertical, horizontal and diagonal
components of wavelet output are evaluated simultaneously and an underground model is obtained by suitable cross-sections.
Thus the geological and tectonic properties of Saros Bay are extracted. Our proposed model is confirmed by deep and shallow
seismic researches of Turkish Petroleum Cooperation (TPAO). The South-East region of Saros Graben is formed by strike slip
Ganos Fault and Anafartalar reverse Fault that lies on the east of Ganos Fault. On the Northwest region, there is strike slip
component fault resulting in the Enez Graben. Here we detected two new oval type geological structure, both of them starting
from the Eastern direction of Canakkale Dardanelles and but one of them continuing through Gelibolu Peninsuls, while the other
tending to the Enez Graben. We think that these structures are the ruins of a very old sea in this region.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献