全文获取类型
收费全文 | 16050篇 |
免费 | 1689篇 |
国内免费 | 2154篇 |
专业分类
测绘学 | 1006篇 |
大气科学 | 2199篇 |
地球物理 | 3528篇 |
地质学 | 6621篇 |
海洋学 | 2180篇 |
天文学 | 1606篇 |
综合类 | 753篇 |
自然地理 | 2000篇 |
出版年
2023年 | 125篇 |
2022年 | 400篇 |
2021年 | 484篇 |
2020年 | 499篇 |
2019年 | 513篇 |
2018年 | 584篇 |
2017年 | 533篇 |
2016年 | 661篇 |
2015年 | 615篇 |
2014年 | 668篇 |
2013年 | 1004篇 |
2012年 | 789篇 |
2011年 | 870篇 |
2010年 | 759篇 |
2009年 | 815篇 |
2008年 | 753篇 |
2007年 | 696篇 |
2006年 | 675篇 |
2005年 | 579篇 |
2004年 | 560篇 |
2003年 | 467篇 |
2002年 | 481篇 |
2001年 | 412篇 |
2000年 | 405篇 |
1999年 | 412篇 |
1998年 | 369篇 |
1997年 | 322篇 |
1996年 | 323篇 |
1995年 | 296篇 |
1994年 | 302篇 |
1993年 | 260篇 |
1992年 | 249篇 |
1991年 | 230篇 |
1990年 | 185篇 |
1989年 | 163篇 |
1988年 | 150篇 |
1987年 | 171篇 |
1986年 | 129篇 |
1985年 | 187篇 |
1984年 | 208篇 |
1983年 | 160篇 |
1982年 | 152篇 |
1981年 | 145篇 |
1980年 | 115篇 |
1979年 | 132篇 |
1978年 | 120篇 |
1977年 | 108篇 |
1976年 | 104篇 |
1975年 | 94篇 |
1973年 | 87篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
Measurement of nuclides of uranium and thorium series of disequilibrium using γ-spectroscopy 总被引:3,自引:0,他引:3
INTRODUCTIONTheradionuclidesofnaturaluraniumandthoriumseriescanbeusedtotracemarinepro cessofvarioustemporalandspatialscaleandpropertiesthatprovideplentifulinformationaboutphysics,chemistry ,geoscienceandbiologyofoceanbecausetheyhavedifferentchemicalpro… 相似文献
152.
AbstractBased on hydrological data obtained during the 7th to 9th Chinese National Arctic Research Expeditions in the summers of 2016–2018, the main water structure on the shelf of the northern Bering Sea and the volume and heat fluxes of the Bering Strait throughflow were analyzed. Distinct variability was identified in the three Pacific water masses feeding the strait - Anadyr Water (AW), Bering Shelf Water (BSW) and Alaskan coastal water (ACW). Overall, the temperature and salinity of the entire section increased each year, with 2018 showing significant anomalies, i.e., a temperature anomaly of up to 1?°C and a maximum salinity anomaly of 2. From 2016 to 2018, the extent of the ACW gradually narrowed in the eastern part of this section, while the AW expanded eastward each year. The net volume transport through each of the three sections increased poleward from 1.65?Sv to 2.76?Sv, with the AW increasing from 0?Sv to 1.03?Sv, the BSW varying between 0.52–1.65?Sv, and the ACW gradually decreasing from 1.04?Sv to disappearing completely. The net heat fluxes were also poleward, varying between 25.77 TW and 61.50 TW, and showing a significant increase. Significant variations in magnitude and extent were observed in each water mass of the Bering Strait throughflow, which could produce widespread effects in the Arctic Ocean and the global ocean beyond. 相似文献
153.
Alkylphenolic compounds are present in estuarine and marine environments. They are moderately bioaccumulative, and oestrogenic to fish following three week, in vivo, exposures. The effects of prolonged exposure are, as yet, unclear. Sand goby (Pomatoschistus minutus) were exposed to measured concentrations of 4-tert-octylphenol (OP) in a 28-day, dose-ranging study, and a six month temporal response study. Following 28-days exposure to measured 31+/-6 or 101+/-47 microg l(-1) OP (mean+/-SD), immature male sand goby showed elevated vitellogenin (VTG) mRNA expression. Plasma alkali-labile phosphate concentrations were elevated in both sexes and were higher in females than males. Although measured OP concentrations were variable, they were significantly different for each treatment and a range of concentration-dependent effects were observed. The LC(50) for chronic OP exposure (8 weeks) was 29+/-6 microg l(-1), and both sexes demonstrated concentration and duration dependent increases in VTG mRNA expression. Exposure to 28+/-20 microg l(-1) OP (median+/-95% CI) for 6 months inhibited development of male nuptial colouration and sperm duct glands. These findings are discussed in relation to environmental concentrations of alkylphenols and ecological concerns. 相似文献
154.
155.
156.
本文介绍一种声遥测海底平面层系声阻抗分布的模拟实验结果。实验在油漆厂冷却水池中进行,采用取样平均迭代的反演方法,对三介质层系的遥测结果与实测值较好地接近。 相似文献
157.
158.
本文研究了虾蟹海产品香味的前体物质在加热前后的变化。实验结果表明:对虾和蟹肌肉中的糖原和不饱和脂肪酸在加热前后含量下降,糖原是Maillard反应的基础物质.不饱和脂肪酸是虾蟹肌肉香味中羰基化合物的前体物质。虾蟹肌肉中主要积累的核苷酸成分AMP在加热后减少,而肌肉提取物中的游离氨基酸和结合氨基酸,特别是疏水氨基酸含量均增加。 相似文献
159.
160.
Eurgain H. John Sonia D. Batten Roger P. Harris Graeme C. Hays 《Journal of Sea Research》2001,46(3-4)
Zooplankton sampling has been carried out by the Continuous Plankton Recorder (CPR) survey since the 1930s enabling the study of long-term changes in plankton populations, the elucidation of seasonal patterns of abundance, and more recently providing zooplankton biomass estimates for ecosystem models. Data for zooplankton abundance collected by CPR tows in the Western English Channel (between 1988 and 1998) were compared to vertically integrated samples collected from station L4 off Plymouth, UK. Comparisons were made for locally abundant copepods (including Acartia, Calanus, Para/Pseudocalanus, Centropages, Oithona and Temora) collected by CPR and WP-2 nets. All dominant species recorded at L4 were also common to the CPR data. However, the position of the taxa in the two datasets was not equivalent. Seasonal cycles revealed by CPR data were significantly similar to those recorded throughout the water column at L4 for most taxa. However, absolute levels of abundance differed for the two datasets: abundances were underestimated by CPR samples when compared to those of vertically integrated samples by a factor of between 2 and 35, with the exception of Centropages. The differing mesh sizes (200 and 270 μm) of the WP-2 net and CPR mesh could only partially explain these differences in abundance, implying that the behaviour of individual taxa and their depth in the water column also influenced the abundance recorded. 相似文献