全文获取类型
收费全文 | 16855篇 |
免费 | 3518篇 |
国内免费 | 4442篇 |
专业分类
测绘学 | 1448篇 |
大气科学 | 3934篇 |
地球物理 | 3782篇 |
地质学 | 8964篇 |
海洋学 | 1808篇 |
天文学 | 423篇 |
综合类 | 1670篇 |
自然地理 | 2786篇 |
出版年
2024年 | 109篇 |
2023年 | 256篇 |
2022年 | 487篇 |
2021年 | 655篇 |
2020年 | 646篇 |
2019年 | 787篇 |
2018年 | 616篇 |
2017年 | 782篇 |
2016年 | 809篇 |
2015年 | 894篇 |
2014年 | 1064篇 |
2013年 | 1252篇 |
2012年 | 1158篇 |
2011年 | 1149篇 |
2010年 | 1024篇 |
2009年 | 1117篇 |
2008年 | 1153篇 |
2007年 | 1265篇 |
2006年 | 1228篇 |
2005年 | 1058篇 |
2004年 | 960篇 |
2003年 | 871篇 |
2002年 | 749篇 |
2001年 | 701篇 |
2000年 | 639篇 |
1999年 | 580篇 |
1998年 | 500篇 |
1997年 | 446篇 |
1996年 | 351篇 |
1995年 | 301篇 |
1994年 | 264篇 |
1993年 | 232篇 |
1992年 | 169篇 |
1991年 | 116篇 |
1990年 | 109篇 |
1989年 | 69篇 |
1988年 | 71篇 |
1987年 | 35篇 |
1986年 | 26篇 |
1985年 | 33篇 |
1984年 | 15篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 11篇 |
1980年 | 15篇 |
1979年 | 5篇 |
1978年 | 11篇 |
1977年 | 13篇 |
1976年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
81.
82.
研究取自于东太平洋CC48柱状样的钙质超微化石和底栖有孔虫的氧同位素成分变化的结果表明,该区下中新统至少可分出九个氧同位素地层(期),反映该区在早中新世期间至少经历了4次气温上升和5次下降的古气候变化。南极大陆冰川应是形成于早中新世而不是前人认为的中中新世。在早中新世,南极冰体体积有较大的变化。受古气候变化的影响,在早中新世期间东太平洋水柱热结构或温度梯度有比较大的变化,海平面出现多次上升与下降。 相似文献
83.
84.
The characteristics of the ratios between cadmium (Cd) and phosphorus (P) in settling particles collected from the Okinawa
Trough in the East China Sea were examined using a sediment trap, moored at a depth of 811 m for one year. The Cd/P ratios
varied within a narrow range throughout the year, in spite of the large seasonal change in the total dry mass, Cd, and P fluxes.
The average Cd/P ratio of settling particles was 0.062 (nmol/μmol), which was obviously lower than that of surface seawater around the study site (0.16). This lower ratio in the Okinawa
Trough particles collected using the 811 m-moored trap certainly reflected the mixture of biologically produced organic matter
around the study site and other components that were mainly transported as lateral flux from the shelf edge and slope area
of the East China Sea. 相似文献
85.
Japanese fisheries production in the Japan/East Sea between 1958 and 2003 increased to their peak (1.76 million tons) in the late 1980s and decreased abruptly with the collapse of Japanese sardine. Catch results for 58 fisheries and various environmental time-series data sets and community indices, including mean trophic level (MTL) and Simpson’s diversity index (DI), were used to investigate the impacts of fishing and climate changes on the structure of the fish community in the Tsushima warm current (TWC) region of the Japan/East Sea. The long-term trend in fisheries production was largely dependent on the Japanese sardine that, as a single species, contributed up to 60% of the total production in the Japanese waters of the Japan/East Sea during the late 1980s. Excluding Japanese sardine, production of the small pelagic species was higher during 1960s and 1990s but lower during 1970s and 1980s. This variation pattern generally corresponds with the trend in water temperature, warmer before early 1960s and after 1990s but colder during 1970s and 1980s. The warm-water, large predatory fishes and cold water demersal species show opposite responses to the water temperature in the TWC region, indicating the significant impact of oceanic conditions on fisheries production of the Japan/East Sea. Declines in demersal fishes and invertebrates during 1970s and 1980s suggested some impact of fishing. MTL and DI show a similar variation pattern: higher during 1960s and 1990s but lower during 1970s and 1980s. In particular, the sharp decline during the 1980s resulted from the abundant sardine catches, suggesting that dominant species have a large effect on the structure of the fish community in the Japan/East Sea. Principal component analysis for 58 time-series data sets of fisheries catches suggested that the fish community varied on inter-annual to inter-decadal scales; the abrupt changes that occurred in the mid-1970s and late 1980s seemed to correspond closely with the climatic regime shifts in the North Pacific. These results strongly suggest that the structure of the fish community in the Japan/East Sea was largely affected by climatic and oceanic regime shifts rather than by fishing. There is no evidence showing “fishing down food webs” in the Japan/East Sea. However, in addition to the impacts of abrupt shifts that occurred in the late 1980s, the large predatory and demersal fishes seem to be facing stronger fishing pressure with the collapse of the Japanese sardine. 相似文献
86.
海浪日最大波高序列的一种标度性质 总被引:1,自引:0,他引:1
应用重标度分析方法研究小麦岛海洋观测站1961-1980年二十年海浪日最大波高序列时发现,该序列并不是相互独立的,而是具有记忆性和持久性,详细的论证表明分式布朗运动模型是描述海浪日最大波高序列的一个较好的模型,同时,应用分式布朗运动模型我们找到了存在于海浪日最大波高序列中的一种标度性质-累积离差(t)的统计自仿射性。 相似文献
87.
弧后盆地的形成与演化探讨:以东亚陆缘区为例 总被引:3,自引:2,他引:3
通过对弧后盆地大地构造体制的讨论,作者认为基属活化作用的产物根据地质,地球物理,地球化学等资料的分析,作者提出结论认为,由于东亚岛弧系岩石圈的均衡作用及海沟外侧冷却大洋岩石圈块体的下沉拖曳牵引等作用,使软流圈在岛弧系下方发生分异,这种分异作用带动东亚陆缘向东扩张,从而产生弧后的张开。 相似文献
88.
89.
90.