全文获取类型
收费全文 | 39424篇 |
免费 | 18838篇 |
国内免费 | 43667篇 |
专业分类
测绘学 | 3018篇 |
大气科学 | 22354篇 |
地球物理 | 13725篇 |
地质学 | 37537篇 |
海洋学 | 16348篇 |
天文学 | 1188篇 |
综合类 | 4926篇 |
自然地理 | 2833篇 |
出版年
2024年 | 163篇 |
2023年 | 417篇 |
2022年 | 787篇 |
2021年 | 1090篇 |
2020年 | 2197篇 |
2019年 | 5589篇 |
2018年 | 5916篇 |
2017年 | 5604篇 |
2016年 | 5699篇 |
2015年 | 4979篇 |
2014年 | 4552篇 |
2013年 | 5068篇 |
2012年 | 4723篇 |
2011年 | 4526篇 |
2010年 | 4481篇 |
2009年 | 3830篇 |
2008年 | 3113篇 |
2007年 | 3136篇 |
2006年 | 2726篇 |
2005年 | 2653篇 |
2004年 | 2875篇 |
2003年 | 2660篇 |
2002年 | 2385篇 |
2001年 | 2150篇 |
2000年 | 1846篇 |
1999年 | 2023篇 |
1998年 | 2017篇 |
1997年 | 2072篇 |
1996年 | 1666篇 |
1995年 | 1585篇 |
1994年 | 1401篇 |
1993年 | 1325篇 |
1992年 | 1127篇 |
1991年 | 853篇 |
1990年 | 785篇 |
1989年 | 667篇 |
1988年 | 554篇 |
1987年 | 442篇 |
1986年 | 351篇 |
1985年 | 278篇 |
1984年 | 294篇 |
1983年 | 181篇 |
1982年 | 213篇 |
1981年 | 149篇 |
1980年 | 128篇 |
1979年 | 113篇 |
1978年 | 52篇 |
1977年 | 45篇 |
1971年 | 53篇 |
1970年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
221.
INTRODUCTIONTheOkinawaTrough (OT) ,locatednorthwestoftheRyukyuTrenchandtheRyukyugunto ,eastoftheEastChinaSeashelf,isaback arcbasinbulgedtotheRyukyuTrench .TheOTextendsfromKyushuinthesouthwestofJapantotheIlanPlaininthenortheasternTaiwan ,Chinainthesouthwest… 相似文献
222.
Glass inclusions in volcanic rocks in the Okinawa Trough back-arc basin:constraints on magma genesis and evolution 总被引:1,自引:0,他引:1
INTROOUcr1ONThe Okinawa Trough is a typical marginal back-arc basin, where its oPening began in rela-tively recent years* There is a great controversy about the origin of its initial magYna. haltand acid volcanic pumice make up the bimedal volcanism in the Okinawa Trough. MOSt of geol-ogists believed that the acid pumice was the preduct of extremely crystal fractionation of baseltInagTna, but the others argued that it should com from the melting of lower-crust. Som de-tailed petrolOgic… 相似文献
223.
一种新的波浪变形三维数值模式──0-1混合型边界元 总被引:4,自引:0,他引:4
为提高边界元法模拟三维波场波浪变形的数值计算精度,借鉴常数元和线性元剖分方式、波势函数及波势函数法向导数对单元节点设定的各自适应性,提出了一种新的单元剖分模式──0-1混合型边界元,以控制和减缓由于计算误差累计而造成的波浪数值计算上的“横向振动”,借此结合边界元法的分区模式可实现较大范围的波场线性波浪变形计算,并为时域内的波浪非线性变形计算提供时间步长的数值保证. 相似文献
224.
盐泽螺旋藻变种的生长和生化特性 总被引:1,自引:0,他引:1
采用1984年在美国加利福尼亚大学培育成功的盐泽螺旋藻变种,经扫描电镜,生物量测定和生化分析,进一步研究其基本特性。结果表明,其藻丝呈紧密的逆时针向等宽螺旋结构。 相似文献
225.
226.
227.
Bacteria abundance, chlorophyll a, ATP and POC concentrations and respiration rates of microorganisms in the Changjiang Estuary and the plume were determined in July 1986. The high values of bacteria abundance occurred in the river mouth in association with suspended matter. It is assumed that bacteria were the major contributor to ATP and the main consumer of dissolved oxygen, and that the relationship between ATP and POC was present in that area. In the dilution zone (salinity; 25-30), instead of bacteria, phytoplankton was the major contributor to ATP and respiration rates, due to diatom bloom. Close relationships between Chi a and ATP, and ATP and POC were observed. Contribution of microbial carbon to POC was also estimated. 相似文献
228.
On the basis of the wave energy balance equation, the response model of mean directions of locally wind-generated waves in slowly turning wind fields has been derived. The results show that in a homogeneous field, the time scale of the response is not only related to the rate of wave growth, but also to the directional energy distribution and the angle between the wind direction and the mean wave direction. Furthermore, the law of change in the mean wave direction has been derived. The numerical computations show that the response of wave directions to slowly turning wind directions can be treated as the superposition of the responses of wave directions to a series of sudden small-angle changes of wind directions and the turning rate of the mean wave direction depends on the turning rate and the total turning angles of the wind direction. The response of wave directions is in agreement with the response for a sudden change of wind directions if the change in wind directions is very fast. Based on the no 相似文献
229.
Gu Jialong Shen Xianrong
Professor Hohai University Nanjing
Engineer The Investigation Design Institute Bureau of Communications of Zhejiang Province Hangzhou 《中国海洋工程》1991,(2)
In accordance with the similarity between breaking waves and hydraulic jumps, the expressions for estimating wave decay and wave energy dissipation in the surf zone are derived based on the fundamental equations of fluid mechanics. Using the numerical solution of cnoidal wave theory, the various kinematic properties of waves in the surf zone, including the relative wave crest height, wave energy, and radiation stress are discussed. The values calculated with the method proposed in this paper are in good agreement with the experimental data gained by other researchers. The present expressions can be used in the studies of sediment transport on gently sloping beaches, especially on muddy beaches. 相似文献
230.
The oceans have rich resources of microbes. In recent years, searching for antibiotic of new structure and special biological activity from marine microbes has received great attention. This paper reports the results of the studies on the distribution and the antibacterial properties of Streptomyces in the intertidal zone of Southern Fujian. These studies have important significance to further investigate 相似文献