全文获取类型
收费全文 | 1406篇 |
免费 | 201篇 |
国内免费 | 299篇 |
专业分类
测绘学 | 132篇 |
大气科学 | 75篇 |
地球物理 | 397篇 |
地质学 | 174篇 |
海洋学 | 857篇 |
天文学 | 29篇 |
综合类 | 194篇 |
自然地理 | 48篇 |
出版年
2024年 | 9篇 |
2023年 | 11篇 |
2022年 | 35篇 |
2021年 | 48篇 |
2020年 | 57篇 |
2019年 | 73篇 |
2018年 | 61篇 |
2017年 | 52篇 |
2016年 | 43篇 |
2015年 | 66篇 |
2014年 | 49篇 |
2013年 | 84篇 |
2012年 | 80篇 |
2011年 | 86篇 |
2010年 | 63篇 |
2009年 | 65篇 |
2008年 | 78篇 |
2007年 | 95篇 |
2006年 | 82篇 |
2005年 | 99篇 |
2004年 | 81篇 |
2003年 | 80篇 |
2002年 | 57篇 |
2001年 | 57篇 |
2000年 | 62篇 |
1999年 | 45篇 |
1998年 | 31篇 |
1997年 | 43篇 |
1996年 | 29篇 |
1995年 | 34篇 |
1994年 | 43篇 |
1993年 | 29篇 |
1992年 | 21篇 |
1991年 | 15篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1988年 | 8篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1954年 | 1篇 |
排序方式: 共有1906条查询结果,搜索用时 203 毫秒
71.
Intensive Pyropia aquaculture in the coast of southwestern Yellow Sea and its subsequent waste, including disposed Ulva prolifera, was speculated to be one of the major sources for the large-scale green tide proceeding in the Yellow Sea since 2007. It was, however, unclear how the detached U. prolifera responded and resumed growing after they detached from its original habitat. In this study, we investigated the growth and photosynthetic response of the detached U. prolifera to various temperature, salinity and irradiance in the laboratory. The photosynthetic rate of the detached U. prolifera was significantly higher at moderate temperature levels(14–27°C)and high salinity(26–32), with optimum at 23°C and 32. Both low(14°C) and highest temperature(40°C), as well as low salinity(8) had adverse effects on the photosynthesis. Compared with the other Ulva species, U. prolifera showed higher saturated irradiance and no significant photoinhibition at high irradiance, indicating the great tolerance of U. prolifera to the high irradiance. The dense branch and complex structure of floating mats could help protect the thalli and reduce photoinhibition in field. Furthermore, temperature exerted a stronger influence on the growth rate of the detached U. prolifera compared to salinity. Overall, the high growth rate of this detached U. prolifera(10.6%–16.7% d~(–1)) at a wide range of temperature(5–32°C) and salinity(14–32) implied its blooming tendency with fluctuated salinity and temperature during floating. The environmental parameters in the southwestern Yellow Sea at the beginning of green tide were coincident with the optimal conditions for the detached U. prolifera. 相似文献
72.
渤海湾曹妃甸深槽海区地形地貌特征及控制因素 总被引:2,自引:2,他引:0
通过研究浅层地震剖面、侧扫声纳和水深地形等数据资料,得出,曹妃甸沙岛的岬角地貌引起深槽海域局部潮流流速增大,甸头前沿深槽区以冲刷为主,最大水深达42 m,刷新了渤海湾最大水深记录,深槽部位的侵蚀量最大,深槽南坡冲刷幅度大于北坡,工程建设后期深槽区侵蚀冲刷程度有变小变缓趋势。早期深槽的形成是由于浅部断层受深部构造影响发生阶梯状错断沉陷,海底地层形成古凹槽,但深槽海底地层沉陷速率略大于沉积速率,使得深槽海域长期保持了渤海湾最大的水深环境。初步得出在历史时期曹妃甸深槽经过2万a以上长期存在,深槽的走向经历了南北向-北东向-北西向的转化过程。认为地质构造、古滦河三角洲演变、海洋水动力作用和人类活动等内外营力作用共同控制了曹妃甸海区地貌体系的发育与演化。达到了研究渤海湾曹妃甸深槽海区地形地貌控制因素和深槽的地质演化的目的,为曹妃甸港的规划、运营期维护和未来发展提供科学依据具有重要意义。 相似文献
73.
74.
继在南极中山站建成我国南极首个永久性验潮站后,2012年1月在南极长城站又建成了我国南极第二个永久性验潮站。通过对长城站验潮站相关数据进行分析处理,得到了验潮基准系统的水准网平差结果和验潮仪零点标定结果,以及长城站附近海域海洋潮汐170个分潮的调和常数,并据此进行了潮汐预报,同时分析了长城站潮汐余水位的变化特征,探讨了利用附近的Antarctic Base Prat验潮站的余水位改正长城站潮汐预报的可行性,结果表明使用Antarctic Base Prat验潮站余水位改正长城站潮汐预报,可以显著提高长城站验潮站潮汐预报的精度,余水位改正后2014时段的潮汐预报中误差为±3.42 cm,明显好于改正前的预报中误差±10.43 cm。 相似文献
75.
A study of SAR remote sensing of internal solitary waves in the north of the South China Sea:I.Simulation of internal tide transformation 总被引:2,自引:1,他引:1
For settlement of the well-known problem of contemporary radar imaging models,i.e.,the pmblem of a general underestimation of radar signatures of hydrodynamic features over oceanic internal waves and underwater bottom topography in tidal watels at at high radar frequency bands(X-band and C-band),the impact of the ocean surface mixed layer turbulence and the significance of strat-ified oceanic model on SAR remote sensing of internal solitary waves are proposed.In the north of the South China Sea by utilizing seme observed data of background field the nonlinearity coefficient,the dispersion coefficient,the horizontal variability coefficient and the phase speed in the generalized K-dV equation are determined approximately.Through simulations of internal tide transfor-mation the temporal evolution and spatial distribution of the vertical displacement and horizontal velocity of intereal wave field are obtained.The simulation results indicate that the maximum amplitudes of internal solitary waves occur at depth 35 m,but the maximum current speeds take place at depth 20 m in this area of the sea(about 20°30'N,114°E)in August.It was noticed that considering the effects of flood current and ebb current respectively is appropriate to investigate influence of the background shear flow on coefficients of the K-dV equation.The obtained results provide the possibility for the simulation of SAR signatures of inter-nal solitary waves under considering the impact of ocean surface mixed layer turbulence in the companion paper. 相似文献
76.
Hiroaki Sasaki Akihiko Tanaka Mitsunori Iwataki Yasuharu Touke Eko Siswanto Chun Knee Tan Joji Ishizaka 《Journal of Oceanography》2008,64(4):511-523
Remote sensing reflectance [R
rs(λ)] and absorption coefficients of red tides were measured in Isahaya Bay, southwestern Japan, to investigate differences in
the optical properties of red tide and non-red tide waters. We defined colored areas of the sea surface, visualized from shipboard,
as “red tides”. Peaks of the R
rs(λ) spectra of non-red tide waters were at 565 nm, while those of red tides shifted to longer wavelengths (589 nm). The spectral
shape of R
rs(λ) was close to that of the reciprocal of the total absorption coefficient [1/a(λ)], implying that the R
rs(λ) peak is determined by absorption. Absorption coefficients of phytoplankton [a
ph(λ)], non-pigment particles and colored dissolved organic matter increased with increasing chlorophyll a concentration (Chl a), and those coefficients were correlated with Chl a for both red tide and non-red tide waters. Using these relationships between absorption coefficients and Chl a, variation in the spectrum of 1/a(λ) as a function of Chl a was calculated. The peak of 1/a(λ) shifted to longer wavelengths with increasing Chl a. Furthermore, the relative contribution of a
ph(λ) to the total absorption in red tide water was significantly higher than in non-red tide water in the wavelength range 550–600
nm, including the peak. Our results show that the variation of a
ph(λ) with Chl a dominates the behavior of the R
rs(λ) peak, and utilization of R
rs(λ) peaks at 589 and 565 nm may be useful to discriminate between red tide and non-red tide waters by remote sensing. 相似文献
77.
The scarcity of tide gauges in a global scale and the variability of the tidal levels along contiguous coasts mainly due to changing hydrographic conditions make the determination of tidal levels, especially of the Mean Sea Level, not an easy task. Determination of such levels with a precision of about 10 cm, necessary for most coastal engineering works, is usually based on records of temporary tide gauges or on geomorphological techniques. In this paper we present an alternative approach permitting to accurately identify tidal levels with a precision suitable for civil engineering applications based on biological observations on rocky shores, including breakwaters and quays. More specifically, we present evidence that the biological zonation, i.e. the distribution of coastal species in well-defined sub-horizontal belts, is practically insensitive to seasonal and other small-scale fluctuations of the sea level and is clearly related to certain levels, mostly the Mean Low Water (MLW). This approach, somewhat similar to what has been used in the past (for instance for the determination of the geodetic vertical datum in the Republic of Venice, Italy, till approximately AD 1800), permits direct determination of the Mean Sea Level or of other tidal levels on the basis of biological observations without statistical analyses of tide-gauge records with an accuracy of 5–10 cm, especially in microtidal, low-energy coasts. 相似文献
78.
中咀湾是一个天然的避风良港,一般情况下外海波浪影响很小,主要受局部风场产生的局部风浪影响。本文采用曹宏生在Massel的扩展缓坡方程基础上推导出来的考虑陡变地形和能量耗散效应的缓坡方程为控制方程,结合固边界的反射边界条件,构成波浪传播变形的联合折射、绕射和反射的数学模型。文中将此方法运用在中国台州市大陈岛中咀湾避风港中,用波浪数学模型计算极端高水位和设计高水位时3种波况分别在3组重现期时工程海域的波浪要素,提供防波堤的堤前波高,并分析比较此处实心式和透空式防波堤的防浪性能。 相似文献
79.
80.
INTRODUCTIONAquiculturearearedtidesignalsoceanpollutionanddisaster.Althoughenvironmentscientistshaveconductedmanyin depthresearchesonthecauseandformationmechanismofredtide ,manyofitsaspectsarestillunknownbecauseredtideisacomplexphenomenonandtheecologic… 相似文献