全文获取类型
收费全文 | 110259篇 |
免费 | 3283篇 |
国内免费 | 3478篇 |
专业分类
测绘学 | 3162篇 |
大气科学 | 8840篇 |
地球物理 | 20847篇 |
地质学 | 43057篇 |
海洋学 | 10259篇 |
天文学 | 22884篇 |
综合类 | 1324篇 |
自然地理 | 6647篇 |
出版年
2022年 | 1217篇 |
2021年 | 1782篇 |
2020年 | 1751篇 |
2019年 | 1932篇 |
2018年 | 5011篇 |
2017年 | 4537篇 |
2016年 | 4339篇 |
2015年 | 2094篇 |
2014年 | 3403篇 |
2013年 | 5253篇 |
2012年 | 4198篇 |
2011年 | 6148篇 |
2010年 | 5458篇 |
2009年 | 6463篇 |
2008年 | 5545篇 |
2007年 | 5963篇 |
2006年 | 4157篇 |
2005年 | 3118篇 |
2004年 | 2981篇 |
2003年 | 2931篇 |
2002年 | 2874篇 |
2001年 | 2400篇 |
2000年 | 2288篇 |
1999年 | 1886篇 |
1998年 | 1862篇 |
1997年 | 1756篇 |
1996年 | 1485篇 |
1995年 | 1481篇 |
1994年 | 1253篇 |
1993年 | 1172篇 |
1992年 | 1072篇 |
1991年 | 1061篇 |
1990年 | 1004篇 |
1989年 | 913篇 |
1988年 | 818篇 |
1987年 | 937篇 |
1986年 | 820篇 |
1985年 | 977篇 |
1984年 | 1100篇 |
1983年 | 1056篇 |
1982年 | 970篇 |
1981年 | 918篇 |
1980年 | 823篇 |
1979年 | 762篇 |
1978年 | 735篇 |
1977年 | 626篇 |
1976年 | 639篇 |
1975年 | 627篇 |
1974年 | 597篇 |
1973年 | 668篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
The results of simultaneous measurements of the bottom (6.25 and 35 m above the bottom) currents, deep currents, and surface currents made at three points in the north-east tropical Pacific Ocean are given. The bottom intensification of the current velocity is revealed in a layer of 35–25 m above the bottom. The estimation of the thickness of the bottom boundary layer (BBL) indicates that the velocity intensification is observed over the boundary layer upper border. A 10-day long benthic storm with a maximum measured velocity of 13 cm/s was revealed 6 m above the bottom. As was found, the origin of the benthic storm is associated with the penetration of an anticyclonic eddy down to the bottom.Translated by Mikhail M. Trufanov. 相似文献
972.
Trends in biomass, density and diversity of North Sea macrofauna 总被引:6,自引:2,他引:6
973.
B. T. G. Gowland A. D. McIntosh I. M. Davies C. F. Moffat L. Webster 《Marine environmental research》2002,54(3-5)
An aluminium smelter on the west coast of Scotland discharges an aqueous effluent containing polycyclic aromatic hydrocarbons (PAHs) at the head of Loch Leven. The loch also supports two mussel (Mytilus edulis) farms. Data are presented on burdens of PAHs in the soft tissues of mussels and the effect of these contaminants on glutathione S-transferase (GST) activity in mussel hepatopancreas. GST activity is shown to be correlated with total PAH burden and also with the concentrations of certain individual PAHs. These field data show that high molecular weight PAHs are closely correlated to GST activity, whereas low molecular weight PAHs are not. This suggests that 5- and 6-ring PAHs have a more pronounced role than 2- to 4-ring compounds in inducing GST activity in mussels from Loch Leven. It is proposed that it may be more appropriate to link GST activity with 5- and 6-ring compounds only, rather than with the total PAH burden. 相似文献
974.
V. A. Ivanov S. P. Lyubartseva N. Mikhailova N. B. Shapiro 《Physical Oceanography》2001,11(6):509-524
We analyze the results of numerical calculations performed according to the three-dimensional interdisciplinary model of an
ecological system of the Black-Sea shelf zone near the estuary of the Danube. The complete system of equations of hydrothermodynamics
is solved together with transport equations of the advection-diffusion-reaction type used to describe the transformation of
a substance (nitrogen) between the components of the characteristic vectors of the ecosystem: plankton, detritus, and biogenic
elements (nitrates). We describe the distinctive features of the circumcontinental distribution of components obtained as
a result of numerical experiments and present arguments for the conclusion that the ecosystem of the Danube estuary water
area plays the role of a buffer zone between the press of the Danubian biogenic pollutions and the neighbouring areas of the
shelf zone and open sea.
Translated by Peter V. Malyshev and Dmitry V. Malyshev 相似文献
975.
S. Vanucci A. Dell'Anno A. Pusceddu M. Fabiano R. S. Lampitt R. Danovaro 《Progress in Oceanography》2001,50(1-4)
Downward fluxes of microbial assemblages associated with sinking particles sampled in sediment traps deployed at nominal depths of 1000 m (trap A), 3000 m (trap B) and 4700 m (trap C) were measured between October 1995 and August 1998 on the Porcupine Abyssal Plain (PAP, NE Atlantic). The goal of the study was to provide detailed information on the microbial contributions to the particulate organic carbon and DNA fluxes. Bacterial fluxes associated with settling particles in the PAP area were generally low and significantly lower than bacterial fluxes reported from the same area during 1989–90. Marked seasonal pulses in the microbial assemblages were observed in all years that were associated with particle flux maxima in April–June. No significant differences were found in microbial fluxes between 1000 and 4700 m depth, but both the bacterial biomass flux and the frequency of dividing bacteria increased with depth, suggesting that organic matter turnover and conversion into bacterial biomass increased in the deeper traps. The structure of microbial assemblages displayed clear changes with increasing depth; the ratios of bacteria to both flagellates and cyanobacteria increased up to 4-fold between 1000 and 4700 m, showing a marked increase in bacterial dominance in the deeper layers of the water column. A parallel increase of the bacterial contribution to particulate organic carbon (POC) and DNA fluxes was observed. Total microbial contribution to the POC flux in the PAP area was about 2%, whereas the contribution of cyanobacteria was negligible. Fluxes of microbial assemblages were significantly correlated with DNA fluxes and on average the bacteria accounted for 5% of DNA fluxes. Data reported here confirm that the “rain” of particulate bacterial DNA may represent an important source of nucleotides for deep-sea bacteria, but also suggests that a much larger pool of detrital DNA is potentially available to deep-sea micro-organisms. 相似文献
976.
为了探讨黄河三角洲附近潮波运动的变化特征,乐肯堂等(1995)用二维数值模式模拟了1855-1984年该海区的潮汐和潮流的分布变化,并着重考察了M2和S2分潮的无潮点,以及规则全日潮区的位置变化。乐肯堂等(1995)的研究表明,黄河尾闾的摆动以及由此而造成的黄河三角洲之进退,是该海区潮波特征发生变化的主要外因。自从1976年黄河尾闾改道清水沟以来,该流路已稳定运行了20多年,由此造成了河口附近沙嘴不断向莱州湾内延伸,因而对该区的潮波分布特征产生了显著影响。从黄河三角洲区的经济可持续发展和海洋生态环境的可持续发展的目的出发来规划今后黄河尾闾的走向,就必须对以下两个问题进行深入研究:(1)清水沟流路是否还能长期稳定下去;(2)如果清水沟流路长期稳定不变,并且按照清水沟流路期间黄河三角洲向莱州湾推进的方式来推演10a后黄河三角洲的形势,那么到2010年该区的潮波运动将会发生什么变化。为此,在本文中我们仍然采用乐肯堂等(1995)已经过验证的数值模式和数值预的方法对上述问题作初步探讨。 相似文献
977.
978.
Developments in the study of wave forces and construction techniques in deep water by the offshore oil industry have increased the use of marine terminals at deep water locations. A thorough understanding of moored ship dynamics when subjected to waves, wind and current combined with the use of flexible mooring lines would help to design berthing terminals for exposed areas. In this paper, the three dimensional problem of wave interactions with a barge moored to a single point is dealt with, based on the finite element method. The effect of flexibility of the mooring line and the point of mooring on the response of the barge as well as the mooring line tension is investigated. The paper compares the numerical results with model tests carried out on a barge moored to a fixed support under regular and random waves in head sea. The effect of stiffness of the mooring line on the barge response for different mooring points is discussed, which would be useful for the designers. The effect of viscous damping is also considered. The analytical results are in good agreement with the experimental results in both regular and random waves. 相似文献
979.
The present paper, of a tutorial nature, solves two different thermoelastic problems using a unified approach: (a) thermoelastic stresses and deflections in thin, rectangular plates with edges elastically restrained against rotation when small-deflection theory is used and stress resultants in the middle plane of the plates are neglected; and (b) thermoelastic plane stress situations in rectangular plates with stress-free edges subjected to a two-dimensional temperature distribution.The first problem is attacked using polynomial coordinate functions which identically satisfy the governing boundary conditions, and the Ritz method is used to determine the plate response. When the flexibility coefficients approach zero (clamped edge conditions) the calculated results practically coincide with the exact solution for the test case treated in this paper. On the other hand this degenerate solution turns out to be a very convenient approximation for obtaining a solution to Airy's problem described in the second place and which is also solved in a straightforward manner using a variational approach. 相似文献
980.
Qian Fenlan Yu Hongjian Lan Youchang Chen Zhi Zhou Mingyu Farn Parungo Wu Peiming 《海洋学报(英文版)》1996,15(1):69-84
AtmosphericinputoftraceelementstothewesternPacificOceanandtheKuroshiooceanarea¥QianFenlan;YuHongjian;LanYouchang;ChenZhi;Zhou... 相似文献