全文获取类型
收费全文 | 17598篇 |
免费 | 2791篇 |
国内免费 | 3451篇 |
专业分类
测绘学 | 3510篇 |
大气科学 | 2169篇 |
地球物理 | 3701篇 |
地质学 | 7813篇 |
海洋学 | 2403篇 |
天文学 | 447篇 |
综合类 | 1249篇 |
自然地理 | 2548篇 |
出版年
2024年 | 86篇 |
2023年 | 240篇 |
2022年 | 674篇 |
2021年 | 741篇 |
2020年 | 821篇 |
2019年 | 973篇 |
2018年 | 685篇 |
2017年 | 858篇 |
2016年 | 891篇 |
2015年 | 914篇 |
2014年 | 1107篇 |
2013年 | 1304篇 |
2012年 | 1133篇 |
2011年 | 1156篇 |
2010年 | 871篇 |
2009年 | 1090篇 |
2008年 | 1136篇 |
2007年 | 1208篇 |
2006年 | 1069篇 |
2005年 | 966篇 |
2004年 | 847篇 |
2003年 | 662篇 |
2002年 | 602篇 |
2001年 | 489篇 |
2000年 | 476篇 |
1999年 | 416篇 |
1998年 | 387篇 |
1997年 | 372篇 |
1996年 | 271篇 |
1995年 | 221篇 |
1994年 | 208篇 |
1993年 | 221篇 |
1992年 | 168篇 |
1991年 | 113篇 |
1990年 | 106篇 |
1989年 | 73篇 |
1988年 | 78篇 |
1987年 | 42篇 |
1986年 | 31篇 |
1985年 | 32篇 |
1984年 | 26篇 |
1983年 | 14篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1978年 | 10篇 |
1977年 | 3篇 |
1954年 | 7篇 |
1900年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
本文探讨东海区近海强风预报模式,首先介绍建立预报模式的思路和步骤,及使用说明,为了验证强风预报模式和判别条件,用1986、1987上日本传真天气图进行试报,准确和基本准确度为91.1%,并给出了1989、1995年随船试验预报结果,准确和基本准确率为90%以上。 相似文献
72.
73.
以1,4—苯二酚和不同的短链脂肪酸为基本原料,经溴代、加成、形成酰卤和酰化等反应,合成了六种新的溴化脂肪酸—2,3,5,6—四溴—1,4—苯二酯。通过对产物的碳、氢、溴等元素的定量分析,以及红外吸收光谱和氢核磁共振谱的研究,验证了化合物的结构。 相似文献
74.
75.
76.
Nowadays there are some chronic serious environmental problems, such as eutrophication, blue tide and so on, in a complicated coastal zone or a semi-enclosed bay, because the water exchanges between an inner bay and an outer sea is weak compared with the supply of contaminant. Under this situation, a method to improve the water quality by 3-dimensional small unsymmetrical structures has been proposed by Komatsu et al. In this paper, several numerical simulations of the tidal current and concentration for various arrangements of bottom roughness in a semi-enclosed model bay are carfled out with a depth-averaged 2-D numerical model. The model is solved by the hybrid finite analytic method with nonstaggered grid. And the SIMPLES algorithm with Rhie and Chow' s momentum interpolation technique is used for the simulation. The effect of Komatsu' s method for water purification is examined by numerical simulation. The result of numerical experiment indicates that it is possible to generate a new tidal residual current and to activate a tidal exchange by bottom roughness arrangement only. 相似文献
77.
Estuary/ocean exchange and tidal mixing in a Gulf of Maine Estuary: A Lagrangian modeling study 总被引:2,自引:0,他引:2
Ata Bilgili Jeffrey A. Proehl Daniel R. Lynch Keston W. Smith M. Robinson Swift 《Estuarine, Coastal and Shelf Science》2005,65(4):607-624
A Lagrangian particle method embedded within a 2-D finite element code, is used to study the transport and ocean–estuary exchange processes in the well-mixed Great Bay Estuarine System in New Hampshire, USA. The 2-D finite element model, driven by residual, semi-diurnal and diurnal tidal constituents, includes the effects of wetting and drying of estuarine mud flats through the use of a porous medium transport module. The particle method includes tidal advection, plus a random walk model in the horizontal that simulates sub-grid scale turbulent transport processes. Our approach involves instantaneous, massive [O(500,000)] particle releases that enable the quantification of ocean–estuary and inter-bay exchanges in a Markovian framework. The effects of the release time, spring–neap cycle, riverine discharge and diffusion strength on the intra-estuary and estuary–ocean exchange are also investigated.The results show a rather dynamic interaction between the ocean and the estuary with a fraction of the exiting particles being caught up in the Gulf of Maine Coastal Current and swept away. Three somewhat different estimates of estuarine residence time are calculated to provide complementary views of estuary flushing. Maps of residence time versus release location uncover a strong spatial dependency of residence time within the estuary that has very important ramifications for local water quality. Simulations with and without the turbulent random walk show that the combined effect of advective shear and turbulent diffusion is very effective at spreading particles throughout the estuary relatively quickly, even at low (1 m2/s) diffusivity. The results presented here show that a first-order Markov Chain approach has applicability and a high potential for improving our understanding of the mixing processes in estuaries. 相似文献
78.
气溶胶的光学厚度与反射率比的处理方法 总被引:2,自引:0,他引:2
气溶胶光学厚度与气溶胶反射率比都是大气校正所需的重要大气参数,同时也是海洋水色卫星主要的数据产品,它们的测量精度将直接到卫星数据产品正演的精度和卫星数据产品的应用。文章在简述气溶胶光学厚度与气溶胶反射率比的基本测量原理和处理方法的基础上,结合多次试验数据结果进行简要的评价。 相似文献
79.
Abstract. The temperate, symbiotic coral Cladocora caespitosa occurs naturally with variable numbers of zooxanthellae. This allows us to study differences in the physiology of symbiotic and "non-symbiotic" polyps and to correlate them with zooxanthellae activities.
Zooxanthellae density in "dark" (normal-colored) polyps was 50 times higher than in "white" (bleached) polyps.
The chlorophyll a content per zooxanthella was 3 times, and Chi c was 13 times higher in white polyps than in dark ones. O2 -flux experiments were conducted with colonies in situ and with single polyps - dark and white - under laboratory conditions. Two approaches were used to evaluate the contribution of zooxanthellae translocation products to animal respiration. Both revealed that the animal tissues derive a higher benefit from the zooxanthellae during periods of low water temperature than during warm periods. 相似文献
Zooxanthellae density in "dark" (normal-colored) polyps was 50 times higher than in "white" (bleached) polyps.
The chlorophyll a content per zooxanthella was 3 times, and Chi c was 13 times higher in white polyps than in dark ones. O
80.
Modelling nitrogen and phosphorus cycles and dissolved oxygen in the Zhujiang Estuary Ⅰ. Model development 总被引:1,自引:0,他引:1
wrmcrloxHuman activities related to the population growth and developrnent of industry and rnwhci-pality have led to the incrouing hadings of various POllutants into estudries during the past fewdecades. These increasing edlutant lOadings have caused declined estuallne hedth which can bemereured by a vdriety of indices. In order to obtain solutions to environrnent problerns, re-sources manageTnnt apencies are supporting a holistic approach to envirorirnental management.An effcient strategy t… 相似文献