全文获取类型
收费全文 | 355篇 |
免费 | 37篇 |
国内免费 | 83篇 |
专业分类
测绘学 | 7篇 |
大气科学 | 3篇 |
地球物理 | 59篇 |
地质学 | 61篇 |
海洋学 | 240篇 |
综合类 | 71篇 |
自然地理 | 34篇 |
出版年
2024年 | 3篇 |
2023年 | 7篇 |
2022年 | 6篇 |
2021年 | 9篇 |
2020年 | 12篇 |
2019年 | 12篇 |
2018年 | 16篇 |
2017年 | 16篇 |
2016年 | 12篇 |
2015年 | 10篇 |
2014年 | 16篇 |
2013年 | 18篇 |
2012年 | 14篇 |
2011年 | 15篇 |
2010年 | 14篇 |
2009年 | 10篇 |
2008年 | 12篇 |
2007年 | 30篇 |
2006年 | 19篇 |
2005年 | 21篇 |
2004年 | 22篇 |
2003年 | 11篇 |
2002年 | 21篇 |
2001年 | 22篇 |
2000年 | 17篇 |
1999年 | 13篇 |
1998年 | 22篇 |
1997年 | 11篇 |
1996年 | 9篇 |
1995年 | 19篇 |
1994年 | 13篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
排序方式: 共有475条查询结果,搜索用时 15 毫秒
81.
This study on the effects of low molecular weight chitosan (LMC- 1) and shrimp preserving agentssuch as phytic acid (PA), sodium bisulfite (SB), and crustacean preservative (CP) on the preservation ofshrimp (Trachypenaeus curvirostris) and the bacteriostasis of LMC-1 showed that: (1) Different LMC-1conontration has different bacteriostasis on E. coIi, B. subtilis and S. aureou: (2) LMC-1 and CP arebetter than PA and SB for preserving the freshness of shrimp stored at 4℃. 相似文献
82.
Lake Ontario water levels have been rising for the past 11 500 years due to differential isostatic rebound of the St. Lawrence outlet. Small scale fluctuations in water level superimposed on this general trend have received little study, with the exception of the Nipissing Flood.The transgression of a Grenadier Pond was studied from cores along a transect from the bar that separates the pond from Lake Ontario to the marsh on the north shore. Radiocarbon dates of the transition from swamp peat to pond marl in five cores provide estimates of the rate of water level rise since 4230 years B.P. These estimates are supported by changes in sediment type and in abundance of pollen and seeds of aquatic plants. There were three short intervals of accelerated water level rise in Grenadier Pond, around 4200, 3000, and 2000 years B.P., when water levels rose up to 2 m instantaneously, within the resolution of radiocarbon dating. Sedimentological and paleobotanical data suggest that Grenadier Pond was an open embayment of Lake Ontario until 1970–1850 years B.P., when it was isolated by the bar, and therefore sediments deposited prior to this time reflect water levels in Lake Ontario.Short term departure of up to 2 m from the average rate of water level rise over the past 4000 years, as observed in the record at Grenadier Pond, is of the same range as historically observed departures from the mean lake stage of Lake Ontario. This implies that a threshold discharge exists above which broadening of the outflow channel occurs to accommodate further increase in discharge with little rise in lake level. The intervals of accelerated water level rise in Lake Ontario broadly coincide with periods of cool, wet climate, suggesting that increased moisture may have caused the short term fluctuations in water level.This is the second of a series of papers to be published by this journal that was presented in the paleolimnology sessions organized by R. B. Davis and H. Löffler for the XIIth Congress of the International Union for Quaternary Research (INQUA), which took place in Ottawa, Canada in August 1987. Drs. Davis and Löffler are serving as guest editors of this series. 相似文献
83.
基于图像处理技术的养殖池集污特性研究 总被引:2,自引:0,他引:2
本文针对养殖池的集污试验,研究了用于量化分析污物聚集面积的图像处理技术,并将其用于方形圆切角养殖池在边侧管式射流方式下的集污特性研究。图像处理技术包括图像预处理、图像增强、图像分割、轮廓提取四个步骤,成功获得了污物的量化分布面积。在养殖池集污特性研究方面,本文研究了射流流速为24cm/s条件下,不同射流角(射流方向与池壁夹角)对污物聚集效果的影响。结果表明,方形圆切角养殖池存在一个最优的射流角度,本文研究条件下,最优角度约为40°。本文研究结果,可为养殖池水力驱动优化布置提供参考。 相似文献
84.
85.
86.
S. G. Marinone O. Q. Gutirrez A. Pars-Sierra 《Estuarine, Coastal and Shelf Science》2004,60(4):611-617
The trajectories of shrimp larvae in the northern part of the Gulf of California were studied from a Lagrangian point of view using a three-dimensional numerical model. The advection of particles was carried out over fortnightly periods starting at spring and neap tides. The northernmost region of the gulf has important shrimp fisheries and nursery areas have been located off the coast of Baja California at San Felipe (SF) and off the Sonora coast at Santa Clara (SC). Though the reproduction zone is believed to be south of these nursery areas, there is much that remains unknown about the zone and the routes used by shrimps to reach these areas. Passive and active simulations of shrimp larvae drift were carried out in order to study the possible areas of shrimp spawning and their migratory routes. The active migration schemes were based on assumptions that the larvae can be advected only: (1) during the day, (2) at night or (3) when the currents flow in the northward direction toward the nursery areas. It was found that the larvae in Santa Clara and San Felipe came from different production zones. No differences were found between the spring and neap tide scenarios except for the diurnal migration experiments. The distance traveled by shrimp larvae was always less than 40–50 km, except in the cases when the larvae selected the appropriate direction to the nursery areas when the larvae travel 140 km to SC and 95 km to SF. 相似文献
87.
Abstract. .Series of experimental trawls repeated over the same area during both 12 and 24 h cycles coupled with an analysis of the stomach contents of the bib demonstrated quantitative and qualitative variations in the predator's diet. The population studied feeds continuously over 24 h, the coefficient of "fullness" is relatively constant, and freshly eaten prey can be observed both during the day and at night. The proportion of brown shrimp in the food increases after high tide, especially when this occurs at night, coinciding with the shrimp's period of maximum activity. However, the overall impact of the bib on the shrimp population depends more on the abundance of the former than on variations in their individual food intake. 相似文献
88.
89.
凡纳对虾(Penaeus vannamei Boone)高产养殖试验 总被引:4,自引:0,他引:4
1999-2001年3a的高产试验结果显示,在符合一定条件的虾塘中和恰当的管理下,在广西沿海进行凡纳对虾(Penaeus vannamei Boone)的集约化养殖是可行的,在平均放苗密度约74尾/m^2时,凡纳对虾的平均单位产量可达到7224.35kg/hm^2。在一定的放苗密度范围(27-81尾/m^2)和养殖期限(99-139d)内,对虾单产与放苗密度和养殖天数正相关,蛋白质水平为35%的配合饲料可以满足集约化养殖的凡纳对虾的需要。 相似文献
90.
虾池长竹蛏肥满度的研究 总被引:2,自引:0,他引:2
本文作者于1997年4月至1998年3月期间,对幸福洋垦区虾池生长的长竹蛏进行了周年肥满度测定研究.结果表明长竹蛏5~9月份较肥,肥满度在60%~80%之间,11月至翌年4月份较瘦,肥满度在55%~47%之间;根据肥满度的测定,长竹蛏的繁殖期为6~8月份. 相似文献