全文获取类型
收费全文 | 2702篇 |
免费 | 449篇 |
国内免费 | 751篇 |
专业分类
测绘学 | 20篇 |
大气科学 | 106篇 |
地球物理 | 314篇 |
地质学 | 589篇 |
海洋学 | 2357篇 |
天文学 | 1篇 |
综合类 | 212篇 |
自然地理 | 303篇 |
出版年
2024年 | 15篇 |
2023年 | 39篇 |
2022年 | 123篇 |
2021年 | 119篇 |
2020年 | 132篇 |
2019年 | 127篇 |
2018年 | 124篇 |
2017年 | 107篇 |
2016年 | 138篇 |
2015年 | 118篇 |
2014年 | 171篇 |
2013年 | 174篇 |
2012年 | 150篇 |
2011年 | 183篇 |
2010年 | 157篇 |
2009年 | 189篇 |
2008年 | 196篇 |
2007年 | 204篇 |
2006年 | 192篇 |
2005年 | 149篇 |
2004年 | 144篇 |
2003年 | 117篇 |
2002年 | 117篇 |
2001年 | 97篇 |
2000年 | 91篇 |
1999年 | 84篇 |
1998年 | 67篇 |
1997年 | 49篇 |
1996年 | 54篇 |
1995年 | 38篇 |
1994年 | 41篇 |
1993年 | 50篇 |
1992年 | 43篇 |
1991年 | 21篇 |
1990年 | 12篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 18篇 |
1984年 | 12篇 |
1983年 | 12篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1979年 | 1篇 |
排序方式: 共有3902条查询结果,搜索用时 31 毫秒
941.
福建福宁湾无机氮含量的变化特征及其对浮游植物的影响 总被引:2,自引:0,他引:2
本文根据2002-2003年福宁湾海域的监测资料对NO2-N、NO3+N、NH4-N三态DIN的变化特征和相互关系进行分析,并分析其对浮游植物生物量的影响.研究表明:NO3-N、DIN含量均呈冬季最高、夏季最低,NO2-N含量秋季最高,冬季最低;福宁湾海域赤潮高发期水体DIN中三氮所占比例与年平均相比变化最大的是NO3-N,其次是NH4-N,NO2-N最小;NO3-N、DIN与盐度均呈明显负相关;NO3-N与DIN呈明显正相关;NO3-N是福宁湾海域DIN的主要存在形式;三态氮中仅NO3-N为福宁湾海域浮游植物生长限制因子;浮游植物对DIN的吸收主要以NO3-N形式为主。 相似文献
942.
根据 1 999年 7月 2 3 - 2 4日胶州湾东部赤潮发生海区的观测资料 ,结合同年 6 ,7,8月3个航次的数据 ,分析了赤潮前后水体浮游植物群落、叶绿素 a和营养盐等要素的变化特征。结果显示 ,本次赤潮为短角弯角藻 (Eucampia Zoodiacus)赤潮 ,总生物密度高达 1 .6× 1 0 10个 /m L。赤潮发生时 ,叶绿素 a浓度范围为 2 8.8~ 3 6 .0 mg/m3 ;温度、盐度变化不大 ,DO,p H值升高 ,营养盐浓度处于较低水平 ,其中 P降幅最大 ,N/P值则急剧上升 ,峰值为 2 4 7,P被认为是本次赤潮的限制因子 ;NO2 - N/NO3 - N的值变化很大 ,高于正常值。赤潮消退 ,各要素恢复正常 相似文献
943.
944.
945.
Jutarat Kittiwanich Tamiji Yamamoto Toshiya Hashimoto Keiko Tsuji Osamu Kawaguchi 《Journal of Oceanography》2006,62(4):493-509
A numerical ecosystem model expressing both phosphorus and nitrogen cyclings in the pelagic system of Hiroshima Bay, Japan,
was developed in order to investigate the seasonal variations of these elements and their annual budgets. Based on the geophysical
and chemical structures of the bay, Hiroshima Bay was divided into northern and southern boxes, themselves divided into two
layers of an upper 5 m and a lower layer according to the stratification of the water column. The model consists of equations
representing all relevant physical and biological processes. The results revealed that the internal regeneration of materials
was an important source of bioavailable nutrients for phytoplankton growth in the water column. The incorporation of phytoplankton
aggregation improved the accuracy of the outputs in comparison to the observed data, especially during the stratified summer
season. The results also indicated that phosphorus limitation of phytoplankton growth occurs in the upper layer during summer
while light limitation occurs in the lower layer. In addition, physical processes such as diffusion and advection were also
important as they ensured that most of regenerated nutrients in the lower layer were transported to the upper layer. Thus,
these processes might support the high primary production and the production of oysters that are extensively cultured in this
bay. Considering the informative results obtained, the model used in this study provides a sound basis and tool to describe
the dynamics of phosphorus and nitrogen cyclings in Hiroshima Bay. 相似文献
946.
Reproductive success of Calanus pacificus during diatom blooms in Dabob Bay, Washington 总被引:1,自引:4,他引:1
While numerous laboratory studies in the last decade have shown that diatoms can induce reproductive failure in copepods, field evidence for a negative diatom effect is equivocal. To unambiguously elucidate the effects diatoms have on copepod reproduction in situ, we undertook a study of the abundance, distribution, grazing rates, and reproductive success of Calanus pacificus in Dabob Bay, Washington, USA, during two spring bloom periods. We simultaneously measured the phytoplankton composition, abundance, and distribution. Here we present results for the reproductive success of C. pacificus using four measurements: egg production rate, clutch size, egg hatching success, and naupliar survival (to the first feeding stage). Egg production rate was positively correlated with chlorophyll a concentration, and egg hatching success and naupliar survival were usually greater than 80%. However, in February 2002 and 2003 – during blooms of diatoms of the genus Thalassiosira – either egg hatching success, naupliar survival, or both were significantly depressed compared to other times in spring and summer. These effects, combined with evidence that C. pacificus was grazing aldehyde-producing Thalassiosira at the time of their blooms, indicate that diatoms can negatively affect copepod reproduction in the field, albeit only under specific circumstances and for brief periods. 相似文献
947.
在杭州湾跨海大桥桥位地形测绘中,采用三角分带解析法进行潮位改正计算,结果表明:合理布设潮位站、合理安排测量时间,可以提高地形测量精度,正确地进行潮位计算。一般应在高平潮前后3h时间内施测,可保证浅滩不出现测量空白区。地形测绘过程中还应布设不少于主测线数量的5%的检查线,以检查其测量精度。在所测的河口湾两岸潮位明显不等时,采用三角分带解析法进行潮位改正计算,其结果合理、正确,可达到规范的要求。 相似文献
948.
分析普里兹湾及其附近海域温、盐分布特征,提出在艾默里冰架外侧有一片温暖水域。指出:1、变性极大的南极绕极深层水的前沿混合水可以影响到陆架上的南纬67°左右;2、在两个“CTD”探头直达海底的测站,深层观测到了温度为负值、盐度为34.67。据此,作者指出该水体属于南极底层水。此外,还对整个海区的跃层现象进行分类,计算了跃层的强度、厚度和深度。 相似文献
949.
Abstract. The changes in the concentrations of silicate, phosphate, and inorganic nitrogen in Eiefsis Bay. an intermittently anoxic basin, arc described and related to the changes in the physical properties of the water. Winter convection resulted in a very small vertical gradient of temperature, salinity, oxygen, and nutrients. Stratification started to develop in May and persisted for about 6 months. High values of silicate, phosphate, and ammonia occurred during the anoxic conditions prevailing in summer. The vertical transport of particulate organic matter and decomposition of abundant pelagic and benthic organic matter during the summer produced a low oxygen level in the bottom layer below the pycnoclinc. A high sea water temperature and vertical stability contributed to the development of anoxic conditions during the summer in the near bottom layer and to mass mortality of benthic macrofauna. Also the Eiefsis Bay anoxia appears to have had significant ecological effects on many other marine species, including several of economic importance. 相似文献
950.
大亚湾海域溶解游离氨基酸及其与环境的关系 总被引:4,自引:0,他引:4
对大亚湾海域溶解游离氨基酸(DFAA)的分布特征及其影响因素进行了研究。现场采样调查分别于1995年5月、11月和2000年4月进行。结果表明 :(1)大亚湾海域DFAA的含量较高 ,在0.69~4.73μmol/L之间 ,平均2.16±0.87μmol/L,可能主要源于较为旺盛的生物活动 ;(2)DFAA含量在海域的平面分布变化较大 ,垂直分布和季节及年变化不明显 ;(3)DFAA与海水中的DOC呈正相关、与叶绿素呈负相关关系 ,与TIN的相关性则呈季节变化 ,生物效应可能是影响该海域DFAA含量的主要因素。 相似文献