全文获取类型
收费全文 | 88068篇 |
免费 | 13978篇 |
国内免费 | 18000篇 |
专业分类
测绘学 | 9487篇 |
大气科学 | 9877篇 |
地球物理 | 16885篇 |
地质学 | 45580篇 |
海洋学 | 10394篇 |
天文学 | 5425篇 |
综合类 | 6217篇 |
自然地理 | 16181篇 |
出版年
2024年 | 326篇 |
2023年 | 912篇 |
2022年 | 2622篇 |
2021年 | 3067篇 |
2020年 | 3027篇 |
2019年 | 3805篇 |
2018年 | 2857篇 |
2017年 | 3417篇 |
2016年 | 3532篇 |
2015年 | 3902篇 |
2014年 | 4800篇 |
2013年 | 5112篇 |
2012年 | 5218篇 |
2011年 | 5509篇 |
2010年 | 4677篇 |
2009年 | 5723篇 |
2008年 | 5572篇 |
2007年 | 6126篇 |
2006年 | 5929篇 |
2005年 | 5297篇 |
2004年 | 4935篇 |
2003年 | 4537篇 |
2002年 | 3921篇 |
2001年 | 3485篇 |
2000年 | 3370篇 |
1999年 | 2966篇 |
1998年 | 2576篇 |
1997年 | 2181篇 |
1996年 | 1891篇 |
1995年 | 1564篇 |
1994年 | 1562篇 |
1993年 | 1310篇 |
1992年 | 1044篇 |
1991年 | 754篇 |
1990年 | 633篇 |
1989年 | 510篇 |
1988年 | 390篇 |
1987年 | 239篇 |
1986年 | 173篇 |
1985年 | 136篇 |
1984年 | 65篇 |
1983年 | 61篇 |
1982年 | 50篇 |
1981年 | 37篇 |
1980年 | 37篇 |
1979年 | 33篇 |
1978年 | 56篇 |
1977年 | 27篇 |
1976年 | 8篇 |
1954年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Abstract. Samples of the polychaete Nereis diversicolor O.F. M üller and surficial sediments from a clean and a polluted estuary were taken during a year at monthly intervals to determine, by comparison, the range of temporal fluctuations in trace metal concentrations. Whereas metal variations in surficial sediments were more pronounced in the polluted estuary, concentrations in N. diversicolor in both estuaries showed a wide range of temporal variation that surpassed that of surficial sediments. A clear decline in all metals studied (except Mn) from polluted sediments was noted after episodes of strong rainfall. In the reference estuary the fluctuations were less pronounced. Metal body burdens in N. diversicolor from the two estuaries were usually quite similar even though total levels in sediments differed considerably, indicating a lack of worm-sediment relationship. The low level of Cu, Cr and Pb in the tissues of N. diversicolor suggest a mechanism which prevents the polychaete from being exposed to these metals in highly polluted sediments. Therefore, it is concluded that N. diversicolor cannot be considered to be an ideal biomonitor of metal contamination in the polluted Bilbao Estuary. 相似文献
942.
南海西南部新生代盆地类型及演化历史 总被引:4,自引:0,他引:4
南海西南部地区发育了多种类型的新生代沉积盆地,各种类型的盆地具有各自的结构特征和演化历史,走滑-周缘前陆盆地-曾母盆地发育了渐新-中中新统层系,晚中新统层系和上新-第四系层系第三套地层,曾母盆地经历了三个发育阶段,拉张剪切盆地-万安盆地发育下第三系-下渐新统层系,上渐新统一中中新统层系和上中新统一第四系层系三套地层,万安盆地经历了四个发育阶段。 相似文献
943.
1993/1994年南极夏季对中国南极长城湾及附近海区表层海水四种营养盐浓度及其分布状况作了调查。结果表明,NH4-N、NO3-N、NO2-N及PO4-P的大致浓度分别是2.13、7.07、0.74和1.12μg·dm-3。一般来说,湾内高于湾外氮盐于12月份常出现高值。四种形态的无机盐类之最高、最低浓度出现的时间和站位不尽一致。∑N/P递减次序大致是12月,2月,1月。水温变化与NH4-N、PO4-P浓度和∑N/P的变化常较一致,而与NO2-N则常不一,一些站位上营养盐浓度偏低可能与浮游植物摄取有关。结果显示了调研海区的浅水内湾特征。浮游植物所需营养充分。该湾仍维持正常状态。 相似文献
944.
王荣良 《中国海洋大学学报(自然科学版)》1996,(1)
讨论调频输入正弦锁相环路方程的调和解、浑饨与分支。利用Melnikov方法确定了产生浑沌与次谐波分支及其稳定性的条件,同时我们证明了当方程的参数适当小时,它必存在调和解。 相似文献
945.
提出用B样条函数求解曲线、曲面上重磁位场的向上延拓,水平、垂向导数计算,磁异常分量互换的方法。该方法的特点是:原理简明,程序通用性强,计算精度高。 相似文献
946.
947.
948.
949.
950.
Species composition and spatial distribution of euphausiids of the yellow sea and relationships with environmental factors 总被引:1,自引:0,他引:1
Won Duk Yoon Joon Yong Yang Donghyun Lim Sung Hwan Cho Gyung Soo Park 《Ocean Science Journal》2006,41(1):11-29
We investigated species composition and spatial distribution of the euphausiid community in the Yellow Sea and identified
the relationship with environmental factors (temperature, salinity, chlorophyll a, nitrate, phosphate, and silicate) using
bimonthly data from June, 1997 to April, 1998. The environment varied during the sampling period. In warm seasons, thermocline
was well developed rendering lower temperature and higher salinity and nutrient concentrations in the bottom layer. During
cold seasons the water column was well mixed and no such vertical stratification was noted. Horizontal distribution of temperature,
however, differed slightly between near-coast and offshore areas because of the shallow depth of the Yellow Sea, and between
southern and northern areas because of the intrusion of water masses such as Yellow Sea Warm Current and Changjiang River
Diluted Water. Four euphausiid species were identified:Euphausia pacifica, E. sanzoi, Pseudeuphausia sp. andStylocheron affine. E. sanzoi andS. affine were collected, just one juvenile each, from the southern area in June and December, respectively.Pseudeuphausia sp. were collected in the eastern area all the year round except June.E. pacifica occurred at the whole study area and were the predominant species, representing at least 97.6% of the euphausiid abundance.
Further, the distribution pattern of the species was varied in regards to developmental stages (adult, furcilia, calyptopis,
egg). From spring to fall,E. pacifica adults were abundant in the central area where the Yellow Sea Bottom Cold Water prevailed. Furcilia and calyptopis extended
their distribution into nearly all the study area during the same period. From late fall to winter, adults were found at the
near-coastal area with similar pattern for furcilia and calyptopis. The distribution pattern ofE. pacifica was consistent regarding temperature, salinity, and three nutrients during the sampling period, whereas chlorophyll a showed
a different pattern according to the developmental stages. The nutrients should indirectly affect via chlorophyll a and phytoplankton
concentration. With respect to these results, we presented a scenario about how the environmental factors along with the water
current affect the distribution ofE. pacifica in the Yellow Sea. 相似文献