全文获取类型
收费全文 | 28915篇 |
免费 | 1110篇 |
国内免费 | 2089篇 |
专业分类
测绘学 | 1582篇 |
大气科学 | 3115篇 |
地球物理 | 5918篇 |
地质学 | 13656篇 |
海洋学 | 1582篇 |
天文学 | 1854篇 |
综合类 | 2591篇 |
自然地理 | 1816篇 |
出版年
2024年 | 16篇 |
2023年 | 67篇 |
2022年 | 203篇 |
2021年 | 258篇 |
2020年 | 167篇 |
2019年 | 251篇 |
2018年 | 4965篇 |
2017年 | 4225篇 |
2016年 | 2804篇 |
2015年 | 466篇 |
2014年 | 406篇 |
2013年 | 287篇 |
2012年 | 1279篇 |
2011年 | 3004篇 |
2010年 | 2278篇 |
2009年 | 2556篇 |
2008年 | 2133篇 |
2007年 | 2568篇 |
2006年 | 271篇 |
2005年 | 374篇 |
2004年 | 530篇 |
2003年 | 573篇 |
2002年 | 390篇 |
2001年 | 173篇 |
2000年 | 214篇 |
1999年 | 206篇 |
1998年 | 214篇 |
1997年 | 171篇 |
1996年 | 153篇 |
1995年 | 167篇 |
1994年 | 135篇 |
1993年 | 136篇 |
1992年 | 95篇 |
1991年 | 59篇 |
1990年 | 49篇 |
1989年 | 51篇 |
1988年 | 44篇 |
1987年 | 42篇 |
1986年 | 25篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 9篇 |
1981年 | 26篇 |
1980年 | 24篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 7篇 |
1958年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
201.
202.
The distribution and geochemical composition of suspended-particulate matter (SPM) in the East China Sea (ECS) were investigated
during the summer period of high continental runoff to elucidate SPM sources, distribution and cross-shelf transport. The
spatial variability of SPM distribution (0.3–6.5 mg l−1) and geochemical composition (POC, Al, Si, Fe, Mn, Ca, Mg and K) in the ECS was pronounced during summer when the continental
fluxes of freshwater and terrestrial materials were highest during the year. Under the influences of Changjiang runoff, Kuroshio
intrusion, surface production and bottom resuspension, the distribution generally showed strong gradients decreasing seaward
for both biogenic and lithogenic materials. Particulate organic carbon was enriched in surface water (mean ∼18%) due to the
influence of biological productivity, and was diluted by resuspended and/or laterally-transported materials in bottom water
(mean 9.4%). The abundance of lithogenic elements (Al, Si, Fe, Mn) increased toward the bottom, and the distribution correlations
were highly significant. Particulate CaCO3 distribution provided evidence that the SPM of the bottom water in the northern part of the study area was likely mixed with
sediments originally derived from Huanghe. A distinct benthic nepheloid layer (BNL) was present in all seaward transects of
the ECS shelf. Sediment resuspension may be caused by tidal fluctuation and other forcing and be regarded as the principal
agent in the formation of BNL. This BNL was likely responsible for the transport of biogenic and lithogenic particles across
or along the ECS shelf. Total inventories of SPM, POC and PN are 46, 2.8 and 0.4 Tg, respectively, measured over the total
area of 0.45 × 106 km2 of the ECS shelf. Their mean residence times are about 27, 13 and 11 days, respectively. The inventory of SPM in the water
column was higher in the northernmost and southernmost transects and lower in the middle transects, reflecting the influences
of terrestrial inputs from Changjiang and/or resuspended materials from Huanghe deposits in the north and perhaps from Minjiang
and/or Taiwan’s rivers in the south. The distribution and transport patterns of SPM and geochemical elements strongly indicate
that continental sources and cross-shelf transport modulate ECS particulate matter in summer. 相似文献
203.
参考鳗鲡等鱼类线粒体 DNA序列进行了中国花鲈线粒体 DNA细胞色素 b基因片断的引物设计、PCR扩增及其序列测定。得到中国花鲈的碱基序列为 4 10 bp,其 A、T、G、C含量分别为 10 1bp(2 4 .6 3% )、112 bp(2 7.32 % )、72 bp(17.56 % )、12 5bp(30 .4 9% ) ,与鳗鲡等其他鱼类相同基因片断序列碱基含量相似。 相似文献
204.
StudiesonmarinenanodiatomsinFujiancoastalwatersofChinainwinter¥LiuShicheng;GaoYahuiandChengZhaodi(ReceivedDecember22,1994;acc... 相似文献
205.
Using benthic macrofauna to assess environmental quality of four intertidal mudflats in Hong Kong and Shenzhen Coast 总被引:4,自引:0,他引:4
Cai Lizhe Nora F. Y. Tam Teresa W. Y. Wong Ma Li Gao Yang Yuk-Shan Wong 《海洋学报(英文版)》2003,22(2):309-319
Abstract-Intertidal zone is a significant wetland between land and ocean. It plays an important rolein maintaining local ecological balance. Both Mai Po and Futian intertidal mudflats are located in Shen-zhen Bay and are important "refueling" point along the East Asian/Australian flyway of migratory birds.The environmental quality of Mai Po and Futian mudflats have aroused great concern due to rapid eco-nomic developments in Hong Kong and Shenzhen in recent decades. Microinfauna of Mai Po and Futianmudflats was investigated in December 2000 and the faunal data were used to assess their environmentalquality. Two other mudflats, namely Ma Wan Typhoon Shelter (a more disturbed area) and Luk Kengintertidal mudflat (a place with relatively less human disturbance), were also sampled for macroinfaunaand used as reference mudflats. Shannon-Weaver species diversity index (I_(sd)), biotic coefficient (C_b)and macrofaunal pollution index (I_(mp)) of the macrofauna community on four intertidal mudflats wereused to 相似文献
206.
207.
山东半岛东部诸岛水域叶绿素—a含量和初级生产力 总被引:1,自引:0,他引:1
据1990.11-1991年8月期间,山东半岛东部诸岛水域调查资料,分析了该水域叶绿素-a含量的时空分布和初级生产力的分布与变化,此分布与该水域的温度和营养盐水含量密切相关。叶绿素-a含量的季节变化分三种类型,年变幅为0.11-12.81mg/m^3,年平均值为1.17mg/m^3。初级生产力夏季〉春季〉秋季〉冬季,年变幅为23.00-791.60mg.c/m^2.d年平均为152.0mg.c/m 相似文献
208.
209.
东太平洋沉积物U的地球化学 总被引:4,自引:0,他引:4
本文对地矿部“海洋四号”科学考察船1987-1989年在东赤道太平洋CC区所取得的27个深海表层沉积样品进行U的地球化学分析,探讨了U在深海沉积中的地球化学行为,结果表明,不同类型沉积的U含量不同,平均值由大至小的次序的含沸石粘土(2.16×10^-6),硅质粘土(1.95×10^-6),硅质软泥(1.65×10^-6),钙质硅质粘土(1.59×10^-6),在同类型沉积中U的分散性较大;U在区域 相似文献
210.
上元-坑园牡蛎礁位于高潮位以下3m,主要成分为长牡蛎和近江牡蛎,其~(14)C年龄为3043±82a,B.P.。据此推算出罗源湾一带海岸处于缓慢上升状态,速率为1.15mm/a。根据上元-坑园牡蛎礁的上述特征,并结合断块差异升降运动的表现,作者认为这一地区中、晚全新世以来以“陆动型”海平面变化占主导地位。 相似文献