全文获取类型
收费全文 | 19239篇 |
免费 | 2103篇 |
国内免费 | 2193篇 |
专业分类
测绘学 | 6032篇 |
大气科学 | 2481篇 |
地球物理 | 2929篇 |
地质学 | 4422篇 |
海洋学 | 2325篇 |
天文学 | 1237篇 |
综合类 | 1858篇 |
自然地理 | 2251篇 |
出版年
2024年 | 97篇 |
2023年 | 218篇 |
2022年 | 540篇 |
2021年 | 731篇 |
2020年 | 776篇 |
2019年 | 823篇 |
2018年 | 620篇 |
2017年 | 1011篇 |
2016年 | 878篇 |
2015年 | 944篇 |
2014年 | 1106篇 |
2013年 | 1363篇 |
2012年 | 1173篇 |
2011年 | 1150篇 |
2010年 | 941篇 |
2009年 | 1115篇 |
2008年 | 1167篇 |
2007年 | 1322篇 |
2006年 | 1215篇 |
2005年 | 998篇 |
2004年 | 924篇 |
2003年 | 699篇 |
2002年 | 636篇 |
2001年 | 536篇 |
2000年 | 432篇 |
1999年 | 408篇 |
1998年 | 307篇 |
1997年 | 233篇 |
1996年 | 199篇 |
1995年 | 196篇 |
1994年 | 161篇 |
1993年 | 141篇 |
1992年 | 88篇 |
1991年 | 78篇 |
1990年 | 53篇 |
1989年 | 52篇 |
1988年 | 44篇 |
1987年 | 28篇 |
1986年 | 21篇 |
1985年 | 18篇 |
1984年 | 20篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1977年 | 11篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1971年 | 6篇 |
1954年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Regional variation in maturation of sandeels in the North Sea 总被引:1,自引:0,他引:1
92.
93.
94.
We describe industry funded contributions to the assessment of the SNA1 snapper (Pagrus auratus) fishery during the 1990s and discuss the advantages and disadvantages of industry funded research. We also provide background on the history of fisheries management in New Zealand, on the current assessment and management processes, and on the SNA1 snapper fishery. In the SNA1 fishery, the contributions of industry and the cooperation with Government scientists has resulted in high quality assessments. In our opinion, the advantages of industry funded research out weigh the disadvantages and suggest that industry funded assessments are highly desirable and should be an integral part of any management system. 相似文献
95.
96.
Combining indicator trends to assess ongoing changes in exploited fish communities: diagnostic of communities off the coasts of France 总被引:1,自引:1,他引:1
97.
State Estimation of the North Pacific Ocean by a Four-Dimensional Variational Data Assimilation Experiment 总被引:1,自引:0,他引:1
Toshiyuki Awaji Shuhei Masuda Yoichi Ishikawa Nozomi Sugiura Takahiro Toyoda Tomohiro Nakamura 《Journal of Oceanography》2003,59(6):931-943
A four-dimensional variational data assimilation system has been applied to an experiment to describe the dynamic state of
the North Pacific Ocean. A synthesis of available observational records and a sophisticated ocean general circulation model
produces a dynamically consistent dataset, which, in contrast to the nudging approach, provides realistic features of the
seasonally-varying ocean circulation with no artificial sources/sinks for temperature and salinity fields. This new dataset
enables us to estimate heat and water mass transports in addition to the qualification of water mass formation and movement
processes. A sensitivity experiment on our assimilation system reveals that the origin of the North Pacific Intermediate Water
can be traced back to the Sea of Okhotsk and the Bering Sea in the subarctic region and to the subtropical Kuroshio region
further south. These results demonstrate that our data assimilation system is a very powerful tool for the identification
and characterization of ocean variabilities and for our understanding of the dynamic state of ocean circulation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
98.
99.
Sequence variation of the first internal transcribed spacer of ribosomal DNA ( ITS - 1 ) was examined and its application to the study of genetic variation was explored in four populations of farter' s scallop Chlamys farreri. ITS - 1 fragments, with a length of about 300 bp,of 78 individuals collected from Dalian, Qingdao, Yantai in China and Korea respectively were amplified via PCR, cloned and sequenced. Intra-genomic variation was examined by sequencing several clones of single individuals. Alignment and polymorphism analysis detected 44 haplotypes and 50 polymorphic sites which consist of 30 substitutions and 20 indels, indicating a high level of polymorphisms. Sequence analysis also showed a very low level of intra-individual variation. All these features validated the feasibility of application of ITS - 1 fragment to population analysis. Polymorphism analysis showed that the Korea sample has the richest genetic variation, followed by Yantai and Qingdao samples. AMOVA (analysis of molecular variance) showed that the majority (96.26%) of genetic variation was distributed within populations and 3.74% resulted from among populations, but with P 〈 0.05 ( = 0.042), indicating that the populations in this study have significant divergence. This output was basically concordant with the result arising from RAPD data and different from that from mitochondrial 16S rDNA sequence data. Discussion on this inconsistency was made accordingly. 相似文献
100.
We propose a framework for enabling a systematic evaluation of a fisheries resource management system, which we define as a feed-back mechanism coupled to a fishery. The resource management system includes four basic functions: diagnostics, intervention, goal setting, and decision making. This model allows for the development of an evaluation framework for fisheries resource management by facilitating a typology of failures. We suggest that the potential for systemic and interdisciplinary learning will be significantly enhanced through the process of developing such a framework. 相似文献