全文获取类型
收费全文 | 33660篇 |
免费 | 5989篇 |
国内免费 | 7988篇 |
专业分类
测绘学 | 2722篇 |
大气科学 | 6977篇 |
地球物理 | 8263篇 |
地质学 | 16065篇 |
海洋学 | 3966篇 |
天文学 | 1411篇 |
综合类 | 3701篇 |
自然地理 | 4532篇 |
出版年
2024年 | 117篇 |
2023年 | 453篇 |
2022年 | 1471篇 |
2021年 | 1707篇 |
2020年 | 1358篇 |
2019年 | 1664篇 |
2018年 | 1838篇 |
2017年 | 1680篇 |
2016年 | 1983篇 |
2015年 | 1746篇 |
2014年 | 2062篇 |
2013年 | 2028篇 |
2012年 | 1989篇 |
2011年 | 2052篇 |
2010年 | 2131篇 |
2009年 | 2010篇 |
2008年 | 1890篇 |
2007年 | 1775篇 |
2006年 | 1385篇 |
2005年 | 1300篇 |
2004年 | 962篇 |
2003年 | 966篇 |
2002年 | 918篇 |
2001年 | 967篇 |
2000年 | 1106篇 |
1999年 | 1497篇 |
1998年 | 1188篇 |
1997年 | 1132篇 |
1996年 | 1049篇 |
1995年 | 910篇 |
1994年 | 790篇 |
1993年 | 714篇 |
1992年 | 565篇 |
1991年 | 451篇 |
1990年 | 331篇 |
1989年 | 308篇 |
1988年 | 276篇 |
1987年 | 151篇 |
1986年 | 144篇 |
1985年 | 91篇 |
1984年 | 101篇 |
1983年 | 79篇 |
1982年 | 67篇 |
1981年 | 58篇 |
1980年 | 36篇 |
1979年 | 34篇 |
1978年 | 14篇 |
1977年 | 14篇 |
1976年 | 10篇 |
1958年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Three continuous marine fish cell lines of FG (i. e., Hounder Gill) from flounder (Paralichthys olivaceus) gill, SPH (i. e. , Sea Perch Heart) from sea perch (Lateolabrax japonicus) heart and RSBF (i.e., Red Sea Bream Fin) from red sea bream (Pagrosomus major) fin, were characterized by lactate dehydrogenase (LDH) isozyme and morphological analysis. The LDH isozyme patterns of these three cell lines and their corresponding tissues of origin were investigated and compared. The results showed: (1) No difference was found in the LDH isozyme patterns of FG and flounder gill tissue. However, the LDH isozyme patterns of SPH and RSBF were significantly different from their corresponding tissues of origin; (2) LDH isozyme patterns of FG, SPH and RSBF were markedly different from each other and could serve as genetic markers for species identification and detection of cross contamination. Morphological change analysis of these three cell lines in comparison to their original tissues indicated that FG cells still appeared epithelioid without morphological transformation. However, morphological changes were found in SPH and RSBF compared to their original tissues. Therefore, the cellular morphology was still plastic in the relatively stable culture conditions, and it was possible that change of LDH patterns wasrelated to morphological changes of fish cells in vitro. 相似文献
82.
Dan Gill 《Mathematical Geology》1993,25(4):471-482
The ability of association analysis to discriminate sedimentary facies was tested on Purdy's modal analyses of modern sediments of the Great Bahama Bank. Purdy's data set has served in the past as a standard reference for evaluating various multivariate classification algorithms. In order to adapt Purdy's data to association analysis, the percent abundance of the 12 constituents was converted to binary form by dichotomizing each variable on its mean value. The results obtained by association analysis are virtually identical to those obtained by Purdy and other authors. The same four main sedimentary facies were discriminated; 86% of the samples were identically classified (97% when misclassified borderline cases are counted as matches); the total partition variance of the classification is only negligibly greater (4%); and the grouping of the variables yielded the same four groups. The rank order of the three division-attributes responsible for the sample classification is fines, oolites, and corals. Association analysis has been employed by other authors to differentiate meaningful facies groups in studies of ancient reef carbonates, modern reef sediments, and heavy minerals in stream sediments. In all these studies, the results were found to be compatible with those obtained by using the continuous quantitative measurements, indicating that qualitative binary data may often be sufficient for the purpose of facies discrimination in many branches of geology and that association analysis is an effective method for this purpose. 相似文献
83.
Technique for Controlling Spread of Limnotic Oncomelania 总被引:1,自引:0,他引:1
Schistosomiasis is a parasitic disease mostly found in areas along the Changjiang River of China. The disease is spread solely through an intermediary named oncomelania, so its spread of schistosomiasis can be controlled by properly designing water intakes which prevent oncomelania from entering farming land or residential areas. This paper reports a successful design process and a new oncomelania-free intake device. The design of the new intake is based on a sound research program in which extensive experimental studies were carried out to gain knowledge of oncomelania eco-hydraulic behavior and detailed flow field information through CFD simulation. 相似文献
84.
本文简述了国际天球参考架的发展历史和现在射电参考架的现状—基准源选择的标准和参考架的稳定性。描述了地面上光学观测在依巴谷参考架的维持和加密的一系列工作。介绍由天体测量卫星GAIA和SIM给出的天球参考架可能逵到的精度。详述了在今后十年中地面天体测量的作用以及正在开展有关天球参考架的研究课题 ,同时也列出了我国正在和即将开展天体测量的几个研究课题 相似文献
85.
The present paper reports 9 species of pontoniine shrimps collected from Hainan IS-land ,South China Sea ,by the Joint Chinese-German Marine Biology Expeditions,in which Peri-climenaeus arabicus (Calman,1939) and Periclimenaeus hecate (Nobili,1904) are recorded for the first time from Hainan Island. 相似文献
86.
地倾斜台站数字化、模拟观测数据频率特性研究 总被引:2,自引:2,他引:0
分析了四川、云南的部分地倾斜数字化观测与模拟观测资料的特性,从频率范围,周期10天以上的FFT谱特性,固体潮波振幅,相位特征值等方面,论述了地倾斜数字化资料较模拟记录资料的信息组成变化,并对资料的分析与应用进行了初步探讨。 相似文献
87.
智能照明系统在现代建筑照明中的应用研究 总被引:1,自引:0,他引:1
陈丹 《成都信息工程学院学报》2007,22(6):735-738
在对传统照明系统和智能照明系统进行对比分析的基础上,剖析了智能照明系统的控制策略,并结合实际的工程应用,着重讨论了基于ABB I-Bus产品的智能照明控制系统的实现,结果表明该系统具有高效、便捷、节约能源等优点.同时,还对系统与建筑物楼宇自控系统问的系统集成方式进行了研究. 相似文献
88.
CORROSION AND ADHERENCE AT SEA OIL-PLATFORM 总被引:1,自引:0,他引:1
Measurements of the adhesive corrosion and protective potentials of 3 Bohai Sea oilplatforms under different cathodic protection showed corrosion still occurred on these platforms undertheir designed protective potentials. Preliminary conclusions from indoor experiments on the relation betweenadhesive corrosion and cathodic protection showed adhering organisms caused the corrosion onthese platforms. 相似文献
89.
网络经济是相对于大工业经济而言的,其网络企业经济效益的评价,可以从网络企业成本及收益两个方面讨论,然后以投入产出比等五个方面来建立其评价指标体系。 相似文献
90.
This study on the distribution features of petroleum hydrocarbon in water and sedi-ment off the Fujian shore using data obtained from the baseline research on oceanic contamination in Fujian showed that:during the research preiod,petroleum hydrocarbon concentrations in water varied from 5.77μg/L to 37.28μg/L,averaged 14.48 μg/L;was lower in the wet seasson than in the dry season;and was highest in the Minjiang Estuary and Jiulong Estuary in both seasons ,The petorleum hydrocarbon concentrations in shore sediment varied from 14.48 mg/kg to 784.36 mg/kg,averaged 133.3 mg/kg ,and was closely related to sediment types (granularity). 相似文献