全文获取类型
收费全文 | 6634篇 |
免费 | 1268篇 |
国内免费 | 1724篇 |
专业分类
测绘学 | 518篇 |
大气科学 | 1390篇 |
地球物理 | 1570篇 |
地质学 | 3309篇 |
海洋学 | 887篇 |
天文学 | 341篇 |
综合类 | 703篇 |
自然地理 | 908篇 |
出版年
2024年 | 28篇 |
2023年 | 116篇 |
2022年 | 340篇 |
2021年 | 380篇 |
2020年 | 302篇 |
2019年 | 317篇 |
2018年 | 385篇 |
2017年 | 322篇 |
2016年 | 383篇 |
2015年 | 338篇 |
2014年 | 399篇 |
2013年 | 414篇 |
2012年 | 380篇 |
2011年 | 399篇 |
2010年 | 410篇 |
2009年 | 400篇 |
2008年 | 379篇 |
2007年 | 341篇 |
2006年 | 258篇 |
2005年 | 202篇 |
2004年 | 190篇 |
2003年 | 164篇 |
2002年 | 187篇 |
2001年 | 176篇 |
2000年 | 179篇 |
1999年 | 281篇 |
1998年 | 290篇 |
1997年 | 257篇 |
1996年 | 259篇 |
1995年 | 196篇 |
1994年 | 178篇 |
1993年 | 134篇 |
1992年 | 115篇 |
1991年 | 90篇 |
1990年 | 95篇 |
1989年 | 72篇 |
1988年 | 59篇 |
1987年 | 54篇 |
1986年 | 43篇 |
1985年 | 25篇 |
1984年 | 20篇 |
1983年 | 10篇 |
1982年 | 15篇 |
1981年 | 13篇 |
1980年 | 10篇 |
1979年 | 5篇 |
1976年 | 3篇 |
1957年 | 2篇 |
1938年 | 2篇 |
1936年 | 3篇 |
排序方式: 共有9626条查询结果,搜索用时 31 毫秒
251.
Xianyu Kong Xiurong Han Min Gao Rongguo Su Ke Wang Xuzhao Li Wei Lu 《中国海洋大学学报(英文版)》2016,15(6):1014-1020
With the global ban on the application of organotin-based marine coatings by the International Maritime Organization, the development of environmentally friendly, low-toxic and nontoxic antifouling compounds for marine industries has become an urgent need. Marine microorganisms have been considered as a potential source of natural antifoulants. In this study, the antifouling potential of marine dinoflagellate Amphidinium carterae, the toxic and red-tide microalgae, was investigated. We performed a series of operations to extract the bioactive substances from Amphidinium carterae and tested their antialgal and antilarval activities. The crude extract of Amphidinium carterae showed significant antialgal activity and the EC50 value against Skeletonema costatum was 55.4 μg mL?1. After purification, the isolated bioactive substances (the organic extract C) exhibited much higher antialgal and antilarval activities with EC50 of 12.9 μg mL?1 against Skeletonema costatum and LC50 of 15.1 μg mL?1 against Amphibalanus amphitrite larvae. Subsequently, IR, Q-TOFMS, and GC-MS were utilized for the structural elucidation of the bioactive compounds, and a series of unsaturated and saturated 16- to 22-carbon fatty acids were detected. The data suggested the bioactive compounds isolated from Amphidinium carterae exhibited a significant inhibiting effect against the diatom Skeletonema costatum and Amphibalanus amphitrite larvae, and could be substitutes for persistent, toxic antifouling compounds. 相似文献
252.
Tongxiang Ren Jun Wang Hai Lu Tao Zhou Yuanjing Zhou 《Geostandards and Geoanalytical Research》2016,40(2):227-238
Due to intensive research into selenium isotopes in recent years, the increasing requirement for reliable and comparable measurement results has created a strong demand for selenium isotopic certified reference materials (iCRM) that were previously not available. To address this, eleven selenium iCRMs were developed, including ten synthetic iCRMs (GBW 04447–GBW 04456) and one natural iCRM (GBW 04457). The synthetic iCRMs were prepared with 76Se, 78Se, 80Se and 82Se solutions and a natural selenium solution; the natural iCRM was prepared with highly pure selenium material. The property values of isotope ratios in these iCRMs were certified by calibrated mass spectrometry with a collision cell multi‐collector ICP‐MS. The mass discrimination effect of the instrument was corrected with corresponding 78Se/76Se isotope mixtures and 82Se/76Se isotope mixtures, which were gravimetrically prepared with purified, isotopically enriched selenium materials. Homogeneity and stability tests were performed, and no significant influences were found. The uncertainty of the property values of the iCRMs was evaluated according to the Guide to the Expression of Uncertainty in Measurement (GUM) of ISO/BIPM and ISO Guide 35. The δ82/76Se value of GBW 04457 relative to NIST SRM 3149 was also calculated. These iCRMs are intended for use in calibration of instruments and evaluation of methods for the determination of selenium isotope ratios. 相似文献
253.
T.-C. Chen E. M. Matira M.-C. Lu M. L. P. Dalida 《International Journal of Environmental Science and Technology》2016,13(4):1017-1028
In this study, fluidized-bed Fenton process (FBF) was used to degrade dimethyl sulfoxide (DMSO), one of the most widely used solvents. Oxidation by Fenton’s reagent, Fe+2 and H2O2, is one of the cheapest advanced oxidation processes due to the high availability of the reagents. FBF is a modified approach that reduces the large amount of iron oxide sludge formed in conventional Fenton process. The optimal treatment efficiencies by FBF with 2 h of reaction were 95.22 % of DMSO degradation and 34.38 % of COD removal at the conditions of 5 mM DMSO, 68.97 g/L SiO2 carrier, pHinitial 3.0, 5 mM Fe2+, and 32.5 mM H2O2. The kinetic study was also done to investigate the two stages involved in the oxidation. The first stage fitted the zero reaction order with overall initial rate’s apparent rate constant, k 1, of ?0.099. The second stage fitted the first order of DMSO degradation, with rate constant, k 2, of ?0.0005. 相似文献
254.
255.
256.
257.
258.
259.
Ridgeia piscesae是唯一一种存在于东北太平洋Juan de Fuca Ridge热液区的管状蠕虫,我们成功通过RACE PCR获得Ridgeia piscesae TAK1(Rp TAK1)基因全长c DNA序列.为深入研究TAK1基因在管状蠕虫中的作用,本文通过显微注射获得Rp TAK1转基因果蝇,并在果蝇体内成功过表达Rp TAK1基因.我们发现由Rp TAK1编码的氨基酸序列具有一定保守性,可能暗示其功能上的保守性,同时也暗示TAK1蛋白在物种进化中的保守性.而过表达突变体果蝇的眼睛出现变异,包括眼睛变得粗糙、单眼排列不整齐及整体形状变小,可以看出Rp TAK1基因影响果蝇的机体发育,我们猜测在Rp TAK1基因在管状蠕虫的生长发育过程中也可能起到重要作用. 相似文献
260.
Cheng Yinhe Zhou Shengqi Wang Dongxiao Lu Yuanzheng Huang Ke Yao Jinglong You Xiaobao 《中国海洋湖沼学报》2016,34(3):619-628
The observed characteristics of lower atmospheric ducts over the South China Sea(SCS) were analyzed based on Global Position Systerm(GPS) radiosonde data collected four times daily during autumn open cruises from 2006 to 2012.Duct occurrence,thickness,and strength over the SCS were about 40%,150-m thick,and 8 M units,respectively,which were larger than during the summer monsoon period.Most ducts occurred at heights 1 500 m and these ducts easily trap electromagnetic wave clusters with wavelengths 2 m.Diurnal variation of the SCS ducts appeared evident.They occurred more often at midnight at higher altitudes(about 1 100 m),with a thickest layer of about 145 m and less frequently during the evening at lower altitudes(about 800 m),with a thinnest layer of about 125 m.Moreover,ducts during the daytime at a mean height of about 900 m,with the greatest strength of about 10 M units.Furthermore,all duct variables observed over the SCS in autumn decreased from north to south.These findings are useful not only in the design of radar and communication systems,but also for evaluating possible effects of anomalous propagation on meteorological radar and military applications. 相似文献