全文获取类型
收费全文 | 2158篇 |
免费 | 279篇 |
国内免费 | 560篇 |
专业分类
测绘学 | 221篇 |
大气科学 | 137篇 |
地球物理 | 300篇 |
地质学 | 827篇 |
海洋学 | 805篇 |
天文学 | 263篇 |
综合类 | 246篇 |
自然地理 | 198篇 |
出版年
2024年 | 9篇 |
2023年 | 30篇 |
2022年 | 59篇 |
2021年 | 70篇 |
2020年 | 78篇 |
2019年 | 71篇 |
2018年 | 72篇 |
2017年 | 101篇 |
2016年 | 86篇 |
2015年 | 143篇 |
2014年 | 167篇 |
2013年 | 140篇 |
2012年 | 151篇 |
2011年 | 143篇 |
2010年 | 124篇 |
2009年 | 151篇 |
2008年 | 165篇 |
2007年 | 177篇 |
2006年 | 137篇 |
2005年 | 131篇 |
2004年 | 112篇 |
2003年 | 103篇 |
2002年 | 103篇 |
2001年 | 72篇 |
2000年 | 80篇 |
1999年 | 67篇 |
1998年 | 47篇 |
1997年 | 59篇 |
1996年 | 28篇 |
1995年 | 18篇 |
1994年 | 18篇 |
1993年 | 17篇 |
1992年 | 12篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 2篇 |
1988年 | 7篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1980年 | 2篇 |
1971年 | 1篇 |
1921年 | 1篇 |
1919年 | 1篇 |
1905年 | 1篇 |
1897年 | 2篇 |
1880年 | 2篇 |
1877年 | 2篇 |
1875年 | 1篇 |
排序方式: 共有2997条查询结果,搜索用时 375 毫秒
191.
Elizabeth A. V. Mackie Jeremy M. Lloyd Melanie J. Leng Michael J. Bentley Carol Arrowsmith 《第四纪科学杂志》2007,22(6):579-591
Carbon isotopes (δ13C) and C/N ratios from bulk organic matter have recently been used as alternative proxies for relative sea‐level (RSL) reconstruction where there are problems associated with conventional biological indictors. A previous study on a single isolation basin (Upper Loch nan Eala) in northwest Scotland has shown a clear relationship between δ13C, C/N ratios and palaeosalinity from Younger Dryas and Holocene aged sediments. In this paper we present results of δ13C and C/N ratio analyses from other isolation basins in northwest Scotland over the Holocene and the Lateglacial period in order to validate this technique. The results from the Holocene sequences support the earlier findings that this technique can be used to identify RSL change from isolation basins over the Holocene in this region. The relationship between δ13C, C/N ratios and RSL change is not apparent in sediments of Lateglacial age. Other environmental variables such as atmospheric CO2 concentration, poor vegetation development and temperature influence δ13C values during this period. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
192.
193.
克隆获得了与中国明对虾(Fenneropenaeus chinensis)C-type lectin 3同源的C-型凝集素LvLec2基因序列,并通过Real-time PCR研究了其在脂多糖(lipopolysaccharide,简称LPS)、灭活溶壁微球菌(Micrococcus lysodeikticus)和白斑综合症病毒(white spot syndrome virus,简称WSSV)刺激后的转录表达变化。结果表明,LvLec2编码157个氨基酸,含有1个糖识别结构域(carbohydrate recognition domain,简称CRD),其CRD结构域中具有决定糖结合特异性的基序"EPS"(Glu118-Pro119-Ser120)序列。系统进化树分析表明LvLec2与已发表的凡纳滨对虾(Litopenaeus vannamei)C-型凝集素亲缘较远。LPS、灭活溶壁微球菌和WSSV刺激后,LvLec2基因在肝胰脏中的转录表达有明显的变化但表达模式不同。LvLec2可能作为模式识别受体参与了对虾对病原的识别或防御。 相似文献
194.
José M. Marques Paula M. M. Carreira Luís Aires-Barros Rui C. Graça 《Environmental Geology》2000,40(1-2):53-63
At the northern part of the Portuguese mainland, the upflow zone of several hot and cold HCO3/Na/CO2-rich mineral waters is mainly associated with important NNE–SSW faults. Several geochemical studies have been carried out
on thermal and non-thermal hydromineral manifestations that occur along or near these long tectonic alignments. The slight
chemical differences that exist between these meteoric hot and cold HCO3/Na/CO2-rich mineral waters seem to be mainly caused by CO2. δ13C(TIDC) values observed in these groundwaters range between –6.00 and –1.00‰ versus V-PDB (V denotes Vienna, the site of the International
Atomic Energy Agency; PDB originates from the CaCO3 of the rostrum of a Cretaceous belemnite, Belemnitella americana, collected in the Peedee formation of South Carolina, USA) indicating a deep-seated (mantle) origin for most of the CO2. Nevertheless, in the case of the heavier δ13C(TIDC) values, the contribution of metamorphic CO2 or the dissolution of carbonate rock levels at depth cannot be excluded. Concerning the hot waters, the lack of a positive
18O-shift should be attributed to water-rock interaction in a low temperature environment, rather than to the isotopic influence
of CO2 on the δ18O-value of the waters.
Received: 9 August 1999 · Accepted: 8 March 2000 相似文献
195.
YU Shanshan KONG Xiaoyu LI Yulong XU Hui 《中国海洋大学学报(英文版)》2007,6(2):187-192
The complete mitochondrial cytochrome oxidase subunit Ⅱ (COⅡ) gene of Penaeinae shrimp Fenneropenaeus chinensis was cloned and sequenced. The gene is 688 bp in length and codes for 229 amino acids. It shows 83.2%, 87.0% and 83.8% sequence similarity to Marsupenaeus Japonicus, Penaeus monodon and Farfantepenaeus notialis, respectively. The A+T content of the whole gene and that at the third position of codons are 64.7% and 78.2%, respectively. The phylogenetic relationship between F. chinensis and three other species representing genera Farfanatepenaeus, Marsupenaeus and Penaeus was analyzed. Results showed that the genetic distances among the four taxa ranged from 0.144 0 to 0.200 5, exceeding those estimated with COⅠ and partial 16S rRNA gene sequences among Marsupenaeus, Litopenaeus and Melicertus, and being therefore larger than the value among subgenera. It has been suggested that the COⅡ gene has a faster evolutionary rate than that of the COⅠ gene and partial 16S rRNA gene and could be used for phylogenetic analysis at genus or species level. The results of the present study indicated that Farfantepenaeus, Fenneropenaeus, Marsupenaeus and Penaeus are at a higher phylogenetic level than subgenus, which supports the opinion of the elevation of phylogenetic status of the four subgenera to genus level. 相似文献
196.
Comparison of ecophysiological characteristics between introduced and indigenous mangrove species in China 总被引:2,自引:1,他引:1
Luzhen Chen Nora F.Y. Tam Jianhui Huang Xueqin Zeng Xiangli Meng Cairong Zhong Yuk-shan Wong Guanghui Lin 《Estuarine, Coastal and Shelf Science》2008,79(4):644-652
Due to its rapid growth, the introduced mangrove species Sonneratia apetala from Bangladesh has been widely used in mangrove restoration in southeastern China since 1985. As an indigenous mangrove species in Hainan, China, Sonneratia caseolaris was also planted in Guangdong Province for afforestation purposes. Both species have developed well in their new habitats, but their ecophysiological differences with the native mangrove species have not been studied. In this study, leaf gas exchange, water and nitrogen use efficiencies of two Sonneratia species were compared with those of selected native mangrove species (Avicennia marina, Aegiceras corniculatum, Kandelia candel, and Excoecaria agallocha) in Hainan and Shenzhen. The introduced S. apetala maintained lower carbon assimilation rate (A) and photosynthetic nitrogen use efficiency (PNUE) than the indigenous S. caseolaris. In Shenzhen, the two introduced Sonneratia had comparable photosynthetic rates and water use efficiency (WUE) with the native mangrove species, except that PNUE in S. caseolaris was significantly higher than in the native mangrove species. The two Sonneratia species showed significant overlap in PNUE and long-term WUE. Photosynthetic parameters derived from leaf photosynthetic light–response curves and A–Ci curves also suggested lower carbon assimilation capacities for the introduced Sonneratia than for the native mangrove species in both study sites. The lower light compensation point (LCP) of two introduced Sonneratia in both study sites also indicated a better adaptation to a low light regime than the native mangrove species. The results of photosynthetic capacities indicated that the introduced mangrove species have little competitive advantage over local native mangrove species in their respective new habitats. 相似文献
197.
Expression of putative zinc-finger protein lcn61 gene in lymphocystis disease virus China (LCDV-cn) genome 总被引:1,自引:0,他引:1
An open reading frame (lcn61) of lymphocystis disease virus China (LCDV-cn), probably responsible for encoding putative zinc-finger proteins was amplified
and inserted into pET24a (+) vector. Then it expressed in E. coli BL21 (DE3), and His-tag fusion protein of high yield was obtained. It was found that the fusion protein existed in E. coli mainly as inclusion bodies. The bioinformatics analysis indicates that LCN61 is C2H2 type zinc-finger protein containing
four C2H2 zinc-finger motifs. This work provides a theory for functional research of lcn61 gene.
Supported by High Technology Research and Development Program of China (863 Program, No. 2006AA100309) 相似文献
198.
199.
传统村落景观基因信息链与自动识别模型构建——以陕西省为例 总被引:2,自引:0,他引:2
传统村落作为活的文化遗产,承载了大量历史记忆,是地域文化景观基因识别与模型构建研究的重要切入点。以陕西省71个国家级传统村落为例,基于景观基因理论建立陕西省传统村落景观基因识别体系,识别出陕西省传统村落景观基因特征;运用类型学原理和N级编码理论对景观基因进行编码,构建陕西省传统村落景观基因信息链并生成基因谱系;借鉴生物学中“胞-链-形”DNA碱基序列模型,提取出环境基因、建筑基因、农耕文化基因和宗族文化基因四个公共基因作为景观基因元(胞),以村内道路系统作为基因链,构建传统村落景观基因DNA模型与自动识别模型,以此对传统村落的区位、类型、特征和文化基因进行自动识别。为传统村落景观基因信息有效传承与存储,以及乡村建设动态发展提供理论借鉴。 相似文献
200.
溶藻弧菌asp基因在大肠杆菌中表达活性研究及条件优化 总被引:1,自引:0,他引:1
为进一步研究溶藻弧菌碱性丝氨酸蛋白酶(ASP)蛋白生物学活性和功能,将构建的pET23d-asp在大肠杆菌BL21(DE3)中表达,对表达产物进行纯化分析,并优化表达条件。结果表明:在咪唑洗脱缓冲液浓度为100 mmol/L时,表达的可溶性ASP被大量洗脱,纯化的ASP相对分子质量约为42 000,具有蛋白活性;在诱导温度28℃、异丙基-β-D硫代半乳糖苷(Isopropyl-β-D-thiogalactopyranoside,IPTG)浓度1 mmol/L及诱导时间16 h时,表达的活性ASP蛋白最多。 相似文献