全文获取类型
收费全文 | 106篇 |
免费 | 19篇 |
国内免费 | 42篇 |
专业分类
测绘学 | 14篇 |
大气科学 | 17篇 |
地球物理 | 16篇 |
地质学 | 57篇 |
海洋学 | 29篇 |
天文学 | 11篇 |
综合类 | 16篇 |
自然地理 | 7篇 |
出版年
2023年 | 1篇 |
2022年 | 7篇 |
2020年 | 5篇 |
2019年 | 8篇 |
2018年 | 7篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2015年 | 5篇 |
2014年 | 7篇 |
2013年 | 12篇 |
2012年 | 7篇 |
2011年 | 10篇 |
2010年 | 4篇 |
2009年 | 9篇 |
2008年 | 9篇 |
2007年 | 8篇 |
2006年 | 15篇 |
2005年 | 5篇 |
2004年 | 5篇 |
2003年 | 7篇 |
2002年 | 2篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1988年 | 3篇 |
1984年 | 1篇 |
排序方式: 共有167条查询结果,搜索用时 93 毫秒
161.
The molecular weight distributions and hydrolysable neutral sugar composition of dissolved organic carbon (DOC) was investigated
in four maritime Antarctic lakes on Signy Island of different trophic status; Heywood Lake (eutrophic), Light Lake (oligo-mesotrophic),
Sombre Lake and Moss Lake (both oligotrophic). Tangential flow ultra-filtration (TFU) was used to separate DOC into high molecular
weight (HMW; >1000 Da) and low molecular weight (LMW; < 1000 Da) size fractions. Pulsed amperometric detection-high performance
liquid chromatography (PAD-HPLC) was used to determine the hydrolysable neutral sugar molecular composition of each size fraction.
Total DOC concentrations defined the trophic trend in the four lakes and ranged from 8 to 303 μM. The <1000 Da fraction of all the lakes dominated the DOC distribution, comprising 76% in Light Lake which also had the
highest chl-a concentrations. Heywood Lake was relatively enriched in >1000 Da total organic carbon and had extremely high concentrations
of total hydrolysable neutral sugars (11 μM) corresponding to 43% of total DOC. However, no clear pattern was apparent with regard to lake trophic status and potential
sources of DOC, and the measured variations in individual aldose concentration, composition and their various molecular weight
fractions. 相似文献
162.
If left unmodeled, the delay suffered by electromagnetic waves while crossing the neutral atmosphere negatively affects Global Navigation Satellite System positioning. The modeling of the delay has been carried out by means of empirical models formulated based on climatological information or using information extracted from numerical weather prediction (NWP) models. This paper explores the potential use of meteorological information of several types that will become available with the increasing number of sensors (e.g. a cell phone, or the thermometer of a nearby smart home) in cyberspace. How can we make use of these potentially huge data-sets, which may help to provide the best possible representation of the neutral atmosphere at any given time, as readily and as accurately as possible? This situation falls in the realm of Big Data. A few potential scenarios, a sequential improvement of Marini mapping function coefficients, a self-feeding NWP, and near real-time empirical model updates, are discussed in this paper. The pros and cons of each approach are discussed in comparison with what is done today. Experiments indicate that they have potential for a positive contribution. 相似文献
163.
不同适温海洋富油微藻在富碳培养条件下的油脂积累特性研究 总被引:1,自引:0,他引:1
本实验分别针对3株低温藻株:微拟球藻Nannochloropsis sp.ZL-12、四爿藻Tetraselmis chui ZL-33和小球藻Chlorellasp.ZL-45,3株中温藻株:球等鞭金藻Isochrysis galbana CCMM5001、等鞭金藻Isochrysis sp.CCMM5002和微拟球藻Nannochloropsis sp.CCMM7001,3株高温藻株:微拟球藻Nannochloropsis sp.JN1、绿色巴夫藻Pavlova viridis JN2和海洋小球藻Chlorellasp.JN3,研究了在通入0.03%(空气)、5%、10%3个CO2浓度梯度条件下的生长特性,同时考察了其总酯及中性脂的累积情况。结果显示,富碳培养有利于不同温度条件下9株藻株的生长,除微拟球藻Nannochloropsis sp.CCMM7001最适生长的CO2浓度为5%外,其余8株藻株最适生长的CO2浓度均为10%。在低温和高温条件下,6株海洋富油微藻在通入10%CO2时具有最大生物量产率,在中温条件下球等鞭金藻和等鞭金藻在通入10%CO2时获得最大生物量产率,而微拟球藻在通入5%时获得最大生物量产率,随着CO2浓度的增加,9株藻株的总脂含量和中性脂含量有明显提高。低温和中温藻株的总脂含量高于高温藻株的总脂含量,从中性脂的累积规律来看,9株藻株均在平台期的累积达到最大值,GC-MS分析结果表明,9株微藻适合制备生物柴油的C14~C18系脂肪酸相对含量在不同CO2条件下基本保持不变,维持在90%左右。实验结果显示,所研究的藻株作为富油高固碳优良藻株,具备用于海洋生物质能耦合CO2减排开发的潜力。 相似文献
164.
Francioni E de L R Wagener A Scofield AL Depledge MH Cavalier B 《Marine pollution bulletin》2007,54(3):329-338
The mussel Perna perna was used to monitor and assess areas suspected of oil contamination by transplanting animals from unimpacted to impacted sites and vice versa. The deployment lasted for three months during which total PAH were measured in seawater samples collected every 15 days. PAH concentrations were determined in mussel tissue monthly. The lysosomal neutral red assay and the condition index were used as biomarkers of the adverse biological effects. The PAH concentration in mussels at unimpacted sites, prior to deployment was ca. 100 microg kg(-1) but increased to 300 microg kg(-1) after three months at the contaminated site. Mussels transplanted to the uncontaminated site showed a decrease from 380 to 80 microg kg(-1). Significant changes in lysosomal stability occurred within one month of the beginning of the transposition; in contrast condition indexes were not correlated with the observed changes in PAH concentration. 相似文献
165.
Geological and Geochemical Characteristics of the Hydrothermal Clay Alteration in South Korea 总被引:1,自引:1,他引:0
Sang-Mo KOH Tetsuichi TAKAGI Moon–Young KIM Kazuki NAITO Sei–Sun HONG Sadahisa SUDO 《Resource Geology》2000,50(4):229-242
Abstract: Hydrothermally altered areas forming pyrophyllite‐kaolin‐sericite‐alunite deposits are distributed in Chonnam and Kyongsang areas, Cretaceous volcanic field of the Yuchon Group. The Chonnam alteration area is located within depression zone which is composed of volcanic and granitic rocks of late Cretaceous age. The clay deposits of this area show the genetic relationship with silicic lava domes. The Kyongsang alteration area is mainly distributed within Kyongsang Basin comprising volcanic, sedimentary and granitic rocks of Cretaceous and Tertiary age. Most of the clay deposits of this area are closely related to cauldrons. Paleozoic clay deposit occurs in the contact zone between Precambrian Hongjesa granite gneiss and Paleozoic Jangsan quartzite of Choson Supergroup. Cretaceous igneous rocks of the both alteration areas belong to high K calc‐alkaline series formed in the volcanic arc of continental margin by subduction‐related magmatism. Chonnam igneous rocks show more enrichment of crustal components such as K, La, Ce, Sm, Nd and Ba, higher (La/Yb)cn ratio, and higher initial 87Sr/86Sr ratio (0. 708 to 0. 712) than those of Kyongsang igneous rocks. This might be due to the difference of degree of crustal contamination during Cretaceous magmatism. The most characteristic alteration minerals of Chonnam clay deposits are alunite, kaolin, quartz, pyrophyllite and diaspore which were formed by acidic solution. Those of Kyongsang clay deposits are sericite, quartz and pyrophyllite which were formed by weak acid and neutral solution. The formation ages of the clay deposits of two alteration areas range from 70. 1 to 81. 4 Ma and 39. 7 to 79. 4 Ma, respectively. The Daehyun clay deposit in Ponghwa area of Kyongsang province shows the alteration age range from 290 to 336 Ma. This result shows the different alteration episode from the hydrothermal alteration of Cretaceous to early Tertiary in the Kyongsang and Chonnam alteration areas. These data indicate, at least, three hydrothermal activities of Tertiary (middle to late Eocene), late Cretaceous (Santonian to Maastrichtian) and Paleozoic Carboniferous Periods in South Korea. 相似文献
166.
Analysis and hydrogeochemical modeling of hydrocarbonate groundwater, including its buffering geochemical properties, have
demonstrated that this water has undergone a geochemical transformation almost throughout the whole of one industrial region.
It is known that hydrocarbonate groundwater possesses a high protective natural geochemical potential, supporting neutralization
of acid atmospheric precipitation. Natural hydrocarbonate water undergoes three stages of anthropogenic transformation caused
by acid atmospheric precipitation over more than 50 years. The first stage is transformation of neutral hydrocarbonate water
into alkaline water, accompanied by calcite precipitation and sodium carbonate dissolution from the unsaturated zone. The
second stage is transformation of alkaline water into neutral hydrocarbonate water; the hydrocarbonate content, being less
than the lower limit for background concentrations, showed reduced water buffering properties or protective potential relative
to acid precipitation. The third stage is transformation of neutral hydrocarbonate water into acidic water, with a complete
loss of protective geochemical potential.
This unfavorable ecological situation with natural geochemically hydrocarbonate groundwater shows that natural groundwater
less protected from the impact of acid atmospheric precipitation is in a worse ecological condition, which is confirmed by
observations in northern and Western Europe and other regions of the world.
Received: 30 October 1997 · Accepted: 23 March 1998 相似文献
167.
近海层大气湍流通量系数研究 总被引:1,自引:0,他引:1
根据1994年9月18~30日南沙群岛海域渚碧礁的近海面大气湍流观测实验资料,分别计算了该海域光滑海面和粗糙海面上的空气动力粗糙度(z0 )、中性曳力系数( C D N)。利用 Butsaert 的假定,推导了求取标量粗糙度(z T、z Q)、整体输送系数(感热交换系数 C H N、水汽交换系数 C E N )的一组公式。在此基础上,分别计算和分析了该海域光滑海面和粗糙海面上空气动力粗糙度(z0 )、标量粗糙度(z T、z Q )、中性曳力系数( C D N)、整体输送系数(感热交换系数 C H N、水汽交换系数 C E N)及其关于水平风速分量的分布,并得到了一些有益的结论。 相似文献