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201.
国内外卡林型金矿对比研究 总被引:9,自引:0,他引:9
卡林型金矿是一种主要产于碳酸盐岩-碎悄岩建造中的微细粒浸染型金矿床,以储量大、品位低、金粒度极细为特点,主要分布于美国和中国,区域地质、成矿条件、控矿因素、矿化特征具有明显的可类比性。卡林型金矿区域成矿模式可概括为:金、汞、砷、锑等成矿元素大规模超常聚集,矿质运移-传输,矿床(矿体)的定位等三大系统(阶段)。文中亦对国内外卡林型金矿的成矿系列、成矿模式作对比研究。 相似文献
202.
203.
本文从三个方面探讨了副鼻窦直接冠状扫描影像:(1)检查前病人的准备;(2)CT 技术;(3)数据显示。最佳 CT 技术主要包括采用俯卧位对副鼻窦前部以3mm 层厚薄层扫描,它可使得窦口鼻道综合体得以最佳显示,余部采用5mm 层厚扫描。扫描角度无意义。 相似文献
204.
Rock cut stability assessment in mountainous regions 总被引:1,自引:0,他引:1
Gorka Uribe-Etxebarria Tomás Morales Jesús A. Uriarte Valentín Ibarra 《Environmental Geology》2005,48(8):1002-1013
Ensuring stability of rock slopes is an essential requirement in the progress of our societies today. Rock determined to be
loose or with potential for failure must be removed or restrained in some way. In our work, after doing an inventory of the
instabilities that occurred in the last 5 years in the Basque Country, we analyse the different factors, in slope stability.
The potential for failure is evaluated for different classes of rock mass, characterized previously by their geomechanical
properties. The characterization of potential risk of each one is undertaken by considering 10 parameters that define the
nature of mass rock, relative orientation and morphological features of the slope (interaction rock massif-slope) and infrastructure
features (interaction rock massif-slope-infrastructure). Each of these parameters is evaluated separately and a Risk Factor
(RF) is determined. The RF reaches a maximum value of 10,000 and allows to differentiate four categories of slopes; each category
has its own priority. Rock mass characteristics also determine the potential damage from instability and the associated correction
measures. The systematic evaluation of instabilities must allow establishing a priority in the correction measures and thus
optimise the available economic resources. 相似文献
205.
The presence of pathogenic bacteria in water, along with the factors that act upon them, constitutes a field that has been little investigated in natural environments. It is clear, however, that these pathogens do have a significant effect on the quality of drinking water. Selected bacteria such as Salmonella, Campylobacter, Yersinia, and Listeria were searched for in groundwaters of mainly mountainous regions. Waters of one or two brooks in the catchment area of each spring were also analysed. Our results show that Campylo bacter and Listeria are frequent in all of these waters, even when land use in the catchment area is extensive (mountain pastures). Salmonella, on the other hand, was never found. Factors influencing the presence of Campylobacter, Yersinia, and Listeria were tested using Spearman rank correlations. The results suggest that the presence in water of some species of these bacteria (C. jejuni, L. monocytogenes 4b, and L. ivanovii) is related to a contaminant input, i.e. to the presence of cattle in the catchment area. For other species (C. coli, L. monocytogenes 1/2a, and Yersinia enterocolitica), however, one is forced to admit that no such connection between the presence of these species and that of an identified, potential contaminant input exists. We are therefore obliged to conclude either that these bacteria multiply in a natural way in the environment, or that they are able to survive in it for a long time. Finally, the present study shows that pathogenic bacteria are not always accompanied by indicators of faecal contamination (Escherichia coli, entero cocci); for this reason, they could potentially pose a risk to public health. 相似文献
206.
207.
This study investigates the performance of an optimum compacted bentonite/sand mixture seal for the isolation of underground waste repositories. Engineering geological tests such as compaction, flow, swelling, mechanical and shear strength tests have been conducted to select an optimum mixture and to recommend a stable bentonite/sand seal length-to-radius ratio (L/a) as far as the factor of safety (F) is concerned. The results of the compaction permeameter tests led to a recommendation to select an optimum compacted bentonite/sand mixture possessing a bentonite content of about 20% to satisfy the minimum regulatory hydraulic conductivity requirement. Engineering geological analysis of the seal/rock mechanical interaction with regard to reduce the possibility of seal slip led to a recommendation to utilize a seal L/a of at least 25. 相似文献
208.
Modern Diatom Assemblages in Surface Sediments from Estuarine Systemsin the Southeastern Buenos Aires Province, Argentina 总被引:1,自引:0,他引:1
Paleoecological reconstructions of Holocene sea-level changes in Argentinean coastal regions were based mainly on ecological
data gathered from other regions, as there was a lack of information on modern estuarine diatom distributions. The aim of
the present work was to assess the spatial variation of diatom assemblages in two representative estuaries of Argentina in
order to gather ecological information for paleoecological reconstructions in the region. The two selected estuaries have
different geomorphologic features and salinity regimes: Mar Chiquita Lagoon is shallow, which prevents the development of
a stable salinity gradient as it occurs in the Quequén Grande River. Surface sediment samples were taken from selected stations
representative of the environmental gradient from the inlet to the inner reaches of both estuaries. Cluster analysis defined
three diatom zones at Mar Chiquita: marine/brackish assemblages dominate the inlet (zone I), where salinity, tidal range and
current speed are higher. The brackish/freshwater tychoplankton Staurosira construens var. venter and Staurosirella pinnata dominate the inner lagoon (zone II), where environmental conditions are very variable and concentrations of suspended sediments
are higher. Brackish/freshwater euryhaline diatoms dominate the headwaters (zone III). On the other hand, the Quequén Grande
River was divided into three diatom zones: coastal taxa are distributed at the inlet (zone I), while the middle estuary (zone
II) is dominated by brackish/freshwater euryhaline taxa. At the upper estuary region (zone III), freshwater diatoms dominate,
and the halophobous Nitzschia denticula increased in abundance values. Diatom distributions were most closely related to the salinity gradient at Quequén Grande
River than at Mar Chiquita Lagoon. Fossil data of a sequence from Mar Chiquita Lagoon (Las Gallinas Creek) were compared to
the modern data set in order to search for analogies between fossil and modern diatom assemblages. DCA results showed that
fossil diatom assemblages have modern counterparts. Most diatom assemblages of Las Gallinas Creek fall within Mar Chiquita
zone III, representing a shallow brackish/freshwater environment, with low salinity fluctuations
(~1–9‰) and no tidal influence. Therefore, our modern diatom data provide useful analogs to interpret paleoenvironments in
the region. 相似文献
209.
The temporal change of driving factors during the course of land desertification in arid region of North China: the case of Minqin County 总被引:3,自引:0,他引:3
Yonghuan Ma Shengyue Fan Lihua Zhou Zhaoyang Dong Kecun Zhang Jianmin Feng 《Environmental Geology》2007,51(6):999-1008
Taking the key research area in the arid region of North China—Minqin County—as a case, this paper analyzes the main factors
impacting land desertification. Based on factor analysis method and the collection of data in the last 50 years, this paper
researches the spatial changes of driving factors during the course of land desertification in Minqin, Gansu Province. The
results of factor analysis indicate that the driving force of human factor on land desertification accounted for 56.33% in
1956–2004 and for 66.19% in 1981–2004, the driving force of nature factor on land desertification accounted for 11.29% in
1956–2004 and 8.11% in 1981–2004, and the synthesis of driving forces of human and natural factors accounted for 11.19% in
1956–2004 and for 14.88% in 1981–2004. This indicated that human driving force on land desertification was increasing in Minqin
County gradually. 相似文献
210.
在18℃的低温条件下,从不同菌源中富集、驯化、筛选得到两株高效苯酚降解菌株A4和B14,在转速为150r·min-1、温度为18℃、pH为6~9的条件下,两株菌对苯酚起始浓度为300mg/L的苯酚降解率分别为90.43%和99.02%.在中性条件下,对苯酚起始浓度小于300mg/L的苯酚降解率均保持在98%以上.经形态特征观察及生理生化实验初步鉴定,结果显示,A4为微球菌属,B14为假单胞菌属.对菌株的降解特性研究表明两株菌最适生长的pH值为6~9,A4菌株比B14菌株具有更广泛的pH适应性;菌株对苯酚的降解率随着生物投加量的增加而升高,在投菌量大于5mL·100 mL-1时,苯酚降解率接近100%;两株菌在通气状况良好的条件下,对苯酚的降解率及其生长情况明显优于缺氧条件.通过对比实验,A4菌株对外界环境的适应性明显强于B14,而后者的生长速率明显高于前者. 相似文献