首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   541篇
  免费   47篇
测绘学   14篇
大气科学   37篇
地球物理   198篇
地质学   211篇
海洋学   6篇
天文学   82篇
综合类   9篇
自然地理   31篇
  2024年   2篇
  2023年   2篇
  2022年   6篇
  2021年   10篇
  2020年   10篇
  2019年   11篇
  2018年   42篇
  2017年   38篇
  2016年   55篇
  2015年   48篇
  2014年   44篇
  2013年   42篇
  2012年   25篇
  2011年   22篇
  2010年   25篇
  2009年   23篇
  2008年   19篇
  2007年   22篇
  2006年   24篇
  2005年   8篇
  2004年   6篇
  2003年   7篇
  2002年   7篇
  2001年   7篇
  2000年   8篇
  1999年   3篇
  1998年   10篇
  1997年   3篇
  1996年   10篇
  1995年   4篇
  1994年   3篇
  1993年   4篇
  1991年   5篇
  1988年   2篇
  1987年   1篇
  1986年   2篇
  1985年   4篇
  1984年   2篇
  1983年   1篇
  1982年   2篇
  1981年   1篇
  1980年   1篇
  1979年   2篇
  1978年   1篇
  1976年   1篇
  1974年   1篇
  1973年   4篇
  1971年   2篇
  1970年   1篇
  1969年   2篇
排序方式: 共有588条查询结果,搜索用时 15 毫秒
81.
GPS Solutions - We present the methodology and results of GPS/GLONASS integration in network code differential positioning for regional coverage across Poland using single frequency. Previous...  相似文献   
82.
Geomorphological diversity is part of geodiversity. Study and evaluation of geodiversity, including geomorphological diversity, is often conducted in uplands and mountains, despite the fact that lowland areas are of equal importance. This paper evaluates geomorphological diversity in a small area of the Polish Lowland, using a variety of methods that have been applied in recent times for evaluating geodiversity, and presents the results on maps. By comparing these maps and analyzing the correlation coefficients of the results obtained, it was possible to identify the two methods that were best suited to indicating areas with the greatest geomorphological diversity in the lowlands. These two methods are least affected by the choice of elementary fields and data classification methods applied. The study identified the two areas with the greatest relief diversity and showed that they distinctly differ from one another. They demonstrate the major influence of processes, not only on the topographic parameters and landform types, but above all on identifying and defining total geomorphological diversity. These methods, which can be used to identify the areas with the greatest total geomorphological diversity, could readily be used in applied studies relating to abiotic ecosystem services and landscape management.  相似文献   
83.
Western Poland is located in the central European climatic transition zone, which separates the mild and humid Atlantic climate of Western Europe and the East European continental climate. This region is sensitive to lateral shifts of the European climate zones and is particularly suitable for reconstructing Holocene climate variability. This paper presents detailed analyses of the sedimentary record from Lake Strzeszyńskie since the Late Pleistocene. These include smear-slide and thin-section observations, X-ray fluorescence core scanning, magnetic susceptibility measurements, pollen analyses, and radiocarbon dating. The sediment record reveals three distinct sedimentary units consisting of: (1) an alternation of sand layers and laminated silt and clay deposits accumulated prior to 14,600 cal yr BP; (2) faintly laminated calcareous sediments intercalated with organic matter-rich layers deposited between 14,600 and 10,200 cal yr BP; and (3) massive calcareous mud deposited after 10,200 cal yr BP. The Holocene period is marked by nine phases of organic-rich sedimentation and enhanced Fe deposition, which occurred at ca. 10.1, 9.3, 6.4–6.1, 5.5–5.1, 4.7–4.5, 2.7–2.4, 1.3–1.2, 0.8–0.6, 0.4–0.2 kyr cal BP. These phases are associated with high lake levels and correspond with wet periods recognized in several other records from Poland and central Europe. These phases partly coincide with North Atlantic cold periods, which may suggest that high lake levels are triggered by an ocean-continent linking mechanism.  相似文献   
84.
Maize is grown by millions of smallholder farmers in South Asia (SA) under diverse environments. The crop is grown in different seasons in a year with varying exposure to weather extremes, including high temperatures at critical growth stages which are expected to increase with climate change. This study assesses the impact of current and future heat stress on maize and the benefit of heat-tolerant varieties in SA. Annual mean maximum temperatures may increase by 1.4–1.8 °C in 2030 and 2.1–2.6 °C in 2050, with large monthly, seasonal, and spatial variations across SA. The extent of heat stressed areas in SA could increase by up to 12 % in 2030 and 21 % in 2050 relative to the baseline. The impact of heat stress and the benefit from heat-tolerant varieties vary with the level of temperature increase and planting season. At a regional scale, climate change would reduce rainfed maize yield by an average of 3.3–6.4 % in 2030 and 5.2–12.2 % in 2050 and irrigated yield by 3–8 % in 2030 and 5–14 % in 2050 if current varieties were grown under the future climate. Under projected climate, heat-tolerant varieties could minimize yield loss (relative to current maize varieties) by up to 36 and 93 % in 2030 and 33 and 86 % in 2050 under rainfed and irrigated conditions, respectively. Heat-tolerant maize varieties, therefore, have the potential to shield maize farmers from severe yield loss due to heat stress and help them adapt to climate change impacts.  相似文献   
85.
Deforestation is expanding and accelerating into the remaining areas of undisturbed forest, and the quality of the remaining forests is declining today. Assessing the climatic impacts of deforestation can help to rectify this alarming situation. In this paper, how historical deforestation may affect global climate through interactive ocean and surface albedo is examined using an Earth system model of intermediate complexity (EMIC). Control and anomaly integrations are performed for 1000 years. In the anomaly case, cropland is significantly expanded since AD 1700. The response of climate in deforested areas is not uniform between the regions. In the background of a global cooling of 0.08 °C occurring with cooler surface air above 0.4 °C across 30° N to 75° N from March to September, the surface albedo increase has a global cooling effect in response to global-scale replacement of forests by cropland, especially over northern mid-high latitudes. The northern mid-latitude (30° N–60° N) suffers a prominent cooling in June, suggesting that this area is most sensitive to cropland expansion through surface albedo. Most regions show a consistent trend between the overall cooling in response to historical deforestation and its resulting cooling due to surface albedo anomaly. Furthermore, the effect of the interactive ocean on shaping the climate response to deforestation is greater than that of prescribed SSTs in most years with a maximum spread of 0.05 °C. This difference is more prominent after year 1800 than that before due to the more marked deforestation. These findings show the importance of the land cover change and the land surface albedo, stressing the necessity to analyze other biogeophysical processes of deforestation using interactive ocean.  相似文献   
86.
Municipal wastes collected in landfills are a significant source of air contamination and frequently characterize by elevated concentrations of different fungi. Posing a serious health threat to landfill workers and local residents, the fungal aerosol has to be monitored with respect to its quantity and quality. In this study, concentrations of airborne fungi, their particle size distribution, species composition and the presence of cytotoxic strains of Aspergillus fumigatus were assessed in different sites within the landfill area. The quantitative and qualitative changes in the fungal aerosol were determined with respect to a season and landfill activity level (i.e. exploitation or standstill periods). Within the landfill area, particular sites were grouped with regard to airborne fungi concentrations and similarities in species composition. The qualitative analysis indicated that 43 species were shared during both sampling times, and only nine species were characteristic for the standstill period. Among fungal isolates, 21 strains of A. fumigatus revealed cytotoxic activity expressed at different levels, depending on the fungal extract concentrations used in the MTT assay. The results suggested that exposure (especially in summer) to small airborne particles, containing distinct species, may occur not only in the active sector but also in close vicinity to the landfill. Hence, microbial monitoring of the landfill and surrounding area should be carried out taking into account both quantitative aspect supplemented by size distribution analysis and qualitative features, especially of those strains possessing cytotoxic activity.  相似文献   
87.
The aim of this study was to characterize both the viable airborne bacteria and fungi collected in different types of wastewater treatment plants in Poland. Bacterial and fungal aerosols in five different wastewater treatment plants in Poland were studied, including the pioneering antibiotic resistance testing of airborne bacteria. Concentration level was measured using the six-stage Andersen impactor. After incubation, bioaerosol particles captured on nutrient media on Petri dishes were quantitatively evaluated and qualitatively identified. It was found that the concentration levels of both airborne bacteria and fungi ranged from 10² to 10³ colony-forming units/m³, in all stages of the wastewater treatment plants. The patterns of size distributions of airborne bacteria and fungi were very similar, showing dominant peaks typically in the size range between 3.3 and 4.7 μm. The majority fraction of small bacterial and fungal particles (less than 4.7 μm) in the studied areas indicates that the bioaerosol is relatively fresh, and mostly of local origin. The Gram-positive cocci and nonsporing Gram-positive rods were the dominating forms in the studied wastewater treatment plants environment. The existing differences in the concentration levels between sampling sites enabled identification of the main bioaerosol sources. The highest concentration of bacterial aerosol appeared in sections, where activated sludge post-processing and mechanical purifying are conducted. The most frequently occurring species in the sampled bacterial aerosol were Gram-positive cocci and nonsporing Gram-positive rods. Multi-antibiotic resistance testing showed that among the isolated airborne bacteria, the most antibiotic-resistant features were present among Bacillus species (especially Bacillus mycoides).  相似文献   
88.
Detailed analyses were conducted of human impact on juniper forest landscapes occurring within the Zarafshan Range (Pamir-Alay). Juniperus seravschanica and J. semiglobosa belong to forest-forming species in Central Asia. At present, juniper forests all over Tajikistan are seriously threatened as a result of excessive logging and cattle grazing. The aim of this paper is to present juniper forest transformation as a result of human activities as well as the diversity of soil properties in the organic and humus horizons in the altitudinal system of soil zonation. Three groups of phytocoenoses were distinguished: those with a dominant share of Juniperus seravschanica; those with a dominant share of J. semiglobosa; and mixed. Associations with Juniperus seravschanica and J. semiglobosa feature several variants of phytocoenoses with dominant species: Artemisia lehmanniana, A. dracunculus, Eremurus olgae, Festuca sulcata, Ligularia thomsonii, Stipa turkestanica, Thymus seravschanicus, and Ziziphora pamiroalaica. The collected soil samples differ in their granulometric composition. Gravelly cobble fractions >2 mm are dominant; the share of sandy particles <2 mm is much lower (about 10–20%). Fraction 0.5–0.05 attains 35% on average. The Corg content of the soil varied from 0.26 to 11.40% in the humus horizon (A) and from 4.3 to 25% in the organic (O). Similar relationships were reported in the case of Ntot concentration. A clear relationship can be observed between concentrations of Corg and Ntot. Soil pH varied, ranging from very low acidic (pH 5.5) to neutral (pH 8.5). The content of available P varied; high concentrations were noted in organic (O) (40.46–211 mg kg?1) and mixed horizons (OA) (2.61–119 mg kg?1). Maximum accumulations of Pavail (1739.6 mg kg?1) and Ptot (9696 mg kg?1) were observed at a site heavily affected by intense grazing. Concentrations of Mgavail varied from 116 to 964 mg kg?1. Most of the analysed soil profiles lacked an organic horizon; only thin humus occurred.  相似文献   
89.
Changes in water chemistry along the High Arctic fluvial–lacustrine system located in Wedel Jarlsberg Land in the SW Spitsbergen (Svalbard) were investigated during the summer season of 2010 and 2011. The newly formed river–lake system consists of three lakes connected with the Brattegg River. The first bathymetric measurements of these lakes were made by the authors in 2010. The Brattegg River catchment represents a partly glaciered Arctic water system. The studied lakes are characterized by low mineralization and temperature of water. The value of the electrolytic conductivity (EC) ranges from 30.2 to 50.5 μS cm?1 and the temperature of surface water from 1.5 to 7.8 °C. The temperature increase takes place downstream starting from Upper Lake to the outflow from Myrktjørna Lake. The waters of lakes have higher temperatures than the stream. The predominant ions are HCO3 ? (up to 16.5 mg L?1), Cl? (6.66–8.53 mg L?1), Ca2+ (2.40–4.45 mg L?1) and Na+ (2.65–3.36 mg L?1). The highest values of ammonium and DOC found in the lowest Myrktjørna Lake seem to be related to the presence of aquatic organisms and also birds. From the group of 10 analyzed microelements, increased concentrations of aluminum, up to almost 500 μg L?1, are present in the lakes’ water. Water isotopic composition ranges for δ18O and δ2H, from ?10.6 to ?10.9‰ and from ?70.8 to ?72.3‰, respectively. The vertical zonality of lake waters is manifested in a decrease in the temperature and increase in EC and chemical elements concentrations.  相似文献   
90.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号