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51.
52.
中缅油气管道国内段沿线存在不连续的长距离砂土液化地带,砂土液化是地下管道遭受地震破坏的主要原因之一.为增强管道抵抗土壤液化的能力,通过对砂土液化现象及其危害进行分析,结合油气管道沿线砂土液化特点,对管道敷设深度内有中等、严重砂土液化趋势的地段采取平衡压袋稳管方式进行液化处理.该处理措施具有经济、环保、便于施工、不影响管道主体工程安装和总体工期等特点,而且对于避免和减轻地震灾害,确保油气管道的安全运行具有重要意义,在类似管道工程建设中值得推广应用.(表2,图3,参4) 相似文献
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Enhancement of photosynthesis and growth of tomato seedlings by forced ventilation within the canopy 总被引:1,自引:0,他引:1
A forced ventilation system that directs airflow upward or downward within a canopy was developed for plant culture in order to enhance photosynthesis and growth of the plant canopy. Tomato seedling canopies including the seedlings, growing medium, and a plastic tray were used for the experiments. In the upward and downward ventilation systems, air flows upward and downward, respectively, within the plant canopy; this is achieved by blowing and drawing air from holes (Ø 6 mm) made in plastic pipes positioned on the surface of the growing medium. A horizontal airflow system was used as a conventional system to compare the performance of the experimental ventilation systems. Using the upward and downward ventilation systems, the effects of air directions and air velocities on the CO2 exchange rate of the tomato seedling canopy and the growth of the seedlings were compared with those observed using the conventional horizontal airflow system. The forced ventilation within the plant canopy enhanced the CO2 exchange rate of the canopy and the dry masses of the seedlings by 1.4–1.5 and 1.2–1.3 times, respectively, as compared to the conventional horizontal airflow. When the leaf area index (LAI) increased from 1.2 to 2.4, there was only a 5% decrease in the CO2 exchange rate per unit leaf area in the downward ventilation system, whereas there was a 20% decrease in the CO2 exchange rate per leaf area in the horizontal airflow system. The coefficient of variation for the dry mass of the seedlings was higher in the downward system than in the other systems. These results demonstrate that forced ventilation within the canopy is an effective technique to enhance the gas exchange of the plant canopy and the consequent plant growth. 相似文献
55.
Nickolee Zollinger Roger Kjelgren Teresa Cerny-Koenig Kelly Kopp Rich Koenig 《Scientia Horticulturae》2006
Although low water use landscaping is becoming common in arid regions, little is known about drought tolerance and drought responses of many ornamental plants, especially herbaceous perennials. Drought responses were assessed for six herbaceous ornamental landscape perennials in a 38 l pot-in-pot system in northern Utah over a 2-year period. The first year was an establishment period. During the second year, drought responses were evaluated for established Echinacea purpurea (L.) Moench, Gaillardia aristata Pursh, Lavandula angustifolia P. Mill., Leucanthemum × superbum (J.W. Ingram) Berg. ex Kent, ‘Alaska’, Penstemon barbatus Roth var. praecox nanus rondo, and Penstemon × mexicali Mitch. ‘Red Rocks’. Plants were irrigated at frequencies of 1 (control), 2, or 4 weeks between June and September, simulating well-watered conditions, moderate drought, or severe drought. Osmotic potential (Ψs), gas exchange, visual quality, leaf area, and dry weight were assessed. In a confined root zone, P. barbatus showed the greatest tolerance to all levels of drought, avoiding desiccation by increasing root:shoot ratio and decreasing stomatal conductance as water became limiting. L. angustifolia and P. × mexicali showed tolerance to moderate drought conditions, but died after exposure to the first episode of severe drought. Neither G. aristata nor L. superbum were able to regulate shoot water loss effectively. Instead, both species displayed drought avoidance mechanisms, dying back when water was limiting and showing new growth after they were watered. Compared to control plants, G. aristata shoot dry weight was reduced by 50% and 84%, and L. superbum shoot dry weight was reduced by 47% and 99% for the 2- and 4-week irrigation intervals, respectively. Root dry weights were affected similarly for both species. E. purpurea exhibited poor visual quality at all irrigation intervals, in particular wilting severely in both drought treatments, but regaining turgor when watered again. P. barbatus is recommended for ornamental landscapes that receive little or no supplemental irrigation, while E. purpurea is not recommended for low water landscapes because of low visual quality under even mild drought. 相似文献
56.
Fabrício de Oliveira Reis Eliemar Campostrini Elias Fernandes de Sousa Marcelo Gabetto e Silva 《Scientia Horticulturae》2006
In papaya plants a study to quantify the water flow through the trunk is important for to promote a good water management in commercial orchard. The objective was to study the relationship between water flow through the trunk and temperature measurements determined by probes inserted in the papaya plant stem in laboratory. In addition, was possible to study the relationship between sap flow and instantaneous gas exchange in field conditions. We constructed an instrument that maintained a stable water flux through a 0.30 m stem section with a constant pressure, simulating the xylem sap flow through the stem. Water flux was adjusted by varying pressure of water in the stem section. The mathematical model used to fit the relation between K (Granier heat coefficient) values and sap flow density was the exponential model: u = 0.5511 × K1.9104. Field studies was conducted in a commercial orchard located in North of the State of Rio de Janeiro, with 12 plants in October 2002, and eight plants in January 2003. We verified that instantaneous transpiration, measured by a portable system of gas exchange (porometry), presented a good (R2 = 0.75) positive relationship with xylem sap flow. Estimates of papaya sap flow can be obtained by scaling portable photosynthesis system measurements with exposed leaves, however the relationship is non-linear in higher instantaneous transpiration rates. The causes of the non-linear relationship in higher transpiration are discussed. In addition, was possible to obtain a good (R2 = 0.76) relationship between net photosynthesis rate and xylem sap flow in papaya field-grown. 相似文献
57.
The factors responsible for widespread declines of grassland birds in the United States are not well understood. This study,
conducted in the short-grass prairie of eastern Wyoming, was designed to investigate the relationship between variation in
habitat amount, landscape heterogeneity, prey resources, and spatial variation in grassland bird species richness. We estimated
bird richness over a 5-year period (1994–1998) from 29 Breeding Bird Survey locations. Estimated bird richness was modeled
as a function of landscape structure surrounding survey routes using satellite-based imagery (1996) and grasshopper density
and richness, a potentially important prey of grassland birds. Model specification progressed from simple to complex explanations
for spatial variation in bird richness. An information-theoretic approach was used to rank and select candidate models. Our
best model included measurements of habitat amount, habitat arrangement, landscape matrix, and prey diversity. Grassland bird
richness was positively associated with grassland habitat; was negatively associated with habitat dispersion; positively associated
with edge habitats; negatively associated with landscape matrix attributes that may restrict movement of grassland bird; and
positively related to grasshopper richness. Collectively, 62% of the spatial variation in grassland bird richness was accounted
for by the model (adj-R2 = 0.514). These results suggest that the distribution of grassland bird species is influenced by a complex mixture of factors
that include habitat area affects, landscape pattern and composition, and the availability of prey. 相似文献
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通过对年产3万m~3中密度纤维板生产线铺装成型工段气力输送系统的设计,以及在设计中注意管网平衡计算、合理选择系统的技术参数及输送装置,实现干纤维的回收及输送,保证中密度纤维板生产线的正常生产. 相似文献
60.
煤焦油瓷漆作为良好的管道防腐材料已得到了广泛的使用。在施工作业中,采用人工浇涂的方法,不仅作业时间长,污染环境,而且涂敷质量难以保证,还造成了大量人力,物力,财力的浪费;采用机械化自动涂敷则具有明显的优势。 相似文献