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201.
为研究不同群体柔鱼 (
202.
自适应模糊控制在配料过程中的研究与应用 总被引:1,自引:1,他引:0
针对工业配料过程中配料精度和速度相矛盾的难题,文中提出了一种专家系统、模糊控制结合自适应控制的新型控制方法。该方法将模糊控制宽范围快速调节和自适应精确调节的特点有机结合起来,当系统偏差大于某一设定值时,采用专家经验和模糊规则控制相结合的控制方法;当系统偏差小于设定值时采用自适应控制。实际应用表明,该方法比一般的模糊控制在系统精度和速度上均有所提高。 相似文献
203.
204.
柑橘黄龙病是严重危害我国柑橘产业的细菌性病害,而柑橘木虱(Diaphorina citri)是柑橘黄龙病的唯一自然传播媒介。本研究利用NetLogo智能体建模平台构建了柑橘木虱空间扩散智能体模型,以广西壮族自治区蒙山县为研究区域,对柑橘木虱空间扩散规律及田管效果进行了模拟与评价。结果表明,柑橘木虱迁飞距离和农药喷施间隔时间对其扩散速度与空间具有显著影响。果园若无管理措施或管理较差的情景下,柑橘木虱扩散风险区总面积占比一直保持着快速上升的趋势,而柑桔木虱的迁飞距离可显著增加其风险区增长的数量级。当农药喷施间隔为1个月内,柑橘木虱的扩散风险可以很快得到遏制。本研究建议柑橘种植区应规范使用高效农药防治好柑橘木虱,并合理优化柑橘果园空间布局,如棋盘式种植,各区域间设置防风林或防虫肉等物理阻隔,可有效遏制柑橘木虱扩散速度和扩散空间,有利于柑橘黄龙病的区域防控。 相似文献
205.
Astrid?P.?Vasquez James?L.?Regens James?T.?GunterEmail author 《Journal of Soils and Sediments》2004,4(3):151-156
Background and Goal A number of global events have generated intense scientific scrutiny and public concern of polychlorinated dibenzo-p-dioxins (dioxin). DIoxins have been associated with a range of adverse health effects. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is recognized as among the most dangerous of the dioxin compounds, and was a contaminant found In one of the
herbicides used for vegetation control during the Vietnam conflict: Agent Orange. As a result of purging spray systems and
leaking drums of Agent Orange concentrate, TCDD contamination occurred in the soils surrounding Hardstand 7 at Eglin Air Force
Base, Florida. This research uses a multimedia model to estimate the TCDD concentrations in surface soil around Hardstand
7 for a 70-year time Interval beginning with observed surface soil concentrations 1984.
Methods Hardstand 7 is a nearly 40-m circular concrete and asphalt aircraft parking area. The hardstand was used as a staging area
for spraying equipment used to disseminate herbicide In a test area called C-52A within EAFB. Concentrated herbicide was also
stored in 208-L barrels for use with the equipment, and later, for disposal. In 1984, a field investigation characterized
the extent of TCDD contamination in surface soils around Hardstand 7 using a radial sampling protocol. The 1984 observed concentrations
and locations was used in a multimedia model, CalTOX, as an initial source term concentrations and locations to estimate expected
concentrations during the subsequent 70-years.
Results The results indicate that more than 94% of the TCDD observed in surface soils 1984 will remain after a 70-year period. Access
restrictions and remediation activities at the site eliminate bar verification of the CalTOX estimates. Conclusions. TCDD
is highly persistent in the soil medium and natural attenuation may not produce a significant decrease In soil concentrations.
Recommendation Active remediation actions may be required to prevent exposure to TCDD contamination surface soils. Verifying CalTOX concentration
estimates an Important step that should be performed, however, the, model provides an easy to use tool to estimate TCDD surface
soil contamination at herbicide storage or dispersion staging sites. 相似文献
206.
Torbjörn Nilsson 《Biological conservation》2004,115(2):227-239
Focusing on the wolf Canis lupus in Scandinavia as an example, criteria are proposed and an analysis performed to assess the effect on extinction risk of various control policies, while accounting simultaneously for effects of inbreeding depression and potential catastrophic events. Each control policy is characterized by a hunting pressure (the increase caused by hunting of annual mortality rates) combined with a hunting threshold (the population size below which hunting is not permitted). Catastrophes are taken into account by including the persistence of a severe catastrophe in the criterion for population viability. Based on these criteria, the results suggest that only a very limited amount of hunting should be permitted at low population sizes. The results also illustrate the importance of including a long-term perspective in modelling threatened populations. 相似文献
207.
Carbon assimilation and allocation were studied in a tundra ecosystem in northern Scandinavia. Seasonal variation in the below-ground carbon allocation to dissolved organic carbon (DOC), coarse-, fine-, and hair roots was investigated using in situ 14C pulse-labelling, adding 2-3 MBq 14CO2 dm−2 to the above-ground vegetation. Combining the allocation data with regression models of the seasonal carbon flux made it possible to estimate a temporally explicit ecosystem carbon allocation budget.The ecosystem was a net source of CO2, losing on average 0.97 g C m−2 d−1 to the atmosphere, with little variation through the season. There was, however, significant temporal variation in partitioning of recently assimilated carbon. Allocation to below-ground compartments over 32 days following labelling increased from 18% in June to 55% in September. Above-ground allocation showed the opposite trend. Hair roots and DOC were strong sinks in the autumn. Transport of newly assimilated carbon occurred rapidly throughout the season, 14C appearing in all sampled pools within 4 h of labelling.The seasonal variation in carbon partitioning observed in this study has implications for the residence time of assimilated carbon in the ecosystem. A relatively greater allocation to rapidly decomposing pools, such as hair roots and DOC, would tend to reduce incorporation into woody tissue, increasing the overall rate of carbon cycling and decreasing ecosystem storage. The results of this study will be of value for building and validating mechanistic models of ecosystem carbon flow in tundra and subarctic ecosystems. 相似文献
208.
滇西泥石流综合防治工程调查 总被引:1,自引:0,他引:1
调查了滇西泥石流综合防治工程的现状,指出了滇西泥石流综合防治工程中存在的主要问题.在此基础上,具针对性地提出今后滇西泥石流综合防治工程应引起足够重视和有待加强的工作环节. 相似文献
209.
Organic amendment is a proved method of improving soil physical properties thus affecting runoff and soil erosion. Urban wastes are a potential source of organic matter and their use would also be a convenient way of disposing of them. A field experiment was conducted from October 1988 to September 1993 in a semiarid Mediterranean site to determine the effect of applying several rates (65, 130, 195 and 260 Mg ha−1) of organic urban solid refuse (USR) on total runoff and soil loss. At the lowest rate, total runoff decreased by 67 per cent compared to the control plot. The decrease was 98 per cent when the highest rate was used. The lowest rate reduced total sediment loss by 81 per cent and the highest rate of 99 per cent. The decrease in soil erodibility at the different USR rates varied from 76 to 95 per cent depending on the year for the lowest rate and between 90 and 99 per cent for the other rates. Clear differences in the hydrologic and erosion responses were found between the eight initial rainfall events (during the first 10 months of the experiment) and the remainder of the events. The causes of such differences were due to the initial tillage of the soil by rotovation and the growth of natural vegetation in the treated plots. The mechanical effect of tillage reduced runoff and increased soil erodibility, although the effect was short‐lived. The addition of USR reduced runoff but lasted longer. An applied rate of 90–100 Mg ha−1 could be considered suitable for application in semiarid zones. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
210.
北京市大兴永定河沙地综合治理效益评价 总被引:6,自引:3,他引:6
建立了一套能完整反映北京市大兴永定河沙地治理中经济发展,社会进步和生态环境改善的效益评价指标体系。采用多层次模糊综合评价方法进行评价,采用层次分析法确定评价因子的权重,实现了效益评价的客观合理性。 相似文献