全文获取类型
收费全文 | 10016篇 |
免费 | 452篇 |
国内免费 | 791篇 |
专业分类
林业 | 553篇 |
农学 | 634篇 |
基础科学 | 442篇 |
2861篇 | |
综合类 | 5391篇 |
农作物 | 167篇 |
水产渔业 | 444篇 |
畜牧兽医 | 349篇 |
园艺 | 160篇 |
植物保护 | 258篇 |
出版年
2024年 | 90篇 |
2023年 | 224篇 |
2022年 | 323篇 |
2021年 | 356篇 |
2020年 | 325篇 |
2019年 | 441篇 |
2018年 | 315篇 |
2017年 | 495篇 |
2016年 | 592篇 |
2015年 | 461篇 |
2014年 | 565篇 |
2013年 | 678篇 |
2012年 | 908篇 |
2011年 | 783篇 |
2010年 | 686篇 |
2009年 | 651篇 |
2008年 | 520篇 |
2007年 | 614篇 |
2006年 | 502篇 |
2005年 | 387篇 |
2004年 | 278篇 |
2003年 | 191篇 |
2002年 | 160篇 |
2001年 | 134篇 |
2000年 | 98篇 |
1999年 | 87篇 |
1998年 | 53篇 |
1997年 | 63篇 |
1996年 | 48篇 |
1995年 | 60篇 |
1994年 | 39篇 |
1993年 | 32篇 |
1992年 | 20篇 |
1991年 | 19篇 |
1990年 | 12篇 |
1989年 | 16篇 |
1988年 | 12篇 |
1987年 | 11篇 |
1986年 | 6篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1962年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
新疆博斯腾湖水环境问题研究 总被引:3,自引:1,他引:3
博斯腾湖是塔里木河流域4大源流--开都河的尾闾湖,孔雀河的源地.位于焉耆盆地东南,是我国最大的一个十分特殊,而又非常重要的内陆淡水湖泊.湖水清澈、水温适中(18.2~19.7 ℃),水生生物资源丰富.湖区西岸大片沼泽湿地是我国优质芦苇生产基地.博斯腾湖不仅对焉耆盆地和孔雀河流域环境具有调节作用,更为重要的是对当地的经济社会环境的可持续发展、对区域环境友好建设具有直接的影响.基于物质和能量的守恒理论,消耗品必须有出处,废弃物必须有去处.河流和气流在给博斯腾湖带来各种径流的同时,也带来了自然和人类活动产生的废弃物,导致湖泊生态功能受损.为适应变化着的湖泊环境,人类曾采取了一些限制自我行为的措施,收到了一定的成效.通过分析博斯腾湖水污染现状、机理,提出进一步适应和改善博斯腾湖水环境的措施. 相似文献
52.
利用东方黄梅和犬地卷微核千分率研究环境污染 总被引:1,自引:0,他引:1
本文通过地衣植物藻类细胞微核检测技术测定了分布于天山菊花台和后峡地区地衣藻类细胞微核千分率(MCN‰)及环境污染指数,并进行了t检查。结果表明(MCN‰)有明显差异。从两个分布区2种地衣细胞观察分析来看,后峡地区地衣藻类细胞的污染指数都在3.5以上,通过t检查也可以看到,差异极度显著所获得的数据表明,后峡区受到严重的污染。 相似文献
53.
Pollution of arable land caused by heavy metals in livestock and poultry manure has become a potential threaten to human health in China. Safe disposal of the contained toxic pollution with animal manure by co-composting with biochar is one of the alternative methods. Biochars from different sources (wheat straw, peanut shells and rice husks) amended with different loading rates were investigated for passivations of copper and zinc (Cu and Zn) in swine manure composting. Results showed that the passivation effects of the three types of biochar on Cu and Zn were enhanced with increasing biochar dose. Contents of Cu and Zn measured by diethylenetriaminepentaacetic acid (DTPA) and Community Bureau of Reference (CBR) showed that wheat straw biochar with the loading rates of 10%-13% (w/w) was superior to the other two types of biochar in this study. Compared with the control, sample from wheat straw biochar was more favorable for the bacterial growth of Proteobacteria, Firmicutes and Actinobacteria. In addition, pot experiment showed that organic fertilizer amended with wheat straw biochar could significantly improve the growth of Chinese pakchoi and enzyme activities (superoxide dismutase, peroxidase, polyphenol oxidase and catalase) as compared with the control. Cu and Zn contents of Chinese pakchoi in the organic fertilizer group containing wheat straw biochar reduced by 73.2% and 45.2%, 65.8% and 33.6%, respectively, compared with the group without loading biochar. There was no significant difference in the contents of vitamin C and reducing sugar between the groups of organic fertilizer amended with/without wheat straw biochar, however, there was significant difference compared with the heavy metal addition group. The application of organic fertilizer formed by adding biochar can effectively reduce the adverse effects of heavy metals on crops. 相似文献
54.
本文以陕西某一火力发电厂为例,通过高斯公式对SO_2扩散着地最大浓度和最大浓度距离的计算及探讨,为工业卫生防护林带绿化位置设计和环境保护提供一定的理论依据。 相似文献
55.
水体重金属污染研究现状及治理技术 总被引:19,自引:0,他引:19
介绍了水体重金属污染物的研究现状,着重阐述了目前国内外治理水体重金属污染的主要技术,并就其原理、实例、优缺点和应用等问题做了简要论述。 相似文献
56.
57.
植物修复与超富集植物 总被引:6,自引:0,他引:6
本文回顾了我国尤其是珠三角地区重金属污染现状,总结了植物修复、超富集植物及当前研究热点问题。 相似文献
58.
Temporal Changes in the State of a Pine Stand in a Bog Affected by Air Pollution in Northeast Estonia 总被引:1,自引:0,他引:1
We used the needle trace method to investigate changes in the state of a Scots pine (Pinus sylvestris L.) stand in a bog (Voorepera) in the north-eastern part of Estonia, the most polluted area of the country. Additionally, we chose six sampling sites in other parts of Northeast Estonia (polluted area) and eight sites in southern Estonia (unpolluted area) to compare the state of pine stands in different bogs. During the period of 1964–1997, the radial growth had increased from 0.27 to 2.16 mm yr–1 and the annual shoot length from 0.10 to 0.28 m in Voorepera. Mean values of the period (1.13 mm yr–1 and 0.26 m, respectively) were two and four times higher in Voorepera than the average of the other bogs (0.5 mm yr–1 and 0.06 m, respectively). Maximum needle age fluctuated between three and five growing seasons in Voorepera, the mean (four growing seasons) was similar to that of other bogs (four growing seasons). Except radial growth, which was 0.6 mm yr–1 in the polluted area and 0.4 mm yr–1 in the unpolluted area, other indices of trees' health (shoot growth, needle age, nitrogen concentration in needles) and substrate conditions (water pH and N concentration) did not show clear differences between polluted and unpolluted areas. We conclude that air pollution from oil shale industry (thermal power plant and chemical factories) enhances the growth of pines in bogs, which can induce drastic changes in these ecosystems. However, the effect is currently obvious only in the vicinity of pollution sources. 相似文献
59.
The Schelde estuary is heavily polluted with many different (micro)pollutants. This results in high concentrations in the abiotic and biotic compartments of the Schelde estuary and in various effects. the present day suboxic and anoxic conditions in the upper estuary are probably responsible for the high distribution coefficients for some trace metals in the lower Schelde estuary (Western Schelde). a future reduction in discharges with a high biological oxygen demand will therefore not only result in higher oxygen concentrations, but probably also in lower distribution coefficients for trace metals in the Western Schelde. Simulations show that lower trace metal distribution coefficients will probably result in higher concentrations of dissolved (bioavailable) trace metals, even with substantially reduced discharge rates, due to the desorption of trace metals from resuspended bottom sediments. 相似文献
60.