全文获取类型
收费全文 | 42598篇 |
免费 | 4623篇 |
国内免费 | 26687篇 |
专业分类
安全科学 | 1919篇 |
废物处理 | 1689篇 |
环保管理 | 5253篇 |
综合类 | 33208篇 |
基础理论 | 11063篇 |
环境理论 | 9篇 |
污染及防治 | 14393篇 |
评价与监测 | 3809篇 |
社会与环境 | 2090篇 |
灾害及防治 | 475篇 |
出版年
2022年 | 309篇 |
2021年 | 343篇 |
2020年 | 811篇 |
2019年 | 2143篇 |
2018年 | 2528篇 |
2017年 | 2500篇 |
2016年 | 2557篇 |
2015年 | 2800篇 |
2014年 | 3742篇 |
2013年 | 5875篇 |
2012年 | 3969篇 |
2011年 | 3801篇 |
2010年 | 3394篇 |
2009年 | 3429篇 |
2008年 | 3288篇 |
2007年 | 3431篇 |
2006年 | 2710篇 |
2005年 | 2164篇 |
2004年 | 2066篇 |
2003年 | 1839篇 |
2002年 | 1665篇 |
2001年 | 2007篇 |
2000年 | 1663篇 |
1999年 | 1182篇 |
1998年 | 899篇 |
1997年 | 843篇 |
1996年 | 949篇 |
1995年 | 879篇 |
1994年 | 712篇 |
1993年 | 615篇 |
1992年 | 653篇 |
1991年 | 623篇 |
1990年 | 607篇 |
1989年 | 565篇 |
1988年 | 489篇 |
1987年 | 365篇 |
1986年 | 321篇 |
1985年 | 323篇 |
1984年 | 376篇 |
1983年 | 346篇 |
1982年 | 375篇 |
1981年 | 314篇 |
1980年 | 242篇 |
1979年 | 290篇 |
1978年 | 220篇 |
1977年 | 192篇 |
1976年 | 179篇 |
1975年 | 172篇 |
1973年 | 166篇 |
1972年 | 170篇 |
排序方式: 共有10000条查询结果,搜索用时 875 毫秒
591.
592.
生物硝化池污水中硝化细菌的快速定量研究 总被引:7,自引:0,他引:7
实验采用聚合酶链式反应(PCR)技术与最大几率数法(MPN)相结合的MPN-PCR法对生物硝化池污水中的硝化细菌进行快速定量。所用的一对PCR引物是在对硝化细菌的16SrRNA基因进行系统比较的基础上设计合成的,可以扩增出大小为388bp的DNA片段。以从生物硝化池污水中抽提的含硝化细菌DNA的混合DNA为模板,进行PCR扩增并确定合适的扩增条件。运用MPN-PCR法进行定量检测的整个过程可在几小时之内完成。 相似文献
593.
594.
595.
选择双氧水作氧化剂,将具有恶臭气味的涕灭威生产的副产物甲硫醚氧化成无臭的二甲基亚砜。通过实验,优化了工艺条件,减少了安全隐患,提高了二甲基亚砜的产率,消除了恶臭污染。 相似文献
596.
S. O. Oikeh R. J. Carsky J. G. Kling V. O. Chude W. J. Horst 《Agriculture, ecosystems & environment》2003,100(2-3):181
Nitrate is prone to leaching in the sandy soils of the West African moist savannas. Better management of nitrogen (N) resources and maize cultivars with enhanced genetic capacity to capture and utilize soil and fertilizer N are strategies that could improve N-use efficiency. In two field experiments conducted at Zaria, northern Nigeria, five maize (Zea mays L.) cultivars planted early in the season were assessed under various N levels for differences in N uptake, soil N dynamics, and related N losses. Cultivar TZB-SR accumulated more N in the aboveground plant parts in both years than the other cultivars. All, except the semi-prolific late (SPL) variety, met about 50–60% of their N demand by the time of silking (64–69 DAP). In both years, SPL had the greatest capacity to take up N during the grain filling period, and it had the highest grain-N concentration and the least apparent N loss through leaching in the second year. There were no significant differences in soil N dynamics among cultivars in both years. At harvest, the residual N in the upper 90 cm of the profile under all the cultivars ranged from 56 to 72 kg ha−1 in the first year and from 73 to 83 kg ha−1 in the second year. Apparent N loss from 0 to 90 cm soil profile through leaching ranged from 35 to 122 kg ha−1 in both years. N application significantly increased N uptake by more than 30% at all sampling dates in the second year of the experiment, but had no effect on apparent N loss. Results indicate that the use of maize cultivars with high N uptake capacity during the grain filling period when maximum leaching losses occur could enhance N recovery and may be effective in reducing leaching losses of mineral N in the moist savanna soils. 相似文献
597.
N. Sanginga K. E. Dashiell J. Diels B. Vanlauwe O. Lyasse R. J. Carsky S. Tarawali B. Asafo-Adjei A. Menkir S. Schulz B. B. Singh D. Chikoye D. Keatinge R. Ortiz 《Agriculture, ecosystems & environment》2003,100(2-3):305
Sustainable resource management is the critical agricultural research and development challenge in sub-Saharan Africa. The accumulated knowledge on soil management gathered over the last 10 years, combined with solid crop improvement and plant health research at farmers’ level, has brought us to a stage where we can now address with confidence the intensification of cereal–grain–legume-based cropping systems in the dry savanna of West Africa in a sustainable and environmentally positive manner.Two sustainable farming systems that greatly enhance the productivity and sustainability of integrated livestock systems have been developed and implemented in the dry savanna of Nigeria. These are: (i) maize (Zea mays L.)–promiscuous soybean [Glycine max (L.) Merr.] rotations that combine high nitrogen fixation and the ability to kill large numbers of Striga hermonthica seeds in the soil; and (ii) miflet [Eleusine coracana (L.) Gaerth] and dual-purpose cowpea [Vigna unguiculata (L.) Walp.]. Improvement of the cropping systems in the dry savanna has been driven by the adoption of promiscuously nodulating soybean varieties (in particular TGx 1448-2E) and dual-purpose cowpea. The rate of adoption is very high, even in the absence of an efficient seed distribution system. The number of farmers cultivating the improved varieties increased by 228% during the last 3 years. Increased production of promiscuous soybean has been stimulated by increased demand from industries and home utilization. Production in Nigeria was estimated at 405,000 t in 1999 compared to less than 60,000 t in 1984. Economic analysis of these systems shows already an increase of 50–70% in the gross incomes of adopting farmers compared to those still following the current practices, mainly continuous maize cultivation. Furthermore, increases in legume areas of 10% in Nigeria (about 30,000 ha in the northern Guinea savanna) and increases of 20% in yield have translated into additional fixed nitrogen valued annually at US$ 44 million. This reflects, at the same time, an equivalent increase in land-use productivity, and with further spread of the improved crops, there are excellent prospects for additional economic and environmental benefits from a very large recommendation domain across West Africa. 相似文献
598.
599.
上海市大气气溶胶中铂元素污染状况调查 总被引:3,自引:0,他引:3
为调查上海市大气气溶胶中铂元素的污染状况,用PM10-2型可吸入颗粒物采样器采集了上海市大气气溶胶样品,采样时间分别为2003-12~2005-12.用微波消解密闭系统消解样品,电感耦合等离子体质谱法(ICP-MS)测定了大气气溶胶中Pt的含量.分析结果表明,同清洁对照点((0.65±0.16)pg·m-3)相比,上海市中心区大气中Pt((1.69±0.93)pg·m-3)的污染是明显的;装有三元催化转化器的汽车尾气中Pt的含量均在100ng·g-1以上,远远高于大气气溶胶样品(人民广场平均值21.7ng·g-1);不同交通密度区Pt含量分析结果表明,Pt含量与交通密度紧密相关,这说明装有三元催化器的汽车尾气是气溶胶中Pt污染的主要来源;此外,上海市大气气溶胶中Pt呈现季节性变化,并受气象条件影响.同世界其它城市相比,上海市气溶胶中铂元素污染程度还较低,但是这种潜在的重金属污染应该引起重视. 相似文献
600.