全文获取类型
收费全文 | 42340篇 |
免费 | 562篇 |
国内免费 | 606篇 |
专业分类
安全科学 | 1493篇 |
废物处理 | 1952篇 |
环保管理 | 5901篇 |
综合类 | 6731篇 |
基础理论 | 11052篇 |
环境理论 | 15篇 |
污染及防治 | 10624篇 |
评价与监测 | 2774篇 |
社会与环境 | 2672篇 |
灾害及防治 | 294篇 |
出版年
2022年 | 403篇 |
2021年 | 442篇 |
2020年 | 340篇 |
2019年 | 351篇 |
2018年 | 638篇 |
2017年 | 659篇 |
2016年 | 1016篇 |
2015年 | 772篇 |
2014年 | 1157篇 |
2013年 | 3489篇 |
2012年 | 1460篇 |
2011年 | 1985篇 |
2010年 | 1593篇 |
2009年 | 1688篇 |
2008年 | 1982篇 |
2007年 | 1944篇 |
2006年 | 1731篇 |
2005年 | 1498篇 |
2004年 | 1463篇 |
2003年 | 1372篇 |
2002年 | 1284篇 |
2001年 | 1524篇 |
2000年 | 1137篇 |
1999年 | 721篇 |
1998年 | 516篇 |
1997年 | 545篇 |
1996年 | 552篇 |
1995年 | 661篇 |
1994年 | 554篇 |
1993年 | 495篇 |
1992年 | 502篇 |
1991年 | 489篇 |
1990年 | 466篇 |
1989年 | 456篇 |
1988年 | 402篇 |
1987年 | 343篇 |
1986年 | 363篇 |
1985年 | 352篇 |
1984年 | 413篇 |
1983年 | 359篇 |
1982年 | 402篇 |
1981年 | 345篇 |
1980年 | 273篇 |
1979年 | 307篇 |
1978年 | 237篇 |
1977年 | 210篇 |
1975年 | 211篇 |
1974年 | 208篇 |
1973年 | 234篇 |
1972年 | 214篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Role of Light Availability and Dispersal in Exotic Plant Invasion along Roads and Streams in the H. J. Andrews Experimental Forest, Oregon 总被引:25,自引:0,他引:25
Abstract: We examined the roles of dispersal mechanism, a biological barrier; light availability, an environmental barrier; and level of disturbance, a physical barrier, in explaining the spatial patterns of exotic plant species along road and stream segments in a forest landscape in the western Cascade Range of Oregon (U.S.A). The presence or absence of 21 selected exotic plant species and light levels were observed along 0.3- to 1.0-km transects within four habitat types. Each habitat represented a different level of disturbance: high-use roads, low-use roads, abandoned roads, and streams in the H. J. Andrews Experimental Forest. Nearly 300 50 × 2–m sampling units were surveyed along five transects in each habitat type. We used ordination (nonmetric multidimensional scaling) and logistic regression to analyze data. All of the nearly 200 sampling units along roads with high and low levels of vehicle traffic contained at least one exotic plant species, and some contained as many as 14. Streams that were most recently disturbed by floods 20–30 years ago and abandoned spur roads with no traffic for 20–40 years also had numerous exotic species. Roads and streams apparently serve multiple functions that enhance exotic species invasion in this landscape: they act as corridors or agents for dispersal, provide suitable habitat, and contain reservoirs of propagules for future episodes of invasion. Species-specific dispersal mechanisms, habitat characteristics, and disturbance history each explain some, but not all, of the patterns of exotic species invasion observed in this study. 相似文献
993.
B. Miller # R. Reading J. Hoogland † T. Clark ‡ G. Ceballos § R. List S. Forrest †† L. Hanebury ‡‡ P. Manzano § J. Pacheco § and D. Uresk§§ 《Conservation biology》2000,14(1):318-321
994.
995.
996.
997.
M. Tufail Sikander M. Mirza Arif Mahmood A. A. Qureshi Yasir Arfat H. A. Khan 《Journal of environmental radioactivity》2000,50(3):283
Using the closed-can technique, radon exhalation rate measurements have been carried out for shale and coal samples collected from various mines located in the Chakwal and Makarwal areas of Pakistan. For the two areas, the measured average values of the exhalation rates from shale are 1.45±0.13 and 0.67±0.25 Bq m−2 h−1 and for coal are 1.0±0.03 and 0.65±0.32 Bq m−2 h−1, respectively. These values are much lower than the measured exhalation rates from alum-shale-based Nordic concrete which has values in the 50–200 Bq m−2 h−1 range. The lower values of the measured exhalation rates from the shale and coal deposits in the Chakwal and Makarwal areas are indicative of their lower uranium contents and mine workers in these areas do not face any abnormal health hazard due to radon since the exhalation rates have been found to be on the low side. 相似文献
998.
Climatic characteristics of the northern Moscow region and the periodicity of seedage in Norway spruce were analyzed retrospectively.
The relationship between the intensity of seedage and weather conditions in the period before seedage was revealed. 相似文献
999.
The interactions of zebra mussels, invertebrates, fish, and microorganisms were studied experimentally. Trends in the distribution
of total bacterial biomass, the abundance of heterotrophic organisms, and their functional activities in water and grounds
were analyzed. The most favorable conditions for development of bacteria developed in June, in the presence of fish and without
zebra mussels. In experimental ecosystems with zebra mussels, a decrease in the abundance and activity of microorganisms and
a change of dominant yeast forms were observed. 相似文献
1000.
The index of cenotic significance and other indices calculated on its basis were used for revealing specific structural features of zooplanktonic communities in lakes differing in productivity. The results showed that new indices (complexity coefficient, index of cenotic significance of dominant species, and integrated cenotic significance of the zooplankton) strongly correlate with the trophic status of the water body and are more responsive to changes in the structure of the community than the Shannon–Weaver index of species diversity. The results confirm the hypothesis that the structure of zooplankton is simplified in the course of lake eutrophication. 相似文献