首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   102811篇
  免费   1736篇
  国内免费   6438篇
安全科学   4534篇
废物处理   4159篇
环保管理   14756篇
综合类   29022篇
基础理论   28360篇
环境理论   74篇
污染及防治   19190篇
评价与监测   5835篇
社会与环境   3936篇
灾害及防治   1119篇
  2023年   635篇
  2022年   1416篇
  2021年   1315篇
  2020年   1029篇
  2019年   1258篇
  2018年   1565篇
  2017年   1769篇
  2016年   2781篇
  2015年   2634篇
  2014年   3691篇
  2013年   10736篇
  2012年   3312篇
  2011年   3563篇
  2010年   4142篇
  2009年   4273篇
  2008年   2815篇
  2007年   2562篇
  2006年   2943篇
  2005年   2742篇
  2004年   2885篇
  2003年   2819篇
  2002年   2323篇
  2001年   2581篇
  2000年   2381篇
  1999年   1963篇
  1998年   1771篇
  1997年   1683篇
  1996年   1786篇
  1995年   1836篇
  1994年   1706篇
  1993年   1495篇
  1992年   1452篇
  1991年   1367篇
  1990年   1303篇
  1989年   1235篇
  1988年   1077篇
  1987年   999篇
  1986年   1013篇
  1985年   1072篇
  1984年   1165篇
  1983年   1179篇
  1982年   1183篇
  1981年   1105篇
  1980年   938篇
  1979年   922篇
  1978年   817篇
  1977年   711篇
  1976年   636篇
  1973年   634篇
  1972年   638篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
A statistical analysis of interannual variation in a set of vegetative and generative characters over 13 years has been performed to characterize the growth and seed production dynamics of the Siberian stone pine (Pinus sibirica Du Tour) in the southeast of the forest zone in western Siberia. The results have shown that the range of fluctuations in most of vegetative characters is ordinary and their distribution is close to normal. The range of fluctuations in many generative characters is enormous (from 0 to +∞), and the distribution of their values is usually skewed, with low values being recorded several times more frequently than high values. Most variable are the proportion of abortive cones and other characters that are determined mainly in the spring of the pollination year. These characters account for a very high level of variation in the total seed production.  相似文献   
82.
83.
Phylogenetic relationships and genetic population structures were analyzed for tideland gastropods in the genus Cerithidea around Japan on the basis of partial sequence of the mitochondrial COI gene. Large genetic divergence was shown between individuals of Cerithidea cingulata in the southern Ryukyus and those in the central Ryukyus and the Japanese Islands. Haplotypes of C. cingulata from the Japanese Islands were paraphyletic with the exclusion of a monophyletic group from the central Ryukyus. Genetic differentiation of C. cingulata was also detected between Amami-Oshima Island and Okinawajima Island. No genetic divergence was found between Cerithidea rhizophorarum in the Japanese Islands and its subspecies C. rhizophorarum morchii in the Ryukyu Islands. The lack of genetic divergence of Cerithidea largillierti between continental China and Japan suggests relatively recent migration between the Japanese Islands and the Asian continent. For all three Cerithidea species distributed in both the Japanese Islands and the Ryukyu Islands, the Tokara Gap and the Kerama Gap were shown to have acted as barriers to the dispersal.  相似文献   
84.
At present, internal rural tourism is at the stage of upgrading and renewing, and ecotourism has been considered to be the main direction. This paper discussed the concepts and criteria of rural tourism and ecotourism, analyzed a typical case of Nongke Village of Chengdu City-being considered to be the first rural tourism site in China, went deep into the problems of the contents and criteria of the development of rural ecotourism, and tried to probe into the principles of the development of rural ecotourism both theoretically and practically so as to understand the rules of the development of rural ecotourism .  相似文献   
85.
86.
Codigestion of five wastes and municipal wastewater sludge was evaluated using full-scale testing. Synergistic, antagonistic, and neutral outcomes were observed depending on codigestate identity and concentration, highlighting the value of careful blending. Yeast waste resulted in notable synergism, increasing biogas production by over 50%, whereas aircraft deicing waste resulted in antagonism at high loadings and neutral outcomes at lower loadings. Restaurant waste codigestion resulted in neutral outcomes. The synergisim with yeast codigestates may have resulted from trace nutrients (i.e., iron, nickel, and cobalt) in the wastes that increased microbiological activity. Antagonist outcomes with deicing waste may have been the result of organic overload or inhibitory deicer constituents. Codigestion of wastes at the feed rates investigated was estimated to produce 0.50 ML/d of methane having an energy equivalent of 17 500 MJ/d. This was estimated to reduce net carbon dioxide emissions by 560 tonnes/y.  相似文献   
87.
88.
89.
90.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号