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   2729篇
  免费   239篇
  国内免费   1308篇
  2024年   44篇
  2023年   110篇
  2022年   137篇
  2021年   160篇
  2020年   181篇
  2019年   176篇
  2018年   139篇
  2017年   178篇
  2016年   179篇
  2015年   157篇
  2014年   130篇
  2013年   204篇
  2012年   168篇
  2011年   179篇
  2010年   140篇
  2009年   209篇
  2008年   214篇
  2007年   218篇
  2006年   198篇
  2005年   144篇
  2004年   115篇
  2003年   97篇
  2002年   92篇
  2001年   82篇
  2000年   59篇
  1999年   61篇
  1998年   37篇
  1997年   43篇
  1996年   40篇
  1995年   42篇
  1994年   29篇
  1993年   25篇
  1992年   34篇
  1991年   27篇
  1990年   29篇
  1989年   27篇
  1988年   14篇
  1987年   18篇
  1986年   36篇
  1985年   18篇
  1984年   14篇
  1983年   5篇
  1982年   12篇
  1981年   7篇
  1980年   10篇
  1979年   7篇
  1978年   10篇
  1977年   9篇
  1976年   6篇
  1973年   2篇
排序方式: 共有4276条查询结果,搜索用时 15 毫秒
51.
V. S. Rao 《Hydrobiologia》1977,53(1):13-32
Data on the ecology of Diatoms, Euglenineae and Myxophyceae in three freshwater ponds, differing in chemical composition and algal flora, situated in the vicinity of Hyderabad-India are presented. An attempt has been made to isolate various genera into groups, as their multiplication depended on particular ranges of a single chemical factor or set of factors. Several species could be separated into seasonal forms as they occur in particular periods of the year. Others could be grouped under indifferent forms as these are neither influenced by fluctuations in chemical factors nor by seasonal changes.  相似文献   
52.
A new variant of the red cell enzyme glucose-6-phosphate dehydrogenase has been detected in a South African male of Indian descent and in several of his relatives. The enzyme variant is characterized by slow electrophoretic mobility, low Michaelis constants for the substrates glucose-6-phosphate and NADP, and increased utilization of the substrate analogues 2-deoxyglucose-6-phosphate and deamino-NADP relative to the normal (B+) enzyme. There is no evidence that the enzyme variant, for which the name G6PD Porbandar is suggested, is associated with any hematological abnormality.The Atomic Energy Board and the South African Medical Research Council provided support for part of this work.  相似文献   
53.
The pteridophytes of Mauritius (Indian Ocean): ecology and distribution   总被引:1,自引:0,他引:1  
A survey of the pteridophytes of Mauritius is presented, including a summary of their habitats, ecology, and phytogeographical affinities. Of the 186 infrageneric taxa recorded from the island, 8 are adventive or naturalized, and 27 are presumed rare or extinct. Major ecological groupings are presented and species are listed for both indigenous and secondary plant communities.  相似文献   
54.
A case of somatic instability affecting aleurone colour in a strain of maize from India with flint background was analysed. The somatic instability is localized to theC 1 (Inhibitor) allele ofC locus on the short arm of chromosome 9. Molecular tests indicated thatAc is not present in the Indian stock and the evidence is consistent with the involvement of theEn (Spm) transposable element in the instability. The presence of theEn (Spm)-like element in the stock would suggest that these elements have been present in the maize genome for a long time. A new allele ofshrunken (sh1) gene with a somewhat unorthodox breeding behaviour is also described.  相似文献   
55.
江西安义潦河发现的旧石器及其意义   总被引:7,自引:5,他引:2  
  相似文献   
56.
汪达 《生态学杂志》1991,10(3):67-71
水是人类赖以生存繁衍的重要资源。我国人口逐年增长,而淡水资源数量有限。多变的自然降水及频繁的旱涝灾害,一直决定着我国农业收成乃至整个国民经济的盛衰。  相似文献   
57.
58.
Within the great expanse of the Brazilian Amazon Basin,Sphagnum has been greatly overlooked, in part because of its scarcity and in part because of the paucity of trained bryological collectors in the area. During a Projeto Flora Amazônica expedition in 1979, seven specimens ofSphagnum were collected, representing six species, five of which are newly described:S. amazonicum, S. dimorphophyllum, andS. subsecundoides in sectionSphagnum;S. curicuriariense andS. ripense in sect.Subsecunda. Also discussed areS. negrense Mitt. andS. sanguinale Warnst.  相似文献   
59.
In 1843 S. B. Buckley (1809–1884) traveled up the St. Johns River, Florida in search of plants, shells, and possibly other natural history objects. Buckley encountered many difficulties in interior Florida and his trip did not live up to his original expectations. It was unfortunate that the took years to distribute his plant specimens, since few botanists or naturalists had preceded him into that poorly explored region.  相似文献   
60.
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