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   1315775篇
  免费   113568篇
  国内免费   1632篇
  2021年   17906篇
  2020年   12639篇
  2019年   16209篇
  2018年   17583篇
  2017年   16309篇
  2016年   28029篇
  2015年   42538篇
  2014年   50633篇
  2013年   76912篇
  2012年   37019篇
  2011年   25626篇
  2010年   43421篇
  2009年   44863篇
  2008年   24394篇
  2007年   22206篇
  2006年   27689篇
  2005年   28577篇
  2004年   27779篇
  2003年   25362篇
  2002年   23426篇
  2001年   31203篇
  2000年   28214篇
  1999年   28848篇
  1998年   25228篇
  1997年   25008篇
  1996年   24562篇
  1995年   22569篇
  1994年   22465篇
  1993年   21483篇
  1992年   25036篇
  1991年   23518篇
  1990年   22017篇
  1989年   23038篇
  1988年   21025篇
  1987年   19983篇
  1986年   18940篇
  1985年   20964篇
  1984年   21111篇
  1983年   18709篇
  1982年   19786篇
  1981年   19187篇
  1980年   17863篇
  1979年   17259篇
  1978年   16593篇
  1977年   16211篇
  1976年   15429篇
  1975年   14715篇
  1974年   15175篇
  1973年   15529篇
  1972年   13042篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
211.
In 1990 and 1994, two males of Golden Eagles were found with small lead particles in their stomachs. Both individuals died soon after they had been taken sitting on the soil in bad condition. There are some findings of dead eagles in the same area which showed no sign of having been injured. The two cases of presumed lead poisoning coincide with intense efforts to reduce the number of ChamoixRupicapra rupicapra by hunting. The bullets used contain a nucleus of lead and eagles were seen taking the entrails of the shot chamoix.  相似文献   
212.
213.
214.
Agapophytinae subf.n. is a highly diverse lineage of Australasian Therevidae, comprising eight described and two new genera: Agapophytus Guérin‐Méneville, Acupalpa Kröber, Acraspisa Kröber, Belonalys Kröber, Bonjeania Irwin & Lyneborg, Parapsilocephala Kröber, Acatopygia Kröber, Laxotela Winterton & Irwin, Pipinnipons gen.n. and Patanothrix gen.n. A genus‐level cladistic analysis of the subfamily was undertaken using sixty‐eight adult morphological characters and c. 1000 base pairs of the elongation factor‐1α (EF‐1α) protein coding gene. The morphological data partition produced three most parsimonious cladograms, whereas the molecular data partition gave a single most parsimonious cladogram, which did not match any of the cladograms found in the morphological analysis. The level of congruence between the data partitions was determined using the partition homogeneity test (HTF) and Wilcoxon signed ranks test. Despite being significantly incongruent in at least one of the incongruence tests, the partitions were combined in a simultaneous analysis. The combined data yielded a single cladogram that was better supported than that of the individual partitions analysed separately. The relative contributions of the data partitions to support for individual nodes on the combined cladogram were investigated using Partitioned Bremer Support. The level of support for many nodes on the combined cladogram was non‐additive and often greater than the sum of support for the respective nodes on individual partitions. This synergistic interaction between incongruent data partitions indicates a common phylogenetic signal in both partitions. It also suggests that criteria for partition combination based solely on incongruence may be misleading. The phylogenetic relationships of the genera are discussed using the combined data. A key to genera of Agapophytinae is presented, with genera diagnosed and figured. Two new genera are described: Patanothrix with a new species (Pat. skevingtoni) and Pat. wilsoni (Mann) transferred from Parapsilocephala, and Pipinnipons with a new species (Pip. kroeberi). Pipinnipons fascipennis (Kröber) is transferred from Squamopygia Kröber and Pip. imitans (Mann) is transferred from Agapophytus. Agapophytus bicolor (Kröber) is transferred from Parapsilocephala. Agapophytus varipennis Mann is synonymised with Aga. queenslandi Kröber and Aga. flavicornis Mann is synonymised with Aga. pallidicornis (Kröber).  相似文献   
215.
216.
From a variety of localities 14 strains of Beggiatoa, 1 ¼–3μ wide, were isolated in axenic heterotrophic culture. Most of these were freshwater forms, 2 were from brackish water, 1 was marine. The widths of the individual strains were constant, independent of conditions. The nutritional requirements of most of the strains are simple. Acetate at low concentrations, an ammonium salt as nitrogen source and the usual inorganic salts including trace elements supported growth. A few strains did not grow well without addition of an amino acid, and 2 (identical) strains required peptone or beef extract. Lactate, succinate, or pyruvate could often replace acetate. Multiplication was in most cases also possible with amino acids alone, without a further organic substrate. The appearance of the various strains on agar plates differs characteristically. Two types could be discerned: one forms spirals and one grows in tongues. These 2 types are not homogeneous for there are within them differences in width, growth rate, nutrition, and salt tolerance, so that a considerable number of independent forms exist even within the narrow limits in width of trichomes to which the investigations were restricted.  相似文献   
217.
218.
219.
220.
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