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   1076854篇
  免费   118188篇
  国内免费   861篇
  1195903篇
  2018年   9314篇
  2016年   12677篇
  2015年   17756篇
  2014年   20777篇
  2013年   29665篇
  2012年   33021篇
  2011年   33486篇
  2010年   22665篇
  2009年   20841篇
  2008年   29689篇
  2007年   30684篇
  2006年   28930篇
  2005年   28003篇
  2004年   27821篇
  2003年   26714篇
  2002年   25976篇
  2001年   48099篇
  2000年   48691篇
  1999年   38890篇
  1998年   13853篇
  1997年   14453篇
  1996年   13473篇
  1995年   12732篇
  1994年   12375篇
  1993年   12281篇
  1992年   31970篇
  1991年   31087篇
  1990年   30340篇
  1989年   29581篇
  1988年   27787篇
  1987年   26029篇
  1986年   24337篇
  1985年   24356篇
  1984年   20261篇
  1983年   17181篇
  1982年   13330篇
  1981年   12099篇
  1980年   11202篇
  1979年   18954篇
  1978年   15012篇
  1977年   13632篇
  1976年   12566篇
  1975年   14037篇
  1974年   15253篇
  1973年   15099篇
  1972年   13652篇
  1971年   12510篇
  1970年   10722篇
  1969年   10513篇
  1968年   9570篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
171.
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   
172.
173.
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   
174.
175.
176.
Synaptonemal complexes and meiosis in myxomycetes   总被引:4,自引:0,他引:4  
Synaptonemal complexes (SC) have been observed in spores 18–24 hr past cleavage in natural fruitings of Physarum cinereum, P. bogoriense, Hemitrichia stipitata, Tubifera ferruginosa, and Arcyria incarnata. Laboratory fruitings of Arcyria cinerea, Stemonitis herbatica, and a homothallic isolate of Physarum pusillum also have SC's present in spores during the same postcleavage period. The presence of these paired chromosomes of meiotic prophase in spores of species collected in nature and in a diversity of taxa suggests that the usual position of meiosis in Myxomycetes is inside the postcleavage spore. Criteria are proposed for evaluating the validity of the SC as an indicator of meiosis.  相似文献   
177.
178.
179.
180.
The cell surface of the parasitic protozoan Leishmania mexicana is coated by glycosylphosphatidylinositol (GPI)-anchored glycoproteins, a GPI-anchored lipophosphoglycan and a class of free GPI glycolipids. To investigate whether the anchor or free GPIs are required for parasite growth we cloned the L.mexicana gene for dolichol-phosphate-mannose synthase (DPMS) and attempted to create DPMS knockout mutants by targeted gene deletion. DPMS catalyzes the formation of dolichol-phosphate mannose, the sugar donor for all mannose additions in the biosynthesis of both the anchor and free GPIs, except for a alpha1-3-linked mannose residue that is added exclusively to the free GPIs and lipophosphoglycan anchor precursors. The requirement for dolichol-phosphate-mannose in other glycosylation pathways in L.mexicana is minimal. Deletion of both alleles of the DPMS gene (lmdpms) consistently resulted in amplification of the lmdpms chromosomal locus unless the promastigotes were first transfected with an episomal copy of lmdpms, indicating that lmdpms, and possibly GPI biosynthesis, is essential for parasite growth. As evidence presented in this and previous studies indicates that neither GPI-anchored glycoproteins nor lipophosphoglycan are required for growth of cultured parasites, it is possible that the abundant and functionally uncharacterized free GPIs are essential membrane components.  相似文献   
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