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   405959篇
  免费   46185篇
  国内免费   171篇
  2018年   3504篇
  2017年   3488篇
  2016年   4684篇
  2015年   6237篇
  2014年   7252篇
  2013年   10854篇
  2012年   12153篇
  2011年   12262篇
  2010年   8208篇
  2009年   7663篇
  2008年   11145篇
  2007年   11295篇
  2006年   10864篇
  2005年   10261篇
  2004年   10163篇
  2003年   9846篇
  2002年   9608篇
  2001年   18898篇
  2000年   19088篇
  1999年   15500篇
  1998年   5432篇
  1997年   5690篇
  1996年   5505篇
  1995年   4997篇
  1994年   5112篇
  1993年   4980篇
  1992年   12914篇
  1991年   12339篇
  1990年   12275篇
  1989年   12240篇
  1988年   11144篇
  1987年   10600篇
  1986年   9822篇
  1985年   9864篇
  1984年   7998篇
  1983年   6968篇
  1982年   5296篇
  1981年   4672篇
  1980年   4551篇
  1979年   7676篇
  1978年   5934篇
  1977年   5294篇
  1976年   5120篇
  1975年   5534篇
  1974年   5783篇
  1973年   5712篇
  1972年   5166篇
  1971年   4567篇
  1970年   4036篇
  1969年   3733篇
排序方式: 共有10000条查询结果,搜索用时 422 毫秒
951.
A North Atlantic right whale (Eubalaena glacialis) genomic library was developed and screened with a (GATA)8 probe to identify tetranucleotide microsatellite loci. Sixteen characterized loci were polymorphic in North Atlantic and/or South Atlantic (Eubalaena australis) right whales, 12 being polymorphic in E. glacialis, and 15 in E. australis. Fourteen of these were combined with 21 other previously identified loci for a suite of 35 loci which can be used to increase resolution of genetic analyses of these species. Multiplex reactions were developed for genotyping samples at these loci, providing a method that is rapid, reliable and cost‐effective.  相似文献   
952.
The multivariate phenetic approach to the classification of Salmo spp. samples from Serbia and adjacent regions of western Balkans for 22 continuous external morphological characters suggests the occurrence of the following distinct stocks: West Danubian (Crno Osoje Stream and upper Zeta River) Salmo taleri , marble trout Salmo marmoratus (Trebuščica River), hatchery-reared Atlantic Salmo trutta , Mlava River drainage (Mlava and Krupaja rivers and Buk Stream) trout Salmo cf. trutta , Velika Morava River system (Godljevača, Bela and Resava rivers) trout S. cf. trutta , Ohrid Lake belvica Salmo ohridana and Aegean coastal drainage Salmo macedonicus (Božica River). In contrast to the phenetic similarity, the phylogenetic reconstruction places the Lake Ohrid belvica as part of an unresolved polytomy with other trout groups. Salmo cf. trutta in the Mlava River appears to form the basal group for the trout species in the region. The position of marble trout implies its independent and more recent origin from the West Danubian trout stock.  相似文献   
953.
954.
955.
956.
957.
958.
959.
The free carboxyl group of hypermodified nucleosides N6-methyl-N6-(threoninocarbonyl)adenosine (mt6A37) and 3-(3-amino-3-carboxypropyl)uridine (acp3U20:1) in tRNAmMet (yellow lupine), and N6-(threoninocarbonyl)adenosine (t6A37) in tRNAiMet (yellow lupine) can be converted quantitatively and under very mild conditions into the respective anilides in a reaction with aniline and a water-soluble carbodiimide. The tRNA reactions proceed with rates very similar to that reported previously for t6A nucleoside. Detailed analysis of the products of tRNA modification with [3H]aniline on tRNA (chromatography on BD-DEAE-cellulose), oligonucleotide (polyacrylamide gel electrophoresis) and nucleoside (HPLC on Aminex A6) levels clearly indicates that only the hypermodified nucleoside residues undergo the reaction. The site of modification is confirmed for mono-modified (at mt6A37) and bis-modified (at mt6A37 and acp3U20:1) tRNAmMet, and for mono-modified (at t6A37) tRNAiMet by sequence analysis using 5'end 32P-labeled tRNAs. The modification procedure seems to be universally applicable for all hypermodified nucleosides bearing a free carboxyl group and for different amine reagents designed for the studies on tRNA function.  相似文献   
960.
Abstract.The stimuli and mechanisms mediating host location and host choice by the bee mite, Varroa jacobsoni (Oudemans), are currently unknown. It is shown that Varroa can use single clean‐air puffs and bee‐odour plumes in a wind tunnel as directional cues. Varroa turned nearly straight upwind in response to single 0.1‐s puffs of clean air directed at 90° to the their anterior‐posterior axis. They turned significantly further to their left side (104°) than to their right (76°), but showed no difference in latency to initiation of the turns (means of 63.3 ms vs. 62.6 ms, respectively). They also followed bee‐odour plumes in a wind tunnel. When released in odour and control plumes mid‐way between the plume's origin and the downwind end of the tunnel, mites responding to bee‐odour walked upwind in, or along the edge of, the odour plume with 38% making contact with the odour delivery tube; mites in clean air did not walk upwind along the air stream, and none made contact with the air delivery tube. Walking speeds were not different between the bee‐odour and control groups (0.28 vs. 0.29 cm s–1); there were also no differences in the turning rates (96.85 vs. 97.16 deg s–1 and 388.08 vs. 379.18 deg cm–1, respectively). Under all conditions, mites walked in a zigzag fashion.  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