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   220145篇
  免费   14337篇
  国内免费   2576篇
林业   24163篇
农学   15810篇
基础科学   4206篇
  41875篇
综合类   16661篇
农作物   17698篇
水产渔业   16150篇
畜牧兽医   70017篇
园艺   7011篇
植物保护   23467篇
  2022年   1488篇
  2021年   3093篇
  2020年   3494篇
  2019年   4210篇
  2018年   4104篇
  2017年   4697篇
  2016年   5144篇
  2015年   5072篇
  2014年   6364篇
  2013年   17137篇
  2012年   6111篇
  2011年   7825篇
  2010年   8104篇
  2009年   8575篇
  2008年   7026篇
  2007年   5878篇
  2006年   6582篇
  2005年   5609篇
  2004年   5207篇
  2003年   4864篇
  2002年   4259篇
  2001年   4402篇
  2000年   4042篇
  1999年   4150篇
  1998年   4161篇
  1997年   4053篇
  1996年   3762篇
  1995年   4428篇
  1994年   3748篇
  1993年   3420篇
  1992年   3167篇
  1991年   3303篇
  1990年   2945篇
  1989年   2933篇
  1988年   2529篇
  1987年   2577篇
  1986年   2434篇
  1985年   2841篇
  1984年   2853篇
  1983年   2786篇
  1982年   2493篇
  1981年   2464篇
  1980年   2468篇
  1979年   2396篇
  1978年   2284篇
  1977年   2202篇
  1976年   2051篇
  1975年   1795篇
  1974年   1800篇
  1973年   1750篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
Landscape Ecology - The effects of changing land use, and especially urbanisation, on species and functional diversity are of global concern. Eco-estates are a form of urban housing development...  相似文献   
73.
A new cytotoxic thiodepsipeptide, verrucosamide (1), was isolated along with the known, related cyclic peptide thiocoraline, from the extract of a marine-derived actinomycete, a Verrucosispora sp., our strain CNX-026. The new peptide, which is composed of two rare seven-membered 1,4-thiazepane rings, was elucidated by a combination of spectral methods and the absolute configuration was determined by a single X-ray diffraction study. Verrucosamide (1) showed moderate cytotoxicity and selectivity in the NCI 60 cell line bioassay. The most susceptible cell lines were MDA-MB-468 breast carcinoma with an LD50 of 1.26 µM, and COLO 205 colon adenocarcinoma with an LD50 of 1.4 µM. Also isolated along with verrucosamide were three small 3-hydroxy(alkoxy)-quinaldic acid derivatives that appear to be products of the same biosynthetic pathway.  相似文献   
74.
75.
Osteomyelitis caused by Cryptococcus neoformans was diagnosed in a three-year-old male Irish wolfhound. The case details and radiological findings of radiolucency and periosteal reaction of the left third metatarsal bone had lead to an initial diagnosis of a malignant bone tumour. Biopsy revealed a fungal granuloma and culture identified the causal organism. A four month course of ketaconazole was instigated and the lameness resolved. Twelve months after the end of treatment there was no recurrence of the problem.  相似文献   
76.
77.
Differences in gas exchange parameters i.e. carbon exchange rate (CER), transpiration (Tr), water vapor conductance (g) were investigated, under a controlled environment, in a semi-dwarf (SD) Triticum aestivum line, its tall (TL) near isoline and the Payne (PA) variety characterized by small leaves. The plants were maintained in: (a) optimal substrate moisture condition (CTR); (b) salinized by watering with a 0.12 m NaCl solution (SLT); (c) water stressed by withholding waterings during a period of six days (STR); (d) stressed and salinized during the same period and with the same saline solution (S + S). CER and Tr were negatively affected by the stresses; SLT and S + S treatments had a higher WUE compared to their respective controls CTR and STR.
SD line had a better performance in terms of CER and WUE, particularly when water and salt stresses interacted. Leaf anatomy and assimilation/internal CO2 concentration curves contributed to explaining the SD performance.  相似文献   
78.
79.
Abstract. A humoral antibody response was demonstrated by ELISA in rainbow trout immunized intraperitoneally with extracts from the branchiuran ectoparasite Argulus foliaceus. A similar immunization protocol produced a higher titre response in a rabbit. Both trout and rabbit identified several antigenic components on immunoblots. ELISA and immunoblotting indicated that rainbow trout and rabbit anti-A. foliaceus sera identified components from the parasitic copepods Lepeophtheirus salmonis and Caligus elongatus.  相似文献   
80.
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