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   279619篇
  免费   16437篇
  国内免费   1994篇
林业   24860篇
农学   15577篇
基础科学   3876篇
  45314篇
综合类   33020篇
农作物   17714篇
水产渔业   17517篇
畜牧兽医   108608篇
园艺   6735篇
植物保护   24829篇
  2021年   2938篇
  2020年   3364篇
  2019年   4115篇
  2018年   4430篇
  2017年   4995篇
  2016年   5319篇
  2015年   4934篇
  2014年   6253篇
  2013年   16919篇
  2012年   7357篇
  2011年   9389篇
  2010年   8246篇
  2009年   8733篇
  2008年   8638篇
  2007年   7675篇
  2006年   8142篇
  2005年   7396篇
  2004年   6928篇
  2003年   6754篇
  2002年   6116篇
  2001年   6702篇
  2000年   6344篇
  1999年   5884篇
  1998年   4363篇
  1997年   4249篇
  1996年   3925篇
  1995年   4689篇
  1994年   4041篇
  1993年   3750篇
  1992年   4625篇
  1991年   4837篇
  1990年   4552篇
  1989年   4527篇
  1988年   4063篇
  1987年   4140篇
  1986年   4101篇
  1985年   4339篇
  1984年   4012篇
  1983年   3692篇
  1982年   2999篇
  1981年   2888篇
  1980年   2830篇
  1979年   3505篇
  1978年   3115篇
  1977年   2902篇
  1976年   2718篇
  1975年   2632篇
  1974年   2928篇
  1973年   2878篇
  1972年   2648篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
广东主要品种(品系)工夫红茶适制性分析   总被引:1,自引:0,他引:1  
对广东省农业科学院茶叶研究所培育的具有代表性的品种(品系)进行工夫红茶适制性分析,结果表明,不同的品种(品系)优势各不相同,但大体上都具有较高的水浸出物和氨基酸含量,揭示了各个品种(品系)的特点,为今后优异红茶品种的选育提供依据和参考。  相似文献   
72.
73.
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   
74.
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   
75.
Landscape Ecology - Several case studies investigated the role of ecosystem services in participatory planning processes. However, no systematic study exists that cuts across a large number of...  相似文献   
76.
77.
The influence of extruded oilseeds on total tract digestibility and ruminal digestion in dairy cows was studied in three cows fed a hay-concentrate (60.5/39.5; 3.7% fatty acids in diet on DM basis) control diet (C) or the same diet supplemented with raw (R) or extruded (ER) rapeseeds (8.0% fatty acids in diet DM). The experimental design was a 3 x 3 Latin square design. Compared with diet C, diets containing rapeseed decreased ruminal OM digestibility (9.5%, P less than .10) and increased (P less than .05) the proportion of propionate in ruminal fluid VFA. Extrusion had no effect on DM and OM total tract digestibilities and increased (P less than .10) N digestion. Microbial N flow at the duodenum was calculated taking into account solid-adherent bacteria (SAB) and liquid-associated bacteria (LAB). Duodenal flows of total, SAB, and LAB of OM and N did not change with diet. Extrusion of the rapeseeds did not modify (P less than .10) the proportion of bacterial N at the duodenum and had no effect on crude fiber digestibility. This trial demonstrates that rapeseeds in hay-based diets can be fed at levels of up to 14% of the diet without adversely affecting crude fiber digestibility.  相似文献   
78.
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   
79.
Findings are presented on the precision of a clinical biochemistry analyser designed specifically for veterinary use. Twenty biochemical analytes have been examined in detail for variation within and between runs. The results indicate that the analyser can provide high precision for all the analytes with the possible exception of calcium, and suggest that the instrument can be used with confidence in the practice laboratory to aid diagnosis and to monitor biochemical changes in animals receiving treatment.  相似文献   
80.
Five studies were performed to determine factors affecting progesterone concentration in skim milk. Results of the first study indicated that progesterone concentration was higher in skim milk of samples kept 16 hours in an ice bath (0 C) than of those left at room temperature (21 C). In the second study, this temperature effect was found to be reversible, with skim milk progesterone concentration increasing when whole milk samples were cooled prior to centrifugation. In the third study, [3H]-labeled progesterone was used to determine the relationship between fat content of foremilk (the first milk obtained from the teats), midmilk (milk obtained midway through milking), and strippings (milk obtained immediately after milking machines have been removed) samples and temperature (4 C and 21 C) on the percentage of progesterone in the skim milk fraction. The relationship between percentage of butterfat and percentage of progesterone in skim milk was linear when the log of these variables was used for calculations. In the fourth study, assayable progesterone in the skim milk fraction of foremilk, midmilk, and strippings was affected by temperature. In the fifth study, a multiple-regression procedure was used to determine the amount of variation in percentage of radioactive progesterone in the skim milk fraction. Independent variables (whole milk butterfat and temperature of incubation [1, 3, 13, 22, 37, and 50 C]) and the natural log of each variable, were entered into a stepwise multiple-regression analysis.(ABSTRACT TRUNCATED AT 250 WORDS)  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