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   289665篇
  免费   16683篇
  国内免费   1984篇
林业   25138篇
农学   15695篇
基础科学   3888篇
  46741篇
综合类   31288篇
农作物   18013篇
水产渔业   18109篇
畜牧兽医   117320篇
园艺   6815篇
植物保护   25325篇
  2021年   2963篇
  2020年   3397篇
  2019年   4136篇
  2018年   4674篇
  2017年   5188篇
  2016年   5438篇
  2015年   5006篇
  2014年   6386篇
  2013年   16990篇
  2012年   8250篇
  2011年   10434篇
  2010年   8683篇
  2009年   9068篇
  2008年   9629篇
  2007年   8764篇
  2006年   9051篇
  2005年   8177篇
  2004年   7787篇
  2003年   7608篇
  2002年   6851篇
  2001年   7771篇
  2000年   7439篇
  1999年   6687篇
  1998年   4415篇
  1997年   4292篇
  1996年   4000篇
  1995年   4701篇
  1994年   4069篇
  1993年   3744篇
  1992年   5042篇
  1991年   5285篇
  1990年   5052篇
  1989年   5059篇
  1988年   4477篇
  1987年   4498篇
  1986年   4355篇
  1985年   4530篇
  1984年   4109篇
  1983年   3822篇
  1982年   3059篇
  1981年   2917篇
  1980年   2862篇
  1979年   3487篇
  1978年   3041篇
  1977年   2812篇
  1976年   2628篇
  1975年   2502篇
  1974年   2670篇
  1973年   2751篇
  1972年   2447篇
排序方式: 共有10000条查询结果,搜索用时 46 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.
76.
In a feeding trial lasting for months Halothane-positive fattening pigs were put on a diet containing different concentrations of vitamin E and selenium. After a Myostress application vitamin E and selenium were additionally injected in order to examine stress resistance (CK-test) and regenerative capacity (histological examination of Musculus longissimus dorsi) of skeletal muscle. The study revealed that neither high dietary levels of vitamin E/selenium nor a vitamin E/selenium treatment applied after stress are capable of preventing stress related myopathy nor can they influence its healing up favourably.  相似文献   
77.
Epidermal growth factor (EGF)-like activity was measured in mares' colostrum and milk by radioreceptor assay. Milk samples were collected from 22 mares 1 or more times during early lactation. Samples of colostrum were taken after parturition and before the foal first suckled (presuckle), within 6 hours after the foal first suckled (postsuckle), and on days 1, 2, 4, and 8 of lactation. In the 5 mares from which milk samples were obtained at each sampling time, presuckle colostral mean EGF-like activity (17.8 ng/ml) was greatest (P less than 0.05). The mean values for EGF-like activity at all other sampling times were not significantly different from each other (postsuckle colostrum, 9.7 ng/ml; day 1, 9.6 ng/ml; day 2, 8.5 ng/ml; day 4, 8.0 ng/ml; day 8, 7.8 ng/ml).  相似文献   
78.
Immune system dysfunction and immunoglobulin deficiency was diagnosed in a 2-year-old horse with disseminated lymphosarcoma. Prolonged (35 days) parenteral nutrition was delivered to support the horse during a period in which immune function studies could be performed. Correction of nutritional compromise by use of parenteral nutrition did not correct the immunoglobulin deficiency, and results of lymphocyte phenotype testing did not indicate abnormal proportions of leukocytes. Lymphoblast transformation studies were suggestive of a circulating immunosuppressive factor in the horse's serum. Normal cell function was detected when the cells were stimulated in precolostral equine serum.  相似文献   
79.
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   
80.
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   
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