全文获取类型
收费全文 | 214675篇 |
免费 | 11476篇 |
国内免费 | 7933篇 |
专业分类
林业 | 14317篇 |
农学 | 16099篇 |
基础科学 | 7792篇 |
28740篇 | |
综合类 | 44837篇 |
农作物 | 8931篇 |
水产渔业 | 9739篇 |
畜牧兽医 | 84990篇 |
园艺 | 3891篇 |
植物保护 | 14748篇 |
出版年
2022年 | 2091篇 |
2021年 | 3358篇 |
2020年 | 3298篇 |
2019年 | 3463篇 |
2018年 | 3324篇 |
2017年 | 4214篇 |
2016年 | 4162篇 |
2015年 | 4674篇 |
2014年 | 4846篇 |
2013年 | 9003篇 |
2012年 | 8010篇 |
2011年 | 9439篇 |
2010年 | 7402篇 |
2009年 | 7205篇 |
2008年 | 8766篇 |
2007年 | 8591篇 |
2006年 | 8341篇 |
2005年 | 7583篇 |
2004年 | 5631篇 |
2003年 | 5445篇 |
2002年 | 4993篇 |
2001年 | 5962篇 |
2000年 | 6070篇 |
1999年 | 5537篇 |
1998年 | 3335篇 |
1997年 | 3052篇 |
1996年 | 2815篇 |
1995年 | 3086篇 |
1994年 | 2752篇 |
1993年 | 2621篇 |
1992年 | 4086篇 |
1991年 | 4061篇 |
1990年 | 3992篇 |
1989年 | 3893篇 |
1988年 | 3487篇 |
1987年 | 3393篇 |
1986年 | 3383篇 |
1985年 | 3160篇 |
1984年 | 2678篇 |
1983年 | 2372篇 |
1982年 | 1624篇 |
1979年 | 2330篇 |
1978年 | 1916篇 |
1977年 | 1630篇 |
1974年 | 2074篇 |
1973年 | 2089篇 |
1972年 | 2054篇 |
1971年 | 1817篇 |
1970年 | 1712篇 |
1969年 | 1573篇 |
排序方式: 共有10000条查询结果,搜索用时 39 毫秒
71.
72.
M Steinhardt S Reimer U Bünger J Kutschke 《Archiv fuer experimentelle veterinaermedizin》1989,43(2):309-314
Comprehensive studies into domestic pigs and wild boars together with literature data provided a basis for an assessment of aerobic metabolic capacity (VO2max) of swine. The values quoted, from 20 to 94 ml/min-1/kg, had been due to several factors of methodological approach, growth, training, and nutrition as well as to pathophysiological aspects. For full capacity utilisation of VO2max, untrained pigs can be challenged at belt velocities between 0.8 and 1.8 m/s-1 and trained animals at 5 m/s-1. 相似文献
73.
White leghorn hens were experimentally infested with northern fowl mites (Ornithonyssus sylviarum) and antibody responses to mite immunogens were monitored over 12 weeks. Mite burdens increased during the early phase of infestation and declined over the latter weeks of the study. Antigen was prepared from homogenized whole mites, which were then sonicated and extracted with non-ionic detergent. Antigen extract was fractionated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and antibody-reactive polypeptides were identified by immunoblotting. At the start of infestation, hens had natural, pre-existing antibodies that reacted with several mite-extract components. Individual hens had different natural antibody reactivities; however, all birds had immunoglobulins reactive with extract polypeptides of 117,000, 77,000 and 36,000 molecular weight. A variety of mite extract components reacted with hen antibodies generated in response to experimental infestation. The number of antibody-reactive mite polypeptides increased through week 8 of infestation and then decreased by week 12. Fifteen polypeptides of northern fowl mite extract were reactive with antibodies developed by the majority of infested birds. These commonly reactive polypeptides had molecular weights ranging from 40,000 to 160,000. Glycoconjugates of fractionated mite extract were identified by blotting with lectins that have different carbohydrate binding specificities. Also identified were lectins that bound extract components with the same molecular weights as those moieties complexed by immunoglobulins of infested birds. 相似文献
74.
A urinary bladder mass in a 12-year-old spayed female West Highland White Terrier was diagnosed after exploratory surgery and biopsy as a transitional cell carcinoma. Four months later the dog presented with an ulcerated plaque-like cutaneous lesion at the previous surgical incision site; concurrent inguinal lymphadenopathy and recurrence of the urinary bladder mass were identified. Transitional cell carcinoma was diagnosed at all 3 sites. Although a definitive relationship cannot be established between the initial surgery for urinary bladder mass and the resultant subcutaneous lesion, surgical implantation should be considered as a source for the neoplastic cells. 相似文献
75.
76.
通过本试验观察表明:黄皮[Clausena Lansium (Lour.)Skeels]的开花与温度有密切关系,温度高,开花过程短;温度低,开花过程长。花穗中的花轴增长速度也随温度升高而加快,花轴增长快,则花轴长,花穗大;反之,花轴增长速度慢,花轴短,花穗小。黄皮开花的顺序是从花穗基部第1—4个分枝开始,每个分枝则先从基部1—8个二次分枝首先开放。31℃是黄皮花粉萌发最适宜温度。在培养基中加入15—20%蔗糖或2.4—D,三十烷醇等生长调节物质,明显可提高黄皮花粉的萌发力。本试验对黄皮的物候期及植物学特性同时进行了研究。 相似文献
77.
论城中村农民的现代化改造 总被引:4,自引:0,他引:4
针对当前我国城中村改造中存在的一些问题,以系统论为基础,对城中村改造工作的方向和改造工作应遵循的基本原则予以一定的分析,提出城中村改造工作的重点和关键所在是对城中村农民的现代化改造。进一步阐述了城中村农民的现代化改造对于推进城中村改造的重要意义。 相似文献
78.
J L Tarigo-Martinie A R Wyatt R M Kaplan 《Journal of the American Veterinary Medical Association》2001,218(12):1957-1960
OBJECTIVE: To determine the prevalence and clinical implications of anthelmintic resistance in cyathostomes of horses. DESIGN: Prospective study. ANIMALS: 80 horses on 10 farms in a 5-county region of northeast Georgia. PROCEDURE: On each farm, horses were stratified in descending order according to pretreatment fecal egg count (FEC), blocked into groups of 4, and then randomly assigned to 1 of 4 treatment groups: no treatment (controls), and treatment with pyrantel pamoate, fenbendazole, or ivermectin. Fecal samples were collected 24 hours prior to treatment and 2, 4, and 6 weeks after treatment for determination of FEC. Mean percentage of reduction in FEC was then calculated for each treatment group. For horses from each farm, the efficacy of each anthelmintic was categorized on the basis of mean percentage of reduction in FEC at 2 weeks after treatment (< 80% reduction = ineffective; 80 to 90% reduction = equivocal; and > 90% reduction = effective). RESULTS: Pyrantel pamoate was effective at reducing FEC in horses from 7 farms, ineffective in horses from 2 farms, and equivocal in horses from 1 farm. Fenbendazole was ineffective at reducing FEC in horses from 9 farms and equivocal in horses from 1 farm. Ivermectin was effective at reducing FEC in horses from all 10 farms. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that cyathostome resistance to fenbendazole is highly prevalent, and resistance to pyrantel pamoate is high enough to warrant concern. Resistance to ivermectin was not detected. On the basis of these data, it appears that ivermectin continues to be fully effective in horses. However, too few farms were used in this study to determine the prevalence of cyathostome resistance to ivermectin. Therefore, the efficacy of ivermectin should continue to be monitored closely. 相似文献
79.
通过对豫南小麦当家品种鄂恩一号和种植多年的7023的对比观察,找出二者在生育规律上的差异,进而分析在栽培措施上的异同。与7023相比,鄂恩一号出叶速度快,容易形成壮苗;抽穗后绿叶保持时间较长,有利后期光合作用;年前分蘖数比例大,总分蘖及成穗数没有7023多;幼穗分化开始早,进程快,小穗数及穗粒数比较少;开花早,灌浆时间长,灌浆强度大,子粒大,千粒重高。基于这些特点,提出了十月下旬播种,三叶期、药隔形成期追肥,四分子期根外喷肥,加强后期管理等针对该品种特性的栽培措施。 相似文献
80.
通过群钻钻头直径D,进给量f和切削速度n对孔径扩张量,圆度,孔中心线垂直度和直线度影响的试验,得出它们的变化规律。 相似文献