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   1386篇
  免费   42篇
林业   74篇
农学   36篇
基础科学   14篇
  130篇
综合类   237篇
农作物   91篇
水产渔业   58篇
畜牧兽医   676篇
园艺   12篇
植物保护   100篇
  2021年   16篇
  2020年   15篇
  2019年   14篇
  2018年   11篇
  2017年   15篇
  2016年   18篇
  2015年   19篇
  2014年   19篇
  2013年   58篇
  2012年   49篇
  2011年   54篇
  2010年   46篇
  2009年   23篇
  2008年   53篇
  2007年   46篇
  2006年   47篇
  2005年   57篇
  2004年   54篇
  2003年   47篇
  2002年   35篇
  2001年   34篇
  2000年   38篇
  1999年   25篇
  1998年   11篇
  1997年   11篇
  1996年   13篇
  1995年   18篇
  1992年   19篇
  1991年   24篇
  1990年   22篇
  1989年   23篇
  1988年   20篇
  1987年   17篇
  1986年   22篇
  1985年   25篇
  1984年   18篇
  1983年   15篇
  1982年   18篇
  1981年   11篇
  1979年   14篇
  1977年   16篇
  1976年   18篇
  1975年   13篇
  1974年   14篇
  1973年   23篇
  1972年   20篇
  1971年   15篇
  1966年   10篇
  1948年   12篇
  1947年   13篇
排序方式: 共有1428条查询结果,搜索用时 15 毫秒
941.
942.
Slaframine (SF), a parasympathomimetic salivary stimulant, was administered i.m. (10, 15 or 20 micrograms SF/kg BW) to ruminally and abomasally fistulated steers at 12-h intervals for 18-d periods in a latin square-designed experiment. Steers were fed semicontinuously (12 times daily) a 40:60 roughage:concentrate diet at twice their net energy requirement for maintenance. Ruminal digestion coefficients for DM, ADF and starch were 10 to 16% lower and linearly related in an inverse manner to the level of SF administered (P less than .05). Postruminal digestion of DM, ADF and starch increased as much as 46.7, 9.5 and 44.0%, respectively, in a fashion linearly related (P less than .05) to the level of SF administered. Total tract digestion of DM and ADF were not affected by SF; however, total tract starch digestion was increased as much as 5% and was related linearly (P less than .05) to SF treatment. With SF administration, as much as 13% more bacterial protein exited the rumen, resulting in a 16.5% linear improvement (P less than .1) in the efficiency of ruminal bacterial protein production per 100 g of OM fermented. Ruminal concentrations of VFA, ammonia and pH were not affected by SF. These results demonstrate a positive relationship between salivation and ruminal bacterial protein synthesis and suggest that feed utilization by ruminants may be improved by pharmacological stimulation of salivary secretions.  相似文献   
943.
Lysosomal storage diseases are inborn errors of metabolism which are common in a number of breeds of dog and cat, due to specific, genetically determined, deficiencies of degradative enzymes. They are generally inherited as autosomal recessive traits. The enzyme substrate may be a complex lipid, glycoprotein or polysaccharide. In enzyme deficiency this substrate accumulates in swollen lysosomes in specific organs. Assay of the enzyme can be employed to detect affected individuals and also heterozygotes. It is possible to control these diseases by the identification of heterozygous animals and refraining from using them for breeding. Affected animals are normal at birth but the onset of disease is generally during the first months of life. The diseases are progressive and fatal. Neurological signs, hepato- and splenomegaly and skeletal abnormalities are commonly seen.  相似文献   
944.
945.
In a switchback experiment, six mature mares were fed a control and a fat-supplemented diet while being exercised in a galloping regimen. After three weeks adaptation to each diet, horses performed an exercise test (ET) consisting of four, 600-m gallops. Muscle biopsies were obtained before and after the ET, and blood samples were taken before, during and throughout recovery from the ET. Resting glycogen concentration in the biceps femoris muscle increased (P<.05) from 15.77 mg/g wet tissue when the horses were fed the control diet to 22.89 mg/g when they were fed the fats-supplemented diet. During the ET, the amount of glycogen mobilized by the muscle increased (P<.05) from 6.99 mg/g when the horses were fed the control diet to 13.09 mg/g when they were fed the fat-supplemented diet. When the horses were fed the fat-supplemented diet, they galloped faster (P<.09), at a constant heart rate, during the last two gallops of the ET. Thus, adapting exercising horses to a fat-supplemented diet increased muscle glycogen concentrations, which appeared to enhance their performance past the anaerobic threshold.  相似文献   
946.
Forty-four female American Shorthair cats with inflammatory uterine disease or infertility were evaluated. Data collected included age, month of diagnosis, housing, reproductive history, results of bacteriologic culture of uterine specimens, serum concentrations of estrogen, progesterone, and prolactin and histopathologic features of the ovaries and uterus. Histologically, the ovaries of 19 cats were dominated by active or cystic follicles, whereas 25 cats had luteal-phase ovaries. Of the 25 cats with active corpora lutea, 20 had either recently weaned litters (n = 11) without subsequent exposure to a male cat, or had been housed individually for lengthy periods (n = 9). The finding of active corpora lutea under these circumstances indicates that in queens, ovulation may occur by mechanisms not involving coitus. Prominent, active corpora lutea on the ovaries were associated with adenomatotic proliferative changes in the superficial and glandular epithelium of the uterus and with myometrial hyperplasia, compared with the uterus of cats with follicular ovaries (P less than 0.01). Serum progesterone concentration greater than or equal to 1.87 ng/ml was consistently associated with luteal-phase ovaries. Serum progesterone values less than or equal to 0.15 ng/ml were consistently associated with follicular-phase ovaries. Escherichia coli was the organism most commonly isolated from uterine contents.  相似文献   
947.
Abstract. The data from the national project to monitor water erosion has mostly been treated in an aggregate form, because in many of the monitored transects in any year too few fields were eroded for the data to be split into its component parts. However, in crop year 1983 erosion affected enough fields in two localities with contrasting soils for their data to be compared. Rainfall patterns in the two localities were similar. The transects covered a sandland area in Nottinghamshire and an area of clayland in and on the margins of Bedfordshire. Compared with the clayland, rilling of the sandland was widespread, related to the greater range of crops grown there, and more severe. On clayland, rills were mainly confined to valley floors, and slopes flanking these valleys generally had lower gradients than those on the sandland. On sandland, slopes were steeper in eroded fields drilled to winter cereals than they were in fields planted to potatoes or sugarbeet. Such field- based studies hint at the complex interactions of rain falling on a cropped field. Erosional thresholds are not static. The areas of fields affected by erosion and deposition were mostly very small. This helps us understand why the farmer often considers erosion unimportant.  相似文献   
948.
949.
950.
The commonly adopted technique and site for intramuscular injection in the cat are described, and the often resulting inadequacy and risk are discussed. An alternative site and technique are suggested to ensure a more reliable effect when an intramuscular injection is indicated. Résumé. On décrit la technique et l'endroit communément adoptés pour injection intramusculaire chez le chat et on discute de l'imperfection et du risque qui résultent souvent. On suggère un endroit alternatif et technique pour s'assurer d'un effet certain quand une injection intramusculaire est indiquée. Zusammenfassung. Die gewǒhnlish angewendete Technik und Stelle fur intramuskulàre Injektionen in Katzen sind beschrieben und das oft folgende Versagen und Risiko wird diskut-iert. Eine andere Stelle und Technik sind vorgeschlagen, um einer zuverlǎssigeren Wirkung sicher zu sein wenn eine intramuskulàre Injektion erforderlich ist.  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