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   86093篇
  免费   4664篇
  国内免费   143篇
林业   3665篇
农学   2424篇
基础科学   530篇
  9895篇
综合类   15912篇
农作物   3509篇
水产渔业   3991篇
畜牧兽医   44919篇
园艺   953篇
植物保护   5102篇
  2020年   793篇
  2019年   1004篇
  2018年   1342篇
  2017年   1463篇
  2016年   1331篇
  2015年   1090篇
  2014年   1455篇
  2013年   3042篇
  2012年   2525篇
  2011年   3005篇
  2010年   1835篇
  2009年   1980篇
  2008年   2949篇
  2007年   2749篇
  2006年   2596篇
  2005年   2438篇
  2004年   2359篇
  2003年   2383篇
  2002年   2210篇
  2001年   2572篇
  2000年   2623篇
  1999年   2016篇
  1998年   765篇
  1997年   763篇
  1996年   758篇
  1995年   845篇
  1993年   772篇
  1992年   1616篇
  1991年   1790篇
  1990年   1682篇
  1989年   1693篇
  1988年   1519篇
  1987年   1573篇
  1986年   1629篇
  1985年   1592篇
  1984年   1215篇
  1983年   1095篇
  1979年   1182篇
  1978年   910篇
  1977年   772篇
  1975年   789篇
  1974年   1041篇
  1973年   1046篇
  1972年   1066篇
  1971年   1010篇
  1970年   1011篇
  1969年   916篇
  1968年   820篇
  1967年   809篇
  1966年   746篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
A systematic immunohistochemical study of the ultimobranchial tubule (UBT) has been carried out in 45 Wistar rats of different ages (0, 5, 10, 15, 20, 25, 30, 60 and 120 days). The existence of calcitonin immunoreactive cells in the UBT wall has been demonstrated in a 5-days old rat. In addition, immunohistochemical studies for thyroglobulin revealed positive staining in follicular cells connected to the UBT and, occasionally, in isolated cells lying within solid clusters from the UBT. These last results together with the continued and repeated existence of numerous mitosis and PAS (+) microfollicles, apparently rising from the UBT, support the hypothesis that the ultimobranchial body (UBB) may contribute partially to the formation of a part of the follicular component.  相似文献   
2.
Abstract.— The freshwater mussel Elliptio complanata was provided water containing green algae and cyanobacteria delivered from the Partitioned Aquaculture System (PAS) at eight flow rates to determine algal filtration rates as mg of particulate organic carbon (POC)/kg wet tissue weight per h. The dominant taxon in cyanobacterial waters was Microcystis while the dominant taxa in green algal waters were Scenedesmus and Ankistrodesmus . The cell counts of Scenedesmus and Ankistrodesmus were the only algal taxa that were significantly different between the incoming water and water filtered by mussels. Filtration rates of POC obtained from green algal water were significantly greater than from cyanobacteria-dominated waters at all flow rates. A significant increase in mean filtration rate was observed as flow rates increased. The filtration rate of green algae increased as POC concentration increased, peaking at 28 mg C/L. A maximum filtration rate was not observed with cyanobacterial waters.  相似文献   
3.
The purpose of this study was to evaluate seasonal influences on thyroid hormone levels of healthy outdoor dogs in Hokkaido. We surveyed serum basal total thyroxine (tT4), free thyroxine (fT4), and canine thyroid-stimulating hormone (cTSH) levels, and tT4 levels after administration of TSH for a year. Basal tT4 levels decreased in January, and increased in August and September. fT4 levels increased in January and November. No significant seasonal variation was found in cTSH. tT4 levels after administration of TSH in August and November increased. These results suggested that the thyroid gland may have been activated in November. We should take seasonal variation into consideration when thyroid function is tested.  相似文献   
4.
The isolation of (+)-totarol as active compound against Mycobacterium tuberculosis is reported from Chamaecyparis nootkatensis outerbark.  相似文献   
5.
6.
7.
8.
Abstract. In field and laboratory experiments the conditioner‘Agri-SC’has shown improvements in the structure of loamy sand soils in east Shropshire, UK. It resulted in statistically significant decreases in soil bulk density values and increases in soil porosity and aggregate stability. Further experiments are in progress on both loamy sand and silt loam soils.  相似文献   
9.
Nephrogenic diabetes insipidus is characterized by polyuria, hyposthenuria and compensatory polydipsia. With conventional clinical and laboratory examinations the diagnosis can be established and the differential diagnostic diseases excluded. In order to verify the diagnosis, differentiate the condition from central and nephrogenic diabetes insipidus and rule out psychogenic polydipsia, additional laboratory studies are required: of these, the concentration test, modified Carter-Robbins test and AVP stimulation test are described.  相似文献   
10.
A survey on coccidial infections in goats from central Spain was carried out. Fifty-five goat farms from 28 localities belonging to the three bioclimatic subregions of the area were visited. Individual samples (702) were obtained from the rectum of 130 young (under 1 year of age) and adult (572 over 1 year of age) goats. Coproscopical analyses showed a 100% prevalence and a moderate average intensity (7606.48 +/- 17918.78 Eimeria oocysts per gram of faeces), although wide variations were seen among herds and among individuals within each goat flock. Statistical analysis showed a strong age-related reduction in oocysts output in goats up to 4 years of age. The intensity of coccidial infections (young and adult goats, herds) was independent of the prevailing bioclimatic conditions. Heavier infections in young goats were found in bigger herds, whereas adult goats from these same big flocks (over 300 animals) showed the lowest oocyst output. Under our conditions, neither the female restocking rate nor the age structure seemed to play a significant role in the intensity of the Eimeria infections.  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