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   132428篇
  免费   6186篇
  国内免费   7890篇
林业   11488篇
农学   13460篇
基础科学   7199篇
  18209篇
综合类   34258篇
农作物   6020篇
水产渔业   4844篇
畜牧兽医   40336篇
园艺   2786篇
植物保护   7904篇
  2022年   1819篇
  2021年   2782篇
  2020年   2701篇
  2019年   2706篇
  2018年   2102篇
  2017年   2830篇
  2016年   2874篇
  2015年   3541篇
  2014年   3451篇
  2013年   5505篇
  2012年   5453篇
  2011年   6162篇
  2010年   5400篇
  2009年   5128篇
  2008年   5551篇
  2007年   5533篇
  2006年   5390篇
  2005年   4942篇
  2004年   3011篇
  2003年   2907篇
  2002年   2493篇
  2001年   2796篇
  2000年   3027篇
  1999年   3062篇
  1998年   2413篇
  1997年   2105篇
  1996年   1941篇
  1995年   1945篇
  1994年   1752篇
  1993年   1681篇
  1992年   2254篇
  1991年   2180篇
  1990年   2119篇
  1989年   2066篇
  1988年   1841篇
  1987年   1621篇
  1986年   1565篇
  1985年   1452篇
  1984年   1222篇
  1983年   1069篇
  1979年   1146篇
  1978年   924篇
  1975年   862篇
  1974年   1127篇
  1973年   1066篇
  1972年   1129篇
  1971年   1081篇
  1970年   1024篇
  1969年   876篇
  1967年   845篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
宁夏中宁等县市区个体养猪户的猪出现以败血性出血和两耳、胸前、腹下、四肢皮肤呈现紫绀为特征的疾病,并引起猪群,尤其是仔猪大批死亡.经临床观察、病理剖检、实验实检查,确诊为猪附红细胞体病.经用金霉素、土霉素拌料饲喂,肌注血虫净及后期用强力霉素拌料喂服和肌注磷酸伯氨喹、青蒿素,病情获控制.  相似文献   
992.
Acetabular angles (AAs) and dorsal acetabular rim angles acquired by computed tomographic (CT) imaging have been used to assess patient response to juvenile pubic symphysiodesis surgery. The purpose of this study was to evaluate the effects of patient positioning and slice selection on these angles, and an attempt was made to devise a repeatable method of measuring these angles that would eliminate positioning effects. We found significant variation in AAs with small differences in pelvic tilt and slice selection. Dorsal acetabular rim angles were not affected. As a result of positioning differences from one CT study to the next, every attempt should be made to standardize pelvic tilt, or eliminate its effect on AAs by standardizing gantry angle in relation to an anatomic landmark that will not change over time. The floor of the sacral vertebral canal may be a reasonable landmark for this purpose and deserves further study.  相似文献   
993.
The objective of this study was to determine the effects of sub-minimum inhibitory concentrations (sub-MICs) of 2 veterinary antibiotic preparations, chlortetracycline (CTC) and chlortetracycline-sulfamethazine (CTC + SMZ), on growth kinetics and outer membrane protein expression in Mannheimia haemolytica and Haemophilus somnus at normal and febrile body temperatures. Sub-minimum inhibitory concentrations of both antibiotics reduced the growth rates of M. haemolytica and H. somnus. Growth of both species was not inhibited when grown at 41 degrees C compared to 37 degrees C. There was no detectable consistent effect of antibiotic or temperature on outer membrane protein expression for either species. Our study indicates that sub-MIC levels of CTC and CTC + SMZ markedly impair growth of clinical M. haemolytica and H. somnus isolates, potentially allowing more effective host clearance during infection.  相似文献   
994.
The objective of this study was to evaluate the efficiency of Ovum Pick Up (OPU) in cycling (n = 5) and lactating, postpartum, swamp buffaloes (n = 6) with and without gonadotropin stimulation. The OPU was performed every two weeks in all groups of animals, for a total of six sessions. Thirty collections were performed in five cycling buffaloes and 36 collections in six lactating postpartum buffaloes. Buffaloes that received hormonal stimulation were given a total of 400 mg, follicle stimulating hormone (FSH), administered twice daily over 3 days in decreasing doses, together with 100 microg of GnRH, 24 h after the last FSH injection. Following a resting period of 1 month, the two groups of buffaloes, were subjected to the same OPU regimen, but without any hormonal treatment for an additional six OPU sessions. The number of aspirated follicles recorded from the hormonal stimulated, cycling animals and lactating, postpartum buffaloes was not significantly different, 7.2 +/- 3.7 and 9.0 +/- 3.2, respectively (p > 0.05). Recovered oocytes collected from the two groups of hormonally stimulated animals were also not statistically different: 3.7 +/- 2.7 in the cycling and 5.9 +/- 3.5 in the lactating postpartum group (p > 0.05). In the two groups of buffaloes not receiving hormonal stimulation, the number of aspirated follicles was not significantly different: 2.1 +/- 1.4 and 1.4 +/- 0.7 in cycling and lactating postpartum buffaloes respectively (p > 0.05). Recovered oocytes in the non-treated groups were also similar: 1.4 +/- 1.3 vs 0.7 +/- 0.8 in cycling and lactating buffaloes (p > 0.05). Among stimulated buffaloes, most aspirated follicles were small in size (< or =5 mm), whereas they were mostly medium and large sizes in the non-treated buffaloes. The oocyte recovery rate in both the groups, cycling and lactating postpartum, were 51.6% and 69.5% in stimulated groups and 55.0% and 53.1% in non-stimulated groups (p > 0.05). The majority of recovered oocytes were single- and multi-layered, and the number was greater in the cycling than in the lactating, postpartum buffaloes. The number and quality of recovered oocytes was similar in all groups of buffaloes whether they were received or did not receive hormonal stimulation. Moreover no difference was found in multi- and single-layered oocytes between cycling and lactating, postpartum buffaloes. In conclusion, OPU can be performed successfully in swamp buffalo in different reproductive status and FSH administration was shown to increase the number of aspirated oocytes in both cycling and lactating, postpartum buffaloes.  相似文献   
995.
996.
Light microscopic observations revealed that in camel foetuses of 25 mm crown‐to‐rump length (CRL) the primordial tubular system of the prospective lung was formed of several tubules lined by undifferentiated columnar epithelium. Intra‐epithelial neuroendocrine cells were the first elements to be differentiated in the lining epithelium of the primordial tubular system of the prospective lung as early as 25 mm CRL. On reaching 50–67 mm CRL, the primordial tubular system started to differentiate into two systems of primordial tubules, the prospective bronchial or light tubules and the future respiratory or dark tubules. The lining epithelium of the prospective bronchial tubules revealed a clear evidence of ciliogenesis as early as 80 mm CRL. From 800 mm CRL onwards, the bronchial epithelium demonstrated ciliated and non‐ciliated secretory cells. The non‐ciliated secretory cells of the bronchial epithelium of fetal camel lung showed moderate reaction to AB/PAS technique, for the first time, in fetuses reaching 600 mm CRL.  相似文献   
997.
本文论述了中国山羊的起源、品种遗传资源及其遗传多样性的研究进展。最新调查 显示中国的山羊品种达50个,其中43个为地方品种,4个培育品种,3个引入品种,许多品种 具有独特的生产性能或适应能力。大量研究表明,我国山羊遗传多样性较为丰富。  相似文献   
998.
The interactive effects of rooting volume and nutrient availability in a skeletal soil medium designed to meet street tree and pavement needs were observed in a containerized experiment. Benjamin fig (Ficus benjamina L.) was grown in a stone-soil blended skeletal soil material (CU-Soil™) and compared to a loam soil. The same topsoil used as the soil component in the skeletal soil material was used as the sole component in the comparison soil-only treatment.Plants grown in the skeletal soil material had reduced leaf tissue N content and depressed growth compared with plants grown in non-diluted soil. No other mineral deficiencies were found. Leaf number, chlorophyll concentration, shoot weight, and root characteristics were all affected.Reduced growth from soil dilution could be offset by the provision of an enlarged rooting volume for root development. Large containers of skeletal soil were observed to have smaller root systems compared to equivalent net volumes of loam soil at the first two harvest dates of the study. By the end of the study, the large containers of skeletal soil were observed to have developed larger root systems compared to equivalent net volumes of loam soil; resulting in comparable leaf N levels and total plant dry matter. Plants in skeletal soil had lower shoot: root ratios at the end of the study. Investing resources to further root growth in times of nutrient shortages is a probable plant reaction as evidenced by differences in specific root length between treatments. The study allowed a method for directly partitioning the containerization effect by having equivalent amounts of soil over two volumes.  相似文献   
999.
综述辣椒红色素的多种检测方法,即溶解性试验、显色反应、分光光度测定法及薄层层析法。  相似文献   
1000.
根据栽培面积以及为农民提供的收入而言,红辣椒在韩国一直是仅次于水稻而居第二位的重要农作物。按人均计算,韩国人均年辣椒粉的消费量达2.5kg以上,可能是世界最高记录。辣椒在韩国主要用作泡菜(韩国称之为Kimchi)香辛料和菜肴中的  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