全文获取类型
收费全文 | 20156篇 |
免费 | 1140篇 |
国内免费 | 2034篇 |
专业分类
林业 | 1822篇 |
农学 | 2076篇 |
基础科学 | 1026篇 |
2314篇 | |
综合类 | 8338篇 |
农作物 | 1407篇 |
水产渔业 | 894篇 |
畜牧兽医 | 3275篇 |
园艺 | 1305篇 |
植物保护 | 873篇 |
出版年
2024年 | 36篇 |
2023年 | 205篇 |
2022年 | 558篇 |
2021年 | 700篇 |
2020年 | 685篇 |
2019年 | 620篇 |
2018年 | 505篇 |
2017年 | 747篇 |
2016年 | 666篇 |
2015年 | 874篇 |
2014年 | 890篇 |
2013年 | 1200篇 |
2012年 | 1543篇 |
2011年 | 1624篇 |
2010年 | 1477篇 |
2009年 | 1300篇 |
2008年 | 1232篇 |
2007年 | 1144篇 |
2006年 | 1186篇 |
2005年 | 1003篇 |
2004年 | 573篇 |
2003年 | 610篇 |
2002年 | 844篇 |
2001年 | 699篇 |
2000年 | 568篇 |
1999年 | 361篇 |
1998年 | 243篇 |
1997年 | 195篇 |
1996年 | 157篇 |
1995年 | 157篇 |
1994年 | 143篇 |
1993年 | 109篇 |
1992年 | 106篇 |
1991年 | 86篇 |
1990年 | 68篇 |
1989年 | 75篇 |
1988年 | 41篇 |
1987年 | 25篇 |
1986年 | 16篇 |
1985年 | 11篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1972年 | 2篇 |
1970年 | 2篇 |
1967年 | 2篇 |
1962年 | 3篇 |
1956年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 416 毫秒
961.
AIM:To determine the relationship between ischemia, hypoxia and the production of vascular endothelial growth factor in rat myocardium and its basic mechanism. METHODS:(1) 28 Wistar rats were randomly divided into 4 groups: group A, normal control;group B, 1 day's acute myocardial infarction;group C, 3 day's acute myocardial infarction;group D, 7 day's acute myocardial infarction. (2) Rat cardiac myocytes cultured were primarily divided into some groups, hypoxia incubated 24 hours; PMA groups, hypoxia incubated 24 hours with PKC activator (PMA), A 0 ng/mL; B 10 ng/mL; C 100 ng/mL; D 1 000 ng/mL; Chelerythrine groups, hypoxia incubated 24 hours with PKC inhibitor (chelerythrine), A 0 nmol/L; B 10 nmol/L. (3) By computer scanned and quantitated, vascular endothelial growth factor (VEGF) protein was detected with immunohistochemical technique. RESULTS:The longer time of ischemia and hypoxia was, the higher the VEGF production.The relat ionship was found between the time of ischemia or hypoxia and the production of VEGF.The product ion of VEGF protein was further promoted by PMA with different concentrat ion, decreased by chelerythrine.CONCLUSION: Ischemia or hypoxia strongly stimulated the production of VEGF in myocardium, which played an important role in autoprotecting of ischemic or hypoxic myocardium. Hypoxia-induced PKC activation is one kind of basic mechanisms in this course. 相似文献
962.
Survey and analysis of common diseases of laboratory monkeys are great significance to understand disease epidemiology, and formulate a set of scientific and reasonable measures for prevention and control disease, to improve the quantity and quality of laboratory monkeys, to ensure the accuracy of the animal experiment results. Through the investigation of the sick and dead animals of a large-scale laboratory monkeys breeding facility in Kunming area in 2014, the animals were classified depends on the main diseases, and the diseases were classified according to adult and juvenile animals, data were analyzed by Excel Office 2010 software. The results showed the common diseases of laboratory monkeys included the digestive system, respiratory system, trauma, reproductive system, and locomotor system disease, which were 47.45%, 13.06%, 12.10%, 11.46% and 8.92% separately; Common diseases included diarrhoea, soft tissue injuries, abortion, lobar pneumonia, dysentery, arthritis, intestinal pneumatosis, chronic colitis, and extreme bad nutrition, the ratio were 18.47%, 11.15%, 8.91%, 8.28%, 8.28%, 7.96%, 5.10%, 5.10% and 5.09% separately. Comprehensive analysis of common diseases and disease occurrence causes of the laboratory monkeys, suggesting that providing better quality laboratory monkeys for scientific research only by constantly improving the scientific breeding management level, constantly strengthening veterinary capacity, mastering the theoretical knowledge and scientific diagnosis method. 相似文献
963.
964.
965.
芸薹根肿菌严重危害大白菜和其他十字花科作物。由于根肿菌通常以多个生理小种混生状态进行侵染,导致抗病品种的抗性不能持久。以沈阳地区根肿菌为材料,进行了单孢分离技术体系构建,结果表明采取冷冻盒接菌法对两日龄大白菜幼苗进行单孢接种,可将侵染率提高到47.86%;采用基质过渡培养可将大白菜植株成活率提高到67%。利用上述根肿菌单孢分离技术体系对沈阳地区根肿菌进行单孢分离和Williams生理小种鉴定,结果表明沈阳地区根肿菌存在4号、8号、9号、11号生理小种,其中4号生理小种为优势小种。 相似文献
966.
基于随机森林算法的自然光照条件下绿色苹果识别 总被引:6,自引:0,他引:6
果实识别是自动化采摘系统中的重要环节,能否快速、准确地识别出果实直接影响采摘机器人的实时性和可靠性。为了实现自然光照条件下绿色苹果的识别,本文采集了果实生长期苹果树图像,并利用随机森林算法实现了绿色苹果果实的分类和识别。针对果树背景颜色和纹理特征的复杂性,尤其是绿色果实和叶片在很多特征上的相似性,论文基于RGB颜色空间进行了Otsu阈值分割和滤波处理,去除枝干等背景,得到仅剩果实和叶片的图像。然后,分别提取叶片和苹果的灰度及纹理特征构成训练集合,建立了绿色苹果随机森林识别模型,并使用像素模板验证数据集,对模型进行预测试验,正确率为90%。最后,选择10幅自然光照条件下不同的果树图像作为检测对象,使用该模型进行果实识别并使用霍夫变换绘制果实轮廓,平均识别正确率为88%。结果表明,该方法具有较高的鲁棒性、稳定性、准确性,能够用于自然光照条件下绿色果实的快速识别。 相似文献
967.
在诠释市场导向概念的基础上,从品牌建设、生态保护、开拓东盟市场三个方面分析了广西企业的市场导向,提出了企业在建立品牌优势、实现绿色营销、走向东盟市场等方面应采取的营销措施。 相似文献
968.
Shuiyang Yu Hai Long Hong Yang Jie Zhang Guangbing Deng Zhifen Pan Erliang Zhang Maoqun Yu 《Euphytica》2012,186(1):247-255
Powdery mildew (Pm), caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most serious diseases for common wheat in many regions around the world. Seeking for new resistance source
is urgently required to meet the challenge of the rapid loss of resistance due to the co-evolution of the pathogen’s virulence.
Wheat line 07jian126 (Triticum aestivum L.) is highly resistant to the Pm disease prevailing in Sichuan province of China. Previous study showed that a SSR marker
Xbarc183 was linked to the Pm resistance in 07jian126, which might be controlled by a single dominant gene, designated as Pm07J126. In this study, two additional F2 populations were used to confirm the linkage between Pm07J126 and Xbarc183. Furthermore, rye chromatin was detected in 07jian126 by molecular analysis of a rye-specific SCAR marker O5 which co-segregated with Pm07J126. This result indicated that Pm07J126 might originate from rye. The reaction patterns to 21 Bgt isolates and molecular marker analysis implied that Pm07J126 might be different from the known rye-derived Pm genes Pm7, Pm8, Pm17 and PmJZHM2RL. Chromosome observation, molecular marker, and A-PAGE analysis suggested that 07jian126 might be a rye introgression line
and neither contain 1RS translocation nor secalins gene. Consequently, 07jian126 could be considered as a valuable resource
for Pm resistance development of wheat. Besides, the molecular markers Xbarc183 and O5 are useful in marker-assisted selection of Pm07J126 in wheat breeding programs. 相似文献
969.
970.