全文获取类型
收费全文 | 42719篇 |
免费 | 2040篇 |
国内免费 | 4129篇 |
专业分类
林业 | 3562篇 |
农学 | 4681篇 |
基础科学 | 3218篇 |
5425篇 | |
综合类 | 19121篇 |
农作物 | 2560篇 |
水产渔业 | 1635篇 |
畜牧兽医 | 4959篇 |
园艺 | 1369篇 |
植物保护 | 2358篇 |
出版年
2024年 | 224篇 |
2023年 | 744篇 |
2022年 | 1400篇 |
2021年 | 1540篇 |
2020年 | 1546篇 |
2019年 | 1834篇 |
2018年 | 1175篇 |
2017年 | 1960篇 |
2016年 | 2236篇 |
2015年 | 2070篇 |
2014年 | 2483篇 |
2013年 | 2556篇 |
2012年 | 3691篇 |
2011年 | 3545篇 |
2010年 | 2816篇 |
2009年 | 2609篇 |
2008年 | 2275篇 |
2007年 | 2483篇 |
2006年 | 2081篇 |
2005年 | 1617篇 |
2004年 | 1200篇 |
2003年 | 904篇 |
2002年 | 723篇 |
2001年 | 606篇 |
2000年 | 553篇 |
1999年 | 553篇 |
1998年 | 464篇 |
1997年 | 415篇 |
1996年 | 348篇 |
1995年 | 374篇 |
1994年 | 291篇 |
1993年 | 267篇 |
1992年 | 280篇 |
1991年 | 233篇 |
1990年 | 214篇 |
1989年 | 204篇 |
1988年 | 142篇 |
1987年 | 89篇 |
1986年 | 46篇 |
1985年 | 13篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1962年 | 9篇 |
1956年 | 5篇 |
1955年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 656 毫秒
81.
82.
试验对5个香菇菌株进行简易开放式栽培并观察其特性,发现菌丝生长速度、锁状联合数与生物学效率相关性不密切,香菇的酶活性,子实体形成所需时间、子实体单重、菌盖重与生物学效率密切相关。 相似文献
83.
分析了牵引犁受力图解法求解所存在的问题,用解析方法建立了牵引犁受力的矩阵方程组并利用计算机进行了求解,预测了各结构参数变化对机组受力工况的影响,从而为牵引犁机组的合理配置和各部件结构的强度计算和优化设计提供了理论依据。 相似文献
84.
电脑图象分析在油菜及其近缘植物染色体研究中的应用 总被引:1,自引:1,他引:0
作者使用电脑图象分析仪对油菜及其近缘植物的9个种、50个品种作了染色体图象分析,并将上述植物的核型数据输入贮存在电脑中,初步建立了油菜及芸苔属植物核型分析数据的电脑数据库。在此基础上,作者讨论了油菜及芸苔属植物染色体电脑图象分析和电脑数据库在油菜基础理论研究和育种实际工作中的利用价值。 相似文献
85.
A method developed to evaluate the cumulative effect of wetland mosaics on water quality was applied to 33 lake watersheds in the seven-county region surrounding Minneapolis-St. Paul, Minnesota. A geographic information system (GIS) was used to record and measure landscape variables derived from aerial photos. Twenty-seven watershed land-use and land-cover variables were reduced to eight principal components which described 85% of the variance among watersheds. Relationships between lake water quality variables and the first six principal components plus an index of lake mixis were analyzed through stepwise multiple regression analysis. A combination of three landscape components (wetland/watershed area, agriculture/wetlands, and forest/soils components) explained 49% of the variance in a trophic state index, even though most of the lakes examined were already highly eutrophic, and thus were influenced by internal loading. The regression equations explained a range of 14 to 76% of the variation in individual water quality variables. Forested land-use was associated with lower lake trophic state, chloride, and lead. High lake trophic state was associated with agricultural land-use and with wetland distance from the lake of interest. The extent of wetlands was associated with low total lead and high color in lakes downstream. Wet meadows or herbaceous, seasonally-flooded wetlands contributed more to lake water color than did cattail marshes. 相似文献
86.
R-41, a sunflower restorer inbred line, carrying two genes for resistance against a highly virulent Spanish population of Orobanche cernua 总被引:1,自引:0,他引:1
J. Domínguez 《Plant Breeding》1996,115(3):203-204
The inheritance of resistance to a highly virulent population of sunflower broomrape (Orobanche cernua) has been studied in R-41, a Spanish sunflower restorer inbred line. Using the cytoplasmic male-sterile inbred line HA-89 (cms; very susceptible to this population of broomrape) as a female parent, progenies of the cross with R-41, i.e. Fl, F2 and BC1 to both parents, as well as the parental lines, were analysed for their reaction to the broomrape population EC-94. The goodness of fit of the observed vs expected segregation ratios indicated that the inheritance of resistance to broomrape in line R-41 is conferred by two independent dominant genes. 相似文献
87.
Mitchell A. Crystal DVM Dominique G. Penninck DVM Michael E. Matz DVM Susan H. Pearson BA Greg O. Freden DVM Richard M. Jakowski DVM 《Veterinary radiology & ultrasound》1993,34(6):438-444
The purpose of this study was to evaluate the usefulness of ultrasound-guided fine-needle aspiration biopsy and core biopsy in the diagnosis of infiltrative gastrointestinal diseases. Six dogs and seven cats with clinical signs of gastrointestinal disease underwent ultrasonography and intestinal lesions were identified. One or more ultrasound-guided fine-needle aspiration biopsy and/or core biopsy procedures were performed in each patient. Each patient also underwent one of the following additional procedures for comparison of results: 1) surgery (n=4), 2) endoscopy (n=2), 3) post mortem exam (n=3), and, 4) for lymphoma diagnosed with ultrasound-guided procedures, response to chemotherapy (n=4). Correct diagnoses were obtained in nine of the 13 patients, incorrect diagnoses in two of the 13 patients, and inconclusive diagnoses in two of the thirteen patients. Of the 16 total ultrasound-guided procedures performed, ten were confirmed as correct, three as incorrect, and three were non-diagnostic. Intestinal lesions with bowel wall thickness greater than 2.0 cm had a higher percentage of correct diagnoses than lesions of lesser wall thickness. Gastric lesions had a higher percentage of correct diagnoses than small and large intestinal lesions. Malignant lesions had a higher percentage of correct diagnoses than benign lesions. There were no complications. Ultrasound-guided gastrointestinal fine-needle aspiration biopsy and core biopsy appears to be a safe, accurate, and rapid procedure for use in the diagnosis of infiltrative gastrointestinal disease. 相似文献
88.
89.
90.