全文获取类型
收费全文 | 174723篇 |
免费 | 9346篇 |
国内免费 | 16693篇 |
专业分类
林业 | 12124篇 |
农学 | 9728篇 |
基础科学 | 9062篇 |
17873篇 | |
综合类 | 82956篇 |
农作物 | 12085篇 |
水产渔业 | 7525篇 |
畜牧兽医 | 28014篇 |
园艺 | 13097篇 |
植物保护 | 8298篇 |
出版年
2024年 | 1475篇 |
2023年 | 3771篇 |
2022年 | 8116篇 |
2021年 | 7980篇 |
2020年 | 7436篇 |
2019年 | 7392篇 |
2018年 | 5413篇 |
2017年 | 8296篇 |
2016年 | 5589篇 |
2015年 | 8388篇 |
2014年 | 8786篇 |
2013年 | 10611篇 |
2012年 | 14533篇 |
2011年 | 15009篇 |
2010年 | 14465篇 |
2009年 | 12685篇 |
2008年 | 13012篇 |
2007年 | 11770篇 |
2006年 | 9570篇 |
2005年 | 7477篇 |
2004年 | 4778篇 |
2003年 | 2993篇 |
2002年 | 3113篇 |
2001年 | 2817篇 |
2000年 | 2667篇 |
1999年 | 1011篇 |
1998年 | 187篇 |
1997年 | 180篇 |
1996年 | 130篇 |
1995年 | 131篇 |
1994年 | 145篇 |
1993年 | 123篇 |
1992年 | 130篇 |
1991年 | 110篇 |
1990年 | 65篇 |
1989年 | 52篇 |
1988年 | 48篇 |
1987年 | 46篇 |
1986年 | 47篇 |
1985年 | 10篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1981年 | 31篇 |
1965年 | 4篇 |
1962年 | 35篇 |
1958年 | 4篇 |
1957年 | 7篇 |
1956年 | 58篇 |
1955年 | 29篇 |
1953年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
In this study, we used microsatellite‐based parentage analysis to assess the mating system of a mass spawning bay scallop, Argopecten irradians irradians. Parental assignment was performed on 237 offspring and 14 candidate parents. Overall, 95% of all offspring were unambiguously allocated to their putative parents based on information from six highly polymorphic loci. Offspring from both the self‐fertilization and cross‐fertilization style were observed, the large variation of self‐fertilization rate among individuals displays a mixed mode of mating. The high variances in reproductive success resulted in a decline in effective breeding numbers (Nb/N = 0.71). The self‐fertilization rate was 32.89% for this mass spawning and the coefficient of inbreeding was estimated at around 16.5% per generation. When selfed larvae were removed, the relationship between relatedness and individual reproductive success was proved insignificant between half‐sibings and unrelated, which suggest that selection pressures other than avoidance of inbreeding may be responsible for the evolution and maintenance of the self‐compatible mating system of A. i. irradians. These results lend insight to A. i. irradians cultivation in present China and provide a genetic basis for the development of more effective spawning techniques. 相似文献
82.
应用投影寻踪技术与聚类分析相结合的数学手段,通过对福建、台湾的81个县(市、区)的数据处理,对森林景观资源进行了分类区划。结果表明:福建生态旅游资源大致由内陆向沿海递减,即由内陆到沿海分别为第一等级、第二等级、第三等级;台湾生态旅游资源由中部山脉向东西两岸递减,即中部第一等级,东部第二等级、西部第三等级,这与福建及台湾的生态资源的地理分布相似。 相似文献
83.
银杏引种丹东地区以后,经长期栽培驯化,已经能完全适应该地区的气候条件,且生长稳定。在丹东地区栽培的银杏品种有10个。调查表明,生长表现的排序依次为大梅核、小梅核、佛指、大园铃、大金坠、大马铃、大白果、龙眼、卵果佛手、洞庭皇。 相似文献
84.
85.
Altitude affects leaf stoichiometry by regulating temperature and precipitation, and influencing soil properties in mountain ecosystems. Leaf carbon concentration(C), leaf nitrogen concentration(N),leaf phosphorous concentration(P), and their stoichiometric ratios of Leontopodium lentopodioides(Willd.)Beauv., a widespread species in degraded grasslands, were investigated to explore its response and adaptation strategy to environmental changes along four altitude gradients(2500, 3000, 3500, and 3... 相似文献
86.
介绍了森林保护机械设备的主要种类及其发展,分析了各种机械的特点及适用场合. 相似文献
87.
88.
89.
QU Shao-hua ZHANG Jie ZHANG Wei HUANG Yan-hua ZHANG Qing WANG Ning-xia L Rong-zhao 《园艺学报》2018,34(10):1900-1904
AIM: To investigate the relationship of tumor budding with clinicopathologic parameters, tumor-infiltrating lymphocytes (TILs) of tumor microenvironment and the prognosis in breast cancer patients.METHODS: A total of 178 HE section samples were collected from the breast cancer patients treated with surgery in the First Affilated Hospital of Jinan University during Jan. 2012 to Dec. 2016. The tumor budding and stromal tumor-infiltrating lymphocytes were observed under light microscope. The correlation of tumor budding with the clinicopathologic status and TILs were analyzed by χ2 test. Kaplan-Meier survival analysis and Log-rank test were used to estimate the disease-free survival (DFS) and overall survival (OS).RESULTS: High tumor budding level was associated with more positive lymph nodes, higher grade, and more lymphovascular invasion. In addition, the patients with higher tumor budding level showed fewer TILs, while the patients with lower tumor budding level had more TILs. Furthermore, the patients with higher tumor budding level had a worse disease-free survival and overall survival than those with lower tumor budding level.CONCLUSION: Tumor budding is significantly associated with adverse clinicopathological characteristics of breast cancer and negatively correlated with TILs. Therefore, tumor budding may serve as a potential biomarker to predict the prognosis of breast cancer. 相似文献
90.