全文获取类型
收费全文 | 402901篇 |
免费 | 21583篇 |
国内免费 | 10285篇 |
专业分类
林业 | 33794篇 |
农学 | 26447篇 |
基础科学 | 10239篇 |
60151篇 | |
综合类 | 71939篇 |
农作物 | 21965篇 |
水产渔业 | 20801篇 |
畜牧兽医 | 148146篇 |
园艺 | 10046篇 |
植物保护 | 31241篇 |
出版年
2022年 | 3607篇 |
2021年 | 5976篇 |
2020年 | 5905篇 |
2019年 | 6641篇 |
2018年 | 6324篇 |
2017年 | 7788篇 |
2016年 | 7757篇 |
2015年 | 8458篇 |
2014年 | 9648篇 |
2013年 | 21057篇 |
2012年 | 13862篇 |
2011年 | 16625篇 |
2010年 | 14162篇 |
2009年 | 13964篇 |
2008年 | 14743篇 |
2007年 | 14101篇 |
2006年 | 14177篇 |
2005年 | 12864篇 |
2004年 | 10357篇 |
2003年 | 10012篇 |
2002年 | 9219篇 |
2001年 | 10028篇 |
2000年 | 9824篇 |
1999年 | 9009篇 |
1998年 | 6040篇 |
1997年 | 5882篇 |
1996年 | 5514篇 |
1995年 | 5968篇 |
1994年 | 5282篇 |
1993年 | 5001篇 |
1992年 | 6677篇 |
1991年 | 6888篇 |
1990年 | 6613篇 |
1989年 | 6412篇 |
1988年 | 5747篇 |
1987年 | 5704篇 |
1986年 | 5655篇 |
1985年 | 5583篇 |
1984年 | 5032篇 |
1983年 | 4581篇 |
1982年 | 3577篇 |
1981年 | 3395篇 |
1980年 | 3308篇 |
1979年 | 4425篇 |
1978年 | 3838篇 |
1977年 | 3415篇 |
1974年 | 3797篇 |
1973年 | 3760篇 |
1972年 | 3509篇 |
1971年 | 3356篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
Still Only One Earth. Progress in the 40 years since the First UN Conference on the Environment. By R.E. Hester & R.M. Harrison (eds). Published by Royal Society of Chemistry,Cambridge, 2015. vii + 285 pp. £67.50. Hardback (ISBN 978‐1‐78262‐076‐1).
下载免费PDF全文
R. L. Hough 《Soil Use and Management》2017,33(1):176-176
33.
Fabio Soller Luke A. Roy D. Allen Davis 《Journal of the World Aquaculture Society》2019,50(1):186-203
Stearine fish oil (SFO) and palm oil (PO) have emerged as promising alternatives for the replacement of fish oil (FO) in aquafeeds. This study evaluated the replacement of FO with alternative oils in practical diets for Litopenaeus vannamei. In a clear brackish water study (14.1 g/L) utilizing shrimp (0.29 ± 0.02 g, initial weight), FO was replaced by SFO at inclusion ratios of 100:0, 75:25, 50:50, 25:75, and 0:100 (FO:SFO) and PO as 90% of FO. After 55 days, no significant differences (p < 0.05) in final weight, growth, or survival of shrimp were observed. A second trial (8 weeks) in low‐salinity water (2.1 g/L) with shrimp (0.92 ± 0.02 g, initial weight) evaluated diets with 100% FO, 100% SFO, 90% PO, 90% soybean oil (SO), or 90% flaxseed oil (FXO) as a replacement for FO and four commercially produced diets with 2% of FO, SO, PO, or FXO. One treatment received half rations of the commercial FO diet, and one treatment was based entirely on natural productivity. Results show that the fatty acid profiles of the tail muscle conformed to the lipids of the feed, and highly unsaturated fatty acids (HUFAs) were preserved. Following 8 weeks of culture, there were no significant differences in production performance. 相似文献
34.
35.
Compatibility of root growth and tuber production of potato cultivars with dynamic and static water‐saving irrigation managements 下载免费PDF全文
S. H. Ahmadi M. Agharezaee A. A. Kamgar‐Haghighi A. R. Sepaskhah 《Soil Use and Management》2017,33(1):106-119
The important root characteristics of root length density (RLD) and root mass density (RMD) generally differ among irrigation managements and potato cultivars. The objective of this study was to investigate the RLD and RMD variations and their functional relationships with gross potato tuber yield for two commercial potato cultivars, Agria and Sante, under different irrigation strategies. Full irrigation and water‐saving irrigation strategies, deficit and partial root drying irrigations, were applied statically (S) and dynamically (D) based on daily crop evapotranspiration. Results showed that SPRD had significantly greater RLD (3.64 cm/cm3) and RMD (132.7 μg/cm3) than other irrigation treatments. Between the potato cultivars, Agria had significantly larger values of RLD (3.50 cm/cm3) and RMD (138.7 μg/cm3) than Sante. The functional relationship between the root growth characteristics and tuber yield showed that under water‐saving irrigations, Agria increased root mass at the expense of gross tuber yield but Sante increased root mass to maintain larger gross tuber yields. However, Agria produced more roots and gross tuber yield than Sante, and it is concluded that Agria is a more drought‐tolerant potato cultivar, which is recommended for tuber production in regions where water might be scarce. It was shown that larger root production in potatoes was associated with improved tolerance to water stress. 相似文献
36.
Lampreys have a complex life cycle which includes a multi‐year infaunal larval stage (ammocoete). Gut content analysis has generally identified detritus (i.e., unidentifiable organic matter) as the major dietary component to ammocoetes, though algae can also be important. However, gut content preserves only a snapshot of the animal's diet and does not reflect assimilated material. In order to better characterise the nutritional sources supporting ammocoete growth, we analysed ammocoete body tissue and potential dietary sources at two streams using natural Δ14C and δ15N to estimate time‐integrated nutritional support. Bayesian isotope mixing models revealed differences in the importance of sources supporting ammocoetes between sites. Ammocoetes from a stream in a mixed land usage area (~50% agriculture, ~40% forest and ~10% developed) were primarily supported (mean: ~50%) by fresh terrestrial organic matter but were also supported by substantial contributions (mean: ~30%) by aged organic matter (AOM) and autochthonous material (algae; mean ~20%). In a predominantly forested (~90%) headwater stream, different modelling scenarios (uninformed or informed priors) suggested that algal support of ammocoete nutrition ranged from 7% to 45%. However, the model relying on informed priors developed from gut content analysis produced the low estimates, suggesting these were more reliable. When algae were a minor component of the nutrition at the forested site, ammocoetes were highly dependent on AOM (83 ± 26%; mean ± SD). Based on these findings, ammocoete growth and development are predicted to be strongly influenced by both land use and the availability of allochthonous and autochthonous materials of varying ages within streams. 相似文献
37.
基于农业科技创新的发展需求,为农业科技资源的有效配置提供支撑,从文献计量角度对全球植物科学领域研究现状及态势进行分析。利用定性、定量相结合的方法构建检索策略,基于Web of Science数据库及文献计量分析工具,对文献发表量、文献主要贡献国家、机构、期刊及发文量较高的作者H指数进行统计分析。结果表明,1995—2018年植物科学领域的文章发表量整体上呈现稳定增长趋势,学科呈现蓬勃发展的整体势头。美国和中国是文献主要贡献国家,文献量和总被引频次显著高于其他国家,但美国及欧洲国家的篇均被引数量高于中国。从全球来看,中国科研机构在发文数量占有绝对优势,而德国马克思普朗克的文章篇均被引数量高,达到10以上。对2016—2018年的高被引文献(Top10)进行内容分析,并通过高频词共现主题聚类可视化分析。从论文影响力及主题词规模2个维度表征领域内研究方向。结果表明,“植物应对生物及非生物胁迫”、“基因编辑技术”、“基因组学分析”、“植物生殖发育调控”是近年来植物科学的高关注度研究方向,主题内容与前期的需求调研相符,初步预测这些研究方向将对农业创新发展起到重要推动作用。 相似文献
38.
39.
40.
通过对白屈菜低温应答过程的转录组分析发现膜脂不饱和化相关基因的表达在一定过程中发生变化,脂肪酸去饱和酶基因FAD2在随温度的变化趋势为正"V"型,且表达量变化显著。利用NCBI等在线软件对序列进行相关生物学信息分析,并对白屈菜FAD家族成员FAD2基因的完整开放阅读框(ORF)进行克隆,并命名为CmFAD2。选用克隆载体pMD-19-T,转化大肠杆菌DH5α,测序验证序列正确性及完整性。将目的基因与植物表达载体pRI-201-AN连接构建重组DNA pRI-201-AN-Cm FAD2,电击法转化农杆菌LBA4404,利用菌液PCR法验证成功。该基因可作为药用植物抗寒品种创制的候选基因。 相似文献