全文获取类型
收费全文 | 40965篇 |
免费 | 2479篇 |
国内免费 | 4175篇 |
专业分类
林业 | 5087篇 |
农学 | 6265篇 |
基础科学 | 3297篇 |
6883篇 | |
综合类 | 12067篇 |
农作物 | 2607篇 |
水产渔业 | 1679篇 |
畜牧兽医 | 5322篇 |
园艺 | 1443篇 |
植物保护 | 2969篇 |
出版年
2024年 | 438篇 |
2023年 | 427篇 |
2022年 | 1146篇 |
2021年 | 1623篇 |
2020年 | 1464篇 |
2019年 | 1476篇 |
2018年 | 1004篇 |
2017年 | 1324篇 |
2016年 | 1281篇 |
2015年 | 1734篇 |
2014年 | 1583篇 |
2013年 | 2086篇 |
2012年 | 2329篇 |
2011年 | 2548篇 |
2010年 | 2381篇 |
2009年 | 2376篇 |
2008年 | 2222篇 |
2007年 | 2310篇 |
2006年 | 2088篇 |
2005年 | 2118篇 |
2004年 | 985篇 |
2003年 | 852篇 |
2002年 | 722篇 |
2001年 | 800篇 |
2000年 | 919篇 |
1999年 | 1293篇 |
1998年 | 1090篇 |
1997年 | 931篇 |
1996年 | 898篇 |
1995年 | 793篇 |
1994年 | 739篇 |
1993年 | 725篇 |
1992年 | 586篇 |
1991年 | 524篇 |
1990年 | 431篇 |
1989年 | 356篇 |
1988年 | 279篇 |
1987年 | 172篇 |
1986年 | 134篇 |
1985年 | 81篇 |
1984年 | 49篇 |
1983年 | 41篇 |
1982年 | 41篇 |
1981年 | 54篇 |
1980年 | 32篇 |
1979年 | 24篇 |
1978年 | 11篇 |
1965年 | 10篇 |
1964年 | 13篇 |
1963年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
11.
The green sea urchin (Strongylocentrotus drobachiensis) fishery is of great importance to Maine’s economy. The fishery took off in the late 1980s as a result of expanding export markets, but has experienced substantial decline in landings since 1992 because of large decreases in urchin stock abundance. Fishery-independent surveys have not been conducted, and no formal stock assessment has been done prior to this study. Using the data collected from the fishery and urchin life history parameters derived from scientific studies, we conducted a formal stock assessment for the urchin stock. A stochastic observation-error length-structured model is used to describe the dynamics of the sea urchin population. A robust Bayesian approach is used for estimating fishery parameters because of concerns of possible outliers in fisheries data and mis-specification of priors. This study shows that the current stock is only 10% of the virgin stock biomass and that the exploitation rate is close to 40% suggesting that a large reduction in exploitation rate is necessary. 相似文献
12.
Tse-Hung Huang Chiao-Hsu Ke Chin-Chang Chen Cheng-Hsun Chuang Kuang-Wen Liao Yi-Hsien Shiao Chen-Si Lin 《Marine drugs》2022,20(4)
Freshwater clam extract (FCE) is a functional food that regulates the immune system and has been demonstrated in numerous studies to display desirable anti–tumor necrosis factor-alpha (TNF-α) responses. In addition, excess TNF-α production is positively associated with type 2 diabetes. However, few longitudinal clinical studies evaluating the efficiency and toxicity of FCE are available. This article reports that patients with prediabetes who received FCE had a desirable outcome of a reduction in serum TNF-α for a long period. This was a double-blind, randomized, parallel clinical trial conducted using FCE intervention and placebo groups, and 36 patients with prediabetes were enrolled. Two grams of FCE or placebo was consumed daily for 180 consecutive days. The serum of the participants was collected at four time points (0M: before the intervention; 3M: after 3 months of intervention; 6M: after 6 months of intervention; 12M: 6 months after cessation of intervention at 6M). A serum TNF-α concentration higher than 4.05 pg/mL was defined as a cut-off value. FCE reduced serum TNF-α in all participants at 6M and 12M. Moreover, FCE significantly suppressed serum TNF-α concentrations at 6M and 12M and inhibited TNF-α release with time series in subjects with elevated TNF-α values. FCE intervention effectively reduced serum TNF-α and persistently sustained the effects for half a year in patients with prediabetes. Gas chromatography–mass spectrometry (GS-MS) analysis revealed that the major components of FCE were phytosterols and fatty acids, which exerted anti-inflammatory and anti-TNF-α abilities. Hence, FCE has the potential to be developed as a natural treatment for prediabetic patients in Taiwan. 相似文献
13.
通过4a来对延平区马铃薯产业的调查研究,脱毒马铃薯品种的引进筛选,示范推广的实践,分析马铃薯产业现状,探讨存在的问题,提出发展对策,为进一步加快延平区的马铃薯产业发展提供依据。 相似文献
14.
“辉杰”为1头黑色、雄性缉毒犬,2001年7月出生于昆明。2002年7月“应征入伍”到云南公安边防总队瑞丽江桥警犬复训基地服现役至今。2002年7月至2004年年底,在训犬员罗祥彬的带领下多次参加边防执勤设伏堵卡和公开查缉查获毒品近4千克,抓获犯罪嫌疑人3名,被上级授予“三级功勋犬”称号。 相似文献
15.
基于单片机的光电式叶片面积测量系统 总被引:1,自引:1,他引:1
在农业生产中,叶片面积及其参数是衡量农作物产量的重要因素。传统叶片面积检测方法过程复杂,不能实现自动测量。为此,针对农业中田间叶片面积的实时测量需要,设计了基于单片机的光电式叶片面积测量系统;阐述了系统的整体设计思路、结构、测量原理、系统误差的计算及外部电路的设计。 相似文献
16.
17.
A possible Lower Cambrian chaetognath (arrow worm) 总被引:1,自引:0,他引:1
18.
19.
20.
Chen Changguo Liao Bogang 《保鲜与加工》1993,(2):70-72
In this paper,we put forward a method of direct factor analysis with discrete X-ray diffraction patterns, which was supported by the experimental measurement with the mixture containing 2,3,4,5 phases respectively. The detailed discussion was also given to its principles,errors and criterion. 相似文献