全文获取类型
收费全文 | 438篇 |
免费 | 24篇 |
国内免费 | 32篇 |
专业分类
林业 | 40篇 |
农学 | 24篇 |
基础科学 | 74篇 |
41篇 | |
综合类 | 128篇 |
农作物 | 18篇 |
水产渔业 | 59篇 |
畜牧兽医 | 80篇 |
园艺 | 14篇 |
植物保护 | 16篇 |
出版年
2024年 | 2篇 |
2023年 | 8篇 |
2022年 | 9篇 |
2021年 | 12篇 |
2020年 | 16篇 |
2019年 | 12篇 |
2018年 | 9篇 |
2017年 | 11篇 |
2016年 | 13篇 |
2015年 | 21篇 |
2014年 | 25篇 |
2013年 | 27篇 |
2012年 | 19篇 |
2011年 | 22篇 |
2010年 | 35篇 |
2009年 | 30篇 |
2008年 | 32篇 |
2007年 | 27篇 |
2006年 | 20篇 |
2005年 | 19篇 |
2004年 | 16篇 |
2003年 | 18篇 |
2002年 | 10篇 |
2001年 | 12篇 |
2000年 | 13篇 |
1999年 | 8篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 10篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有494条查询结果,搜索用时 31 毫秒
31.
Judging watermelon quality based on its apparent properties such as size or skin color is difficult. A non-destructive method is employed here, based on vibrational response spectrum, to determine the quality indices of watermelon (Charleston gray). The responses of samples to vibration excitation were recorded by laser Doppler vibrometry (LDV). The phase shift between input and output signals were extracted over a wide frequency range. The total soluble solids (TSS), titratable acidity (TA) and TSS/TA ratio also measured as watermelon quality characters. Stepwise multiple linear regression (SMLR) as well as partial least square regression (PLS) was applied to extracted vibration spectrums to construct prediction models of watermelon quality. The results showed that performance of SMLR models were better than PLS. The determination coefficients (R2) of SMLR validation models were 0.9976, 0.9985 and 0.9542 for TSS, TA and TSS/TA respectively. It is likely that reduction of cell wall materials to soluble solids during ripening process changes viscoelastic properties of watermelon reflected by vibrational response. This study demonstrated the feasibility of mentioned method for predicting the quality of watermelons in an industrial grading system. 相似文献
32.
激光技术在木材无损检测中的应用 总被引:2,自引:0,他引:2
本文总结了用于木材中的无损检测技术 ,着重论述了几种常用的激光无损检测技术在木材中应用的可能性 相似文献
33.
34.
在南朝鲜于1999年的2月至12月间,根据有关文献,调查问卷和对原麝的种类,粪便,及其在有雪和无雪的季节里的野外踪迹的调查,作者概述了50年中原麝的数量和分布区的变化。结果表明:从50年代至1999间,原麝(Moschus moschiferus parvipes)的分布区呈明显缩减之势。由于在原麝分布区中大规模地进行公路及林道的建设,导致了其生境片断化和丢失。而且牟取利润的非法猎捕也是造成原麝的种群数量和分布区缩减的主要原因,在高海拔地区的林道也常被盗猎者所利用。为保护韩国原麝资源,急待严格禁止非法猎捕行为。原麝生活习性方面的研究,为合理的保护和管理原麝提供了重要的基础信息。图1参9。 相似文献
35.
为合理开发利用巴蛸资源,为29.4~58.8kW渔船巴蛸拖网进行了改进设计,改成低口、长袖的结构形式,并配置驱赶铁链。与原拖网对比试验结果表明,新型巴蛸拖网比原底拖网增产巴蛸60%以上,增加产量50%以上,同时对传统经济鱼虾类有一定保护作用。 相似文献
36.
37.
38.
J.F. Hawkins L. Couetil M.A. Miller 《Veterinary journal (London, England : 1997)》2014,199(2):275-280
The objective was to evaluate CO2 laser debridement of the cricoarytenoid joint (CAJ) combined with prosthetic laryngoplasty to prevent post-operative loss of arytenoid abduction in seven horses. Horses were assigned to either laser debridement of the left CAJ and laryngoplasty (laser treated, n = 5) or control laryngoplasty (sham, n = 2), and were evaluated with endoscopic examinations and measurement of right to left angle quotients (RLQ) to assess maintenance of arytenoid abduction. The animals were euthanased at intervals after surgery and larynges were harvested for post-mortem testing, including determination of translaryngeal flow, pressure, impedance and RLQ. Measurements were obtained under increasing vacuum-generated negative pressure with laryngoplasty sutures intact and with the knot/crimp of the laryngoplasty sutures removed. Following post-mortem testing the cricoarytenoid joints were examined histologically.Post-operative endoscopic examinations revealed no significant differences between RLQ measurements calculated for day 1 following surgery to the termination date of the study for the seven horses. Post-mortem RLQ at airflows of 10 and 60 L/s was significantly higher in sham than in laser treated horses both before and after knot/crimp removal. Translaryngeal impedance at 10 and 60 L/s was not statistically different between groups. Histopathology revealed necrosis and loss of articular cartilage in the laser treated horses. The lymphoid cell infiltration subsided but joint capsule and periarticular fibrosis increased over the course of the study. Post-operative loss of arytenoid abduction after laryngoplasty can be minimized with CO2 laser debridement of the CAJ joint. 相似文献
39.
I. G. BAIRD 《Fisheries Management and Ecology》2006,13(1):1-8
Abstract Fish sanctuaries are types of aquatic protected areas common throughout the landlocked country of Lao PDR. The key to their successful implementation in Laos appears to be local support. Therefore, they fit well within the context of community-based fisheries/co-management programmes. Fish sanctuaries are almost always established in deep-water pools, which serve as important dry season refuges for fish. The best-known fish sanctuaries in Laos are known as Fish Conservation Zones (FCZs), and are found in the mainstream Mekong River in Khong district, Champasak province, southern Laos. In Khong, there is increasing evidence that FCZs established by villagers, but with government support, are important places of concentration for various fish species. FCZs can benefit fish stocks, especially relatively sedentary species, but also highly migratory ones. FCZs are not panaceas for solving all the fisheries problems in Laos or the Mekong River Basin, but they represent important management tools that should not be overlooked. 相似文献
40.
1PJ-4.0型水田激光平地机设计与试验 总被引:8,自引:0,他引:8
设计了三点悬挂1PJ-4.0型水田激光平地机。水田激光平地机液压系统,包括高程液压油路、水平液压油路和折叠液压油路,平地铲高程运动采用平行四连杆结构。对水田激光平地机的高程运动和水平运动性能进行了测试试验,分析结果表明:平地铲上升过程响应时间为下降过程响应时间的2倍,全程400 mm上升所需时间为3.31~4.23 s,下降所需时间稳定在1.7 s左右;上升速度随油门开度增大而加快,平地铲下降速度较稳定。平地铲水平调节时,顺时针转动全程20°所需时间与逆时针转动所需时间一致。田间平整作业试验表明,与拖拉机配套的三点悬挂1PJ-4.0型水田激光平地机可以稳定工作,能显著改善田面平整情况,田面最大高程差从平地前的32 cm降低到4.9 cm,相对高度的标准偏差值从平地前的12.28 cm下降到平地后的2.64 cm,平地后绝对差值小于等于3 cm采样测量点累计百分数达69.4%。 相似文献