全文获取类型
收费全文 | 27746篇 |
免费 | 1322篇 |
国内免费 | 2355篇 |
专业分类
林业 | 3062篇 |
农学 | 2131篇 |
基础科学 | 4024篇 |
3822篇 | |
综合类 | 13364篇 |
农作物 | 788篇 |
水产渔业 | 834篇 |
畜牧兽医 | 1941篇 |
园艺 | 541篇 |
植物保护 | 916篇 |
出版年
2024年 | 109篇 |
2023年 | 360篇 |
2022年 | 558篇 |
2021年 | 704篇 |
2020年 | 737篇 |
2019年 | 842篇 |
2018年 | 538篇 |
2017年 | 861篇 |
2016年 | 1160篇 |
2015年 | 1020篇 |
2014年 | 1464篇 |
2013年 | 1415篇 |
2012年 | 2201篇 |
2011年 | 2324篇 |
2010年 | 1813篇 |
2009年 | 1867篇 |
2008年 | 1799篇 |
2007年 | 2115篇 |
2006年 | 1748篇 |
2005年 | 1463篇 |
2004年 | 1061篇 |
2003年 | 905篇 |
2002年 | 688篇 |
2001年 | 590篇 |
2000年 | 459篇 |
1999年 | 394篇 |
1998年 | 353篇 |
1997年 | 295篇 |
1996年 | 272篇 |
1995年 | 255篇 |
1994年 | 207篇 |
1993年 | 197篇 |
1992年 | 157篇 |
1991年 | 97篇 |
1990年 | 137篇 |
1989年 | 90篇 |
1988年 | 99篇 |
1987年 | 37篇 |
1986年 | 13篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1956年 | 2篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Improved milk production through PG–PL system by provision of in‐house shelter management in lactating Murrah buffaloes during winter season 下载免费PDF全文
N. Haque M. Singh S. A. Hossain 《Journal of animal physiology and animal nutrition》2018,102(1):166-174
Comprehensive information on the role of β‐casein and plasminogen–plasmin (PG–PL) system in milk secretion of Murrah buffaloes during winter season is lacking, although effects of cold stress can be ameliorated to an extent by altering microclimate at farm level. Hence, this study was aimed to determine the changes in productivity along with PG–PL system of milk, plasma hormones and metabolites of buffaloes during winter (December–January) season under two different management systems. Average minimum temperature and wind chill index during this season were 7.02 and 12.74 °C respectively. Buffaloes were divided in two groups of six animals each: control and treatment, where treatment group animals were placed in‐house with floor bedding of paddy straw and the control group animals in loose housing system without straw bedding. Physiological responses were recorded, and milk and blood samples were collected at weekly intervals for six‐week experimental period. Under in‐house management system, buffaloes experienced better comfort by alleviating environmental stress as their physiological responses such as respiration rate and pulse rate were significantly reduced (p < 0.01) as compared to the control, which subsequently resulted higher milk yield by 9.92% (p < 0.05). Analysis of milk samples revealed higher concentration of plasminogen (10.6 vs. 8.05 μg/ml; p < 0.01) and β‐casein (p < 0.05), and lower plasmin level (0.299 vs. 0.321 μg/ml; p < 0.05) in buffaloes under treatment group. It was also found that plasma cortisol, glucose and non‐esterified fatty acids levels were higher (p < 0.01) in control group as compared to the treatment animals by 13.6%, 8.14% and 12.6% respectively. However, milk composition, growth hormone, epinephrine and norepinephrine level in plasma were similar in both the groups. Hence, it may be concluded that provision of in‐house shelter management with floor bedding of paddy straw during winter was effective to minimize environmental stress and improved milk production through manipulation of PG–PL system in buffaloes. 相似文献
122.
ACE inhibition in goats under fixed‐time artificial insemination protocol increases the pregnancy rate and twin births 下载免费PDF全文
VP Fernandes Neto MNN Silva AS Costa D Kunkel AS Júnior LCS Feitosa MCS Muratori APR Costa 《Reproduction in domestic animals》2018,53(4):1006-1008
To assess the effect of the angiotensin‐converting enzyme (ACE) inhibition on the efficiency of the fixed‐time artificial insemination (TAI), 69 goats were divided randomly into two groups: enalapril (n = 35) and control (n = 34). In the experiment, all animals underwent the protocol of fixed‐time artificial insemination for 12 days. Enalapril group received enalapril maleate dissolved in saline (Enalapril, Lab Teuto Ltda) subcutaneously at the following doses: 0.2 mg/kg/day in D0‐D2; 0.3 mg/kg/day in D3‐D6 and 0.4 mg/kg/day in D7‐D11. The control group received the corresponding volume of 0.9% saline solution. We performed a single insemination 36 hr after sponge removal using frozen semen from two adult male goats with recognized fertility. The ultrasound pregnancy diagnosis was 30 days after the artificial insemination (AI). There was significant increase in pregnancy rates and twinning as well as a decrease in foetal loss in animals receiving enalapril (p < .01). The use of ACE inhibitors during the TAI protocol was shown to be a promising alternative to increase the efficiency of such reproductive biotechnology. 相似文献
123.
随着社会经济的发展,人们对户外登山健身的需求日益迫切。近年来,宁波市登山健身步道建设发展迅速,登山健身步道长度和登山游客规模快速增长,"步道经济"初步形成。为了适应宁波市登山健身步道建设发展的需要,该文在全面调查全市登山步道空间分布、沿线自然景观、游客规模及其需求的基础上,针对如何更好的利用宁波市优越的自然、历史、人文资源,从步道空间布局、自然和历史文化特色、基础设施建设、步道沿线自然景观优化等方面,对全市登山健身步道建设进行了初步探索,以期为其建设提供有价值的参考意见和建议。 相似文献
124.
Ecological ravages, environmental pollution, and the developmental problems of regional ecology, economy, and society are not geographical restrictions. The synergistic development of the ecology-economy-society system in forestry was quantitatively assessed by system theory and synergistic dynamic models, illustration of the metering principle and corresponding theory, assessing and quantizing synergistic development status of ecology-economy-society system, and the orderliness of the subsystem of the last decade. The orderliness of the ecology and ecological subsystems developed unstably with an increasing trend. The eco-environment construction and eco-conservation achievement of forestry in China are effective and need to be maintained. The industry structure should be improved to promote the growth of the forestry economy. The society subsystem development is increasing but is not at a high level, which indicates that the public demand to ecological service was not satisfied. The theoretical analysis and numerical examples show that the development of the forestry system has a good development state. The synergy changes of forestry system in the 0 to 0.951 range, which is in the intermediate degree of synergy during this period. It still needs much improvement on efficiency of synergy. The orderliness and the relationship among the subsystems of forestry should be improved in future. 相似文献
125.
Emin Zeki Başkent Ali İhsan Kadıoğulları 《Scandinavian Journal of Forest Research》2014,29(7):121-131
Decision support systems (DSSs) are indispensable tools in preparing a forest management plan for a better combination of multiple forest values. This study attempted to develop and explain a stand-based forest management DSS (Ecosystem-based multiple-use forest planning [ETÇAP]) comprising a traditional simulation, linear programming (LP), metaheuristics and geographic information system. The model consists of five submodels; traditional management approach to handle inventory data, an empirical growth and yield model, a simulation to conceptualize management actions, a LP technique to optimize resource allocation and a simulated annealing approach to directly create a spatially feasible harvest schedule. The ETÇAP model has been implemented in a comparative two case study areas; Denizli–Honaz and Akseki–Ibrad?. Both simulation and optimization models outperformed to the traditional management plan. The periodical change of growing stock, allowable cuts, carbon sequestration and water production are used as performance indicators. The results showed that more amount of wood could be harvested over time compared to traditional level of harvesting. It could be concluded that various management strategies allowed managers to stimulate more decision options for better outputs through intertemporal trade-offs of management interventions as the model provided tools to quantify forest dynamics over time and space. Challenges exist to establish the functional relationships between forest structure and values for better quantification and integration into the management plans. 相似文献
126.
控制系统是密闭式猪舍环境调控的关键组成部分.该研究系统归纳分析了应用于密闭式猪舍环境调控的4种控制系统,包括基于单片机控制系统、基于PLC控制系统、基于CAN总线的分布式控制系统和基于物联网的监控系统,总结出了各自的结构特点.结合工业控制技术、计算机技术和网络通讯技术的发展,提出了密闭式猪舍环境控制系统的发展趋势,对密闭式猪舍环境控制系统的设计具有一定的参考价值. 相似文献
127.
Within this paper we describe an unmanned aerial vehicle (UAV) based method to estimate the spatial feed pellet distribution in salmon fish-cages and exploit it within a case study to determine the radial pellet distribution for different rotor spreaders and blower configurations. Compared to previously used methods, capturing pellets thrown from a rotary feed spreader in rows of Styrofoam boxes, the UAV based method is simpler and faster to setup and allows to cover a larger portion of the sea cage surface area. We compare results obtained with the Styrofoam box method with results we obtained by an automatic analysis of aerial videos taken by the UAV during feeding experiments. The employed method helps to gain insight into the spatial feed pellet distribution in full-scale salmon fish-cages where the feeding pipe and actual fixation of the spreader may influence the dynamic behaviour of the feeding system. This can also be seen as a step towards a continuous measuring of the feed pellet distribution, particularly in view of possible future feeding systems that may allow to adapt the feed pellet distribution to the actual fish distribution. 相似文献
128.
自助借还作为一种先进的图书馆管理设备,已在很多图书馆中使用。本文通过自助借还机在石河子大学的使用实践,分析了自助借还系统的优势和不足,并提出相应的改进措施。 相似文献
129.
为了积极应对气候变化,促进低碳经济发展,分析了当前应对气候变化立法方面的研究进展,认为尽管取得了一定进展,但现有法律既不能满足我国气候外交的需求,也不足以担当气候治理的重任,我国还缺乏系统性专门性的应对气候变化法律.为了应对气候变化的挑战,必须充分整合国内外应对气候变化立法方面的科技资源,以保证我国气候外交和气候治理战略的科学性. 相似文献
130.
在地铁深基坑施工中,围护结构对基坑的安全起着至关重要的作用。本文依据合肥地铁一号线明光路站,施工过程中,由于车站3号出入口为出土口,原计划的第一道钢筋混凝土支撑无法实现,更改为钢支撑,通过有限元分析软件MIDAS-GTS\NX,建立二维模型进行数值模拟,对围护结构的变形和地表沉降进行分析,结果表明:第一道支撑采用钢支撑代替钢筋混凝土支撑对围护结构的侧移值影响不大,钢筋混凝土支撑控制地表沉降的效果要比钢支撑好,对今后类似工程变更提供依据。 相似文献