全文获取类型
收费全文 | 1978篇 |
免费 | 81篇 |
国内免费 | 78篇 |
专业分类
林业 | 183篇 |
农学 | 262篇 |
基础科学 | 53篇 |
462篇 | |
综合类 | 283篇 |
农作物 | 141篇 |
水产渔业 | 130篇 |
畜牧兽医 | 443篇 |
园艺 | 50篇 |
植物保护 | 130篇 |
出版年
2023年 | 12篇 |
2022年 | 55篇 |
2021年 | 59篇 |
2020年 | 54篇 |
2019年 | 49篇 |
2018年 | 48篇 |
2017年 | 53篇 |
2016年 | 60篇 |
2015年 | 59篇 |
2014年 | 56篇 |
2013年 | 128篇 |
2012年 | 104篇 |
2011年 | 108篇 |
2010年 | 95篇 |
2009年 | 72篇 |
2008年 | 103篇 |
2007年 | 77篇 |
2006年 | 90篇 |
2005年 | 80篇 |
2004年 | 32篇 |
2003年 | 38篇 |
2002年 | 42篇 |
2001年 | 43篇 |
2000年 | 42篇 |
1999年 | 44篇 |
1998年 | 33篇 |
1997年 | 43篇 |
1996年 | 33篇 |
1995年 | 18篇 |
1994年 | 18篇 |
1993年 | 13篇 |
1992年 | 17篇 |
1991年 | 20篇 |
1990年 | 21篇 |
1989年 | 16篇 |
1988年 | 22篇 |
1987年 | 19篇 |
1986年 | 9篇 |
1985年 | 13篇 |
1983年 | 13篇 |
1981年 | 9篇 |
1979年 | 23篇 |
1977年 | 10篇 |
1976年 | 12篇 |
1971年 | 22篇 |
1970年 | 14篇 |
1969年 | 14篇 |
1967年 | 21篇 |
1966年 | 21篇 |
1965年 | 10篇 |
排序方式: 共有2137条查询结果,搜索用时 15 毫秒
101.
M Shahab Uddin S M Shamsul Rahman M Ekram Azim M Abdul Wahab M C Jarc Verdegem & Johan A J Verreth 《Aquaculture Research》2007,38(16):1759-1769
The present research investigated the effect of stocking density on pond (75 m2, depth 1.2 m) production of Nile tilapia (Oreochromis niloticus) and freshwater prawn (Macrobrachium rosenbergii) stocked at a fixed 3:1 tilapia:prawn ratio. Three stocking densities were tried in triplicate: 20 000 ha−1 (treatment TP‐20), 30 000 ha−1 (TP‐30) and 40 000 ha−1 (TP‐40). The ponds were provided with bamboo as substrate for periphyton development. Bamboo poles (mean diameter 5.5 cm and 5.0 poles m−2) were posted vertically into pond bottoms, resulting in 60% additional substrate area in each pond. On average, 43 genera of algae and 17 genera of zooplankton were identified from pond water, whereas 42 genera of algae and six genera of microfauna were attached to bamboo substrates. No differences were observed between treatments in the ash‐free dry matter (AFDM), chlorophyll a and phaeophytin a content of periphyton (P>0.05). Survival of tilapia and prawn and individual weight gain of tilapia were lower (P<0.05) in treatment TP‐40. The net yields were higher (P<0.05) in treatments TP‐30 (2209 and 163 kg ha−1 105 day−1 of tilapia and prawn respectively) and TP‐40 (2162 and 141 kg ha−1 of tilapia and prawn respectively) than in treatment TP‐20 (1505 and 136 kg ha−1 of tilapia and prawn respectively). The net tilapia yields were quadratic correlated (R2=0.92) with fish stocking density. The cost–benefit analysis shows that the net profit margin was highest in treatment TP‐30 (69%), followed by TP‐20 (50%) and TP‐40 (44%). 相似文献
102.
103.
Oliver Schneider Abdul K Amirkolaie Jordi Vera-Cartas Ep H Eding Johan W Schrama & Johan A J Verreth 《Aquaculture Research》2004,35(14):1370-1379
This study shows that alternatives for fishmeal in a fish diet affect not only fish growth but also faeces stability and nitrogen (N) and phosphorus (P) waste production. Wheat gluten diet (WGD), soybean meal extract diet (SBE), soybean meal diet (SBM), duckweed diet (DWD) and single‐cell protein diet (SCP) were evaluated as a fishmeal replacement on a 15% weight weight?1 basis in tilapia diets. Fishmeal replacement affected dry matter (dm), protein, ash and P digestibility significantly. Faeces recovery (6.8–11.2%) was not significantly affected, although the amount of non‐recovered faeces and total faeces showed significant differences. Duckweed diet and SCP resulted in the largest amounts of non‐recovered and total faeces (199–210, 224–225 g dm kg?1 feed dm). Compared with fishmeal diet (FMD), the WGD and SBE resulted in similar growth, but higher non‐faecal N losses (471–495 vs. 416 g N kg?1 N). Soybean meal diet, DWD and SCP resulted in lower growth but less non‐faecal loss (409–450 g N kg?1 N). The DWD and FMD had the highest N retention (480 g N kg?1 N) compared with the other diets (431–451 g N kg?1 N). Carbon retention, faecal and non‐faecal losses and P retention were similar for all diets (302–358, 142–176 and 489–523g C kg?1 C, 606–704 g P kg?1 P). Phosphorus faecal loss was lower for all diets (329–381 g P kg?1 P) than for the FMD (401 g P kg?1 P). 相似文献
104.
Das Gour Gobindo Malek Md. Abdul Shamsuddin A. K. M. Sagor G. H. M. 《Genetic Resources and Crop Evolution》2022,69(3):1009-1018
Genetic Resources and Crop Evolution - Brassica napus L is an important oilseed crops grown throughout many parts of the world. It is well adapted to long day photoperiods. Synthetic B. napus was... 相似文献
105.
Liu Y. F. Liu Z. L. Rao H. Y. Wan X. Li L. H. Sun S. Y. Che M. X. Liu M. X. 《Eurasian Soil Science》2022,55(6):781-789
Eurasian Soil Science - Eight soil samples from the Jurassic Shaximiao Formation (J2s) in the Sichuan Basin, China, were taken as the research object to explore the correlation and quantitative... 相似文献
106.
Asma Ali Abahussain Abdelhadi Abdelwahab Mohamed Ahmed Ali Salih Ahmad Al Safe Nader Abdul Hamed Mosa Yahya Othman 《农业科学与技术》2014,(2):112-122
Monitoring and assessment of agricultural land degradation is of vital importance for better land and water management planning and reclamation. It requires setting baseline information and basic analysis at specific time and space. About 33 geo-referenced soil sampling spots were selected in two agricultural production locations in the Kingdom of Bahrain to assess the status and preliminary causes of land degradation. Soil samples were taken from 13 sites in Diraz location while 19 samples were taken from Budayyi location. The samples were taken to 90 cm depth at 30 cm intervals. Standard procedures were followed to determine soil physiochemical properties. In addition, field observations on farm condition, distance from the sea, method of irrigation and irrigation water source were taken. Some of the soil samples were deliberately taken from outside the irrigated basins among trees compared with samples taken from inside the actively growing area for comparison. The results indicated that the salinity level was significantly (P 〈 0.001) higher at the 0-30 cm soil depth compared with 30-60 cm or 60-90 cm depths in both locations. The distance from the sea did not show clear correlation with surface soil salinity in Budayyi area compared with Diraz. Both locations showed significantly higher salinity levels on samples taken outside the actively growing areas compared with those taken from within. The effect is more prominent at the 0-30 cm depth. The observed variability on salinity levels may be attributed to farm management practices and deteriorating quality of ground water. Thus, agricultural land degradation in Bahrain cannot be attributed to ground water deterioration alone. The use of tertiary treated sewage water (TSE) may ease the pressure on ground water, but the pH of the TSE should be carefully monitored and managed with proper studies on leaching requirements to avoid further salinity complications. 相似文献
107.
108.
The view that biodiversity-rich areas partially or largely managed by local residents, sometimes referred to as community-conserved areas (CCAs), can be effective in biological conservation has gained considerable ground over the past decade. In this paper, we review available scientific information on the conservation effectiveness of such areas globally. We compiled studies undertaken during the last 5 years (2004-2009) that use quantifiable ecological attributes to: (1) compare CCAs with strictly protected areas (SPAs); (2) compare CCAs with open-access ecosystems and (3) study trends in biological attributes of CCAs over time. We found that there were few consistent differences in diversity/species richness of flora or fauna protected under the two types of management or in deforestation rates. However, CCAs tend to harbour a species complement distinct from that of SPAs and show lowered abundances of monitored taxa that are of conservation importance. CCAs conserve biological values more effectively than open-access areas. Also, biological values tend to decline in CCAs over time. We conclude that CCAs could represent a significant improvement over open-access areas in terms of conservation effectiveness, yet fall short of the needs of comprehensive biological conservation. While extremely few studies have been undertaken in India, the trends seen largely concur with global ones. This review, based on a limited sample size, is only a beginning, and is expected to serve as an invitation for further research to address both the question of biological effectiveness of diverse forest governance regimes as well as the socio-economic, demographic and institutional reasons underlying these differences. 相似文献
109.
Qayyum Husain Zoheb Karim Zeeshan Zahoor Banday 《Water, air, and soil pollution》2010,212(1-4):319-328
Peroxidase from fenugreek (Trigonella foenum-graecum) seeds was highly effective in the decolorization of textile effluent. Effluent was recalcitrant to the action of fenugreek seeds peroxidase (FSP). However, in order to effectively decolorize effluent by peroxidase, the role of six redox mediators has been investigated. The maximum decolorization of textile effluent was observed in the presence of 1.0 mM 1-hydroxybenzotrizole, 0.7 mM H2O2, and 0.4 U ml?1 of FSP in the buffer of pH 5.0 at 40°C in 2.5 h. The decolorization of textile effluent in a batch process by peroxidase was 85% in 5 h, whereas the complete decolorization of textile effluent by membrane-entrapped FSP was observed within 11 h of its operation. The absorption spectra of treated effluent exhibited a marked diminution in the absorbance at different wavelengths compared to untreated effluent. 相似文献
110.