首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   24671篇
  免费   571篇
  国内免费   50篇
林业   4093篇
农学   1683篇
基础科学   214篇
  4191篇
综合类   1310篇
农作物   2492篇
水产渔业   2424篇
畜牧兽医   5050篇
园艺   1228篇
植物保护   2607篇
  2023年   81篇
  2022年   129篇
  2021年   261篇
  2020年   261篇
  2019年   324篇
  2018年   2929篇
  2017年   2912篇
  2016年   1485篇
  2015年   292篇
  2014年   340篇
  2013年   495篇
  2012年   1275篇
  2011年   2617篇
  2010年   2338篇
  2009年   1514篇
  2008年   1715篇
  2007年   1976篇
  2006年   412篇
  2005年   461篇
  2004年   438篇
  2003年   449篇
  2002年   394篇
  2001年   250篇
  2000年   283篇
  1999年   207篇
  1998年   58篇
  1997年   59篇
  1996年   55篇
  1995年   54篇
  1994年   37篇
  1993年   50篇
  1992年   86篇
  1991年   56篇
  1990年   64篇
  1989年   71篇
  1988年   72篇
  1987年   52篇
  1986年   46篇
  1985年   58篇
  1984年   38篇
  1983年   43篇
  1982年   30篇
  1980年   24篇
  1979年   37篇
  1978年   21篇
  1977年   23篇
  1974年   23篇
  1973年   25篇
  1972年   25篇
  1970年   26篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
101.
102.
Umma Tamima 《林业研究》2016,27(4):853-861
The objective was to evaluate the performance of the co-management of Nishorgo Support Project at Chunati Wildlife Sanctuary in Bangladesh. I adopted the Focus Groups Discussion method for opinion survey and applied the SWOTAHP technique for data analysis. Local people did not participate in the decision-making process of forest management and they perceived co-management as a threat to their livelihoods. Moreover, mistrust and misunderstanding among different stakeholders, political and ethical conflicts, lack of property rights of tribal communities, and lack of accountability and transparency were identified as the drawbacks of co-management.  相似文献   
103.
104.
105.
106.
Different stunning methods (carbon dioxide [CO2] and hypothermia) used in industrial fish processing were compared with asphyxia in air, which is used in traditional fishing, to evaluate the effects of these methods on the stress responses and the meat quality of the Amazon hybrid surubim, Pseudoplatystoma fasciatum female × Leiarius marmoratus male. After the application, blood and behavioral indicators were evaluated. Following death by gill cutting, the fish were gutted, and analyses of muscle pH, rigor mortis, the exudation of the meat, and coloration were performed. Significantly higher levels of cortisol and glucose were exhibited by the fish subjected to asphyxia than by the fish stunned by either CO2 or hypothermia. The fish subjected to asphyxia displayed decreasing muscle pH during the first 2 h after death and showed higher rates of rigor mortis after 3 h than the fish that were stunned by the other two methods. The asphyxia is a practice that exposes fish to suffering by causing an increase in stress responses, which affects meat quality. The immersion of fish in water and ice (hypothermia) for 5 min was more effective stunning method than the use of CO2, resulting in higher loss of sensibility and greater welfare.  相似文献   
107.
The aim was to evaluate the effect of different concentrations of caffeine added in activating solution over sperm motility in fresh and thawed semen of pacu, Piaractus mesopotamicus, and curimba, Prochilodus lineatus. The activating solutions were prepared with sodium bicarbonate solution of 0.76% (NaHCO3) and caffeine was added at concentrations of 2.5, 5.0, 10.0, and 20.0 mM. As control, a solution of NaHCO3 0.76 without caffeine was used. Eight males of pacu and 20 males of curimba were used. Aliquots of 200 μL of semen were diluted in 800 μL extender solution (DMSO 10% and BTS 5%), placed in 0.5 mL straws and cryopreserved for 7 d in a liquid nitrogen tank. There was a linear increase in sperm motility for fresh semen of pacu, and for curimba fresh and thawed semen (P < 0.05), due to the increase in the concentration of caffeine. There was a quadratic response for duration of motility for thawed semen of pacu and for fresh semen of curimba (P < 0.05), respectively. These results indicate that addition of caffeine in the activator solution can improve sperm motility parameters, however, is dependent on the species and concentration used.  相似文献   
108.
This study aimed to evaluate the exogenous progesterone (P4) effect on the luteal function from Day 16 to Day 21 of the oestrous cycle in inseminated goats with unknown pregnancy status. A total of 54 does passed through a short progestin-based synchronization protocol and, on Day 16 of the following oestrous cycle, 27 does received a new P4 device which was retained until Day 21. Blood samples were collected daily from all does during this period, as well as on Day 24. Pregnancy diagnoses were performed on Day 30. Serum P4 values from 26 animals (GNPSP: Group of non-pregnant does with second sponge: n = 8; GNPNSP: Group of non-pregnant does without second sponge: n = 6; GPSP: Group of pregnant does with second sponge: n = 5; GPNSP: Group of pregnant does without second sponge: n = 7) were determined by radioimmunoassay commercial kits. No P4 differences were found between groups (GNPSP: 3.1 ± 2.8; 1.7 ± 1.8; 0.4 ± 1.0; and 0.0 ± 0.0 vs. GNPNSP: 4.4 ± 1.8; 3.0 ± 2.2; 0.8 ± 0.8; and 0.0 ± 0.0 or GPSP: 4.2 ± 1.0; 3.4 ± 0.6; 3.3 ± 1.6; 3.2 ± 0.9; 3.6 ± 1.2; 3.5 ± 1.3; 2.7 ± 1.3 vs. GPNSP: 4.4 ± 1.6; 3.6 ± 1.5; 3.7 ± 1.5; 3.8 ± 1.4; 3.2 ± 1.2; 3.1 ± 1.2; 3.6 ± 1.1; D16, D17, D18, D19, D20, D21, D24, respectively) or for the interaction of group and time. In conclusion, a second progestogen device had no effect on luteolysis or early pregnancy in the following oestrous cycle.  相似文献   
109.
It is desirable to develop an objective Soil Quality Index (SQI) to guide sustainable agronomic intensification, thereby promoting socio‐economic well‐being. This study pioneers the use of Ward's cluster and principal component regression methods to evaluate soil homogeneity and construct a SQI (expressed as %). Field data were acquired from five different sites within Ohio, USA, that were under no‐till (NT), conventional till (CT) management and natural vegetation (NV) land use. Soil pH, carbon/nitrogen (C/N) ratio, nitrate and soil organic carbon (SOC) concentrations were identified as primary drivers of soil quality. Based on Ward's cluster method, the soil properties of croplands were not significantly different from those under NV land use. However, SQI ranked surface soils under CT management as higher in quality than NV and NT managed soils, respectively. The coefficient of determination (R2) between SQI and corn (Zea mays L.) and soya bean [Glycine max (L.) Merr.] yields was 0.7 and 0.9, respectively, implying this SQI effectively relates soil properties, a function of anthropogenic land management practices, with crop yields. In future, time series analyses will be used to assess SQI versus crop yield dynamics, with key socio‐economic and climate variables.  相似文献   
110.
The effects of water and salt stress on rate of germination and seedling growth were investigated under laboratory conditions in 46 soya bean genotypes from Central-West region of Brazil to verify how these stresses may limit crop establishment during the initial growth stage and also to identify the most tolerant genotypes to drought and salinity. Mild water and salt stresses were imposed by seed exposure to –0.20 MPa iso-osmotic solutions with polyethylene glycol—PEG 6000 (119.57 g/L) or NaCl (2.357 g/L) for 12 days at 25°C. The germination percentage, seedling length and seedling dry matter were measured, and then, salt or drought tolerance indexes were calculated. The “NS 5909 RG,” “NS 7000 IPRO,” “NS 7338IPRO,” “FPS Solimões RR,” “NS 5151 IPRO,” “SYN 13610 IPRO,” “LG 60177 IPRO,” “NS 6909 IPRO” and “BMX Desafio RR” were identified as the most drought-tolerant genotypes, whereas under salinity conditions, the genotypes “5D 615 RR,” “BMX Desafio RR,” “5D 6215 IPRO” and “BMX Ponta IPRO” were identified as tolerant. The “BMX Desafio RR” is the genotype most adapted to both stress conditions and, therefore, should be used under conditions of water shortage and excess salt in the soil at sowing time.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号