全文获取类型
收费全文 | 19517篇 |
免费 | 900篇 |
国内免费 | 1987篇 |
专业分类
林业 | 1024篇 |
农学 | 1677篇 |
基础科学 | 465篇 |
3077篇 | |
综合类 | 7212篇 |
农作物 | 1225篇 |
水产渔业 | 946篇 |
畜牧兽医 | 4497篇 |
园艺 | 1422篇 |
植物保护 | 859篇 |
出版年
2024年 | 75篇 |
2023年 | 283篇 |
2022年 | 529篇 |
2021年 | 722篇 |
2020年 | 693篇 |
2019年 | 832篇 |
2018年 | 542篇 |
2017年 | 837篇 |
2016年 | 1027篇 |
2015年 | 927篇 |
2014年 | 1042篇 |
2013年 | 1274篇 |
2012年 | 1505篇 |
2011年 | 1586篇 |
2010年 | 1359篇 |
2009年 | 1383篇 |
2008年 | 1134篇 |
2007年 | 1249篇 |
2006年 | 1050篇 |
2005年 | 741篇 |
2004年 | 600篇 |
2003年 | 467篇 |
2002年 | 393篇 |
2001年 | 291篇 |
2000年 | 280篇 |
1999年 | 260篇 |
1998年 | 144篇 |
1997年 | 166篇 |
1996年 | 171篇 |
1995年 | 142篇 |
1994年 | 106篇 |
1993年 | 103篇 |
1992年 | 87篇 |
1991年 | 72篇 |
1990年 | 62篇 |
1989年 | 54篇 |
1988年 | 49篇 |
1987年 | 39篇 |
1986年 | 33篇 |
1985年 | 22篇 |
1984年 | 15篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1962年 | 4篇 |
1956年 | 9篇 |
1955年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
《Communications in Soil Science and Plant Analysis》2012,43(15-20):2819-2831
Abstract Plant‐available phosphorus (P) measured by routine soil‐test methods is poorly correlated with rice grain yield in Arkansas. Our objective was to determine whether soil water pH (pHw) and Mehlich‐3 P were correlated with growth and yield of rice grown on silt loam soils. Data from 35 field studies were used to correlate Mehlich‐3 P and pHw with relative yield, dry matter accumulation, and P concentration at the midtillering stage. Significant linear or nonlinear relationships between pHw or Mehlich‐3 P with rice growth parameters were delineated but explained less than 27% of the variability in dry matter and P concentrations at the midtillering stage and grain yield at maturity. Mehlich‐3 P and pHw together explained 61% of the variability in midtillering P concentrations. Midtillering whole‐plant P concentrations were positively related to relative grain yield and dry matter production and will be used to identify soils with limited P availability for rice in Arkansas. 相似文献
992.
《Communications in Soil Science and Plant Analysis》2012,43(11):1133-1149
Abstract Excessive soil erosion and use of nitrogen fertilizer are costly to the Atlantic Coastal Plain corn (zea mays L., ’Funks G 4507') producer and both may serve to create environmental hazards. An in‐row chisel (36 cm deep) tillage method was compared with the standard 5 cm fluted coulter method for planting corn in premature wheat (Triticim aestivum L.) residues grown on an Orangeburg sandy loam (Typic Paleudult). Five orthogonal N levels ranging up to 440 kg of N/ha were used to determine an economic N optimum for each tillage method. The in‐row chisel tillage method provides a possible yield advantage in the Atlantic Coastal Plain because of observed restricting soil layers within the normal corn rooting zone. The estimated profit‐maximizing quantities of N fertilizer were 262 and 295 kg of N/ha (234 and 263 1b of N/acre) for the fluted coulter and in‐row tillage procedures, respectively. Corn grain yields associated with these inputs were 9.6 × 103 and 12.6 × 103 kg/ha (153 and 200 bu/acre), respectively. The yield increase associated with in‐row chiseling through a 2.5 metric ton mulched surface is attributed to potentially improved rooting and more efficient water storage and use. 相似文献
993.
以食品中分离到的L.mXFL0605株为试验菌株,PCR扩增得到iap全基因。将iap连接到pET-28a(+)载体进行原核表达,分别采用培养温度为25℃或37℃,IPTG浓度为5μg/mL或10μg/mL优化组合进行诱导。结果显示,当采用37℃培养和10μg/mLIPTG诱导时可以获得部分可溶性表达的p60,重组p60蛋白分子质量约60 ku。 相似文献
994.
依据高等院校实验教学管理的应用需求,在分析开源框架体系结构的基础上,通过整合Struts、Spring和Hibernate,利用分层解耦、框架管理层次的思想构建了一个基于开源J2EE的应用架构,并据此架构开发了高校实验教学管理系统。系统可靠性高,安全性好,可扩展性和可维护性强,能有效提高高校实验教学管理和服务效率。 相似文献
995.
996.
997.
Digestates vary in composition and studies regarding their impact on C and N dynamics in soils are scarce. The objective was to analyse the C and N dynamics of digestates originating from various substrates applied to a sandy Cambisol and a silty Anthrosol. In three laboratory experiments (4–6 weeks), the effects of digestate properties, N rate and water content were tested. Averaged over both soils, 21% of the C supplied was emitted as CO2. Potential NH3 emissions during the first week ranged between 6% and 12% of NH4+ present in the digestates. The emission factors in the sandy Cambisol were on average 1.2 and 2 times higher for CO2 and potential NH3, respectively, compared to the silty Anthrosol. Similarly, net nitrogen mineralization in the sandy Cambisol was approximately twice the N mineralized in the silty Anthrosol. Net nitrification was not influenced by soil texture or different digestates, but increased with increasing application rates and had highest values at 75% of water holding capacity. Our results indicate that the type of substrate input for anaerobic digestion influences the properties of the digestate and therefore the dynamics of C and N. However, soil texture can affect these dynamics markedly. 相似文献
998.
Independent and combined effects of stocking density and algal concentration on the survival, growth and metamorphosis of the Bobu Ivory shell Babylonia formosae habei larvae were assessed using a 5 × 5 factorial design with densities of 0.25, 0.5, 0.75, 1.00 and 1.50 larvae mL−1 and algal concentrations of 5, 10, 15, 20 and 25 × 104 cells mL−1 in the laboratory. Larval growth, survival and metamorphosis were significantly affected by both the independent effects of stocking density and algal concentration and by their interaction. The highest per cent survival (72.5%) and metamorphosis (49.5%), fastest growth (41.57 μm day−1) and shortest time to initial metamorphosis (10 days) all occurred at the lowest stocking density and the highest algal concentration. Both crowding and food limitation had independently negative impacts on the survival, growth and metamorphosis of larvae, and these negative impacts were further strengthened by the interaction of a higher stocking density and a lower algal concentration. Moreover, the results suggest that stocking density and algal concentration obviously played different roles in determining larval survival and growth. To maximize survival and growth, B. formosae habei larvae should be reared at a lower stoking density of 0.25 larvae mL−1 and fed a higher algal concentration of 25 × 104 cells mL−1 in large-scale hatchery seed culture. 相似文献
999.
Abstract In a lysimeter study it was found that moderate rates of ammonium nitrate increased utilization percentages in spring wheat, and the leaching was 10% or less of added N. Over-optimal rates reduced utilization percentages and increased leaching to almost 50% of the highest doses. Late split application of calcium nitrate increased the percentage of N in grain. Furthermore, leaching of N was not reduced, but occurred somewhat later in the fall and winter seasons. Leaching of Cl? was more rapid and that of SO4 2- was delayed relative to the leaching of NO3 ?. Rather large negative N balances were obtained, also after over-optimal application rates, and total N content of the soil was reduced. Compared with the N0 treatment, differences in soil N residues amounted to 15–25% of added N in seven years. Gaseous losses had apparently taken place both from the added N and from soil N according to the total-N analysis. 相似文献
1000.