全文获取类型
收费全文 | 5516篇 |
免费 | 328篇 |
国内免费 | 398篇 |
专业分类
林业 | 433篇 |
农学 | 394篇 |
基础科学 | 73篇 |
1725篇 | |
综合类 | 2093篇 |
农作物 | 260篇 |
水产渔业 | 164篇 |
畜牧兽医 | 549篇 |
园艺 | 169篇 |
植物保护 | 382篇 |
出版年
2024年 | 16篇 |
2023年 | 76篇 |
2022年 | 121篇 |
2021年 | 149篇 |
2020年 | 148篇 |
2019年 | 176篇 |
2018年 | 167篇 |
2017年 | 237篇 |
2016年 | 263篇 |
2015年 | 229篇 |
2014年 | 249篇 |
2013年 | 375篇 |
2012年 | 565篇 |
2011年 | 392篇 |
2010年 | 287篇 |
2009年 | 299篇 |
2008年 | 262篇 |
2007年 | 314篇 |
2006年 | 232篇 |
2005年 | 254篇 |
2004年 | 216篇 |
2003年 | 151篇 |
2002年 | 115篇 |
2001年 | 111篇 |
2000年 | 110篇 |
1999年 | 103篇 |
1998年 | 92篇 |
1997年 | 72篇 |
1996年 | 70篇 |
1995年 | 76篇 |
1994年 | 58篇 |
1993年 | 40篇 |
1992年 | 56篇 |
1991年 | 33篇 |
1990年 | 35篇 |
1989年 | 36篇 |
1988年 | 19篇 |
1987年 | 13篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有6242条查询结果,搜索用时 46 毫秒
991.
《Communications in Soil Science and Plant Analysis》2012,43(6):557-563
Abstract Three greenhouse experiments were conducted to compare the response of five tobacco (Nicotiana tabacum L.) cultivars to different levels of NaH2PO4 and ammonium polyphosphate (APP) in nutrient media by measuring tissue content of selected nutrient elements (P, Na, K, Ca and Mg). Plants were grown in sand cultures fertilized with nutrient solutions in two experiments and a soil‐sand mix fertilized with solid materials in a third experiment. Plant P and Na content increased as the concentrations of these elements increased in nutrient solution. Plant K content was not generally affected by treatments. Magnesium was reduced in flue‐cured and cigar‐filler tobaccos but was not changed in cigar‐wrapper and Turkish types by increasing amounts of NaH2PO4. All of the cultivars responded similarly to NaH2PO4 with respect to plant Ca. High levels of P in the nutrient media were consistently related to low levels of Ca in plant tissue. 相似文献
992.
《Communications in Soil Science and Plant Analysis》2012,43(2):121-128
Abstract Experiments were conducted to evaluate DTPA as an extractant of available soil Fe and to establish interpretive guides. A critical level of 6 ppm DTPA‐extractable soil Fe correctly predicted Fe deficiency of field grown plants at 11 of 13 locations. In a greenhouse experiment increased yields of sorghum from treatments that increased soil Fe availability were correctly predicted on 13 of 14 soils by a critical level of 5 ppm. 相似文献
993.
《Communications in Soil Science and Plant Analysis》2012,43(6):499-505
Abstract Lead is being added to the environment in automotive exhausts and as an industrial pollutant. To understand its fate in the environment, it is necessary that factors affecting the capacity of soils to sorb Fb be determined. The capacity of soils to sorb Fb from aqueous solutions vas measured for selected Illinois soils via column leaching experiments and adsorption isotherms. A regression equation was determined that predicted the capacity of a soil to sorb Fb based on its C.E.C., pH and soluble F level. Results of the regression analysis indicated that soil properties associated with increasing C.E.C., i.e. higher organic matter content, higher surface area, and higher clay content have a greater effect on Fb sorption than soil pH, and that soil pH has a greater effect than soluble P. 相似文献
994.
《Communications in Soil Science and Plant Analysis》2012,43(3):503-511
Abstract The Langmuir parameters of orthophosphate (OP) and pyrophosphate (PP) sorption for the ammoniated tropical soils were determined. Positive linear relationships between OP and PP sorption maxima and amounts of anhydrous NH3 added were noticed. Indexes of bonding energy of OP and PP increased exponentially as ammoniation level of the soils increased from 33 to 100% of ammonia retention capacity. 相似文献
995.
《Communications in Soil Science and Plant Analysis》2012,43(11):1129-1146
Abstract Cultivars of triticale, wheat, and rye were grown with different N‐fertilizer rates and sampled at various maturity stages in 1975 to 1977. ‘6TA 131’ triticale, ‘Arthur’ wheat, and ‘Abruzzi’ rye were used as checks. Increasing N fertilizer rates increased dry matter and N accumulation in the above‐ground plant parts. However, after flowering losses of dry matter and N from the plants increased with N fertilizer rates. Triticale and rye generally absorbed more N from the soil than wheat. Triticale and wheat straw had higher P concentrations than rye. The head/straw concentration ratios were: triticale and rye>wheat for P, wheat>triticale and rye for K while Ca and Mg ratios were triticale>wheat>rye. 相似文献
996.
《Communications in Soil Science and Plant Analysis》2012,43(9):889-894
Abstract Malting barley is a specialized agricultural crop in which high yields and quality are production objectives. We evaluated the effects of different N rates on barley yields and selected malting quality parameters grown on irrigated silt loam soils (Xerollic calciorthids). Maximum barley yields having acceptable malting quality parameters were obtained when the preplant soil NO3‐N plus fertilizer N was between 100 to 120 kg N/ha. About 33 kg N/ha was taken up by the plants from the mineralization of soil organic N. Higher available N levels decreased malting quality parameters below acceptable levels. Germination percentage was not changed by the different N rates. 相似文献
997.
《Communications in Soil Science and Plant Analysis》2012,43(8):909-927
Abstract Results from a commercially available portable soil test laboratory were compared to standard soil test procedures used by a public soil testing laboratory. Standard soil tests examined were water extracted NO3‐N, pH, Acid‐P, NaHCO3‐P, and ammonium acetate extracted K. Approximately 35 to 55 different soils were used to compare methods for each soil test. Linear regression equations between the portable laboratory soil test values and those from the standard procedures were developed. The r2 values for NO3‐N, pH, Acid‐P, NaHCO3‐P, and K were 0.970, 0.891, 0.734, 0.742, and 0.887, respectively. The coefficient of variability values for NO3‐N, pH, Acid‐P, NaHCO3‐P, and K were 10, 1, 13, 15, and 6%, respectively for the portable laboratory, and 9, 2, 8, 9, and 5%, respectively for the public soil testing laboratory. Multiple regression was used to relate soil properties to soil test results. The R2 values for NO3‐N, pH, Acid‐P, NaHCO3‐P, and K were 0.970, 0.911, 0.860, 0.940, and 0.936, respectively. 相似文献
998.
《Communications in Soil Science and Plant Analysis》2012,43(8):969-983
Abstract Birdsfoot trefoil (Lotus tenius), red clover (Trifolium pratense) and white clover (Trifolium repens) were evaluated as potential forage legumes on andic soils. A greenhouse study was used to evaluate the influence of soil pH on: (1) the establishment and growth of these forage legumes, (2) N and P quantity and concentration, and (3) Rhizobium lupini and Rhizobium trifolii survival. Aluminum sulfate and finely‐ground calcium carbonate were used to adjust soil pH. Soil pH's were 4.8, 5.1, 5.6, 6.2, 6.4, 6.9, 7.0 and 7.4. Birdsfoot trefoil, red clover and white clover were grown in 15 cm pots in the greenhouse and harvested five times at approximately 20‐day intervals. Yield was measured and plant material was analyzed for total N and P. Populations of R. lupini and R. trifolii were monitored using the MPN technique. Manipulation of pH in the Mission soil was found to have a significant effect on the growth of the three forage legumes, tissue N and P concentration and uptake, and on the survival of R. lupini and R. trifolii in the soil. In general, tested parameters increased with increasing soil pH. Greatest forage yield occurred in the 6.9–7.0 pH range. The andic nature of the Mission soil requires a pH adjustment above pH 6.2 for acceptable establishment and yields of the three forage legumes studied. This is in sharp contrast to non‐andic northern Idaho soils where forage legume yields are usually not adversely affectea above pH 5.5. All three legumes appeared to have good potential ana should be evaluated under field conditions. 相似文献
999.
《Communications in Soil Science and Plant Analysis》2012,43(9):775-792
Abstract This research was undertaken on a paleudult soil in southern Brazil, 30° south latitude, to quantify lime and P effect upon soybean (Glycine max (L.) Merrill). A lime x P factorial experience with lime treatments of 0, 0.5, 1, and 2 times SMP interpretation to pH 6.5, and 0, 44, 88, 132, and 176 kg P/ha with 3 replications were installed. The experiment was conducted for 2 years (1973–74, 1974–75), with leaf‐N, P, and K; yield; seed‐N, P, and K; Bray P2 (0.03N NH4F + 0.1N HC1) avail‐able‐P and soil pH measurements completed each year. Data was evaluated with linear, quadratic, logarithmic, polynomial, segmented line, and multiple regression using the coefficient of determination as goodness of fit. The best model fit between P treatment and Bray P2 available‐P was a quadratic equation; the model between relative yield and Bray P2‐P with 54% of the relative yield attributed to Bray P2 available‐P, a sigmented line. This model indicated point of maximum yield (91% relative yield) was obtained at 7.4 ppm‐P, with no increase in relative yield with increasing levels of soil available‐P. To calculate the P fertilizer necessary to increase available soil‐P to the level of maximum yield of equation Yp = [1639(7.4 ‐ xs)]1/2, where Yp = kg P/ha fertilizer needed; and xs = initial Bray P2 soil available‐P in ppm's. The lime effect upon soil pH was best described as a linear relationship. Yield increase with lime at this site was not significant at the 5% level. The leaf‐N, P, and K increased significantly with soil available‐P levels. A second degree polynomial with logarithmic function best defined these relationships. The calculated DRIS indices and sum proved useful to evaluate the plant‐N, P, and K balance of each treatment. Only seed‐P level was directly related to soil available‐P. Both seed‐N and seed‐K were highly correlated with indirect effects of soil available‐P levels. Results from this study suggest the segmented line model would best interpret soybean yield response to Bray P2 available‐P for this soil. To obtain maximum yield using this model rather than the second degree polynomial would require less fertilizer P. Foliar analyses interpretation confirmed adequate plant‐P level would be supplied for maximum yield at this level of fertilization. 相似文献
1000.
Change of dry bulk density and Ksat after incubation of a soil in the presence of organic amendments
《Communications in Soil Science and Plant Analysis》2012,43(7):787-798
Abstract Kamouraska Ap horizon samples were incubated in the presence of organic amendments, peat moss, straw, compost and green manure, applied at a rate equivalent to 7.5 t of carbon/ha. Water was added to reach 80% of field capacity. The soil‐amendement mixtures were incubated at 37°C for periods of 4, 8, 16, 32 or 64 weeks. Settling tests were performed using a jolting volumeter. Minimum dry bulk density (mDBD), saturated hydraulic conductivity (Ksat) and water content at field capacity were determined. For the unamended soil, mDBD corresponded to 1.1 g.cm‐3 and Ksat max to 265 cm/h. After incubation, mDBD varied from 1.02 to 1.12 g.cm‐3 and Ksat max values were generally below 150 cm/h. The results were discussed in relation to the decomposition of the organic amendments and the formation of stable aggregates. 相似文献