全文获取类型
收费全文 | 5511篇 |
免费 | 354篇 |
国内免费 | 205篇 |
专业分类
林业 | 287篇 |
农学 | 420篇 |
基础科学 | 67篇 |
942篇 | |
综合类 | 786篇 |
农作物 | 358篇 |
水产渔业 | 376篇 |
畜牧兽医 | 2192篇 |
园艺 | 129篇 |
植物保护 | 513篇 |
出版年
2023年 | 35篇 |
2022年 | 43篇 |
2021年 | 95篇 |
2020年 | 88篇 |
2019年 | 103篇 |
2018年 | 133篇 |
2017年 | 157篇 |
2016年 | 158篇 |
2015年 | 126篇 |
2014年 | 157篇 |
2013年 | 247篇 |
2012年 | 272篇 |
2011年 | 303篇 |
2010年 | 247篇 |
2009年 | 226篇 |
2008年 | 287篇 |
2007年 | 284篇 |
2006年 | 244篇 |
2005年 | 228篇 |
2004年 | 207篇 |
2003年 | 266篇 |
2002年 | 328篇 |
2001年 | 323篇 |
2000年 | 191篇 |
1999年 | 147篇 |
1998年 | 46篇 |
1997年 | 50篇 |
1996年 | 40篇 |
1995年 | 50篇 |
1994年 | 49篇 |
1993年 | 40篇 |
1992年 | 50篇 |
1991年 | 41篇 |
1990年 | 56篇 |
1989年 | 51篇 |
1988年 | 35篇 |
1987年 | 40篇 |
1986年 | 31篇 |
1985年 | 34篇 |
1984年 | 53篇 |
1983年 | 28篇 |
1982年 | 27篇 |
1980年 | 23篇 |
1979年 | 28篇 |
1978年 | 28篇 |
1977年 | 27篇 |
1975年 | 25篇 |
1974年 | 37篇 |
1972年 | 30篇 |
1971年 | 37篇 |
排序方式: 共有6070条查询结果,搜索用时 15 毫秒
111.
W. De Boer M. P. J. Hundscheid J. M. T. Schotman S. R. Troelstra H. J. Laanbroek 《Biology and Fertility of Soils》1993,15(2):120-126
Summary The effect of liming on in-situ N transformations was studied in two stands of different ages of each of Scots pine (Pinus sylvestris L.), Douglas fir [Pseudotsuga menziesii (Mirb.) Franco], and common oak (Quercus robur L.). The stands were located on acid sandy soils in an area with high atmospheric N input. The organic matter of the upper 10-cm layer of the soil, including the forest floor, had a relatively high N content (C: N ratio <25) in all stands. Using a sequential core technique, N transformations were measured in both control plots and plots that had been limed 3 years previously with 3 t ha-1 of dolomitic lime. Limed plots had a higher net NO
inf3
sup-
production and a higher potential for NO
inf3
sup-
leaching than the controls in all stands except that of the younger oak. Net N mineralization did not differ significantly between limed and control plots in oak stands and younger coniferous stands but was significantly lower in the limed plots of the older coniferous stands. It is concluded that long-term measurements of net N mineralization in limed forest soils are needed to evaluate the effect of liming with respect to the risk of groundwater pollution. 相似文献
112.
Cultrone G. De la Torre M. J. Sebastian E. M. Cazalla O. Rodriguez-Navarro C. 《Water, air, and soil pollution》2000,119(1-4):191-207
The weathering of different brick samples ina range of aggressive environments has been studied.Brick samples were prepared using two clay types (fromGranada, Spain), different additives, and a range offiring temperatures (850–1100 °C). The brickscompositional and textural characteristics wereevaluated using XRD, SEM, hydric tests and mercuryintrusion porosimetry (MIP). The samples weresubjected to accelerate aging, including wet-dry,freeze-thaw and salt crystallization cycles. The decayof the bricks in polluted atmospheres was simulated ina static chamber containing sulfur dioxide (SO2)at 25 °C and 50% relative humidity. Samplesfired at 1000 °C proved to be the most durable,with better hydric behavior (fast drying and slowwater absorption) and fewer micropores. However, theywere not suitable for salt-rich environments (badperformance in the salt decay test). Samples fired at850 °C turned out to be more resistant to saltdecay, but they showed a poor hydric behavior (slowdrying and rapid water absorption) and littleresistance to freeze-thaw and wet-dry cycles. Samplesfired at 1100 °C had good hydric behavior, theyperformed well in the salt decay test, but they didnot perform as well as the samples fired at1000 °C in most accelerated aging tests. Gypsumformed on all the brick samples submitted to SO2atmosphere regardless exposure time (e.g. gypsumappears following just 24 h of exposure),composition, or firing temperature. Samples withdeposited particulate matter collected from vehicleexhausts (diesel, as well as leaded and non-leadedgasoline motor cars) resulted in the fastest gypsumdevelopment and greater abundance. On the other hand,the blank samples, and the samples withpollution-derived dust collected from historicalbuildings showed little gypsum development. Theimplications of these results in historicalbrick-building preservation in a range of aggressiveenvironments, and in polluted atmospheres inparticular, are discussed. 相似文献
113.
114.
Development of an indirect competitive ELISA for flumequine residues in raw milk using chicken egg yolk antibodies 总被引:3,自引:0,他引:3
Van Coillie E De Block J Reybroeck W 《Journal of agricultural and food chemistry》2004,52(16):4975-4978
To detect flumequine in raw milk, an indirect competitive enzyme-linked immunosorbent assay (ELISA) was developed. By carbodiimide conjugation, flumequine was conjugated to cationized bovine serum albumin (cBSA-flumequine) and to cationized ovalbumin (cOVA-flumequine). For the immunization of chickens, cBSA-flumequine was used, which allowed the isolation of specific chicken egg yolk immunoglobulins (IgY) for flumequine. As the coating antigen in the immunoassay, cOVA-flumequine was used. In the indirect competitive assay, standard flumequine was incubated together with the anti-flumequine antibodies. The antibody by which the lowest concentration of free flumequine that gives 50% inhibition of binding (IC50) was found in aqueous dilution was further tested for the applicability to detect flumequine in raw milk. An IC50 level in milk was reached that was about 5 times lower than in aqueous solution. So flumequine can be detected directly in raw milk at maximum residue level (50 microg/kg). No cross-reactivity was noticed with various related quinolones. 相似文献
115.
长期免耕水稻田土壤的生物特征研究 总被引:40,自引:8,他引:40
对经过 10年半旱式免耕定位试验的水稻土主要微生物类群数量和微生物生物量的变化进行对比研究 ,结果表明 :实行半旱式厢作及垄作免耕法能够迅速地提高土壤有机质、全氮、全磷和速效氮、磷的水平 ;微生物数量和微生物生物量变化一般存在季节性规律 :春季高 ,夏季至夏末降低 ;各处理土体上层和下层 (0~ 7.5 cm,7.5~15 cm)的基本肥力特征及微生物特征无明显区别 ;免耕处理土壤 ,其微生物的季节性变幅较小 ,垄上或厢上土壤微生物生物量甚至表现反季节性 ,整个生长季节内稳中有升 ,有利于土壤有机物质的转化和土壤肥力的发挥 相似文献
116.
不同雨强和坡度条件下紫色土养分流失规律研究 总被引:58,自引:1,他引:58
采用室内模拟降雨装置,研究了三峡库区紫色土在不同雨强和坡度条件下的养分流失规律。结果表明,紫色土坡面流失养分主要由径流和泥沙携带,其中径流养分含量与雨强和坡度无关,但与产流过程一致。泥沙中养分含量与雨强无关,但随坡度增加而降低;泥沙养分含量与产沙量过程无关,但其流失量与产沙量过程一致。泥沙中各养分含量略大于降雨前表土养分含量,远大于径流养分含量,但由于径流中以速效养分为主,故径流携带的养分流失量不容忽视。 相似文献
117.
118.
Vági E Simándi B Daood HG Deák A Sawinsky J 《Journal of agricultural and food chemistry》2002,50(8):2297-2301
Extraction of pigments (chlorophylls and carotenoids) from marjoram (Origanum majorana L.) with supercritical carbon dioxide was investigated. The aim of this study was to map the effects of extraction pressure and temperature on the yield of coloring materials by applying a 3(2) full factorial design with three repeated tests in the center of the design. For comparison, laboratory and pilot plant Soxhlet extractions were carried out using ethanol and n-hexane solvents. The compositions of pigments in marjoram extracts were determined by HPLC. Similar amounts of carotenoids, in addition to 40% of chlorophylls and their derivatives, were recovered from the supercritical fluid extraction, in comparison to the ethanol Soxhlet extraction. 相似文献
119.
Cruciferous oilseeds are important sources of oil, proteins, and glucosinolates (GLs), potentially available when biorefinery processes are used. The proposed extraction technology is based on the use of reverse micelles (RMs) made with cetyltrimethylammonium bromide (CTAB) dispersed in organic solvent. The physicochemical properties of this extraction system and the good water solubility of many high value compounds, such as GLs and some proteins, permit the simultaneous extraction of oil, and these products from cruciferous oilseed meals. This procedure is based on three main steps: (i) seed conditioning; (ii) solid-liquid extraction by RM solution; and (iii) back-transfer of the RM solution for recovery of the extracted compounds. The method makes it possible to simultaneously extract almost the same amount of oil as with pure organic solvents used in the current extraction plants and more than 90% of soluble proteins and GLs. It is a promising biorefinery technology alternative to traditional oil extraction processes. 相似文献
120.
信阳土壤锌的现状及杂交水稻施锌技术研究 总被引:1,自引:0,他引:1
信阳地区位于河南省南部,土壤类型有黄棕壤、黄褐土、潮土、水稻土等。通过土壤普查,发现全区土壤表层速效锌含量普遍偏低,土壤缺锌已成为限制作物产量和品质的重要障碍因素。1994~1996年我们在对信阳土壤锌的现状进行分析的基础上,对杂交水稻施锌技术作了系统试验,结果表明,杂交水稻锌肥耖口基施30~45kg/hm2和蘸秧根3~9kg/hm2增产效果十分显著。 相似文献