全文获取类型
收费全文 | 13576篇 |
免费 | 594篇 |
国内免费 | 1456篇 |
专业分类
林业 | 1166篇 |
农学 | 1572篇 |
基础科学 | 741篇 |
2736篇 | |
综合类 | 5432篇 |
农作物 | 1368篇 |
水产渔业 | 421篇 |
畜牧兽医 | 1131篇 |
园艺 | 462篇 |
植物保护 | 597篇 |
出版年
2024年 | 100篇 |
2023年 | 223篇 |
2022年 | 362篇 |
2021年 | 440篇 |
2020年 | 455篇 |
2019年 | 536篇 |
2018年 | 371篇 |
2017年 | 644篇 |
2016年 | 733篇 |
2015年 | 534篇 |
2014年 | 733篇 |
2013年 | 967篇 |
2012年 | 1079篇 |
2011年 | 1041篇 |
2010年 | 774篇 |
2009年 | 821篇 |
2008年 | 725篇 |
2007年 | 794篇 |
2006年 | 703篇 |
2005年 | 542篇 |
2004年 | 400篇 |
2003年 | 317篇 |
2002年 | 248篇 |
2001年 | 238篇 |
2000年 | 197篇 |
1999年 | 214篇 |
1998年 | 182篇 |
1997年 | 150篇 |
1996年 | 150篇 |
1995年 | 158篇 |
1994年 | 115篇 |
1993年 | 112篇 |
1992年 | 108篇 |
1991年 | 87篇 |
1990年 | 88篇 |
1989年 | 74篇 |
1988年 | 57篇 |
1987年 | 42篇 |
1986年 | 28篇 |
1985年 | 13篇 |
1984年 | 10篇 |
1982年 | 4篇 |
1981年 | 9篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1955年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
在三种库房里对五种不同含水率、两种包装的华北落叶松种子进行了60个月的贮藏试验。结果认为,含水率5.19/5~8.0%的落叶松种子可以在三种库房密封贮藏39个月。种子贮藏的最佳含水率为6.6%~8.0%,最佳的库房是冷库(0C~5C)。磨口瓶与布袋在冷库贮藏效果差异不明显;地下库不能用布袋贮藏;在普通常温库中磨口瓶比布袋能多贮藏12个~18个月。 相似文献
23.
陆家宝 《青海畜牧兽医杂志》1995,25(3):21-22
1990~1993年在柴达盆地尕海地区弃耕地进行土壤可溶性盐分测定,测定结果,该地区土壤盐分组成为氯化物-硫酸盐和硫酸盐-氯化物,大部分地区耕层盐分含量小于10g.kg^-1,少部分盐荒地表层含盐量高达70g.kg^-1,牧草生长季节中,土壤盐分含量最低期在6月份。 相似文献
24.
Alba Marina Cotes Philippe Lepoivre Jean Semal 《European journal of plant pathology / European Foundation for Plant Pathology》1996,102(5):497-506
An experimental protocol consisting in the colonisation of pregerminated bean seeds dressed withTrichoderma sp. was used in order to study the mechanisms correlated with the protective effect againstPythium splendens. Seed dressed with TH-11 (T. koningii) for 24 h presented a higher protective effect and a higher level of seed colonisation as compared to those dressed with TH-13 (T. longibranchiatum). The levels of seed coat colonisation by TH-11 and TH-13 was shown to be correlated with the carboxymethylcellulase activity, as measured in the seed coats retreived from germinating dressed bean seeds. The seed coat colonisation was also associated with an increased activities of endo-1,3--glucanase and endochitinase measured in seed extracts, and an inhibitory effect of seed extracts onPythium sporangia germination. Pretreatment of TH-13-dressed seeds with a commercial cellulase improved all parameters mentioned above, thus suggesting a role of cellulase activity in the colonisation process and the linked protective effect. The possible role of hydrolytic enzymes in the protective effects is discussed. 相似文献
25.
G. Tuitert Y. Hofmeester 《European journal of plant pathology / European Foundation for Plant Pathology》1994,100(1):19-53
A field experiment was set up in 1988 to study the development of rhizomania disease of sugar beet at different inoculum levels of beet necrotic yellow vein virus (BNYVV) in soil. Five, tenfold different, inoculum levels were created by addition of the approximate amounts of 0, 0.5, 5, 50 and 500 kg infested soil per ha (the latter corresponding to 0.01% v/v calculated to the tillage layer). A drip irrigation treatment was applied to study the influence of soil moisture on disease. Susceptible sugar beet, cv. Regina, was grown for three consecutive years.In the first year, root symptoms were not observed, but BNYVV-infected plants were detected by ELISA in low numbers at all inoculum levels at harvest. After late drilling in 1989, high numbers of infected plants, up to 90–100% in plots with the highest inoculum level, were detected already in June. Root symptoms were also observed from June onwards. In both these years disease incidence increased in time and was significantly influenced by the initial inoculum level. In the third year, the whole field was heavily diseased, and only for the non-irrigated plots incidence differed for different initial inoculum levels. The expression of symptoms by BNYVV-infected plants was influenced by initial inoculum level, thus by the amount and timing of primary infection.Root weight at harvest was not affected, but sugar content decreased with increasing inoculum level already in 1988, leading to a reduction in sugar yield of 10% at the highest inoculum level. In 1989, both root weight and sugar content decreased progressively with increasing inoculum level, resulting in sugar yield reductions of 11–66% (down to approximately 3000 kg ha–1) for low to high inoculum levels compared to the control. As the control plots became contaminated, all yields were low in 1990, still showing a decrease with increasing inoculum level in the non-irrigated plots, but an overall mean sugar yield of 3323 kg ha–1 for the irrigated ones.Sodium and -amino nitrogen content of the root, additional quality parameters determining extractability of sucrose, showed an increase and decrease, respectively, with increasing initial inoculum level already in the first year. The relative differences in contents compared to those from the control were largest for Na content. A significant negative correlation was found between Na (mmol kg–1 root) and sugar content (% of fresh weight); linear for 1988, exponential for 1989 and 1990.In spring 1989, the infestation of individual plots was assessed using a quantitative bioassay estimating most probable numbers (MPNs) of infective units of BNYVV per 100 g dry soil. The relationship between the MPns determined and root weight, sugar content and sugar yield at harvest could be described by Gompertz curves. The increase in disease incidence with increasing MPN in 1989 was adequately fitted with a logistic equation. 相似文献
26.
土壤水热参数是研究土壤水热传输的基本物理参数。当前热脉冲探针法(HPP)可同步测定土壤水热参数,但该方法仅限于在点尺度下测定。与其具有相同理论基础的加热光纤法(SPHP-DTS),可将测定尺度增大至田间千米尺度,但其测定精度尚未得到有效验证。为了探知SPHP-DTS法的误差,本研究进行了SPHP-DTS法与HPP法测定土壤水热参数的对比试验。结果表明,以HPP为标准,加热光纤法测定热导率的精度RMSE为0.13 W?m-1?℃-1。SPHP-DTS法测定的热导率显著高于HPP法,主要原因在于加热光纤时产生的温度效应。通过热导率法测定土壤含水率时,在热导率测定误差的影响下,SPHP-DTS法的测定精度明显低于HPP法。SPHP-DTS法测定土壤水热参数的其他误差来源包括光纤与土壤之间多个界面的接触热阻、光纤的温度敏感性、噪音干扰以及温度梯度驱动下的水分迁移。本研究可为SPHP-DTS法提升土壤水热参数测定精度提供理论参考。 相似文献
27.
28.
J. Guan J. C. Kapteyn A. Kerkenaar M. A. De Waard 《European journal of plant pathology / European Foundation for Plant Pathology》1992,98(5):313-324
Differential accumulation of [14C]imazalil and [14C]fenarimol by germlings of wild-type and DMI-resistant isolates ofPenicillium italicum was studied at various pH values. At pH 7 and 8 the low-resistant isolate E300–3 accumulated 22% and 35%, respectively, less imazalil than the wild-type isolate W5. Imazalil accumulation at pH 5 and 6 was similar. Isolate E300–3 also accumulated less fenarimol as compared with the wild-type isolate. This difference was much more obvious than for imazalil and was observed at all pH values tested. Differences in accumulation of both imazalil and fenarimol between low (E300–3), medium (H17) and high resistant (I33) isolates were not observed. These results suggest that decreased accumulation of DMIs is responsible for a low level of resistance only and that additional mechanisms of resistance might operate in isolates with a medium and high degree of resistance. With all isolates fenarimol accumulation was energy-dependent. This was not obvious for imazalil.The wild-type and DMI-resistant isolates had a similar plasma membrane potential as determined with the probe [14C]tetraphenylphosphonium bromide ([14C]TPP+). Various test compounds, among which ATPase inhibitors, ionophoric antibiotics and calmodulin antagonists, affected the accumulation of [14C]TPP+, [14C]imazalil and [14C]fenarimol. No obvious correlation between the effects of the test compounds on accumulation levels of the fungicides and [14C]TPP+ could be observed. These results indicate that the plasma membrane potential does not mediate the efflux of DMI fungicides byP. italicum. 相似文献
29.
R. Van Peer A. J. Van Kuik H. Rattink B. Schippers 《European journal of plant pathology / European Foundation for Plant Pathology》1990,96(3):119-132
In carnations grown on rockwool disease incidence of fusarium wilt caused byFusarium oxysporum f.sp.dianthi (Fod) was reduced when Fe-EDDHA instead of Fe-DTPA was used as iron source in the nutrient solution. Addition ofPseudomonas sp. strain WSC417r intensified this reduction in the cultivar Pallas, moderately resistant to Fusarium, but not in the susceptible cultivar Lena. Treatment of plants with Fe-EDDHA instead of Fe-DTPA as iron source resulted in higher numbers and percentages on the roots, ofin vitro antagonistic fluorescent pseudomonads. However, differences were only significant at 56 days after planting for cv. Lena and at 14 and 28 days after planting for cv. Palas. Both chelators, at different concentrations, had no effect on root colonization by eitherPseudomonas sp. strain WCS417r orFod strain WCS816. However, when coinoculated, reduced numbers of propagules ofFusarium were found at concentrations of Fe-EDDHA lower than 10–5 M.Higher concentrations of the siderophore fusarine produced byFod strain WCS816 were demonstrated when Fe-EDDHA instead of Fe-DTPA was used as iron source in culture media. At equal concentrations, no such differences were found in the amount of siderophore produced by WCS417r. Germ tube length ofFod was less with Fe-EDDHA than with Fe-DTPA. The reduction of germ tube length was stronger when the purified siderophore of WCS417r was added in excess to the culture media with Fe-EDDHA than those with Fe-DTPA. Therefore, the observed reduction of germ tube growth can not completely be explained by iron deprivation. It appeared that EDDHA exhibited a toxic effect for conidia ofFod strain WCS816 as well.we conclude that the observed disease reduction by Fe-EDDHA is a consequence of a limitation of iron availability forFod. This limitation is possibly intensified by the increase in number or percentage of antagonistic fluorescent pseudomonads that strongly compete for iron. The additional effect after bacterization withPseudomonas strain WCS417r in Fe-EDDHA treated carnations of cv. Pallas is likely to be due, at least partly, to a direct competition for iron between the siderophores ofFod strain WCS816 and ofPesudomonas sp. strain WCS417r.Samenvatting Verwelkingsziekte in anjers op steenwol, veroorzaakt doorFusarium oxysporum f. sp.dianthi (Fod), werd gereduceerd indien het ijzer-chelaat Fe-EDDHA in plaats van Fe-DTPA werd toegevoegd aan de nutriëntenvloeistof. Bacterisatie metPseudomonas sp. stam WCS417r had een additioneel effect bij de matig resistence cultivar Pallas maar niet bij de vatbare cultivar Lena. Toevoeging van Fe-EDDHA in plaats van Fe-DTPA aan planten als ijzerbron resulteerde op de wortels in hogere aantallen en percentages fluorescerende pseudomonaden, diein vitro antagonistisch waren ten opzichte vanFod. De verschillen waren echter alleen significant 56 dagen na planten voor de cultivar Lena en 14 en 28 dagen na planten voor de cultivar Pallas. Beide chelaten vertoonden bij verschillende concentraties geen effect op de kolonisatie van de wortel door beide microorganismen. Echter, wanneer beide micro-organismen gezamelijk werden toegevoegd nam de wortelkolonisatie doorFod stam WCS816 af bij concentraties lager dan 10–5 M Fe-EDDHA. Er werd meer van het siderofoor fusarine doorFod stam WCS816 geproduceerd bij concentraties lager dan 10–4 M Fe indien Fe-EDDHA in plaats van Fe-DTPA als ijzerbron aan het cultuurmedium was toegevoegd. Er werd geen effect van beide chelaten gevonden op de siderofoorproduktie door WCS417r. Indien een overmaat van het gezuiverde siderofoor van WCS417r werd toegevoegd aan Fe-EDDHA werden een sterkere afname van de kiembuislengte gevonden dan toevoeging aan Fe-DTPA. De reductie van de kiembuislengte bleek niet volledig verklaard te kunnen worden door een afname van de ijzerbeschikbaarheid. Het chelaat EDDHA heeft ook een toxisch effect op conidiën van fusarium.Wij concluderen, dat de waargenomen reductie van de verwelkingziekte door Fe-EDDHA een gevolg is van de afname van de ijzerbeschikbaarheid voorFod. Dit wordt waarschijnlijk versterkt door de ontwikkeling van een antagonistische, fluorescerendePseudomonas-populatie die sterk concurreren om ijzer. Het additioneel effect dat door bacterisatie metPseudomonas sp. WCS417r van de met Fe-EDDHA behandelde matig resistante anjers (Pallas) werd verkregen is voor een deel het gevolg van een directe concurrentie om ijzer tussen de sideroforen vanFod stam WCS816 en vanPseudomonas sp. stam WCS417r. 相似文献
30.
新鲜蔬菜硝酸盐含量测定的改进试粉法 总被引:11,自引:0,他引:11
为适应新鲜蔬菜硝酸盐快速检测的需要, 在现有试粉法的基础上对硝酸盐测定的试粉法进行了改良研究。结果表明, 本研究建立的直接以去离子水浸提蔬菜匀浆, 混合试粉配方为柠檬酸∶一水硫酸锰∶无水对氨基苯磺酸∶N - 1 - 萘乙二胺盐酸盐∶细锌粉= 30∶4∶1.6∶0.8∶1, 其加入量为0.1 g的改进试粉法, 对于溶液中硝酸盐含量在0~20 mg/L范围时, 显色吸光值与硝酸盐含量呈现良好的线性关系, 相关系数达0.9999, 方法回收率在97.7%~104.5%之间, 相对标准偏差2.71%。用本改进试粉法测定11种蔬菜的硝酸盐含量与国标法测定结果的t检验具有一致性。 相似文献