全文获取类型
收费全文 | 10535篇 |
免费 | 439篇 |
国内免费 | 1373篇 |
专业分类
林业 | 648篇 |
农学 | 1113篇 |
基础科学 | 583篇 |
1377篇 | |
综合类 | 4682篇 |
农作物 | 710篇 |
水产渔业 | 505篇 |
畜牧兽医 | 1473篇 |
园艺 | 686篇 |
植物保护 | 570篇 |
出版年
2024年 | 49篇 |
2023年 | 131篇 |
2022年 | 265篇 |
2021年 | 306篇 |
2020年 | 369篇 |
2019年 | 490篇 |
2018年 | 417篇 |
2017年 | 488篇 |
2016年 | 597篇 |
2015年 | 474篇 |
2014年 | 519篇 |
2013年 | 582篇 |
2012年 | 648篇 |
2011年 | 638篇 |
2010年 | 597篇 |
2009年 | 560篇 |
2008年 | 510篇 |
2007年 | 487篇 |
2006年 | 432篇 |
2005年 | 323篇 |
2004年 | 271篇 |
2003年 | 233篇 |
2002年 | 198篇 |
2001年 | 177篇 |
2000年 | 181篇 |
1999年 | 171篇 |
1998年 | 155篇 |
1997年 | 240篇 |
1996年 | 221篇 |
1995年 | 201篇 |
1994年 | 226篇 |
1993年 | 224篇 |
1992年 | 267篇 |
1991年 | 263篇 |
1990年 | 222篇 |
1989年 | 86篇 |
1988年 | 40篇 |
1987年 | 25篇 |
1986年 | 13篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1956年 | 5篇 |
1955年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
781.
P.O. Anegbeh C. Usoro V. Ukafor Z. Tchoundjeu R.R.B. Leakey K. Schreckenberg 《Agroforestry Systems》2003,58(3):213-218
Domestication of Irvingia gabonensis, a fruit tree grown in agroforestry systems in West and Central Africa, offers considerable scope for enhancing the nutritional
and economic security of subsistence farmers in the region. Assessments of phenotypic variation in ten fruit, nut and kernel
traits were made on twenty-four ripe fruits from 100 Irvingia gabonensis trees in Ugwuaji village in southeast Nigeria, a center of genetic diversity for this species. There were important differences
between the young planted trees of this study and the older unplanted trees of a similar study in Cameroon. Significant and
continuous tree-to-tree variation was found in fruit mass(69.0–419.8 g), flesh mass (59.5–388.8 g), nut mass (9.5–40.6 g),
shell mass (4.9–30.9 g) and kernel mass (0.41–7.58 g); fruit length (49.2–89.3 mm) and width (46.2–100.5 mm) and flesh depth
(12.9–31.4 mm), as well as considerable variation in flesh colour, skin colour, fruit taste and fibrosity. Some fruits were
considerably bigger than those found in Cameroon. These quantitative results will help in the development of cultivars within
participatory approaches to agroforestry tree domestication, and so promote poverty alleviation and sustainable agriculture.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
782.
783.
Tsuyoshi Kajisa Takuhiko Murakami Nobuya Mizoue Shigejiro Yoshida 《Journal of Forest Research》2007,12(6):435-441
Our objective was to investigate the differences in the spectral trajectory of the LANDSAT Thematic Mapper with stand volume
development between Japanese larch (Larix kaempferi) and Japanese oak (Quercus mongolica var. crispula) in the experimental forest of Kyushu University, Hokkaido, Japan. We used nonlinear regression and a categorical variable
to investigate the relationship between spectral reflectance factor and stand volume for each forest type. This research showed
that the reflectance factor of Japanese larch and Japanese oak reached saturation and that both forest types had different
spectral trajectories with stand development. In addition, we found that middle of development stage (stand volume was between
100 and 200 m3/ha) of each forest type had similarity in reflectance factor. 相似文献
784.
Sugi (Cryptomeria japonica D. Don) wood was treated with supercritical water (374°C, 22.1MPa), and fractionated into the water-soluble portion, the methanol-soluble portion, and the methanol-insoluble residue. The methanol-soluble portion mainly consisted of the lignin-derived products. To characterize the compounds in the methanol-soluble portion, gel permeation chromatographic (GPC) and gas chromatographic-mass spectrometric (GC-MS) analyses were performed. The GPC analysis indicated that the methanol-soluble portion contained lignin-derived monomeric and dimeric products. GC-MS analysis detected 31 products which were expected to be monomeric compounds, and 18 of these were identified to be guaiacol, methylguaiacol, ethylguaiacol, vinylguaiacol, eugenol, propylguaiacol, vanillin, cis-isoeugenol, homovanillin, trans-isoeugenol, acetoguaiacone, propioguaiacone, guaiacylacetone, 2-methoxy-4-(1-hydroxypropyl)phenol, homovanillic acid, 2-methoxy-4-(prop-1-en-3-one)phenol, coniferyl aldehyde, and ferulic acid. In addition, 22 dimeric products were detected, and 4 of these were believed to be compounds with biphenyl type (5-5), diphenylethane type (-1), stilbene type (-1), and phenylcoumaran type (-5) structures. These results clearly indicated that the methanol-soluble portion included various monomeric and dimeric compounds produced as a result of the cleavage of ether linkages and propyl chains of lignin. 相似文献
785.
低毒防腐剂百菌清及铜制剂对木材尺寸稳定及力学性能的影响 总被引:6,自引:0,他引:6
百菌清(CTL)、氨浴季铵铜(ACQ)、氨溶柠檬酸铜(ACC)处理马尾松(Pinus massoniana)、毛白杨(Populus tomentosa)后对木材尺寸稳定性及MOE/MOR的影响本文进行了研究。结果表明,除剂量11.48kg/m^3的百菌清处理的毛白杨外,以上防腐剂处理试材后吸水至饱和时的尺寸稳定性与对照相比有不同程度的增加,幅度为3.9%-28.05;各处理对抗弯弹性模量(MOE)影响幅度不大,其中对于马尾松,MOE差异不明显,对于毛白杨,各处理对MOE稍有增加(百菌清乳剂处理除外),幅度6.3%-8.1之间。各制剂处理马尾松、毛白杨后对抗弯强度(MOR)影响不明显。 相似文献
786.
沼液施肥对杨树林地土壤微生物量碳氮的影响 总被引:2,自引:0,他引:2
沼液是沼气发酵过后的液体残留物,是一种优质的有机肥料。研究了不同沼液施肥对杨树林地土壤微生物量碳氮的影响。结果表明:施用沼液可以提高土壤微生物量碳、氮的含量,微生物量碳、氮含量增加范围分别为4.29%~61.62%和6.08%~76.10%,土壤微生物量碳氮含量随沼液施用量增加逐渐提高。土壤微生物量碳氮呈正相关。土壤微生物量碳氮比随沼液施用量增加逐渐下降,其变化范围为9.92~10.81,土壤微生物量碳氮比与微生物量碳、氮含量负相关。 相似文献
787.
为获得可用于鸡传染性法氏囊病病毒(IBDV)抗体检测的重组抗原VP2蛋白,根据GenBank中发表的IBDV VP2序列设计一对特异性引物,应用RT-PCR技术克隆IBDV经典标准攻毒株(BC6/85株)的VP2基因,插入质粒pET-32a中构建重组表达质粒pET-32a-VP2,经IPTG诱导后获得了以包涵体形式表达的重组蛋白。重组蛋白纯化后,Western-blot检测表明具有良好的反应原性。本研究为下步建立IBDV抗体的间接ELISA方法及新型疫苗的研制奠定了基础。 相似文献
788.
为了建立同时测定猪粪便中二甲氧苄啶、磺胺对甲氧嘧啶、恩诺沙星、金霉素、泰乐菌素5种兽药残留量的超高效液相色谱-串联质谱(UPLC-MS/MS)分析方法,样品经McIllvaineNa_2EDTA缓冲溶液提取,C18粉吸附杂质,HLB固相萃取小柱净化,浓缩富集后用0.1%甲酸甲醇溶液复溶,过滤上机,基质液外标法定量。结果显示,5种兽药在10~500μg/kg的质量浓度范围内线性良好,在添加浓度50~500μg/kg,平均回收率为53%~85%,RSD为1.87%~18.81%。该方法具有较好的准确度与精密度,能快速、准确测定猪粪便中5种兽药残留,为养殖环节实时监测兽药使用情况提供了技术支持。 相似文献
789.
建立了动物源食品中酰胺醇类药物(氯霉素CAP、甲砜霉素TAP、氟苯尼考FF)及其代谢物(氟苯尼考胺FFA)残留检测的超高效液相色谱-串联质谱(UPLC-MS/MS)法。样品经氨化乙酸乙酯提取,正已烷脱脂,氨化乙酸乙酯反萃取,电喷雾正/负离子多反应监测(MRM)模式检测。四种药物在0.2~50μg/L的系列浓度范围呈线性相关,样品中CAP的检测限为0.1μg/kg,定量限为0.2μg/kg;TAP、FF、FFA检测限为0.5μg/kg,定量限为1.0μg/kg。在0.2~5μg/kg的添加浓度范围内平均回收均为80%~120%,变异系数均小于15%。结果表明该方法简单快速、灵敏度高、重复性好,适用于动物源食品中酰胺醇类及其代谢物残留检测。 相似文献
790.
Kouko HAMAMOTO Yasuharu MIZUNO 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2015,77(11):1527-1529
We assessed ampicillin (ABPC) concentrations of kidney, muscle and intestine
after a 5–day withdrawal period in 2 male and a female young Large White pigs fed the diet
containing ABPC (ABPC medicated feed, 24 mg/kg/day) for a week. The ABPC residues were
measured with liquid chromatography–tandem mass spectrometry, and the mean recoveries and
quantitation limits ranged from 91.8 to 97.2% and from 0.1 to 0.12 ng/g,
respectively. The residual ABPC concentrations were ≤1.18 ng/g for the
muscle, ≤0.53 ng/g for the kidney and ≤1.93 ng/g for the
intestine, suggesting below the Japanese provisional maximum residue limits. These results
reveal that the analytical method is developed for residual ABPC and that the withdrawal
period is appropriate. 相似文献