全文获取类型
收费全文 | 598篇 |
免费 | 28篇 |
专业分类
林业 | 92篇 |
农学 | 8篇 |
基础科学 | 1篇 |
130篇 | |
综合类 | 41篇 |
农作物 | 18篇 |
水产渔业 | 31篇 |
畜牧兽医 | 214篇 |
园艺 | 27篇 |
植物保护 | 64篇 |
出版年
2023年 | 8篇 |
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 12篇 |
2019年 | 14篇 |
2018年 | 14篇 |
2017年 | 4篇 |
2016年 | 13篇 |
2015年 | 5篇 |
2014年 | 15篇 |
2013年 | 31篇 |
2012年 | 41篇 |
2011年 | 53篇 |
2010年 | 25篇 |
2009年 | 24篇 |
2008年 | 40篇 |
2007年 | 30篇 |
2006年 | 35篇 |
2005年 | 36篇 |
2004年 | 31篇 |
2003年 | 31篇 |
2002年 | 19篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1995年 | 4篇 |
1992年 | 4篇 |
1988年 | 4篇 |
1986年 | 2篇 |
1984年 | 4篇 |
1978年 | 3篇 |
1976年 | 3篇 |
1968年 | 3篇 |
1967年 | 2篇 |
1966年 | 3篇 |
1965年 | 2篇 |
1964年 | 2篇 |
1963年 | 2篇 |
1962年 | 2篇 |
1959年 | 2篇 |
1954年 | 3篇 |
1941年 | 4篇 |
1937年 | 12篇 |
1935年 | 9篇 |
1934年 | 5篇 |
1933年 | 8篇 |
1927年 | 2篇 |
1916年 | 2篇 |
排序方式: 共有626条查询结果,搜索用时 78 毫秒
531.
Richard D. Scheffe Joseph V. DePinto Kurt R. Bilz 《Water, air, and soil pollution》1986,31(3-4):799-807
A deterministic lake dose calculation model has been applied to estimate the quantity of Ca carbonate-based material needed to achieve a desired initial water chemistry in a whole lake treatment of two Adirondack acid lakes. The study lakes were treated with calcite during May 30–31, 1985. The model accurately simulated laboratory column water chemistry profiles (spatially and temporally) and dissolution efficiencies; however, the model predicted conservative efficiencies for the study lakes. Time-series water chemistry profiles of the lakes suggest that epilimnetic mixing extended suspension time of fine calcite particles, and that atmospheric carbon dioxide intrusion rate was greater than expected. The combination of these factors enhanced dissolution efficiency. 相似文献
532.
Three wheat categories with different biomass production were studied on tropical Inceptisols in Rwanda. Growth parameters such as number of tillers per square meter, average plant height, and shoot and root biomass were determined, and elemental concentrations of roots and leaves measured. In order to identify reasons for inhibited wheat growth soil parameters such as pH, exchangeable cations, Corg and Ntot were determined. As aluminum toxicity was suspected on the acid soils, aluminum fractionation was carried out in water extracts of the soil samples using 8-hydroxyquinoline. Growth parameters correlated well with exchangeable aluminum and with soil pH. These findings, along with root morphology, indicated aluminum toxicity at the low productivity plots. Aluminum fractionation results strengthened this hypothesis, but did not give much additional information. The reasons for this are discussed. Simultaneously, the elemental concentrations of the leaves suggested Ca, Mg and P deficiencies. 相似文献
533.
Kurt Mantel 《Forstwissenschaftliches Centralblatt》1935,57(12):390-406
Ohne Zusammenfassung 相似文献
534.
535.
536.
537.
Kurt Mantel 《Forstwissenschaftliches Centralblatt》1935,57(13):432-438
Ohne Zusammenfassung 相似文献
538.
Sibel Dervis Latife Erten Soner Soylu Fatih M. Tok Sener Kurt Mehmet Yıldız E. Mine Soylu 《European journal of plant pathology / European Foundation for Plant Pathology》2007,119(4):437-447
Verticillium wilt, caused by Verticillium dahliae, is the most serious disease in olive cultivation areas in western Turkey. Two hundred and eight isolates of V. dahliae from olive (Olea europea var. sativa) trees were taken for vegetative compatibility analysis using nitrate non-utilizing (nit) mutants. One isolate did not produce a nit mutant. Nit mutants of 207 isolates were tested against tester strains of internationally known vegetative compatibility groups (VCGs) 1A, 2A, 2B, 3, 4A and 4B, and also paired in many combinations among themselves. One hundred and eighty nine of the isolates (90.9%) were strongly compatible with T9, the tester strain of VCG1A, and thus were assigned to VCG1A. Eight isolates were assigned to VCG2A and four isolates to VCG4B. One isolate was heterokaryon self-incompatible (HSI) and five isolates could not be grouped to any of the VCGs tested. Pathogenicity assays were conducted on a susceptible olive cultivar (O. europea cv. Manzanilla) and a susceptible local cotton cultivar (Gossypium hirsutum cv. Çukurova 1518). Both cotton and olive inoculated with all VCG1A isolates showed defoliating symptoms in greenhouse tests. This is the first report on VCGs in V. dahliae from olive trees in Turkey which demonstrates that VCG1A of the cotton-defoliating type is the most commonly detected form from olive plants in the western part of Turkey. 相似文献
539.
Katrijn Cobbaut Kurt Houf Glenn Buvens Ihab Habib Lieven De Zutter 《Veterinary microbiology》2009,138(1-2):174-178
Escherichia coli O157 is often associated with hemorrhagic colitis and the hemolytic uremic syndrome (HUS). The verocytotoxins are considered to be the major virulence determinants. However, vt-negative E. coli O157 were recently isolated from patients with HUS. Several transmission routes to humans are described, but cattle feces are the primary source from which both the food supply and the environment become contaminated with E. coli O157.In a prevalence study performed on dairy, beef, mixed dairy/beef and veal farms in the summer of 2007, vt-negative isolates were detected on 11.8% (8/68) of the positive farms. From these eight farms, a total of 43 sorbitol-negative E. coli O157:H7 were collected. On five farms, only strains negative for the vt genes were present whereas both vt-negative and vt-positive strains could be detected on three other farms. Further characterization revealed that all isolates carried the eaeA and hlyA genes. Pulsed-field gel electrophoresis (PFGE) of all isolates resulted in nine different PFGE types and within the vt-negative strains, four different genotypes were identified, indicating that certain genetic clones are widespread over the cattle population. 相似文献
540.
Organic matter returns to soils must be higher under organic compared to conventional farming 总被引:1,自引:0,他引:1 下载免费PDF全文
The aim of this paper is to discuss the demand of fresh organic matter (FOM) supply to maintain soil organic matter (SOM) levels and productivity of arable soils under organic management. The basic question is whether the different frame conditions in organic vs. conventional farming result in a different and system‐specific FOM demand. If this is the case, it would follow that the farming system has to be considered in the calculation of SOM balances. SOM balances are the most common decision support tools in organic matter management. A conversion to organic farming in practice usually leads to an increase of SOM levels as well as soil microbial activity over time. The system‐specific driver of this effect is the indispensable extension of the share of (perennial) legumes in crop rotations at the expense of non‐legumes such as cereals, row crops, and maize. Extended legume cropping is essential for N supply in crop rotations as the import of N fertilizer in total is limited by organic farming regulations and mineral N fertilizer may not be used at all. Based on this characteristic of organic management, we argue that the demand of FOM supply to soils must be higher than in conventional crop production. The most relevant factors are (1) the non‐existence of mineral N fertilizer as an external N source that supports the maintenance of SOM by decreasing the demand for SOM‐N, (2) benefits of increasing SOM stocks and turnover for soil productivity under organic management, and, (3) increased mass‐losses of FOM and easily degradable SOM compartments due to higher microbial activity in soils. These effects have to be quantified and must be considered in SOM balances in order to avoid misleading assessments and erroneous decisions. 相似文献