全文获取类型
收费全文 | 928篇 |
免费 | 54篇 |
专业分类
林业 | 102篇 |
农学 | 33篇 |
基础科学 | 2篇 |
197篇 | |
综合类 | 67篇 |
农作物 | 63篇 |
水产渔业 | 56篇 |
畜牧兽医 | 325篇 |
园艺 | 33篇 |
植物保护 | 104篇 |
出版年
2023年 | 7篇 |
2022年 | 7篇 |
2021年 | 17篇 |
2020年 | 19篇 |
2019年 | 26篇 |
2018年 | 52篇 |
2017年 | 42篇 |
2016年 | 47篇 |
2015年 | 21篇 |
2014年 | 43篇 |
2013年 | 42篇 |
2012年 | 55篇 |
2011年 | 93篇 |
2010年 | 38篇 |
2009年 | 36篇 |
2008年 | 55篇 |
2007年 | 64篇 |
2006年 | 50篇 |
2005年 | 43篇 |
2004年 | 39篇 |
2003年 | 37篇 |
2002年 | 28篇 |
2001年 | 13篇 |
2000年 | 10篇 |
1999年 | 8篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 6篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1985年 | 3篇 |
1983年 | 2篇 |
1980年 | 3篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1972年 | 2篇 |
1969年 | 3篇 |
1966年 | 2篇 |
1965年 | 2篇 |
1963年 | 2篇 |
1932年 | 1篇 |
1926年 | 2篇 |
1918年 | 2篇 |
排序方式: 共有982条查询结果,搜索用时 15 毫秒
101.
Rafael S. Teixeira Ivan F. Souza Rafael S. Santos Lucas C. Gomes Silvano R. Borges Leonardus Vergütz Ivo R. Silva 《植物养料与土壤学杂志》2019,182(4):515-523
The reclamation of bauxite‐mined areas can be favored by the application of organic and/or chemical fertilization to restore the vegetation. Otherwise, the impact of fertilizations on soil microbiota or plant–microbe interactions as land reclamation progresses is less understood. To address this issue, we evaluated the impact of organic and chemical fertilization on plants and soil microbial community within the first 36 months of land reclamation in a bauxite‐mined site. The experiment was set up according to a split‐plot design in which the main plots received fertilizations [non‐fertilized control (NF), chemical fertilization (CF; NPK and rock phosphate), organic fertilization (OF; poultry litter), and CF+OF combined], and the subplots received cover crops [no cover crops (NC), grass (B; Brachiaria), legume (S, Stylosanthes), and B+S combined]. Cover crops biomass yield was assessed annually with five field campaigns per year. We used phospholipid fatty acids (PLFAs) to infer the impacts of mining and restoration practices on actinobacteria, Gram‐negative and Gram‐positive bacteria, arbuscular mycorrhizal fungi, and fungi. Accordingly, PLFAs were determined before bauxite mining (pre‐mining), six months after topsoil reconfiguration (post‐mining), and after 14 and 36 months following the application of the fertilizations and cover crops. PLFAs results indicated that in post‐mining, the living microbiota was significantly lower than in pre‐mining. Cover crops biomass yield was highest for B and B+S fertilized with CF+OF at 14 and 36 months. Both parametric and non‐parametric statistics showed a temporal variation in the response of living microbes to the treatments applied. After 14 months, living microbes showed greatest response to OF, while at 36 months their response was strongest in the treatments with highest plant biomass production (B and B+S). These results suggest that in the early stages of land reclamation, living microbial biomass benefit the most from organic fertilizers. As this initial boost decline, living microbes are more likely to thrive in areas undergoing reclamation where they can develop synergistic interactions with plants. 相似文献
102.
Maćerak Anita Leovac Ivančev-Tumbas Ivana Börnick Hilmar Ilić Gordana Isakovski Marijana Kragulj Maletić Snežana 《Journal of Soils and Sediments》2019,19(2):964-972
Journal of Soils and Sediments - This study utilizes column tests to investigate the retardation of certain herbicides with different hydrophobicities (atrazine, alachlor and trifluralin) during... 相似文献
103.
Contamination history of suspended river sediments accumulated in oxbow lakes over the last 25 years 总被引:3,自引:2,他引:1
Ondrej Bábek Klára Hilscherová Slavomír Nehyba Josef Zeman Martin Famera Juraj Francu Ivan Holoubek Jirí Machát Jana Klánová 《Journal of Soils and Sediments》2008,8(3):165-176
Background, aims, and scope Embankment of meandering river systems in many industrial areas results in the formation of artificial oxbow lakes that may
act as perennial or intermittent traps for river sediments. Their deposits can be dated using a combination of historical
and stratigraphic data, providing a good means to study historical records of contamination transported by rivers. Contamination
history over the last few decades is of special significance for Central and Eastern Europe as it can reflect high pollutant
levels in the second half of the twentieth century and the subsequent improvement after the fall of the Iron Curtain. The
purpose of this study was to investigate recent sediments of an oxbow lake of the Morava River, Czech Republic, their stratigraphic
records, sediment architecture, and history of contamination.
Materials and methods Seven ground-penetrating radar (GPR) profiles and three sediment cores up to 4 m deep were studied. The stratigraphy of the
cores was inferred from visible-light spectrophotometry, X-ray radiography, grain size analysis, and semiquantitative modal
analysis of sandy fractions. The sediments were dated using the 137Cs mass activity and combinations of stratigraphic and historical data. The cores were sampled for concentrations of heavy
metals and persistent organic pollutants. Wet sampled, lyophilized, and sieved sediments were extracted and analyzed for heavy
metals by inductively coupled plasma mass spectrometry (ICP-MS) of aqua regia leachate and for persistent organic pollutants
by gas chromatography (GC-ECD and GC-MS).
Results Three distinct sedimentary sequences (S1, S2, and S3) were identified. The basal sequence S1 represents river channel sediments
deposited before the formation of the oxbow lake, most likely before the 1930s. The boundary between the S1 and S2 sequence
correlates with the level of sediment dredging from 1981 evidenced from historical data. The overlying sequences S2 and S3
represent a postdredging sediment wedge, which progrades into the lake. 137Cs dating revealed a distinct Chernobyl 1986 peak at ∼150 cm depth inferring sedimentation rates up to 7.7 cm/year. Sediment
contamination abruptly increased from the pre-1930s deposits to the post-1981 deposits. The concentration levels increased
two to five times for Pb, As, Zn, and Cu, about 10 to 15 times for Cr, Sb, and Hg, up to 34 times for Cd, and 25 to 67 times
for DDTs, PCBs, and PAHs. The concentrations of most contaminants remained approximately constant until the late 1980s when
they started to decrease slowly. The decreasing trends were most prominent for heavy metals and anthracene, less prominent
for DDTs, and almost absent for PCBs and most PAHs.
Discussion Different temporal and spatial patterns for various contaminants make it possible to distinguish between anthropogenic point
sources from local industry (anthracene, Cr, Cd), possible diffuse sources (most PAHs), and geological background (V, Co,
Ni, and Mo). The observed recent trends in heavy metal and persistent organic pollutant contamination are generally consistent
with data from other Central European rivers. The roughly balanced contamination levels in sediments from the lake and the
adjacent river channel suggest that the oxbow lake deposits reflect immediate levels of the contamination bound to suspended
particulate matter passing through the river.
Conclusions The investigated oxbow lake accumulated suspended sediment from Morava River, developing a thick sedimentary body. The sediments
offer a good time framework to study historical contamination of the river on a decade time scale. Continuous contamination
trends can be traced back to the early 1980s. The results show that stratigraphic analysis of cores has a good potential for
identification of uninterrupted historical trends and unconformities, e.g., due to dredging.
Recommendations and perspectives Oxbow lakes may provide an alternative to floodplains and reservoir deposits when studying river contamination history. High
sedimentation rates of up to 7.7 cm/year offer a very good stratigraphic resolution, making it possible to study contamination
patterns on annual or even seasonal time scales. On the other hand, oxbow lakes may represent long-term contamination stores,
which are unlikely to be redistributed by river erosion and, hence, may possess significant environmental risks for the farther
future. 相似文献
104.
Branimir Jovančićević Mališa Antić Ivona Pavlović Miroslav Vrvić Vladimir Beškoski Alexander Kronimus Jan Schwarzbauer 《Water, air, and soil pollution》2008,190(1-4):299-307
This paper presents transformations of saturated hydrocarbons of petroleum type pollutants during ex situ bioremediation of soil on the pilot heap (halde), during a period of 6 months, within the grounds of Petroleum Refinery Pan?evo (Serbia). Samples for analysis were taken in time intervals of 2 weeks (P1–P12 samples). Organic substance was extracted by Soxhlet’s method and quantified. Isoprenoid aliphatics, in particular pristane and phytane, and polycyclic aliphatics of sterane and triterpane types in saturated hydrocarbon fractions were analysed by GC-MS (SIM method). Significant amounts of n-alkanes have not been detected. The MS-chromatogram revealed only marginal amounts of pristane and phytane in sample P1. Pristane and phytane occurred in sample P8, and in even higher quantities in the final sample P12. The proceeding bioremediation process was accompanied by the decrease of the relative amounts of pentacyclic terpanes of hopane type, compared to tri- and tetracyclic terpanes. In the initial sample P1 the distribution of steranes and hopanes follows a pattern, which is characteristic for crude oils. However, their identification by SIM method was not possible in samples P8 and P12 because of the reduced concentration. The observed changes in the alkane fractions’ compositions may be considered as atypical, referring to the fact that during oil biodegradation under natural conditions, decomposition of isoprenoids occurs much easier and faster than decomposition of polycyclic alkanes of tri-, tetra- and pentacyclic terpane, sterane and diasterane types, after the decomposition of n-alkanes has been almost completed. 相似文献
105.
Alessio Dileta Regina Moro Velho João Pedro Tambara Antônio Augusto Cortiana de Oliveira Gomes Ivan Pedro Knob Deise Aline Haygert-Velho Ione Maria Pereira Busanello Marcos Thaler Neto André 《Tropical animal health and production》2020,52(1):185-193
Tropical Animal Health and Production - To reduce costs, lactating cows are often fed a higher proportion of roughage and alternative feeds; however, such protocols may not lead to optimal milk... 相似文献
106.
Seven healthy sheep and 10 sheep diagnosed with piroplasmosis based on clinical signs were tested for the presence of babesiae and theileriae. Using the molecular techniques, two species of theileriae were detected and characterized. Theileria ovis was present mostly in healthy sheep and in Rhipicephalus ticks collected from infected sheep. Theileria sp. OT3 parasite was detected mostly in ill animals which represent additional evidence to the possible pathogenic nature of Theileria sp. OT3. The presence of babesiae in sheep or in ticks was not determined. The results of this study showed that ovine piroplasmosis due to Theileria is present in Southern Croatia. It was concluded that clinical diagnosis of ovine piroplasmosis should be confirmed by molecular analysis in order to identify the species of piroplasm, to select the appropriate treatment and to exclude the threat for public health. 相似文献
107.
In order to determine the mutations responsible for virulence, three Croatian field infectious bursal disease viruses (IBDV), designated Cro-Ig/02, Cro-Po/00, and Cro-Pa/98 were characterized. Coding regions of both genomic segments were sequenced, and the nucleotide and deduced amino acid sequences were compared with previously reported full-length sequenced IBDV strains. Phylogenetic analysis, based on the nucleotide and deduced amino acid sequences of polyprotein and VP1, was performed. Eight characteristic amino acid residues, that were common to very virulent (vv) IBDV, were detected on polyprotein: 222A, 256I, 294I, 451L, 685N, 715S, 751D, and 1005A. All eight were found in Cro-Ig/02 and Cro-Po/00. C-Pa/98 had all the characteristics of an attenuated strain, except for glutamine on residue 253, which is common for vv, classical virulent, and variant strains. Between less virulent and vvIBDV, three substitutions were found on VP5: 49 G --> R, 79 --> F, and 137 R --> W. In VP1, there were nine characteristic amino acid residues common to vvwIBDV: 146D, 147N, 242E, 390M, 393D, 511S, 562P, 687P, and 695R. All nine residues were found in A-Ig/02, and eight were found in B-Po/00, which had isoleucine on residue 390. Based on our analyses, isolates Cro-Ig/02 and Cro-Po/00 were classified with vv IBDV strains. C-Pa/98 shared all characteristic amino acid residues with attenuated and classical virulence strains, so it was classified with those. 相似文献
108.
Dinorah Vargas Lilia Gutierrez Ivan Juárez Francisco Gonzalez Héctor Sumano 《American journal of veterinary research》2008,69(8):1085-1090
OBJECTIVE: To determine the pharmacokinetics after SC administration of an experimental, long-acting parenteral formulation of doxycycline hyclate in a poloxamer-based matrix and after IV and IM administration of an aqueous formulation of doxycycline hyclate in goats. ANIMALS: 30 clinically normal adult goats. PROCEDURES: Goats were allocated to 3 groups (10 goats/group). One group of goats received doxycycline hyclate (10 mg/kg) IM, a second group received the same dosage of doxycycline hyclate IV, and the third group received the long-acting parenteral formulation of doxycycline hyclate SC. Serum concentrations of doxycycline were determined before and at various intervals after administration. RESULTS: The long-acting parenteral formulation of doxycycline hyclate had the greatest bioavailability (545%); mean +/- SD maximum serum concentration was 2.4 +/- 0.95 microg/mL, peak time to maximum concentration was 19.23 +/- 2.03 hours, and elimination half-life was 40.92 +/- 4.25 hours. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that the long-acting parenteral formulation of doxycycline hyclate distributed quickly and widely throughout the body after a single dose administered SC, and there was a prolonged half-life. Bioavailability of the longacting parenteral formulation of doxycycline hyclate after SC administration was excellent, compared with bioavailability after IV and IM administration of an aqueous formulation of doxycycline hyclate. Although no local tissue irritation and adverse effects were detected, clinical assessment of drug-residues and toxicologic evaluations are warranted before this long-acting parenteral formulation of doxycycline hyclate can be considered for use in goats with bacterial infections. 相似文献
109.
Nikolić A Dimitrijević S Katić-Radivojević S Klun I Bobrć B Djurković-Djaković O 《Acta veterinaria Hungarica》2008,56(3):335-340
To identify areas of risk for canine-related zoonoses in Serbia, the aim of this study was to provide baseline knowledge about intestinal parasites in 151 dogs (65 household pets, 75 stray and 11 military working dogs) from Belgrade. The following parasites, with their respective prevalences, were detected: Giardia duodenalis (14.6%), Ancylostomatidae (24.5%), Toxocara canis (30.5%), Trichuris vulpis (47.0%) and Taenia-type helminths (6.6%). Of all examined dogs, 75.5% (114/151) were found to harbour at least one parasite species. Of these, mixed infections with up to four species per dog occurred in 44.7% (51/114). Infections with all detected species were significantly higher (p < 0.05) in military working (100%) and stray dogs (93.3%) versus household pets (50.8%). Among all parasites, agents with zoonotic potential including Giardia, Ancylostomatidae and Toxocara were detected in 58.3% (88/151) of all examined dogs with a significant difference (p < 0.05) among the subgroups (100%, 62.7% and 46.2% for military working dogs, stray dogs and household pets, respectively). The high prevalence of zoonotic parasites registered in the dog population from a highly urban area in south-eastern Europe indicates a potential risk to human health. Thus, veterinarians should play an important role in helping to prevent or minimise zoonotic transmission. 相似文献
110.
The first weeks of lactation in dairy cows are characterised by elevated bone resorption. The connection between lactation and bone metabolism is still much discussed. In this work, changes in the concentration of plasma parathyroid hormone-related peptide (PTHrP) and markers of bone metabolism were studied in Holstein cows and heifers in the dry period and early lactation to determine the role of PTHrP in the relationship between the rate of bone remodelling and the onset of lactation in dairy cows. Blood samples were taken 14 days before calving ('D-14', n = 23) and then on day 10 ('D+10', n = 21) and day 30 after calving ('D+30', n = 23). Using enzyme immunoassay (EIA), the concentrations of PTHrP, parathyroid hormone (PTH), carboxyterminal cross-linked telopeptide of type I collagen (CTX) and oestradiol and the activity of bone specific alkaline phosphatase (BSALP) were determined. The results showed a statistically significant increase in plasma PTHrP (p < 0.005) and CTX (p < 0.0001) in cows on 'D+10' as compared to 'D-14' and CTX on 'D+30' as compared to 'D-14' (p < 0.0001). Significant negative correlations were found between the concentrations of PTHrP and oestradiol (r = -0.29, p < 0.05) and those of CTX and oestradiol (r = -0.54, p < 0.0001). In nonpregnant heifers (n = 6), the concentration of CTX and the activity of BSALP were significantly higher (p < 0.0001) than in dry cows. The observed increments of PTHrP and bone resorption after parturition reveal adaptations of bone metabolism to lactation in dairy cows. 相似文献