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541.
Ovine enzootic abortion (OEA) remains a major problem in sheep-rearing countries despite the availability of protective vaccines. The causative agent, Chlamydophila abortus, is a Gram-negative bacterium that can induce a persistent, subclinical infection in non-pregnant sheep. The development of a new safe, effective and practical vaccine requires a detailed understanding of host-pathogen interactions and the identification of clear correlates of protection. Since disease (abortion) is only observed during pregnancy, the nature of host immunity to C. abortus and the specialised immunological features that permit maternal acceptance of the semi-allogeneic fetus are central to the pathogenesis of OEA. We review the current literature on persistence of C. abortus, host immunity to infection and mechanisms of abortion. We identify the key outstanding questions surrounding OEA and discuss the current knowledge gaps with a view to developing improved control strategies. 相似文献
542.
543.
Chemical and biological characteristics of alkaline saline soils from the former Lake Texcoco as affected by artificial drainage 总被引:3,自引:0,他引:3
M. L. Luna-Guido R. I. Beltrán-Hernández N.A. Solís-Ceballos N. Hernández-Chávez F. Mercado-García J. A. Catt V. Olalde-Portugal L. Dendooven 《Biology and Fertility of Soils》2000,32(2):102-108
Soils from the former Lake Texcoco are alkaline saline and were artificially drained and irrigated with sewage effluents
since the late 1980s. Undrained soil and soil drained for 1, 5 and 8 years were sampled, characterized and incubated aerobically
for 90 days at 22±1 °C while production of CO2, available P and concentrations of NH4
+, NO2
– and NO3
– were monitored. Artificial drainage decreased pHH2O, water holding capacity, organic C, total N, and Na+, K+, Mg2+, B, Cl– and SO4
2– concentrations, increased inorganic C and Ca2+ concentrations more than 5-fold while total P was not affected. Microbial biomass C decreased with increased length of drainage
but bacteria, actinomycetes, denitrifiers and cellulose-utilizing bacteria tended to show opposite trends. CO2 production was less in soils drained ≥5 years compared to undrained soil but more than in soils drained for 1 year. Emission
of NH3 was negligible and concentrations of NH4
+ remained constant over time in each soil. Nitrification, as witnessed by increases in NO3
– concentrations, occurred in soil drained for 8 years. NO2
– concentrations decreased in soils drained ≤1 year in the first 7 days of the incubation and remained constant thereafter.
It was found that artificial drainage of soils from the former Lake Texcoco profoundly affected soil characteristics. Decreases
in pH and Na+, K+, Cl– and SO4
2– concentrations made conditions more favourable for plant growth, although low concentrations of inorganic N and available
P might be limiting factors.
Received: 1 December 1999 相似文献
544.
545.
Sean C Anderson Joanna Mills Flemming Reg Watson Heike K Lotze 《Fish and Fisheries》2011,12(3):317-339
In recent decades, invertebrate fisheries have expanded in catch and value worldwide. One increasingly harvested group is sea cucumbers (class Holothuroidea), which are highly valued in Asia and sold as trepang or bêche‐de‐mer. We compiled global landings, economic data, and country‐specific assessment and management reports to synthesize global trends in sea cucumber fisheries, evaluate potential drivers, and test for local and global serial exploitation patterns. Although some sea cucumber fisheries have existed for centuries, catch trends of most individual fisheries followed boom‐and‐bust patterns since the 1950s, declining nearly as quickly as they expanded. New fisheries expanded five to six times faster in 1990 compared to 1960 and at an increasing distance from Asia, encompassing a global fishery by the 1990s. Global sea cucumber production was correlated to the Japanese yen at a leading lag. Regional assessments revealed that population declines from overfishing occurred in 81% of sea cucumber fisheries, average harvested body size declined in 35%, harvesters moved from near‐ to off‐shore regions in 51% and from high‐ to low‐value species in 76%. Thirty‐eight per cent of sea cucumber fisheries remained unregulated, and illegal catches were of concern in half. Our results suggest that development patterns of sea cucumber fisheries are largely predictable, often unsustainable and frequently too rapid for effective management responses. We discuss potential ecosystem and human community consequences and urge for better monitoring and reporting of catch and abundance, proper scientific stock assessment and consideration of international trade regulations to ensure long‐term and sustainable harvesting of sea cucumbers worldwide. 相似文献
546.
Sean D W Comber 《Pest management science》1999,55(7):696-702
Hydrolysis and photolysis experiments have been undertaken to investigate the abiotic persistence of atrazine and simazine in a variety of waters. Hydrolysis only occurs to a significant extent at pH values at the lower limit of those found in the natural aquatic environment (pH 4.0 or less). Photolysis was initiated by a wide range of wavelengths in waters at pH 4.0, but only by more energetic wavelengths of less than 300 nm at higher pH values (pH 6 to 8). Based on these data, the aquatic half-life of atrazine and simazine in well-lit acidic upland waters will be typically six days. In lowland rivers with higher pH (7 to 8.5), these triazines are likely to exhibit half-lives of months rather than days. In groundwaters, atrazine and simazine will have half-lives in the order of years, due to the exceedingly slow rate of hydrolysis. © 1999 Society of Chemical Industry 相似文献
547.
Chan Sol Kang Il Jae Lee Moo Song Seo Sun Hong Kim Doo Hyun Baik 《Fibers and Polymers》2017,18(8):1580-1585
We purified as-received CNT fibers (CNTFs) with four different methods and systematically examined effects of various purifications on the morphology, structure, and electrical conductivity of the resultant CNTFs, respectively. The purified CNTFs were characterized by an optical microscope, transmission electron microscope (TEM) coupled with an energy dispersive X-ray spectrometer (EDS), Raman spectroscopy, and multiple source meters. Optical images showed that morphology of CNTFs did not largely change after purification. TEM images and EDS results showed that the Fe impurities, 21.9 wt%, in CNTFs were decreased to 0.17-1.20 wt% and were nearly eliminated by acid and alkali purifications, respectively. Raman results identified the ID/IG ratio of CNTFs was 0.71, while those of HCl treatment after steam with heat (HSCNTFs-HCl), NaOCl treatment after steam with heat (HSCNTFs-NaOCl), and NaOH treatment with heat without steam (NaOH-HCNTFs) were 0.45, 0.49, and 0.57, respectively, which means that purification methods of CNTFs performed in this study are thought to be satisfactory for manufacturing high-purity CNTFs. Electrical conductivity (1.4×104 S/m) of NaOH-HCNTFs (one-step procedure) was twice as high as that (7.3×103 S/m) of CNTFs, but lower than those (2.1-2.3×104 S/m) of HSCNTFs-HCl and HSCNTFs-NaOCl (two-step processes), which demonstrates that two-step processes rather than one-step procedure would have a positive effect on the electrical conductivity of the resultant CNTFs. 相似文献
548.
Two experiments over 21 days were conducted to assess the effect of different ionic profiles (mainly K+) of inland saline water (ISW) on the survival, growth, osmoregulation and moisture content of juvenile greenlip abalone Haliotis laevigata. In experiment I, the juveniles were cultured in five different water types: ocean water (OW) as a control, inland saline water (ISW or ISW K+0), ISW fortified with 33%, 66% and 100% K+ as in OW (ISW K+33, ISW K+66 and ISW K+100 respectively). In experiment II, five different culture media, 100% OW(control), 75% OW mixed with 25% ISW (ISW25), 50% OW mixed with 50% ISW (ISW50), 25% OW mixed with 75% ISW (ISW75) and 100% ISW (ISW or ISW100), were tested. Within 21 days, all of the abalone in ISW (ISW K+0 and ISW100; Na+/K+ ratio of 111 L?1) died compared with 100% survival in OW. One‐hundred per cent K+ fortification of ISW increased the specific growth rate (SGR) and serum osmolality of the surviving juveniles. The 96 h acute LC50 value was between ISW50 and ISW75. The increased proportion of ISW in OW resulted in significantly (P<0.05) lower survival, SGR and serum osmolality of juveniles. The moisture content of the juveniles was not influenced by any water type. The results suggested that abalone cannot survive in raw ISW, but survival can increase when it is fortified with K+ and ionic ratios of ISW are brought closer to OW by mixing it with OW. Furthermore, abalone survival is influenced by other ions in ISW besides K+. 相似文献
549.
Jaeyoung Kim Michael Sean Kent Alain Pierre Théon Amandine Tamara Lejeune Katherine Sarah Hansen 《Veterinary and comparative oncology》2023,21(3):419-426
Published radiotherapy results for spinal nephroblastomas in dogs are limited. In this retrospective longitudinal study (1/2007–1/2022), five dogs with a median age of 2.8 years received post-operative 3D conformal, conventional fractionated radiotherapy (CFRT) with 2–4 fields (parallel-opposed with or without two hinge-angle fields), for an incompletely resected nephroblastoma. Clinical findings prior to surgery included one or more of the following: pelvic limb paresis (5), faecal incontinence (2), flaccid tail (1), non-ambulatory (2) and deep pain loss (1). All masses were located between T11 and L3 and surgically removed via hemilaminectomy. Dogs received 45–50 Gray (Gy) in 18–20 fractions, and no dogs received chemotherapy post-radiation. At analysis, all dogs were deceased, with none lost to follow-up. The median overall survival (OS) from first treatment to death of any cause was 3.4 years (1234 days; 95% CI 68 days-upper limit not reached; range: 68–3607 days). The median planning target volume was 51.3 cc, with a median PTV dose of 51.4 Gy and median D98 = 48.3 Gy. Late complications or recurrence was difficult to fully determine in this small dataset; however, some degree of ataxia persisted throughout life in all dogs. This study provides preliminary evidence that post-operative radiotherapy may result in prolonged survival times dogs with spinal nephroblastomas. 相似文献