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排序方式: 共有1404条查询结果,搜索用时 156 毫秒
1.
A.J.A. Vinten D.R. Lewis D.R. Fenlon K.A. Leach R. Howard I. Svoboda I. Ogden 《Soil Use and Management》2002,18(3):223-231
Abstract. Slurry from farm animals may contaminate water supplies, rivers and bathing waters with faecal coliforms, such as Escherichia coli . Where animals harbour the O157 strain the hazard to human health is particularly high, but both the hazard level, and the low incidence and sporadic nature of the excretion of E. coli O157 make it difficult to study this strain under field conditions. The survival of total E. coli and of E. coli O157 were compared in the laboratory for two soils under controlled temperature and moisture. E. coli O157 die-off rate was the same as or quicker than for total E. coli . This result meant that field experiments studying the fate of total E. coli should give a satisfactory evaluation of the risk of water contamination by the O157 strain. In four field experiments at three sites, slurry containing total E. coli numbers of 2.2 × 104 to 5.7 × 105 colony forming units per mL (c.f.u. mL–1 ) was applied to drained field plots. Field die-off was faster than expected from laboratory experiments, especially in one experiment where two weeks dry weather followed application. In all but this experiment, the first drain flow events after slurry application led to very high E. coli concentrations in the drains (103 to 104 c.f.u. mL–1 ). E. coli O157 was present in the slurry used for two of the experiments (33 c.f.u. per 100 mL in each case). However the proportion of E.coli O157 was very low (about 1 in 105 ) and it was not detected in the drainage water. After the first week E. coli drainage water numbers decreased rapidly but they were 1–10 c.f.u. mL–1 for much of the sampling period after slurry application (1–3 months). 相似文献
2.
1. Brown egg laying pullets were transferred from an 8‐h photoperiod to an 8‐, 10‐, 13‐ or 16‐h photoperiod at 6, 9, 12, 15, 18 or 20–3 weeks of age. Plasma luteinising hormone (LH) concentrations were measured at transfer and 7 and 14 d afterwards.
2. Significant increases in plasma LH occurred following light stimulations at 6, 9 and 12 weeks of age.
3. Changes in LH concentration 7 d after a light increase from 8 h to 8, 10, 13, 16 h were highly correlated with photoperiod length at 9 and 12 weeks of age.
4. Changes in LH were generally poorly correlated with age at sexual maturity, although the reduced influence on age at first egg of a light increase given close to sexual maturity was reflected in minimal LH responses at 18 and 20.3 weeks. 相似文献
3.
A model to evaluate economic criteria involved when cattle are raised on high-forage diets prior to finishing or finished directly after weaning was developed using data from two experiments. In Exp. 1, each year for 3 yr, 136 Charolais-cross calves were weaned and allotted to either an intensive system, in which they were immediately finished on a high-grain diet, or an extensive system, in which they were wintered on crop residues, grazed on summer pasture and finished on a high-grain diet. In Exp. 2, 160 British breed steers were wintered, in one of eight different wintering systems utilizing crop residues, using supplemental protein and(or) alfalfa hay. After wintering, the steers grazed summer pasture and then were finished on a high-grain diet. Overall cost of gain and final "break-even" price were lower for cattle finished through the extensive system except when the price of corn was very low in relationship to other inputs. Interest costs were higher for cattle in the extensive system. Increasing the feeder calf purchase price had almost no effect on differences between the systems. Corn price and purchase price affected both systems similarly, whereas interest rate, wintering yardage and finishing yardage affected each system differently. Because of the additional weight produced through the extensive system, it yielded lower final "break-even" prices in most situations. 相似文献
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The effects on DNA synthesis of the fungicide captan and several structurally related compounds were investigated in isolated bovine liver nuclei. Captan, folpet, captafol, and trichloromethanesulfenyl chloride inhibited DNA synthesis to the same degree with ID50 values of approximately 50 μM in a 40-min assay. The inhibition is concentration dependent and the degree of inhibition increases with time. Studies with structural analogs of captan indicated that inhibition of DNA synthesis by captan is mediated through the trichloromethylthio moiety of the captan molecule. In addition, the data indicate thiophosgene is probably not the toxic species involved in the inhibition of DNA synthesis. The isolated nuclei used in this study were shown to exhibit only a single DNA polymerase activity which was determined to be of the β or low-molecular-weight type. In addition to its inhibition in intact nuclei, captan inhibited the activity of the β polymerase in nuclear extracts as well as in partially purified enzyme preparations. These results indicate that captan inhibits DNA synthesis in our preparation of isolated nuclei by acting directly on the DNA polymerase-catalyzed reaction rather than by causing a nonspecific or indirect effect in the nuclear system such as alterations in the nuclear membrane or aggregation of the nuclei. The site of captan's inhibitory action is the DNA polymerase molecule. The interaction of captan with the polymerase results in irreversible inhibition of the enzyme. Interaction of captan with the template, if it occurs, does not appear to be involved in mediating the inhibition. 相似文献
6.
John C M Lewis 《Journal of zoo and wildlife medicine》2004,35(3):303-311
Conventional inhalation anesthesia of wildlife species within natural habitats presents significant practical problems. Heavy cylinders of medical grade oxygen are often unavailable in field situations. Equipment has been modified to permit the delivery of isoflurane in ambient air as the carrier and to be fitted with circuitry adaptable for different species and anesthetic situations. Preliminary empirical studies at low altitude in a range of small mammalian and avian species demonstrate the suitability of this combination and these techniques for inducing and maintaining anesthesia in clinically normal patients undergoing relatively minor procedures. The equipment has also been used to deepen and prolong anesthesia in several larger species, including great apes and large cats, after induction with injectable agents. These techniques, in combination with pulse oximetry to detect hypoxemia, provide a cheap, robust, and portable inhalation anesthetic system for field situations that is not dependent on compressed gasses. 相似文献
7.
K Ashley S Wilson JR Young HP Chan S Vitou S Suon PA Windsor RD Bush 《Tropical animal health and production》2018,50(1):63-73
Forage technology has been successfully introduced into smallholder cattle systems in Cambodia as an alternative feed source to the traditional rice straw and native pastures, improving animal nutrition and reducing labour requirements of feeding cattle. Previous research has highlighted the positive impacts of forage technology including improved growth rates of cattle and household time savings. However, further research is required to understand the drivers, challenges and opportunities of forage technology for smallholder cattle households in Cambodia to facilitate widespread adoption and identify areas for further improvement. A survey of forage-growing households (n = 40) in July–September 2016 examined forage technology adoption experiences, including reasons for forage establishment, use of inputs and labour requirements of forage plot maintenance and use of forages (feeding, fattening, sale of grass or seedlings and silage). Time savings was reported as the main driver of forage adoption with household members spending approximately 1 h per day maintaining forages and feeding it to cattle. Water availability was reported as the main challenge to this activity. A small number of households also reported lack of labour, lack of fencing, competition from natural grasses, cost of irrigation and lack of experience as challenges to forage growing. Cattle fattening and sale of cut forage grass and seedlings was not found to be a widespread activity by interviewed households, with 25 and 10% of households reporting use of forages for these activities, respectively. Currently, opportunities exist for these households to better utilise forages through expansion of forage plots and cattle activities, although assistance is required to support these households in addressing current constraints, particularly availability of water, if the sustainability of this feed technology for smallholder cattle household is to be established in Cambodia. 相似文献
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10.
Paul C. Stoy Mathew Williams Mathias Disney Ana Prieto-Blanco Brian Huntley Robert Baxter Philip Lewis 《Landscape Ecology》2009,24(7):971-986
Transferring ecological information across scale often involves spatial aggregation, which alters information content and
may bias estimates if the scaling process is nonlinear. Here, a potential solution, the preservation of the information content
of fine-scale measurements, is highlighted using modeled net ecosystem exchange (NEE) of an Arctic tundra landscape as an
example. The variance of aggregated normalized difference vegetation index (NDVI), measured from an airborne platform, decreased
linearly with log(scale), resulting in a linear relationship between log(scale) and the scale-wise modeled NEE estimate. Preserving
three units of information, the mean, variance and skewness of fine-scale NDVI observations, resulted in upscaled NEE estimates
that deviated less than 4% from the fine-scale estimate. Preserving only the mean and variance resulted in nearly 23% NEE
bias, and preserving only the mean resulted in larger error and a change in sign from CO2 sink to source. Compressing NDVI maps by 70–75% using wavelet thresholding with the Haar and Coiflet basis functions resulted
in 13% NEE bias across the study domain. Applying unique scale-dependent transfer functions between NDVI and leaf area index
(LAI) decreased, but did not remove, bias in modeled flux in a smaller expanse using handheld NDVI observations. Quantifying
the parameters of statistical distributions to preserve ecological information reduces bias when upscaling and makes possible
spatial data assimilation to further reduce errors in estimates of ecological processes across scale. 相似文献