全文获取类型
收费全文 | 713篇 |
免费 | 33篇 |
国内免费 | 2篇 |
专业分类
林业 | 28篇 |
农学 | 11篇 |
基础科学 | 4篇 |
73篇 | |
综合类 | 72篇 |
农作物 | 30篇 |
水产渔业 | 67篇 |
畜牧兽医 | 367篇 |
园艺 | 17篇 |
植物保护 | 79篇 |
出版年
2021年 | 11篇 |
2020年 | 11篇 |
2019年 | 18篇 |
2018年 | 6篇 |
2017年 | 8篇 |
2016年 | 10篇 |
2015年 | 5篇 |
2014年 | 10篇 |
2013年 | 27篇 |
2012年 | 22篇 |
2011年 | 29篇 |
2010年 | 19篇 |
2009年 | 23篇 |
2008年 | 36篇 |
2007年 | 43篇 |
2006年 | 28篇 |
2005年 | 28篇 |
2004年 | 35篇 |
2003年 | 40篇 |
2002年 | 34篇 |
2001年 | 18篇 |
2000年 | 24篇 |
1999年 | 23篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1996年 | 12篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 11篇 |
1992年 | 11篇 |
1991年 | 6篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 11篇 |
1985年 | 13篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1979年 | 10篇 |
1978年 | 11篇 |
1977年 | 5篇 |
1976年 | 9篇 |
1975年 | 9篇 |
1974年 | 16篇 |
1973年 | 7篇 |
1972年 | 3篇 |
1947年 | 3篇 |
排序方式: 共有748条查询结果,搜索用时 445 毫秒
661.
Allan J. Cessna 《Pest management science》1987,19(1):79-83
Residues of the herbicide dinoseb were determined gas chromatographically in lentils which had been treated at two locations in Saskatchewan with post-emergence applications of dinoseb at 1.4 and 1.7 kg ha?1. Herbicide residues, determined at selected times after application, were not detected at the limit of detection of the analytical method (0.05 mg kg?1) in either the seed and straw at maturity, or in the green foliage six to eight weeks after application. Recoveries of dinoseb were 76% from fortified green foliage at the 0.1 mg kg?1 level, and 64% from fortified seed at the 0.05 mg kg?1 level. 相似文献
662.
Rae DO Chenoweth PJ Genho PC McIntosh AD Crosby CE Moore SA 《Journal of the American Veterinary Medical Association》1999,214(7):1051-1055
OBJECTIVE: To determine prevalence of infection with tritrichomonas fetus in a bull population; assess influence of age, breed, and grouping; assess effects on measures of cow performance (pregnancy rate, weaning percentage, weaning weight); and estimate test sensitivity. DESIGN: Epidemiologic study. ANIMALS: 1,383 bulls and records for 28,471 cows bred by these bulls in the immediate past breeding season. PROCEDURE: Bulls in 11 cattle units on a large ranch were tested for T fetus colonization by vigorous preputial scraping and protozoologic culture until no newly infected bulls were identified. Bull infection prevalence within units was calculated and correlated to production measurements reported for each cattle unit. RESULTS: Mean prevalence of T fetus-infected bulls was 11.9% (range, 0 to 35.9%). Significant difference was detected between mean age of infected bulls (5.5 years) and noninfected bulls (3.9 years). Difference in prevalence among breeds was found, although other factors may have influenced this finding. Cow performance measurements (weaning percentage, mean weaning weight, and adjusted mean weaning weight/exposed cow) for cows exposed by breeding to bull groups with the highest prevalence of infection (35.9%) were significantly different from mean values for the entire study population. Test sensitivity for this study (73%) was less than that reported in other studies. CLINICAL IMPLICATIONS: T fetus infection in a natural service beef herd has an adverse impact on several production measures: Severity of impact is related to prevalence of infection in the bull population, where prevalence is bull age and population dependent. 相似文献
663.
ACTH is the primary regulator of adrenal function during acute stress. However, during chronic inflammatory stress additional factors play a major role in the regulation of adrenal secretion. Many cytokines circulate in the blood and are synthesized and released from adrenal tissue. Furthermore, these peptides modify adrenal function. Recently, interleukin-4 (IL-4) was demonstrated to be released from a human adrenal tumor cell line. Therefore, we hypothesized that normal bovine adrenocortical cells could express IL-4 and that this cytokine may modify adrenal function. We determined that IL-4 and IL-4 receptors (IL-4R) are expressed in the bovine adrenal cortex whereas the expression of IL-4 and IL-4R in the adrenal medulla was not apparent. Exposure of dispersed bovine adrenocortical cells isolated from the zona fasciculate to IL-4 did not modify basal release of cortisol. However, the ACTH-stimulated release of cortisol from the bovine adrenal cells was augmented by IL-4. IL-4 exposure had no affect on adrenal androgen release from bovine zona reticularis cells, but IL-4 inhibited the ACTH-stimulated release of adrenal androgens from these cells. The effects of IL-4 on ACTH-stimulated cortisol and adrenal androgen release were dependent upon the IL-4 incubation interval and the IL-4 concentration. Because communication between the immune and endocrine systems is important in inflammatory conditions, IL-4 may play a role in coordinating the adrenal response to inflammatory stress. 相似文献
664.
Blood was collected the day before slaughter from pigs fed fine, medium or coarse ground grain and examined in accordance with Tables 1–3. Of the 15 pigs (group 1) on the finest meal all except one developed parakeratotic or erosive changes (Figs. 1–5) in the pars oesophagea of the stomach. In group 2 (medium ground) the corresponding number was seven out of 18. No pathological alterations could be detected in the stomach of the pigs on coarse grain.Statistically significant or almost significant differences were obtained between the groups for hemoglobin, hematocrit, number of erythrocytes, urea-N and pepsinogen. A much wider range was observed in the γ-globulins of the group on fine grain than in the other two groups. The differences in proteins were, however, not significant. To see whether the observed differences between the groups were related to the gastric pathological alterations or to the feed, a comparison was made between pigs with and without pathological changes (Table 3). There were still significant, though smaller, differences in the hemoglobin and hematocrit values. A higher level of significance was only obtained for pepsinogen. 相似文献
665.
Lucélia Tessaro Cesar Pereira Rebechi de Toledo Giovano Neumann Ricardo Andrei Krause Fábio Meurer Maria Raquel Marçal Natali Robie Allan Bombardelli 《Aquaculture Research》2014,45(9):1425-1433
This study was conducted to evaluate the effects of different diet energy levels on animal performance. Specifically, this investigation examined the reproductive and histological aspects of the liver and gonads of female silver catfish (Rhamdia quelen). These fish were fed for 210 days with diets containing 30% digestible protein (DP) and digestible energy (DE) that corresponded to 11.93, 12.98, 14.03, 15.07 and 16.12 MJ of DE kg?1. The initial and final lengths, weights, and weight gains, the visceral, gonadal, and hepatosomatic indices, and the histological parameters hepatocytes area and gonadal stages were evaluated. In the reproductive season, the fish were submitted to an artificial reproduction protocol and the percentage of spawning females and their relative and absolute fecundity were evaluated. DE did not affect reproductive or animal performance aspects (P > 0.05). Cytoplasmic vacuoles in hepatocytes were observed in higher DE levels. Thus, female Rhamdia quelen can be fed a diet of 30% DP with 11.93 MJ of DE kg?1 without reproductive or performance losses. 相似文献
666.
Background
Understanding and predicting the response of tree populations to climate change requires understanding the pattern and scale of their adaptation. Climate is often considered the major driver of local adaptation but, although biotic factors such as soil pathogens or mutualists could be as important, their role has typically been neglected. Biotic drivers might also interact with climate to affect performance and mycorrhizae, in particular, are likely to play a key role in determining drought resistance, which is important in the context of adaptation to future environmental change. To address these questions, we performed a fully reciprocal soil–plant transplant experiment using Fagus sylvatica seedlings and soils from three regions in Germany. To separate the biotic and abiotic effects of inoculation, half of the plants were inoculated with natural soil from the different origins, while the rest were grown on sterilized substrate. We also imposed a drought stress treatment to test for interactions between soil biota and climate. After 1 year of growth, we measured aboveground biomass of all seedlings, and quantified mycorrhizal colonization for a subset of the seedlings, which included all soil–plant combinations, to disentangle the effect of mycorrhiza from other agents.Results
We found that plant origin had the strongest effect on plant performance, but this interacted with soil origin. In general, trees showed a slight tendency to produce less aboveground biomass on local soils, suggesting soil antagonists could be causing trees to be maladapted to their local soils. Consistently, we found lower mycorrhizal colonization rate under local soil conditions. Across all soils, seedlings from low elevations produced more annual biomass than middle (+?290%) and high (+?97%) elevations. Interestingly, mycorrhizal colonization increased with drought in the two provenances that showed higher drought tolerance, which supports previous results showing that mycorrhizae can increase drought resistance.Conclusions
Our findings suggest that soil communities play a role in affecting early performance of temperate trees, although this role may be smaller than that of seed origin. Also, other effects, such as the positive response to generalists or negative interactions with soil biota may be as important as the highly specialized mycorrhizal associations.667.
668.
H. Allan Bremner 《Journal Of Aquatic Food Product Technology》2013,22(1):16-19
Fillets from Pacific cod (Gadus macrocephalus) were salted with and without polyphosphates (PP) by means of a short three-step salting process. The changes in phosphate and water content during different steps of production were determined by comparing fillets with and without addition of PP. While fillet samples after salt injection and wet-salting contained different water content, from 80.1% to 74.6% depending on processing step and PP addition or not, after dry-salting there was no significant difference in water content between fillets with (58.1%) or without PP (58.9%). Dry-salted fillets with PP addition showed a phosphate content of 6.1 mg P2O5/g. In the following rehydration process (48 h), the total phosphate content dropped down to 2.9 mg P2O5/g, which was lower than the natural total phosphate content of 4.4 mg P2O5/g in the raw material. 相似文献
669.
Olav Sigurd Kjesbu Maud Alix Anne Britt Sandø Espen Strand Peter J. Wright David G. Johns Anders Thorsen C. Tara Marshall Kjell Gunnar Bakkeplass Frode B. Vikebø Mari Skuggedal Myksvoll Geir Ottersen Bridie J. M. Allan Maria Fossheim Jan Erik Stiansen Geir Huse Svein Sundby 《Fish and Fisheries》2023,24(2):297-320
The reproductive success of marine ectotherms is especially vulnerable in warming oceans due to alterations in adult physiology, as well as embryonic and larval survival prospects. These vital responses may, however, differ considerably across the species' geographical distribution. Here we investigated the life history, focusing on reproductive ecology, of three spatially distant populations (stocks) of Atlantic cod (Gadus morhua, Gadidae) (50–80° N), in the Irish/Celtic Seas-English Channel Complex, North and Barents Seas, under past and projected climate. First, experimental tracking of spawning behaviour evidenced that the ovulation cycle is highly distressed at ≥9.6 (±0.25)°C (Tup). This knife-edge threshold resulted in erratic spawning frequencies, whereas vitellogenin sequestration remained unaffected, indicating endocrine rather than aerobic scope constraints. Cod in the Celtic Sea-English Channel are, therefore, expected to show critical stock depensation over the next decades as spawning grounds warm above Tup, with Irish Sea cod subsequently at risk. Second, in the relatively cooler North Sea, the northward retraction of Calanus finmarchicus (Calanidae) and Para-Pseudocalanus spp. (Clausocalanidae) (1958–2017) limit cod larvae feeding opportunities, particularly in the southernmost subarea. However, the contrasting increase in Calanus helgolandicus (Calanidae) does not counteract this negative effect, likely because cod larvae hatch ahead of its abundance peaks. Overfishing again comes as a twin effect. Third, in the still relatively cold Barents Sea, the sustainably harvested cod benefit from improved food conditions in the recent ice-free polar region but at the energetic cost of lengthier and faster spawning migrations. Consequently, under climate change local stocks are stressed by different mechanistic factors of varying management severity. 相似文献
670.
Loke WM Proudfoot JM McKinley AJ Needs PW Kroon PA Hodgson JM Croft KD 《Journal of agricultural and food chemistry》2008,56(10):3609-3615
This study examined the effects of metabolic transformation of the common dietary flavonoid, quercetin, on its ability to protect low-density lipoprotein (LDL) from neutrophil-mediated modification. Quercetin was shown to be effective in protecting LDL against neutrophil-mediated modification at physiological concentrations (1 microM) and appears to act by inhibiting myeloperoxidase (MPO)-catalyzed oxidation (IC(50) = 1.0 microM). Quercetin was also shown to protect against radical-induced [2,2'-azobis(2-methylpropionamidine)dihydrochloride] oxidation (IC(50) = 1.5 microM). Studies of structure-activity relationships showed that methylation at the 3'-position or glucuronidation at the 3-position did not significantly affect inhibition by quercetin of the MPO activity, but conjugations at both positions significantly reduce its activity. Our results suggest that the common dietary flavonoid, quercetin, and some of its major in vivo metabolites are potential inhibitors of MPO at physiological concentrations. Dietary flavonoids that could modify MPO activity could protect lipoproteins from damage in chronic inflammatory states such as cardiovascular disease. 相似文献