全文获取类型
收费全文 | 1702篇 |
免费 | 89篇 |
国内免费 | 2篇 |
专业分类
林业 | 110篇 |
农学 | 27篇 |
基础科学 | 4篇 |
261篇 | |
综合类 | 196篇 |
农作物 | 79篇 |
水产渔业 | 86篇 |
畜牧兽医 | 872篇 |
园艺 | 33篇 |
植物保护 | 125篇 |
出版年
2023年 | 17篇 |
2022年 | 6篇 |
2021年 | 28篇 |
2020年 | 39篇 |
2019年 | 47篇 |
2018年 | 38篇 |
2017年 | 42篇 |
2016年 | 45篇 |
2015年 | 43篇 |
2014年 | 42篇 |
2013年 | 82篇 |
2012年 | 105篇 |
2011年 | 144篇 |
2010年 | 41篇 |
2009年 | 71篇 |
2008年 | 106篇 |
2007年 | 113篇 |
2006年 | 91篇 |
2005年 | 99篇 |
2004年 | 87篇 |
2003年 | 86篇 |
2002年 | 67篇 |
2001年 | 21篇 |
2000年 | 27篇 |
1999年 | 25篇 |
1998年 | 17篇 |
1997年 | 18篇 |
1996年 | 14篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 9篇 |
1992年 | 16篇 |
1991年 | 13篇 |
1990年 | 16篇 |
1989年 | 10篇 |
1988年 | 5篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 11篇 |
1982年 | 6篇 |
1980年 | 5篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1975年 | 19篇 |
1974年 | 5篇 |
1971年 | 5篇 |
排序方式: 共有1793条查询结果,搜索用时 15 毫秒
81.
Richard J Onders Steven D Mims Barbara A Wilhelm & Jesse D Robinson 《Aquaculture Research》2005,36(16):1602-1610
Paddlefish are gaining increasing acceptance as an aquaculture species worldwide. Commercial trout feeds, containing high protein and lipid levels, are currently used in intensive culture; however, nutritional requirements of paddlefish are not currently known. A study was conducted examining the effects on growth, survival and fillet composition of juvenile paddlefish when fed commercial feeds differing in protein and lipid levels. Paddlefish larvae were first stocked in 14.0 m3 round tanks and fed trout starter feeds for 43 days until trained to accept a 1.6 mm pellet. Paddlefish juveniles of mean weight (±SE) 20±0.27 g were randomly stocked into six0.02 ha ponds at 12 500 ha?1 and fed floating commercial trout or catfish (lower protein and lipid) feeds, twice daily (08:00 and 15:30 hours) for 92–97 days. At harvest, there were no significant differences in final weight, percent survival, specific growth rate , relative growth and feed conversion ratio between treatments, which averaged 223.6 g, 96.2%, 2.5% day?1, 10.2 and 1.98 respectively. Surface feeding activity index was significantly higher in ponds supplied with catfish feed than in ponds supplied with trout feeds. Relative pellet buoyancy was not a factor in feeding activity. Fulton's condition factor averaged0.238, was not significantly different, and was similar to a reported value for extensively cultured paddlefish (zooplanktivore). There was no significant difference in liver somatic index between treatments, which averaged 1.91%. Percent protein and moisture of fillets averaged 14.9% and 80.9%, respectively, and were not significantly different between treatments. However, lipid content of fillets was significantly higher in paddlefish fed the trout feed (4.45%), compared with paddlefish fed the catfish feed (2.42%). Fillet lipid content for both treatments was higher than reported values for extensively cultured paddlefish. Percent abdominal fat was significantly higher (0.82%) in paddlefish fed the trout feed compared with paddlefish fed the catfish feed (0.52%). Results from this study indicate that paddlefish can be fed a commercial catfish feed labeled to contain 32% protein and 4.5% lipid without adverse effects on growth, survival and fillet composition, lowering production costs. 相似文献
82.
Kathleen G. Haynes Xinshun Qu Barbara J. Christ 《American Journal of Potato Research》2014,91(3):254-259
Foliar late blight, caused by Phytophthora infestans, is an important disease problem worldwide. Foliar resistance to late blight was found in a hybrid population of the cultivated diploid species Solanum phureja-S. stenotomum (phu-stn). The objective of this study was to determine if resistance to late blight could be improved by recurrent maternal half-sib selection in the phu-stn population. Four clones from each of 72 maternal half-sib families plus the check cultivar ‘Atlantic’ were evaluated for late blight resistance in replicated field trials in Pennsylvania. The most late blight resistant clone from each of the 72 families was randomly intermated to advance the population. The cycle 1, 2, and 3 populations were evaluated in 1996–1997, 2003–2004, and 2009–2010, respectively. Percent infected foliage was recorded several times towards the end of the growing season and used to compute area under the disease progress curve (AUDPC). Mean AUDPC was 652 (cycle 1), 556 (cycle 2), and 276 (cycle 3), whereas the mean AUDPC of ‘Atlantic’ ranged from 775 to 863 each cycle. Narrow-sense heritability for resistance was estimated as 0.78, 0.77, and 0.80 in cycles 1, 2, and 3, respectively. Recurrent maternal half-sib selection continues to improve the levels of resistance to late blight in this diploid population with no adverse effect on the amount of additive genetic variance. Additional improvements for late blight resistance are likely to occur if this approach is continued. 相似文献
83.
Effect of selected metrological parameters of dyed polyester textiles on their UV-barrier properties
This paper presents the results of studies on the effect of some metrological parameters of polyester textiles dyed with a disperse dye, C. I. Disperse Red 54, on the level of their UV-barrier properties. It has been found that the UV-barrier properties of textiles not always depend on fabric parameters such as thickness and tightness/porosity as suggested by many research works. The parameters mentioned above, due to their interaction with a dye applied (that absorbs UV radiation), one may treat as indirect factors. It is the surface weight of a fabric that seems to be the direct factor and the most important metrological parameter in this regard. This is indicated by spectrophotometric measurements of dyed fabrics of different surface weights. Higher values of this parameter result in higher levels of UV-barrier properties. Increase in the barrier properties with increasing dyeing percentage is also higher for fabrics with greater surface weights. To confirm this fact, we presented in this paper a physical-mathematical model accepted for a dyed woven fabric, treated as an optical filter containing a dye. The model is based on Lambert-Beer’s law. The dye plays the part of a UV radiation absorber, occurring in the fiber material in the state of monomolecular dispersion (a solid solution). 相似文献
84.
Gary S. Burr Peng Li Jonathan B. Goff Delbert M. Gatlin III Barbara Grisdale-Helland Ståle J. Helland 《Journal of the World Aquaculture Society》2006,37(4):421-430
To investigate potential use of increasing nutritional density of diets for rapid growth of warm‐water fishes, a feeding trial was conducted in which growth performance, body indexes, and whole‐body composition of juvenile hybrid striped bass fed diets comprising protein (49, 54, and 59%), lipid (16, 20, 23, and 28%), and energy (22.0–25.1 kJ/g) concentrations beyond established minimum levels were compared to those of fish fed a more typical commercial reference diet (37.5% crude protein, 10.5% crude lipid, and 19.6 kJ/g energy on a dry matter basis). A subset of the experimental diets and the commercial reference diet also were fed to juvenile red drum. After 6 wk of feeding, hybrid striped bass fed the high‐protein and high‐lipid diets showed much greater growth performance compared to fish fed the commercial diet. Increasing dietary protein level, but not lipid level, tended (P ≤ 0.1) to enhance weight gain and feed efficiency of hybrid striped bass. Hepatosomatic index (HSI), intraperitoneal fat (IPF) ratio, and whole‐body protein were significantly (P < 0.01) influenced by dietary protein level. The dietary lipid and associated energy level had significant negative linear effects on daily feed intake. Linear regression analysis showed that dietary energy : protein ratio, largely influenced by dietary protein level, moderately but significantly influenced weight gain, HSI, IPF ratio, and whole‐body protein of hybrid striped bass and red drum. Red drum grew very similar to hybrid striped bass in response to the experimental diets. However, significant differences in HSI, IPF ratio, whole‐body protein, lipid, moisture, and ash between hybrid striped bass and red drum were observed, indicating species differences in protein and energy partitioning. In particular, the excessive lipid in the diet increased HSI and whole‐body lipid of red drum but not of hybrid striped bass. 相似文献
85.
86.
Barbara Sherman Simpson Mark G Papich 《Veterinary Clinics of North America: Small Animal Practice》2003,33(2):365-404, vii
As our knowledge expands, behavioral pharmacology plays an increasingly important role in behavioral medicine. Drugs traditionally categorized as anxiolytics, antidepressants, anticonvulsants, and hormones may be used to help manage a range of animal behavioral problems. Knowledge of how these agents act in the body and interact with other agents is imperative for safe and efficacious use. 相似文献
87.
The objective of this study was to understand the effects of fumarate addition on methane (CH4) and VFA production in the rumen through a meta-analysis of its effects on ruminal batch cultures. Because the reduction of fumarate to succinate can draw electrons away from ruminal methanogenesis, fumarate has been studied as a potential feed additive to decrease CH4 production in ruminants. The average decrease in CH4 in batch cultures was of 0.037 micromol/micromol of added fumarate, which is considerably lower than 0.25 micromol/micromol, the decrease predicted from the stoichiometry of the reactions involved. One reason that fumarate was not effective at decreasing CH4 in batch cultures was that only an average of 48% of added fumarate appeared to be converted to propionate. Secondly, the incorporation of reducing equivalents in the conversion of fumarate to propionate was almost entirely offset by their release from an average of 20% of added fumarate that appeared to be converted to acetate. Thermodynamic calculations indicated that the conversion of added fumarate to both propionate and acetate was feasible. Fumarate appears to be more effective in decreasing CH4 production and increasing propionate in continuous culture than in batch culture. This suggests that microbial adaptation to fumarate metabolism can be important. Variation in populations of fumarate-reducers, methanogens, and protozoa could all be involved. Fumarate supplementation for an extended period may result in the amplification of otherwise small populations of fumarate-reducers. Addition of some of these organisms may be helpful to improve fumarate conversion to propionate. Strategies based on enhancing the rumen's capacity to convert fumarate to propionate by maintaining a low fumarate concentration have been effective. Thermodynamic considerations should be taken into account when designing strategies for CH4 abatement through the addition of external electron acceptors. 相似文献
88.
The aim of this study was to examine the embryogenic potential of floral material of the cassava cultivar MCOL 1505. Macerated
immature inflorescences were found to be highly embryogenic, with almost 78% of the explants producing somatic embryos. Somatic
embryos were also produced from whole male florets and half florets although at much lower rates. No regeneration was obtained
from anther, microspore or floret wall tissue. Somatic embryos derived from immature inflorescences were regenerated via organogenesis
and the plants derived from this process were assessed in terms of phenotype and ploidy level. If haploid plants could be
produced by this method, this would have significant implications in assisting traditional cassava breeding, as this would
allow homozygosity to be reached more rapidly. In a crop such as cassava, which is highly heterozygous in nature, the use
of haploids in a breeding programme could considerably shorten the time taken to produce new desirable cultivars. This is
the first report on plant regeneration through somatic embryogenesis from floral tissue of cassava.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
89.
Abstract: Local communities are frequently displaced from areas selected for environmental protection. Development of nature‐based tourism, believed to be more environmentally benign than traditional agricultural systems, has been encouraged by governments and national park managers in the hope of providing alternative livelihoods for local people. This paper examines the extent to which indigenous peoples resettled from within one Vietnamese national park have engaged with the nascent tourism industry, thereby providing a perspective on the success of their resettlement, through the eyes of those communities affected. The perspectives of resettled peoples are contrasted with those of villagers who have continued to reside within the national park, using traditional means of survival, along with new initiatives designed to supplement their livelihoods and to reduce their dependence on national park resources for survival. Resettled villagers are unable to survive on agricultural activity alone, tourism has done little to provide an alternate livelihood and the park environment is still threatened by the use of park resources by resettled communities in their struggle to survive. 相似文献
90.
Summary Wide hybridizations between M. arvensis and Brassica amphidiploid species (B. napus and B. juncea) were carried out in order to incorporate desirable traits of M. arvensis into Brassica crops. Crossing barriers between them were present without the use of in vitro techniques. F1 hybrids have been produced through ovary culture, when M. arvensis were used as a female parent. Higher hybrid embryo productivity (3.07 embryos per pollination) was obtained in the cross of M. arvensis x B. napus than in that of M. arvensis x B. juncea (0.79 embryos). The hybridity was confirmed by morphology, cytology, isozyme and Southern analyses. The first backcrossing progenies and open pollinated ones were produced. 相似文献