全文获取类型
| 收费全文 | 4964篇 |
| 免费 | 894篇 |
| 国内免费 | 92篇 |
专业分类
| 林业 | 191篇 |
| 农学 | 219篇 |
| 基础科学 | 131篇 |
| 469篇 | |
| 综合类 | 1808篇 |
| 农作物 | 163篇 |
| 水产渔业 | 124篇 |
| 畜牧兽医 | 2618篇 |
| 园艺 | 52篇 |
| 植物保护 | 175篇 |
出版年
| 2025年 | 81篇 |
| 2024年 | 184篇 |
| 2023年 | 212篇 |
| 2022年 | 266篇 |
| 2021年 | 252篇 |
| 2020年 | 196篇 |
| 2019年 | 192篇 |
| 2018年 | 156篇 |
| 2017年 | 222篇 |
| 2016年 | 238篇 |
| 2015年 | 178篇 |
| 2014年 | 277篇 |
| 2013年 | 329篇 |
| 2012年 | 418篇 |
| 2011年 | 360篇 |
| 2010年 | 291篇 |
| 2009年 | 262篇 |
| 2008年 | 217篇 |
| 2007年 | 292篇 |
| 2006年 | 241篇 |
| 2005年 | 192篇 |
| 2004年 | 138篇 |
| 2003年 | 133篇 |
| 2002年 | 90篇 |
| 2001年 | 85篇 |
| 2000年 | 61篇 |
| 1999年 | 38篇 |
| 1998年 | 42篇 |
| 1997年 | 41篇 |
| 1996年 | 30篇 |
| 1995年 | 30篇 |
| 1994年 | 35篇 |
| 1993年 | 36篇 |
| 1992年 | 16篇 |
| 1991年 | 22篇 |
| 1990年 | 18篇 |
| 1989年 | 16篇 |
| 1988年 | 16篇 |
| 1987年 | 7篇 |
| 1986年 | 6篇 |
| 1985年 | 3篇 |
| 1984年 | 3篇 |
| 1983年 | 2篇 |
| 1982年 | 7篇 |
| 1981年 | 3篇 |
| 1979年 | 6篇 |
| 1978年 | 2篇 |
| 1975年 | 2篇 |
| 1973年 | 1篇 |
| 1956年 | 3篇 |
排序方式： 共有5950条查询结果，搜索用时 15 毫秒
41.
Angel Rolando Endara Agramont Sergio Franco Maass Gabino Nava Bernal Juan Ignacio Valdez Hernández Todd S. Fredericksen 《林业研究》2012,23(1):39-44
Sample plots were established in the principal forest types in the the Nevado de Toluca National Park, Mexico including those dominated by Pinus hartwegii, Abies religiosa, Quercus laurina and Alnus jorullensis. The vertical structure was defined by three strata in the coniferous forests and two strata in the broadleaved forests. Timber harvesting in Abies religiosa and Quercus laurina forests and fires generated by humans in Pinus hartwegii forests impeded the recruitment of saplings. Mature trees were also heavily impacted by logging in Pinus hartwegii forests. On the contrary, Alnus jorullensis forests were increasing due to the disturbance of Pinus and Quercus forests, as well abandoned crop lands within the park. A combination of logging, uncontrolled fire, and grazing appears to be compromising the recruitment of important tree species in this national park. These factors, together with human settlements, have also increased the proportion of early successional species. Changes in forest structure from human disturbance indicate a need to control these activities if conservation goals are not to be compromised. 相似文献
42.
我国非法证据排除规则的完善——评《办理死刑案件证据规定》和《非法证据排除规定》 总被引：1，自引：0，他引：1
胡志中 《信阳农业高等专科学校学报》2011,21(1):16-18
"两高三部"的《办理死刑案件证据规定》和《非法证据排除规定》,细化和完善了法律和司法解释关于非法证据排除的规定,进一步确立和完善了我国非法证据排除规则。这"两个规定"对司法机关及人员公正办理刑事案件、依法惩治犯罪、切实保障人权具有十分重要的意义。但也有其不足,需要建立和完善相关的配套措施。 相似文献
43.
Two experiments comprising 24 calves, lasting 44–46 days, have been carried out in order to examine the influence of powders from heat-treated skim milk and whey on indigestion in young calves. The frequency of diarrhoea increased much (P < 0.01) in the first experiment when feeding the heat-treated products, but little in the other. Possible reasons for this difference are discussed. Calves fed heat-treated products in the first experiment consumed 13.8 1 of electrolyte fluid per head per day 14–22 days after commencing the test, when both diarrhoea and fluid consumption reached peak values. It is postulated that some of the calves might have succumbed without electrolyte fluid. 相似文献
44.
Tropical Animal Health and Production - 相似文献
45.
Elizabeth A Fulton Anthony D M Smith David C Smith Ingrid E van Putten 《Fish and Fisheries》2011,12(1):2-17
There is broad consensus that the main problem facing fisheries globally is too many boats chasing too few fish. Unfortunately it is also possible to argue that there are too many proposed solutions and not enough practical answers to improving fisheries management. There is a deepening divide between those who propose alternative regulatory controls on fishers, including establishing large areas permanently closed to fishing, and those who argue for better alignment of incentives combined with broad participation of resource users in fishery management decisions (in simple terms, between top down and bottom up systems of governance). However despite the choice of policy instruments used, a consistent outcome is that resource users behave in a manner that is often unintended by the designers of the management system. Hence whilst uncertainty is broadly recognized as a pervasive feature of fisheries management, to date most of the attention has focussed on only part of that uncertainty – scientific uncertainty about the status of exploited resources. The effect of uncertainty generated on the human side of fisheries science and management has received much less attention. However, the uncertainty generated by unexpected resource user behaviour is critical as it has unplanned consequences and leads to unintended management outcomes. Using empirical evidence of unexpected resource user behaviour and reviewing current responses to unexpected management outcomes, we identify different approaches that both improve prediction of human behaviour in fisheries systems and identify management measures that are more robust to these sources of uncertainty. However, unless the micro scale drivers of human behaviour that contribute to macro scale implementation uncertainty are communicated effectively to managers and considered more regularly and in greater depth, unanticipated responses to management actions will continue to undermine management systems and threaten the sustainability of fisheries. 相似文献
46.
Coix seed, which is a traditional Chinese medicine, has been used to treat hypertension for thousands of years. It has been shown that Coix prolamin peptides display high levels of angiotensin I converting enzyme (ACE) inhibitory activity. Hence, we purified the ACE inhibitory peptides from Coix prolamin hydrolysates and evaluated the influence of the most potent peptide on the renin-angiotensin system (RAS) genes expression in human umbilical vein endothelial cells (HUVECs). In this study, Coix prolamin peptides were sequentially separated by ultrafiltration, ion exchange chromatography, gel filtration chromatography and RP-HPLC, while the peptide structure was analyzed by mass spectrometry. Next, in silico proteolysis, pharmacophore and molecular docking were further applied to screen and optimize the structure of peptides. Finally, a novel ACE inhibitory peptide VDMF was obtained, in which its influence on the gene expression of RAS signaling pathway in AngⅡ-injury HUVECs was evaluated by quantitative real-time PCR. VDMF significantly down-regulated ACE, AngII type 1 receptor (AT1R) and ACE2 mRNA expression in comparation with model group, while up-regulating Mas gene expression. Hence, we obtained a novel antihypertensive candidate that was derived from the Coix peptides, which could involve a multi-modulation mechanism that regulates blood pressure. 相似文献
47.
Atsuko Matsubara Hideyuki Takahashi Akira Saito Aoi Nomura Khounsaknalath Sithyphone Christopher D. Mcmahon Ryoichi Fujino Yuji Shiotsuka Tetsuji Etoh Mitsuhiro Furuse Takafumi Gotoh 《Animal Science Journal》2016,87(9):1130-1136
This study aimed to determine the effects of feeding an increased volume of high‐fat milk during the early post‐natal life on metabolite concentrations in the blood, the expression of key genes regulating intermediary metabolism in the skeletal muscles, and the rate of growth of Japanese Black cattle. All calves were fed a high‐fat milk replacer (crude protein, 26%; crude fat, 25.5%; total dissolved nitrogen, 116%). Control calves (n = 4) were nursed with 500 g milk replacer until 3 months of age, whereas calves in the experimental group (n = 4) were nursed with 1800 g milk replacer until 3 months, and then the volume was gradually reduced until 5 months. Body weight was significantly higher in the experimental group than in the control group at 7 months. Plasma glucose concentrations were significantly lower in the experimental group. Expression of glucose‐transporter‐4 messenger RNA (mRNA) was lower, whereas that of glucose transporter 1, cluster of differentiation 36, and carnitine palmitoyltransferase‐1b mRNA was significantly higher in the Longissimus thoracis of the experimental group. Nutritional status during early post‐natal life appears to strongly influence the growth rate and glucose and lipid metabolism in Japanese Black cattle. 相似文献
48.
The performance was compared of cows sired by Holstein, Jersey or Brown Swiss bulls out of Holstein-Friesian×Gir dams of 1/2 to 3/4 Holstein-Friesian content. The animals were kept in a single herd under the same management. The data were analysed by least-squares techniques under a model that included the fixed effects of breed of sire, Bos taurus fraction of the dam, parity, year and season of calving, and a random cow effect. Based on 480 observations, the milk yields per lactation for the Holstein, Jersey and Brown Swiss sired groups were 2821±163, 2320±61 and 2418±119 kg, respectively. The corresponding means for fat yield per lactation were 96.9±6.6, 86.8±2.5 and 92.8±4.8 kg; for protein yield per lactation were 85.3±5.1, 71.3±1.9 and 76.3±3.7 kg; for lactation length, 339±18, 283±7 and 313±14 days for fat percentage, 3.37±0.10, 3.73±0.04 and 3.77±0.07%; and for protein percentage, 3.02±0.05, 3.10±0.02 and 3.16±0.04%. The respective calving intervals were 487±24, 408±11 and 461±245 days. The yields of milk and protein per day of calving interval were similar in the Jersey and Holstein sired groups, while the former had higher yields of fat, implying that production economics might favour the smaller Jersey crosses in production systems in which the males were not reared. Crossing with Brown Swiss did not improve performance over the Holstein sired crosses. 相似文献
49.
Fifty-six litters from first-parity sows standardized to 12 piglets were used to determine the effects of creep feed composition and form and the provision of low- or high-complexity nursery diets on the evolution of small intestinal histomorphology and jejunal mucosa-specific enzyme activities postweaning. At 5 d of age, litters (initial bodyweight [BW] 2.31 ± 0.61 kg) were assigned to one of four creep feeding regimens (n = 14): 1) commercial creep feed (COM), 2) liquid milk replacer (LMR), 3) pelleted milk replacer (PMR), or 4) no creep feed (NO). At weaning (21 d of age), six pigs per litter were provided a HIGH- (contained highly digestible animal proteins) or LOW- (contained corn and soybean meal as main protein sources) complexity nursery diet (n = 7). At 21, 28, and 59 d of age, two pigs per pen (one castrated male and one female) were euthanized, and ileal and jejunal segments for histomorphological measurements and jejunal mucosal scrapings were collected to determine specific mucosa enzyme activities. At weaning, pigs provided COM had a greater ileal absorptive capacity (M) than LMR or NO, which were not different (14.1 vs. 10.4 and 10.5 ± 0.9 μm2; P < 0.05); PMR was intermediate. On days 28 and 59, M was not different among pigs regardless of creep feed treatments. Pigs fed LOW had reduced jejunal villus height (VH; P < 0.001) and M (P < 0.001) on day 28 vs. day 21. The VH and M were not different for pigs fed HIGH or LOW by the end of the nursery period. For all dietary treatments except COM-HIGH and COM-LOW, jejunal mucosal maltase-specific activity was not different between days 21 and 28 of age but greater on day 59 (P < 0.05). For pigs that received COM-HIGH, maltase-specific activity was not different between days 21 and 28 but greater on day 59 than day 28 (P < 0.05). For pigs that received COM-LOW, maltase-specific activity was not different between days 21, 28, and 59. Regardless of creep or nursery treatment, sucrase-specific activity was the greatest on day 59, followed by days 21 and 28 (P < 0.001), and lactase-specific activity was greater on day 21 than on days 28 and 59 (P < 0.001), which were not different. Therefore, pigs that provided LOW diet had greater villus atrophy and reduced M during the first week after weaning vs. pigs that provided HIGH, regardless of creep feeding regimen, but were able to recover by the end of the nursery period. 相似文献
50.
Adam Edge Michelle Henley Jerry Daday Bruce A. Schulte 《Human Dimensions of Wildlife》2017,22(3):231-245
African elephants (Loxodonta africana) and large trees have ecological and human value, but elephant impact on large trees may influence conservation strategies. We used a self-administered questionnaire to examine perceptions of elephants, large trees, and elephant management endeavors among tourists and residents in the Associated Private Nature Reserves, South Africa to inform management approaches. The questionnaire included photographs of different elephant types and of vegetation with varying degrees of elephant-impact. Respondents reported high attractiveness rankings for all elephant types, but they scored non-impacted trees higher than photos of trees with visible elephant impact. Results also revealed a significant positive correlation between elephant types known to cause high tree impact and attractiveness of non-impacted trees. Residents favored more intrusive elephant management methods, with environmental manipulation representing the most supported and balanced option for both interest groups. Respondents advocated management that focuses on ecosystem functioning more so than elephant population control. 相似文献