全文获取类型
收费全文 | 2886篇 |
免费 | 348篇 |
国内免费 | 225篇 |
专业分类
林业 | 69篇 |
农学 | 81篇 |
基础科学 | 26篇 |
80篇 | |
综合类 | 774篇 |
农作物 | 57篇 |
水产渔业 | 1448篇 |
畜牧兽医 | 811篇 |
园艺 | 10篇 |
植物保护 | 103篇 |
出版年
2024年 | 16篇 |
2023年 | 41篇 |
2022年 | 58篇 |
2021年 | 85篇 |
2020年 | 127篇 |
2019年 | 153篇 |
2018年 | 114篇 |
2017年 | 165篇 |
2016年 | 167篇 |
2015年 | 124篇 |
2014年 | 118篇 |
2013年 | 147篇 |
2012年 | 196篇 |
2011年 | 238篇 |
2010年 | 143篇 |
2009年 | 159篇 |
2008年 | 171篇 |
2007年 | 138篇 |
2006年 | 148篇 |
2005年 | 114篇 |
2004年 | 117篇 |
2003年 | 97篇 |
2002年 | 59篇 |
2001年 | 72篇 |
2000年 | 79篇 |
1999年 | 71篇 |
1998年 | 44篇 |
1997年 | 58篇 |
1996年 | 50篇 |
1995年 | 42篇 |
1994年 | 29篇 |
1993年 | 26篇 |
1992年 | 24篇 |
1991年 | 27篇 |
1990年 | 15篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 1篇 |
1984年 | 3篇 |
1982年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有3459条查询结果,搜索用时 0 毫秒
21.
Improved performance of gilthead sea bream, Sparus aurata, larvae after ozone disinfection of the eggs 总被引:1,自引:0,他引:1
Isashar Ben-Atia Sigal Lutzky Yoav Barr Kutsal Gamsiz Yariv Shtupler Amos Tandler & William Koven 《Aquaculture Research》2007,38(2):166-173
Ozone (O3) dissolved in seawater (ODS) was evaluated, as an egg disinfectant, on the spawn of captive gilthead sea bream, Sparus aurata, brood stock. Four contact times (CT) were tested (0.6, 1.2, 2.4 and 4.8 mg min L−1) where CT was calculated by multiplying the dissolved O3 concentration (0.3 mg L−1) by different exposure periods (2, 4, 8, 16 min). There was also a disinfected seawater treatment that contained no O3 or derived compounds (CT 0) and an untreated seawater control. All ODS treatments reduced egg surface bacterial counts to zero, which was significantly (P<0.05) lower than the CT 0 and the control groups (194 and 1320 plate−1 respectively). Nevertheless, the hatching rate was high in the control and the CT treatments 0, 0.6 and 1.2 (88.7%, 87.3%, 89.5% and 83.7% respectively) while eggs exposed to a CT 2.4 and 4.8 hatched poorly (36.5% and 20.4% respectively), which was likely due, at least in part, to larvae unable to break the egg chorion successfully. Swim‐bladder inflation was significantly higher in the ODS groups (>97%) compared with the control and CT 0 treatments (ca. 70%). The results suggest that a 2‐min exposure of eggs to 0.3 mg O3 L−1 of ODS (CT 0.6) would improve current protocols in marine larviculture. 相似文献
22.
The ontogenetic development of the digestive enzymes amylase, lipase, trypsin, and alkaline phosphatase and the effect of
starvation in miiuy croaker Miichthys miiuy larvae were studied. The activities of these enzymes were detected prior to exogenous feeding, but their developmental patterns
differed remarkably. Trypsin activity continuously increased from 2 days after hatching (dah), peaked on 20 dah, and decreased
to 25 dah at weaning. Alkaline phosphatase activity oscillated at low levels within a small range after the first feeding
on 3 dah. In contrast, amylase and lipase activities followed the general developmental pattern that has been characterized
in fish larvae, with a succession of increases or decreases. Amylase, lipase, and trypsin activities generally started to
increase or decrease at transitions from endogenous to exogenous feeding or diet changes, suggesting that these enzymatic
activities can be modulated by feeding modes. The activities of all the enzymes remained stable from 25 dah onwards, coinciding
with the formation of gastric glands and pyloric caecum. These results imply that specific activities of these enzymes underwent
changes due to morphological and physiological modifications or diet shift during larval development but that they became
stable after the development of the digestive organs and associated glands was fully completed and the organs/glands functioned.
Trypsin and alkaline phosphatase were more sensitive to starvation than amylase and lipase because delayed feeding up to 2 days
after mouth opening was able to adversely affect their activities. Enzyme activities did not significantly differ among feeding
groups during endogenous feeding; however, all activities were remarkably reduced when delayed feeding was within 3 days
after mouth opening. Initiation of larvae feeding should occur within 2 days after mouth opening so that good growth and survival
can be obtained in the culture. 相似文献
23.
L. A. Copeman C. C. Parrish J. A. Brown M. Harel 《Aquaculture (Amsterdam, Netherlands)》2002,210(1-4):285-304
The role of dietary ratios of docosahexaenoic acid (DHA, 22:6n−3), eicosapentaenoic acid (EPA, 20:5n−3) and arachidonic acid (AA, 20:4n−6) on early growth, survival, lipid composition, and pigmentation of yellowtail flounder was studied. Rotifers were enriched with lipid emulsions containing high DHA (43.3% of total fatty acids), DHA+EPA (37.4% and 14.2%, respectively), DHA+AA (36.0% and 8.9%), or a control emulsion containing only olive oil (no DHA, EPA, or AA). Larvae were fed differently enriched rotifers for 4 weeks post-hatch. At week 4, yellowtail larvae fed the high DHA diet were significantly larger (9.7±0.2 mm, P<0.05) and had higher survival (22.1±0.4%), while larvae fed the control diet were significantly smaller (7.3±0.2 mm, P<0.05) and showed lower survival (5.2±1.9%). Larval lipid class and fatty acid profiles differed significantly among treatments with larvae fed high polyunsaturated fatty acid (PUFA) diets having higher relative amounts of triacylglycerols (18–21% of total lipid) than larvae in the control diet (11%). Larval fatty acids reflected dietary levels of DHA, EPA and AA while larvae fed the control diet had reduced amounts of monounsaturated fatty acids (MUFA) and increased levels of PUFA relative to dietary levels. A strong relationship was observed between the DHA/EPA ratio in the diet and larval size (r2=0.75, P=0.005) and survival (r2=0.86, P=0.001). Following metamorphosis, the incidence of malpigmentation was higher in the DHA+AA diet (92%) than in all other treatments (50%). Results suggest that yellowtail larvae require a high level of dietary DHA for maximal growth and survival while diets containing elevated AA exert negative effects on larval pigmentation. 相似文献
24.
Md. Abdul Kader Shunsuke Koshio Manabu Ishikawa Saichiro Yokoyama Mahbuba Bulbul Binh Thanh Nguyen Jian Gao Asda Laining 《Aquaculture Research》2012,43(10):1427-1438
An experiment was carried out to evaluate fermented soybean meal and squid by‐product blend (1:1) (FP) as replacement of fishmeal (FM) for Japanese flounder, Paralichthys olivaceus. Five isocaloric (19 kJ g?1) diets were prepared by replacing 0 (FP0), 12 (FP12), 24 (FP24), 36 (FP36) and 48% (FP48) FM protein with FP. Triplicate groups of juveniles (mean weight of 3.9 g) were delivered the test diets for 8 weeks in a flow‐through sea water system. The results showed that there were no significant differences (P > 0.05) among the growth rates of fish fed FP0, FP12, FP24 and FP36 diets. Growth and nutrient utilization parameters were significantly reduced in fish fed FP48 diet. Although, whole body proximate composition of fish were not significantly affected by the dietary treatments compared to the control; methionine and phenylalanine contents were significantly decreased in FP48 group. Protein retention was also significantly decreased in the similar group of fish. Dietary treatments did not alter most of the plasma metabolites, while some of the health parameters were improved in the replacement groups. Results suggested that FP is a potential candidate for alternative protein ingredient in aquafeed and can replace 36% FM protein in the diet of Japanese flounder. 相似文献
25.
Mike Greenblatt Christopher L. Brown Michael Lee Silvia Dauder Howard A. Bern 《Fish physiology and biochemistry》1989,6(5):261-278
Developmental profiles of thyroxin (T4), triiodothyronine (T3) and radioactive iodide uptake were established for eggs and T4 and T3 profiles were established for larvae (whole-body, yolk-only and body-only) of coho and chinook salmon. T4 and T3 were consistently present in all samples. In eggs, hormone levels remained fairly constant in all cohorst for at least the first three weeks of incubation, but then fluctuated in both directions in some sample groups. Large increases in T4 (from 9 ng/g to 245 ng/g) were seen in 1985 chinook eggs 28 days after fertilization. Radioactive iodide uptake (which was used as a possible indicator of thyroxinogenesis) increased at least 10-fold in both 1986 coho and chinook eggs from 23–30 days after fertilization. T4 (62 ng/g) and T3 (393 ng/g) were found in the bodies of 28-day-old 1986 chinook embryos. In whole larvae, hormone levels varied depending upon the cohort studied. In general, initial body-only concentrations of both T4 and T3 decreased as body weight increased, but before yolksac resorption was completed, both thyroid hormone content and concentration increased (except for chinook T3). T4 and T3 content in larval yolk stayed constant as yolksac size decreased, resulting in increased thyroid hormone concentration in the yolksac. All of these data suggest that the initial source of thyroid hormones in coho and chinook salmon eggs is maternal, but that by approximately 3–4 weeks after fertilization, the developing embryos begin to produce their own thyroid hormones. After hatching, increases in tissue T4 and T3 concentration coupled with constant T4 and T3 content in diminishing yolksacs suggest that larvae also produce their own thyroid hormones; yolksac content then may reflect both the original maternal hormones and the larva-producted hormones. 相似文献
26.
美洲鲥仔稚鱼脊柱及附肢骨骼系统的早期发育 总被引:1,自引:1,他引:1
使用软骨-硬骨双染色技术,描述了美洲鲥(Alosa sapidissima)仔稚鱼(1~51日龄)脊柱、胸鳍、尾鳍、背鳍等附肢骨骼的形态发育特征。结果显示,脊柱的发育开始于10日龄仔鱼尾部的髓弓、脉弓和尾下骨的出现,16日龄髓弓和脉弓延伸形成髓棘和脉棘,19日龄脊柱出现分节的硬骨环,23日龄所有椎体形成。各附鳍支鳍骨发育顺序先后依次为胸鳍、尾鳍、背鳍、臀鳍和腹鳍。胸鳍在2日龄时出现乌喙骨,13日龄形成软骨质的胸鳍支鳍骨,19日龄仔鱼肩带和上匙骨开始骨化;尾鳍的尾下骨最早出现在5日龄,12日龄尾鳍形成2枚尾上骨、1枚尾杆骨和6枚尾下骨,19日龄仔鱼尾椎和尾鳍率先开始骨化,直至23日龄尾鳍骨骼系统钙化完全。最终背鳍和臀鳍分别形成18和22根鳍条。美洲鲥骨骼发育研究对其早期发育功能趋向、环境优化及分类鉴定有重要作用。 相似文献
27.
- 1. River lamprey (Lampetra fluviatilis) and sea lamprey (Petromyzon marinus) are designated features of the River Derwent Special Area of Conservation (SAC) and the Humber Estuary (a possible SAC). This study determined the condition of lamprey populations in the Yorkshire Ouse catchment by assessing the species composition, distribution, abundance and size‐structure of larval (ammocoete) populations in five major tributary rivers (Derwent, Swale, Ure, Nidd and Wharfe).
- 2. According to EU condition assessment criteria, Lampetra populations (assumed to be mostly river lamprey) are at present in favourable condition, with site mean (±SE) densities ranging from 2.7 (±1.2) to 160.3 (±50.5) individuals m?2 (all river means >2 individuals m?2), and at least two size (≈age) classes present in optimal microhabitats. By contrast, no sea lamprey larvae were recorded, suggesting that populations of this species are in unfavourable condition.
- 3. Actions to protect and enhance nationally or internationally important stocks must be implemented from at least a catchment perspective, because many of the issues affecting such species are not localized. With respect to lampreys, particular attention should be given to protecting spawning and nursery habitats, improving water quality, reducing impingement at abstraction points, preventing exploitation at spawning grounds and increasing passage at potential physical obstructions.
28.
日粮中鱼蛋白水解物对黄颡鱼生长、体成分和血清生理指标的影响 总被引:2,自引:0,他引:2
为了探讨鱼蛋白水解物对黄颡鱼生产性能的影响,以日本鳀粉为对照,以实用型黄颡鱼饲料配方模式为基础开展实验:1以30.5%鱼粉为对照(FM),在相同配方模式下,以6%鱼蛋白水解物(MPH6)替代20%的鱼粉;2以30.5%鱼粉为对照(FM),在无鱼粉日粮中分别添加3%(FPH3)、6%(FPH6)、12%(FPH12)鱼蛋白水解物;共设计5组等氮等能实验日粮,在池塘网箱中养殖黄颡鱼[初始体质量(30.08±0.35)g]60 d。结果显示:与FM相比,FPH12在SGR、FCR、PRR和FRR方面均无显著差异,而MPH6、FPH3、FPH6组SGR降低了15.45%~24.39%,FCR升高了32.14%~42.86%,MPH6、FPH6差异显著,在PRR和FRR方面,MPH6、FPH3、FPH6组PRR降低了21.11%~27.78%,MPH6组FRR降低了41.51%;全鱼水分、粗蛋白、粗脂肪和灰分各组间差异不显著,FPH3、FPH6、FPH12肌肉多种游离氨基酸水平显著高于FM,其中Thr、Val、His与其在日粮中的水平显著相关;FPH6组HSI显著低于FM,鱼蛋白水解物对CP、VSI、肠体比的影响不显著;血清AST、ALT、HDL、LDL、TP、CHOL、TG无显著差异,FPH3组ALB显著低于FM。研究表明:黄颡鱼日粮中,12%鱼蛋白水解物(干物质)与30.5%鱼粉在生长速度、饲料效率、血清生理指标等方面具有一定的等效性;过高的植物蛋白日粮影响了黄颡鱼的生产性能;饲喂鱼蛋白水解物日粮使黄颡鱼肌肉游离氨基酸的含量升高,特别是呈味氨基酸的含量增加。 相似文献
29.
菜籽粕对异育银鲫免疫应答能力的影响 总被引:2,自引:0,他引:2
试验鱼以投喂饲料的不同和是否注射抗原共分为10组,即免疫组:A、B、C、D、E组,免疫对照组:a、b、c、d、e组,饲料对照组:A、a组.饲料试验组B、C、D、b、c、d、e组.其中,饲料对照组以豆粕和鱼粉为基础蛋白源,饲料试验组分别以双低菜籽粕和普通菜籽粕等氮替代对照组中50%(B、b;D、d)和100%(C、c;E、e)的豆粕蛋白,测定异育银鲫血液白细胞和头肾吞噬细胞的吞噬活性、血清溶菌酶活性、血清补体(C3,C4)含量、血清凝集抗体效价及免疫保护率.结果表明:从免疫后21 d开始,饲料试验组E、e、C、c组的各项免疫指标都显著低于相应饲料对照组;在49 d,D、d组的部分免疫指标也显著低于相应饲料对照组;B、b组和相应饲料对照组之间没有显著的变化.免疫组的各项免疫指标均显著高于相对应的投喂相同饲料的免疫对照组. 相似文献
30.
浙江中北部沿岸春、夏季鱼卵和仔稚鱼种类组成与数量分布 总被引:8,自引:0,他引:8
根据2008年4,5,6月在浙江中北部沿岸禁渔区线内45个站位开展的产卵场调查资料,研究分析了该海域鱼卵、仔稚鱼的种类组成和数量分布。结果表明,本海区共出现鱼卵、仔稚鱼64个种类,分别隶属13目36科47属,能鉴定到种的有47种,鉴定到科的有17种。3个航次的调查共采集到鱼卵5 846个和仔稚鱼5 502个。其中4月最少,仅采集到鱼卵366个和仔稚鱼1 445个,分别占鱼卵和仔稚鱼总数量的6.26%、26.26%;5月份共采集到鱼卵1 530个和仔稚鱼1 551个,分别占鱼卵和仔稚鱼总数量的26.17%、28.19%;6月份数量最多,共采集到鱼卵3 950个和仔稚鱼2 506个,分别占总数的67.57%、45.55%,4—6月鱼卵、仔稚鱼的数量呈月递增趋势。鱼卵中石首鱼科未定种最多占10.06%,其次黄姑鱼占6.45%,再次为凤鲚占总数的6.06%。凤鲚仔稚鱼数量最多,占总种类数的34.06%,其次为虾虎鱼科仔稚鱼,占24.25%,再次为鲻科鱼类仔稚鱼,占23.57%。调查发现杭州湾是凤鲚的主要产卵场,其仔稚鱼也主要分布在杭州湾内,少量分布在舟山渔场和鱼山渔场。小黄鱼产卵场主要分布在舟山渔场、鱼山渔场外侧。从产卵时间和渔场分布来看,鱼山渔场是最早集中的水域,随着时间推移,产卵场的中心区向北部水域的舟山渔场转移。研究的海域内重要经济鱼类大黄鱼、小黄鱼、银鲳的鱼卵数量百分比明显下降,由1960年的优势种成为现在的非优势种;主要经济鱼类中鳓、凤鲚所占比例相对增加,但绝对数量有所下降。在某种程度上说明,沿岸水域资源补充量有所减少,这可能与水域环境变化及过度捕捞导致亲体量减少有关。 相似文献