全文获取类型
收费全文 | 31240篇 |
免费 | 2066篇 |
国内免费 | 2282篇 |
专业分类
林业 | 3900篇 |
农学 | 2288篇 |
基础科学 | 546篇 |
2828篇 | |
综合类 | 11779篇 |
农作物 | 1592篇 |
水产渔业 | 4496篇 |
畜牧兽医 | 5202篇 |
园艺 | 1664篇 |
植物保护 | 1293篇 |
出版年
2024年 | 151篇 |
2023年 | 504篇 |
2022年 | 892篇 |
2021年 | 1075篇 |
2020年 | 1150篇 |
2019年 | 1478篇 |
2018年 | 942篇 |
2017年 | 1564篇 |
2016年 | 1658篇 |
2015年 | 1379篇 |
2014年 | 1685篇 |
2013年 | 2052篇 |
2012年 | 2439篇 |
2011年 | 2322篇 |
2010年 | 1965篇 |
2009年 | 1917篇 |
2008年 | 1651篇 |
2007年 | 1823篇 |
2006年 | 1468篇 |
2005年 | 1153篇 |
2004年 | 891篇 |
2003年 | 758篇 |
2002年 | 619篇 |
2001年 | 566篇 |
2000年 | 475篇 |
1999年 | 433篇 |
1998年 | 328篇 |
1997年 | 313篇 |
1996年 | 308篇 |
1995年 | 294篇 |
1994年 | 253篇 |
1993年 | 225篇 |
1992年 | 160篇 |
1991年 | 147篇 |
1990年 | 151篇 |
1989年 | 123篇 |
1988年 | 86篇 |
1987年 | 63篇 |
1986年 | 34篇 |
1985年 | 24篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1956年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
Optimal dietary taurine level for growth of juvenile Japanese flounder Paralichthys olivaceus 总被引:5,自引:0,他引:5
GWANG-Sic PARK TOSHIO TAKEUCHI MASAHITO YOKOYAMA TADAHISA SEIKAI 《Fisheries Science》2002,68(4):824-829
The requirement for taurine in juvenile Japanese flounder Paralichthys olivaceus was determined by feeding diets containing various levels of taurine and cystine. Test diets supplemented with 0.5, 1.0 and 1.5% of taurine or with 0.5, 1.0 and 1.5% of L -cystine were prepared. The basal diet contained 55% protein from white fish meal. These diets were fed to juvenile Japanese flounder with an initial mean bodyweight of 0.9 g (total length (TL) 48 mm) for 5 weeks. Approximately 1.4% taurine content in the diet was required for optimum growth of juvenile flounder. A positive linear relationship was noted between the content of taurine accumulated in the muscle, liver and brain and the level of taurine in the diet. However, there was no increased taurine content in tissues of fish fed the cystine-supplemented diet. In contrast, the fish fed control and cystine-supplemented diets showed higher contents of cystathionine in the tissues. The concentration of cystathionine in tissues rapidly decreased with an increase of taurine in the diet. It was also observed that for each of the dietary groups, a trace amount of taurine was excreted. These results suggest that the taurine content in the diet affects the sulfur amino acid metabolism of juvenile Japanese flounder, and indicate that juvenile flounder are unable to biosynthesize taurine from cystine. 相似文献
73.
本实验以初始体重为(5.85±0.19)g红白锦鲤(Cyprinus carpio L)幼鱼为实验对象,研究在螺旋藻添加量为12%时,饲料脂肪水平对锦鲤生长、饲料表观消化率、肠道消化酶和血液生化指标的影响。实验设5.36%、7.74%、10.52%、12.85%、15.45%5个脂肪梯度,每组设3个重复,每个重复10尾鱼,表观饱食投喂60 d。结果显示:脂肪水平为5.36%~10.52%,锦鲤增重率(BWG)、特定生长率(SGR)随脂肪水平的升高而升高,均在脂肪水平为10.52%时,达到最大值。实验鱼血清谷丙转氨酶(ALT)随脂肪添加比例呈现先下降再升高的趋势,脂肪水平为12.85%后,血清ALT显著升高(P<0.05),脂肪水平为15.45%时,血清GLU浓度显著升高(P<0.05),而甘油三酯(TG)、总胆固醇(CHOL)随脂肪水平的升高各实验组间无显著性差异(P>0.05)。结果表明,螺旋藻添加量一定时,锦鲤适宜脂肪添加水平为10.52%。 相似文献
74.
稳定性肥料在中国不同区域的施用效果及施用量 总被引:1,自引:1,他引:1
75.
水稻物质生产特性及其与产量的关系研究 总被引:3,自引:0,他引:3
以汕优63、Ⅱ优162、Ⅱ优419、K18A/149和65002为材料,在云南省涛源乡、宾川县和杭州市富阳县进行试验,分析了水稻高产的物质生长特性,并比较了不同环境下物质生长特性的差异及原因。结果表明:云南涛源和宾川产量分别比杭州高80%和66%,导致云南产量较高的主要原因是生物产量较高。生物产量差异主要在幼穗分化以后,尤其是灌浆结实期。在云南生态条件下,中后期能容纳较高的叶面积系数(LAI),群体生长速率(CGR)较高,使花后物质生产量大,且花后物质运转量也较高。 相似文献
76.
The aim of the present study was to provide a method for evaluating bone toxicity induced by drugs in various bones in aged rats. Male Crl:CD (SD) rats at 46 weeks of age were administered 15 mg/m(2) body surface area of doxorubicin, which effects the growth plate in weanling rats, weekly for 9 weeks by intravenous injection, and the femur, sternum, humerus and tibia were examined histopathologically. In the doxorubicin-treated group, thinning of the growth plate was remarkably observed in the proximal tibia and humerus; however, these changes were not observed in other regions. In addition, the osteoclast number per bone perimeter in the proximal tibia was significantly higher than others in control aged rat. Thus, recognizing the various histological reactions related to the time of epiphyseal closure is important for evaluating bone toxicity in aged rats. 相似文献
77.
试验选用罗曼1日龄蛋雏鸡200羽,采用单因子随机设计,分成4组(空白组、试验1组、试验2组、试验3组),每组5个重复,分别饲喂添加0、500、1000、1500 mg/kg大枣低聚糖的基础日粮,试验期35 d,探讨大枣低聚糖对蛋雏鸡生产性能和免疫机能的影响。结果表明:与对照组相比,试验2组、3组日均采食量分别提高了9.4%和8.9%(P<0.05),平均日增重分别提高了14.8%和13.1%(P<0.05);试验2、3组脾脏指数、胸腺指数、法氏囊指数、IgA和IgG水平均显著提高(P<0.05);试验1组脾脏指数、胸腺指数和IgA水平均显著提高(P<0.05)。本试验表明,饲料中添加大枣低聚糖可提高蛋雏鸡的生产性能和免疫机能,其中日粮中添加量为1000 mg/kg效果较理想。 相似文献
78.
选择用笼养和平养两种育雏方式对不同品种1日龄雏鸡进行饲养,试验设计分处理组与对照组,试验组为笼养育雏,对照组为平面育雏,都以煤炉作为育雏保温源.每处理10个重复,每重复120只鸡,试验全期记录鸡的采食量、疾病发生率,并分别在第10、20、30日龄时,称取每重复体重,计算处理组保温成本(煤耗费用)、日增重、料肉比、生长均匀度、疾病发生率等指标.结果显示,与平养育雏相比,30日龄时笼养育雏4个品种(青脚麻E、广西花鸡、广西土2号、新矮脚黄A)的保温费用分别减少0.12、0.24、0.30、0.12元,累积增重分别提高170 g(P<0.05)、102 g (P<0.05)、35 g(P>0.05)、60 g(P<0.05);料肉比分别降低0.23 (P<0.05)、0.12(P>0.05)、0.23 (P<0.05)和0.21(P<0.05);30日龄鸡群均匀度分别提高11% (P<0.05)、7%(P>0.05)、9%(P>0.05)、15%(P<0.05);笼养育雏组未发生球虫病,呼吸道疾病发生率显著低于平养育雏.结果表明,笼养育雏显著降低成本,提高生产性能,是有效阻断疾病发生的科学育雏方式. 相似文献
79.
OBJECTIVE: To investigate the relationship between diet, growth rate and the presence of caudal cervical malformation in Doberman puppies. DESIGN: A prospective study of 15 Dobermann puppies from three unrelated litters, aged from 0 to 16 weeks. PROCEDURE: The growth rate in terms of body weight gain and increase in ulna length were measured weekly for all puppies. In addition the nutritional quality of the diets was assessed. Radiographs of the cervical spine were taken at 6 and between 12 and 16 weeks of age and examined for the presence of caudal cervical vertebral malformation. A mixed model for repeated measures data was used to investigate the relationship between the growth rate of the puppies and the fixed effects age, dam, diet, gender and presence of caudal cervical malformation. RESULTS: Five of the puppies had changes consistent with caudal cervical malformation. The diets fed were either balanced or transiently deficient in protein, calcium, phosphorus and/or magnesium. There was no significant association between growth rate and the variables dam, gender and the presence of caudal cervical vertebral malformation. There was no significant association between diet and increase in ulna length, but a trend existed between body weight gain and the feeding of a balanced diet (P = 0.0672). CONCLUSION: Caudal cervical vertebral changes can be detected radiographically as early as 6 weeks of age in some Dobermann puppies. A balanced diet and growth rate are not significant factors in its initial development. 相似文献
80.