全文获取类型
收费全文 | 7430篇 |
免费 | 301篇 |
国内免费 | 678篇 |
专业分类
林业 | 983篇 |
农学 | 1336篇 |
基础科学 | 585篇 |
1218篇 | |
综合类 | 2099篇 |
农作物 | 427篇 |
水产渔业 | 279篇 |
畜牧兽医 | 922篇 |
园艺 | 176篇 |
植物保护 | 384篇 |
出版年
2024年 | 19篇 |
2023年 | 68篇 |
2022年 | 174篇 |
2021年 | 268篇 |
2020年 | 270篇 |
2019年 | 263篇 |
2018年 | 179篇 |
2017年 | 233篇 |
2016年 | 224篇 |
2015年 | 311篇 |
2014年 | 260篇 |
2013年 | 363篇 |
2012年 | 399篇 |
2011年 | 483篇 |
2010年 | 427篇 |
2009年 | 431篇 |
2008年 | 433篇 |
2007年 | 420篇 |
2006年 | 396篇 |
2005年 | 389篇 |
2004年 | 156篇 |
2003年 | 146篇 |
2002年 | 133篇 |
2001年 | 132篇 |
2000年 | 144篇 |
1999年 | 245篇 |
1998年 | 201篇 |
1997年 | 162篇 |
1996年 | 197篇 |
1995年 | 160篇 |
1994年 | 128篇 |
1993年 | 129篇 |
1992年 | 82篇 |
1991年 | 83篇 |
1990年 | 57篇 |
1989年 | 59篇 |
1988年 | 46篇 |
1987年 | 42篇 |
1986年 | 27篇 |
1985年 | 11篇 |
1984年 | 11篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1969年 | 2篇 |
1965年 | 3篇 |
1964年 | 4篇 |
1940年 | 2篇 |
排序方式: 共有8409条查询结果,搜索用时 15 毫秒
101.
Effect of dietary phosphorus levels on growth and body composition of crucian carp,Carassius auratus under indoor and outdoor experiments 下载免费PDF全文
Indoor and outdoor experiments were carried out simultaneously to evaluate the effects of dietary phosphorus levels on growth performance and body composition of crucian carp. Monocalcium was used to formulate extruded feed containing available phosphorus (AP) of 1.5 (D1), 4.7 (D2), 6.3 (D3) and 9.0 (D4) g kg?1. Twelve 500‐L recirculating tanks were assigned to four triplicate groups with each tank stocked with 15 juveniles (39.88 ± 0.14 g) for indoor experiment. Twelve polyethylene enclosures were assigned to four groups with each one stocked with 120 juveniles (44.08 ± 1.36 g). After 8 weeks of feeding, survival ranged from 96% to 100%. Weight gain, special growth rate, protein efficiency ratio and feed conversion rate did not show significant differences among dietary treatments in both experiments. Fish cultured in the enclosures grew better, although D1 and D2 treatments did not reach significant level. Crude protein and phosphorus content of the fish were not significantly affected by dietary phosphorus level. Moisture, crude lipid, crude ash and vertebrae phosphorus were significantly affected by different phosphorus levels. Based on vertebrae phosphorus, crucian carp cultured in the tanks and in the enclosures showed phosphorus deficiency under 4.7 g kg?1 and 6.3 g kg?1 AP, respectively. 相似文献
102.
Qiufen Li Y. Zhang D. Juck N. Fortin Charles W. Greer Qisheng Tang 《Aquaculture International》2010,18(6):977-990
In this study, we investigated the bacterial communities in the shrimp and sea cucumber culture environment, including shrimp ponds (SP), sea cucumber ponds (SCP), mixed-culture ponds (MCP) and the effluent channel (EC) in Qingdao, China. Bacteria cultivation showed that the counts of heterotrophic, nitrate-reducing and sulfate-reducing bacteria in the sediment of SP were higher than that in the sediment of SCP and MCP, varying between 8.7 × 104 and 1.86 × 106, 2.1 × 104 and 1.1 × 105, and 9.3 × 101 and 1.1 × 104 CFU g?1, respectively. In contrast, the counts of ammonium-oxidizing and nitrifying bacteria in the sediment of SP was lower than that in the sediment of SCP and MCP. Denaturing gradient gel electrophoresis (DGGE) of 16S rDNA gene and dendrogram analyses showed that bacterial diversity in the mixed-culture environment was higher than that in the monocultures. The similarity of bacterial community between EC and SCP or MCP was higher than that between EC and SP. These results indicated that sea cucumber culture played a significant role in influencing the environmental bacterial communities that were composed mainly of Flavobacteriaceae (64.3%), Bacteriodetes (21%) and delta proteobacteria (14.7%), including the genera of Croceimarina, Lutibacter, Psychroserpens and so on. The results explained the benefit of sea cucumber culture in shrimp ponds at the level of microbial ecology. 相似文献
103.
104.
AIM: To investigate the mechanisms of transdifferentiation of renal tubular epithelial cells by the observation of serial activation of embryonic pax2 and WT1 genes in chronic renal failure model of 5/6 nephrectomized injury. METHODS: Embryo of mice, cultured renal tubule cells and chronic renal failure rat model of 5/6 nephrectomized injury were established. The expressions of paired Box gene (pax2) and Willm’s tumor gene (WT1), as well as α-smooth muscle actin (α-SMA), a phenotype of mesenchymal cells, were detected by RT-PCR and immunohistochemistry techniques. RESULTS: (1) Expressions of pax2 and WT1 mRNA began at 11.5 d and 14 d of embryo and increased gradually, and expression in trace quantity at 2 weeks after birth. Immunohistochemistry analysis revealed that WT1 only expressed in the glomerular podocytes and expressions of pax2 and WT1 in adult renal tubular cells were negative. (2) Deno-expression of pax2 and WT1 in some tubular cells appeared at week 2 and peaked at week 4 in 5/6 nephrectomized rats, both showing a same trend of expression. However, pax2 showed another peak at week 10 afterwards. (3) Re-expressions of pax2 and WT1 in TEC at 0.5 and 24 h after treated with IL-1α (10 μg/L) or AngII (10-9 mol/L) were observed respectively, followed by upregulation of α-SMA expression, and mesenchymal cells characters were shown. The effects were inhibited by Ang II receptor 2 antagonist and WT1 antibody, respectively. CONCLUSION: Adult renal tubule cells acquire re-activation of embryonic pax2 and WT1 genes and phenotypes of mesenchymes when challenge with certain injuries. Deno-expression of pax2 and WT1 genes closely relates with high concentration of bioactive facors, such as AngII and IL-1, which are involved in the mechanisms of renal tubule cells transdifferentiation. 相似文献
105.
106.
xPC环境下CMAC NN在淀粉生产线液位控制中的应用 总被引:1,自引:1,他引:0
在分析CMAC神经网络的基础上,提出了利用自适应CMAC神经网络来调节淀粉生产线中乳液的液位.通过对淀粉生产线中某一液位回路进行数学建模,然后对常规PID和自适应CMAC神经网络两种控制器进行了设计与仿真.仿真结果表明,自适应CMAC神经网络在控制效果上明显优于常规PID,并且具有很高的鲁棒性.在Matlab实时开发环境xPC Target下建立了液位实时控制系统,采用快速原型控制方式,具有系统组建方便、成本低、开发周期短等特点,该系统可实现精确的过程控制. 相似文献
107.
108.
介绍了一种利用非接触式速度测量装置驱动排种器的工作原理.该装置用前后两个光电传感器来探测路面的反射光信号,根据两路信号的时间差得到相对速度,并用该测速装置来驱动步进电机,步进电机带动排种器转动,以达到排种和速度同步的目的.此装置可以改善现有播种机靠地轮驱动时由于打滑造成的排种不均匀的问题,使排种更加均匀化. 相似文献
109.
Clostridium butyrium CB2 isolated from chickens was tested as a potential fish probiotic in the Chinese drum, Miichthys miiuy . Fish were fed live (CB), dead CB2 (D-CB) cells (108 cells g−1 ) or spent culture supernatant (SCS), for 30 days and challenged with Vibrio anguillarum or Aeromonas hydrophila . Survival was higher in both the CB and the CB-D fed groups, but the SCS group was not significantly different from the control. After feeding live or dead CB2 cells, there was increase in phagocytic activity of the head kidney macrophages, the lysozyme activity of serum and gut mucosa and immunoglobulin (Ig) level. The SCS group showed no obvious change in immune parameters. The results suggest that live or dead Clostridium butyrium CB2 has an immunomodulatory effect on fish. 相似文献
110.
对麻竹笋用林进行施肥试验研究,分析得知,鸡粪、复合肥、配方肥3种肥料对竹笋产量和经济纯收入有显著影响,均与竹笋产量、经济纯收入呈抛物线型关系,竹笋产量、经济纯收入随施肥量增加呈现先上升后下降的趋势;3种肥料的影响程度顺序依次为:配方施肥、鸡粪、复合肥,配方施肥的最佳施肥方案为鸡400+复60+硫酸锌0.9。 相似文献