首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   21306篇
  免费   1394篇
  国内免费   1778篇
林业   1769篇
农学   1976篇
基础科学   967篇
  2570篇
综合类   8144篇
农作物   1326篇
水产渔业   1259篇
畜牧兽医   3597篇
园艺   1423篇
植物保护   1447篇
  2024年   135篇
  2023年   370篇
  2022年   696篇
  2021年   817篇
  2020年   844篇
  2019年   995篇
  2018年   632篇
  2017年   940篇
  2016年   1106篇
  2015年   988篇
  2014年   1096篇
  2013年   1200篇
  2012年   1601篇
  2011年   1726篇
  2010年   1316篇
  2009年   1274篇
  2008年   1152篇
  2007年   1270篇
  2006年   1116篇
  2005年   858篇
  2004年   679篇
  2003年   545篇
  2002年   444篇
  2001年   369篇
  2000年   338篇
  1999年   275篇
  1998年   204篇
  1997年   194篇
  1996年   165篇
  1995年   155篇
  1994年   150篇
  1993年   145篇
  1992年   118篇
  1991年   94篇
  1990年   78篇
  1989年   80篇
  1988年   47篇
  1987年   39篇
  1986年   31篇
  1985年   38篇
  1984年   30篇
  1983年   33篇
  1982年   15篇
  1981年   18篇
  1980年   15篇
  1979年   14篇
  1978年   10篇
  1977年   6篇
  1976年   4篇
  1956年   5篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
AIM To investigate the mechanism of long noncoding RNA (lncRNA) FEZF1-AS1 regulating microRNA-363-3p (miR-363-3p) on the viability and apoptosis of lipopolysaocharide (LPS)-induced vascular endothelial cells. METHODS Human umbilical vein endothelial cells (HUVECs) were cultured in vitro. pcDNA-NC, pcDNA-FEZF1-AS1, anti-miR-NC, anti-miR-363-3p, miR-NC and miR-363-3p mimics were transfected into the HUVECs and LPS stimulation was applied for 24 h. RT-qPCR was used to detect the expression of FEZF1-AS1 and miR-363-3p. The cell viability was measured by MTT assay. The apoptotic rate was analyzed by flow cytometry. The dual-luciferase reporter experiment was used to verify the targeted regulation of FEZF1-AS1 and miR-363-3p. Western blot was used to determined the expression of cyclin D1, Ki67 and cleaved caspase-3. RESULTS Compared with control group, the expression level of FEZF1-AS1 in LPS group was significantly reduced (P<0.05), and the expression level of miR-363-3p was significantly increased (P<0.05). Compared with pcDNA-NC+LPS group, the cell viability in pcDNA-FEZF1-AS1+LPS group was significantly increased (P<0.05), the apoptotic rate was significantly reduced (P<0.05), the protein levels of cyclin D1 and Ki67 were significantly increased (P<0.05), and the protein level of cleaved caspase-3 was significantly reduced (P<0.05). Compared with anti-miR-NC+LPS group, the cell viability in anti-miR-363-3p+LPS group was significantly increased (P<0.05), the apoptotic rate was significantly reduced (P<0.05), the protein levels of cyclin D1 and Ki67 were significantly increased (P<0.05), and the protein level of cleaved caspase-3 was significantly reduced (P<0.05). Dual-luciferase reporter experiment confirmed that FEZF1-AS1 targeted miR-363-3p. Compared with miR-NC+pcDNA-FEZF1-AS1+LPS group, the cell viability in miR-363-3p+pcDNA-FEZF1-AS1+LPS group was significantly reduced (P<0.05), the apoptotic rate was significantly increased (P<0.05), the protein levels of cyclin D1 and Ki67 were significantly reduced (P<0.05), and the protein level of cleaved caspase-3 was significantly increased (P<0.05). CONCLUSION Over-expression of FEZF1-AS1 promotes the viability and inhibits apoptosis of LPS induced vascular endothelial cells by inhibiting the expression of miR-363-3p.  相似文献   
152.
AIM To study the effect of dihydroartemisinin (DHA) on the radiotherapy efficiency in hepatocellular carcinoma H22 cell tumor-bearing mice and the role of phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway in this process. METHODS A model of H22 cell tumor-bearing mice was established. The mice was divided into model group, single radiotherapy group, 5-fluorouracil (5-FU) group, and low-, medium- and high-dose DHA groups. The body weight and tumor volume in each group were measured every other day. At the end of administration, blood was collected from the tail of the mice and the animals were killed by neck removal immediately. The synergistic effect of DHA on radiotherapy was determined, and tumor growth inhibitory rate was calculated. The degree of lymphocyte transformation and natural killer (NK) cell activity were measured by MTT, the serum levels of interleukin-2 (IL-2) and IL-4 were measured by ELISA, and the protein levels of PI3K, AKT and p-AKT were determined by Western blot. RESULTS The H22 cell tumor-bearing mouse model was successfully constructed. Compared with model group, the TGT3 (tumor growth time to reach 3 times of volume) of single radiotherapy group was remarkably increased (P<0.05), while tumor weight, lymphocyte transformation degree, NK cell activity, IL-2 and IL-4 levels, PI3K protein level and AKT phosphorylation level were remarkably decreased (P<0.05). Compared with single radiotherapy group, TGT3, EF (enhancement factor), tumor inhibitory rate, lymphocyte transformation degree, NK cell activity, IL-2 level and IL-4 level were increased with the increase in DHA dose (P<0.05), and the PI3K protein level and AKT phosphorylation level were decreased (P<0.05). CONCLUSION DHA may enhance the immunity of tumor-bearing mice by inhibiting the activity of PI3K/AKT signaling pathway, thereby enhancing the efficacy of radiotherapy.  相似文献   
153.
AIM To explore the effects of oxidative stress and inflammatory response on kidney injury induced by hyperthyroidism in mice. METHODS Forty male Kunming mice were randomly divided into control group (n=20) and L-thyroxine (T4) group (n=20). The mice in T4 group were intraperitoneally injected with T4 diluent at a dose of 1 mg/kg to induce hyperthyroidism, and those in control group were injected with normal saline of the same volume. After 7 weeks, the mice were weighed and dissected, the kidneys were removed and weighed, and the length of tibia was also measured. The activity of superoxide dismutase (SOD) and the content of malondialdehyde (MDA) in the kidney tissues were detected. The pathological changes of the kidney tissues were observed by HE staining. The levels of 4-hydroxynonenal (4-HNE)-modified proteins, interleukin-1 receptor-associated kinase 1 (IRAK1) and tumor necrosis factor receptor-related factor 6 (TRAF6) were determined by Western blot and immunohistochemistry. RESULTS Compared with control group, the body weight of the mice was decreased, while the kidney size and weight were increased significantly in T4 group. In addition, the ratios of kidney weight/body weight and kidney weight/tibia length were also increased (P<0.05). In T4 group, the renal tubules were enlarged, and the epithelial cells of renal tubules were swollen and exfoliated, with vacuolar degeneration. Furthermore, reduced SOD activity, and increased MDA content and 4-HNE-modified proteins were found in T4 group, all of which were related to oxidative stress (P<0.05). The levels of inflammation-related proteins IRAK1 and TRAF6 were significantly increased in T4 group (P<0.05). CONCLUSION Excessive T4 may lead to kidney hypertrophy and injury in mice, and the mechanism may be related to oxidative stress and inflammatory response.  相似文献   
154.
高效节能型日光温室黄瓜养分的吸收规律   总被引:8,自引:2,他引:6  
高效节能型日光温室黄瓜干物质和氮、磷、钾的积累都呈“S”形曲线 ;氮、磷、钾吸收最大期为盛瓜初期至盛瓜后期 ,占总吸收量的 80 %以上 ;每形成 10 0kg黄瓜需吸收N量0 .2 0 0 2kg ,P2 O50 .0 92 1kg ,K2 O 0 .2 32 2kg ,其比例为 1∶0 .4 6∶1.16 ;每 6 6 7m2 产 130 0 0kg黄瓜 ,在盛瓜期氮、磷、钾吸收速率分别为N 190~ 2 70、P2 O577~ 135、K2 O 199~ 347g·(d·6 6 7m2 ) - 1。  相似文献   
155.
节能日光温室番茄长季节高产栽培研究初报   总被引:10,自引:1,他引:9  
对日光温室番茄长季节栽培进行了品种筛选及施肥指标和环境调控的研究 ,筛选出适宜日光温室番茄长季节栽培的品种 4个 ,提出 6 6 7m2 产量 2 0 0 0 0kg番茄的复合肥和钾肥施肥指标及采用遮阳网、反光幕、防虫网、诱虫色板、膜下滴灌等环境调控技术和措施。  相似文献   
156.
Model uncertainty in the ecosystem approach to fisheries   总被引:2,自引:0,他引:2  
Fisheries scientists habitually consider uncertainty in parameter values, but often neglect uncertainty about model structure, an issue of increasing importance as ecosystem models are devised to support the move to an ecosystem approach to fisheries (EAF). This paper sets out pragmatic approaches with which to account for uncertainties in model structure and we review current ways of dealing with this issue in fisheries and other disciplines. All involve considering a set of alternative models representing different structural assumptions, but differ in how those models are used. The models can be asked to identify bounds on possible outcomes, find management actions that will perform adequately irrespective of the true model, find management actions that best achieve one or more objectives given weights assigned to each model, or formalize hypotheses for evaluation through experimentation. Data availability is likely to limit the use of approaches that involve weighting alternative models in an ecosystem setting, and the cost of experimentation is likely to limit its use. Practical implementation of an EAF should therefore be based on management approaches that acknowledge the uncertainty inherent in model predictions and are robust to it. Model results must be presented in ways that represent the risks and trade‐offs associated with alternative actions and the degree of uncertainty in predictions. This presentation should not disguise the fact that, in many cases, estimates of model uncertainty may be based on subjective criteria. The problem of model uncertainty is far from unique to fisheries, and a dialogue among fisheries modellers and modellers from other scientific communities will therefore be helpful.  相似文献   
157.
辣椒新品种平椒3号的选育   总被引:3,自引:0,他引:3  
何志兰 《辣椒杂志》2006,4(3):14-16
平椒3号是以自交系99101为母本,自交系9949为父本配制的早熟一代杂种。果实羊角形,青熟果深绿色,果纵径17.7cm,果肩径3.0cm,果肉厚0.25cm,平均单果质量29.5g,肉质脆嫩,辣味浓且有香味,商品性好。田间对疫病、炭疽病、病毒病的抗性明显优于猪大肠。露地栽培每667m2青椒产量为3700kg左右,适宜西北地区及四川、山西、湖南等嗜辣地区露地栽培。  相似文献   
158.
苹果酒酵母融合子W1发酵工艺参数的优化研究   总被引:2,自引:2,他引:0  
该文利用所构建的苹果酒的模糊综合评判模型,以评判结果为目标,采用响应界面法研究了苹果酒发酵的规律,建立了优质苹果酒发酵的二次多项式数学模型,同时验证了模型的有效性,并考察了接种量、初始pH值和发酵温度对苹果酒品质的影响,优化出最佳发酵工艺参数为接种量5.33%、初始pH值3.37、发酵温度22.14℃。  相似文献   
159.
农业区位理论与西部退耕还林区农业产业布局研究   总被引:2,自引:0,他引:2  
西部是我国重要的生态屏障和重要河流的源头,又是我国重要的农业区,如何在实施退耕还林过程中,兼顾生态效益和经济效益协调、可持续发展,是该项工程能否成功的关键。本文按照农业区位理论和产业布局演变的一般规律,在分析西部退耕还林区现状及农业产业发展趋势的基础上,对西部退耕还林区农业产业布局进行科学规划,并用“吴旗模式”验证其可行性,为西部区域经济发展提供现实的指导意义。  相似文献   
160.
以大麦胚芽鞘为材料,研究了生长素吲哚乙酸(indole-3-acetic ac id,IAA)和2,4表油菜素内酯(2,4-ep ibras-sinolide,ep iBR)对胚芽鞘伸长的影响。结果表明:200μmol.L-1IAA和1μmol.L-1ep iBR在黑暗条件下均促进大麦胚芽鞘的伸长生长,而且在该过程中二者存在协同作用,但必须是在IAA之前施用ep iBR或两者共同处理时才能表现;100 mg.L-12,3,5三碘苯甲酸(2,3,5-triiodobenzoic ac id,TIBA)能抑制ep iBR诱导的胚芽鞘伸长生长,暗示IAA的极性运输是ep iBR促进大麦胚芽鞘伸长生长所必需的;内源激素分析表明,ep iBR处理后胚芽鞘内源IAA含量上升,暗示ep iBR对大麦胚芽鞘伸长的促进作用在一定程度上通过调控内源IAA的水平起作用。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号