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   14726篇
  免费   838篇
  国内免费   1330篇
林业   864篇
农学   1361篇
基础科学   133篇
  745篇
综合类   4858篇
农作物   1183篇
水产渔业   568篇
畜牧兽医   3724篇
园艺   2648篇
植物保护   810篇
  2024年   52篇
  2023年   213篇
  2022年   450篇
  2021年   554篇
  2020年   595篇
  2019年   718篇
  2018年   527篇
  2017年   659篇
  2016年   902篇
  2015年   842篇
  2014年   891篇
  2013年   850篇
  2012年   1128篇
  2011年   1216篇
  2010年   973篇
  2009年   949篇
  2008年   873篇
  2007年   968篇
  2006年   716篇
  2005年   624篇
  2004年   424篇
  2003年   351篇
  2002年   225篇
  2001年   191篇
  2000年   191篇
  1999年   140篇
  1998年   103篇
  1997年   89篇
  1996年   81篇
  1995年   49篇
  1994年   49篇
  1993年   53篇
  1992年   29篇
  1991年   27篇
  1990年   19篇
  1989年   28篇
  1988年   21篇
  1987年   18篇
  1986年   20篇
  1985年   12篇
  1984年   8篇
  1983年   4篇
  1982年   3篇
  1981年   17篇
  1980年   7篇
  1977年   2篇
  1976年   4篇
  1962年   6篇
  1956年   12篇
  1955年   5篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
OBJECTIVE: The aim of this study was to characterize the clinical and morphologic features of neuronal ceroid lipofuscinosis (NCL) in the Polish Owczarek Nizinny (PON) breed of dog. ANIMALS: Nine Swedish PON dogs of both sexes were included in the study. PROCEDURE: All dogs underwent a detailed clinical evaluation, with emphasis on ophthalmic exams. Histopathology and electron microscopy were performed on the eyes, brain and various internal organs. Immunohistochemical staining for detection of sphingolipid activator proteins (SAPs) and mitochondrial ATP synthase (SCMAS) was performed on the eyes and brain. RESULTS: The dogs showed behavioral abnormalities, motor disturbances and visual impairment or blindness. Pupillary responses were abnormal while fundus changes varied from normal to severe retinal atrophy. Electroretinography (ERG) showed variable changes, from slight alterations in the process of dark adaptation to severely reduced or nonrecordable ERG a- and b-wave amplitudes. Histopathology revealed intracytoplasmic storage bodies within neurons of the brain and in retinal cells, especially the retinal pigment epithelium (RPE). Round to oval granular type of inclusion bodies, known as granular osmiophilic dense deposits (GRODS), were found in neuronal cells in the brain and in the retina. Immunohistochemistry identified the storage material in the brain and retina as consisting of SAPs. CONCLUSION: The presently described NCL disease in PON dogs shows similarities to previously recorded cases in the Miniature Schnauzer. The closest human equivalent to this disease is infantile NCL (CLN1), in which the major stored proteins are SAPs and the ultrastructure of the inclusion bodies of neuronal cells is granular.  相似文献   
142.
This study was conducted to investigate the effects of compound p1ant nutrients (CPN) on rumen fermentation parameters, rumen microbiota and fatty acid composition of longissimus dorsi musc1e in finishing sma11 tai1 Han sheep. Sixteen 4-month-o1d finishing sma11 tai1 Han sheep with an initia1 body weight (BW) of (24.18±0.31) kg were random1y divided into two groups, name1y, with 8 rep1icates per group and 1 sheep per rep1icate. The sheep in the contro1 group were fed a basa1 diet, whereas the sheep of the contro1 group (CPN group) was fed the basa1 diet supp1ementation with 3‰ CPN. The experiment 1asted for 97 days after 7 days adaption. The resu1ts showed as fo11ows: compared with the contro1 group, 1) adding CPN decreased the concentration of ammonia nitrogen (NH3-N) (P<0.05); 2) CPN supp1ementation affected beta diversity of rumen microbiota; 3) the re1ative abundance of Acidobacteriota, Erysipe1otrichaceae_UCG-002, Lactobacillus, and Megasphaera were enhanced by adding CPN (P<0.05), whereas, the re1ative abundance of Bacteroidetes and Prevotella was 1ower (P<0.05); 4) the supp1ementation of CPN had no significant effect on fatty acid composition of longissimus dorsi musc1e of fattening sma11-tai1ed Han sheep (P>0.05); 5) the contents of tota1 MUFA, C18:1n9c, C14:1, C16:1, C18:2n6c, C18:3n3 and n-3PUFA in the longissimus dorsi musc1e were corre1ated with the re1ative abundance of Megasphaera, Erysipe1otrichaceae_UCG-002, Succiniclasticum and Ruminococcus (P<0.05). In conc1usion, CPN can regu1ate the rumen microbiota structure and reduce the rumen NH3-N concentration of fattening sma11-tai1ed Han sheep. In production practice, CPN can be used as a rumen eco1ogica1 regu1ator. © 2023 Authors. All rights reserved.  相似文献   
143.
144.
甘肃省“121”雨水集流工程经济   总被引:1,自引:0,他引:1  
甘肃中东部地区地处黄土高原,气候干旱,水资源缺乏,农村人畜饮水困难。“121”雨水集流工程的实施,有效地解决了这些地区的人畜饮水困难。为了客观评价“121”雨水集流工程的经济效益和作用,利用建设项目后评价理论与方法,对工程的经济效益进行了科学评价,国民经济评价结果可行,其结果可用于指导全省雨水利用工程的规划、设计,加强雨水利用工作的决策、管理。  相似文献   
145.
以成年油木奈树为材料,对其初始坐果进行了研究。结果表明,盛花后2周内,油木奈出现大量的落花落果;幼果(子房)低水平的GA1 3与油木奈的落花落果高峰关系密切,而内源细胞分裂素ZRs和[diH]ZRs以及ABA与幼果(子房)的生长呈显著的正相关;初始坐果期,油木奈的雌配子体发育缓慢,且有相当数量的胚囊中途退化、败育,无法正常受精,从而导致其大量的落花落果。文中就油木奈的初始坐果机制进行了讨论。  相似文献   
146.
通过对蒙古沙棘亚种优良品种与中国沙棘亚种优良类型F1代雄株的变异特性分析,建立了选择优 良单株的标准,为叶用型沙棘选择育种提供了科学依据。  相似文献   
147.
AIM To analyze the regulatory effect of quercetin (QUE) on PTEN-induced putative kinase 1 (PINK1)/parkin mitochondrial autophagy pathway, and to explore the mechanism of quercetin in relieving cerebral ischemia/reperfusion (I/R) injury. METHODS Sixty SD male rats were randomly divided into sham operation group, model group (I/R group), QUE group,3-methyladenine (3-MA) group and QUE+3-MA group. Administration started in each group 3 days before modeling, once a day, at 30 min after the last administration,except sham group, the other groups used 4-vessel blockage method to establish the whole brain I/R model. On the day after modeling, the neural function was evaluated by neuropathy disability score (NDS). The volume of cerebral infarction was measured by 2,3,5-triphenyltetrazolium chloride (TTC) staining. The morphological changes of mitochondria in hippocampus were observed by transmission electron microscopy. The contents of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in hippocampus were measured by ELISA. The activity of superoxide dismutase (SOD) and contents of malondialdehyde (MDA) in hippocampus were detected by xanthine oxidase method, thiobarbituric acid condensation method. Western blot was used to detect the proteinex pression of PINK1, parkin and LC3-II in brain tissue. RESULTS Compared with sham group, the hippocampus of the rats in I/R group and QUE+3-MA group showed swelling of mitochondria, destruction or disappearance of internal crista and other pathological damage,also the volume of cerebral infarction, the contents of IL-6, TNF-α and MDA, the protein expression levels of PINK1, parkin and LC3-II were increased (P<0.05), while NDS score and activity of SOD were decreased (P<0.05). Compared with I/R group and QUE+3-MA group, the pathological damage degree of hippocampus in QUE group was reduced, the volume of cerebral infarction, the contents of IL-6, TNF-α and MDA were decreased (P<0.05), the proteinexpression levels of PINK1, parkin and LC3-II, and NDS score and activity of SOD were increased (P<0.05).The above indexes in 3-MA group were opposite to QUE group. No significant difference in the above indexes between I/R group and QUE+3-MA group was observed (P>0.05). CONCLUSION Quercetin activates mitochondrial autophagy and reduces cerebral I/R by regulating the expression of PINK1/parkin pathway proteins.  相似文献   
148.
149.
AIM To observe effects of emotional stimulation on expression of stromal cell-derived factor-1(SDF-1) and CXC chemokine receptor 4 (CXCR4) in plasma, platelets, aortas, hippocampus and bone marrow of apolipoprotein E gene knockout (ApoE-/-) mice, and to reveal the possible mechanism of the aggravated atherosclerotic plaque vulnerability by emotional stimulation. METHODS Thirty 8-week-old male ApoE-/- mice were randomly divided into normal control group, high fat group, and emotional stimulation group. Ten 8-week-old inbred C57BL/6J mice served as blank control group. After 12 weeks of intervention, the serum levels of SDF-1 and CXCR4 were investigated by ELISA. The protein levels of SDF-1 and CXCR4 in platelets, aortas, hippocampus and bone marrow were determined by Western blot. The pathological damage of aortas was observed by oil red O staining. RESULTS Compared with blank control group, normal control group and high fat group, the mice subjected to emotional stimulation showed more serious atherosclerosis in aortas detected by oil red O staining, and increased levels of SDF-1 and CXCR4 in the plasma and aortas were also observed (P<0.05). The results of Western blot showed that the protein levels of SDF-1 and CXCR4 in platelets, aortas and hippocampus were increased in the mice subjected emotional stimulation, but the expression of SDF-1 and CXCR4 in the bone marrow was decreased (P<0.05). CONCLUSION Imbalance of SDF-1/CXCR4 may be the key target by which emotional stimulation accelerates the progression of atherosclerosis.  相似文献   
150.
"雄心一号"是以菜心细胞质雄性不育系BC-31-10-5-2-1-1为母本,以早熟白菜2-1-1-1-1-1-1-2-1为父本配制而成的,不需要春化、高产的白菜薹新品种。表现:生长势强,中早熟,播种至初收约55 d,延续采收约48 d,抽薹整齐,商品综合性状好,每667 m~2产量在1 500 kg以上。最适合生长温度15~25 ℃,适宜我国宁夏、甘肃、河南、云南、长江流域和华南地区等主要薹菜栽培区适时栽培。  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