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   5167篇
  免费   305篇
  国内免费   507篇
林业   132篇
农学   295篇
基础科学   97篇
  402篇
综合类   1899篇
农作物   155篇
水产渔业   337篇
畜牧兽医   2216篇
园艺   187篇
植物保护   259篇
  2024年   10篇
  2023年   69篇
  2022年   144篇
  2021年   167篇
  2020年   167篇
  2019年   218篇
  2018年   113篇
  2017年   199篇
  2016年   254篇
  2015年   199篇
  2014年   274篇
  2013年   266篇
  2012年   406篇
  2011年   406篇
  2010年   302篇
  2009年   328篇
  2008年   247篇
  2007年   323篇
  2006年   287篇
  2005年   241篇
  2004年   196篇
  2003年   153篇
  2002年   133篇
  2001年   111篇
  2000年   110篇
  1999年   92篇
  1998年   86篇
  1997年   60篇
  1996年   55篇
  1995年   49篇
  1994年   43篇
  1993年   50篇
  1992年   44篇
  1991年   32篇
  1990年   36篇
  1989年   32篇
  1988年   24篇
  1987年   13篇
  1986年   9篇
  1985年   3篇
  1984年   4篇
  1983年   2篇
  1982年   2篇
  1981年   3篇
  1980年   6篇
  1979年   3篇
  1977年   1篇
  1974年   1篇
  1956年   6篇
排序方式: 共有5979条查询结果,搜索用时 15 毫秒
1.
Cuticular proteins(CPs) are major components of the insect cuticle-associated organs such as integument and wings, although the importance of CPs for wing development and function in hemimetabolous insects remains understudied. In the present study, a wing cuticular protein LmACP8 was identified from Locusta migratoria, which belongs to the RR-2 subfamily of cuticular protein RR consensus(CPR) chitin-binding proteins. LmACP8 was mainly expressed in the wing pads and showed high expression levels before ecdysis of third-, fourth-, and fifth-instar nymphs, with its encoded protein located in the procuticle of wing pads and adult wings. Depletion of LmACP8 by RNA interference markedly reduced the amount of its protein, which consequently caused abnormal wing morphogenesis in the transition from nymph to adult of L. migratoria. We further demonstrated that the abnormal morphogenesis was caused by severe damage of the endocuticle in the wings. LmACP8 was suppressed by 20-hydroxyecdysone(20 E) in vivo, however, its expression was significantly up-regulated after knocking down the hormone receptor gene LmHR39. Thus, the LmACP8 that is negatively regulated by the LmHR39-mediated 20 E signaling pathway is involved in wing development during the nymph to adult transition.  相似文献   
2.
Headwater streams play a major role for provision of ecosystem services, e.g. drinking water. We investigated a high-altitude headwater catchment of the Kharaa River (including 41 1st-order rivers) to understand the impact of land cover (especially forest cover), environment and human usage on runoff, chemical water quality and macroinvertebrate fauna in a river basin under discontinuous permafrost conditions in an arid, sparsely populated region of Mongolia. To verify our hypotheses that different landuses and environmental impacts in permafrost headwaters influence water quality, we investigated 105 sampling sites, 37 of them at intermittent stream sections without water flow. Discharge was positively impacted by land cover types steppe, grassland and forest and negatively by shrubland, forest burnt by wild fires (indicating a reduction of permafrost) and slope. Water quality was affected by altitude, longitude and latitude, shrub growth and water temperature. Shannon diversity of macroinvertebrates was driven by water temperature, iron content of the water, flow velocity, and subbasin size (adjusted R2 = 0.54). Sample plots clustered in three groups that differed in water chemistry, macroinvertebrate diversity, species composition and bio-indicators. Our study confirms that steppes and grasslands have a higher contribution to runoff than forests, forest cover has a positive impact on water quality, and diversity of macroinvertebrates is higher in sites with less nutrients and pollutants. The excellent ecological status of the upper reaches of the Kharaa is severely threatened by forest fires and human-induced climate change and urgently needs to be conserved.  相似文献   
3.
为了筛选生长快、毒力强、免疫原性好、副反应小的牛源荚膜A型多杀性巴氏杆菌(Pasteurella multocida,Pm)灭活疫苗菌株,本试验选取6株来自不同地区致犊牛肺炎死亡的牛源荚膜A型多杀性巴氏杆菌分离株,测定了培养基生长曲线、小鼠毒力、菌体脂多糖(LPS)含量及各菌株灭活菌苗免疫小鼠和家兔后的抗体效价,并进行了攻毒保护试验。结果显示,分离株Pm2、Pm3、Pm5生长速度较快、毒力较强、LPS含量较多,均含有与毒力和免疫相关的ptfA和fimA基因;免疫小鼠及家兔未发现明显不良反应,在二免后14 d血清抗体达1:64~1:128,强毒攻毒后全部存活,而PBS对照组全部死亡。本试验结果表明,Pm2、Pm3、Pm5均可作为多杀性巴氏杆菌灭活菌苗的候选菌株,其中Pm3作为首选株。  相似文献   
4.
[Objective] The genetic diversity of semi-wild cotton was abundant, so more new elite resistant genes could be found and applied to improve the resistance of cotton. The aim of this study was to primarily study on the regulation of response to salt-alkali stress, explore the method of integrated evaluation and characterize the resistance of semi-wild cotton. [Method] Four semi-wild and two cultivated Gossypium hirsutum accessions were evaluated for phonotypical, physiological and biochemical traits under alkali-salt versus normal conditions in hydroponic solutions. The alkali-salt tolerance was determined based on principal component analysis, cluster analysis, correlation analysis, grey rational analysis and analysis of variance. [Result] On the basis of the overall results, the alkali-salt stress tolerance of the six accessions was ranked as: Marie-galante85 > Latifolium32 > CRI16 > CRI12 > Latifolium40 > Latifolium130. Roots were found to be the most important responsive systems to complex alkali-salt stress. At seedling growth stage, the active scavenging system played a crucial role in response to alkali-salt stress. In addition, the salt tolerant and salt sensitive accessions showed different response tends towards leaf peroxidase, root ascorbate peroxidase and root catalase within 48 h, suggesting the accessions have different levels of response to salt stress. [Conclusion]Our study identified the most alkali-salt tolerant accessions and provided basic concept of complex alkali-salt tolerance mechanism within cotton accessions. And, our study provided a simple and rapid, highly accurate and precise method for evaluating salt resistance of cotton, and proved that the balance of ROS system play an important role in response to salt-alkali stress. Hence, mining of salt tolerant genes from these accessions may facilitate the development of novel salt tolerant variety.  相似文献   
5.
The bivalve mollusks Paphia malabarica and Villorita cyprinoides collected from the estuarine system located in the southwest coastal waters of India were evaluated for their nutritional composition. A balanced essential to nonessential amino acid ratio (> 1.0) with a greater quantity of sulfur-containing amino acids in these species demonstrated that they could provide well-balanced protein depositions. The n-3/n-6 polyunsaturated fatty acid ratio in P. malabarica was found to be greater than 2, and, therefore, can be considered as a healthy diet. The C20–C22 long-chain polyunsaturated n-3 fatty acids (for example, docosahexaenoic acid and eicosapentaenoic acid) accounted for more than 23% of the total fatty acid content in P. malabarica as compared to about 7% in V. cyprinoides. P. malabarica showed greater hypocholesterolemic/hypercholesterolemic ratio (1.7) and lesser atherogenicity (0.7), thrombogenicity (0.3) indices when contrasted with those in V. cyprinoides, thereby indicating the nutritional superiority of the former. A greater content of vitamin D3 (> 150 IU), along with significant quantities of calcium and phosphorus (> 500 mg/100 g) in the clams, signified their importance in preventing osteoporosis. This study demonstrated the importance of bivalves, in particular, P. malabarica as a valued species for human consumption.  相似文献   
6.
White spot syndrome virus (WSSV), an enveloped double‐stranded DNA virus, is the causative agent of a disease that has led to severe mortalities of cultured shrimps in Taiwan and many other countries. In the previous study, Penaeus monodon chitin‐binding protein (CBP) and glucose transporter 1 (Glut1), two cell membrane proteins, were found to at least interact with other 10 WSSV envelope proteins including VP51B. These envelope proteins might form a protein complex. According to the known information, VP51B was used to identify its role in the protein complex. Western blotting of the intact viral particles and fractionation of the viral components confirmed that VP51B is one of WSSV envelope proteins. In this study, the protein–protein interaction between VP51B and other WSSV envelope proteins was identified by far‐western blot experiment and VP51B was found to interact with VP24, VP31, VP32, VP39B and VP41A. Furthermore, the in vivo neutralization experiment using recombinant VP51B plus with VP39B showed the best inhibition. These data indicate that VP51B participates in the WSSV protein complex and plays an important role in WSSV infection.  相似文献   
7.
蔡鑫  邓灯  王颖  王文琪 《水产科学》2017,(3):303-310
采用激光共聚焦扫描显微镜技术、免疫印迹技术和流式细胞术3种方法对鼠抗三疣梭子蟹血细胞多克隆抗体与黄道蟹、日本蟳、中华绒螯蟹、勘察加帝王蟹血细胞的免疫交叉反应进行分析。激光共聚焦扫描显微镜结果表明,该抗体与黄道蟹、日本蟳、勘察加帝王蟹、中华绒螯蟹血细胞均发生了免疫交叉反应,且发生反应的抗原决定簇均位于细胞膜上;流式细胞术测定该抗体与黄道蟹颗粒血细胞和透明血细胞交叉反应阳性率最高,分别为99.45%、98%,与中华绒螯蟹颗粒血细胞和透明血细胞交叉反应阳性率最低,阳性率分别为81.34%、78.56%;免疫印迹结果显示该抗体与日本蟳血细胞结合的蛋白分子量是80、38.5ku;与勘察加帝王蟹血细胞结合的蛋白分子量是80、93ku;与中华绒螯蟹血细胞结合的蛋白分子量是82、41、30ku;与黄道蟹血细胞结合的蛋白分子量是70、43ku。  相似文献   
8.
9.
10.
文章通过对田园综合体的概念进行介绍,找出广西田园综合体发展情况和存在的问题,最后 提出解决广西田园综合体存在问题的对策和建议,从而促进广西农业的快速发展,带动当地经济稳步 提升。  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