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   24863篇
  免费   1285篇
  国内免费   10篇
林业   876篇
农学   752篇
基础科学   154篇
  3613篇
综合类   3528篇
农作物   909篇
水产渔业   1338篇
畜牧兽医   13164篇
园艺   268篇
植物保护   1556篇
  2019年   249篇
  2018年   415篇
  2017年   507篇
  2016年   470篇
  2015年   337篇
  2014年   457篇
  2013年   959篇
  2012年   794篇
  2011年   949篇
  2010年   686篇
  2009年   669篇
  2008年   965篇
  2007年   916篇
  2006年   808篇
  2005年   735篇
  2004年   643篇
  2003年   705篇
  2002年   605篇
  2001年   803篇
  2000年   799篇
  1999年   633篇
  1998年   274篇
  1997年   282篇
  1995年   259篇
  1994年   227篇
  1993年   232篇
  1992年   424篇
  1991年   516篇
  1990年   434篇
  1989年   411篇
  1988年   400篇
  1987年   409篇
  1986年   363篇
  1985年   388篇
  1984年   339篇
  1983年   287篇
  1982年   243篇
  1979年   383篇
  1978年   289篇
  1977年   290篇
  1976年   299篇
  1975年   317篇
  1974年   332篇
  1973年   302篇
  1972年   290篇
  1971年   245篇
  1969年   289篇
  1968年   269篇
  1967年   326篇
  1966年   304篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Five Boxer dogs with a new neurological disease are described. There is a progressive ataxia and weakness, initially in the hind-legs but later involving forelegs. The onset of signs is usually around 6 months of age although an older dog was affected. Proprioceptive function, muscle tone and tendon reflexes are diminished or absent while pedal reflexes and pain sensation are preserved. Muscle atrophy is minimal. The peripheral nerves are depleted in myelinated fibres. Nerve roots and, to a lesser extent, peripheral nerves show demyelination/remyelination changes and in the cervical ventral roots in particular, regenerative clusters are present. Forelimb muscles show evidence of re-innervation. In the CNS numerous swollen axons are present. The dorsolateral and ventral columns of the spinal cord are affected throughout their length. In the brain a number of nuclei and tracts, particularly in the lower brain stem, are affected and the superior olives are severely involved. The cerebral cortex and subcortical white matter appear normal. Various portions of the auditory and optic pathways are affected pathologically as are a number of cranial nerves. The axonal swellings contain a number of organelles including smooth endoplasmic reticulum, disordered neurofilaments, vesicles and mitochondria. The disease may be specific to Boxer dogs and may be inherited.  相似文献   
102.
Cephalosporins form a large group of β-lactam antibiotics which are used extensively in human medicine and to a lesser extent in domestic animals. In veterinary dermatology, the principle use for the cephalosporins is the clinical management of canine pyoderma associated with Staphylococcus intermedius . In practice, the use of orally administered first generation cephalosporin drugs to affected dogs is well tolerated and highly efficacious. Bacterial drug resistance appears to occur rarely.  相似文献   
103.
Immunization of dogs with a Leishmania infantum-derived vaccine   总被引:2,自引:0,他引:2  
A partially-purified extract of Leishmania infantum has been administered to healthy dogs. Post-immunization sera were found to neutralize the infectivity of L. infantum and to abate the development of L. major. Muramyl dipeptide and one of its derivates, murabutide, were the best adjuvants.  相似文献   
104.
105.
The use of retrobulbar block in conjunction with general anesthesia was evaluated in the horse. A prospective study of 12 cases fulfilling criteria for application of retrobulbar block was compared to a retrospective survey of 25 cases (control group) in which retrobulbar block was not performed. Retrobulbar block was done using a modified Peterson technique and 2% lidocaine HCI without epinephrine. In the control group, four horses exhibited signs compatible with initiation of the oculocardiac reflex; three horses developed bradyarrhythmias and hypotension during global traction related to enucleation, and cardiac arrest occurred in one horse during cataract extraction. In the retrobulbar block group, one horse developed bradyarrhythmia subsequent to retrobulbar block.  相似文献   
106.
The effect of electroimmobilisation on the plasma concentrations of beta-endorphin/beta-lipotrophin (beta-EP/beta-LPH), cortisol and prolactin (PRL) has been assessed in sheep. Serial blood samples were collected from control and electroimmobilised animals during the first and fourth of a series of four repeated treatments over two days. After electroimmobilisation the mean (+/- SEM) plasma concentrations of beta-EP/beta-LPH increased significantly from 132 +/- 19 pg ml-1 to 545 +/- 111 pg ml-1; the plasma concentrations of cortisol also increased significantly from 22.3 +/- 3.5 ng ml-1 to 108.0 +/- 12.9 ng ml-1. There was no significant change in plasma PRL concentrations after electroimmobilisation and also no significant difference between the plasma concentrations of PRL in the control and electroimmobilised animals. There was no significant difference between the effects of the first and fourth exposure to electroimmobilisation on the plasma concentrations of beta-EP/beta-LPH, cortisol and PRL. These results suggest that the endocrine response to electroimmobilisation may be specific to the pituitary-adrenal axis.  相似文献   
107.
108.
The detection of 4-hydroxycoumarin rodenticides in poisoned domestic animals requires a highly sensitive method as tissue and serum levels of anticoagulants may be very low owing to rapid elimination, metabolism or post-mortem degradation. Thin-layer chromatography (TLC) and reversed-phase high-performance liquid chromatography (RP-HPLC) with fluorescence detection were used to identify the anticoagulants in spiked tissues and in suspicious samples. The analysis of ten suspicious samples highlighted the limitations of both methods. Only the three samples of baits were found positive by TLC whereas one of the five anticoagulants was detected in eight samples by RP-HPLC with fluorescence detection. Therefore, RP-HPLC with fluorescence detection proved to be the more sensitive method for detecting low levels of 4-hydroxycoumarins in blood serum, liver and ingesta, whereas TLC is usually sufficient for analysing baits.Abbreviations RP-HPLC reversed-phase high-performance liquid chromatography - TLC thin-layer chromatography  相似文献   
109.
The tone of respiratory smooth muscle is largely determined by the input from autonomic nerves. The distribution of adrenergic and selected nonadrenergic, non-cholinergic (NANC) nerves in the normal equine trachealis muscle was investigated using immunohistochemistry. The smooth muscle of the trachealis was found to contain numerous nerves immunoreactive for an enzymatic marker of adrenergic nerves, as well as many nerves immunoreactive for a putative NANC neurotransmitter, peptide histidine isoleucine, a potent bronchodilator. The tissues surrounding the respiratory smooth muscle contained numerous nerves immunoreactive for the neuropeptides substance P and calcitonin gene-related peptide, which can cause marked vasodilation and bronchoconstriction. The complex innervation of the equine trachea should be kept in mind when interpreting the results of physiological experiments.  相似文献   
110.
1. CVI-ChNL 74·3, a dendritic cell-specific monoclonal antibody (mAb) also identifies chicken lung granular pneumocytes (type II pneumocytes), which produce surfactant.

2. The 74·3 mAb does not cross-react with any other avian or mammalian granular pneumocyte, and provides a convenient tool for monitoring the status of type II pneumocytes in the chicken lung.  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