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   253593篇
  免费   15266篇
  国内免费   641篇
林业   23401篇
农学   13991篇
基础科学   2948篇
  42657篇
综合类   25306篇
农作物   17078篇
水产渔业   16709篇
畜牧兽医   97249篇
园艺   6307篇
植物保护   23854篇
  2021年   2461篇
  2020年   2876篇
  2019年   3674篇
  2018年   3954篇
  2017年   4344篇
  2016年   4781篇
  2015年   4300篇
  2014年   5665篇
  2013年   16231篇
  2012年   6285篇
  2011年   8201篇
  2010年   7269篇
  2009年   7875篇
  2008年   7570篇
  2007年   6621篇
  2006年   7276篇
  2005年   6494篇
  2004年   6332篇
  2003年   6122篇
  2002年   5453篇
  2001年   6137篇
  2000年   5734篇
  1999年   5402篇
  1998年   4143篇
  1997年   4190篇
  1996年   3916篇
  1995年   4507篇
  1994年   3888篇
  1993年   3630篇
  1992年   4347篇
  1991年   4408篇
  1990年   4142篇
  1989年   4190篇
  1988年   3658篇
  1987年   3757篇
  1986年   3716篇
  1985年   3994篇
  1984年   3668篇
  1983年   3480篇
  1982年   2884篇
  1981年   2812篇
  1980年   2768篇
  1979年   3096篇
  1978年   2818篇
  1977年   2632篇
  1976年   2460篇
  1975年   2307篇
  1974年   2492篇
  1973年   2469篇
  1972年   2205篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Twenty two dogs with an infiltrative lipoma had computed tomographic (CT) images acquired to evaluate the extent of local disease. Ten dogs had undergone at least one cytoreductive surgical procedure (range = 1-3; median = 2) prior to imaging. Twenty dogs had measurable disease on CT images; 2 dogs had diffuse disease at a previous surgical site that could not be measured. Tumor volume (n = 20) ranged from 20 to 5,632 cm3 (median = 345 cm3; mean = 996 cm3). None of the dogs had evidence of bone involvement on the CT images; 2 of the 22 dogs had tumors that did not come into direct contact with osseous structures. All dogs with measurable disease had evidence of a fat opacity mass with variable degrees of muscle infiltration. Eleven of 22 dogs were given intravenous contrast medium prior to image acquisition and there was not evidence of enhancement of the infiltrative lipoma in any dog. Based on CT images, tumors were classified as well-defined in 9 dogs, moderately well-defined in 4, not well-defined in 3 and a mix of well-defined and not well-defined in 6 dogs. Tumors tended to be less well-defined in regions where the infiltrative lipoma interdigitated with normal body fat. It appears CT imaging allows adequate discrimination of tumor with the caveat that differentiation of normal fat from infiltrative lipoma can be problematic.  相似文献   
102.
103.
104.
    
Ohne Zusammenfassung  相似文献   
105.
Star catalogues     
  相似文献   
106.
The medical records of 38 horses with puncture wounds of the navicular bursa were reviewed. Only 12 horses had a satisfactory outcome (breeding or riding). Of the remaining 26 horses, 19 were euthanized, five were sold due to persistent severe lameness, one died, and one was lost to long-term follow-up. Different combinations of conservative management prior to surgical debridement and drainage of the navicular bursa were unsuccessful in resolving the condition. Horses that were treated surgically within 1 week of the injury and had a hind leg affected had the best chance of a satisfactory outcome. Additional wound debridement was necessary in 15 horses after initial surgical treatment. The most common complications encountered were navicular bone osteomyelitis and sepsis of the deep digital flexor tendon. Thirteen of 14 horses that had rupture of the deep digital flexor tendon and subluxation of the distal interphalangeal joint had an unsatisfactory outcome. One mare subsequently developed ankylosis of the distal interphalangeal joint and was a useful brood mare. Two horses that had biaxial palmar digital neurectomy because of persistent lameness were later euthanized because of navicular bone fracture and rupture of the deep digital flexor tendon. Results from limited numbers of bacterial cultures and antibiotic sensitivities suggest that penicillin and an aminoglycoside antibiotic should be used as initial antibiotic therapy. Immediate surgical debridement and appropriate antibiotic treatment are recommended as the minimum therapy for penetrating wounds of the navicular bursa in horses.  相似文献   
107.
GRAY  S. J.; PRICE  COLIN 《Forestry》1990,63(2):161-175
Traditional forest economics deals with regularly-ordered activities.For many reasons, however, choices must often be made amongconflicting operational priorities. In these circumstances,maximizing net discounted revenue per hectare does not maximizeglobal profit. Priorities for action should be chosen in orderof urgency index ratio, defined as the cost of delaying an operationdivided by the units of limited resource needed to undertakethe operation. Forest managers tend to use informal and sometimesconflicting rules to assign priorities among uses of limitedresources. These priorities often differ from those indicatedby urgency index ratio. Urgency index ratio can be determinedby simple calculations based on readily-available data. Theconcept can be extended to include multiple constraints.  相似文献   
108.
Mid-storage hydration-dehydration treatments with medium-vigour lettuce seed very effectively reduced physiological deterioration in storage and ultimately showed better field emergence and final yield. Soaking-drying treatment of high-vigour lettuce seed was not effective. Pre-sowing treatment of medium-vigour lettuce seed, though less effective than mid-storage treatment, gave better field performance, but high-vigour seed did not benefit from the treatment. For carrot, both mid-storage and pre-sowing seed treatments proved beneficial, with the former showing better performance than the latter. Unlike lettuce, well-preserved carrot seed responded positively to the pre-sowing treatment.  相似文献   
109.
Characterization of monoclonal antibodies directed against swine leukocytes   总被引:3,自引:0,他引:3  
Hybridomas were produced from fusions of the SP2/0 mouse myeloma with splenic cells from: 1) an outbred Sprague Dawley rat immunized with swine peripheral blood mononuclear (PBM) cells; 2) a (CBA/NDub X BALB/c Dub) F1 mouse immunized with concanavalin A (Con A) activated swine PBM cells and 3) a (BALB/c Dub X C3H/He Dub) F1 mouse immunized with swine thymocytes. The resulting supernatants were screened by a microcytotoxicity assay for activity against swine PBM cells. Four hybridomas (MSA1, MSA2, MSA3 and MSA4) were selected, cloned and characterized by their cell reactivity and effect on mitogenic assays. MSA1 and MSA2 belong to the rat IgG2b subclass. MSA3 and MSA4 are of the mouse IgG2a subclass. These monoclonal antibodies reacted in the following manner: MSA1 with monocytes, granulocytes, red blood cells and bone marrow cells; MSA2 with subset of T cells; MSA3 with B cells and subsets of T cells and monocytes (class II molecule) and MSA4, a pan-T cell reagent (E-rosette receptor). The involvement of the various cell types reactive to the different monoclonal antibodies in the mitogenic response of swine PBM cells to Con A, phytohemagglutinin (PHA) or pokeweed mitogen (PWM) was investigated by cellular depletion with monoclonal antibody plus complement. Cellular depletion of PBM cells with the following monoclonal antibodies plus complement treatment resulted in: MSA1, almost total reduction in the mitogenic response to low doses of Con A or PWM; MSA2, partial reduction in the proliferative responses to any concentration of Con A, PHA or PWM; MSA3, partial reduction in proliferative responses to low concentrations of Con A or PWM and 4) MSA4, total elimination of any proliferative response to Con A, PHA or PWM.  相似文献   
110.
Washed and unwashed red blood cells (RBC) from young calves, adult cattle, hamsters and humans were incubated with Leptospira interrogans serovars pomona and ballum. Washed cells suspended in saline were always haemolysed while unwashed cells and those which were washed and resuspended in plasma were never haemolysed, despite the presence of large numbers of organisms within the culture supernatant. Pomona produced greater haemolysis of cattle and human RBC than did ballum, but with hamster RBC ballum produced greater haemolysis than did pomona. A group of 6- to 9-month-old cattle infected with pomona showed no signs of clinical disease and RBC taken from them before infection and during the development of antibodies to pomona were haemolysed by pomona only after the cells were washed. Plasma therefore appears to have a protective function. This in vitro protective function of plasma even extended to plasma from young seronegative calves.  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