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   347篇
  免费   10篇
林业   5篇
农学   3篇
基础科学   1篇
  20篇
综合类   116篇
农作物   1篇
水产渔业   5篇
畜牧兽医   198篇
园艺   3篇
植物保护   5篇
  2017年   7篇
  2016年   4篇
  2015年   3篇
  2014年   3篇
  2013年   8篇
  2012年   8篇
  2011年   5篇
  2010年   7篇
  2008年   10篇
  2007年   10篇
  2006年   6篇
  2005年   9篇
  2004年   6篇
  2003年   14篇
  2002年   10篇
  2001年   8篇
  2000年   6篇
  1999年   7篇
  1998年   8篇
  1996年   5篇
  1995年   5篇
  1994年   3篇
  1993年   3篇
  1992年   8篇
  1991年   14篇
  1990年   10篇
  1989年   18篇
  1988年   17篇
  1987年   9篇
  1986年   16篇
  1985年   17篇
  1984年   5篇
  1983年   5篇
  1980年   4篇
  1979年   4篇
  1977年   5篇
  1976年   3篇
  1975年   3篇
  1974年   5篇
  1973年   4篇
  1972年   2篇
  1971年   2篇
  1970年   2篇
  1938年   4篇
  1932年   2篇
  1924年   2篇
  1922年   2篇
  1918年   2篇
  1905年   3篇
  1884年   3篇
排序方式: 共有357条查询结果,搜索用时 31 毫秒
291.
The human T-lymphotropic viruses types I and II (HTLV-I and -II) have been etiologically linked with certain T-cell leukemias and lymphomas that characteristically display membrane receptors for interleukin-2. The relation of these viruses to this growth factor receptor has remained unexplained. It is demonstrated here that introduction of the trans-activator (tat) gene of HTLV-II into the Jurkat T-lymphoid cell line results in the induction of both interleukin-2 receptor and interleukin-2 gene expression. The coexpression of these cellular genes may play a role in the altering T-cell growth following retroviral infection.  相似文献   
292.
Reproductive behavior and health in consanguineous marriages   总被引:11,自引:0,他引:11  
In many regions of Asia and Africa, consanguineous marriages currently account for approximately 20 to 50% of all unions, and preliminary observations indicate that migrants from these areas continue to contract marriages with close relatives when resident in North America and Western Europe. Consanguinity is associated with increased gross fertility, due at least in part to younger maternal age at first livebirth. Morbidity and mortality also may be elevated, resulting in comparable numbers of surviving offspring in consanguineous and nonconsanguineous families. With advances in medicine and public health, genetic disorders will account for an increased proportion of disease worldwide. Predictably, this burden will fall more heavily on countries and communities in which consanguinity is strongly favored, as the result of the expression of deleterious recessive genes. However, studies conducted in such populations indicate that the adverse effects associated with inbreeding are experienced by a minority of families.  相似文献   
293.
294.
295.
296.
Hemothorax in a dog was attributed to bleeding from an intrathoracic mass attached to the sixth through the tenth ribs. The mass contained numerous cavernous, blood-filled spaces as well as bands of osteoid and occasional foci of osseous tissue. The diagnosis was telangiectatic osteosarcoma. Telangiectatic osteosarcoma is an uncommon variant of osteosarcoma. Cavernous, blood-filled spaces and paucity of bone are important histologic features. Metastasis was described in one of the seven telangiectatic osteosarcomas reported in dogs, and none was found in this case.  相似文献   
297.
Three groups of cats were given aspirin in single dosages of 5, 10, and 25 mg/kg. A 4th group was given 2 dosages of 25 mg/kg, 3 days between doses. The degree of inhibition of platelet function and the duration of antagonism to platelet aggregation were studied. The dosage of 25 mg/kg (single and repeated) consistently inhibited platelet function, and the effects lasted 3 to 5 days. Additive drug effect was not noted in group 4, since the 2nd dosage antagonized platelet function to a degree and duration similar to the effects of the 1st. The dosage of aspirin recommended for antiplatelet activity in the average-sized cat (3 kg) equals approximately 1 pediatric aspirin (90 mg) given twice a week. Propranolol, given to cats at dosages of 2.5 to 15 mg had no effect on platelet aggregation.  相似文献   
298.
Serum samples from 89 cats with serologic evidence of toxoplasmosis were identified by using an enzyme-linked immunosorbent assay (ELISA) that detected Toxoplasma gondii -specific immunoglobulin M (IgM) or T. gondii -specific immunoglobulin G (IgG). Concurrent feline immunodeficiency virus (FIV) infection was detected in 36 cats using an ELISA for detection of FIV-specific IgG. The majority of the cats in both the FIV-seropositive and FIV-seronegative groups were male and >5 years of age. FIV-seropositive cats were more likely to have T. gondii IgM titers without IgG ( P > 0.05) or any T. gondii IgM titer ( P > 0.05) than were FIV-seronegative cats. FIV-seronegative cats (1328) had a higher T. gondii IgG geometric mean titer than did FIV-seropositive cats (724) and were more likely to have T. gondii IgG titers 1:2048 than were FIV-seropositive cats ( P > 0.05). Cats with serologic evidence of both T. gondii and FIV infections had persistent T. gondii IgM titers for >12 weeks. Lymphoblast transformation in response to concanavalin A, T. gondii -specific intracellular antigens, and T. gondii -specific secretory antigens was compared in T. gondii seropositive and FIV-seronegative cats, cats with serologic evidence of T. gondii infection alone, and cats with serologic evidence of concurrent FIV and T. gondii infections. Lymphocytes from all but one cat in the FIV-seropositive group responded to concanavalin A. Whereas lymphocytes from FIV-seronegative cats with serologic evidence of toxoplasmosis responded to T. gondii -specific antigens, four of five of the FIV-seropositive cats with concurrent serologic evidence of toxoplasmosis did not.  相似文献   
299.
Thirty-two mature, pregnant beef cows (avg age 8 yr, body wt 550 kg) grazing oat pastures were used to determine the effects of lasalocid on serum mineral and ruminal fluid volatile fatty acid (VFA) concentrations. Cows were blocked by breed type and assigned randomly to eight, 2-ha pastures containing oat forage from December 17, 1985 to May 6, 1986. The cows were fed .25 kg of ground corn with or without 200 mg of lasalocid daily. Based upon analyses of forage mineral composition (.53, .25, .14, .3 and 2.5% of dry matter for Ca, P, Mg, Na and K, respectively), all macrominerals except Mg were in sufficient quantities to meet the requirement for lactating cows. Lasalocid supplementation did not affect serum Mg, K or Zn concentrations (P greater than .05). During the April sampling, serum Ca was higher (P less than .05) and serum Na was lower (P less than .05) in cows supplemented with lasalocid compared with controls. The molar proportion of acetate was decreased (P less than .05) in ruminal fluid of cows fed lasalocid by d 56 (February 11); the molar proportions of acetate and butyrate were decreased (P less than .05), which decreased (P less than .05) the acetate: propionate ratio by d 84 (March 11) of supplementation. This study suggests that lasalocid is effective in altering ruminal VFA and serum mineral concentrations in cows grazing small grain forages.  相似文献   
300.
Calves with serum immunoglobulin levels less than 800 mg/dl have a failure of passive transfer of maternal antibodies, those with 800-1600 mg/dl have a partial failure of passive transfer, and those with greater than 1600 mg/dl have adequate immunoglobulin levels. Tests for immunoglobulin level evaluation are most accurate when serum from healthy animals 1-8 days old is used. Of the sodium sulfite precipitation, zinc sulfate turbidity and glutaraldehyde coagulation tests, the first is the most useful field test for evaluation of serum immunoglobulin levels in calves. It is inexpensive, easy to perform and relatively accurate.  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