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   109727篇
  免费   6138篇
  国内免费   71篇
林业   5145篇
农学   3667篇
基础科学   594篇
  13025篇
综合类   15904篇
农作物   3838篇
水产渔业   5482篇
畜牧兽医   60423篇
园艺   1335篇
植物保护   6523篇
  2018年   1645篇
  2017年   1759篇
  2016年   1624篇
  2015年   1441篇
  2014年   1665篇
  2013年   4501篇
  2012年   3136篇
  2011年   3785篇
  2010年   2472篇
  2009年   2373篇
  2008年   3561篇
  2007年   3531篇
  2006年   3315篇
  2005年   3068篇
  2004年   2896篇
  2003年   2973篇
  2002年   2759篇
  2001年   3726篇
  2000年   3606篇
  1999年   2879篇
  1998年   1171篇
  1997年   1126篇
  1996年   1052篇
  1995年   1208篇
  1994年   1091篇
  1993年   1058篇
  1992年   2292篇
  1991年   2535篇
  1990年   2501篇
  1989年   2398篇
  1988年   2214篇
  1987年   2220篇
  1986年   2201篇
  1985年   2154篇
  1984年   1757篇
  1983年   1521篇
  1982年   1019篇
  1979年   1566篇
  1978年   1255篇
  1977年   1102篇
  1976年   1153篇
  1975年   1158篇
  1974年   1419篇
  1973年   1360篇
  1972年   1357篇
  1971年   1253篇
  1970年   1287篇
  1969年   1206篇
  1968年   1053篇
  1967年   1086篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Since the International Society of Veterinary Acupuncture (IVAS) was founded in 1974, acupuncture (AP) has received greater acceptance by veterinary professionals throughout the world. This article introduces some important animal diseases that respond well to AP therapy. These include resuscitation of small animals, treatment of anoestrous gilts and sows, bovine reproductive disease, canine vertebral problems and equine backpain, etc. Conventional medicine considers these to be difficult cases to treat. Veterinarians have become more aware of the benefits of AP especially for those diseases, thanks to the efforts of experienced practitioners and scientists, and the many published reports on veterinary AP that have introduced some good indications for AP therapy in veterinary practice. Possible mechanisms behind the effectiveness of AP are discussed. This article aims to introduce veterinarians to good indications for AP to initiate their interest in the practice of AP. Although this is a rapidly expanding field, a long march must begin with one step. We wish this article to be the shoes for such a march. For more information on veterinary AP, contact IVAS , P.O. Box 1478, Longmont, CO.. 80502, USA (http://www.ivas.org), or your national veterinary acupuncture society (http://www.komvet.at/ ivadkom/vapsocs.htm).  相似文献   
42.
43.
Various combinations of reoviruses and coccidia were studied to see if interactions would occur. Two reoviruses were used: virus 2035, a moderate to low pathogen, and virus 2177, a nonpathogen. Coccidia used were Eimeria acervulina, E. mitis, and E. maxima at dosages of 10(3) or 10(4) sporulated oocysts/chick and E. brunetti at 10(4) sporulated oocysts/chick. In Hubbard-Hubbard cockerels, a combination of virus 2035 and E. acervulina (10(4) oocysts/chick) or E. maxima (10(3) oocysts/chick) significantly (P less than or equal to 0.05) increased the frequency of stunting (% of chicks with body weight less than 80% of controls) and further depressed weight gain over that seen with either virus or coccidia alone. Conversely, virus 2177 ameliorated the same effects in Shaver-Arbor Acre cockerels given 10(4) oocysts/chick of E. mitis or E. maxima. The interaction could not be attributed to changes in the degree of coccidial infection based on oocyst production. Reovirus did not generally change the effect of coccidia on levels of plasma pigment and plasma protein. In Hubbard-Hubbard cockerels, coccidia-induced effects were not ameliorated by virus 2177, suggesting that breed difference in interaction can be expected.  相似文献   
44.
Images with high resolution and exceptionally broad gray scale can be obtained by the application of video contrast enhancement to an optimized procedure for imaging transparent objects with oblique rays of illumination. This technique is simple to set up. A conventional microscope with a light source whose position can be adjusted and a video camera with controls for gain and black level are the only essential components. Features such as high resolution, optical sectioning, control of contrast, and operation under low light intensity make this technique preferable, in several instances, to currently used video microscopy techniques.  相似文献   
45.
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   
46.
Vanilla is a large genus of about 110 species in the orchid family (Orchidaceae), including the species Vanilla planifolia from which commercial vanilla flavoring is derived. Since most species of vanilla are considered rare and endangered there is an urgent need to conserve them through genetic analysis and propagation/conservation studies on this crop.The present study investigated the genetic diversity among nine leafy- and leaf-less Vanilla species employing 30 decamer RAPD primers and 10 ISSR primers. The species under study were diverse and displayed a range of variability (0–66% and 0–81% for RAPD and ISSR, respectively). A total of 154 RAPD polymorphic markers (83.24%, h = 0.378) and 93 ISSR polymorphic markers (86.11%, h = 0.363) were used to generate a genetic similarity matrix followed by the cluster analysis. Specific groupings were revealed by each cluster analysis with slight variation between two different markers. Among the nine species studied, V. planifolia, Vanilla aphylla and Vanilla tahitensis revealed very low level of variation within their collections, thus indicating a narrow genetic base. The large genetic distance of Vanilla andamanica from other species suggests its different origin. A close genetic affinity was observed between the pairs V. planifolia, V. tahitensis and Vanilla albida, V. aphylla. These are the first comparative results for RAPD and ISSR reporting inter-relationship among nine cultivated, wild and hybrid Vanilla species.  相似文献   
47.
48.
49.
50.
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