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   150728篇
  免费   8565篇
  国内免费   94篇
林业   5413篇
农学   4480篇
基础科学   976篇
  17115篇
综合类   28178篇
农作物   5952篇
水产渔业   7251篇
畜牧兽医   78670篇
园艺   1792篇
植物保护   9560篇
  2018年   1931篇
  2017年   2254篇
  2016年   2055篇
  2015年   1810篇
  2014年   2209篇
  2013年   5644篇
  2012年   4070篇
  2011年   4982篇
  2010年   3175篇
  2009年   3262篇
  2008年   4784篇
  2007年   4562篇
  2006年   4398篇
  2005年   4053篇
  2004年   3900篇
  2003年   3953篇
  2002年   3728篇
  2001年   4830篇
  2000年   4788篇
  1999年   3786篇
  1998年   1560篇
  1997年   1515篇
  1996年   1408篇
  1995年   1724篇
  1994年   1550篇
  1993年   1504篇
  1992年   3229篇
  1991年   3371篇
  1990年   3182篇
  1989年   3279篇
  1988年   2982篇
  1987年   3179篇
  1986年   3244篇
  1985年   3097篇
  1984年   2483篇
  1983年   2187篇
  1982年   1537篇
  1981年   1346篇
  1979年   2197篇
  1978年   1817篇
  1977年   1573篇
  1976年   1491篇
  1975年   1601篇
  1974年   2014篇
  1973年   2073篇
  1972年   1989篇
  1971年   1857篇
  1970年   1779篇
  1969年   1607篇
  1967年   1402篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Crown reduction is a sterile endodontic procedure indicated for reducing the crown height of teeth. The procedure is used primarily on canine teeth as a disarming technique in aggressive biting pets or to treat traumatic occlusion. Recommendations for using this technique for biting pets are described.  相似文献   
72.
Several surgical conditions affecting the foot can be successfully managed with the horse standing. Many factors affect the clinician's choice of whether to perform surgery with the horse standing or anesthetized. Temperament or pregnancy of the horse and economics may influence the decision to perform surgery with the horse standing. This article discusses several foot conditions that can be treated successfully in the ambulatory horse.  相似文献   
73.
For practical reasons, a large volume (i.e. 5 ml) of frozen boar semen per insemination dose is desirable, but successful freezing has not been achieved, since optimal cooling rates have not yet been established. Post-thaw motility and the acrosome intep'ty of semen from four boars frozen with a programmable freezin machine, in mini-(0.25 ml), maxi-(5 ml) plastic straws and in 10 × 5 cm PVC- or Teflon FEP-plastic bags (0.35 – 0.12 mm thick, 5 ml) was studied. The freezing of the semen was monitored using thermocouples placed in the straws and the bags. The freezing curve started from +5°C, at a rate of −3°C/min, to – 6°C, it was held for 1 min at −6°C, and was followed by further drop to −100°C at a rate of −20°C/min, with subsequent storage in LN2. The bags had a much shorter freezing point plnteau, compared to the maxi-straws. Post-thaw sperm motility was significantly higher when semen was frozen in mini-straws or in bags than in maxi-straws. The freezing procedure did not cause major acrosomal damages, significantly more normal apical ridges being present in the bags and mini-straws than in the maxi-straws. This in vitro evaluation indicates that the freezing method employed is satisfactory for freezing large volumes of boar semen into plastic bags .  相似文献   
74.
The diagnosis of any viral respiratory disease relies on laboratory procedures to isolate the virus and demonstrate a significant rise in serum antibody titers. To isolate viruses from the upper respiratory tract, it is imperative that nasopharyngeal swabs are obtained from animals in the early acute stage of illness, i.e., during the pyrexic phase when the virus is replicating. Nasopharyngeal swabs must be placed in a virus transport medium and forwarded immediately to the laboratory at refrigerated temperature. Equine influenza, rhinopneumonitis, and equine viral arteritis are the three viral infections causing outbreaks of respiratory disease in North America. African horse sickness, although foreign to North America, could be introduced despite stringent horse importation regulations. Specific antiviral therapy is not available to treat viral respiratory disease in the horse. A variety of inactivated and modified live vaccines, however, are available to prevent clinical disease and the spread of infection caused by the common viral respiratory pathogens. A considerable amount of research is underway to enhance the potency and duration of immunity of the present vaccines against influenza and rhinopneumonitis. This research is directed at defining and characterizing the importance of specific glycoprotein antigens on the surface of the virus, which trigger the various host immune responses, and determining whether they are stimulatory or suppressive.  相似文献   
75.
Individual antigens of goats   总被引:1,自引:0,他引:1  
  相似文献   
76.
As anaerobic sampling and culture techniques improved, the documented prevalence of anaerobic bacteria in periodontal disease has increased. The anaerobic bacteria have become more well-known in humans and consequently in dogs, since this species is a major model in periodontal studies. A review of the literature related to anaerobic flora is described.  相似文献   
77.
RNA was extracted from single or small groups of ovine ovarian follicles after treatment of ewes with FSH and/or LH. The content of mRNA for the alpha-inhibin and beta A-inhibin subunits was analyzed by hybridization with specific cDNA probes. All ewes were treated with progestin vaginal pessaries to suppress spontaneous preovulatory follicle maturation and ewes were given three intramuscular injections of gonadotropins at 8-hr intervals starting 24 hr prior to collection of ovaries. In experiment I, both Schering-FSH and NIDDK-oFSH-17 (oFSH) significantly increased alpha- and beta A-inhibin mRNA per ewe in 2-5 mm follicles and tended to increase alpha- and beta A-inhibin mRNA in large (greater than 5 mm) follicles. In experiment II, oFSH and NIDDK-oLH-25 (oLH) were administered in a 2X2 factorial arrangement. Separate administration of oFSH or oLH increased (P less than .05) the alpha-inhibin mRNA concentration in large follicles. alpha-inhibin mRNA concentration in 4-5 mm follicles was also increased by oFSH but was decreased by oLH. Concomitant treatment with oFSH and oLH did not change alpha-inhibin mRNA concentrations from those measured in oFSH treated ewes. In experiment II, beta A mRNA concentrations followed a pattern similar to that of alpha A mRNA, but the differences were not statistically significant. We conclude that, in the ewe, exogenous FSH increases the concentration of inhibin mRNA in the whole follicle. The ability of exogenous oLH to alter expression of the inhibin subunit genes may depend upon the stage of follicle maturation.  相似文献   
78.
79.
80.
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