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   17088篇
  免费   904篇
  国内免费   18篇
林业   828篇
农学   562篇
基础科学   122篇
  2506篇
综合类   2687篇
农作物   912篇
水产渔业   950篇
畜牧兽医   8319篇
园艺   201篇
植物保护   923篇
  2020年   163篇
  2019年   183篇
  2018年   312篇
  2017年   369篇
  2016年   265篇
  2015年   199篇
  2014年   317篇
  2013年   666篇
  2012年   498篇
  2011年   622篇
  2010年   428篇
  2009年   418篇
  2008年   640篇
  2007年   554篇
  2006年   516篇
  2005年   456篇
  2004年   420篇
  2003年   430篇
  2002年   369篇
  2001年   486篇
  2000年   475篇
  1999年   373篇
  1998年   182篇
  1997年   202篇
  1996年   158篇
  1995年   192篇
  1993年   164篇
  1992年   280篇
  1991年   313篇
  1990年   307篇
  1989年   313篇
  1988年   289篇
  1987年   247篇
  1986年   295篇
  1985年   253篇
  1984年   210篇
  1983年   207篇
  1979年   251篇
  1978年   165篇
  1977年   155篇
  1975年   171篇
  1974年   234篇
  1973年   215篇
  1972年   251篇
  1971年   230篇
  1970年   203篇
  1969年   192篇
  1968年   158篇
  1967年   160篇
  1966年   161篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
A survey of 287 dogs for antibodies against Babesia canis in dogs in an endemic area, using ELISA, produced a prevalence of 43 per cent. Antibodies occurred in dogs of all age groups, the prevalence being significantly lower in dogs aged 1 to 6 months than in older dogs. There were no differences between indigenous Nigerian dogs and exotic (foreign) dogs; and between the sexes in the prevalence of antibodies. Antibodies were more prevalent in dogs with B. canis parasitaemia and in those with a higher risk of infection. Also antibodies were detected in some puppies born to seropositive bitches. The ELISA test failed to detect antibodies in 36.1 per cent of dogs with B. canis parasitaemia.  相似文献   
142.
Electromyographic (EMG) activity of 4 muscles of the cubital joint and the strain of forelimb hooves were recorded telemetrically in 4 Thoroughbreds (with and without a rider) standing, walking, trotting, and cantering. Bipolar fine wire electrodes were inserted into the muscles, and strain gauges were attached to the hoof wall. Motion pictures (16 mm), synchronized with EMG tracings, were taken to obtain kinematic data. When horses were standing, the biceps brachii had tonic activity, but the brachialis and the caput longum and the caput laterale of the triceps brachii had no EMG activity. The biceps brachii had EMG activity during the stance phase. The brachialis had EMG activity from the end of the stance phase to the middle of the swing phase. Unlike the biceps brachii, the brachialis acted as a flexor muscle of the cubital joint during locomotion. The EMG activity of the caput longum of the triceps brachii was detected from midswing phase to early stance phase. The EMG activity of the caput laterale of the triceps brachii began in midswing or late-swing phase and ceased in early stance or midstance phase. During locomotion, caput longum EMG activity always preceded caput laterale activity. When horses were cantering, the brachialis and the caput longum (acting mainly in the swing phase) had an EMG activity phase different from those in leading and trailing forelimbs. These 4 muscles had similar EMG activity patterns during locomotion in horses with and without a rider.  相似文献   
143.
An adult female bearded vulture (Gypaetus barbatus) in the Tel Aviv University Research Zoo was found dead without previous clinical signs. The predominant pathologic changes were considerable bloody content in the intestines and enlargement of the liver, which had a rubbery consistency with color changes. Microscopic lesions consisted of multifocal histiocytic infiltration in the liver. Newcastle disease virus (NDV) was isolated from a cloacal swab and from the lungs and liver. Intracerebral pathogenicity index of the virus, as estimated in 1-day-old chicks, was repeated three times and had an average value of 1.68, indicating a velogenic strain. Numerous Clostridium septicum bacteria were found on the intestinal surface, but bioassays in which they were orally administered into chickens and mice revealed that, even though they were heavily multiplied in the intestines, they were nonpathogenic. It seems that NDV, documented for the first time in a bearded vulture in Israel, was the likely cause of sudden death.  相似文献   
144.
145.
The effect of microgravity on functional development of the small intestine of Japanese quails incubated for 2-3 d and hatched on the orbital station MIR was examined. After 5 d of space flight duodenal and jejunal alkaline phosphatase (AP) activity of the experimental group was compared with the AP activity in quails of the same age hatched on the Earth (laboratory controls). Short-term microgravity leading to decreased food intake resulted in significant increase of AP activity in both duodenal and jejunal enterocytes (P<0.001) of the experimental quails. The results suggest that increased AP activity probably reflects the delayed functional development of the small intestine as a consequence of inappropriate food intake during non-physiological conditions of space flight.  相似文献   
146.
The European Union (EU) countries are searching for new ways to certify meat free of Trichinella; however, with the expansion of the EU, the acceptance of a unilateral method is complicated by the variability of pig and human trichinellosis among EU countries, where significantly higher prevalence rates have been observed in the newly added eastern countries. Several attempts have been made to define Trichinella-free areas, but certification of Trichinella-free pig production farms appears to be the only feasible approach. The increasing prevalence of the non-encapsulating species, Trichinella pseudospiralis, in game, domestic pigs and humans has eliminated the compression technique from the new EU legislation to be enacted in 2006. Also, the observation that several species of Trichinella tolerate freezing in horse meat for up to 4 weeks has forced a change in legislation as well where freezing is no longer an option for certifying horse meat. Because current serological detection methods are not suited for meat inspection, classical direct detection methods and inactivation by freezing remain the methods of choice for pork. It has been proposed, therefore, to automate direct inspection methods as a cost effective alternative to certify pig farms free of Trichinella.  相似文献   
147.
A 5-year-old pit bull-type dog was examined because of lethargy and black feces, and a presumptive diagnosis of methemoglobinemia was made on the basis of grossly visible brown discoloration of the mucous membranes and urine. Heinz body formation was seen on examination of blood smears, and severe anemia developed 3 days later. The dog did not have any history of exposure to toxins or drugs that have been associated with Heinz body formation. The only remarkable historical finding was that the dog had been wandering loose the day prior to initial examination and returned home smelling strongly of skunk spray. Skunk spray contains thiols and other compounds that are strong oxidizing agents. It was speculated that the methemoglobinemia and Heinz body anemia were a result of exposure to these compounds. Skunk interactions with dogs usually have malodorous but otherwise harmless results. However, findings in this dog suggest that more serious consequences may develop in isolated cases.  相似文献   
148.
The safety and protective efficacy of a horse antiserum raised against inactivated whole cell preparations of Streptococcus suis serotype 2 was investigated in pigs by experimental challenge. The antiserum was evaluated in two similar experiments each comprising 12 4-week-old pigs treated with 6 ml of antiserum the day before challenge and four pigs used as challenge controls. Pigs were infected by subcutaneous injection with approximately 10(11) colony forming units of S. suis serotype 2. Clinical disease in the pigs that could be attributed to infection with S. suis was reduced from 88 to 35% (P = 0.015). The percentage of pigs with lesions that could be associated with S. suis was reduced from 88 to 22% (P = 0.002) and isolation of S. suis serotype 2 was reduced from five (63%) out of eight pigs in the combined challenge control groups to 3 (13%) out of 23 pigs in the combined treatment groups. These results indicate that passive immunization of pigs may be a way to reduce or control S. suis serotype 2 infections in pigs.  相似文献   
149.
An 8-year-old ovariohysterectomized Chow Chow was referred because of dermatologic lesions diagnosed as pemphigus foliaceus. Intolerance to orally administered corticosteroids necessitated the use of methylprednisolone pulse therapy. One week after treatment, diabetes mellitus was diagnosed on the basis of blood and urine test results. For 3 years after treatment, the dog has remained a well-regulated diabetic. Complete remission of pemphigus foliaceus is maintained by alternate-day, orally administered prednisone (0.5 mg/kg of body weight).  相似文献   
150.
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