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   179128篇
  免费   9791篇
  国内免费   123篇
林业   7749篇
农学   5981篇
基础科学   1167篇
  22784篇
综合类   29747篇
农作物   7175篇
水产渔业   8998篇
畜牧兽医   90909篇
园艺   2444篇
植物保护   12088篇
  2019年   1729篇
  2018年   2605篇
  2017年   2937篇
  2016年   2720篇
  2015年   2277篇
  2014年   2884篇
  2013年   6996篇
  2012年   5291篇
  2011年   6537篇
  2010年   4286篇
  2009年   4451篇
  2008年   6540篇
  2007年   6077篇
  2006年   5770篇
  2005年   5402篇
  2004年   5228篇
  2003年   5314篇
  2002年   4887篇
  2001年   5605篇
  2000年   5605篇
  1999年   4540篇
  1998年   2066篇
  1997年   1942篇
  1996年   1825篇
  1995年   2104篇
  1994年   1935篇
  1993年   1791篇
  1992年   3592篇
  1991年   3750篇
  1990年   3720篇
  1989年   3604篇
  1988年   3347篇
  1987年   3260篇
  1986年   3365篇
  1985年   3252篇
  1984年   2669篇
  1983年   2425篇
  1982年   1612篇
  1979年   2465篇
  1978年   1995篇
  1977年   1684篇
  1976年   1720篇
  1975年   1819篇
  1974年   2042篇
  1973年   2143篇
  1972年   2018篇
  1971年   1870篇
  1970年   1802篇
  1969年   1861篇
  1967年   1616篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Lytic lesions occurring in conjunction with plasma cell sarcoma (multiple myeloma) have rarely been reported in cats.

A plasma cell sarcoma was diagnosed in a 13 year old castrated male Siamese cat with hind limb paresis resulting from osteolysis of the second lumbar vertebra. Serum electrophoresis showed a monoclonal gammopathy. A uniform population of plasma cells was found in and around the second lumbar vertebra and in the bone marrow of the femora, humeri, pelvis and the fifth lumbar vertebra. The neoplastic cells were identified as IgA and kappa chain specific by direct immunofluorescence.

  相似文献   
952.
953.
954.
Infection with Fascioloides magna, the large American liver fluke, was diagnosed in two moose (Alces alces) and six wapiti (Cervus elaphus) from central Saskatchewan. This is believed to be the first record of the parasite in the province. Fecal samples collected from wild wapiti at five sites in the commercial forest zone in Saskatchewan contained eggs believed to be those of F. magna. Trematode eggs were not found in feces from five captive herds of wapiti in the province, nor in samples from wild wapiti in Moose Mountain Provincial Park. Operculate eggs were found in feces of wild wapiti from Cypress Hills, but these were believed to be from trematodes other than F. magna. The distribution and significance of F. magna in Canada, based partially on responses to a mail questionnaire, are reviewed.  相似文献   
955.
Reference ranges for five parameters of blood coagulation were established in clinically normal farmed fallow deer (Dama dama) and red deer (Cervus elaphus). Storage of plasma at -15 degrees C resulted in small increases in activated partial thromboplastin time (APTT) for both species, and in the one stage prothrombin time (OSPT) of fallow deer, between days 1 and 30. These times were then stable between days 30 and 60. The fibrinogen levels of fallow deer plasma showed a small apparent increase over 60 days. These storage artefacts were not of sufficient magnitude to preclude the use of such plasma for diagnostic purposes although they could limit its use in research. Levels of fibrin/fibrinogen degradation products (FDP) were not affected by storage at -15 degrees C. Rabbit brain thromboplastin appeared adequate for OSPT determination in both species. The activated clotting time (ACT) is recommended as a field test for screening the intrinsic and common pathways of blood coagulation in deer.  相似文献   
956.
A controlled slaughter trial was undertaken to evaluate the efficacy of ivermectin (0.2 mg/kg) and levamisole (8 mg/kg) against a morantel-resistant field strain of Trichostrongylus colubriformis in sheep. Mean worm count reductions of greater than 99% were recorded with both anthelmintics. The apparent contradiction between the high efficacy of levamisole and the common belief that resistance to levamisole and morantel is co-inherited, is discussed.  相似文献   
957.
The temporary dentitions of 18 to 39-week-old lambs with a very light or a very heavy parasite burden are compared. The heavily parasitised lambs developed longer temporary incisors which tended to protrude further forward in relation to the upper dental pad. They showed absolute hypocalcaemia and hypoalbuminaemia and relative hypophosphataemia and hypoproteinaemia and in the alveolar bone of the mandible there was a reduction in ash and matrix densities and matrix mineralisation. The incisor protrusion and lengthening may have been a consequence of the loss of supporting bone, but inappetance was likely to have been a factor contributing to the lengthening.  相似文献   
958.
959.
A transitional cell carcinoma of the urinary bladder was found in a beluga whale stranded in the St. Lawrence middle estuary. Various organs of this animal were submitted to high resolution gas chromatography coupled with mass spectrometry analysis. High frequency of urinary bladder cancer in the human population of the same area and the presence of carcinogenic compounds in the marine environment of this animal are discussed.

Concurrent isolation of Edwardsiella tarda from various organs of this whale is also reported.

  相似文献   
960.
In this review, "productive efficiency" in dairy cows is defined as the yield of milk obtained in ratio to the nutritional costs associated with maintenance, milk synthesis and loss of body condition during lactation. Improvements in efficiency could occur as a result of changes in digestion and nutrient absorption, maintenance requirement, utilization of metabolizable energy for production or nutrient partitioning. Digestibility can be greatly enhanced by appropriate dietary manipulation. Likewise, it may be possible to reduce maintenance requirements and improve the efficiency with which metabolizable energy is used for milk synthesis by manipulation of the pattern of nutrients presented to tissues. However, these factors apparently do not respond to selection for increased milk yield, and little variation is observed among cows. In contrast, individual cows differ substantially in feed intake and in the partitioning of nutrients among body tissues. Techniques associated with genetic engineering and the early prediction of genetic merit have the potential to improve productive efficiency by manipulation of these processes. However, changes in nutrient partitioning and feed intake during lactation are coordinated by a complex network of controls that accommodate the nutrient requirements of each tissue while maintaining homeostatic balance. Future improvements in productive efficiency will therefore depend on our ability to understand the manner in which these controls operate.  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