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   163660篇
  免费   8638篇
  国内免费   141篇
林业   6940篇
农学   4637篇
基础科学   1088篇
  18277篇
综合类   32563篇
农作物   6492篇
水产渔业   7242篇
畜牧兽医   83853篇
园艺   1889篇
植物保护   9458篇
  2018年   1993篇
  2017年   2233篇
  2016年   2057篇
  2015年   1761篇
  2014年   2182篇
  2013年   5875篇
  2012年   4136篇
  2011年   5090篇
  2010年   3303篇
  2009年   3358篇
  2008年   5113篇
  2007年   4727篇
  2006年   4525篇
  2005年   4245篇
  2004年   4277篇
  2003年   4283篇
  2002年   4049篇
  2001年   4970篇
  2000年   4968篇
  1999年   3752篇
  1998年   1589篇
  1997年   1595篇
  1995年   1853篇
  1994年   1664篇
  1993年   1681篇
  1992年   3383篇
  1991年   3727篇
  1990年   3624篇
  1989年   3614篇
  1988年   3274篇
  1987年   3395篇
  1986年   3563篇
  1985年   3474篇
  1984年   2745篇
  1983年   2509篇
  1982年   1673篇
  1981年   1629篇
  1979年   2583篇
  1978年   2045篇
  1977年   1709篇
  1976年   1618篇
  1975年   1730篇
  1974年   2277篇
  1973年   2325篇
  1972年   2303篇
  1971年   2210篇
  1970年   2103篇
  1969年   1929篇
  1968年   1605篇
  1967年   1720篇
排序方式: 共有10000条查询结果,搜索用时 568 毫秒
961.
The results obtained following both maxillectomy and mandibulectomy in animals with benign disease show that these procedures are practical. The challenge is to select those animals with malignant disease where the disease is sufficiently localized so that radical resection will be curative, or where residual disease can be controlled by adjuvant therapy. The series of cases reported in Tables 1 and 2 represent animals treated during the "developmental phase" of these procedures. With 5 years of case experience now available, the usefulness and limitations of these procedures are becoming clearer.  相似文献   
962.
963.
A ram lamb with congenital goitre showed signs of respiratory distress at birth. All previously affected lambs from this flock bad been born dead or bad died soon after birth. The serum free-thyroxine level at 1 birth was low (9.8 pmol/l) but treatment with oral L-thyroxine resulted in an increase in thyroxine blood levels to above normal and regression of the goitre. Four weeks after withdrawal of thyroid supplementation and when the lamb was eight weeks old, the radio iodide uptake mechanism of the thyroid glands was shown to be intact but the iodide was not organified. Low normal peroxidase activity was demonstrated in fresh thyroid tissue but gel electrophoresis demonstrated an absence of normal thyroglobulin from extracts of the goitrous thyroid. This lamb and the other affected lambs of this flock have an inherited defect in thyroglobulin synthesis and it is likely that the respiratory distress was associated with the low levels of thyroid hormone affecting foetal lung development.  相似文献   
964.
965.
On a property in the Nelson District, blood and urine samples were taken from red deer (Cervus elaphus) from which low (<1:100) antibody titres to serovar copenhageni and suspected leptospiral abortions had previously been reported. A total of 27 hinds were sampled. Microscopic agglutination test (MAT) titres in sera ranging from 1:32 to 1:128 were found in six animals. Thirteen leptospiral isolations were made from nine of the 27 urine samples. Four of these were typed as copenhageni and nine as hardjo. Two cultures were prepared from each urine sample and hardjo and copenhageni were both isolated from single urine samples from two animals. None of the 27 deer had serum MAT titres at 1:32 or above to copenhageni.  相似文献   
966.
Of 32 calves given an unknown amount of a pluronic bloat mixture with their milk, 28 died in convulsions over 24 hours. Supportive therapy was unsuccessful. Concentrations of pluronic present in abomasal and rumenal contents supported a diagnosis of pluronic poisoning.  相似文献   
967.
This article describes the surgical procedures for the ovariectomy, ovariohysterectomy and orchidectomy in rodents and rabbits. The indications for each procedure are outlined and effective and safe anesthetics are described. Preoperative and postoperative care is also discussed.  相似文献   
968.
Three trials using 240 weanling pigs were conducted during winter months to determine the influence of nursery temperature ("comfortable" vs "cold") on the response of weanling pigs to added vitamin C (700 ppm) or E (55 IU/kg) to a corn-soybean meal diet. A "comfortable" temperature schedule (27 C initially with a weekly 2 C drop) was maintained in one nursery, with the temperature schedule in the "cold" nursery about 8 C lower. Plasma concentrations of vitamin C and vitamin E were elevated when the respective vitamins were added to the diet, but were not consistently influenced by nursery temperatures. Daily gain, daily feed intake and feed efficiency were not improved with the added C or E. Daily feed intake was increased and feed-to-gain ratios were larger for pigs housed in the "cold" nursery compared with pigs housed in the "comfortable" nursery; however, daily gains were similar in the two environments. Pigs housed in the "cold" nursery were slightly stressed, as indicated by heavier adrenal glands, but the antibody response and serum glucocorticoid concentrations were not significantly affected by either diet or temperature.  相似文献   
969.
Twelve isolates of bovine rotavirus, originating from eight dairy herds in Quebec known to have frequent epizootics of diarrhea in young calves in the last five years, were successfully propagated in cell cultures. The 12 isolates produced clear-cut plaques in BSC-1 cells and, except for one isolate, agglutinated human group "O" erythrocytes to an higher titer than bovine erythrocytes. Antisera to each isolate were produced in rabbits and used to study their antigenic relationships. All the isolates shared the group-specific immunofluorescent antigen and were antigenically related as demonstrated by the seroneutralization and hemagglutination-inhibition tests. However, the relationships to the Nebraska rotavirus was quite weak in cases of two Quebec isolates. When the genomes of the various isolates were compared by polyacrylamide gel electrophoresis, at least three different reproducible fractionation patterns could be identified.  相似文献   
970.
A review of the current literature available on feline serum proteins is presented. Early studies concentrated on comparative aspects of species variations in the electrophoretic pattern. The feline electrophoretogram was divided into five basic regions: albumin, alpha-1, alpha-2, beta and gamma. Different subdivisions of these areas were recognized depending on the support medium used. Current papers have compared the relative migration distances of each globulin peak to the migration of albumin. This "Rf" value enables reliable peak identification. To date, no data exists identifying the individual proteins responsible for the peaks in the alpha and beta regions. The only feline globulin to be studied is haptolobin; however its precise location on the electrophoretic strip was not identified.  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