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   188070篇
  免费   10150篇
  国内免费   147篇
林业   7457篇
农学   5784篇
基础科学   1220篇
  23188篇
综合类   32468篇
农作物   7391篇
水产渔业   9220篇
畜牧兽医   96839篇
园艺   2441篇
植物保护   12359篇
  2019年   1760篇
  2018年   2598篇
  2017年   3018篇
  2016年   2735篇
  2015年   2304篇
  2014年   2906篇
  2013年   7328篇
  2012年   5293篇
  2011年   6707篇
  2010年   4257篇
  2009年   4447篇
  2008年   6509篇
  2007年   6139篇
  2006年   5816篇
  2005年   5356篇
  2004年   5093篇
  2003年   5221篇
  2002年   4735篇
  2001年   5766篇
  2000年   5881篇
  1999年   4659篇
  1998年   1983篇
  1997年   1931篇
  1996年   1821篇
  1995年   2198篇
  1994年   1962篇
  1993年   1827篇
  1992年   3857篇
  1991年   4041篇
  1990年   3883篇
  1989年   3886篇
  1988年   3620篇
  1987年   3648篇
  1986年   3773篇
  1985年   3638篇
  1984年   2934篇
  1983年   2599篇
  1982年   1779篇
  1979年   2744篇
  1978年   2223篇
  1977年   1855篇
  1976年   1887篇
  1975年   1995篇
  1974年   2444篇
  1973年   2474篇
  1972年   2320篇
  1971年   2170篇
  1970年   2078篇
  1969年   2013篇
  1967年   1802篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
The association between ocular squamous cell tumors and various measures of solar radiation was evaluated for 2,775 contemporaneous Hereford cattle. The animals were from 34 herds located in 21 states in the United States and in one Canadian province. Examinations and photographs were made of the eyes of all cows and heifers in a herd; 33 herds were examined between June and August 1957 and 1 herd was examined in 1958. Solar radiation was measured by altitude and mean annual hours of sunshine applying to an individual herd, and global radiation, a cloudiness index, and elevation of nearby National Weather Service stations. All measures of solar radiation provided evidence of a significant association between increasing risks of developing cancer eye and increasing levels of radiation; adjustments were made for possible confounding effects of age and corneoscleral pigmentation. Associations were evident whether affliction was defined as the occurrence of any type of tumor (ie, plaque, papilloma, or carcinoma), or as the occurrence of only papilloma or carcinoma. Average ages of affected cattle also tended to be lower at high radiation levels than at low levels, further supporting the hypothesis that solar radiation has an important role in the development of this disease. In view of the heritability of eye pigmentation and its inhibitory effect on lesions, cancer eye may be controlled by selective breeding for increased pigmentation in and around the eye to afford protection against the harmful effects of incident UV radiation.  相似文献   
143.
144.
Seven foci of pain (trigger points) were identified in the triceps brachii, infraspinatus, adductor-pectineus, peroneus longus, gluteus medius, ileocostorum lumborum, and quadriceps femoris muscles in 48 lame dogs. The dogs had been lame for 1 day to 150 weeks (mean, 24 weeks). Thirty-one dogs had been treated unsuccessfully with corticosteroids, nonsteroidal anti-inflammatory drugs, analgesics, or acupuncture. Palpating the trigger points induced severe pain. Treatment consisted of weekly stimulation of the trigger points by needling or injection of a local anesthetic. The mean treatment period was 2.8 weeks. Excellent results and complete recovery were observed in 34 dogs (60%).  相似文献   
145.
146.
147.
Thirty-eight dogs with hip dysplasia were studied to evaluate the use of gold wire implants at acupuncture points around the hip joints. They were assigned at random into two groups of 19. In the treated group, gold wire was inserted through hypodermic needles at electrically found acupuncture points around both hips. In the control group, the areas were prepared in the same way but had only the skin pierced at sites which were not acupuncture points, with a needle of the same size as that used in the treated group. Over a period of six months the dogs were studied repeatedly by two veterinarians and by the dogs' owners who were unaware of the treatments the dogs had received; they assessed the dogs' locomotion, hip function and signs of pain. Radiographs were taken at the beginning and end of the study. Although the data collected from both groups by the veterinarians and the owners showed a significant improvement of locomotion and reduction in signs of pain (P=0.036 for the veterinary evaluation and locomotion and P=0.0001 and P=0.0034 for the owners' evaluation of locomotion and pain, respectively), there were no statistically significant differences between the treated and control groups (P=0.19 and P=0.41, P=0.24, respectively).  相似文献   
148.
Humoral immune responses of black-footed penguins (Spheniscus demersus) to DNA-mediated immunization with a beta-galactosidase reporter gene expression plasmid were evaluated. Six male and 6 female adult penguins received either test plasmid, pCMV-beta, containing the beta-galactosidase gene or control plasmid, pCI, lacking a gene for expression. Three birds from each group were used previously in a diluent control group and given one injection of sterile saline. All samples were screened for anti-beta-galactosidase antibodies by indirect enzyme-linked immunosorbent assay with anti-chicken immunoglobulin G as secondary antibody. Antibodies to beta-galactosidase were detected in the sera of pCMV-beta-inoculated penguins, with a peak response on day 21. Antibody titers of the test plasmid group versus both control groups on days 21, 28, and 42 differed significantly. These results demonstrate that black-footed penguins can be safely transfected with the gene encoding beta-galactosidase and will mount a humoral response against the in vivo-expressed protein. Knowledge from this initial study can be applied to the development of DNA-mediated vaccines against specific infectious diseases of penguins.  相似文献   
149.
The effects of lipopolysaccharide ( Escherichia coli , O55:B5), administered 18 h after ovulation in the second oestrus after weaning on the hormonal profiles in 14 Swedish cross-bred (Landrace × Yorkshire) multiparous sows were studied. The endotoxin group (E-group) sows were administered with 300 ng/kg of lipopolysaccharide (LPS) whereas the control group (C-group) sows were administered 5 ml of saline intravenously via an indwelling jugular cannula. Blood samples for hormonal analyses were collected from all sows until slaughter. In the E-group, progesterone, cortisol and prostaglandin F metabolite levels increased significantly (p < 0.05) following LPS compared with the C-group. It can be concluded from this study that apart from elevating cortisol and prostaglandin F metabolite, LPS also elevates progesterone levels.  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