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   86553篇
  免费   7224篇
  国内免费   48篇
林业   4014篇
农学   3279篇
基础科学   482篇
  11946篇
综合类   9941篇
农作物   3186篇
水产渔业   6618篇
畜牧兽医   47562篇
园艺   990篇
植物保护   5807篇
  2020年   1035篇
  2019年   1680篇
  2018年   2043篇
  2017年   2251篇
  2016年   2183篇
  2015年   1831篇
  2014年   2109篇
  2013年   4039篇
  2012年   2966篇
  2011年   3496篇
  2010年   2587篇
  2009年   2249篇
  2008年   3127篇
  2007年   2979篇
  2006年   2810篇
  2005年   2524篇
  2004年   2350篇
  2003年   2366篇
  2002年   2181篇
  2001年   3045篇
  2000年   2937篇
  1999年   2270篇
  1998年   928篇
  1997年   872篇
  1996年   792篇
  1995年   900篇
  1994年   773篇
  1993年   762篇
  1992年   1631篇
  1991年   1850篇
  1990年   1824篇
  1989年   1685篇
  1988年   1593篇
  1987年   1587篇
  1986年   1475篇
  1985年   1438篇
  1984年   1202篇
  1983年   971篇
  1982年   734篇
  1979年   1126篇
  1978年   882篇
  1976年   794篇
  1975年   786篇
  1974年   930篇
  1973年   878篇
  1972年   886篇
  1971年   817篇
  1970年   781篇
  1969年   795篇
  1967年   790篇
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
91.
Twenty-five dogs with malignant lymphoma refractory to chemotherapy were treated with actinomycin D at a median dose of 0.7 mg/m2 (range, 0.5 to 0.9 mg/m2) every 3 weeks. The dogs treated had received between 2 and 8 chemotherapeutic agents (median 7), for a median of 266 days before being treated with actinomycin D. For 23 of the 25 dogs, previous chemotherapy included doxorubicin. No dog responded to actinomycin D chemotherapy.  相似文献   
92.
A 20-year-old pony mare with persistent ventricular tachycardia (VT) was examined cardiopathologically. At necropsy, the heart was enlarged and rounded with both ventricular dilatation. In a longitudinal section of the ventricular septum, a large grayish white patchy lesion (5 x 25 mm) was detected in the relatively higher portion. Microscopically, the lesion was extensive myocardial fibrosis located in the vicinity of the proximal part of the left bundle branch. Partially the fibrotic lesion was in contact with the branch. Such a lesion might play an important role in creating a suitable background for the development of VT via automaticity or reentry mechanism.  相似文献   
93.
94.
1. The concentration of zinc in seminal plasma at two different ages was measured in two breeds of domestic fowl. In the heavy strain, the motility and fertilising ability of spermatozoa stored for 24 h at 4 degrees C was also studied. 2. The concentration of zinc in the seminal plasma of the breeds studied was between 1 to 3 micrograms/ml. Age had no effect on it. 3. Zinc concentrations of 1, 3 or 9 micrograms/ml in the storage medium had no effect on sperm motility but in young animals reduced the fertilising ability of stored spermatozoa at the two highest concentrations and in older animals at all three concentrations tested.  相似文献   
95.
To evaluate the transplacental transfer of Theileria sergenti infection in cattle, we used DNA probes to detect T. sergenti in 6 pregnant cows and their calves. All the animals were monitored by parasitologic, serologic, and polymerase chain reaction (PCR) assays for a predicted 875-base-pair (bp) DNA product and a 684-bp amplicon detected by nested PCR in the blood and spleens of aborted fetuses. An open reading frame (ORF) starting at nucleotide 170 and terminating at position 1021 was shown to code for a polypeptide of 283 amino acid residues. All 6 dams and 5 calves were positive for T. sergenti in all tests. One calf was positive only with nested PCR. We conclude that transplacental transmission of T. sergenti is a significant problem. The relevance of the data in the programmed introduction of new (especially pregnant) animals into established clean herds needs serious consideration with regard to control of theileriosis and other tickborne diseases.  相似文献   
96.
97.
The use of phytotherapy to treat human diseases has its roots in pre-historical times. Despite the modern advances achieved in the field of synthetic chemistry, the most efficient drugs available have their genesis directly or indirectly related with the vegetal kingdom. Indigenous communities have long used plant extracts to treat illnesses. Many of these extracts have shown effective action, with new bioactive compounds being extracted and screened every year. These extracts have also proven to be good sources of therapeutic agents to the treatment of Leishmaniasis. This work highlights some of these agents, while trying to emphasize the importance of plants as a source of new and powerful drugs against this widespread disease.  相似文献   
98.
99.
100.
The 1998 Report of the American Association of Feline Practitioners and Academy of Feline Medicine Advisory Panel on Feline Vaccines was developed to help veterinary practitioners formulate vaccination protocols for cats. The current panel report updates information, addresses questions, and speaks to concerns raised by the 1998 report. In addition it reviews vaccine licensing, labeling, and liability issues and suggests ways to successfully incorporate vaccination protocol changes into a private practice setting.  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