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   10936篇
  免费   787篇
  国内免费   45篇
林业   891篇
农学   452篇
基础科学   99篇
  2806篇
综合类   422篇
农作物   604篇
水产渔业   1151篇
畜牧兽医   4249篇
园艺   227篇
植物保护   867篇
  2024年   15篇
  2023年   84篇
  2022年   139篇
  2021年   266篇
  2020年   262篇
  2019年   266篇
  2018年   456篇
  2017年   479篇
  2016年   449篇
  2015年   352篇
  2014年   457篇
  2013年   725篇
  2012年   826篇
  2011年   842篇
  2010年   469篇
  2009年   460篇
  2008年   649篇
  2007年   623篇
  2006年   510篇
  2005年   454篇
  2004年   473篇
  2003年   424篇
  2002年   341篇
  2001年   270篇
  2000年   258篇
  1999年   235篇
  1998年   72篇
  1997年   55篇
  1996年   47篇
  1995年   54篇
  1994年   32篇
  1993年   31篇
  1992年   50篇
  1991年   47篇
  1990年   43篇
  1989年   59篇
  1988年   28篇
  1987年   45篇
  1986年   32篇
  1985年   36篇
  1984年   23篇
  1983年   27篇
  1982年   15篇
  1979年   26篇
  1978年   20篇
  1976年   19篇
  1973年   22篇
  1968年   15篇
  1967年   16篇
  1966年   17篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
971.
Restriction endonuclease analysis (REA) and plasmid profile were used to study the epidemiology of Pasteurella multocida in a swine pyramid structure. The studied pyramid was comprised of a group of 12 swine farrow-to-finish farms related by unidirectional animal movement. P. multocida isolates were obtained from the lungs of 275 slaughtered pigs. Serotyping was performed by hyaluronidase sensitivity test and toxicity was investigated by the ELISA test. HpaII was used to cleave the P. multocida extracted DNA. REA patterns relationships were studied using the Sokal-Michener coefficients, and the dendrogram was built using the UPGMA system. The 218 P. multocida isolates obtained were distributed in 17 REA patterns. In 9 of the 12 farms studied only 2-3 REA patterns were detected, with one clearly predominant pattern. The 81 strains with plasmids were assigned to six plasmid profiles. REA and plasmid profiles proved to be good epidemiological tools for identifying different strains of P. multocida with the same phenotype.  相似文献   
972.
Twenty Merino lambs of four age groups (1 day, 2, 4 and 7 weeks) and 8 adult Merino wethers were killed. The development of pancreatic and gastrointestinal enzymes was followed by determining RNase, amylase, lipase, trypsin, chymotrypsin and total proteolytic (azocaseinase) activity. Pancreatic protein content, rumen and abomasal pH and abomasal clotting time were also determined. Pancreatic RNase was already present in the newborn lambs and significantly rose in the first 2 weeks of life and before reaching adult values. The increase was more marked and went to higher adult values than in the pig (Baintner and Farkas, 1989). The time-course resembled that of pancreatic amylase and chymotrypsin; pancreatic trypsin and azocaseinase also showed some similarities, but pancreatic lipase had a different time course. Small intestinal RNase also changed differently; it showed a maximum at 4 weeks and had trends opposite to total proteolytic activity, indicating partial digestion of the enzyme by intestinal proteases. Rumen and caecal RNase activities may be indicative of microbial growth and fermentation rate; they showed mostly opposite tendencies in the two localities. In contrast to the pig (Baintner and Farkas, 1989), pancreatic and small intestinal trypsin:chymotrypsin ratios did not show significant increase during development in sheep.  相似文献   
973.
The effect was investigated of the Ralgro preparation with the active substance zeranol on histological and histochemical properties of bull muscles. The anabolic effect was displayed by a trend toward greater thickness of muscle fibres in m. longissimus thoracis, m. semitendinosus and m. triceps brachii, whilst differences between the muscles of experimental and control animals were not statistically significant. The bulls administered zeranol had the higher proportions as well as the higher relative volumes of white (aW) muscle fibres, but neither were these differences statistically significant in comparison with the control. The growth and development of testicles are inhibited by zeranol. The inhibition is significant and persists during 30 days after the last administration. Later on, the rate of development and growth are increased with the testicles reaching the weight of the sexual glands of control animals in 90 days after the last administration; the coiled seminiferous tubules grow and spermiogenesis occurs.  相似文献   
974.
In a study of the development of two oviparous species (domestic chicken and Japanese quail) and one ovoviviparous species (a common lizard), the relationship to alterations in egg size and weight during incubation was examined. It was observed, as reported by others that the avian egg diminishes in size during incubation, but that the lizard egg increases in size and weight. This investigation examines these relationships and suggests that the increase in the size and weight of the lizard egg is a result of an increase of liquid content. The mechanism is discussed.  相似文献   
975.
976.
977.
Fiber fermentation using the in situ bag technique was studied in a hay-fed cow. Entry of fine particles into bags of varying pore size, the effect of sample size, rumen contractions, bag porosity and rumen contraction (bags suspended in vitro or in situ) and obstruction of liquid flow through the bag cloth were investigated (Exp. 1). In Exp. 2 fiber degradation in vitro and in situ with 5- and 37-micron pore size bags was measured utilizing six fistulated heifers (four large: 610 kg and two small: 243 kg), two sheep and two goats (30 kg), three ponies (130 kg) and four rabbits (3.2 kg). Degradation rate (k) and indigestible fiber (B) were determined after curve fitting. Lag of fermentation was also calculated. Results of Exp. 1 showed that plant fiber containing approximately 50% lignin and 2.9% N entered even 20-micron pores, that rumen contractions increased fiber disappearance and that obstructing liquid exchange limited fermentation. Results of Exp. 2 showed lower fiber residues for 37-micron than for 5-micron pore size bags and that in situ method, time and species were highly significant (P less than .0001). All model factors differed significantly among species (P less than .05), but not among the three methods. Lag approached significance for methods (P = .07), but not for species. In situ measurements (37-micron) resulted in the following values for k (h-1), B (%) and lag (h): large heifers .040, 39 and -1; small heifers .025, 39 and 0; sheep-goats .051, 42 and 2; ponies .030, 59 and -5 and rabbits .107, 85 and 3.  相似文献   
978.
979.
Mycoplasmas were isolated from yak calves in Mongolia, the 1st experience worldwide with this species. They were also isolated from pathologically affected sheep and goat lambs. The disease was experimentally reproduced in yak calves as well as in sheep and goat lambs. Clinical manifestations were identical with those recordable from animals with spontaneous outbreak of the disease. This had been for the 1 time ever that a therapy was tested on animals with mycoplasmosis, using water with addition of oligodynamic silver. Something between 95 and 100% of all patients were clinically cured. The experimental vaccine involved was found to offer protection against mycoplasmosis to sheep and goat lambs. Damage association with mycoplasmosis was found to occur 1st in liver, spleen, and lymph nodes and to be subsequently proliferated to lung and other organs. Respiratory mycoplasmosis is the common definition used at present but is not in conformity with the pathological processes involved, as the major role is played by liver damage. Mycoplasmosis in these 3 species, therefore, should better be named mycoplasmosis bovi hepatica.  相似文献   
980.
The Bulbus oculi of 25 buzzards of both sexes and of nearly the same age and weight, was examined with regard to its gross anatomy, strucutre, ultrastructure and size. The volume of the eyeball is of 9.5 cm3. In the Anulus sclerae there are about a dozen of cartilagineous plates, and in the Corpus ciliare there can be found between 112 and 115 Processus ciliares. The muscle of Müller was not observed. Morphological details of the Pecten are given and its functional significance is discussed.  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