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   11363篇
  免费   784篇
林业   995篇
农学   417篇
基础科学   56篇
  2401篇
综合类   393篇
农作物   448篇
水产渔业   988篇
畜牧兽医   5160篇
园艺   176篇
植物保护   1113篇
  2023年   77篇
  2022年   104篇
  2021年   230篇
  2020年   214篇
  2019年   142篇
  2018年   484篇
  2017年   528篇
  2016年   511篇
  2015年   368篇
  2014年   466篇
  2013年   646篇
  2012年   791篇
  2011年   700篇
  2010年   388篇
  2009年   363篇
  2008年   563篇
  2007年   512篇
  2006年   417篇
  2005年   450篇
  2004年   367篇
  2003年   350篇
  2002年   296篇
  2001年   259篇
  2000年   252篇
  1999年   223篇
  1998年   53篇
  1997年   38篇
  1996年   49篇
  1992年   134篇
  1991年   116篇
  1990年   110篇
  1989年   129篇
  1988年   124篇
  1987年   124篇
  1986年   115篇
  1985年   104篇
  1984年   81篇
  1983年   75篇
  1982年   47篇
  1981年   57篇
  1980年   51篇
  1979年   106篇
  1978年   93篇
  1977年   85篇
  1976年   55篇
  1975年   48篇
  1974年   100篇
  1973年   71篇
  1972年   96篇
  1971年   87篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
A comparative trial was conducted with the oral administration of zinc sulphate to pregnant cows and heifers aimed at influencing the selected metabolic parameters in the dam-calf line. The total daily ZnSO4.7H2O dose of 3 g (680 mg Zn++) was given to dry standing cows and heifers for 35 days on an average (15-65) before the expected date of calving. The breeding conditions in the stock were problematic: losses of calves suffered in the last half-a-year period were higher than 30% of born calves; the main causes of this high mortality were coli-septicaemia and coli-enteritis. As compared with the eight control animals, the experimental cows and heifers (12 head) exhibited a transient increase in zincaemia, followed by a tendency to proteinaemia; aspartate aminotransferase activity increased, total immunoglobulins remained unchanged, and decreases were recorded in the activities of alanine aminotransferase, alkaline phosphatase, creatine phosphokinase and aldolase. On the other hand, the concentration of total bilirubin tended to increase. In 77% of the cows and first-calvers of the experimental group the quality of colostrum complied with the standard; in the case of the control animals this proportion was 83%. Significant zincaemia occurred in the calves of the experimental cows between the first and 14th day of their age; no differences from the control calves were recorded in immunoglobulinaemia, proteinaemia, albuminaemia and in the activities of alanine aminotransferase and creatine phosphokinase. On the other hand, aspartate aminotransferase activity tended to grow and alkaline phosphatase activity tended to sink. Neonatal hyperbilirubinaemia disappeared within the first 14 days of age in both the experimental and the control calves. The results failed to show clearly that the intention to increase the values of the studied parameters of immunopoiesis was met.  相似文献   
992.
After the second and fourth parturition of piglets, ten clinically healthy sows, weaned on the second day of life, were subjected to examination two to three days before heat, during heat (defined by typical changes on the outer genitals and immobilization in the presence of a boar) and two days after insemination. During the morning hours, four hours after the last feeding, blood was taken from V. cava cranialis. Seventeen parameters were determined in whole blood and in the blood serum. In the period of oestrus, compared with the period two to three days before this period and two days after insemination, a marked increase was observed in the concentration of the serum levels of 11-hydroxycorticosteroids, iron, and in the activity of alanine aminotransferase. The activity of aspartate aminotransferase was increased in heat only in comparison with the period of the two days after insemination. The concentration of haemaglobin in whole blood was significantly increased in comparison with the period before oestrus and after insemination. Further, in the heat period -- as compared with the time before it -- a considerable drop was observed in the content of inorganic phosphorus and vitamin A. The possible mechanism of the occurrence of other changes is discussed.  相似文献   
993.
Very little information about NH4+ assimilation paths in rumen anaerobic bacteria is available, and the information about wild animals is completely missing. Glutamate dehydrogenase (GDH) isolated from the rumen strain B. ruminicola in fallow deer was purified and its properties were specified after crystalline ammonium sulphate precipitation and gel filtration on Sephadex G-200. The properties of partly purified GDH were specified. One of the first specifications concerning GDH from various sources was to determine its coenzyme specificity. The results of these determinations enabled to draw a general conclusion that GDH from non-animal sources was specific to only one coenzyme while GDH from animal sources could utilize the two coenzymes (Frieden, 1964). In our study the specificity of GDH isolated from the rumen strain B. ruminicola in fallow deer to the coenzyme NADH (Tab. I) was determined; this specificity was different from the coenzyme specificity of GDH isolated from the rumen strain B. ruminicola in calves where GDH was found to be specific to the coenzyme NADPH. The effect of increasing concentrations of NADH, 2-oxoglutarate and NH4+ on the enzyme reaction velocity was also investigated and Km was determined for NADH, 2-oxoglutarate and NH4+ (Tab. II). The kinetic properties of GDH isolated from different sources are considerably variable. Michaelis constants for GDH range from 0.003 to 0.125 mmol/dm3 for NADPH (NADH), from 0.95 to 7.4 mmol/dm3 for 2-oxoglutarate, and from 0.25 to 16 mmol/dm3 for NH4+ (Misono et al., 1985). The average value of Km for NH4+ in a mixed rumen population was 33 mmol/dm3 (Erfle et al., 1977).(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
994.
The biochemical profile [levels of calcium, phosphorus, magnesium, chlorides and iron, the activities of alkaline phosphatase (ALP), aspartate aminotransferase (AST) and alanine aminotransferase (ALT), and the concentrations of total protein, albumin, cholesterol, urea, glucose, and vitamins A and E] was studied in the blood serum of 40 anoestrous and 40 control inseminated animals in a production herd with an increased occurrence of anoestrus in gilts. The anoestrous gilts showed significantly lower levels of albumin (P less than 0.01) and glucose (P less than 0.01) and ALP activity (P less than 0.05), and significantly higher concentrations of urea (P less than 0.01), vitamin A (P less than 0.01) and vitamin E (P less than 0.05) and ALT activity (P less than 0.05), as compared with the inseminated controls. An extended enzymatological examination consisting of the evaluation of the activities of ALP, AST, ALT and gamma-glutamyl transferase (GMT) was performed in another set of 22 anoestrous and 20 mated gilts. The anoestrous gilts showed a statistically significant increase in the activities of AST (P less than 0.01), GMT (P less than 0.01) and ALT (P less than 0.05) and an insignificant increase in the activity of ALP in comparison with the control animals. The comparison of the obtained values of the studied biochemical criteria with literary data indicated a lower concentration of magnesium and a higher ALP and ALT activities in the anoestrous and inseminated gilts in both groups under study. A high acidity of fat and a medium to high fungus infestation (Mucor sp., Aspergillus sp.) were found by chemical and mycological examination of the administered feed mixtures. The histological examination of the ovaries of anoestrous animals showed cystically degenerative changes, proliferations of fibrous elements, and partial atrophy of ovarial cortex. It has been inferred from the observations that mycotoxins may be involved in the increase in the occurrence of anoestrus, either by a direct effect on sexual organs or by impairing the function of liver which, secondarily contributes to the rise of ovarial dysfunctions.  相似文献   
995.
996.
A procedure for the production of biologically active substances from pine and spruce needles was worked out within the research project Utilization of Tree Verdure. The product was referred to as a biologically active preparation. The fields of its possible uses include agriculture (animal production-feeding), cosmetics (production of pastes, soaps, etc.), pharmaceutical industry (after additional conditioning the product can be used for manufacturing medicinal drugs for the control of inflammatory diseases and the like). The biologically active preparation, i. e. the pine needle extract, was studied as to its effect on some of the most numerous microorganisms in the intestines of ruminants. As found, this preparation has a partial inhibitive action on the growth and reproduction of microorganisms. The biologically active preparation is an extract isolated from the needles by means of 0.3% sodium hydroxide. Besides extractive substances it also contains the residues of organellae of cellular nature (which got into the extract through the filter during the process of preparation) and a small amount of fibre (0.33%). The chemical composition of the biologically active preparation is varied: until now about 220 substances, many of which are biologically active, have been found to be present in the product.  相似文献   
997.
For the assessment of the degree of meat freshness of stored unbleeded carp some simple chemical methods were tested to be used as auxiliary criteria for veterinary decisions regarding the edibility. Under the experimental conditions where the suffocated carp were stored at cooling and room temperatures in water or in the air, differences were determined in the followed criteria between fresh and deteriorating fish which were statistically insignificant for most indicators. In view of requirements regarding chemical indicators only the determination of ribose content was found to be expedient. Changes in the levels of ribose were significantly correlated with the sense-detected changes in meat freshness of the stored carp.  相似文献   
998.
999.
1000.
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