全文获取类型
收费全文 | 105932篇 |
免费 | 5472篇 |
国内免费 | 68篇 |
专业分类
林业 | 5642篇 |
农学 | 4137篇 |
基础科学 | 673篇 |
14352篇 | |
综合类 | 14675篇 |
农作物 | 3955篇 |
水产渔业 | 5701篇 |
畜牧兽医 | 54018篇 |
园艺 | 1793篇 |
植物保护 | 6526篇 |
出版年
2019年 | 837篇 |
2018年 | 2588篇 |
2017年 | 2729篇 |
2016年 | 1998篇 |
2015年 | 1362篇 |
2014年 | 1599篇 |
2013年 | 3755篇 |
2012年 | 3174篇 |
2011年 | 4473篇 |
2010年 | 3383篇 |
2009年 | 3122篇 |
2008年 | 4055篇 |
2007年 | 4193篇 |
2006年 | 3089篇 |
2005年 | 2907篇 |
2004年 | 2816篇 |
2003年 | 2814篇 |
2002年 | 2526篇 |
2001年 | 3689篇 |
2000年 | 3655篇 |
1999年 | 2811篇 |
1998年 | 1138篇 |
1997年 | 1037篇 |
1996年 | 951篇 |
1995年 | 1166篇 |
1994年 | 1014篇 |
1993年 | 959篇 |
1992年 | 2214篇 |
1991年 | 2360篇 |
1990年 | 2340篇 |
1989年 | 2224篇 |
1988年 | 2109篇 |
1987年 | 2126篇 |
1986年 | 2038篇 |
1985年 | 1895篇 |
1984年 | 1580篇 |
1983年 | 1298篇 |
1982年 | 886篇 |
1979年 | 1336篇 |
1978年 | 1055篇 |
1977年 | 870篇 |
1976年 | 875篇 |
1975年 | 899篇 |
1974年 | 1094篇 |
1973年 | 1064篇 |
1972年 | 1106篇 |
1971年 | 1009篇 |
1970年 | 967篇 |
1969年 | 958篇 |
1967年 | 851篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
961.
Digestibility trials were performed with laying hens receiving 3 types of rations containing equal proportions of the same dietary components. The percentage of high-protein wheat in these rations was 74%. Ration I was supplemented with 0.12% lysine while 0.06% lysine was added to ration II; ration III remained unsupplemented. The crude protein content of rations 1 to 3 was 16.1%, 16.5% and 16.6%, respectively. The corresponding lysine percentages were 0.66, 0.62 and 0.56. Studies were made to investigate the influence of different lysine levels on the rate of N excretion and various amino acid data. These studies were carried out during two successive laying periods. Only random differences between the data for urinary N excretion and N balances per kg liveweight were obtained in the two laying periods and for the different lysine levels. The true lysine digestibility was significantly lower in the poor-lysine ration as compared with the ration with 0.66% lysine. Moreover, the absorptive capacity for thio-amino acids is influenced by the lysine level of the ration. The proportion of lysine contained in faecal crude protein increased with the decreasing lysine content of the ration. Similarly, the total number of amino acids present in faecal crude protein increased with the declining supply of lysine. These findings suggest that relatively more NPN compounds are excreted in the faeces if adequate amounts of amino acids are supplied rather than when one amino acid is deficient. 相似文献
962.
J Marcaník J Kocisová K Bod'a T Pauer M Belák R Skarda 《Archives of Animal Nutrition》1976,26(11):757-763
Histological and histochemical studies were carried out on the gastro-intestinal mucosa of three experimental cows (roughages/maize silage) and three control animals. The animals were slaughtered on termination of the long-term trial. Mucosa samples were taken, for further study, from the rumen, the duodenum, the jejunum, the large intestine and the appendix. Histochemical analysis did not reveal any essential differences in the activities of non-specific esterase, alkaline and acid phosphatase and lactic acid dehydrogenase in the mucosa of the rumen, the large and the small intestine and the appendix of both the experimental animals and the controls. The experimental animals were found to exhibit a higher rate of glutamate-dehydrogenase activity in the ruminal mucosa and in the mucosa of the large and small intestine. A higher succinate dehydrogenase activity was observed in the ruminal mucosa of the experimental animals, relative to that of the controls, while the activity in the intestinal mucosa was decreased. Only slight changes were noted in the activity of the enzymatic systems tested. Electron microscopic studies did not reveal any differences in the ultrastructure of the epithelial cells of the ruminal mucosa in both the experimental animal and the controls. 相似文献
963.
A method for the separation of leucocytes from bovine blood and its separation into lymphocyte and granulocyte fractions is described. The method, involving flash lysis of the erythrocyte population, was found to yield large numbers of viable cells suitable for maintenance in tissue culture medium and hence of value in immunological studies. 相似文献
964.
965.
I W Lesslie C N Herbert K J Burn B N MacClancy W J Donnelly 《The Veterinary record》1975,96(15):332-334
A tuberculin testing trial in cattle was carried out in the Republic of Ireland to compare the specificity for bovine tuberculosis of a human purified protein derivative (PPD) tuberculin (Weybridge) with that of a bovine PPD (Rotterdam), and to determine whether discrimination between specific and non-specific reactions to mammalian tuberculin is better with doses of tuberculins smaller than those traditonally used for testing cattle. Tests were carried out in 510 cattle, 395 of which were shown by post mortem examination to be tuberculous and 115 non-tuberculous. Three dilutions at five-fold intervals of both mammalian tuberculins were used together with two dose levels of avian tuberculin PPD (Weybridge), and all reactions were measured both by increase in skin fold thickness and by diameter of induration. In the environment of this trial, the bovine PPD was shown to be more specific for bovine tuberculosis than the human PPD, and particularly in differentiating from "skin tuberculosis". There was no indication of greater specificity at lower doses of tuberculin. Measurement of induration diameter proved a satisfactory alternative method of reading tuberculin reactions in cattle under field conditions. 相似文献
966.
967.
The protective effect of a lyophilized vaccine against Marek's disease ("Keramvac"--Pfizer), prepared from a cell-free turkey's herpesvirus (strain FC 126), was compared in field trials with losses in the group of non-vaccinated chickens. Under the indicated conditions, the vaccine had only a 50.86% effectiveness. The possible causes of the reduced vaccination effect are discussed with regard to the pathomorphological and virological findings suggesting, among others, an increased incidence of the symptoms of the classical form of Marek's disease in the population investigated. 相似文献
968.
T S Baskett 《Pesticides monitoring journal》1975,9(2):67-78
Samples of breast muscle from 327 ducks collected from October 1970 to March 1971 in the conterminous United States were analyzed for total mercury by flameless atomic absorption spectrometry. Mercury levels for the entire collection ranged from less than 0.01 to 3.91 ppm wet weight with a median of 0.10 ppm. Twenty-five ducks had levels equalling or exceeding the 0.5 ppm guideline for fish and shellfish established by the Food and Drug Administration, U.S. Department of Health, Education, and Welfare. Dabbling ducks, which are shallow-water feeders and mostly vegetarian in fall, winter, and spring, usually had lower levels than diving and sea ducks. Levels were generally higher in ducks collected in areas where environmental mercury levels were known to be greater than in ducks from nonsuspect areas. Despite the mobility of the ducks, levels seemed more closely linked to local environmental contamination than to various factors associated with large geographic areas. 相似文献
969.
K J S?rensen 《Nordisk veterinaermedicin》1975,27(4):208-212
In 1956 a disease of nursing pigs previously unreported in Denmark, was observed in several swine herds. The disease syndrome appeared identical with that later described by Roe and Alexander in 1958 and by S. F. Cartwright and M. Lucas in 1968. Since 1956 there have been no reports of such outbreaks in Danish herds. To investigate whether the virus is still present, a survey was carried out to detect neutralizing antibodies in sera from a number of boars using a micro technique. In 144 sera from Jutland 12% had titers ranging from 10 to 32 ND-50, 22% from 32 to 90, 37% from 90 to 256, 14% from 256 to 724 and 3% above 724 ND-50 with a total of 86% positive. Of 174 sera from the rest of the country 16% had titers ranging from 10 to 32 ND-50, 18% from 32 to 90, 28% from 90 to 256, 13% from 256 to 724 and 3% exceeding 724 ND-50 with a total of 79% positive. 相似文献
970.