全文获取类型
收费全文 | 58843篇 |
免费 | 3300篇 |
国内免费 | 37篇 |
专业分类
林业 | 3062篇 |
农学 | 2222篇 |
基础科学 | 353篇 |
7466篇 | |
综合类 | 6822篇 |
农作物 | 2116篇 |
水产渔业 | 3196篇 |
畜牧兽医 | 32917篇 |
园艺 | 726篇 |
植物保护 | 3300篇 |
出版年
2019年 | 504篇 |
2018年 | 958篇 |
2017年 | 1040篇 |
2016年 | 1014篇 |
2015年 | 867篇 |
2014年 | 1020篇 |
2013年 | 2339篇 |
2012年 | 1813篇 |
2011年 | 2204篇 |
2010年 | 1440篇 |
2009年 | 1373篇 |
2008年 | 2038篇 |
2007年 | 2042篇 |
2006年 | 1937篇 |
2005年 | 1789篇 |
2004年 | 1688篇 |
2003年 | 1667篇 |
2002年 | 1538篇 |
2001年 | 2332篇 |
2000年 | 2186篇 |
1999年 | 1725篇 |
1998年 | 684篇 |
1997年 | 623篇 |
1996年 | 601篇 |
1995年 | 671篇 |
1994年 | 574篇 |
1993年 | 558篇 |
1992年 | 1262篇 |
1991年 | 1397篇 |
1990年 | 1450篇 |
1989年 | 1332篇 |
1988年 | 1243篇 |
1987年 | 1230篇 |
1986年 | 1167篇 |
1985年 | 1104篇 |
1984年 | 917篇 |
1983年 | 723篇 |
1982年 | 524篇 |
1979年 | 792篇 |
1978年 | 616篇 |
1977年 | 469篇 |
1976年 | 524篇 |
1975年 | 502篇 |
1974年 | 624篇 |
1973年 | 605篇 |
1972年 | 633篇 |
1971年 | 601篇 |
1970年 | 588篇 |
1969年 | 537篇 |
1967年 | 497篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
171.
Through the use of a critical electrolyte concentration staining technique, the glycosaminoglycans (GAGs) in the nucleus pulposus region of the canine intervertebral disc were arbitrarily identified as "hyaluronic acid", chondroitin sulphate and keratan sulphate. Approximate estimates of GAG concentration could be qualitatively deduced by determining the appropriate GAG "ALCIANOPHILIC INDEX". This index was considered to be an effective qualitative adjunct to chemical quantitation of GAGs in the intervertebral disc. 相似文献
172.
T C McGuire K L Banks D R Evans M J Poppie 《American journal of veterinary research》1976,37(1):41-46
Agammaglobulinemia was diagnosed in a 1-year-old Thoroughbred horse on the basis of the following observations: (1) absence of serum immunoglobulins M, A, and G(T); (2) small amounts of serum immunoglobulin G (16 mg/100 ml); (3) absence of specific antibody in the serum of the horse following immunization and challenge exposure to 2 antigens; (4) absence of plasma cells, primary follicles, and germinal centers in a lymph node removed after antigenic stimulation; (5) absence of "natural" serum antibodies to rabbit-erythrocytes which were easily detectable in age-matched control horse serums; and (6) increased susceptibility to infections. There was evidence of functional cell-mediated immunity which included a skin response to injected phytolectins, skin response to antigen challenge following sensitization, and in vitro proliferative response of lymph node cells to phytohemagglutinin. An intact cell-mediated immune response was also supported by the observation that the horse lived to 17 months of age without antibody production, whereas horses with an absence of both antibody production and cell-mediated immunity (combined immunodeficiency) die by 4 months of age without immunologic intervention. The known features of agammaglobulinemia in this horse are similar to those in sex-linked agammaglobulinemia in persons and are unique among the immunodeficiences described in other animals. 相似文献
173.
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
174.
175.
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
176.
177.
178.
A large-scale trial was carried out under commercial conditions to investigate to which extent the feeding of rations with varying lysine content to young hens would influence the crude nutrient content of the body fractions and might change the pattern of amino acid composition and the activity of GOT in the blood. Four rations were fed each containing 14.2% crude protein, 626-633 EFh units/kg and 0.59%, 0.61%, 0.54% and 0.46% lysine. The crude protein and crude fat content of the total body and of body fractions were in no case found to be related to the feeding regime. The proportion of crude ash in the "remainder of non-utilizable parts", in "bones", "intestinal and abdominal fat", "ovaries" and "small intestine" decreased with the decreasing lysine content of the rations. The concentrations of free lysine, histidine, arginine, and phenylalanine in the deproteinized blood plasma of the young hens were significantly (a = 0.01) lower in the birds of the lysine deficient group than in the hens of the other groups. Positive regressions were calculated for the lysine content or the content of aspartic acid in the ration and the pattern of free amino acids in blood plasma. Positive and negative linear relationships were found to exist between the concentrations of free lysine, and those of histidine, arginine or threonine, and serine. A close correlation existed between the total amount of essential amino acids in blood plasma and the lysine concentrations of the plasma. Increasing lysine supplementation produced a decline in the N content of the whole blood and blood corpuscles but a rise in the N content of blood plasma. The activity of GOT in the blood of young hens was not found to be useful as an indicator of the quality of dietary proteins. 相似文献
179.
180.