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   1014篇
  免费   64篇
  国内免费   1篇
林业   27篇
农学   20篇
  121篇
综合类   150篇
农作物   125篇
水产渔业   35篇
畜牧兽医   574篇
园艺   4篇
植物保护   23篇
  2021年   18篇
  2020年   7篇
  2019年   35篇
  2018年   12篇
  2017年   21篇
  2016年   21篇
  2015年   12篇
  2014年   27篇
  2013年   66篇
  2012年   35篇
  2011年   44篇
  2010年   26篇
  2009年   27篇
  2008年   52篇
  2007年   50篇
  2006年   45篇
  2005年   45篇
  2004年   27篇
  2003年   28篇
  2002年   28篇
  2001年   29篇
  2000年   31篇
  1999年   29篇
  1998年   15篇
  1997年   9篇
  1996年   9篇
  1995年   13篇
  1994年   10篇
  1992年   14篇
  1991年   13篇
  1990年   19篇
  1989年   17篇
  1988年   16篇
  1986年   9篇
  1985年   13篇
  1984年   10篇
  1983年   11篇
  1980年   9篇
  1979年   13篇
  1978年   7篇
  1975年   7篇
  1974年   7篇
  1973年   11篇
  1972年   6篇
  1971年   12篇
  1970年   13篇
  1969年   5篇
  1968年   8篇
  1967年   5篇
  1966年   8篇
排序方式: 共有1079条查询结果,搜索用时 15 毫秒
941.
Avena magna is a new tetraploid species morphologically similar to the hexaploid A. sterilis, having a high concentration of protein, large caryopses, and outstanding resistance to crown rust. One genome in A. magna appears homologous to the As genome present in hexaploid, tetraploid, and one group of diploid species. Avena magna is a possible ancestor of cultivated oats.  相似文献   
942.
Blood and serum from normal degus (Octodon degus) that ranged in age from 3 to 48 months were analyzed to determine reference hematologic and serum protein values. Both sexes were evaluated and were similar. The hematologic and serum protein values for males were: erythrocytes, 8.69 +/- 0.19 X 10(6) /microliter; packed cell volume, 42.1% +/- 0.59%; hemoglobin, 12.0 +/- 0.15 g/dl; leukocytes, 8.50 +/- 0.39 X 10(3)/microliter; neutrophil-to-lymphocyte ration, 40:60; and total protein, 5.70 +/- 0.20 g/dl. The hematologic and serum protein values for females were: erythrocytes, 8.94 +/- 0.16 X 10(6)/microliter; packed cell volume, 40.0% +/- 0.61%; hemoglobin, 11.7 +/- 0.17 g/dl; leukocytes, 8.20 +/- 0.36 X 10(3)/microliter; neutrophil-to-lymphocyte ratio, 40:60; and total protein, 5.62 +/- 0.18 g/dl. The hematologic and serum protein values for the degu were similar in some respects to values reported for guinea pigs and rats.  相似文献   
943.
The efficacy of antigens based on modified GnRH peptides in stimulating the production of antibodies against GnRH in sheep was tested. In the first study cysteine-containing GnRH peptides were conjugated to keyhole limpet haemocyanin (KLH) in 3 different orientations. The 3 conjugates were prepared in an emulsion of Freund's complete adjuvant (FCA) and were injected into 3 groups of 6 castrated male lambs. The 3 vaccines efficiently induced anti-GnRH titers in all the animals treated. The specificity of the GnRH antisera raised varied depending on the orientation of the GnRH molecule in the antigen and on the individual animal.

In a second trial designed to evaluate carrier molecules, a cysteine-containing GnRH peptide was conjugated to either KLH, equine serum albumin, ovalbumin or tetanus toxoid. The conjugates were prepared with FCA and injected into intact male lambs. All 4 vaccines stimulated the production of antibodies against GnRH in all the animals treated. The conjugates prepared with equine serum albumin or ovalbumin were the most effective in raising high anti-GnRH titers. In 18 of 20 lambs treated, anti-GnRH titers resulted in a marked atrophy of the testes.

We conclude that: 1) the different epitopes of the GnRH molecule are equally immunogenic in sheep; 2) the GnRH antibody response is affected by the carrier used; and, 3) anti-GnRH vaccines based on cysteine-substituted GnRH analogues show potential for use in immunocastration of livestock.  相似文献   

944.
An abattoir survey was carried out on 1657 cattle to determine the incidence and parameters of teat and udder papillomas and their causal viruses. Recent research has characterised six different bovine papillomaviruses of which three have been found to be particularly associated with teat tumours. Of the population studied 37.3 per cent had teat warts and 86.2 per cent of these had multiple infections; 28.4 per cent had papillomas attributed to bovine papillomavirus 1, 88.5 per cent to bovine papillomavirus 5 and 92.3 per cent to bovine papillomavirus 6. There was no predilection site between teats. Herefords and their crosses dominated the breed incidence and showed the highest numbers of warts but it was not possible to make a realistic comparison with other breeds. Dairy cattle were poorly represented. Bovine papillomavirus 4 was never found and from this it was concluded that there is no association between alimentary and teat papillomas. The implications of these findings in terms of prophylaxis and control are discussed.  相似文献   
945.
To determine the extent and significance of changes in heart rate and rhythm noticed previously in dogs paralysed with Ixodes holocyclus, two studies were undertaken. In one the electrocardiogram was recorded at stages throughout the disease and the traces analysed for changes, while in the second a detailed study of the effect of Ixodes holocyclus on the cardiovascular system was undertaken. The electrocardiographic changes were extremely variable between stages and between dogs. Generally, if a dysrhythmia occurred in stages 1, 2 or 3 it tended to be sinus tachycardia, ventricular tachycardia or sinus arrest. In stage 4 sinus arrest, sinus bradycardia, or sinus or ventricular tachycardia were the prominent dysrhythmias, whereas in stage 5 sinus bradycardia predominated. Cardiovascular measurements indicated an increase in peripheral vascular resistance leading to a significant elevation in mean arterial pressure at all stages of the disease. Cardiac output was decreased significantly only at stage 2, although it was below the control measurements at all stages. Pulmonary arterial pressure was significantly elevated at stages 2, 3 and 4 due most probably to an increase in pulmonary vascular resistance. Myocardial contractility was not significantly changed throughout the disease. The changes observed in the electrocardiogram and the cardiovascular system in stages 1, 2 and 3 are unlikely to be due to hypoxia and could represent dysfunction of the autonomic nervous system. During stages 4 and 5 oxygen levels were below normal and the bradycardia seen terminally is almost certainly due to hypoxaemia.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
946.
Effects of animal gender and age, use of a growth stimulant, and supplementation with grain alone or grain plus other substances on ADG by growing beef cattle grazing bermudagrass paddocks with sod-seeded rye, wheat, and ryegrass were determined. Two grazing experiments (Exp. 1: late winter through mid-spring; Exp. 2: late spring through mid-summer) were conducted. Experiment 1 used 96, 12- to 13-mo-old Simmental-cross calves (heifers, 240 kg; steers, 272 kg), half of which were implanted with zeranol. Within each implant treatment, cattle received no supplement or .5% BW (DM) of ground corn alone or plus a mix of protein meals, zinc sulfate, thiamin-HCl, or salt. Daily gain was higher (P less than .05) with than without supplementation and was similar (P greater than .10) among supplement treatments. In Exp. 2, 96 crossbred beef steers, approximately 7 (230 kg) or 15 mo old (250 kg), were not supplemented (control) or received .5% BW (DM) of ground corn on d 1 to 84 (C-C), corn plus a protein meal mix on d 1 to 84 (CP-CP), corn on d 43 to 84 (O-C), corn plus the protein meal mix on d 43 to 84 (O-CP), or corn on d 1 to 42 and corn plus the protein meal mix on d 43 to 84 (C-CP). Daily gain on d 1 to 84 was affected (P less than .05) by supplement, age, implant, and the supplement x implant interaction (nonimplanted: .37, .56, .68, .40, .49, and .49; implanted: .37, .62, .54, .49, .70, and .71 kg for control, C-C, CP-CP, O-C, O-CP, and C-CP, respectively).  相似文献   
947.
Approximately 12% of a herd of 68 crossbred cows aborted third-trimester fetuses after consuming moldy peanuts for 4 days. Further investigation revealed that less than 20% of the herd had access to this supplemental feed. Results of serum biochemical analysis indicated liver damage in the affected cows. All of these cows died within 8 days of aborting. The peanuts contained 77 micrograms aflatoxin B1/g, as determined by liquid chromatography. Tissues were submitted from 1 cow, and liver contained 5 ng aflatoxin B1/g. Results of other laboratory tests were negative for common toxins and abortifacients.  相似文献   
948.
Disseminated adenocarcinoma with ocular involvement in a cat   总被引:1,自引:0,他引:1  
Disseminated adenocarcinoma was associated with unilateral uveitis and multiple subcutaneous nodules in an 8-year-old domestic shorthair cat. Erythroleukemia and hind limb paresis developed over a 5-month period. At necropsy, numerous sites of metastases were found that had histologic features similar to the neoplasm in the left eye. Neoplastic cells were identified in the lungs, mediastinum, muscles, subcutaneous tissues, lymph nodes, and vasculature associated with the meninges of the brain and spinal cord. Morphologic associations were not found between erythroleukemia and the neoplastic process.  相似文献   
949.
Twenty-two non-lactating dairy cattle from a sentinel herd previously described (St. George, 1985) were monitored daily during an outbreak of ephemeral fever. Nine developed clinical ephemeral fever between 25 December 1981 and 30 January 1982. There were no subclinical infections with bovine ephemeral fever virus in the group. There were, however, subclinical infections with CSIRO Village, Akabane, Aino, Tinaroo and Kimberley viruses as described by St. George et al. (1984). Six of the nine affected cattle showed a neutrophilia with a concurrent lymphopaenia on the day of pyrexia; however, the differential white cell profile had begun to change up to 24 h prior to leucocytosis. Serum carboxypeptidase values fell by 24 h following the febrile response. Plasma fibrinogen rose rapidly in all six cows. The peak concentration (15.6 ± 2.70 g l−1) occurred 3 days after pyrexia with the highest individual increase being from 6.05 to 19.6 g l−1. Plasma fibrinogen levels remained elevated for at least 7 days.

Serum calcium fell significantly during Day 1 of the disease, the mean decline being 0.22 ± 0.08 mmol l−1. The greatest individual fall was from 2.33 to 1.92 mmol l−1. None of the affected cattle showed any compensatory change in serum magnesium. There was no change in the normal values of creatinine, urea, γ-GT, AST and alkaline phosphatase. Bovine ephemeral fever virus was isolated from only four of the six cases, whereas specific antibody was detected in all cattle 3–4 days after recovery.  相似文献   

950.
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