全文获取类型
收费全文 | 6658篇 |
免费 | 276篇 |
国内免费 | 8篇 |
专业分类
林业 | 230篇 |
农学 | 343篇 |
基础科学 | 82篇 |
831篇 | |
综合类 | 359篇 |
农作物 | 248篇 |
水产渔业 | 199篇 |
畜牧兽医 | 3681篇 |
园艺 | 105篇 |
植物保护 | 864篇 |
出版年
2023年 | 30篇 |
2022年 | 41篇 |
2021年 | 57篇 |
2020年 | 81篇 |
2019年 | 87篇 |
2018年 | 100篇 |
2017年 | 101篇 |
2016年 | 113篇 |
2015年 | 95篇 |
2014年 | 130篇 |
2013年 | 489篇 |
2012年 | 298篇 |
2011年 | 348篇 |
2010年 | 172篇 |
2009年 | 172篇 |
2008年 | 332篇 |
2007年 | 319篇 |
2006年 | 270篇 |
2005年 | 272篇 |
2004年 | 284篇 |
2003年 | 254篇 |
2002年 | 247篇 |
2001年 | 234篇 |
2000年 | 215篇 |
1999年 | 195篇 |
1998年 | 53篇 |
1997年 | 53篇 |
1996年 | 55篇 |
1995年 | 62篇 |
1994年 | 38篇 |
1993年 | 45篇 |
1992年 | 105篇 |
1991年 | 116篇 |
1990年 | 133篇 |
1989年 | 108篇 |
1988年 | 100篇 |
1987年 | 84篇 |
1986年 | 67篇 |
1985年 | 71篇 |
1984年 | 66篇 |
1983年 | 44篇 |
1982年 | 30篇 |
1981年 | 41篇 |
1980年 | 44篇 |
1979年 | 45篇 |
1975年 | 25篇 |
1974年 | 25篇 |
1973年 | 26篇 |
1972年 | 35篇 |
1971年 | 32篇 |
排序方式: 共有6942条查询结果,搜索用时 31 毫秒
41.
Lewis RE van Walsum KL Spafford MM Edwards JC Turnwald GH 《Journal of veterinary medical education》2004,31(2):128-137
The veterinary school admission interview is a widely used selection tool, yet concerns persist about its reliability, validity, and cost. Relative to medicine, optometry, and dentistry schools, veterinary schools have been more likely to conduct panel interviews and to fix the interview's weight in selection decisions, strategies that increase interview validity. This article provides strategies for further increasing the veterinary school interview's validity. Interview reliability and validity studies point to key strategies the veterinary school admissions committee can implement before the interview: (1) establishing the interview's purpose(s); (2) conducting a "job" analysis to identify desirable candidate skills, knowledge, and attributes; (3) developing a structured and panel interview where interviewers, if possible, are blind to other admission data; (4) training interviewers; (5) setting a reasonable interview schedule; and (6) determining methods for analyzing applicant data. During the interview, interviewers should proceed through a structured series of steps: (1) open the interview with a specified agenda; (2) probe for information using structured questions and anchored rating scales; (3) close the interview to allow for candidate questions; and (4) evaluate the interview data. After the interview, the admissions committee should (1) analyze the interview data within and across interviewers and (2) analyze the data across all selection tools in order to assign relative weights to the selection tools. 相似文献
42.
de Bruin T de Rooster H van Bree H Cox E 《Journal of veterinary medicine. A, Physiology, pathology, clinical medicine》2005,52(9):460-465
Proliferation assays performed on peripheral blood mononuclear cells (PBMC) are commonly used in experimental and clinical immunology. A prerequisite for an in vitro assay is the ability to obtain relatively pure populations of mononuclear cells from whole blood, as contaminating polymorphonuclear cells may affect the proliferation of lymphocytes. Purification of canine leucocytes from whole blood is associated with difficulties in obtaining pure lymphocytes in high yields. The aim of this study was to optimize the lymphocyte purification from canine whole blood in terms of total cell recovery and purity, while not influencing the proliferation capacity of the isolated cells. To acquire optimal isolation of canine lymphocytes several density gradient media of different densities and osmolalities were examined. For optimal phagocyte removal, pre-treatment of whole blood with carbonyl iron/arabic gum and/or adherence to fibrinogen pre-coated polystyrene tissue flasks were examined. Lectin-induced proliferation was used as measurement of cell activity of the obtained cell fractions after the different separation procedures. Canine blood pre-treated with carbonyl iron/arabic gum followed by density gradient centrifugation with medium 'G' (density: 1.079 g/cm(3), osmolality: 256 mOsm) and adherence to pre-coated polystyrene tissue flask obtained the best PBMC cultures with a median lymphocyte purity of 88% and a median yield of recovered lymphocytes of 54%. This culture also resulted in the highest proliferation and subsequently the highest stimulation index upon lectin stimulation. 相似文献
43.
Verhoeckx KC Doornbos RP van der Greef J Witkamp RF Rodenburg RJ 《Journal of veterinary pharmacology and therapeutics》2005,28(6):531-537
In this study the anti-inflammatory properties of zilpaterol, a beta2-adrenergic receptor (AR) agonist specifically developed as a growth promoter in cattle were investigated. Although zilpaterol has a different structure compared with the beta2-AR agonists known to date, it was noted that it was able to bind to both the beta2-AR (Ki = 1.1 x 10(-6)) and the beta1-AR (Ki = 1.0 x 10(-5)). Using lipopolysaccharide (LPS)-exposed U937 macrophages, the production of cyclic adenosine-3',5'-cyclic monophosphate (cAMP) and tumor necrosis factor alpha (TNF-alpha) were investigated. Zilpaterol inhibited TNF-alpha release and induced intracellular cAMP levels in a dose-dependent manner. The inhibition of TNF-alpha release and induction of cAMP production was mainly mediated via the beta2-AR, as indicated by addition of beta1- and beta2-specific antagonists. The effects of zilpaterol were investigated in LPS-treated male Wistar rats after pretreatment with zilpaterol. Zilpaterol dosed at 500 microg/kg body weight reduced the TNF-alpha plasma levels. In conclusion, zilpaterol is a beta2-adrenergic agonist and an inhibitor of TNF-alpha production induced by LPS both in vivo and in vitro. 相似文献
44.
This study sought to determine the efficacy of isopathic and pluralist homeopathic treatment of colibacillosis in broiler chickens and thereby contribute to the evaluation of homeopathy in general. In each of two experiments three groups of broilers, infected intratracheally at 8 days of age with E. coli (O78:K80), were treated with different combinations of homeopathic remedies. Control groups and an infected, doxycyline-treated group were included. Experiments differed only in the dose of E. coli. Efficacy of treatment was evaluated based on the parameters mortality, body weight gain and colibacillosis lesions. In both experiments doxycyline prevented mortality and reduced E. coli lesions and stunting. None of the homeopathically treated groups differed significantly with respect to any of the parameters from the non-medicated, infected control group. It is concluded that the results of this study do not justify use of these homeopathic remedies for treatment of colibacillosis in broilers. Furthermore, no significant effects of this homeopathic treatment were established. 相似文献
45.
van de Sandt RR Boevé MH Stades FC Kik MJ Kirpensteijn J 《The Journal of small animal practice》2004,45(7):372-374
A 10-year-old German shepherd dog was presented with unilateral uveitis and hyphaema. Treatment was unsuccessful and the eye was enucleated. Intraocular osteosarcoma was diagnosed by histological examination. 相似文献
46.
47.
48.
Vlaeminck B Fievez V van Laar H Demeyer D 《Journal of animal physiology and animal nutrition》2004,88(11-12):401-411
A first aim of this batch in vitro experiment (21 h) was to use changes in odd and branched chain fatty acid (OBCFA) patterns to suggest shifts in microbial populations, associated with four types of incubated whole dairy cow diets. Principal component analysis suggested higher dietary starch increased the proportion of C15:0 and C17:0, whereas increased neutral detergent fibre content was positively related to anteiso C15:0 concentrations, which is in agreement with the importance of these fatty acids in respectively amylolytic and cellulolytic bacteria. A second aim of the experiment was to relate rumen volatile fatty acid proportions to OBCFA by principal component regression and to compare these relations with predictions based on diet proximate composition. The R2 values achieved for the regressions between acetate, propionate and butyrate, and OBCFA were 79.6%, 86.6% and 84.9% respectively. Moreover, in the current study, predictions of the rumen fermentation pattern showed higher R2 (p < 0.01) when based on OBCFA compared with proximate feed composition. If relations persist in vivo, there could be scope for milk OBCFA to predict the supply of specific rumen nutrients. 相似文献
49.
50.
This brief review describes types and quality (efficacy and safety) of bovine viral diarrhoea virus (BVDV) vaccines that are in the market or under development. Both conventional live and killed vaccines are available. The primary aim of vaccination is to prevent congenital infection, but the few vaccines tested are not highly efficacious in this respect, as shown in vaccination-challenge experiments. Vaccination to prevent severe postnatal infections may be indicated when virulent BVDV strains are prevalent. Live BVDV vaccines have given rise to safety problems. A complication for the development of BVDV vaccines is the wide antigenic diversity among wild-type BVDV. There is ample room for improvement of both the efficacy and safety of BVDV vaccines, and it may be expected that better vaccines, among which marker vaccines, will be launched in the future. 相似文献