全文获取类型
收费全文 | 84135篇 |
免费 | 4645篇 |
国内免费 | 317篇 |
专业分类
林业 | 4005篇 |
农学 | 2822篇 |
基础科学 | 520篇 |
10710篇 | |
综合类 | 15023篇 |
农作物 | 3284篇 |
水产渔业 | 3882篇 |
畜牧兽医 | 42406篇 |
园艺 | 970篇 |
植物保护 | 5475篇 |
出版年
2019年 | 857篇 |
2018年 | 1408篇 |
2017年 | 1499篇 |
2016年 | 1343篇 |
2015年 | 1169篇 |
2014年 | 1444篇 |
2013年 | 3371篇 |
2012年 | 2584篇 |
2011年 | 2971篇 |
2010年 | 1994篇 |
2009年 | 2097篇 |
2008年 | 2906篇 |
2007年 | 2780篇 |
2006年 | 2604篇 |
2005年 | 2357篇 |
2004年 | 2257篇 |
2003年 | 2234篇 |
2002年 | 2051篇 |
2001年 | 2584篇 |
2000年 | 2530篇 |
1999年 | 2012篇 |
1998年 | 800篇 |
1997年 | 844篇 |
1996年 | 778篇 |
1995年 | 860篇 |
1994年 | 776篇 |
1993年 | 735篇 |
1992年 | 1490篇 |
1991年 | 1620篇 |
1990年 | 1503篇 |
1989年 | 1542篇 |
1988年 | 1439篇 |
1987年 | 1434篇 |
1986年 | 1462篇 |
1985年 | 1409篇 |
1984年 | 1123篇 |
1983年 | 1012篇 |
1979年 | 1145篇 |
1978年 | 920篇 |
1977年 | 789篇 |
1976年 | 785篇 |
1975年 | 857篇 |
1974年 | 1099篇 |
1973年 | 1032篇 |
1972年 | 1065篇 |
1971年 | 961篇 |
1970年 | 931篇 |
1969年 | 942篇 |
1968年 | 773篇 |
1967年 | 828篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
T M Frye S N Williams T W Graham 《Veterinary Clinics of North America: Food Animal Practice》1991,7(1):217-275
Deficiencies of vitamins A, D, K, E and thiamin can cause severe limitations in beef production. In particular, vitamin A and E can be common causes of lost profit, secondary to limitations of reproductive and growth potential. Prolonged dry periods will reduce available A and E in pasture forage, as can ensiling and prolonged storage of harvested feedstuffs. Polioencephalomalacia is a thiamin responsive disorder, associated with high concentrate feeding and lush pastures. Antimetabolites, such as amprolium, will cause thiamine deficiency when fed in excess. Recent information has shown improved performance with supplemental beta carotene and niacin. The positive responses in reproductive performance, noted with cattle fed supplemental beta carotene, was independent of vitamin A. Supplementation of vitamins above National Research Council recommendations can be justified. However, proper evaluation of feed and animal status, and documentation of a response to supplementation is necessary before diagnosing deficiencies of specific nutrients. 相似文献
82.
N Saito H Yamanaka S Nagasawa 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》1991,53(1):1-4
The activity of rat liver glutathione-insulin transhydrogenase (GIT) was measured by HPLC. The degradation of fluorescein isothiocyanate-I (FITC-I)-labeled insulin is separated into several peaks, which are bound different amount of FITC-I. We selected mono-fluorescein-thiocarbamylated insulin to estimate the decrease of insulin content and it became possible to assay GIT activity. This novel method was time-saving and simple, and this system could utilize instead of previous method. 相似文献
83.
84.
J. F. AYRES 《Grass and Forage Science》1991,46(1):89-97
A series of experiments was undertaken to determine population statistics for in vitro organic matter digestibility ( in vitro OMD) data and to examine the effects of basal diet, donor animal and precollection fasting interval on the activity and specificity of rumen fluid inoculum. The experiments utilized wether sheep, a diverse set of pasture grass and legume feeds prominent in the Australian subtropics and the Tilley and Terry in vitro digestibility procedure running under the operating pressure of a practicing feeds evaluation laboratory.
The standard errors of in vitro OMD estimates for within and between batch runs were ±0·88 × 10−2 and 0·62 × 10−2 , respectively. These error terms were used to develop protocols to accept, reject or scale raw in vitro OMD data. Differences between donor animals in the activity of rumen fluid were highly significant. Extending the precollection fasting interval beyond 16 h was associated with a substantial decline in inoculum activity.
An in vitro-in vivo calibration relationship based on fifteen test feeds and using lucerne ( Medicago sativa ) as basal diet was described by the linear model y = 1·3 x-0·195±4·9 × 10−2 r = 0·79 (y = in vivo OMD, x = in vitro OMD). Despite large effects of basal diet on both the absolute values and relative ranking of test feeds, neither the RSD nor r values were improved using alternative diets to Lucerne chaff.
The results highlight the need to formally standardize the analytical and biological components of the in vitro digestibility procedure to safeguard the integrity of data. 相似文献
The standard errors of in vitro OMD estimates for within and between batch runs were ±0·88 × 10
An in vitro-in vivo calibration relationship based on fifteen test feeds and using lucerne ( Medicago sativa ) as basal diet was described by the linear model y = 1·3 x-0·195±4·9 × 10
The results highlight the need to formally standardize the analytical and biological components of the in vitro digestibility procedure to safeguard the integrity of data. 相似文献
85.
AM Mwanza A Madej H Kindahl N Lundeheim & S Einarsson 《Reproduction in domestic animals》2001,36(3-4):157-161
The effects of lipopolysaccharide ( Escherichia coli , O55:B5), administered 18 h after ovulation in the second oestrus after weaning on the hormonal profiles in 14 Swedish cross-bred (Landrace × Yorkshire) multiparous sows were studied. The endotoxin group (E-group) sows were administered with 300 ng/kg of lipopolysaccharide (LPS) whereas the control group (C-group) sows were administered 5 ml of saline intravenously via an indwelling jugular cannula. Blood samples for hormonal analyses were collected from all sows until slaughter. In the E-group, progesterone, cortisol and prostaglandin F2α metabolite levels increased significantly (p < 0.05) following LPS compared with the C-group. It can be concluded from this study that apart from elevating cortisol and prostaglandin F2α metabolite, LPS also elevates progesterone levels. 相似文献
86.
Fluid accumulation in mouse ligated intestine inoculated with the vascular permeability factor produced by Bacillus cereus. 总被引:1,自引:0,他引:1
K Shinagawa K Sato H Konuma N Matsusaka S Sugii 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》1991,53(2):167-171
Partially purified vascular permeability (VP) factor (VPF) of Bacillus cereus induced fluid accumulation in the ligated intestinal loops of mouse (MIL) and rabbit (RIL), suggesting that the VP activity may correlate with fluid accumulation in ligated intestinal loops of these animals. Fluid accumulation was observed at 6-8 hr in 55-67% of mouse intestinal loops inoculated with 40-50 immunodiffusion units (IDU) of partially purified VPF, whereas it was found at 2 hr in all loops with 400-600 IDU of partially purified VPF. In rabbit intestinal loops with 120-190 IDU of partially purified VPF, fluid accumulation was observed at 6 hr. From these findings, VPF produced by B. cereus can be easily detected in both MIL and RIL. The intestinal tissue of mouse intestinal loops was histopathologically damaged at different concentrations of the VPF to induce fluid accumulation. With 50 IDU of partially purified VPF, severe edema was found in the laminia proprial layer and submucosa. With 600 IDU of partially purified VPF, on the other hand, severe necrosis in the surface epithelium of villus and laminia proprial layer, and hyperemia in the submucosa were observed, suggesting that partially purified VPF may be cytotoxic and/or intestinecrotic. 相似文献
87.
88.
89.
2 groups of 20 cocks each were selected at random from non-dwarf White Leghorn (28 weeks post-hatch) and dwarf Krishna-J (38 weeks post-hatch) genotypes. The treated groups comprised 10 White Leghorn and 10 Krishna-J cocks. The remaining birds served as controls. 8 weeks prior to furazolidone treatment, semen was collected from both control groups at regular 4-day intervals, for 4 weeks. Cocks of the treated groups of both genotypes were administered furazolidone (0.14 g/bird/day) for 7 consecutive days. Semen was collected from all cocks at regular 4-day intervals for 4 weeks. Semen from the cocks of the same group was pooled. The pooled ejaculate volume and sperm density did not differ significantly in the 2 genotypes. The semen output as well as sperm density increased along with progressive attainment of sexual maturity. Furazolidone treatment caused significant reduction in semen volume as well as sperm concentration in either genotype. 相似文献
90.
The records of 71 horses with small intestinal disorders requiring surgical correction were disorders requiring surgical correction were reviewed to compare the prevalence of laminitis in those horses treated prophylactically with heparin and the prevalence of horses not treated with heparin. The prevalence of laminitis was 13% (9/71), and there was no significant difference (P less than 0.05) in the prevalence of laminitis between the 2 groups. The lack of significant benefit after treatment with heparin indicates that further work needs to be done on the equine coagulation system before heparin can be advocated for prevention of laminitis. 相似文献