全文获取类型
收费全文 | 143377篇 |
免费 | 7872篇 |
国内免费 | 99篇 |
专业分类
林业 | 6374篇 |
农学 | 4679篇 |
基础科学 | 899篇 |
19480篇 | |
综合类 | 21902篇 |
农作物 | 5837篇 |
水产渔业 | 7770篇 |
畜牧兽医 | 72386篇 |
园艺 | 2008篇 |
植物保护 | 10013篇 |
出版年
2021年 | 1223篇 |
2020年 | 1432篇 |
2019年 | 1607篇 |
2018年 | 2486篇 |
2017年 | 2794篇 |
2016年 | 2557篇 |
2015年 | 2077篇 |
2014年 | 2670篇 |
2013年 | 5914篇 |
2012年 | 4828篇 |
2011年 | 5769篇 |
2010年 | 3645篇 |
2009年 | 3793篇 |
2008年 | 5545篇 |
2007年 | 5211篇 |
2006年 | 4775篇 |
2005年 | 4520篇 |
2004年 | 4202篇 |
2003年 | 4282篇 |
2002年 | 3830篇 |
2001年 | 4329篇 |
2000年 | 4416篇 |
1999年 | 3528篇 |
1998年 | 1532篇 |
1997年 | 1425篇 |
1996年 | 1332篇 |
1995年 | 1568篇 |
1994年 | 1382篇 |
1993年 | 1262篇 |
1992年 | 2691篇 |
1991年 | 2799篇 |
1990年 | 2692篇 |
1989年 | 2710篇 |
1988年 | 2473篇 |
1987年 | 2458篇 |
1986年 | 2522篇 |
1985年 | 2433篇 |
1984年 | 1952篇 |
1983年 | 1748篇 |
1979年 | 1841篇 |
1978年 | 1479篇 |
1977年 | 1222篇 |
1976年 | 1260篇 |
1975年 | 1333篇 |
1974年 | 1583篇 |
1973年 | 1574篇 |
1972年 | 1482篇 |
1971年 | 1381篇 |
1970年 | 1277篇 |
1969年 | 1314篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
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
93.
94.
C. P. Verschueren P. J. Selman J. J. M. de Vijlder J. A. Mol 《Domestic animal endocrinology》1991,8(4):509-519
Canine thyroglobulin (cTg) has been isolated and purified. It has similar electrophoretic patterns as Tg from other mammalian species. The main fraction had a MW of 660,000, whereas also fractions of a MW of approximately 1,300,000 (dimer) and 330,000 (subunit) were present. The iodine content was 0.8 to 1.0 % (w/w). cTg did not cross-react with antibodies against human Tg to a degree that would allow the use of a radioimmunoassay for human Tg for the determination of cTg in serum or plasma. Therefore a polyclonal antiserum was raised against cTg and a homologous radioimmunoassay was developed, which was sensitive (0.4 μg/l) and specific (cross-reactivity in cTg assay of human Tg, goat Tg, T4, T3, and DIT < 0.01 %).
Plasma Tg levels in normal dogs of both sexes and aged 3–15 years amounted to 192 ± 73 μg/l (mean ± SD, n=30). There was no relation between plasma Tg and T4 levels. 相似文献
95.
96.
J.A. Díez P. Hernaiz M.J. Muñoz A. de la Torre A. Vallejo 《Soil Use and Management》2004,20(4):444-450
Abstract. The repeated application of pig slurry to agricultural soils may result in an accumulation of salts and a risk of aquifer pollution due to nitrate leaching and salinization. Under Mediterranean conditions, a field experiment on a sandy loam soil (Typic Xerofluvent) was performed with maize (Zea mays) in 1998, 1999 and 2001 to study the effects of applying optimal (P1) and excessive rates (P3) of pig slurry on soil salinization, nitrate leaching and groundwater pollution. The rate of pig slurry was established considering the optimal N rate for maize in this soil (170, 162 and 176 kg N ha?1 for 1998, 1999 and 2001, respectively). Pig slurry treatments were compared to an optimal N rate supplied as urea (U) and a control treatment without N fertilizer (P0). The composition of the slurries showed great variability between years. Mean NO3? leaching losses from 1998 to 2001 were 329, 215, 173 and 78 kg N ha?1 for P3, P1, U and P0 treatments, respectively. The amount of total dissolved salts (TDS) added to the soil in slurry application between 1998 and 2001 was 2019 kg TDS ha?1 for the P1 treatment and 6058 kg TDS ha?1 for the P3 treatment. As a consequence, the electrical conductivity (EC) of the slurry‐treated soils was greater than that of the control soil. The EC correlated significantly with the sodium concentration of the soil solution. Over the entire experimental period, 2653, 2202 and 2110 kg Na ha?1 entered the aquifer from the P3, P1 and P0 treatments, respectively. The P3 treatment did not significantly increase grain production in 1999 and 2001 compared with that achieved with the optimal N rate treatment (P1). This behaviour shows the importance of establishing application guidelines for pig slurry that will reduce the risk of soil and groundwater pollution. 相似文献
97.
The utilization of dietary lysine for protein synthesis is affected by the digestibility of protein-bound lysine, by its intestinal resorption and by its oxidative catabolism. The approach chosen in this paper enables a comparison of the cumulative effect of these processes on the utilization of free and protein-bound lysine, respectively. The principle of the approach is based on a quantification of the expiration of 14C-labelled carbon dioxide after an oral administration of a diet, which contains L-(U-14C)-lysine either as a free amino acid or bound to yeast proteins. During an adaptation phase cockerels of the Japanese quail received a diet based mainly on ground wheat and wheat gluten. This diet was supplemented either with yeast proteins or with a mixture of L-amino acids which simulates the composition of the yeast proteins. In the main experiment the expiration of labelled carbon dioxide was measured during 240 minutes after the administration of the corresponding labelled diets. Just before treatment the animals were either in the postprandial phase or in a state of slight hunger. The maximum of expiration of labelled carbon dioxide occurred around the 60th minute after administration of the corresponding labelled diets. The cumulative expiration of labelled carbon dioxide, expressed in per cent of the radioactive dose used, amounts to 15.5% and 14.3% for free and protein-bound lysine, respectively. The utilization of both forms of lysine in the Japanese quail is lower than in broilers. 相似文献
98.
Four commercially available semiquantitative milk progesterone tests (Ovucheck-Praxistest: Cambridge Veterinary Science/Smith Kline), Progestassay-Milchprogesteron (Pitman-Moore/Janssen), Reprostrip-Progesteron-Schnelltest (Noctech/Albrecht), Enzygnost-Milchprogesteron (IQ, 'Bio' UK/Hoechst Veterin?r) were examined for their accuracy by using them for the determination of progesterone levels of 64 milk samples, i.e. 1556 single assays. Several test series were performed, using codified samples and changing sequences. Three or four test persons respectively, performed the tests independently and classified the samples semiquantitatively. These test results were then compared to the results acquired by measuring the progesterone levels of the same samples by means of an approved quantitative, labor-bound progesterone test (Hormonost: Biolab). These control tests were performed at a specialized routine labor, by different personnel and at a different location. Lastly, in 48 out of the 64 sampled animals the reproductive status could be evaluated clinically and was taken into account as well. Samples yielding high progesterone levels, i.e. greater than or equal to 9 ng/ml were classified correctly in 84.4 to 96.5% of the cases, whereas samples with low levels (less than or equal to 2.5 ng/ml) were classified correctly in 68.8 to 90.0% of the cases only. Samples ranging between this spectrum (greater than 2.5 less than 9 ng/ml) were classified correctly only in 42.1 to 52.6% of the cases. However, this range appears to be of the most interest for the veterinary practitioner since cows in proestrus or early interestrus tend to have mild progesterone levels within these values. On the other hand, clinical findings are often insufficient for a proper diagnosis just in these animals.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
99.
100.
A review of investigations of the functional anatomy of the equine foot is presented. Emphasis is placed on the relationships of structures involved in the major diseases of the foot. 相似文献