全文获取类型
收费全文 | 66234篇 |
免费 | 3835篇 |
国内免费 | 48篇 |
专业分类
林业 | 3992篇 |
农学 | 2149篇 |
基础科学 | 305篇 |
9300篇 | |
综合类 | 10689篇 |
农作物 | 2658篇 |
水产渔业 | 3809篇 |
畜牧兽医 | 31780篇 |
园艺 | 818篇 |
植物保护 | 4617篇 |
出版年
2021年 | 696篇 |
2020年 | 692篇 |
2019年 | 766篇 |
2018年 | 1413篇 |
2017年 | 1516篇 |
2016年 | 1384篇 |
2015年 | 1171篇 |
2014年 | 1418篇 |
2013年 | 2704篇 |
2012年 | 2556篇 |
2011年 | 2657篇 |
2010年 | 1648篇 |
2009年 | 1641篇 |
2008年 | 2434篇 |
2007年 | 2397篇 |
2006年 | 2161篇 |
2005年 | 2045篇 |
2004年 | 1901篇 |
2003年 | 1845篇 |
2002年 | 1704篇 |
2001年 | 1848篇 |
2000年 | 1779篇 |
1999年 | 1467篇 |
1998年 | 523篇 |
1997年 | 529篇 |
1996年 | 530篇 |
1995年 | 561篇 |
1993年 | 516篇 |
1992年 | 1062篇 |
1991年 | 1042篇 |
1990年 | 1029篇 |
1989年 | 1050篇 |
1988年 | 995篇 |
1987年 | 1022篇 |
1986年 | 1007篇 |
1985年 | 1003篇 |
1984年 | 810篇 |
1983年 | 733篇 |
1979年 | 764篇 |
1978年 | 637篇 |
1977年 | 551篇 |
1976年 | 507篇 |
1975年 | 549篇 |
1974年 | 794篇 |
1973年 | 698篇 |
1972年 | 773篇 |
1971年 | 764篇 |
1970年 | 628篇 |
1969年 | 629篇 |
1967年 | 540篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
83.
Effect of dietary protein content on episodic growth hormone secretion and on heat production of male broiler chickens. 总被引:1,自引:0,他引:1
1. The effect of the crude protein content (200 and 150 g/kg) of isoenergetic diets on episodic growth hormone (GH) release and on heat production was investigated in male broiler chickens. 2. Decreasing the crude protein content of isoenergetic diets from 200 g/kg (HP diet) to 150 g/kg (LP diet) resulted in depressed body weight gain, impaired food conversion efficiency and increased abdominal fat deposition. 3. The pattern of growth hormone secretion was markedly affected by dietary treatment. Broiler chickens fed on the LP diet had higher overall mean, amplitude, baseline and peak frequency than the HP chickens. 4. The LP chickens produced more heat per unit of metabolic body weight than the HP chickens. 5. The hypothesis relating the pattern of GH secretion to protein conversion efficiency was corroborated. 相似文献
84.
Linear functions of body weight and condition score at weaning and 18 mo of age were used to predict the mature weight (A) and maturing rate (k) parameters of an asymptotic growth model of Angus cows at the Subtropical Agricultural Research Station, Brooksville, FL. From 1981 through 1988 a heavy-mature-weight line (Line A) and a rapid-maturing line (Line K) were selected based on predicted A and k values. Linear contrasts (A-K) of least squares means for weight at fixed ages indicated that the weight difference between lines increased from birth to maturity during the period of the study. Animals from Line A were heavier (P less than .01) at all ages. A negative response in maternal ability, relative to increased growth potential of their calves, seems to have occurred in the cows of Line A. Mature weight was reached at approximately 4.5 yr of age in Line K and at approximately 5.5 yr in Line A. Brody's three-parameter and Richards' four-parameter functions were fitted to 2,855 quarterly weights of cows, from birth to 6.5 yr of age, to estimate the average growth curve for each line. Brody's model gave better estimates of weights from 18 mo to maturity, but the asymptotic residual mean squares were slightly higher because early weights were overestimated. Linear and nonlinear regression analyses of weight-age data and comparisons of degree of maturity at different premature ages showed differences in the growth patterns of the two lines selected for early predicted values of A and k. 相似文献
85.
W F Immink A J van Toor J H Vos J S van der Linde-Sipman A A Lubberink 《The Veterinary quarterly》1992,14(3):81-85
This paper describes four cats with hyperadrenocorticism. Cat 1 showed polydipsia and polyphagia. Diabetes mellitus was initially diagnosed. As the animal appeared to be insulin resistant, pituitary and adrenocortical function tests were performed and the diagnosis of hyperadrenocorticism was made. Resistance to the high-dose dexamethasone suppression test was noticed in this cat. Pathological examination revealed a pituitary chromophobe adenoma. Cat 2 presented with diabetes mellitus, which was treated with insulin. The animal had a pendulous abdomen and its coat was in a poor condition. The low-dose dexamethasone suppression test demonstrated hyperadrenocorticism. Necropsy findings of pituitary tumour and hyperplasia of the adrenal cortex confirmed the diagnosis. Cat 3 showed clinical abnormalities indicative of hyperadrenocorticism, for instance, muscle weakness, alopecia, multiple abscesses. The diagnosis of hyperadrenocorticism was confirmed by the results of the lowe-dose dexamethasone suppression test. Pathological examination revealed an adrenocortical carcinoma. Cat 4 presented with polydipsia. The cause of this symptom was not found initially. One and a half years later additional symptoms, such as nephritis and polyphagia developed. Hyperadrenocorticism was diagnosed because of a palpable mass cranial to the left kidney. The diagnosis was confirmed by the results of the lowe-dose dexamethasone suppression test and the necropsy findings. 相似文献
86.
87.
88.
P O Ahmed M F Miller S D Shackelford L P Johnson S E Williams M A McCann J O Reagan 《Journal of animal science》1992,70(2):439-443
Thirty-two crossbred cattle (steers = 17; heifers = 15) exhibiting an ultrasound fat thickness at the 12 to 13th rib region of at least 10 mm were selected from a slaughter shift at a commercial packing plant. After splitting, alternating sides of each carcass were trimmed of 1) subcutaneous fat in excess of 6.4 mm; 2) all kidney, pelvic, and heart fat; and 3) all cod or udder fat and fat in the flank region. Both sides of each carcass were fabricated into subprimals (final trim level of 6.4 mm) according to normal industry procedures. Effect of hot-fat trimming, yield grade (3, 4, and 5), and gender on hot-fat trim, fabrication fat trim, major subprimal, and total subprimal yield of untrimmed and trimmed carcasses were determined. Higher numerical yield grade (YG) corresponded with higher (P less than .05) percentages of hot-fat trim. Hot-fat trimming increased (P less than .05) the difference in fabrication fat trim between steers and heifers and between YG 3 and YG 5. Steers and heifers differed (P less than .05) in percentage of major subprimals and total subprimals when processed conventionally, whereas hot-fat trimming eliminated this difference (P less than .05). Untrimmed YG 3 carcasses had 3.1 and 5.0% higher major subprimal yield (P less than .05) than untrimmed YG 4 and YG 5 carcasses, respectively, whereas hot-fat trimming reduced this difference to 2.5% for YG 4 and to 3.7% for YG 5.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
89.
90.
The plants of field bean var. Nadwiślaνski were detopped after about 1 month since the beginning of flowering and after that all flower buds were removed from some plants. The effect of a change in the trophic balance on the setting and subsequent growth of root nodules was studied.
The removal of pods had the greater effect on the increase in the weight of the remaining organs than the detopping of plants. Detopping retarded the ageing of the plants and delayed the phase of the greatest reduction of the number of pods. The detopping of plants revealed their considerable compensative possibilities in terms of production of the pod weight and the potential of leaves for biomass production. The data obtained indicate that plant detopping may disturb the root–bacteria exchange of signals, necessary to initiate the nodule development, while the further growth of nodules depends, above all, on the amount of available photosynthates.
A very high correlation between the dry weight of the whole plant to the dry weight of leaves ratio and the weight of nodules was observed. It proves the importance of the trophic balance of the plant for the root nodule weight production. 相似文献
The removal of pods had the greater effect on the increase in the weight of the remaining organs than the detopping of plants. Detopping retarded the ageing of the plants and delayed the phase of the greatest reduction of the number of pods. The detopping of plants revealed their considerable compensative possibilities in terms of production of the pod weight and the potential of leaves for biomass production. The data obtained indicate that plant detopping may disturb the root–bacteria exchange of signals, necessary to initiate the nodule development, while the further growth of nodules depends, above all, on the amount of available photosynthates.
A very high correlation between the dry weight of the whole plant to the dry weight of leaves ratio and the weight of nodules was observed. It proves the importance of the trophic balance of the plant for the root nodule weight production. 相似文献