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   540篇
  免费   35篇
  国内免费   1篇
林业   53篇
农学   18篇
基础科学   2篇
  96篇
综合类   60篇
农作物   30篇
水产渔业   78篇
畜牧兽医   196篇
园艺   9篇
植物保护   34篇
  2024年   1篇
  2023年   10篇
  2022年   11篇
  2021年   24篇
  2020年   42篇
  2019年   28篇
  2018年   22篇
  2017年   23篇
  2016年   20篇
  2015年   19篇
  2014年   25篇
  2013年   28篇
  2012年   48篇
  2011年   43篇
  2010年   22篇
  2009年   22篇
  2008年   15篇
  2007年   39篇
  2006年   15篇
  2005年   17篇
  2004年   19篇
  2003年   15篇
  2002年   10篇
  2001年   4篇
  2000年   4篇
  1999年   3篇
  1997年   4篇
  1996年   4篇
  1995年   2篇
  1994年   1篇
  1993年   3篇
  1992年   5篇
  1991年   1篇
  1990年   3篇
  1989年   1篇
  1988年   4篇
  1986年   3篇
  1985年   1篇
  1984年   3篇
  1982年   1篇
  1981年   1篇
  1979年   2篇
  1977年   1篇
  1975年   1篇
  1972年   1篇
  1965年   3篇
  1963年   1篇
  1957年   1篇
排序方式: 共有576条查询结果,搜索用时 15 毫秒
1.
The effect of a decrease (and/or fermentation) in the lactose content during milk storage under different conditions was investigated on the accuracy of the results obtained on a Milko-Scan apparatus to contribute to the present knowledge of this problem. The results were in agreement with some results cited in the literature. These wavelengths are used for infrared spectrophotometry on the above apparatus: for fat 3.48 microns, for proteins 6.46 microns and for lactose 9.60 microns. Bulk milk samples used for the tests were untreated or treated with potassium dichromate, bronopol, sodium azide and Milkofix at the temperatures of storage in darkness 20 degrees C and 4 degrees C. The differences against the reference values (measured on the first day) were determined and evaluated in milk composition and characteristics as arising during milk storage. These differences were used in form of either cumulative means of differences (Figs. 1 to 5) or individual differences (Fig. 8). In the first part significant correlation coefficients (P less than 0.001) were calculated for the relationship between the variations of lactose content and the fat and protein contents: r = -0.59 and/or -0.73 (Figs. 6 and 7). This suggests that the decrease in the lactose content by 0.10% recorded by the infrared analysis and caused by lactose decomposition is accompanied by a "seeming" increase in the fat and protein content by about 0.04%. In the second part the correlation coefficients for the fat and protein contents r = -0.96 and -0.96 (P less than 0.001; Figs. 9 and 10; Tab. II) were calculated on the basis of an observation of the lactose decrease in an untreated milk sample (20 degrees C for 28 hours). These coefficients are somewhat different from the preceding ones; this is due to the lower homogeneity of the first set where the milk samples were treated in a different way, but the coefficients confirm the same conclusions. The values of the correlation coefficients for the dependence between the development of the acquired titratable acidity (SH) and the variations of fat (F), protein (P) and lactose (L) contents were as follows: r = 0.95; 0.95; -0.99 (P less than 0.001; Figs. 12, 13; Tab. II). Thus the above-mentioned "seeming" increase in the F and P contents can be explained to the extent of 92.2% from the decrease in the L content, which also causes the increase in titratable acidity to the extent of 98.0%.(ABSTRACT TRUNCATED AT 400 WORDS)  相似文献   
2.
Tropical Animal Health and Production - This study evaluated the effect of two doses of prostaglandin at different intervals on reproductive parameters of crossbred ewes. In Experiment 1, 30 ewes...  相似文献   
3.
This study aimed to evaluate the exogenous progesterone (P4) effect on the luteal function from Day 16 to Day 21 of the oestrous cycle in inseminated goats with unknown pregnancy status. A total of 54 does passed through a short progestin-based synchronization protocol and, on Day 16 of the following oestrous cycle, 27 does received a new P4 device which was retained until Day 21. Blood samples were collected daily from all does during this period, as well as on Day 24. Pregnancy diagnoses were performed on Day 30. Serum P4 values from 26 animals (GNPSP: Group of non-pregnant does with second sponge: n = 8; GNPNSP: Group of non-pregnant does without second sponge: n = 6; GPSP: Group of pregnant does with second sponge: n = 5; GPNSP: Group of pregnant does without second sponge: n = 7) were determined by radioimmunoassay commercial kits. No P4 differences were found between groups (GNPSP: 3.1 ± 2.8; 1.7 ± 1.8; 0.4 ± 1.0; and 0.0 ± 0.0 vs. GNPNSP: 4.4 ± 1.8; 3.0 ± 2.2; 0.8 ± 0.8; and 0.0 ± 0.0 or GPSP: 4.2 ± 1.0; 3.4 ± 0.6; 3.3 ± 1.6; 3.2 ± 0.9; 3.6 ± 1.2; 3.5 ± 1.3; 2.7 ± 1.3 vs. GPNSP: 4.4 ± 1.6; 3.6 ± 1.5; 3.7 ± 1.5; 3.8 ± 1.4; 3.2 ± 1.2; 3.1 ± 1.2; 3.6 ± 1.1; D16, D17, D18, D19, D20, D21, D24, respectively) or for the interaction of group and time. In conclusion, a second progestogen device had no effect on luteolysis or early pregnancy in the following oestrous cycle.  相似文献   
4.
Spheroid cell culture emerges as powerful in vitro tool for experimental tumour research. In this study, we established a scaffold‐free three‐dimensional spheroid system built from canine osteosarcoma (OS) cells (D17). Spheroids (7, 14 and 19 days of cultivation) and monolayer cultures (2 and 7 days of cultivation) were evaluated and compared on light and electron microscopy. Monolayer and spheroid cultures were tested for vimentin, cytokeratin, alkaline phosphatase, osteocalcin and collagen I by means of immunohistochemistry. The spheroid cell culture exhibited a distinct network of collagen I in particular after 19‐day cultivation, whereas in monolayer cultures, collagen I was arranged as a lamellar basal structure. Necrotic centres of large spheroids, as observed in 14‐ and 19‐day cultures, were characterized by significant amounts of osteocalcin. Proliferative activity as determined by Ki‐67 immunoreactivity showed an even distribution in two‐dimensional cultures. In spheroids, proliferation was predominating in the peripheral areas. Metastasis‐associated markers ezrin and S100A4 were shown to be continuously expressed in monolayer and spheroid cultures. We conclude that the scaffold‐free spheroid system from canine OS cells has the ability to mimic the architecture of the in vivo tumour, in particular cell–cell and cell–matrix interactions.  相似文献   
5.
An 8-month-old, male, crossbreed dog was presented for macroglossia, reduced mandibular extension, ptyalism, dysphagia, and regurgitation. Serum creatine kinase and aspartate aminotransferase activity were markedly increased. Thoracic radiographs showed an axial gastro-esophageal hiatal hernia, diaphragmatic thickening, and asymmetry. Magnetic resonance imaging of the head showed a severely enlarged tongue, symmetric increase in size of the geniohyoid and mylohyoid muscles, and diffuse masticatory hypomyotrophy. Whole-body CT ruled out other musculoskeletal abnormalities and further characterized the radiographic and MRI findings. Muscular histopathology was consistent with Becker muscular dystrophy.  相似文献   
6.
The commercial, welfare and environmental impacts of rearing small colonies of free-range chickens in newly planted woodland at two sites in the UK, during the first 2 years of the enterprise, were investigated. Newly planted rather than established trees were used so that commercially viable species could be planted in a way that would suit the management of the chicken enterprise, and small colonies were used so that farmers wishing to diversify could buy into the system progressively. It was anticipated that marketing a high specification product would provide an immediate income, whilst waiting for the future investment in trees to grow.  相似文献   
7.
Beyer  Nicole  Kirsch  Felix  Gabriel  Doreen  Westphal  Catrin 《Landscape Ecology》2021,36(9):2657-2671
Landscape Ecology - Pollinator declines and functional homogenization of farmland insect communities have been reported. Mass-flowering crops (MFC) can support pollinators by providing floral...  相似文献   
8.
A new cytotoxic thiodepsipeptide, verrucosamide (1), was isolated along with the known, related cyclic peptide thiocoraline, from the extract of a marine-derived actinomycete, a Verrucosispora sp., our strain CNX-026. The new peptide, which is composed of two rare seven-membered 1,4-thiazepane rings, was elucidated by a combination of spectral methods and the absolute configuration was determined by a single X-ray diffraction study. Verrucosamide (1) showed moderate cytotoxicity and selectivity in the NCI 60 cell line bioassay. The most susceptible cell lines were MDA-MB-468 breast carcinoma with an LD50 of 1.26 µM, and COLO 205 colon adenocarcinoma with an LD50 of 1.4 µM. Also isolated along with verrucosamide were three small 3-hydroxy(alkoxy)-quinaldic acid derivatives that appear to be products of the same biosynthetic pathway.  相似文献   
9.
10.
Three species of fish were studied: Atlantic cod (Gadus morhua), sculpin (Myoxocephalus scorpius) (from the North Sea, temperature 2 to 12°C) andNotothenia neglecta (from Antarctica, temperature –2 to +2°C). Single fast muscle fibres were isolated from anterior myotomes and skinned with detergent in order to directly determine the effects of pH and temperature on force production and shortening velocity.In all species maximum force production (Po) was independent of pH over the range 7.3–8.0. Decreasing the pH from 7.3 to 6.6 reduced maximum force by 28% in fibres fromG. morhua andN. neglecta but had no effect on fibres fromM. scorpius. The depression in maximum force with acidosis was accompanied by a proportional decrease in stiffness and an increase in the rate of force recovery after stretch.Unloaded contraction velocity of cod fibres (Vmax) showed a pH optimum at around pH 7.6 decreasing by 31% at pH 6.6. Vmax of fibres from the other species was independent of pH over the range 6.6–8.0.The effects of pH on Po and Vmax were similar at 0 and 10°C. Thus for maximally activated fibres both force and contraction velocity are independent of temperature induced changes in pH. In some species acidosis depresses contractility and is likely to be a contributory factor to muscle fatigue.  相似文献   
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