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   260篇
  免费   22篇
林业   7篇
农学   11篇
基础科学   3篇
  27篇
综合类   31篇
农作物   8篇
水产渔业   49篇
畜牧兽医   109篇
园艺   11篇
植物保护   26篇
  2022年   4篇
  2021年   6篇
  2020年   10篇
  2019年   4篇
  2018年   11篇
  2017年   4篇
  2016年   5篇
  2015年   2篇
  2014年   4篇
  2013年   15篇
  2012年   10篇
  2011年   12篇
  2010年   9篇
  2009年   7篇
  2008年   10篇
  2007年   5篇
  2006年   7篇
  2005年   8篇
  2004年   11篇
  2003年   13篇
  2002年   13篇
  2000年   6篇
  1999年   6篇
  1998年   7篇
  1996年   4篇
  1995年   4篇
  1993年   4篇
  1992年   4篇
  1991年   3篇
  1990年   4篇
  1989年   4篇
  1988年   4篇
  1986年   3篇
  1983年   2篇
  1982年   7篇
  1981年   3篇
  1979年   4篇
  1978年   3篇
  1977年   2篇
  1976年   6篇
  1975年   4篇
  1974年   3篇
  1973年   5篇
  1970年   2篇
  1942年   1篇
  1941年   1篇
  1939年   1篇
  1933年   1篇
  1916年   1篇
  1893年   1篇
排序方式: 共有282条查询结果,搜索用时 531 毫秒
31.
The depletion of residues of benzolyprop-ethyl ( I ) and its hydrolysis product N-benzoyl-N-(3,4-dichlorophenyl)-DL -alanine ( II ) in soils is reported from various trials following applications of I to soil and crops at up to 3 kg ha?1. Quite rapid hydrolysis of I to II occurred in most soils and depletion of II followed. The total residue of I and II in the soil often initially increased, probably because of transfer of chemical from the crop to the soil, but the time for 50% disappearance of the total residue ( I+II ) was normally between 4 and 16 weeks. When four sites were treated for three successive years, carry-over of residues was negligible in three sites and showed no progressive increase in the fourth.  相似文献   
32.
33.
34.
Traditionally, chapattis are flatbreads made from atta (wholemeal Indian wheat flour). Non-atta chapattis have not been popular due to substandard product quality. To investigate what makes atta special for making chapattis, products were made using atta, Australian wholemeal wheat flour, gluten-free lupin flour, and a blend of lupin and wheat flours. Doughs were characterised by measuring strain-hardening and elastic recovery in compression and also bubble structures via 3-D X-ray micro-tomography. A method was developed to identify and separate bran, which appears as bubbles, in scans of doughs.  相似文献   
35.
Volitional dispersal is a ubiquitous strategy characteristic of species across major faunal groups. Dispersal during the juvenile life stage is of interest because early performance can be critical for determining future success (survival/reproduction). For salmonids, dispersal can influence local density, competition, individual growth and survival, though drivers of dispersal at meso-scales are rarely quantified. Here, we evaluate dispersal of tagged juvenile steelhead (Oncorhynchus mykiss) through habitat units in extended stream reaches (500 m) at sites across a watershed from July to October 2017. Our aim was to quantify the frequency and spatial extent of dispersal, identify links to biotic and abiotic factors, evaluate the implications for individual growth and test for associations between dispersal and migration initiation. Dispersal rates varied between sites, but were consistently higher for age 1+ than for age 0 steelhead (avg. 21% vs. 6% respectively). Age 1+ dispersal probability was positively correlated with time between recapture events and body mass, and negatively correlated with growth rate, maximum temperature experienced and age 1+ density. At sites where there appeared to be growth benefits to remaining sedentary compared to moving, proportionally fewer fish performed dispersal. We found no links between dispersal and timing or probability of migration initiation the following spring. Our results support the hypothesis that although dispersal over intermediate scales (10–1,000 m) might be rare, it could be an important strategy that permits fish to seek out better opportunities (foraging, shelter or otherwise) in underutilised areas.  相似文献   
36.
The convergence hypothesis from neoclassical growth theory is examined for per capita incomes of counties within a large subnational region, the Great Plans. Convergence of the β and σ varieties are considered. The former describes the tendency for economies with low per capita incomes in an initial period to grow faster than those with higher incomes. The latter describes the tendency for the dispersion of incomes to fall over time and eventually stabilize. Total per capita incomes across the region show a β convergence speed over the past quarter century roughly equal to that found for activity measures in previous analyses of nation groups, continental regions, and states of the U.S. As concerns σ convergence, the dispersion of total per capita incomes in the region stabilized during the past decade. However, when transfer payments and dividends, interest, and rents are deducted from income, β convergence speeds drop markedly and the dispersion of incomes rises over the study period.  相似文献   
37.
Wheat and barley yields from three farms in the Ebro river valley are shown to be strongly dependent on seasonal rainfall, particularly that during November-January and March-May of the cropping season. In the driest farm, in Monegrillo, Zaragoza province (seasonal rainfall, 251 mm), yields increased by c. 5.9 (wheat) and 9.4 (barley) kg ha−1 per mm of extra rain during the entire cropping season, taken as October-May inclusive. The other farms, at El Canós and Selvanera in Lleida province, had seasonal rainfalls of 364 and 334 mm, and yields of barley increased by 4.3 and 9.0 kg ha−1, respectively, per mm of extra rain in the cropping season, taken as September to May inclusive.

In Monegrillo, cereals are grown in a cereal-fallow rotation. Normal fallowing (duration 17 months) compared to minimum fallowing (5 months) increased the calculated water content of the top 100 cm of the dominant soils by 19 mm. This extra water was estimated to benefit yield by 7.0% (wheat) and 6.2% (barley), raising the average yields of crops greater than 300 kg ha−1 to 1222 and 1522 kg ha−1, respectively. Agronomic practices in Monegrillo during the fallow should focus on means of increasing the proportion of the rain stored in the profile during the fallow. At all three locations, decreasing water evaporation from the soil during the cropping season would likely benefit yield.  相似文献   

38.
Two experiments were conducted to determine the effects of ruminal protein degradability, supplementation frequency, and increasing dietary protein on the expression and distribution of urea transporter-B (UT-B) in lambs fed low-quality forage (mature crested wheatgrass hay; 4.2 to 4.7% CP). In Exp. 1, 15 Dorset wether lambs (initial BW=45.8+/-1.3 kg) were blocked by initial BW and assigned to 1 of 3 treatments within a randomized complete block design for 28 d, with supplements fed to achieve 7, 10, or 13% total dietary CP. In Exp. 2, 13 Dorset wether lambs (initial BW=34+/-4 kg) were used in a completely randomized design and given 1 of 4 isonitrogenous supplements: 1) ruminally degradable protein (RDP) fed daily (n=3), 2) RDP fed on alternate days (n=3), 3) ruminally undegradable protein (RUP) fed on alternate days (n=3), or 4) a 50:50 mixture of RDP and RUP fed on alternate days (n=4) for 18 d. Alternate-day treatments were fed at twice that of daily supplementation. On the last day of both experiments, lambs were killed and samples taken for Western blot analyses for UT-B. Immunoblotting using a rabbit polyclonal antibody to UT-B confirmed the presence of distinct 32-kDa (consistent with a nonglycosylated UT-B protein) and 47-kDa (probable N-glycosylated form of UT-B) protein bands in all 9 tissues analyzed. In both experiments, the liver, dorsal rumen, reticulum, and ventral rumen displayed strong bands at 32 kDa and lighter bands at 47 kDa, whereas the cecum, large colon, spiral colon, and parotid salivary gland displayed slight 32-kDa bands and stronger, more visible bands at 47 kDa. Both protein bands were apparent in the kidney at similar visual intensities in Exp. 1, whereas the relative intensities of the 2 UT-B bands in the kidney were variable, and appeared somewhat reciprocal among animals in Exp. 2. Although the abundance of the 47-kDa UT-B band in the ventral rumen was greater (P=0.03) in lambs fed RDP daily in Exp. 2, no other treatment differences (P >or= 0.15 to 0.99) in the abundance of the 32- or 47-kDa UT-B proteins within tissues were observed in either experiment. Although protein supplementation strategy had little effect on UT-B expression in tissues other than the ventral rumen, differences in the degree of glycosylation of UT-B across tissues may provide insight into its regulation.  相似文献   
39.
Patterns of shoot development and the production of different types of shoots were compared with scion leaf area index (LAI) to identify how eight clonal Actinidia rootstocks influence scion development. Rootstocks selected from seven Actinidia species (A. chrysantha Merri., A. deliciosa (A. Chev.) C. F. Liang et A.R. Ferguson, A. eriantha Benth., A. hemsleyana Dunn, A. kolomikta (Maxim. et Rupr.) Maxim., A. kolomikta C.F. Liang and A. polygama (Sieb. et Zucc.) Maxim.) were grafted with the scion Actinidia chinensis Planch. var. chinensis 'Hort16A' (yellow kiwifruit). Based on an earlier architectural analysis of A. chinensis, axillary shoot types produced by the scion were classified as short, medium or long. Short and medium shoots produced a restricted number of preformed leaves before the shoot apex ceased growth and aborted, resulting in a 'terminated' shoot. The apex of long shoots continued growth and produced more nodes throughout the growing seasons. Mid-season LAI of the scion was related to the proportion of shoots that ceased growth early in the season. Scions on low-vigor rootstocks had 50% or less leaf area than scions on the most vigorous rootstocks and had a higher proportion of short and medium shoots. On low-vigor rootstocks, a higher proportion of short shoots was retained during pruning to form the parent structure of the following year. Short parent shoots produced a higher proportion of short daughter shoots than long parent shoots, thus reinforcing the effect of the low-vigor rootstocks. However, overall effects of rootstock on shoot development were consistent regardless of parent shoot type and nodal position within the parent shoot. Slower-growing shoots were more likely to terminate and scions on low-vigor rootstocks produced a higher proportion of slow-growing shoots. Shoot termination also occurred earlier on low-vigor rootstocks. The slower growth of terminating shoots was detectable from about 20 days after bud burst. Removal of a proportion of shoots at the end of bud burst increased the growth rate and decreased the frequency of termination of the remaining shoots on all rootstocks, indicating that the fate of a shoot was linked to competitive interactions among shoots during initial growth immediately after bud burst. Rootstock influenced the process of shoot termination independently of its effect on final leaf size. Scions on low-vigor rootstocks had a higher proportion of short shoots and short shoots on all rootstocks had smaller final leaf sizes at equivalent nodes than medium or long shoots. Only later in the development of long shoots was final leaf size directly related to rootstock, with smaller leaves on low-vigor rootstocks. Thus, the most important effect of these Actinidia rootstocks on scion development occurred during the initial period of shoot growth immediately after bud burst.  相似文献   
40.
Vibrios are Gram-negative rod-shaped bacteria that are widespread in the coastal and estuarine environments. Some species, e.g. Vibrio anguillarum and V. tapetis, comprise serious pathogens of aquatic vertebrates or invertebrates. Other groups, including Grimontia (=Vibrio) hollisae, Photobacterium (=Vibrio) damselae subsp. damselae, V. alginolyticus, V. harveyi (=V. carchariae), V. cholerae, V. fluvialis, V. furnissii, V. metschnikovii, V. mimicus, V. parahaemolyticus and V. vulnificus, may cause disease in both aquatic animals and humans. The human outbreaks, although low in number, typically involve wound infections and gastro-intestinal disease often with watery diarrhoea. In a minority of cases, for example V. vulnificus, there is good evidence to actually associate human infections with diseased animals. In other cases, the link is certainly feasible but hard evidence is mostly lacking.  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