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   194篇
  免费   4篇
林业   1篇
基础科学   2篇
  15篇
综合类   32篇
农作物   53篇
水产渔业   7篇
畜牧兽医   84篇
植物保护   4篇
  2023年   2篇
  2020年   2篇
  2017年   2篇
  2015年   2篇
  2014年   4篇
  2012年   6篇
  2011年   3篇
  2010年   3篇
  2009年   5篇
  2008年   6篇
  2007年   8篇
  2006年   5篇
  2005年   5篇
  2004年   4篇
  2003年   4篇
  2001年   4篇
  2000年   4篇
  1998年   2篇
  1996年   3篇
  1993年   2篇
  1992年   2篇
  1991年   7篇
  1990年   3篇
  1989年   4篇
  1987年   6篇
  1986年   3篇
  1985年   2篇
  1981年   2篇
  1979年   2篇
  1978年   4篇
  1977年   5篇
  1975年   2篇
  1974年   2篇
  1973年   6篇
  1972年   4篇
  1970年   3篇
  1968年   2篇
  1966年   4篇
  1965年   2篇
  1964年   2篇
  1963年   2篇
  1962年   10篇
  1961年   6篇
  1960年   7篇
  1959年   2篇
  1958年   5篇
  1955年   2篇
  1921年   1篇
  1919年   1篇
  1880年   3篇
排序方式: 共有198条查询结果,搜索用时 31 毫秒
91.
An indirect immunoperoxidase procedure was developed to detect viral antigens in bluetongue virus (BTV)-infected tissues. Embryonating chicken eggs were infected with BTV serotypes 10, 11, 13, or 17, and the chorioallantoic membranes were subsequently fixed in formalin and embedded in paraffin. The peroxidase-antiperoxidase (PAP) system was used to examine the infected membranes for the presence of viral antigens. Sheep antisera raised against BTV serotypes 10, 11, 13, and 17 served as the primary antibodies in the PAP procedure. Specific staining was observed when each of these antisera was applied to membranes expressing antigens of homologous and heterologous BTV serotypes. The PAP method was rapid, reliable, and specific in its detection of BTV.  相似文献   
92.
Crossbred pigs (n = 216) were used to test the effect of supplemental L-carnitine (CARN) on the fatty acid composition and quality characteristics of fresh pork bellies from pigs fed diets formulated with different inclusion levels of corn oil. Pigs were blocked by BW (43.6 ± 1.0 kg) and allotted randomly to pens of 6 pigs within blocks. Then, within blocks, pens were assigned randomly to 1 of 6 dietary treatments in a 2 × 3 factorial arrangement, with either 0 or 100 mg/kg of supplemental CARN and 3 dietary inclusion levels (0, 2, or 4%) of corn oil (CO). When the lightest block weighed 125.0 kg, all pigs were slaughtered, and left-side bellies were captured during carcass fabrication for quality data collection. Fresh pork bellies were evaluated for length, width, thickness, and firmness (bar-suspension and Instron-compression methods) before a 2.5-cm-wide strip of belly was removed and subsequently dissected into subcutaneous fat, primary lean (latissimus dorsi), secondary lean (cutaneous trunci), and intermuscular fat for fatty acid composition determination. Although belly length, width, and thickness of fresh pork bellies were not affected by CARN (P ≥ 0.128) or CO (P ≥ 0.073), belly firmness decreased linearly (P < 0.001) with increasing dietary CO, but there was no (P ≥ 0.137) effect of CARN on any belly firmness measure. Dietary CARN increased (P < 0.05) the proportion of total SFA in the intermuscular fat layer, increased (P < 0.05) the proportion of total MUFA in the primary and secondary lean layers, and decreased (P < 0.05) the proportion of total PUFA in the intermuscular fat and secondary lean layers of pork bellies. Moreover, the SFA and MUFA compositions decreased linearly (P < 0.001) with increasing dietary CO, and the rate of the decrease in SFA composition was greater (P < 0.001) in the fat layers than the lean layers. Conversely, the PUFA content increased linearly (P < 0.001) with increasing dietary CO, and the rate of the increase in PUFA was greater (P < 0.001) in the fat than the lean layers, and greater (P = 0.022) in the primary than secondary lean layer. Results from this study would indicate that differences in the amount and rate of fatty acid deposition associated with feeding increased amounts of CO, along with moisture differences among the belly layers, combine to negatively affect fresh pork belly firmness.  相似文献   
93.
A detailed schematic representation of high-resolution G-banding patterns was prepared from elongated and finely banded mitotic chromosomes of the mouse. Such chromosomes can be obtained from both animal tissue and cell lines by a simple protocol, facilitating precise demarcation of breakpoints in chromosome rearrangements and aiding in the sublocalization of genes. Regions of subbanding homology were observed between human and mouse chromosomal segments known to have conserved gene assignments, an indication that, at the cytogenetic level, extensive regions of the mammalian genome may remain intact after 60 million years of species divergence.  相似文献   
94.
Robot ethics     
  相似文献   
95.
Many properties of chemical reactions are determined by the transition state connecting reactant and product, yet it is difficult to directly obtain any information about these short-lived structures in liquids. We show that two-dimensional infrared (2D-IR) spectroscopy can provide direct information about transition states by tracking the transformation of vibrational modes as a molecule crossed a transition state. We successfully monitored a simple chemical reaction, the fluxional rearrangement of Fe(CO)5, in which the exchange of axial and equatorial CO ligands causes an exchange of vibrational energy between the normal modes of the molecule. This energy transfer provides direct evidence regarding the time scale, transition state, and mechanism of the reaction.  相似文献   
96.
A soil incubation study was conducted to evaluate the effect of winter cereal rye (Secale cereale L.) cover crop (CC) biomass and fertilizer nitrogen (N) addition on soil inorganic-N. Rye aboveground biomass was collected following corn (Zea mays L.) and soybean [Glycine max (L.) Merr.], and incubated at equivalent field temperatures for 105 d at rates of 1120, 2240, and 3360 kg dry matter (DM) ha?1. Despite N addition from the rye biomass at any rate, there was no real effect on ammonium (NH4)-N, and only from 63 d to 105 d a limited net increase in nitrate (NO3)-N and inorganic-N was observed compared to no-rye. Nitrate-N and inorganic-N concentrations change per heat unit (HU) accumulation was negative with rye addition through 7 d, but was positive consistently across the remaining incubation period with or without rye. Overall, the rye CC biomass had only a neutral to small positive effect on soil inorganic-N.  相似文献   
97.
It has been evident the improvement of in vitro embryo production (IVEP) in dairy cows. Nevertheless, it is known that differences in the number and quality of oocytes between taurine and zebu females impact the efficiency and economic viability of IVEP. As the insulin‐like growth factor (IGF) system is related to follicular and oocyte development, we aimed to quantify mRNA abundance of IGF system members and pregnancy‐associated plasma protein‐A (PAPPA) in the cumulus–oocyte complexes (COCs) of Gir, 1/2 Holstein × 1/2 Gir and Holstein cows. Four pools of 30 immature COCs from Gir, 1/2 Holstein × 1/2 Gir and Holstein cows were obtained by ovum pickup (OPU), and the oocytes and cumulus cells (CC) were mechanically separated and stored at ?80°C. Total RNA was extracted from pools of 30 oocytes and their respective CC. Expression of target genes was assessed by real‐time RT‐PCR. In oocytes, the abundance of IGFR1 mRNA was higher (< .05) in Gir cows compared with the other breeds. In contrast, in CC, mRNA encoding IGF2 (< .05), IGFR2 (< .05) and IGFBP4 (< .01) was higher in Holstein donors compared with Gir and 1/2 Holstein × 1/2 Gir cows. Additionally, the abundance of PAPPA mRNA was higher in oocytes (< .001) and CC (< .01) in Gir and 1/2 Holstein × 1/2 Gir cows compared with the Holstein donors. In conclusion, the higher abundance of PAPPA mRNA in the oocytes and CC from Gir and cross‐breed donors combined with the low expression of IGFBP4 in the CC suggests an enhancement of the bioavailability of IGF‐free when compared with Holstein COCs.  相似文献   
98.
A 3-year-old Quarter Horse stallion was presented for evaluation of potential fertility. An impairment in spermatogenesis was suspected as the stallion produced semen with reduced percentages of progressively motile and morphologically normal spermatozoa. In addition, when semen was collected daily from the stallion, daily spermatozoal output (DSO) was found to be below normal. Semen from this stallion also contained spherical cells of unknown origin. The following report describes the identification of these cells as degenerating spermatids by the use of light and electron microscopy.  相似文献   
99.
100.
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