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   322篇
  免费   15篇
  国内免费   4篇
林业   39篇
农学   33篇
基础科学   3篇
  39篇
综合类   17篇
农作物   12篇
水产渔业   39篇
畜牧兽医   131篇
园艺   2篇
植物保护   26篇
  2023年   1篇
  2022年   10篇
  2021年   19篇
  2020年   9篇
  2019年   1篇
  2018年   15篇
  2017年   5篇
  2016年   9篇
  2015年   15篇
  2014年   22篇
  2013年   17篇
  2012年   19篇
  2011年   16篇
  2010年   9篇
  2009年   7篇
  2008年   23篇
  2007年   21篇
  2006年   23篇
  2005年   21篇
  2004年   18篇
  2003年   14篇
  2002年   14篇
  2001年   6篇
  2000年   6篇
  1999年   5篇
  1998年   4篇
  1997年   2篇
  1996年   2篇
  1995年   1篇
  1991年   1篇
  1985年   2篇
  1984年   1篇
  1983年   1篇
  1978年   1篇
  1977年   1篇
排序方式: 共有341条查询结果,搜索用时 46 毫秒
331.
Changes in immune factors expressed by milk somatic cells from Holstein cows with hypocalcemia after calving were investigated in this study. Fourteen multiparous Holstein cows after their 3rd or 4th calving in one farm were used. The cows were divided into 2 groups: 7 cows needing treatment due to onset of hypocalcemia (hypocalcemia group; age = 5.53 ± 0.27 years, parity = 3.14 ± 0.14) and 7 cows without health problems (control group; age = 5.88 ± 0.31 years, parity = 3.57 ± 0.26). Milk samples were collected aseptically using a cannula and mRNA of immune factors expressed by milk somatic cells were analyzed. Milk samples (50 mL) were collected from the right rear mammary gland of cows before milking at day 1 and weeks 1, 2, 4, and 8 after calving. All milk samples showed a negative reaction to the California Mastitis Test. Levels of relative interleukin (IL)-6 and cathelicidin in the hypocalcemia group were lower than those in the control group in weeks 1 to 8. A significant difference in relative IL-6 levels was found in week 4 (P < 0.05). These results suggest that levels of IL-6 expressed by milk somatic cells may be affected by hypocalcemia in dairy cows.  相似文献   
332.
This study aimed to detect filarial parasites in blood samples of Japanese black bears (Ursus thibetanus japonicus) collected from Iwate Prefecture, Japan. Positive amplicons were obtained from 26 out of 30 samples by nested PCR targeting 18S ribosomal RNA gene and first internal transcribed spacer regions. DNA sequences of Mansonella sp. close to M. ozzardi and Dirofilaria sp. were detected for eight and 11 positive amplicons, respectively. Co-infection was detected for the remaining seven amplicons. Dirofilaria sp. was identified as D. ursi by further genetic analysis of 5S ribosomal RNA gene sequence. The results of this study will contribute to further investigations of Japanese black bears for monitoring their risk as a reservoir of possible zoonotic filarial parasites.  相似文献   
333.
We report the direct observation of dioxygen molecules physisorbed in the nanochannels of a microporous copper coordination polymer by the MEM (maximum entropy method)/Rietveld method, using in situ high-resolution synchrotron x-ray powder diffraction measurements. The obtained MEM electron density revealed that van der Waals dimers of physisorbed O2 locate in the middle of nanochannels and form a one-dimensional ladder structure aligned to the host channel structure. The observed O-O stretching Raman band and magnetic susceptibilities are characteristic of the confined O2 molecules in one-dimensional nanochannels of CPL-1 (coordination polymer 1 with pillared layer structure).  相似文献   
334.
The electronic structure of Mott insulators continues to be a major unsolved problem in physics despite more than 50 years of research. Well-developed momentum-resolved spectroscopies such as photoemission or neutron scattering cannot probe the full Mott gap. High-resolution resonant inelastic x-ray scattering revealed dispersive charge excitations across the Mott gap in a high-critical temperature parent cuprate (Ca(2)CuO(2)Cl(2)), shedding light on the anisotropy of the Mott gap. These charge excitations across the Mott gap can be described within the framework of the Hubbard model.  相似文献   
335.
畜禽废弃物高温好氧堆腐过程中气体产生与变化   总被引:2,自引:4,他引:2  
利用通气方法对3种禽畜废弃物进行了高温好氧堆腐发酵试验,堆腐物内部温度维持在70℃左右,对发酵过程中O2、CO2、NH3、CH4、H2S的逐日变化量进行了测定。结果表明,CO2、NH3的产生量与堆腐材料的C/N有关。对于发酵中产生恶臭的NH3,猪粪发酵中最高值比试验开始时增加了350倍,鸡粪增加了120倍,而乳牛粪只增加了23倍,其最高值远低于猪粪和鸡粪。猪、鸡粪发酵过程中有CH4、H2S产生,乳牛粪中未被检出。易分解有机物含量高、C/N低的堆腐材料,在充气、高温条件下,2~3d可达到腐解高峰,l周左右气体产生趋于平稳下降,完成1次发酵。  相似文献   
336.
Magnetic domain wall motion induced by magnetic fields and spin-polarized electrical currents is experimentally well established. A full understanding of the underlying mechanisms, however, remains elusive. For the ferromagnetic semiconductor (Ga,Mn)As, we have measured and compared such motions in the thermally activated subthreshold, or "creep," regime, where the velocity obeys an Arrhenius scaling law. Within this law, the clearly different exponents of the current and field reflect different universality classes, showing that the drive mechanisms are fundamentally different.  相似文献   
337.
Beet necrotic yellow vein virus (BNYVV) is the causal agent of rhizomania, the most serious sugar beet disease worldwide. Since the first finding in Japan in 1969, BNYVV became widespread throughout Hokkaido in a few decades and led to the introduction of Rz1-resistant sugar beet cultivars in the 1990s. Here, we report the historical progress of the BNYVV epidemic in Hokkaido from 1969 to 2019. Previous analysis on samples from 1991 showed that BNYVV isolates were classified into three strains (named O, D, and T) based on the RNA3-encoded p25 gene. The O-type viruses were widely detected in Hokkaido, while the D- and T-type viruses were detected in limited areas. The RNA5, encoding the p26 gene, was initially contained in some D- and O-type isolates but not in any T-type isolates. Interestingly, recent sample analysis revealed that RNA5-containing T-type viruses, seemingly more virulent than the other two strains, were widely detected in Hokkaido. Additionally, a small group of virus isolates harbouring a new p25 gene (named C) was found in limited areas. These results suggest that the T-type viruses, which accompanied RNA5, have been preferentially spread from a limited area to other districts over the last few decades and that this spread might be strongly associated with the recent introduction of Rz1-resistant sugar beet cultivars. BNYVV-positive samples also contained mainly beet soil-borne virus and traces of beet virus Q, both of which are the first to be recorded in Japan.  相似文献   
338.
Green stem disorder (GSD) in soybean (Glycine max (L.) Merrill) retains green stems and leaves as the pods mature, thereby reducing the harvest efficiency and impairing seed quality. In order to elucidate the causes of GSD, the factors that promote GSD need to be identified. In our experiments, we adjusted plant density at the developmental growth stage R1 (the beginning of flowering) or at R5 (the beginning of seed filling), from dense (22.2 plants m–2) to sparse (5.56 plants m–2) by thinning. We found that GSD occurrence was increased when plant density was changed, compared to the treatments that were maintained under either dense or sparse conditions. GSD was promoted more strongly when thinning was conducted at R5 than at R1 stage. Shading equipment surrounding plants, except for their upper-most leaves, was implemented to determine the association of shading and GSD. The results of the shade experiment revealed that GSD occurrence generally increased in treatments subjected to shade removal, compared to those that were shaded until R8 stage (full maturity) or never shaded since the time of sowing. GSD was strongly promoted by shade removal at R5 than at R1 stage. The shading results coincide with the results of the plant density experiment, indicating that an increase in light availability enhances source activity relative to sink at R5 stage, thereby promoting GSD occurrence in soybean. Thinning is expected to be used as an easy experimental method to create GSD for research purpose.  相似文献   
339.
We examined the potential for biological control of black rot of broccoli, caused by Xanthomonas campestris pv. campestris (Xcc), using nonpathogenic Xanthomonas sp. strain 11-100-01 (npX) mixed with bacteriophage XcpSFC211 (pXS). Inoculation of intact broccoli plants in greenhouse trials with either npX or pXS did not control black rot. After injured plant inoculation, however, npX alone or npX with pXS significantly controlled black rot. When a mixed suspension of npX with pXS was placed on a membrane filter, then washed with distilled water and air-dried, a substantial amount of pXS adsorbed to the surface of npX. In a field trial, broccoli plants were sprayed with a suspension of npX with pXS, then inoculated with Xcc. A meta-analysis of the results from five field trials showed an integrated risk ratio (IRR, the ratio of disease incidence in inoculated broccoli plants to the incidence in control plants) of 0.69 after treatment with only npX and 0.59 with npX with pXS, indicating that black rot incidence was significantly reduced by each treatment. The difference between these two treatments was also significant. IRR was 1.24 when comparing suppression by npX with pXS and that by basic copper sulfate wettable powder; thus, their control was comparable. The combination of npX with pXS improved the preventive effect against black rot. This is the first report describing that a nonpathogenic Xanthomonas sp. strain mixed with a bacteriophage effectively controlled black rot of broccoli in field trials.  相似文献   
340.
The D-genome progenitor of hexaploid wheat, Aegilops tauschii Coss., has a wide natural species range in central Eurasia and possesses wide natural variation in heading and flowering time. Here, we report identification of two Ae. tauschii accessions insensitive to short day length. Similarly to a loss or reduced degree of vernalization requirement, the photoperiod-insensitive mutations were found only in the early flowering sublineage (TauL1b) of Ae. tauschii. Quantitative trait locus (QTL) analyses using two F2 mapping populations showed that a QTL for heading time on the long arm of chromosome 5D was related to the early heading phenotype of the photoperiod-insensitive accessions under short-day conditions. In the photoperiod-insensitive accession, expression patterns of two flowering-related genes were altered under short-day conditions compared with the patterns in photoperiod-sensitive accessions. This study indicates that analysis of natural variations in the Ae. tauschii population is useful to find novel genetic loci controlling agronomically important traits.  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