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   430篇
  免费   19篇
  国内免费   4篇
林业   62篇
农学   22篇
基础科学   3篇
  38篇
综合类   19篇
农作物   29篇
水产渔业   55篇
畜牧兽医   196篇
园艺   2篇
植物保护   27篇
  2022年   13篇
  2021年   20篇
  2020年   9篇
  2019年   4篇
  2018年   17篇
  2017年   10篇
  2016年   10篇
  2015年   15篇
  2014年   24篇
  2013年   27篇
  2012年   20篇
  2011年   28篇
  2010年   12篇
  2009年   11篇
  2008年   27篇
  2007年   19篇
  2006年   25篇
  2005年   23篇
  2004年   18篇
  2003年   11篇
  2002年   22篇
  2001年   10篇
  2000年   9篇
  1999年   4篇
  1998年   3篇
  1996年   2篇
  1992年   1篇
  1990年   1篇
  1989年   1篇
  1988年   2篇
  1987年   5篇
  1986年   5篇
  1985年   4篇
  1984年   4篇
  1983年   5篇
  1982年   1篇
  1981年   4篇
  1980年   1篇
  1979年   4篇
  1978年   4篇
  1977年   1篇
  1976年   1篇
  1975年   2篇
  1974年   1篇
  1972年   1篇
  1971年   3篇
  1970年   2篇
  1968年   2篇
  1967年   1篇
  1966年   1篇
排序方式: 共有453条查询结果,搜索用时 15 毫秒
81.
The three-spot wrasse (Halichoeres trimaculatus), which inhabits the coral reefs of Okinawa, changes sex from female to male. Sex change in this species is controlled by a social system. Oocytes disappear completely from the ovary, and male germ cells and somatic cells comprising testicular tissue arise a new during the sex change process. However, little is known of the fate and origin of the gonadal tissue-forming cells during sex change. In particular, the fate of ovarian somatic cells has not been determined, although the ovarian tissue regresses histologically. To approach this question, we analyzed apoptosis and cell proliferation in the sex-changing gonads. Unexpectedly, we found that few apoptotic somatic cells were present during sex change, suggesting that ovarian somatic cells might survive during the regression of the ovarian tissue. On the other hand, cell proliferation was detected in many granulosa cells surrounding the degenerating oocytes, a few epithelial cells covering ovigerous lamella and a few somatic cells associated with gonial germ cells at an early stage of sex change. Then, we found that proliferative ovarian somatic cells remained in the gonads late in the sex change process. Based on these results, we concluded that some functional somatic cells of the ovary are reused as testicular somatic cells during the gonadal sex change in the three-spot wrasse.  相似文献   
82.
The impact of genetically modified canola (Brassica napus) on biodiversity has been examined since its initial stage of commercialization. Various research groups have extensively investigated crossability and introgression among species of Brassicaceae. B. rapa and B. juncea are ranked first and second as the recipients of cross-pollination and introgression from B. napus, respectively. Crossability between B. napus and B. rapa has been examined, specifically in terms of introgression from B. napus to B. rapa, which is mainly considered a weed in America and European countries. On the other hand, knowledge on introgression from B. napus to B. juncea is insufficient, although B. juncea is recognized as the main Brassicaceae weed species in Asia. It is therefore essential to gather information regarding the direct introgression of B. napus into B. juncea and indirect introgression of B. napus into other species of Brassicaceae through B. juncea to evaluate the influence of genetically modified canola on biodiversity. We review information on crossability and introgression between B. juncea and other related Brassicaseae in this report.  相似文献   
83.
The effect of irradiance and temperature on the photosynthesis of two Japanese agarophytes, Gelidium elegans and Pterocladiella tenuis (Gelidiales), was determined using dissolved oxygen sensors and pulse amplitude modulated (PAM) fluorometry. Gross photosynthesis and dark respiration rates were determined over a range of temperatures (8–36 °C). The highest gross photosynthetic rates were 40.3 and 37.0 mg O2 g ww ?1  min?1 and occurred at 24.3 and 25.5 °C [95 % Bayesian credible interval (BCI) 20.7–28.0 and 23.4–28.3 °C], respectively. The dark respiration rate in G. elegans and P. tenuis increased with increasing temperature at a rate of 0.10 and 0.31 mg O2 g ww ?1  min?1 °C?1 , respectively. Modeling the net photosynthesis–irradiance (PE) responses of G. elegans and P. tenuis at 20 °C revealed that the net photosynthetic rates quickly increased at irradiance levels below the estimated saturation irradiance of 88 and 83 µmol photons m?2 s?1, with a compensation irradiance of 14 and 19 µmol photons m?2 s?1, respectively. The highest value of the maximum effective quantum yield (Φ PSII) occurred at 20.1 °C (BCI 18.9–21.5 °C) and 21.3 °C (BCI 20.2–22.5 °C) for G. elegans and P. tenuis and was 0.49 and 0.45, respectively. These optimal temperatures of Φ PSII were relatively lower than those determined by the photosynthesis–temperature model of oxygen evolution. The temperature response of these species indicates that they are probably well adapted to the current range of seawater temperatures in the study site but that they are near the boundary of their tolerable limits.  相似文献   
84.
A 3‐year‐old, spayed female, Domestic Shorthair cat presented with anorexia, lethargy, vomiting, probable hemoabdomen, and multiple masses on the right lateral liver lobe. Clinicopathologic and imaging abnormalities included anemia, azotemia, icterus, and hepatomegaly with hypoechoic masses. On cytologic evaluation of a fine‐needle aspiration of a liver mass there was abundant extracellular pink‐ to purple‐colored material between hepatocytes. The amorphous material was stained with direct fast scarlet (DFS), and green birefringent areas were observed under polarized light, confirming the presence of amyloid. A unique finding on the cytologic smear were macrophages containing amorphous and fibrillar amyloid‐like protein. Histopathologic examination using H&E and Congo red staining confirmed amyloid deposits within the space of Disse, along the sinusoids, portal tracts, blood vessel walls, and within the cytoplasm of macrophages. Immunohistochemical staining with anti‐AA amyloid antibodies further confirmed the presence of AA amyloid. To the author's knowledge, this is the first report of the cytologic finding of AA amyloid protein within macrophages and DFS stain detection of amyloid on a cytologic smear.  相似文献   
85.
The objectives of this study were to detect effective genetic polymorphisms of bovine growth hormone (bGH) gene associated with calf weight in Japanese Black cattle. Fifty‐eight sires and 47 breeding cows were used to detect the polymorphisms in exons by single‐strand conformation polymorphism (SSCP). Four homozygous and six heterozygous SSCP genotypes were identified in exon 5. Although each single nucleotide polymorphism (SNP) had been reported, these genotypes were caused by three SNPs at the nucleotide positions 2141, 2277 and 2291. Four haplotypes C‐C‐A, G‐C‐A, C‐C‐C and G‐T‐A were newly identified. It was suggested that other haplotypes not detected in this study may not exist, considering the allele frequencies reported in Bos taurus and Bos indicus, and the migrating process of native Japanese cattle. Thereafter, we examined associations between the detected polymorphic sites in exon 5 by PCR – restriction fragment length polymorphism and calf weight using 53 breeding dams and 135 calves. The birth weights of calves with haplotype G‐C‐A are significantly lighter and calves' weights produced by cows with such haplotype are also lighter at 30 days old, using regression analysis. Although further research is necessary, these results may serve as a useful criterion to select breeding stocks, especially in maternal abilities.  相似文献   
86.
Pacific Russet is a high-yielding, early maturing, oblong russet fresh market cultivar with excellent tuber appearance and culinary quality. In trials conducted in western Canada the yield of the new cultivar was generally superior to Russet Burbank, Ranger Russet, and Atlantic at 80, 90, and 110 days after planting. In the North Central Regional Variety Trial the yield of Pacific Russet exceeded that of Russet Norkotah in four of the eight sites in 2000 and three of the eight sites in 2001. In trials conducted in Ontario (Canada) Pacific Russet exceeded the yield of Goldrush at both sites in 2001 and in 2002 at two of the three sites that included both cultivars. External and internal defects occur at very low levels. The new cultivar is resistant to common scab and moderately resistant to Verticillium and Fusarium wilt, but susceptible to Fusarium dry rot and late blight (foliar). Pacific Russet shows clear foliar but not tuber symptoms when infected with bacterial ring rot.  相似文献   
87.
We have shown phosphoinositide 3-kinase (PI3K)/Akt signaling activation in thyroid capsular invasive carcinomas (CICs), which are highly induced by promotion with sulfadimethoxine (SDM) in a rat 2-stage thyroid carcinogenesis model. To examine the potency of calcitriol, a synthetic vitamin D3 analog, on the development or progression of CICs, male F344 rats were injected with calcitriol (0.1 μg/kg body weight) three times a week intraperitoneally, during an entire period of SDM-promotion for 13 weeks (Experiment 1) or during the last 2 weeks of a 15-week SDM-promotion (Experiment 2). Initiation with N-bis(2-hydroxypropyl)nitrosamine preceded all treatments. In Experiment 1, long-term calcitriol treatment reduced the multiplicity of CICs, while cell proliferation activity, estimated by Ki-67 cell index in the induced CICs, was unchanged with SDM-promotion alone. Considering the strong dependency of promotion with SDM during the early stages on thyroid-stimulating hormone, the reduced multiplicity in Experiment 1 may be due to the effect on an early stage of neoplastic proliferation. Although the magnitude was mild, cell proliferation activity was decreased in existing CICs after short-term calcitriol treatment in Experiment 2, which was associated with a mild decrease in cyclin-dependent kinase-2-positive cells, cytoplasmic immunolocalization of phosphorylated, inactive, Rb protein and a mild increase in nucleocytoplasmic expression of p27(kip1). Although the effect was mild at the late stage of SDM-promotion in this hypothyroidism-related thyroid carcinogenesis model, our results suggest that calcitriol targets cell proliferation via inhibition of a molecular cascade downstream of PI3K/Akt signaling, controlling G1/S transition.  相似文献   
88.
Embryonated chicken eggs (ECEs) are routinely used to isolate equine influenza virus. Propagation of the virus in ECEs results in selection of variants. In the present study, we determined nucleotide sequences of entire coding regions of parent A/equine/Tottori/1/07 (H3N8) and its derivatives that have different passage histories in ECE. After 12 passages, nucleotide sequence analysis predicted 3 amino acid substitutions in hemagglutinin (HA; 2 in HA1 and 1 in HA2). The two amino acid substitutions in HA1 were located in the vicinity of the cell receptor-binding site. Three other amino acid substitutions were predicted in internal proteins, 1 in the M1, 1 in the NP and 1 in the PA. This is the first report showing mutations in the internal protein genes of equine influenza virus associated with adaptation to ECE.  相似文献   
89.
The aim of the present study was to optimize the conditions for in vitro development and postvitrification survival of somatic cell cloned feline embryos. To determine the effects of cell cycle synchronization of the nuclear donor cells, we cultured preadipocytes under serum starvation or conventional conditions. After two days in serum starvation culture, the proportion of synchronized donor cells at the G0/G1 phase was 91.6%. This was significantly higher than the proportion of non-synchronized cells in the proliferative phase (72.6%, P<0.05). The in vitro development of somatic cell nuclear transfer (SCNT) embryos reconstructed using donor cells treated under serum starvation conditions (normal cleavage rate of 65.7%, 46/70, and blastocyst formation rate of 20.0%, 14/70) was comparable to that of the serum supplemented group (52.5%, 31/59, and 20.3%, 12/59). Use of in vitro or in vivo matured oocytes as recipient cytoplasts equally supported development of the SCNT embryos to the blastocyst stage (11.9%, 5/42, vs. 9.5%, 2/21). SCNT-derived blastocysts were vitrified using the original minimum volume cooling (MVC) or the modified (stepwise) MVC method. Although none (n=10) of the SCNT blastocysts survived following vitrification by the original MVC method, the stepwise MVC method resulted in 100% survival after rewarming (n=11). In conclusion, we demonstrated that feline somatic cell cloned embryos with a high developmental ability can be produced irrespective of cell cycle synchronization of donor cells using either in vivo or in vitro matured oocytes. Furthermore, by utilizing a stepwise vitrification method, we showed that it is possible to cryopreserve cloned feline blastocysts.  相似文献   
90.
Salmonella enterica subsp. enterica serovar Enteritidis (S. Enteritidis) was responsible for a worldwide pandemic during the 1980s and 1990s; however, changes in the dominant lineage before and after this event remain unknown. This study determined S. Enteritidis lineages before and after this pandemic event in Japan using multilocus sequence typing (MLST). Thirty S. Enteritidis strains were collected in Japan between 1973 and 2004, consisting of 27 human strains from individual episodes, a bovine strain, a liquid egg strain and an eggshell strain. Strains showed nine phage types and 17 pulsed-field profiles with pulsed-field gel electrophoresis. All strains had homologous type 11 sequences without any nucleotide differences in seven housekeeping genes. These MLST results suggest that S. Enteritidis with the diversities revealed by phage typing and pulsed-field profiling has a highly clonal population. Although type 11 S. Enteritidis may exhibit both pleiotropic surface structure and pulsed-field type variation, it is likely to be a stable lineage derived from an ancestor before the 1980s and/or 1990s pandemic in Japan.  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