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   1155篇
  免费   55篇
  国内免费   1篇
林业   40篇
农学   67篇
基础科学   4篇
  177篇
综合类   69篇
农作物   155篇
水产渔业   94篇
畜牧兽医   545篇
园艺   9篇
植物保护   51篇
  2024年   1篇
  2023年   8篇
  2022年   5篇
  2021年   35篇
  2020年   30篇
  2019年   30篇
  2018年   36篇
  2017年   32篇
  2016年   27篇
  2015年   45篇
  2014年   55篇
  2013年   80篇
  2012年   81篇
  2011年   109篇
  2010年   65篇
  2009年   43篇
  2008年   85篇
  2007年   49篇
  2006年   69篇
  2005年   51篇
  2004年   51篇
  2003年   59篇
  2002年   45篇
  2001年   47篇
  2000年   23篇
  1999年   18篇
  1998年   4篇
  1997年   2篇
  1996年   1篇
  1994年   3篇
  1993年   6篇
  1992年   4篇
  1990年   1篇
  1989年   4篇
  1986年   1篇
  1983年   2篇
  1977年   2篇
  1971年   1篇
  1967年   1篇
排序方式: 共有1211条查询结果,搜索用时 15 毫秒
71.
In order to implement reliable marker-assisted selection systems for the restorer-of-fertility locus (Ms) in onions (Allium cepa L.), simple PCR-based codominant markers linked to the Ms locus were developed. Based on the EST probe sequences of previously reported RFLP markers, full-length genomic sequences of the gene encoding putative oligopeptide transporter (OPT) was obtained by RACE. The first intron contained two 108 and 439-bp indel polymorphisms between the two Ms allele-linked OPT alleles. A simple PCR marker for OPT was developed by designing a primer pair on the flanking regions of the 108-bp indel which is created by two tandem repeats. The second simple PCR marker was developed from the EST probe encoding photosystem I subunit O (PsaO). Two 14 and 39-bp tandem repeats were identified from the 5′ upstream sequences of the PsaO-coding gene, which were isolated by genome walking. Three different compositions of these tandem repeats were identified from diverse onion germplasm. A primer set binding to the flanking sequence of these polymorphic repeats was used to amplify three different marker haplotypes. The OPT marker was tightly linked to the Ms locus at a distance of 1.5 cM, but the analysis of the linkage relationship showed little linkage disequilibrium between the marker and the Ms locus. Even so, these simple PCR markers are valuable tools for the marker-assisted selection of segregating individuals in onion F1 hybrid breeding programs.  相似文献   
72.
We analyzed the technical basis for a major global program to reduce disease among the poor. Effective interventions exist against the few diseases which most account for excess mortality among the poor. Achieving high coverage of effective interventions requires a well-functioning health system, as well as overcoming a set of financial and nonfinancial constraints. The annual incremental cost would be between $40 billion and $52 billion by 2015 in 83 low-income and sub-Saharan African countries. Such a program is feasible and would avoid millions of child, maternal, and adult deaths annually in poor countries.  相似文献   
73.
Many animals, including the fruit fly, are sensitive to small differences in ambient temperature. The ability of Drosophila larvae to choose their ideal temperature (18°C) over other comfortable temperatures (19° to 24°C) depends on a thermosensory signaling pathway that includes a heterotrimeric guanine nucleotide-binding protein (G protein), a phospholipase C, and the transient receptor potential TRPA1 channel. We report that mutation of the gene (ninaE) encoding a classical G protein-coupled receptor (GPCR), Drosophila rhodopsin, eliminates thermotactic discrimination in the comfortable temperature range. This role for rhodopsin in thermotaxis toward 18°C was light-independent. Introduction of mouse melanopsin restored normal thermotactic behavior in ninaE mutant larvae. We propose that rhodopsins represent a class of evolutionarily conserved GPCRs that are required for initiating thermosensory signaling cascades.  相似文献   
74.
75.
Because of its requirement for signaling by multiple cytokines, Janus kinase 3 (JAK3) is an excellent target for clinical immunosuppression. We report the development of a specific, orally active inhibitor of JAK3, CP-690,550, that significantly prolonged survival in a murine model of heart transplantation and in cynomolgus monkeys receiving kidney transplants. CP-690,550 treatment was not associated with hypertension, hyperlipidemia, or lymphoproliferative disease. On the basis of these preclinical results, we believe JAK3 blockade by CP-690,550 has potential for therapeutically desirable immunosuppression in human organ transplantation and in other clinical settings.  相似文献   
76.
Columnar defects generated by heavy-ion irradiation are promising structures for pinning magnetic flux lines and enhancing critical currents in superconductors with high transition temperatures. An approach that combines chemical etching and magnetic decoration was used to highlight simultaneously the distributions of columnar defects and magnetic flux lines in Bi(2)Sr(2)CaCu(2)O(8) superconductors. Analyses of images of the columnar defects and flux-line positions provide insight into flux-line pinning by elucidating (i) the occupancy of columnar defects by flux lines, (ii) the nature of topological defects in the flux-line lattice, and (iii) the translational and orientational order in this lattice.  相似文献   
77.
Park HG  Kim SH  Kwon SH  Ju YG  Yang JK  Baek JH  Kim SB  Lee YH 《Science (New York, N.Y.)》2004,305(5689):1444-1447
We report the experimental demonstration of an electrically driven, single-mode, low threshold current (approximately 260 microA) photonic band gap laser operating at room temperature. The electrical current pulse is injected through a sub-micrometer-sized semiconductor wire at the center of the mode with minimal degradation of the quality factor. The actual mode of interest operates in a nondegenerate monopole mode, as evidenced through the comparison of the measurement with the computation based on the actual fabricated structural parameters. As a small step toward a thresholdless laser or a single photon source, this wavelength-size photonic crystal laser may be of interest to photonic crystals, cavity quantum electrodynamics, and quantum information communities.  相似文献   
78.
Zeolites are crystalline nanoporous aluminosilicates widely used in industry. In order for zeolites to find applications as innovative materials, they need to be organized into large two- and three-dimensional (2D and 3D) arrays. We report that uniformly aligned polyurethane films can serve as templates for the synthesis of uniformly aligned 2D and possibly 3D arrays of silicalite-1 crystals, in which the orientations of the crystals are controlled by the nature of the polymers. We propose that the supramolecularly organized organic-inorganic composites that consist of the hydrolyzed organic products and the seed crystals are responsible for this phenomenon.  相似文献   
79.
80.
Carbohydrate digestion by α-glucosidase and subsequent glucose uptake at the brush border are critical for postprandial blood glucose control. Any specific inhibitors are useful as hyperglycemia modulating agents. In this study, it was postulated that an array of active components in mulberry leaf extract (MLE) may provide higher potency in inhibiting intestinal glucose absorption compared to the single component 1-deoxynojirimycin (DNJ), which is recognized as a promising inhibitor of intestinal glucose absorption. Both MLE and DNJ were active in inhibiting α-glucosidase. However, in Caco-2 cells, only MLE showed significant inhibition of 2-deoxyglucose uptake, whereas DNJ was ineffective. For glucose loading, co-administration of MLE resulted in potent inhibitions of glucose responses compared to those by DNJ in Sprague Dawley (SD) rats, but this was not found for maltose loading. These novel findings add evidence that the unabsorbed phytochemicals in MLE compete with glucose for intestinal glucose transporters, but DNJ itself does not. We also evaluated the timing of MLE consumption. By administering MLE for 30 min before glucose loading, the incremental area under the curve (IAUC) was significantly lowered in the rats, as compared to a simultaneously administered group. Similarly, cellular glucose uptake was significantly reduced in Caco-2 cells following pretreatment.  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