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   476篇
  免费   34篇
  2023年   3篇
  2022年   3篇
  2021年   4篇
  2020年   3篇
  2019年   6篇
  2018年   5篇
  2017年   9篇
  2016年   6篇
  2015年   20篇
  2014年   13篇
  2013年   24篇
  2012年   34篇
  2011年   32篇
  2010年   10篇
  2009年   12篇
  2008年   24篇
  2007年   28篇
  2006年   27篇
  2005年   23篇
  2004年   18篇
  2003年   20篇
  2002年   27篇
  2001年   8篇
  2000年   7篇
  1999年   11篇
  1998年   9篇
  1997年   5篇
  1996年   7篇
  1995年   7篇
  1994年   4篇
  1993年   7篇
  1992年   6篇
  1991年   7篇
  1990年   3篇
  1989年   8篇
  1988年   5篇
  1987年   6篇
  1986年   4篇
  1985年   10篇
  1984年   4篇
  1983年   4篇
  1982年   8篇
  1981年   4篇
  1980年   4篇
  1979年   4篇
  1978年   3篇
  1976年   3篇
  1975年   3篇
  1974年   3篇
  1973年   3篇
排序方式: 共有510条查询结果,搜索用时 15 毫秒
81.
Cucurbita foetidissima (buffalo gourd), a semiaridland plant native to the Greater Southwest, has been utilized by humans for thousands of years, primarily as food and medicine. In recent years, buffalo gourd has been the focus of an important domestication program at the University of Arizona. This research has led to 2 main cultural systems, an annual mode for root-starch production, and a perennial mode primarily for seed-oil production. In our paper, over 75 references are analyzed to evaluate the potential of buffalo gourd as an energy, chemical-products, and food crop. Priorities are suggested, including investigation of buffalo gourd as a novel crop for New Mexico's developing fuel ethanol industry.  相似文献   
82.
83.
84.
Abstract. Coding sequences (5,334 nt total) from elongation factor-1α, elongation factor-2, and the largest subunit of RNA polymerase II were determined for 6 species of Tardigrada, 2 of Arthropoda, and 2 of Onychophora. Parsimony and likelihood analyses of nucleotides and amino acids yielded strong support for Tardigrada and all internal nodes (i.e., 100% bootstrap support for Tardigrada, Eutardigrada, Parachela, Hypsibiidae, and Macrobiotidae). Results are in agreement with morphology and an earlier molecular study based on analysis of 18S ribosomal sequences. Divergence times have been estimated from amino acid sequence data using an empirical Bayesian statistical approach, which does not assume a strict molecular clock. Divergence time estimates are pre-Vendian for Tardigrada/Arthropoda, Vendian or earlier for Eutardigrada/Heterotardigrada, Silurian to Ordovician for Parachela/Apochela, Permian to Carboniferous for Hypsibiidae and Macrobiotidae, and Mesozoic for Isohypsibius/Thulinia (both within Hypsibiidae) and Macrobiotus/Richtersius (both within Macrobiotidae).  相似文献   
85.
Fibroblast lines derived from normal skin and spontaneous or experimentally induced fibropapillomas of green turtles (Chelonia mydas) were established and propagated in medium composed of a combination of Dulbecco's minimal essential with F12 medium plus 10% fetal bovine serum at 30 degrees C. Fibropapilloma-derived fibroblasts were indistinguishable from normal skin fibroblasts in vitro. Tumor lines did not exhibit loss of contact inhibition, anchorage independence, or reduced serum requirements. Inoculation of primary and early-passage tumor cells into the medial margin of the pinna of C57BL/6J-nu/nu, C.B17-scid/scid, or NOD-scid/scid mice, however, resulted in fibroma formation, whereas inoculation of normal skin fibroblasts did not. Tumor-derived cells inoculated into the flanks of mice did not form tumors. The turtle origin of fibroblasts in tumors from mouse ears was confirmed by immunohistochemical and karyotype analysis. Fibroblast lines that were established from mouse ear fibromas had the normal karyotype (modal 2N = 55) of C. mydas. The cooler anatomic sites (ears) of immunodeficient mice are useful for confirming the tumorigenic (transformed) phenotype of green turtle fibropapillomatosis-derived fibroblasts. This mouse ear tumorigenicity test should facilitate studies of mechanisms of cellular transformation in green turtle fibropapillomatosis and other neoplastic diseases of poikilothermic vertebrates.  相似文献   
86.
Role of Organotellurium Species in Tellurium Neuropathy   总被引:3,自引:0,他引:3  
Exposure of weanling rats to a diet containing 1% elemental tellurium causes segmental demyelination of peripheral nerve, and an inhibition of squalene epoxidase. This inhibition is thought to be the mechanism of action leading to demyelination. Tellurite appears to be the active inhibitory species in a cell-free system but the active species in vivo is unknown. We examined potassium tellurite (K2TeO3) and three organotellurium compounds for their ability to inhibit squalene epoxidase in Schwann cell cultures and to induce demyelination in weanling rats. K2TeO3 had no effect on squalene epoxidase activity in cultured Schwann cells and caused no demyelination in vivo. All three organotellurium compounds caused inhibition of squalene epoxidase in vitro and caused demyelination in vivo. (CH3)2TeCl2 was the most potent of these compounds and its neuropathy most resembled that caused by elemental tellurium. These data are consistent with the hypothesis that tellurium-induced demyelination is a result of squalene epoxidase inhibition and suggest that a dimethyltelluronium compound may be the neurotoxic species presented to Schwann cells in vivo.  相似文献   
87.
The distribution of interlocus genotypic combinations was examined in Mytilus edulis for interdependence between two loci synthesizing functionally related isoenzymes. There is significant dependence between the Leucine Aminopeptidase and Aminopeptidase loci, which we attribute to epistasis, since the magnitude of dependency varies with age. Furthermore, dependency varies in magnitude with position in the intertidal zone from which samples were taken, suggesting that epistasis is a function of the combination of certain non-homologous alleles as well as of the environmental circumstance in which the combinations occur.  相似文献   
88.
The host-parasite interactions of Brugia malayi in mice are complex and multifactorial. In order to study the role of T cells in early B. malayi development, we infected TCRalpha(null) mice, which retain a population of CD4+ TCRbeta+ cells and TCRbeta(null) mice, which lack all TCRalphabeta(+) T cells. TCRalpha(null) mice were permissive to L4 larval and adult worm development but TCRbeta(null) mice were not. Depletion of the CD4(+) T cells in the former abrogated the permissive phenotype. It appears that the CD4(+) TCRbeta(+) T cells that have been described in TCRalpha(null) mice may facilitate early B. malayi development. These data are similar to our earlier demonstration of the role of NK cells in facilitating worm growth in SCID mice.  相似文献   
89.
Since the osteopetrotic (op/op) mouse was demonstrated to have a mutation within the coding region of the CSF-1 gene itself, it serves as a model for investigating the differentiation mechanism of macrophage populations in the absence of functional CSF-1. The op/op mice were severely monocytopenic and showed marked reduction and abnormal differentiation of tissue macrophages. Osteoclasts as well as marginal metallophilic macrophages and marginal zone macrophages in the spleen were absent. Most of the tissue macrophages were reduced in number and ultrastructurally immature. However, the degree of reduction in numbers of macrophages in the mutant mice was variable among tissues, suggesting that the heterogeneity of macrophages was generated by their different dependency on CSF-1. After daily CSF-1 injection, the numbers of monocytes, tissue macrophages, and osteoclasts were remarkably increased, and the macrophages showed morphological maturation. However, the numbers of macrophages in the ovary, uterus, and synovial membrane were not increased. In the bone marrow, macrophage precursors detected by monoclonal antibody ER-MP58 proliferated and differentiated into preosteoclasts and osteoclasts. In the spleen, marginal metallophilic macrophages and marginal zone macrophages developed slowly. In this manner, CSF-1 plays an important role in the development, proliferation, and differentiation of certain tissue macrophage populations and osteoclasts. In the op/op mice, Kupffer cells proliferated, transformed into epithelioid cells and multinucleated giant cells, and participated in glucan-induced granuloma formation. In CSF-1-treated op/op mice, the process of granuloma formation was similar to that in normal littermates due to increased monocytopoiesis and monocyte influx into the granulomas. These results indicate that CSF-1 is a potent inducer of the development and differentiation of CSF-1-dependent monocyte/macrophages, and that CSF-1-independent macrophages also play an important role in granuloma formation. Mol Reprod Dev 46:85–91, 1997. © 1997 Wiley Liss, Inc.  相似文献   
90.
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