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   483篇
  免费   41篇
  国内免费   1篇
  525篇
  2022年   4篇
  2021年   9篇
  2019年   7篇
  2018年   10篇
  2017年   11篇
  2016年   19篇
  2015年   28篇
  2014年   33篇
  2013年   28篇
  2012年   38篇
  2011年   29篇
  2010年   14篇
  2009年   15篇
  2008年   20篇
  2007年   15篇
  2006年   17篇
  2005年   24篇
  2004年   22篇
  2003年   14篇
  2002年   11篇
  2001年   7篇
  2000年   5篇
  1999年   9篇
  1998年   6篇
  1997年   9篇
  1996年   6篇
  1995年   2篇
  1994年   3篇
  1993年   2篇
  1992年   5篇
  1991年   3篇
  1989年   5篇
  1987年   4篇
  1986年   5篇
  1985年   4篇
  1984年   8篇
  1983年   8篇
  1982年   3篇
  1981年   4篇
  1980年   4篇
  1979年   3篇
  1978年   12篇
  1977年   3篇
  1976年   5篇
  1975年   8篇
  1974年   4篇
  1973年   2篇
  1966年   2篇
  1965年   3篇
  1959年   2篇
排序方式: 共有525条查询结果,搜索用时 0 毫秒
401.
402.
A new cell culture supplement, platelet lysate, was evaluated with reference to fetal bovine serum (FBS), an established industrial medium for animal cell culture. Chemical and bacteriological profiles were conducted including the presence of platelet-derived growth factor (PDGF). PDGF was detected in the platelet lysate but it was not present in FBS. The platelet lysate medium demonstrated lack of microorganisms, mycoplasma and endotoxins. The platelet lysate was investigated in culture studies (cell growth, viability and product formation) towards a number of target cells including myelomas, hybridomas, hepatocytes, fibroblasts and epithelial cells. In general the platelet lysate medium supported cell growth and maintained viabilities comparable or superior to fetal bovine serum. Productivity studies of antibodies (hybridomas) and transferrin (hepatocytes) showed similar or enhanced production in platelet-derived medium in comparison with FBS. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
403.
PCR detection methods are useful in studies of organisms not amenable to culture. Inhibitors in environmental samples can interfere with such assays. We describe a magnetic bead DNA capture protocol that removes inhibitors from outdoor air samples, maintaining the sensitivity of a 16S Pneumocystis carinii mitochondrial rRNA gene-based PCR.  相似文献   
404.
This paper reports the most cost-effective policy options to support and improve breast cancer control in Costa Rica and Mexico. Total costs and effects of breast cancer interventions were estimated using the health care perspective and WHO-CHOICE methodology. Effects were measured in disability-adjusted life years (DALYs) averted. Costs were assessed in 2009 United States Dollars (US$). To the extent available, analyses were based on locally obtained data. In Costa Rica, the current strategy of treating breast cancer in stages I to IV at a 80% coverage level seems to be the most cost-effective with an incremental cost-effectiveness ratio (ICER) of US$4,739 per DALY averted. At a coverage level of 95%, biennial clinical breast examination (CBE) screening could improve Costa Rica''s population health twofold, and can still be considered very cost-effective (ICER US$5,964/DALY). For Mexico, our results indicate that at 95% coverage a mass-media awareness raising program (MAR) could be the most cost-effective (ICER US$5,021/DALY). If more resources are available in Mexico, biennial mammography screening for women 50–70 yrs (ICER US$12,718/DALY), adding trastuzumab (ICER US$13,994/DALY) or screening women 40–70 yrs biennially plus trastuzumab (ICER US$17,115/DALY) are less cost-effective options. We recommend both Costa Rica and Mexico to engage in MAR, CBE or mammography screening programs, depending on their budget. The results of this study should be interpreted with caution however, as the evidence on the intervention effectiveness is uncertain. Also, these programs require several organizational, budgetary and human resources, and the accessibility of breast cancer diagnostic, referral, treatment and palliative care facilities should be improved simultaneously. A gradual implementation of early detection programs should give the respective Ministries of Health the time to negotiate the required budget, train the required human resources and understand possible socioeconomic barriers.  相似文献   
405.
Glycoproteins derived from intestinal mucus were isolated by phenol-water extraction of feces from germ-free rats. The water-soluble glycoproteins were subjected to alkaline-borohydride degradation, and three different oligosaccharide alditols were isolated. The structures of these were determined by using methylation analysis and n.m.r. spectroscopy as the principal methods. One disaccharide alditol and one trisaccharide alditol were characterised as β-D-GlcNAcp-(1→3)-D-GalNAcol and α-L-Fucp-(1→2)-β-D-Galp-(1→3)-D-GalNAcol. The third oligosaccharide alditol was a blood-group A-active tetrasaccharide alditol for which the structure α-D-GalNAcp-(1→3)-[α-L-Fucp-(1→2)]-β-D-Galp-(1→3)-D-GalNAcol is proposed.  相似文献   
406.
We report that CCR3 is not expressed on freshly isolated peripheral and germinal B cells, but is up-regulated after stimulation with IL-2 and IL-4 (approximately 98% CCR3(+)). Ligation of CCR3 by eotaxin/chemokine ligand (CCL) 11 induces apoptosis in IL-2- and IL-4-stimulated primary CD19(+) (approximately 40% apoptotic cells) B cell cultures as well as B cell lines, but has no effect on chemotaxis or cell adhesion. Freshly isolated B cells express low levels of CD95 and CD95 ligand (CD95L) (19 and 21%, respectively). Expression is up-regulated on culture in the presence of a combination of IL-2, IL-4, and eotaxin/CCL11 (88% CD95 and 84% CD95L). We therefore propose that ligation of such newly induced CCR3 on peripheral and germinal B cells by eotaxin/CCL11 leads to the enhanced levels of CD95 and CD95L expression. Ligation of CD95 by its CD95L expressed on neigboring B cells triggers relevant death signaling pathways, which include an increase in levels of Bcl-2 expression, its functional activity, and the release of cytochrome c from the mitochondria into the cytosol. These events initiate a cascade of enzymatic processes of the caspase family, culminating in programmed cell death. Interaction between CCR3 and eotaxin/CCL11 may, besides promoting allergic reactions, drive activated B cells to apoptosis, thereby reducing levels of Ig production, including IgE, and consequently limit the development of the humoral immune response. The apoptotic action of eotaxin/CCL11 suggests a therapeutic modality in the treatment of B cell lymphoma.  相似文献   
407.
High-value oils from plants   总被引:5,自引:3,他引:5  
The seed oils of domesticated oilseed crops are major agricultural commodities that are used primarily for nutritional applications, but in recent years there has been increasing use of these oils for production of biofuels and chemical feedstocks. This is being driven in part by the rapidly rising costs of petroleum, increased concern about the environmental impact of using fossil oil, and the need to develop renewable domestic sources of fuel and industrial raw materials. There is also a need to develop sustainable sources of nutritionally important fatty acids such as those that are typically derived from fish oil. Plant oils can provide renewable sources of high-value fatty acids for both the chemical and health-related industries. The value and application of an oil are determined largely by its fatty acid composition, and while most vegetable oils contain just five basic fatty acid structures, there is a rich diversity of fatty acids present in nature, many of which have potential usage in industry. In this review, we describe several areas where plant oils can have a significant impact on the emerging bioeconomy and the types of fatty acids that are required in these various applications. We also outline the current understanding of the underlying biochemical and molecular mechanisms of seed oil production, and the challenges and potential in translating this knowledge into the rational design and engineering of crop plants to produce high-value oils in plant seeds.  相似文献   
408.
Currently, an assay based on fatal sensitization of mice to histamine challenge is widely used for testing absence of residual pertussis toxin in acellular pertussis containing vaccines. For replacement of this lethal end-point assay, an alternative method based on body temperature measurement in mice has been presented, and in this study the specificity and detection limit of a dermal temperature-based assay were assessed. Test preparations containing pertussis toxin were prepared in aluminum-adjuvanted pertussis toxoid vaccine and injected intraperitoneally in histamine sensitive mice. Later the mice were challenged with histamine and the pertussis toxin-induced decrease in dermal temperature recorded. By comparison of mice treated with pertussis toxoid vaccine spiked with pertussis toxin with mice treated with pertussis toxoid vaccine alone, the assay gave a response that specifically could detect presence of pertussis toxin. The acellular pertussis containing vaccine did not interfere with the pertussis toxin-induced temperature response recorded. In tests for presence of pertussis toxin in the pertussis vaccine preparation, the detection limit of the assay was estimated to approximately 5 ng pertussis toxin per human dose of pertussis toxoid. The dermal temperature-based assay was found to be a valid method to be applied in routine quality control of vaccines.  相似文献   
409.
Tumor development and progression are influenced by macrophages of the surrounding microenvironment. To investigate the influences of an inflammatory tumor microenvironment on the growth and metastasis of prostate cancer, the present study used a co-culture model of prostate cancer (PCa) cells with tumor-associated macrophage (TAM)-conditioned medium (MCM). MCM promoted PCa cell (LNCaP, DU145 and PC-3) growth, and a xenograft model in nude mice consistently demonstrated that MCM could promote tumor growth. MCM also stimulated migration and invasion in vitro. Somatostatin derivate (smsDX) significantly attenuated the TAM-stimulated proliferation, migration and invasion of prostate cancer. Immunohistochemistry revealed that NF-κB was over-expressed in PCa and BPH with chronic inflammatory tissue specimens and was positively correlated with macrophage infiltration. Further investigation into the underlying mechanism revealed that NF-κB played an important role in macrophage infiltration. SmsDX inhibited the paracrine loop between TAM and PCa cells and may represent a potential therapeutic agent for PCa.  相似文献   
410.
Although it is an uncommon distribution in seed plants, many bryophytes occur around the Pacific Rim of north‐western North America and eastern Asia. This work focuses on a clade of peatmosses (Sphagnum) that is distributed around the Pacific Rim region, with some individual species found across the total range. The goals were to infer divergent phylogenetic relationships among haploid species in the clade, assess parentage of allopolyploid taxa, and evaluate alternative hypotheses about inter‐ and intraspecific geographical range evolution. Multiple data sets and analyses resolved an ‘Alaska’ clade, distributed across western North America, eastern China and Japan, and an ‘Asia’ clade that includes western Chinese, Thai, Korean, eastern Chinese and Japanese lineages. Allopolyploids have arisen at least four times in the Pacific Rim clade of Sphagnum subgen. Subsecunda; it appears that all allopolyploid origins involved closely related haploid parental taxa. Biogeographical inferences were impacted by topological uncertainty and especially by the biogeographical model utilized to reconstruct ancestral areas. Most analyses converge on the conclusion that the ancestor to this clade of Pacific Rim Sphagnum species was widespread from Alaska south to eastern Asia, but a northern origin for the Alaska subclade was supported by one of the two biogeographical models we employed, under which it was robust to phylogenetic uncertainty.  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