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   439篇
  免费   16篇
  2022年   2篇
  2021年   8篇
  2020年   4篇
  2019年   11篇
  2018年   9篇
  2017年   10篇
  2016年   4篇
  2015年   13篇
  2014年   20篇
  2013年   30篇
  2012年   35篇
  2011年   37篇
  2010年   20篇
  2009年   14篇
  2008年   24篇
  2007年   20篇
  2006年   17篇
  2005年   35篇
  2004年   9篇
  2003年   25篇
  2002年   12篇
  2001年   5篇
  2000年   5篇
  1999年   5篇
  1998年   5篇
  1997年   3篇
  1996年   8篇
  1995年   4篇
  1994年   9篇
  1992年   3篇
  1990年   9篇
  1989年   2篇
  1988年   1篇
  1987年   1篇
  1986年   5篇
  1985年   2篇
  1984年   4篇
  1983年   2篇
  1982年   3篇
  1981年   4篇
  1980年   2篇
  1979年   1篇
  1978年   1篇
  1977年   1篇
  1976年   2篇
  1974年   2篇
  1973年   1篇
  1971年   1篇
  1970年   1篇
  1968年   1篇
排序方式: 共有455条查询结果,搜索用时 15 毫秒
21.
22.
Objective: We investigated occupational risk of multiple myeloma (MM) in a pooled analysis of five international case–control studies. Methods: We calculated the odds ratio and its 95% confidence interval for selected occupations with unconditional regression analysis in 1959 MM cases and 6192 controls, by pooling study-specific risks using random-effects meta-analysis. Exposure to organic solvents was assessed with a job-exposure matrix (JEM). Results: Gardeners and nursery workers combined, most likely exposed to pesticides, showed a 50% increase in risk (OR = 1.50, 95% CI 0.9–2.3), while other farming jobs did not. Metal processors (OR = 1.55, 95% CI 0.9–2.3), female cleaners (OR = 1.32, 95% CI 1.0–1.8), and high level exposure to organic solvents (OR = 1.38, 95% CI 0.96–1.8) also showed moderately increased risks. Conclusions: Additional case–control studies of MM aetiology are warranted to further investigate the nature of the repeatedly reported increase in MM risk in several occupational groups.  相似文献   
23.
Extremophiles - The extremophile green alga Coccomyxa melkonianii SCCA 048 was investigated to evaluate its ability to grow in culture media with different pH. Specifically, Coccomyxa melkonianii...  相似文献   
24.
Several clinical studies indicated that the daily use of aspirin or acetylsalicylic acid reduces the cancer risk via cyclooxygenases (Cox-1 and Cox-2) inhibition. In addition, aspirin-induced Cox-dependent and -independent antitumor effects have also been described. Here we report, for the first time, that aspirin treatment of human glioblastoma cancer (GBM) stem cells, a small population responsible for tumor progression and recurrence, is associated with reduced cell proliferation and motility. Aspirin did not interfere with cell viability but induced cell-cycle arrest. Exogenous prostaglandin E2 significantly increased cell proliferation but did not abrogate the aspirin-mediated growth inhibition, suggesting a Cox-independent mechanism. These effects appear to be mediated by the increase of p21 waf1 and p27 Kip1, associated with a reduction of Cyclin D1 and Rb1 protein phosphorylation, and involve the downregulation of key molecules responsible for tumor development, that is, Notch1, Sox2, Stat3, and Survivin. Our results support a possible role of aspirin as adjunctive therapy in the clinical management of GBM patients.  相似文献   
25.
Conifers possess chemical and anatomical defences against tree‐killing bark beetles that feed in their phloem. Resins accumulating at attack sites can delay and entomb beetles while toxins reach lethal levels. Trees with high concentrations of metabolites active against bark beetle‐microbial complexes, and more extensive resin ducts, achieve greater survival. It is unknown if and how conifers integrate chemical and anatomical components of defence or how these capabilities vary with historical exposure. We compared linkages between phloem chemistry and tree ring anatomy of two mountain pine beetle hosts. Lodgepole pine, a mid‐elevation species, has had extensive, continual contact with this herbivore, whereas high‐elevation whitebark pines have historically had intermittent exposure that is increasing with warming climate. Lodgepole pine had more and larger resin ducts. In both species, anatomical defences were positively related to tree growth and nutrients. Within‐tree constitutive and induced concentrations of compounds bioactive against bark beetles and symbionts were largely unrelated to resin duct abundance and size. Fewer anatomical defences in the semi‐naïve compared with the continually exposed host concurs with directional differences in chemical defences. Partially uncoupling chemical and morphological antiherbivore traits may enable trees to confront beetles with more diverse defence permutations that interact to resist attack.  相似文献   
26.
A set of recombinant inbred lines (RIL) derived from a cross between the cultivar Messapia of durum wheat (Triticum turgidum var. durum) and the accession MG4343 of T. turgidum var. dicoccoides was analysed to increase the number of assigned markers and the resolution of the previously constructed genetic linkage map. An updated map of the durum wheat genome consisting of 458 loci was constructed. These loci include 261 Restriction Fragment Length Polymorphisms (RFLPs), 91 microsatellites (Simple Sequence Repeats, SSRs), 87 Amplified Fragment Length Polymorphisms (AFLPs), two ribosomal genes, and nine biochemical (seven seed storage proteins and two isozymes) and eight morphological markers. The loci were mapped on all 14 chromosomes of the A and B genomes, and covered a total distance of 3038.4 cM with an average distance of 6.7 cM between adjacent markers. The molecular markers were evenly distributed between the A and the B genomes (240 and 218 markers, respectively). An additional forty loci (8.8%) could not be assigned to a specific linkage group. A fraction (16.4%) of the markers significantly deviated from the expected Mendelian ratios; clusters of loci showing distorted segregation were found on the 1B, 2A, 2B, 3A, 4A, 7A and 7B chromosomes. The genetic lengths of the chromosomes range from 148.8 cM (chromosome 6B) to 318.0 cM (chromosome 2B) and approximately concur with their physical lengths. Chromosome 2B has the largest number of markers (47), while the chromosomes with the fewest markers are 3A and 6B (23). There are two gaps larger than 40 cM on chromosomes 2A and 3B. The durum wheat map was compared with the published maps of bread and durum wheats; the order of most common RFLP and SSR markers on the 14 chromosomes of the A and B genomes were nearly identical. A core-map can be extracted from the high-density Messapia x dicoccoides map and a subset of uniformly distributed markers can be used to detect and map quantitative trait loci.  相似文献   
27.
The solution behaviour of some novel organogold(III) compounds was investigated, and their cytotoxic properties evaluated against a few human tumour cell lines (A2780/S, A2780/R, MCF7, HT29 and A549). Specifically, the following compounds were considered: [Au(bipy(dmb)-H)(2,6-xylidine-H)][PF(6)] (AuXyl) and [Au(bipy(dmb)-H)(p-toluidine-H)][PF(6)] (AuTol) (in which bipy(dmb)=6-(1,1-dimethylbenzyl)-2,2'-bipyridine), [Au(py(dmb)-H)(AcO)(2)] (AuPyAcO) (in which py(dmb)=2-(1,1-dimethylbenzyl)-pyridine) and [Au(pz(Ph)-H)Cl(3)]K (AuPzCl) (in which pz(Ph)=1-phenylpyrazole). The solution chemistry of these compounds, under physiological-like conditions, was investigated through UV-vis absorption and (1)H NMR spectroscopies. Significant cytotoxic effects in vitro were observed in selected cases.  相似文献   
28.
Cigarette smoke is a mixture of chemicals having direct and/or indirect toxic effects on different lung cells. We investigated the effect of cigarette smoke on human lung fibroblasts (HFL-1) oxidation and apoptosis. Cells were exposed to various concentrations (1, 5, and 10%) of cigarette smoke extract (CSE) for 3 h, and oxidative stress and apoptosis were assessed by fluorescence-activated cell sorting and confocal laser fluorescence microscopy. Both oxidative stress and apoptosis exhibited a dose-response relationship with CSE concentrations. Lung fibroblasts also showed marked DNA fragmentation at the Comet assay after exposure to 10% CSE. Coincubation of HLF-1 cells with N-acetylcysteine (1 mM) during CSE exposure significantly reduced oxidative stress, apoptosis, and DNA fragmentation, whereas preincubation (3 h) with the glutathione-depleting agent buthionine sulfoximine (125 microM) produced a significant increase of oxidative stress. Cigarette smoke is a potent source of oxidative stress, DNA damage, and apoptosis for HFL-1 cells, and we speculate that this could contribute to the development of pulmonary emphysema in the lungs of smokers.  相似文献   
29.
30.
Olianas MC  Onali P 《Life sciences》2003,72(25):2905-2914
The pseudopeptide [Nphe(1)]N/OFQ(1-13)NH(2) (Nphe) has been shown to act as a pure, selective and competitive antagonist of nociceptin/orphanin FQ (N/OFQ) receptors in different tissues. However, Nphe displayed a highly variable potency, with pA(2) values ranging from 5.96 to 8.45. In the present study, we show that sodium ions and GTP markedly affect the potency of Nphe in blocking N/OFQ receptors coupled to cyclic AMP inhibition in different cellular systems. In intact N1E-115 neuroblastoma cells, the pA(2) value of Nphe increased from 7.13 to 8.02 when the extracellular sodium concentration was reduced from 138 to 2.5 mM. When N/OFQ inhibition of adenylyl cyclase activity was assayed in cell membranes, 100 mM NaCl decreased the pK(i) value of Nphe from 8.38 to 7.32, but increased that of the nonpeptide N/OFQ receptor antagonist CompB from 8.61 to 8.92. Similar effects of sodium ions on the potencies of Nphe and CompB were observed when the compounds were used to antagonize the N/OFQ inhibition of adenylyl cyclase activity in membranes of the external plexiform layer of the rat olfactory bulb. In the same assay, the increase of GTP concentration from 0.1 to 200 micro M decreased Nphe potency by 8-fold. These data demonstrate that sodium ions and GTP affect the potency of Nphe in a manner similar to that of agonists but not of pure antagonists and suggest that these factors may contribute to the reported variability of Nphe affinity constant.  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