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   1198篇
  免费   35篇
  国内免费   2篇
  1235篇
  2024年   2篇
  2023年   3篇
  2022年   7篇
  2021年   21篇
  2020年   8篇
  2019年   16篇
  2018年   10篇
  2017年   21篇
  2016年   21篇
  2015年   38篇
  2014年   45篇
  2013年   77篇
  2012年   73篇
  2011年   84篇
  2010年   49篇
  2009年   37篇
  2008年   74篇
  2007年   63篇
  2006年   80篇
  2005年   67篇
  2004年   77篇
  2003年   87篇
  2002年   76篇
  2001年   11篇
  2000年   10篇
  1999年   6篇
  1998年   18篇
  1997年   12篇
  1996年   16篇
  1995年   17篇
  1994年   9篇
  1993年   7篇
  1992年   9篇
  1991年   7篇
  1990年   4篇
  1989年   5篇
  1988年   10篇
  1987年   8篇
  1986年   3篇
  1985年   4篇
  1984年   5篇
  1983年   6篇
  1982年   8篇
  1981年   4篇
  1980年   2篇
  1979年   3篇
  1978年   2篇
  1977年   3篇
  1974年   3篇
  1972年   3篇
排序方式: 共有1235条查询结果,搜索用时 15 毫秒
21.
“Nagashima-type” palmoplantar keratosis (NPPK) is an autosomal recessive nonsyndromic diffuse palmoplantar keratosis characterized by well-demarcated diffuse hyperkeratosis with redness, expanding on to the dorsal surfaces of the palms and feet and the Achilles tendon area. Hyperkeratosis in NPPK is mild and nonprogressive, differentiating NPPK clinically from Mal de Meleda. We performed whole-exome and/or Sanger sequencing analyses of 13 unrelated NPPK individuals and identified biallelic putative loss-of-function mutations in SERPINB7, which encodes a cytoplasmic member of the serine protease inhibitor superfamily. We identified a major causative mutation of c.796C>T (p.Arg266) as a founder mutation in Japanese and Chinese populations. SERPINB7 was specifically present in the cytoplasm of the stratum granulosum and the stratum corneum (SC) of the epidermis. All of the identified mutants are predicted to cause premature termination upstream of the reactive site, which inhibits the proteases, suggesting a complete loss of the protease inhibitory activity of SERPINB7 in NPPK skin. On exposure of NPPK lesional skin to water, we observed a whitish spongy change in the SC, suggesting enhanced water permeation into the SC due to overactivation of proteases and a resultant loss of integrity of the SC structure. These findings provide an important framework for developing pathogenesis-based therapies for NPPK.  相似文献   
22.
The effects of substituting l-deoxynucleotide for d-deoxynucleotide at duplex termini were evaluated and the terminal substitutions were found to show much less effects on duplex destabilization and to show a similar tendency in base pairing selectivity, compared with internal chiral substitutions.  相似文献   
23.
Many rate-related phenomena occur in food manufacturing processes. This review addresses four of them, all of which are topics that the author has studied in order to design food manufacturing processes that are favorable from the standpoint of food engineering. They include chromatographic separation through continuous separation with a simulated moving adsorber, lipid oxidation kinetics in emulsions and microencapsulated systems, kinetic analysis and extraction in subcritical water, and water migration in pasta.  相似文献   
24.
Male sterility induced by low temperatures (LTs) during the reproductive stage is a major constraint for temperate zone rice. To detect physiological quantitative trait loci (QTLs), we modeled genotypic variation in the physiological processes involved in low temperature spikelet sterility on the basis of anther length (AL), a proxy for microspore and pollen grain number per anther. The model accounted for 83% of the genotypic variation in potential AL at normal temperature and the ability to maintain AL at LT. We tested the model on 208 recombinant inbred lines of cold‐tolerant ‘Tohoku‐PL3’ (PL3) × cold‐sensitive ‘Akihikari’ (AH) for 2 years. QTLs for spikelet fertility (FRT) at LT were detected on chromosomes 5 (QTL for Cold Tolerance at Reproductive stage, qCTR5) and 12 (qCTR12). qCTR12 was annotated with the ability to maintain AL under LTs. qCTR5 was in a region shared with QTLs for culm length and heading date. Genome‐wide expression analysis showed 798 genes differentially expressed in the spikelets between the parents at LTs. Of these, 12 were near qCTR5 and 23 were near qCTR12. Gene expression analysis confirmed two candidate genes for qCTR5 (O‐methyltransferase ZRP4, Os05g0515600; beta‐1,3‐glucanase‐like protein, Os05g0535100) and one for qCTR12 (conserved hypothetical protein, Os12g0550600). Nucleotide polymorphisms (21 deletions, 2 insertions and 10 single nucleotide polymorphisms) in PL3 were found near the candidate conserved hypothetical protein (Os12g0550600) and upstream in PL3, but not in AH. Haplotype analysis revealed that this gene came from ‘Kuchum’. The combination of mapping physiological QTLs with gene expression analysis can be extended to identify other genes for abiotic stress response in cereals.  相似文献   
25.
26.
The heart is divided into four chambers by membranous septa and valves. Although evidence suggests that formation of the membranous septa requires migration of neural crest cells into the developing heart, the functional significance of these neural crest cells in the development of the endocardial cushion, an embryonic tissue that gives rise to the membranous appendages, is largely unknown. Mice defective in the protease region of Meltrin beta/ADAM19 show ventricular septal defects and defects in valve formation. In this study, by expressing Meltrin beta in either endothelial or neural crest cell lineages, we showed that Meltrin beta expressed in neural crest cells but not in endothelial cells was required for formation of the ventricular septum and valves. Although Meltrin beta-deficient neural crest cells migrated into the heart normally, they could not properly fuse the right and left ridges of the cushion tissues in the proximal outflow tract (OT), and this led to defects in the assembly of the OT and AV cushions forming the ventricular septum. These results genetically demonstrated a critical role of cardiac neural crest cells expressing Meltrin beta in triggering fusion of the proximal OT cushions and in formation of the ventricular septum.  相似文献   
27.
28.
The chilling sensitivity of several plant species is closely correlated with the levels of unsaturation of fatty acids in the phosphatidylglycerol (PG) of chloroplast membranes. Plants with a high proportion of unsaturated fatty acids, such as Arabidopsis thaliana, are resistant to chilling, whereas species like squash with only a low proportion are rather sensitive to chilling. The glycerol-3-phosphate O-acyltransferase (GPAT) enzyme of chloroplasts plays an important role in determining the levels of PG fatty acid desaturation.A cDNA for oleate-selective GPAT of Arabidopsis under the control of a maize Ubiquitin promoter was introduced into rice (Oryza sativa L.) using the Agrobacterium-mediated gene transfer method. The levels of unsaturated fatty acids in the phosphatidylglycerol of transformed rice leaves were found to be 28% higher than that of untransformed controls. The net photosynthetic rate of leaves of transformed rice plants was 20% higher than that of the wild type at 17°C. Thus, introduction of cDNA for the Arabidopsis GPAT causes greater unsaturation of fatty acids and confers chilling tolerance of photosynthesis on rice.  相似文献   
29.
30.
Poly(ADP-ribose) polymerase (PARP) may play important roles in nuclear events such as cell cycle, cell proliferation, and maintenance of chromosomal stability. However, the exact biological role played by PARP or how PARP is involved in these cellular functions is still unclear. To elucidate the biological functions of PARP in vivo, we have constructed transgenic flies that overexpress Drosophila PARP in the developing eye primordia. These flies showed mild roughening of the normally smooth ommatidial lattice and tissue polarity disruption caused by improper rotation and chirality of the ommatidia. To clarify how this phenotypical change was induced, here we analyzed transgenic flies overexpressing PARP in the developing eye, embryo, and adult in detail. PARP mRNA level and the phenotype were enhanced in flies carrying more copies of the transgene. Developing eyes from third instar larvae were analyzed by using the neural cell marker to examine the involvement of PARP in cell fate. Morphological disorder of non-neuronal accessory cells was observed in PARP transgenic flies. Interestingly, overexpression of PARP did not interfere with the cell cycle or apoptosis, but it did disrupt the organization of cytoskeletal F-actin, resulting in aberrant cell and tissue morphology. Furthermore, heat-induced PARP expression disrupted organization of cytoskeletal F-actin in embryos and tissue polarity in adult flies. Because these phenotypes closely resembled mutants or transgenic flies of the tissue polarity genes, genetic interaction of PARP with known tissue polarity genes was examined. Transgenic flies expressing either PARP or RhoA GTPase in the eye were crossed, and co-expression of PARP suppressed the effect of RhoA GTPase. Our results indicate that PARP may play a role in cytoskeletal or cytoplasmic events in developmental processes of Drosophila.  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