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   2258篇
  免费   136篇
  2023年   18篇
  2022年   30篇
  2021年   53篇
  2020年   37篇
  2019年   34篇
  2018年   66篇
  2017年   39篇
  2016年   68篇
  2015年   104篇
  2014年   109篇
  2013年   152篇
  2012年   184篇
  2011年   133篇
  2010年   82篇
  2009年   74篇
  2008年   101篇
  2007年   114篇
  2006年   95篇
  2005年   90篇
  2004年   78篇
  2003年   60篇
  2002年   59篇
  2001年   51篇
  2000年   42篇
  1999年   32篇
  1998年   27篇
  1997年   21篇
  1996年   10篇
  1995年   19篇
  1993年   10篇
  1992年   26篇
  1991年   37篇
  1990年   24篇
  1989年   12篇
  1988年   22篇
  1987年   26篇
  1986年   23篇
  1985年   23篇
  1984年   24篇
  1983年   12篇
  1982年   12篇
  1981年   13篇
  1980年   9篇
  1979年   18篇
  1978年   9篇
  1977年   9篇
  1976年   10篇
  1975年   17篇
  1974年   11篇
  1973年   10篇
排序方式: 共有2394条查询结果,搜索用时 15 毫秒
81.
Oral sub-mucous fibrosis (OSF) is a pathophysiological state of oral cavity or oropharynx having a high chance of conversion to oral squamous cell carcinoma (OSCC). It involves fibrotic transformation of sub-epithelial matrix along with epithelial abnormalities. The present work aims to unveil the mechanistic domain regarding OSF to OSCC conversion exploring the scenario of hypoxia associated oxidative stress, epithelial-mesenchymal transition (EMT), metastasis and stemness acquisition. The study involves histopathological analysis of the diseased condition along with the exploration of oxidative stress status, assessment of mitochondrial condition, immunohistochemical analysis of HIF-1α, E-cadherin, vimentin, ERK, ALDH-1, CD133, Shh, Gli-1 and survivin expressions in the oral epithelial region together with the quantitative approach towards collagen deposition in the sub-epithelial matrix. Oxidative stress was found to be associated with type-II EMT in case of OSF attributing the development of sub-epithelial fibrosis and type-III EMT in case of OSCC favoring malignancy associated metastasis. Moreover, the acquisition of stemness during OSCC can also be correlated with EMT. Alteration of Shh and Gli-1 expression pattern revealed the mechanistic association of hypoxia with the phenotypic plasticity and disease manifestation in case of OSF as well as OSCC. Shh/ Gli-1 signaling can also be correlated with survivin mediated cytoprotective phenomenon under oxidative stress. Overall, the study established the correlative network of hypoxia associated oxidative stress, EMT and manifestation of oral pre-cancerous and cancerous condition in a holistic approach that may throw rays of hope in the therapeutic domain of the concerned diseases.  相似文献   
82.
The present study estimated length–weight relationships (LWRs) for six indigenous fish species (Barilius gatensis, Salmostoma acinaces, S. boopis, Puntius amphibius, Hemibagrus punctatus and Ambassis miops) based on specimens collected from River Cauvery (including estuary) during July 2017–January 2020. The sampling surveys were carried out in three distinct sampling seasons, viz., the pre-monsoon (March–May), the monsoon (July–October) and the post-monsoon (November–February). Majority of the fish specimens dealt in the study were collected from multi-meshed monofilament gill nets (mesh sizes 18, 30, 45, 60, 90, 110, 120 and 150 mm) operated by local fishers. For those sites situated in the protected areas, sampling was carried out by cast nets with prior permission from the local administration and the collected fishes were released back into river after length–weight measurements. The length measurements were noted as total length (TL) measured to the nearest 0.1 cm by using a digital Vernier caliper. A digital balance was used for weight measurements with an accuracy of 0.01 g. The study recorded a new maximum length of 48 cm for H. punctatus. The LWR data generated from the present study are significant for proper assessment of the stock status and their management, if collected together with other essential biological and physical parameters.  相似文献   
83.
Molecular Biology Reports - RUNX1T1 is extensively studied in the context of AML1-RUNX1T1 fusion protein in acute myeloid leukemia. Little is known about the function of RUNX1T1 itself, although...  相似文献   
84.
Molecular Biology Reports - Plant-derived phytochemicals such as flavonoids have been explored to be powerful antioxidants that protect against oxidative stress-related diseases. In the present...  相似文献   
85.
Infection of human cells by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) relies on its binding to a specific receptor and subsequent fusion of the viral and host cell membranes. The fusion peptide (FP), a short peptide segment in the spike protein, plays a central role in the initial penetration of the virus into the host cell membrane, followed by the fusion of the two membranes. Here, we use an array of molecular dynamics simulations that take advantage of the highly mobile membrane mimetic model to investigate the interaction of the SARS-CoV2 FP with a lipid bilayer representing mammalian cellular membranes at an atomic level and to characterize the membrane-bound form of the peptide. Six independent systems were generated by changing the initial positioning and orientation of the FP with respect to the membrane, and each system was simulated in five independent replicas, each for 300 ns. In 73% of the simulations, the FP reaches a stable, membrane-bound configuration, in which the peptide deeply penetrated into the membrane. Clustering of the results reveals three major membrane-binding modes (binding modes 1–3), in which binding mode 1 populates over half of the data points. Taking into account the sequence conservation among the viral FPs and the results of mutagenesis studies establishing the role of specific residues in the helical portion of the FP in membrane association, the significant depth of penetration of the whole peptide, and the dense population of the respective cluster, we propose that the most deeply inserted membrane-bound form (binding mode 1) represents more closely the biologically relevant form. Analysis of FP-lipid interactions shows the involvement of specific residues, previously described as the “fusion-active core residues,” in membrane binding. Taken together, the results shed light on a key step involved in SARS-CoV2 infection, with potential implications in designing novel inhibitors.  相似文献   
86.
87.
We have optimized a procedure for genetic transformation of a major leafy vegetable crop, Amaranthus tricolor L., using epicotyl explant co-cultivation with Agrobacterium tumefaciens. Two disarmed A. tumefaciens strains EHA 105 and LBA 4404, both carrying the binary plasmid p35SGUSINT harboring the neomycin phosphotransferase II gene (nptII) and the β-glucuronidase gene (gus), were evaluated as vector systems. The former displayed a higher transforming efficiency. Several key factors influencing the transformation events were optimized. The highest percentage of transformed shoots (24.24%) was achieved using hand-pricked epicotyl explants, a 10-min infection period, with 100 μM acetosyringone-pretreated Agrobacterium culture corresponding to OD600???0.6 and diluted to 109 cells ml?1, followed by 4 d co-cultivation in the regeneration medium. Putative transformed explants capable of forming shoots were selected on medium supplemented with 75 μg?ml?1 kanamycin, and transient as well as stable glucuronidase expression was determined by histochemical analysis. From a total of 48 selected shoot lines derived from independent transformation events with epicotyl explants co-cultivated with EHA 105, 32 showed positive PCR amplification for both the nptII and gus genes. Germ line transformation and transgene stability were evident in progeny of primary transformed plants (T0). Among T1 seedlings of 12 selected transgenic plant lines, kanamycin-resistant and kanamycin-sensitive seedlings segregated in a ratio typical of the Mendelian monohybrid pattern (3:1) as verified by the chi-square (χ 2) test. Southern hybridization of genomic DNA from kanamycin-resistant T1 transgenic segregants to an nptII probe substantiated stable integration of the transgene. Neomycin phosphotransferase (NPTII) activity was detected in leaf protein extracts of selected T1 transgenic plants, thereby confirming stable expression of the nptII gene.  相似文献   
88.
This paper continues a discussion on the number of pearl mussel species of the genus Margaritifera in northern Europe. A biometric study of 1711 pearl mussel Margaritifera margaritifera shells from 15 rivers in Russia and Latvia (basins of the White and Baltic seas) has been conducted. All the examined samples fall into two groups: the northern group (with the shells more flattened on average, f. margaritifera) and the southern one (with more convex shells, f. elongata); the boundary between these groups is at 63° N. Analysis of intrapopulation variation has shown that the samples contain individuals that correspond to f. margaritifera, f. elongata, and f. borealis. However, any hiatus between these forms is absent in all the samples, and individuals belonging to two intermediate forms are rather frequent. The hypothesis on the species specificity of the shell valve frontal section has not been confirmed based on examination of large shell samples. The pearl mussels inhabiting rivers of Northern Europe belong to a single species, M. margaritifera.  相似文献   
89.
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