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   479篇
  免费   32篇
  511篇
  2022年   3篇
  2021年   7篇
  2020年   4篇
  2019年   5篇
  2018年   20篇
  2017年   10篇
  2016年   16篇
  2015年   13篇
  2014年   31篇
  2013年   32篇
  2012年   29篇
  2011年   34篇
  2010年   22篇
  2009年   22篇
  2008年   23篇
  2007年   20篇
  2006年   18篇
  2005年   16篇
  2004年   13篇
  2003年   17篇
  2002年   5篇
  2001年   10篇
  2000年   24篇
  1999年   13篇
  1998年   5篇
  1997年   7篇
  1996年   3篇
  1995年   3篇
  1994年   6篇
  1993年   4篇
  1992年   5篇
  1991年   3篇
  1990年   4篇
  1989年   5篇
  1988年   3篇
  1987年   2篇
  1986年   6篇
  1985年   4篇
  1984年   5篇
  1983年   7篇
  1982年   3篇
  1981年   10篇
  1979年   3篇
  1978年   2篇
  1974年   2篇
  1972年   4篇
  1971年   1篇
  1968年   1篇
  1956年   1篇
  1952年   1篇
排序方式: 共有511条查询结果,搜索用时 15 毫秒
51.
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   
52.
In vertebrates, genome size has been shown to correlate with nuclear and cell sizes, and influences phenotypic features, such as brain complexity. In three different anuran families, advertisement calls of polyploids exhibit longer notes and intervals than diploids, and difference in cellular dimensions have been hypothesized to cause these modifications. We investigated this phenomenon in green toads (Bufo viridis subgroup) of three ploidy levels, in a different call type (release calls) that may evolve independently from advertisement calls, examining 1205 calls, from ten species, subspecies, and hybrid forms. Significant differences between pulse rates of six diploid and four polyploid (3n, 4n) green toad forms across a range of temperatures from 7 to 27 °C were found. Laboratory data supported differences in pulse rates of triploids vs. tetraploids, but failed to reach significance when including field recordings. This study supports the idea that genome size, irrespective of call type, phylogenetic context, and geographical background, might affect call properties in anurans and suggests a common principle governing this relationship. The nuclear‐cell size ratio, affected by genome size, seems the most plausible explanation. However, we cannot rule out hypotheses under which call‐influencing genes from an unexamined diploid ancestral species might also affect call properties in the hybrid‐origin polyploids. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 584–590.  相似文献   
53.
54.
55.
The differential alterations of the spliceosomal UsnRNAs (U1, U2, U4, U5, and U6) were reported to be associated with cellular proliferation and development. The attempt was made in this study to analyze the metabolic pattern of the spliceosomal UsnRNAs during the development of pre-malignant lung lesions induced in experimental mice model system by benzo(a)pyrene (BP) and also to see how tea polyphenols, epigallocatechin gallate (EGCG) and epicatechin gallate (ECG), modulate the metabolism of these UsnRNAs during the lung carcinogenesis. No significant changes in the level of the UsnRNAs were seen in the inflammatory lung lesions at 9th week due to treatment of BP. However, there was significant increase in the level of U1 (∼2.5 fold) and U5 (∼47%) in the hyperplastic lung lesions at 17th week. But in the mild dysplastic lung lesions at 26th week, the level of UsnRNAs did not change significantly. Whereas, in the dysplastic lung lesions at 36th week there was significant increase in the level of the U2 (∼2 fold), U4 (∼2.5 fold) and U5 (∼2 fold). Due to the EGCG and ECG treatment the lung lesions at 9th week appeared normal and in the 17th, 26th, and 36th week it appeared as hyperplasia. The level of the UsnRNAs was significantly low in the lung lesions at 9th week (only U2 and U4 by EGCG), at 17th week (only U1 by EGCG/ECG), at 26th week (U1 by ECG; U2, U4 and U5 by EGCG/ECG) and at 36th week (U1 by ECG, U2 and U4 by EGCG/ECG). Whereas, there was significant increase in the level of U5 (by EGCG/ECG) and U6 (by EGCG only) in the lung lesions at 36th and 26th week respectively. This indicates that the metabolism of the spliceosomal UsnRNAs differentially altered during the development of pre-malignant lung lesions by BP as well as during the modulation of the lung lesions by the tea polyphenols.  相似文献   
56.
Nephrogenic diabetes insipidus (NDI) is an inherited disorder characterized by renal resistance to the antidiuretic effect of arginine vasopressin (AVP), resulting in polyuria, polydipsia, and hypoosmolar urine. In the vast majority of cases, NDI is associated with germ-line mutations in the vasopressin receptor type 2 gene (AVPR2) and in about 8% of the cases with the water channel aquaporin-2 gene (AQP-2) mutations. To date, approximately 277 families with 185 germ-line mutations in the AVPR2 gene have been described worldwide. In the present study, the AVPR2 gene was genotyped in eight unrelated Brazilian kindred with NDI. In five of these NDI families, novel mutations were noted (S54R, I130L, S187R, 219delT, and R230P), whereas three seemingly unrelated probands were found to harbor previously described AVPR2 gene mutations (R106C, R137H, R337X). Additionally a novel polymorphism (V281V) was detected. In conclusion, although NDI is a rare disease, the findings of mutations scattered over the entire coding region of the AVPR2 gene are a valuable model to determine structure function relationship in G-protein-coupled receptor related diseases. Furthermore, our data indicate that in Brazil the spectrum of AVPR2 gene mutations is "family specific".  相似文献   
57.
58.
Human dendritic cells (DCs) stimulated with cytokines and LPS down regulate the expression of proto-oncogene HER-2/neu and GPI linked protein CD24 in breast cancer cell lines. We demonstrated that na?ve DC from human peripheral blood, when stimulated with IFN-γ, IL-15 or LPS reduces the expression of HER-2/neu and CD24, via activation of TNF-α. Pretreatment of tumor cells with STAT3 specific inhibitors or knocking down of STAT3 by SiRNA makes the tumor cell more susceptible to apoptosis and DC mediated inhibition of both CD24 and HER-2/neu. Thus DC could acts as an inhibitory regulator in suppressing oncogene and prevention of metastasis.  相似文献   
59.
The protein kinase C (PKC) family of serine/threonine kinases is an attractive drug target for the treatment of cancer and other diseases. Natural product curcumin is known to interact with PKC isoforms through the C1 domain and modulate PKC activity. The reported results demonstrate that the symmetric curcumin molecule might act as two separate units during its recognition of C1 domains. To understand the importance of the two halves of curcumin in PKC binding and to develop effective PKC regulators, we synthesized a series of alkyl cinnamates (1-8), characterized absorption and fluorescence properties and measured binding affinities with the C1b subdomains of PKC isoforms. The binding parameters of the monomeric compounds and liposomes containing compounds confirmed their interaction with the C1b subdomains of PKCδ and PKCθ. The molecular docking analysis with PKCδ and PKCθ C1b subdomains revealed that the alkyl cinnamates form hydrogen bond with the backbone of the protein at the same binding site as that of diacylglycerol and phorbol esters. The results show that the alkyl cinnamates bind to the activator binding site of PKCs and both methoxy and hydroxyl groups play important roles in the binding process.  相似文献   
60.
Manna P  Sil PC 《Biochimie》2012,94(3):786-797
Vascular inflammation and cardiac dysfunction are the leading causes of mortality and morbidity among the diabetic patients. Type 1 diabetic mellitus (T1DM) is associated with increased cardiovascular complications at an early stage of the disease. The purpose of the present study was to explore whether arjunolic acid (AA) plays any protective role against cardiovascular complications in T1DM and if so, what molecular pathways it utilizes for the mechanism of its protective action. Streptozotocin (STZ) was used to induce T1DM in experimental rats. Alteration in plasma lipid profile and release of membrane bound enzymes like LDH (lactate dehydrogenase) and CK (creatine kinase) established the association of hyperlipidemia and cell membrane disintegration with hyperglycemia. Hyperglycemia altered the levels of oxidative stress related biomarkers, decreased the intracellular NAD and ATP concentrations. Hyperglycemia-induced enhanced levels of VEGF, ICAM-1, MCP-1 and IL-6 in the plasma of STZ treated animals indicate vascular inflammation in T1DM. Histological studies and FACS analysis revealed that hyperglycemia caused cell death mostly via the apoptotic pathway. Investigating molecular mechanism, we observed NF-κB and MAPKs (p38 and ERK1/2) activations, mitochondrial membrane depolarization, cytochrome C release, caspase 3 activation and PARP cleavage in apoptotic cell death in the diabetic cardiac tissue. Treatment with AA (20 mg/kg body weight) reduced hyperglycemia, membrane disintegration, oxidative stress, vascular inflammation and prevented the activation of oxidative stress induced signaling cascades leading to cell death. Results suggest that AA possesses the potential to be a beneficial therapeutic agent in diabetes and its associated cardiac complications.  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