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   401篇
  免费   31篇
  2023年   5篇
  2022年   12篇
  2021年   21篇
  2020年   11篇
  2019年   19篇
  2018年   23篇
  2017年   13篇
  2016年   12篇
  2015年   18篇
  2014年   24篇
  2013年   37篇
  2012年   35篇
  2011年   16篇
  2010年   12篇
  2009年   7篇
  2008年   20篇
  2007年   13篇
  2006年   13篇
  2005年   13篇
  2004年   5篇
  2003年   12篇
  2002年   9篇
  2001年   13篇
  2000年   13篇
  1999年   5篇
  1998年   1篇
  1995年   1篇
  1994年   1篇
  1993年   4篇
  1992年   3篇
  1991年   3篇
  1990年   10篇
  1988年   5篇
  1987年   3篇
  1986年   1篇
  1985年   3篇
  1984年   1篇
  1983年   1篇
  1982年   2篇
  1980年   1篇
  1979年   1篇
  1977年   1篇
  1974年   5篇
  1973年   1篇
  1971年   1篇
  1969年   1篇
  1967年   1篇
排序方式: 共有432条查询结果,搜索用时 406 毫秒
71.
Microorganisms play integral roles in the cycling of carbon (C) and nitrogen (N) in recirculating aquaculture systems (RAS) for fish and shellfish production. We quantified the pathways of shrimp fecal bacterial activities and their role in C- and N-flux partitioning relevant to culturing Pacific white shrimp, Penaeus (Litopenaeus) vannamei, in RAS. Freshly produced feces from P. vannamei contained 0.6-7 × 10(10) bacteria g(-1) dry wt belonging to Bacteroidetes (7%), Alphaproteobacteria (4%), and, within the Gammaproteobacteria, almost exclusively to the genus Vibrio (61%). Because of partial disintegration of the feces (up to 27% within 12 h), the experimental seawater became inoculated with fecal bacteria. Bacteria grew rapidly in the feces and in the seawater, and exhibited high levels of aminopeptidase, chitinase, chitobiase, alkaline phosphatase, α- and β-glucosidase, and lipase activities. Moreover, fecal bacteria enriched the protein content of the feces within 12 h, potentially enriching the feces for the coprophagous shrimp. The bacterial turnover time was much faster in feces (1-10 h) than in mature RAS water (350 h). Thus, shrimp fecal bacteria not only inoculate RAS water but also contribute to bacterial abundance and productivity, and regulate system processes important for shrimp health.  相似文献   
72.
Present study investigates relationships between total and bioaccessibility of trace elements (Cd, Co, Cr, Cu, Mn, NI, Pb, V, and Zn) concentrations in sediment and their bioaccumulation in species in Shadegan wetland in southwest of Iran. Bioavailability factor (BAF) and translocation factor (TF) were calculated in plants and trophic transfer factor (TTF) was determined in bird species. For this purpose, sampling of sediments, aquatic plants including Phragmites australis, Typha australis, Scripus maritimus and two bird species encircling Porphyrio porphyrio and globally threatened Marmaronetta angustirostris were carried out during winter 2009. Result of chemical analysis show that bioaccessibility concentrations of Mn (8.31 mg/kg), V (1.33 mg/kg), and Pb (1.03 mg/kg) are higher than other metals. The uptake trend of trace elements in plant decreases as root > stem > leaf. Accumulation levels of trace elements in different tissues of P. porphyrio and M. angustirostris are almost identical and considerable. Accumulation and toxicity of Cd in birds is more than plants. In addition, BAF of V, Pb, and Cr indicates high accumulation by plants and great pollution rate in the area of study. In S. maritimus TF for Mn, Cu, Pb, and V are high whereas in T. australis, Cu and Pb posses the highest TF. Also Cr, Co, Mn, Ni, and Zn have higher TF from stem to leaf than root to stem in P. australis. Finally, TTFs were compared in various bird species.  相似文献   
73.
Thiosemicarbazones (1-7) and their palladium(II) complexes (1a-7a) of the type [Pd(TSCN)Cl(2)] (where TSCN=thiosemicarbazone) were prepared from 5-nitro thiophene-2-carboxaldehyde and [Pd(DMSO)(2)Cl(2)], respectively. Coordination via the thionic sulphur and the azomethine nitrogen atom of the thiosemicarbazones to the metal ion were confirmed by spectral data. These compounds were screened in vitro against (HK-9) strain of Entamoeba histolytica possess amoebicidal properties. Enhancement of antiamoebic activity resulted due to the introduction of palladium metal in the thiosemicarbazone moiety. The most promising of the group tested are [Pd(5-N-2-TCA-COTSCN)Cl(2)] and [Pd(5-N-2-TCA-AdmTSCN)Cl(2)] comparable to that of metronidazole.  相似文献   
74.
The Pyrus species exhibit the so-called S-RNase-based gametophytic self-incompatibility system, which is considered to be the most widespread self-incompatibility system among flowering plants. In this study, 57 Iranian pear (Pyrus communis L.) domestic cultivars and wild genotypes, plus 21 European pear cultivars used as references, were genotyped adopting a PCR-based genotyping assay using consensus and allele-specific primers. The results revealed traces of significant genetic contribution in the Iranian traditional varieties and genotypes from other Pyrus species; the genetic contribution of Japanese pear clearly emerged with the detection of some Pyrus pyrifolia S-RNase alleles. Moreover, our results highlighted the presence of three new S-RNase alleles (named S126, S127, and S128) that were not previously identified in P. communis, possibly introduced in the germplasm of cultivated pear through gene transfer from other cultivated or wild species.  相似文献   
75.
BACKGROUNDImportance of androgen receptor (AR) as an independent prognostic marker in Pakistani women with breast cancer (BCa) remains unexplored. Our aim was to identify the expression and potential prognostic value of AR, its upstream regulator (pAkt) and target gene (pPTEN) in invasive BCa.METHODSThis study used a cohort of 200 Pakistani women with invasive BCa diagnosed during 2002-2011. Expression of AR, pAkt and pPTEN was determined on formalin fixed paraffin embedded tissue sections by immunohistochemistry. The association of AR, pAkt and pPTEN with clinicopathological parameters was determined. Survival analyses were undertaken on patients with ≥ 5 years of follow-up (n = 82).RESULTSExpression of AR, pAkt and pPTEN was observed in 47.5%, 81.3% and 50.6% of patients, respectively. AR-expressing tumors were low or intermediate in grade (P < .001) and expressed ER (P = .002) and PR (P = .001). Patients with AR+ tumors had significantly higher OS (Mean OS = 10.2 ± 0.465 years) compared to patients with AR? tumors (Mean OS = 5.8 ± 0.348 years) (P = .047). Furthermore, AR-positivity was associated with improved OS in patients receiving endocrine therapy (P = .020). Patients with AR+ /pAkt+ /pPTEN? tumors, had increased OS (Mean OS = 7.1 ± 0.535 years) compared to patients with AR?/pAkt+/pPTEN? tumors (Mean OS = 5.1 ± 0.738 years).CONCLUSIONAR-expressing tumors are frequently characterized by low or intermediate grade tumors, expressing ER and PR. In addition, expression of AR, pAkt and pPTEN, could be considered in prognostication of patients with invasive BCa.  相似文献   
76.
Recurrent pregnancy loss is usually defined as the loss of two or more consecutive pregnancies before 20 weeks of gestation, which occurs in approximately 5% of reproductive-aged women. It has been suggested that women with thrombophilia have an increased risk of pregnancy loss and other adverse pregnancy outcomes. Thrombophilia is an important predisposition to blood clot formation and is considered as a significant risk factor for recurrent pregnancy loss. The inherited predisposition to thrombophilia is most often associated with factor V Leiden mutation, prothrombin G20210A mutation, and methylenetetrahydrofolate reductase C677T and A1298C gene variants. The net effect is an increased cleavage of prothrombin to thrombin and excessive blood coagulation. Key Words: Recurrent pregnancy loss, Hereditary thrombophilia, Factor V Leiden mutation  相似文献   
77.
78.
79.
We report here the synthesis, characterization and in vitro antiamoebic activity of 5-nitrothiophene-2-carboxaldehyde thiosemicarbazones (TSC), 1–5, and their bidentate complexes [Ru(η4-C8H12)(TSC)Cl2] 1a–5a. The biological studies of these compounds were investigated against HK-9 strain of Entamoeba histolytica and the concentration causing 50% cell growth inhibition (IC50) was calculated in the micromolar range. The ligands exhibited antiamoebic activity in the range (2.05–5.29 μM). Screening results indicated that the potencies of the compounds increased by the incorporation of ruthenium(II) in the thiosemicarbazones. The complexes 1a–5a showed antiamoebic activity with an IC50 of 0.61–1.43 μM and were better inhibitors of growth of E. histolytica, based on IC50 values. The most promising among them is Ru(II) complex 2a having 1,2,3,4-tetrahydroquinoline as N4 substitution.  相似文献   
80.
Myostatin mutations in mice and cattle are associated with increased muscularity, suggesting that myostatin is a negative regulator of skeletal muscle mass. To test the hypothesis that myostatin inhibits muscle cell growth, we examined the effects of recombinant myostatin in mouse skeletal muscle C2C12 cells. After verification of the expression of cDNA constructs in a cell-free system and in transfected Chinese hamster ovary cells, the human recombinant protein was expressed as the full-length (375-amino acid) myostatin in Drosophila cells (Mst375D), or the 110-amino acid carboxy-terminal protein in Escherichia coli (Mst110EC). These proteins were identified by immunoblotting and were purified. Both Mst375D and Mst110EC dose dependently inhibited cell proliferation (cell count and Formazan assay), DNA synthesis ([3H]thymidine incorporation), and protein synthesis ([1-14C]leucine incorporation) in C2C12 cells. The inhibitory effects of both proteins were greater in myotubes than in myoblasts. Neither protein had any significant effects on protein degradation or apoptosis. In conclusion, recombinant myostatin proteins inhibit cell proliferation, DNA synthesis, and protein synthesis in C2C12 muscle cells, suggesting that myostatin may control muscle mass by inhibiting muscle growth or regeneration.  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