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   770篇
  免费   46篇
  国内免费   2篇
  2024年   5篇
  2023年   11篇
  2022年   21篇
  2021年   25篇
  2020年   16篇
  2019年   23篇
  2018年   26篇
  2017年   20篇
  2016年   25篇
  2015年   39篇
  2014年   48篇
  2013年   54篇
  2012年   45篇
  2011年   43篇
  2010年   37篇
  2009年   33篇
  2008年   26篇
  2007年   30篇
  2006年   27篇
  2005年   37篇
  2004年   23篇
  2003年   25篇
  2002年   21篇
  2001年   8篇
  2000年   4篇
  1999年   12篇
  1998年   3篇
  1996年   3篇
  1993年   4篇
  1992年   4篇
  1991年   9篇
  1990年   6篇
  1989年   16篇
  1988年   6篇
  1987年   4篇
  1986年   6篇
  1984年   6篇
  1983年   3篇
  1982年   4篇
  1981年   5篇
  1980年   4篇
  1979年   6篇
  1978年   6篇
  1975年   2篇
  1974年   6篇
  1973年   4篇
  1972年   3篇
  1971年   3篇
  1965年   4篇
  1964年   5篇
排序方式: 共有818条查询结果,搜索用时 31 毫秒
761.
762.
BRAF mutations are relatively common in many cancers, particularly melanoma, colorectal cancer, and thyroid cancer and to a lesser extent in lung cancer. These mutations can be targeted by BRAF and MEK inhibitors, which exhibit good clinical activity. There are conflicting reports of the various relative rates of BRAF Class I mutations (V600 locus), defined as those that exhibit extremely strong kinase activity by stimulating monomeric activation of BRAF, Class II, define as non-V600 mutations that activate BRAF to signal as a RAS-independent dimer, and Class III mutations, defined as “kinase-dead” with low kinase activity as compared to wild type BRAF. Prospective studies have largely focused on patients with tumors harboring Class I BRAF mutations (limited to the V600 locus) where response rates up to 70% with BRAF plus MEK inhibition have been demonstrated. We report on the relative prevalence of various types of BRAF mutations across human cancers in a cohort of 114,662 patients that received comprehensive genomic profiling using next-generation sequencing. Of these patients, 4517 (3.9%) a pathogenic or presumed pathogenic BRAF mutation (3.9%). Of these, 1271 were seen in melanoma, representing 39.7% of all melanomas sequenced, representing the highest rate in all tumors. Class I (V600) mutations were seen overall in 2841 patients (62.1% of BRAF mutations, 2.4% of total cancers). Class II mutations were seen in 746 tumors (16.5% of BRAF mutant, 0.7% of total), and Class III mutations were seen in 801 tumors (17.7% of BRAF, 0.7% of total). Knowledge of the relative prevalence of these types of mutations can aid in the development of agents that might better address non-V600 mutations in cancer.Impact statementThese data represent the largest aggregation of BRAF mutations within a single clinical database to our knowledge. The relative proportions of both BRAF V600 mutations and non-V600 mutations are informative in all cancers and by malignancy, and can serve as a definitive gold-standard for BRAF mutation cancer incidence by malignancy. The rate of BRAF mutation in human cancer in a real-world large database is lower than previously reported likely representing testing more broadly across tumor types. The relative percentages of Class II and Class III BRAF mutations are higher than previously reported, representing almost 35% of BRAF mutations in cancer. These findings provide support for the development of effective treatments for non-V600 BRAF mutations in cancer.  相似文献   
763.
This study was conducted to investigate the toxicity of 12 heavy metals (i.e., HM), namely Hg, Cd, Co, Ni, Cr, Cu, Ag, Mo, Zn, Pb, Li and Na on bacterial isolates from the rumen of sheep, cattle and buffaloes. Rumen samples were collected immediately after slaughter during the dry season. Ruminal bacterial isolates, 59, were obtained from two sheep, five cows and nine buffaloes. Sensitivity of ruminal bacterial isolates to each HM was determined by the clearance zone (CZ) using the Kirby-Bauer disc diffusion susceptibility test. Bacterial populations isolated from the rumens of sheep and buffalo had a lower resistance (P<0.001) to HM toxicity than did cattle. Regardless of ruminant species, bacterial isolates revealed a higher tolerance (P<0.001) to Li and Na, whereas Hg and Cd were the most toxic HM for all isolates. We conclude that inhibition of these HM to the isolated microbial population of sheep, cattle and buffalo is ranked: Hg (most toxic) > Cd > Co  Ag  Cu  Cr  Ni > Mo  Zn  Pb > Li  Na. Further research is required to explain the mechanism of toxicity of these HM, and also to explore the variation among ruminant species.  相似文献   
764.
An indiscriminate use of antibiotics in humans and animals has led to the widespread selection of antibiotic‐resistance, thus constricting the use of antibiotics. A possible solution to counter this problem could be to develop alternatives that can boost the host immunity, thus reducing the quantity and frequency of antibiotic use. In this work, for the first time, citric acid and laccase were used as extracellular inducers of melanin production in yeast cells and human cell lines. It is proposed that the formulation of laccase and citric acid together could further promote melatonin‐stimulated, melanocyte‐derived melanin production. Melanization as a probe of immunity described in this study, is an easy and a rapid test compared to other immunity tests and it allows performing statistical analyses. The results showed the synergistic effect of citric acid and laccase on melanin production by yeast cells, with significant statistical differences compared to all other tested conditions (p: 0.0005–0.005). Laccase and citric acid together boosted melanin production after 8 days of incubation. An increase in melanin production by two human colon cells lines (Cacao‐2/15 and HT‐29) was observed on supplementation with both laccase and citric acid in the cell growth medium. Produced melanin showed antimicrobial properties similar to antibiotics. Therefore, a formulation with citric acid and laccase may prove to be an excellent alternative to reduce the antibiotic use in human and animal subjects.  相似文献   
765.
International Journal of Peptide Research and Therapeutics - The COVID-19 disease is caused by SARS-CoV-2 and spreading rapidly worldwide with extremely high infection rate. Since effective and...  相似文献   
766.
The behaviour towards periodate of the brown-algal polysaccharide sargassan before and after partial hydrolysis, alkali treatment, and methanolysis has been studied. Evidence is thereby provided that the sargassan backbone is composed of (1→4)-linked β-D-glucuronic acid and β-D-mannose residues. Heteropolymeric, partially sulphated branches are attached to the backbone, and these branches comprise various proportions of(l→4)-linked, β-D-galactose, β-D-galactose 6-sulphate, and β-D-galactose 3,6-disulphate residues, (1→2)-linked α-L-fucose 4-sulphate residues, and (1→3)-linked β-D-xylose residues.  相似文献   
767.
Treatment of the C6 glioblastoma cell with trinitrobenzenesulfonic acid (TNBS) resulted in the selective inactivation of ecto-5'-nucleotidase under conditions which maintained cell viability. Cells respond to ecto-enzyme inactivation by replacing 80% of lost activity within 24 hrs. A lag time of 4-6 hrs before ecto-5'-nucleotidase replacement began and its complete blockage by cycloheximide indicated that the source of replaced enzyme was de novo synthesis and not an intracellular pool. Release of 5'-nucleotidase activity into culture medium in the form of membraneous vesicles slowed during the active recovery period and then steadily increased with time as the plasma membrane enzyme level approached normal. TNBS did not exert a direct inhibitory action upon the exfoliative process as release of vesicular GM1 and protein were little affected. Decrease in exfoliated 5'-nucleotidase activity may be due to a selective conservation of the enzyme in the exfoliative process.  相似文献   
768.
Synthesis of a series of 3,6-dinitro-1:8-naphthaloylamino acids (II-IX) and some of their corresponding methyl esters (X-XVI) and 3,6-diamino-1:8-naphthaloylamino acid derivatives (XXIX-XXXVI) is described. Coupling of 3,6-dinitro-1:8-naphthaloylamino acids with amino acid methyl ester hydrochlorides in dioxane-DMF-Et3N medium using DCC method furnishes the desired 3,6-dinitro-1:8-naphthaloyldipeptide methyl esters (XVII-XXVIII). Most of the synthesized 3,6-dinitro-1:8-naphthaloylamino acids, esters and dipeptide derivatives (compounds III-VI, XI-XV, XVII, XIX-XXI, XXIII and XXV) and 3,6-diamino-1:8-naphthaloylamino acid derivatives (XXIX-XXXV) were found to be active against a number of microorganisms.  相似文献   
769.
The present work aims to exploit the possibility of using the tautomerism in 2-hydroxy Schiff bases for molecular switching. The enol imine (E)? enaminone (K) tautomerization in a series of 2-hydroxy Schiff bases have been investigated theoretically at the DFT/B3LYP/6-311G** level of theory. The intramolecular proton transfer processes have been explored, transition structures have been located and characterized. The kinetics and thermodynamics of the proton transfer process, and its time scale have been computed and discussed in the framework of the suitability as molecular switches. Substituent effects have been computed and its effect on the enthalpy changes (?H*) and activation energies (?G*) have been analyzed and discussed. Nonspecific solvent effects have also been taken into account by using the polarized continuum model (IPCM) of two different solvent. The tautomerization energies are decreased and hence the endothermic nature of the enol imine ? enaminone tautomerization. The potential energy barriers, on the other hand, are increased due to the relative destabilization of the transition states. The NBO charge populations show that there is a high positive charge on the hydrogen atom during the process in all cases, which confirms that the proton transfer proceeds through a three-center interaction. The proton transfer processes, in all cases studied are kinetically allowed. The low potential energy barrier suggests that interconversion between the two tautomeric forms is spontaneous and the two forms may coexist.  相似文献   
770.
The effectiveness of attenuated Salmonella in inhibiting tumor growth has been demonstrated in many therapeutic models, but the precise mechanisms remain incompletely understood. In this study, we show that the anti-tumor capacity of Salmonella depends on a functional MyD88-TLR pathway and is independent of adaptive immune responses. Since myeloid suppressor cells play a critical role in tumor growth, we investigated the consequences of Salmonella treatment on myeloid cell recruitment, phenotypic characteristics, and functional activation in spleen and tumor tissue of B16.F1 melanoma-bearing mice. Salmonella treatment led to increased accumulation of splenic and intratumoral CD11b+Gr-1+ myeloid cells, exhibiting significantly increased expression of various activation markers such as MHC class II, costimulatory molecules, and Sca-1/Ly6A proteins. Gene expression analysis showed that Salmonella treatment induced expression of iNOS, arginase-1 (ARG1), and IFN-γ in the spleen, but down-regulated IL-4 and TGF-β. Within the tumor, expression of iNOS, IFN-γ, and S100A9 was markedly increased, but ARG1, IL-4, TGF-β, and VEGF were inhibited. Functionally, splenic CD11b+ cells maintained their suppressive capacity following Salmonella treatment, but intratumoral myeloid cells had significantly reduced suppressive capacity. Our findings demonstrate that administration of attenuated Salmonella leads to phenotypic and functional maturation of intratumoral myeloid cells making them less suppressive and hence enhancing the host’s anti-tumor immune response. Modalities that inhibit myeloid suppressor cells may be useful adjuncts in cancer immunotherapy.  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