全文获取类型
收费全文 | 2732篇 |
免费 | 237篇 |
国内免费 | 212篇 |
出版年
2024年 | 5篇 |
2023年 | 29篇 |
2022年 | 67篇 |
2021年 | 113篇 |
2020年 | 75篇 |
2019年 | 93篇 |
2018年 | 92篇 |
2017年 | 74篇 |
2016年 | 101篇 |
2015年 | 171篇 |
2014年 | 180篇 |
2013年 | 217篇 |
2012年 | 267篇 |
2011年 | 228篇 |
2010年 | 150篇 |
2009年 | 148篇 |
2008年 | 174篇 |
2007年 | 144篇 |
2006年 | 109篇 |
2005年 | 99篇 |
2004年 | 95篇 |
2003年 | 68篇 |
2002年 | 82篇 |
2001年 | 53篇 |
2000年 | 39篇 |
1999年 | 45篇 |
1998年 | 24篇 |
1997年 | 14篇 |
1996年 | 17篇 |
1995年 | 19篇 |
1994年 | 20篇 |
1993年 | 13篇 |
1992年 | 20篇 |
1991年 | 20篇 |
1990年 | 15篇 |
1989年 | 23篇 |
1988年 | 5篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1974年 | 6篇 |
1973年 | 3篇 |
1966年 | 2篇 |
排序方式: 共有3181条查询结果,搜索用时 15 毫秒
31.
Protein expression by Haemophilus influenzae under iron-limiting growth conditions was examined. The five type b strains and four nontypeable strains studied all expressed a new protein of about 40 kDa when deprived of iron during growth. Most strains also expressed a protein of about 31 kDa under the same growth conditions. Both the 40- and 31-kDa proteins were not expressed by cells grown in iron-replete medium. The 40- and 31-kDa proteins were not expressed in iron-deficient medium to which an excess of ferric nitrate had been added, and therefore it was concluded that their expression was iron regulated. These iron-repressed proteins were localized to the periplasmic space. The amino-terminal sequences of both proteins were determined. The N-terminal sequence of the 40-kDa protein had 81% similarity to the N terminus of Fbp, the major iron-binding protein of Neisseria gonorrhoeae and N. meningitidis. The 31-kDa protein sequence showed no homology with any known protein sequence. As no plasmids were found in the strains, it was concluded that these proteins were chromosomally encoded. 相似文献
32.
Identification of T-cell epitopes on E2 protein of rubella virus, as recognized by human T-cell lines and clones. 总被引:3,自引:0,他引:3 下载免费PDF全文
D Ou P Chong Y Choi P McVeigh W A Jefferies G Koloitis A J Tingle S Gillam 《Journal of virology》1992,66(11):6788-6793
T-cell epitopes on the E2 protein of rubella virus were studied by using 15 overlapping synthetic peptides covering the E2 protein sequence. The most frequently recognized epitopes on E2 were E2-4 (residues 54 to 74), with 5 of 10 tested T-cell lines responding to it. Two CD4+ cytotoxic T-cell cloned isolated from one T-cell line responded strongly in proliferation assays with peptide E2-4 and were cytotoxic to target cells presenting the E2-4 determinant. Truncated peptides contained within the E2-4 peptide sequence were used to define the T-cell determinants. Results indicated that amino acid residues 54 to 65 were directly involved. Human cell lines with different HLA phenotypes were tested for the capacity to present the antigenic determinants. The results suggested that recognition of peptide E2-4 by T-cell clones was associated with HLA DR7. 相似文献
33.
Constitutive expression of human double-stranded RNA-activated p68 kinase in murine cells mediates phosphorylation of eukaryotic initiation factor 2 and partial resistance to encephalomyocarditis virus growth. 总被引:20,自引:8,他引:12 下载免费PDF全文
E F Meurs Y Watanabe S Kadereit G N Barber M G Katze K Chong B R Williams A G Hovanessian 《Journal of virology》1992,66(10):5805-5814
The cDNA encoding interferon-induced human double-stranded RNA-activated p68 kinase was expressed in murine NIH 3T3 cells by using the pcDNA1/neo vector. Several stable clones were selected which expressed either the wild-type kinase or an inactive mutant possessing a single amino acid substitution in the invariant lysine 296 in the catalytic domain II. The transfected wild-type kinase showed properties similar to those of the natural kinase, such as subcellular ribosomal localization and dependence on double-stranded RNA for autophosphorylation. Upon infection with encephalomyocarditis virus (EMCV), wild-type- but not mutant-expressing clones were found to partially resist virus growth. Such natural antiviral activity was virus specific, since no inhibition was observed in the case of vesicular stomatitis virus infection. In accord with EMCV inhibition, the wild-type p68 kinase was found to be highly phosphorylated during infection. Furthermore, its natural substrate, the small subunit of protein synthesis initiation factor eIF2, was phosphorylated. These results demonstrate that p68 kinase is activated during EMCV infection, leading to reduced virus production. 相似文献
34.
Conditions affecting direct gene transfer into rodent muscle in vivo. 总被引:23,自引:0,他引:23
This report extends our previous findings that mouse muscle cells in situ can take up naked DNA injected intramuscularly in vivo. Various conditions such as needle type, speed of injection, volume of injection fluid, tonicity of injection fluid, type of solute, type of muscle, physiologic condition of the muscle and age of the animals were appraised for their effect on the levels of luciferase activity expressed from the pRSVL plasmid. Specific conditions such as the use of normal saline as an injection fluid increased the efficiency of expression. The implantation of DNA pellets was an effective way to deliver DNA to muscle, especially for smaller muscle groups. Also, newborn and adult rat muscles expressed plasmid DNA delivered intramuscularly. 相似文献
35.
Thermal and dynamic properties of dehydroergosterol (DHE) in 1-stearoyl-2-capryl-sn-glycero-3-phosphocholine [C(18):C(10)PC] have been studied by differential scanning calorimetry (DSC) and multifrequency phase-modulation fluorometry. C(18):C(10)PC is an asymmetric mixed-chain phosphatidylcholine known to form highly ordered mixed interdigitated bilayers below the maximal transition temperature, Tm, and partially interdigitated bilayers above Tm. This lipid system is thus unique in assessing the interactions between sterols and interdigitated lipid bilayers. DHE is a fluorescent analogue of cholesterol shown in previous studies to behave like cholesterol in noninterdigitated symmetric diacylphosphatidylcholines. DSC data show that DHE exhibits similar characteristics to cholesterol [Chong & Choate (1989) Biophys. J. 55, 551-556] in C(18):C(10)PC bilayers. DHE abolishes the phase transition of C(18):C(10)PC at 27 mol % compared to 25 mol % for cholesterol and decreases Tm, the onset temperature (To), and the completion temperature (Tc), at a similar rate to cholesterol at about -0.25 degrees C per mole percent DHE. Fluorescence data show that the rotational motion of DHE can be described by a hindered anisotropic model. In the gel state of C(18):C(10)PC, the rotational correlation of DHE decreases monotonically with increasing DHE content up to 24 mol %, suggesting that DHE causes a disordering/spacing effect on the packing of mixed interdigitated C(18):C(10)PC bilayers. The rotational correlation time undergoes an abrupt increase from 24 to 27 mol % DHE. Abrupt changes in the DSC parameters were also observed in the neighborhood of 27 mol %, suggesting that major reorganization takes place around this concentration.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
36.
Summary The 11- and 19-hydroxylation enzyme(s) of Pellicularia filamentosa IFO 6298 have been shown to be inducible by Reichstein's Substance S. By using the protein synthesis inhibitor, cycloheximide, in fermenter culture the effects of dissolved oxygen tension (DOT) on enzyme induction and enzyme expression have been separately investigated. For both hydroxylations, an optimum DOT for induction has been shown at 15% of saturation, while the optimum for expression is at 30% of saturation. The results have been verified in the absence of cycloheximide. Thus, maximum rates of hydroxylation are achieved when induction is performed at low DOT, followed by elevation to ensure maximum expression. 相似文献
37.
38.
The dynamic behaviour of model membranes in the form of sonicated liposomes in excess water was studied by means of 90 °C light scattering and turbidity measurements. Computer calculations based on the Rayleigh-Gans theory of light scattering were used to estimate the average size of lipid vesicles dispersed in water, taking into account the various structures of the vesicles. Normal reversible changes in the scattered light intensity and turbidity with temperature could be accounted for mainly by the change in the refractive index of the lipid and irreversible anomalous changes were explained on the basis of fusion of smaller aggregated vesicles. 相似文献
39.
Kuankuan Ai Yanli Jia Jin Li Chong Wang Yan Wang 《Journal of cellular biochemistry》2019,120(5):8069-8077
Gastric cancer (GC) is the second most common cause of cancer death worldwide but could be more curable if diagnosed at an earlier stage. At present, the capability to predict the efficaciousness of molecular diagnosis for GC for each patient remains elusive. The purpose of this study was to identify tumor biomarkers through systems analysis of multigene predictors exploiting the available data resource. In this study, we investigated the top 10% overexpressed genes in GC from five data sets of the Oncomine platform, with 265 GC samples versus 174 normal gastric mucosa samples. Sixteen candidate genes were identified as predictors of GC, of which 14 genes were verified through the comparison of expression levels in specimens from normal (chronic gastritis, 21 samples) and GC groups (38 samples). In addition, unique molecular portraits of diffuse adenocarcinoma (DA), intestinal adenocarcinoma (IA), and mixed adenocarcinoma (MA) were studied through Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analysis, where DA showed higher extracellular matrix alteration while IA and MA showed higher cell-cycle alteration than other types. We also found that the elevated expressions of genes during GC progression were independent of gene mutations, and high core-binding factor subunit β expression is correlated with a high overall survival rate in GC patients. Our research may provide an efficient clinical diagnosis of GC at an early stage with high accuracy and thus help improve the overall survival rate through early therapeutic interventions. 相似文献
40.
Jordan Bai Muhammad Farid Abdul-Rahman Anne Rifkin-Graboi Yap-Seng Chong Kenneth Kwek Seang-Mei Saw Keith M. Godfrey Peter D. Gluckman Marielle V. Fortier Michael J. Meaney Anqi Qiu 《PloS one》2012,7(10)
We studied a sample of 75 Chinese, 73 Malay, and 29 Indian healthy neonates taking part in a cohort study to examine potential differences in neonatal brain morphology and white matter microstructure as a function of ethnicity using both structural T2-weighted magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI). We first examined the differences in global size and morphology of the brain among the three groups. We then constructed the T2-weighted MRI and DTI atlases and employed voxel-based analysis to investigate ethnic differences in morphological shape of the brain from the T2-weighted MRI, and white matter microstructure measured by fractional anisotropy derived from DTI. Compared with Malay neonates, the brains of Indian neonates’ tended to be more elongated in anterior and posterior axis relative to the superior-inferior axis of the brain even though the total brain volume was similar among the three groups. Although most anatomical regions of the brain were similar among Chinese, Malay, and Indian neonates, there were anatomical variations in the spinal-cerebellar and cortical-striatal-thalamic neural circuits among the three populations. The population-related brain regions highlighted in our study are key anatomical substrates associated with sensorimotor functions. 相似文献