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   1005篇
  免费   90篇
  国内免费   1篇
  2024年   2篇
  2023年   11篇
  2022年   36篇
  2021年   35篇
  2020年   55篇
  2019年   80篇
  2018年   66篇
  2017年   32篇
  2016年   37篇
  2015年   40篇
  2014年   42篇
  2013年   71篇
  2012年   81篇
  2011年   52篇
  2010年   22篇
  2009年   32篇
  2008年   26篇
  2007年   54篇
  2006年   33篇
  2005年   36篇
  2004年   27篇
  2003年   26篇
  2002年   17篇
  2001年   27篇
  2000年   18篇
  1999年   18篇
  1998年   5篇
  1997年   5篇
  1996年   4篇
  1995年   7篇
  1994年   5篇
  1992年   11篇
  1991年   6篇
  1990年   8篇
  1989年   4篇
  1988年   4篇
  1987年   4篇
  1986年   8篇
  1985年   11篇
  1984年   5篇
  1983年   2篇
  1981年   3篇
  1980年   3篇
  1979年   4篇
  1978年   3篇
  1977年   2篇
  1974年   2篇
  1973年   4篇
  1972年   2篇
  1964年   1篇
排序方式: 共有1096条查询结果,搜索用时 15 毫秒
941.
Prevalence of Dermatophytoses in the Zarqa District of Jordan   总被引:6,自引:0,他引:6  
A total of 350 clinically suspected cases of dermatomycoses were examined for causative fungi during July 1997 to September 1998. Mycotic infection was demonstrable by microscopy and culture in 199 (56.8%) cases. The most common superficial mycotic infections were tinea pedis (35.2%) followed by tinea capitis (23.1%), tinea unguium (21.6%) and tinea corporis (10.6%). Most of the infected patients were 1–9, 20–29 and 30–39 years old. Men were mainly infected with tinea cruris and tinea pedis, while women were infected with tinea pedis, tinea unguium and tinea capitis. The frequencies of etiological agents isolated from patients were as follows: Trichophyton mentagrophytes var. interdigitale (32.7%), T. rubrum (28.6%), Epidermophyton floccosum (20.1%), Microsporum canis (11.1%), T.schoenleinii (4%), T.verrucosum (2%), T.violaceum (1%), and M. gypseum (0.5%). The number of infections varied with the seasons. The highest number of cases of tinea pedis and tinea cruris occurred in the summer months, while tinea capitis, tinea corporis and tinea unguium occurred in the spring and winter months. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   
942.
Rhizoctonia solani is a destructive fungal pathogen with a wide host range. The R. solani complex species includes several divergent groups delimited by affinities for hyphal anastomosis. In this study, genetic variation among 20 isolates of R. solani anastomosis group 1 (AG1) subgroups (AG1‐IA and AG1‐IB) collected from Mâzandaran province, Iran, and standard isolates of these subgroups, was determined by isozyme analysis and total soluble protein profile. Mycelial protein pattern and isozyme analysis were studied using denaturing and non‐denaturing polyacrylamide gel electrophoresis, respectively. A total of 15 enzyme systems were tested, among which six enzymes including esterase, alkaline phosphatase, superoxide dismutase, octanol dehydrogenase, lactate dehydrogenase and mannitol dehydrogenase generated distinct and reproducible results. The soluble protein patterns were similar among the R. solani isolates examined; however, minor differences in banding pattern were observed between the two subgroups. In isozyme analysis, a total of 64 electrophoretic phenotypes were detected for all six enzymes used. Based on cluster analysis and similarity matrix, the fungal isolates were divided into two genetically distinct groups of I and II consistent with the previously reported AG1‐IA and AG1‐IB subgroups in AG1. Group I represented all isolates belonging to AG1‐IA subgroup, whereas group II represented all isolates belonging to AG1‐IB subgroup. Results from isozyme analysis suggest that the subgrouping concept within AGs is genetically based.  相似文献   
943.
Twenty-four strains of Xanthomonas axonopodis pv. citri ( Xac ), the causal agent of bacterial canker of citrus, isolated from Mexican lime ( Citrus aurantifolia ) and lemon ( Citrus limon ) in southern Iran, were characterized phenotypically. Strains were all pathogenic on C. aurantifolia . Sodium dodecyl sulphate-polyacrylamide gel electrophoresis analysis revealed slight differences in soluble protein profiles among the strains. Based on host range specificity and phenotypic characteristics, representative strains were differentiated into two groups of Asiatic (A) and atypical Asiatic (aA) forms. DNA fingerprinting analysis using Eco RI as the restriction endonuclease showed a negligible difference in restriction pattern between the two groups. On the basis of isozymic analysis, the two groups were distinct with respect to superoxide dismutase (SOD) and esterase (EST) banding patterns. Plasmid DNA profile analysis showed that the bacterial strains were different from each other in terms of plasmid number and molecular weight. Phage typing study revealed that most of group A strains were susceptible to Cp1 and/or Cp2 and some were resistant to both phage types including the strain in aA group. Bacteriocin production test indicated that there was a variation among Xac strains using different indicators for each bacteriocin producer. It is concluded that the Iranian strains of Xac are heterogeneous and constitute a subgroup(s) within the pathotype A.  相似文献   
944.
Joel A Malek  Daniel H Haft 《Genome biology》2001,2(5):preprint00-23

Background  

Conserved domains (CD) in proteins play a crucial role in protein interactions, DNA binding, enzyme activity, and other important cellular processes. We proposed to study ratios of genes containing these domains to ratios of proteome size of different eukaryotes.  相似文献   
945.

Scientists consider saltwater one of the effective environmental stress that negatively affects the growth and establishment of trees and shrubs worldwide. Utilizing the potential of Bio-stimulant compounds present in the brown seaweed extract is an alternative strategy to improve crop tolerance to salinity. This study focused on the application of seaweed extract as a Bio-stimulant agent to counteract the salt stress on the growth and some physiochemical aspects of milkweed seedlings. In this experiment, the seedlings were treated with seaweed extract (SWE) of Sargassum angustifolium at four concentrations (non-SWE or control, 0.5, 1.0, and 1.5%) and then exposed to salt stress at four levels (0, 7.5, 15, and 30 dS m?1 of diluted seawater) in a completely randomized design (four replications per treatment) over a time-span of 3 months. The results indicated that SWE-treated seedlings could tolerate salinity up to 15 dS m?1 and also increase the survival rate by 69%. The growth parameters like height, specific leaf area, root length and volume, root and shoot dry weight were considerably enhanced by SWE (1%) from 7.5 to 30 dS m?1. Moreover, gas exchanges and chlorophyll pigments were markedly increased using SWE (0.5%) under salt lower 15 dS m?1 than control. Also, both SWE and salt stress significantly enhanced antioxidant enzymes over control, but SWE more increased the parameters. SWEs agent at different dosages significantly decreased electrolyte leakage at all salinity levels (except in 7.5 and 15 dS m?1) compared to control. SWEs (1%) resulted in increasing K+ uptake but decreasing Na+ uptake and markedly enhancing K+/Na+ ratio in stressed-milkweed versus free-salt stress. Totally, this research illustrates the potential of SWEs (at lower dosages) for elevating milkweed tolerance to moderate salinity stress and highlights the possibility of applying it as Bio-stimulant fertilizer.

  相似文献   
946.
A new series of spiro[indene-1,2′-quinazolin]-4′(3′H)-one derivatives 4a–m were synthesized via a one-pot method and evaluated for anticonvulsant activities using pentylenetetrazole (PTZ) and maximal electroshock (MES)-induced seizures. Obtained results demonstrated that these compounds have not anticonvulsant activity in PTZ test while are active in the MES test. Among the synthesized compounds, the best anticonvulsant activity was obtained with compound 4h . This compound also was not neurotoxic. Given that the title new compounds have the pharmacophore requirement for benzodiazepine (BZD) receptor agonist, the most potent compound was assayed in vivo and in silico as BZD receptor agonist. After treatment with flumazenil as a standard BZD receptor antagonist, anticonvulsant activity of compound 4h decreased. Therefore, the involvement of BZD receptors in anticonvulsant activity of this compound confirmed. Furthermore, docking study of compound 4h in the BZD-binding site of GABAA receptor confirmed that this compound interacted with the important residues.  相似文献   
947.
948.
Two glucoamylases, gluc I and gluc II, were purified to homogeneity from the culture filtrate of a Myrothecium strain M1 by chromatography on DEAE-cellulose and concanavalin A-sepharose. Molecular masses deduced by SDS-PAGE were 72000 ± 2500 for gluc I and 96 000 ± 4000 for glue II. The temperature optima of the enzymes were both about 70°C and their pH optima were around 4.0. Both enzymes were glycoprotein and preferentially hydrolysed high molecular mass substrates. Hg2+ was a potent inhibitor of both glucoamylases. Glue II had higher debranching activity than gluc I.  相似文献   
949.
We have studied the cellular basis for differential expression of the Ly-6A/E alloantigen on T cells obtained from mice of the Ly-6 a (10–20% Ly-6A/E +) and Ly-6 b (50–60% Ly-6A/E +) haplotypes. During T-cell ontogeny only a small fraction (< 12 %) of thymocytes expressed Ly-6A/E. By 4 weeks of age adult levels of Ly-6A/E bearing lymphocytes were seen in peripheral lymphoid tissue. Immunohistochemical studies of the thymus revealed that Ly-6A/E+ cells were located predominantly in the medulla with small clusters of Ly-6A/E+ cells throughout the cortex. Consistent with this result, phenotypic studies showed that in the adult thymus the majority of Ly-6A/E expression was on mature CD4+ CD8 and CD4 CD8+ cortisone-resistant and precursor CD4 CD8 thymocytes. However, a much higher percentage of CD4+ CD8 and CD4 CD8 thymocytes as well as CD4+ CD8 peripheral T cells expressed Ly-6A/E from Ly-6 b mice. Furthermore, although gamma interferon induced increased Ly-6A/E expression in certain thymocyte and T-cell subsets, this induction functioned preferentially for cells obtained from Ly-6 b mice. Studies using F1 hybrid mice (Ly-6 a × Ly-6 b) indicated that the basal level of Ly-6A/E expression on these subsets appeared to be under codominant genetic control, whereas gamma interferon-induced regulation of Ly-6A/E expression appeared to be under dominant genetic control. Collectively, these results suggest that the expression of Ly-6A/E on a particular T-cell subset is established in the thymus and is a stable characteristic of each haplotype. In addition, the low levels of Ly-6A/E expression for the Ly-6 a haplotype appear to be partially due to the inability of the majority of resting CD4+ T cells to express Ly-6A/E and to the relatively poor induction of this protein by gamma interferon.  相似文献   
950.
A new live attenuated mumps vaccine was developed in human diploid cells. The S-12 virus was isolated from a 10-year-old girl showing typical symptoms of mumps infection, the diagnosis was confirmed by a pediatrician. The virus was isolated in green monkey kidney cells, without passage in chick embryo cavity or chick embryo fibroblasts. Attenuation of the wild virus was performed by serial passages in human diploid cells (MRC-5). The attenuated virus was characterized by identity tests, as well as by a reduction in plaque size, as marker tests. The virus was free from adventitious agents and safe for laboratory animals as well as for monkeys. The reactogenicity and immunogenicity of the S-12 virus for man was investigated by administration of a monovalent vaccine to 20 seronegative adult male volunteers and 30 children aged 1 to 5 years without history of mumps infection or vaccination. Seroconversion was obtained in 95% of the vaccinees. The new vaccine has the advantage of not requiring specific pathogen-free eggs, and being free from avian proteins and therefore can be used in sensitized patients.  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