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   1182篇
  免费   49篇
  国内免费   3篇
  2022年   10篇
  2021年   8篇
  2020年   8篇
  2019年   11篇
  2018年   13篇
  2017年   11篇
  2016年   21篇
  2015年   35篇
  2014年   38篇
  2013年   65篇
  2012年   73篇
  2011年   75篇
  2010年   42篇
  2009年   54篇
  2008年   82篇
  2007年   74篇
  2006年   69篇
  2005年   87篇
  2004年   70篇
  2003年   72篇
  2002年   65篇
  2001年   16篇
  2000年   14篇
  1999年   13篇
  1998年   13篇
  1997年   11篇
  1996年   8篇
  1995年   8篇
  1994年   15篇
  1993年   8篇
  1992年   13篇
  1991年   15篇
  1990年   12篇
  1989年   14篇
  1988年   8篇
  1987年   4篇
  1986年   6篇
  1985年   7篇
  1984年   9篇
  1983年   6篇
  1982年   4篇
  1981年   9篇
  1980年   4篇
  1979年   5篇
  1978年   2篇
  1976年   5篇
  1975年   4篇
  1974年   4篇
  1973年   3篇
  1967年   4篇
排序方式: 共有1234条查询结果,搜索用时 15 毫秒
21.
Prostate glands of adult guinea pigs were stained for nerve growth factor (NGF) and epidermal growth factor (EGF) by immunohistochemical methods. Both NGF and EGF were localized diffusely in the cytoplasm of the glandular epithelial cells, and also in their secretory products. These findings suggest that NGF and EGF are synthesized, stored, and secreted by the glandular epithelial cells of the prostate.  相似文献   
22.
Circular diochroism (CD) spectra of four p-nitrophenyl glycosides and their cycloamylose complexes were investigated at various concentrations of cycloamylose and at temperatures ranging from 20 to 60°C. The CD spectra of p-nitrophenyl glycosides changed remarkably in the presence of cycloamyloses, and significant differences in spectral shape and intensity were observed between the cyclohexaamylose complex and the cycloheptaamylose complex. The difference CD spectra between the free guest and its complex indicates that the nitrophenyl group is included in the cycloamylose cavity but its disposition is different between the complexes with cyclohexaamylose and cycloheptaamylose. Values of enthalpy and entropy of the cyclohexaamylose complex are considerably larger than those of the corresponding cycloheptaamylose complex, although the free energy differs only slightly. It is suggested that the nitrophenyl group is more loosely bound to the cycloheptaamylose cavity than to the cyclohexaamylose cavity, and has much more flexibility in its disposition.  相似文献   
23.
Inbred E1 mice are highly susceptible to convulsive seizures upon “throwing” stimulation. The strain is known to have an abnormal 5-hydroxytryptamine (5-HT) metabolism. In the study here 5-HT level, [14C]5-hydroxytryptophan (5-HTP) metabolism, MAO activity and [3H]5-HT receptor binding were examined in the cortex, brainstem and cerebellum. In the interictal period cortical and brainstem 5-HT level and [3H]5-HT receptor binding were significantly lower. In the same period cortical biosynthesized [14C]5-HT from [14C]5-HTP taken up was higher, and MAO activity was not changed.L-DOPA with MK486 induced a low threshold of seizures and decreased cortical 5-HT level. Abnormally functioning 5-HT neurones may exist in the E1 mouse cortex.  相似文献   
24.
Molecular cloning and nucleotide sequence analysis were performed for the identification of the regulator genes of methicillin resistance in the genome of a MRSA strain N315. Two open reading frames (orfs) were identified in the 5'-flanking region of the mecA gene. Predicted amino acid sequences of these orfs showed extensive homology to the co-inducer and the repressor protein of the penicillinase (PCase) production in Staphylococcus aureus as well as in Bacillus licheniformis. These orfs are considered to encode putative co-inducer and repressor proteins specific for the regulation of methicillin resistance in MRSA.  相似文献   
25.
Bio-catalyzer alpha.rho No.11 (Bio-normalyzer) and its by-product are natural health products made by yeast fermentation of glucose, Carica papaya Linn., Pennisetum pupureum Schum., and Sechium edule Swartz. Their effects on free radicals were examined by electron spin resonance spectrometry using spin trapping agent 5,5-dimethyl-1-pyrroline-1-oxide (DMPO). It was observed that both Bio-catalyzer and its by-product scavenged 95% of DMPO-OH spin adducts (89 x 10(15) spins/ml) generated by FeSO4-H2O2-diethylene triamine pentaacetic acid system at 45.45 mg/ml each. Five percent of DMPO-O2- spin adducts (27 x 10(15) spins/ml) generated by hypoxanthine-xanthine oxidase system and 11% of 1,1-diphenyl-2-picrylhydrazyl radicals (7 x 10(15) spins/ml) were quenched using 25 mg/ml of Bio-catalyzer while 5% of superoxide and nil DPPH radicals were scavenged by its by-product. Vivo tests showed that oral administration of 1-g/kg body weight of Bio-catalyzer significantly inhibited thiobarbituric acid reactive substances formation, which is an index of lipid peroxidation, in the FeCl3-induced epileptic focus of rats. These findings suggest that Bio-catalyzer or its by-product may be useful health foods against neural lipid peroxidation, traumatic epilepsy and aging.  相似文献   
26.
Hybrid cell lines were established by fusion between keyhole limpet hemocyanin(KLH) binding T cells of A/J mice and an AKR T cell tumor line, BW5147. Hybrids were selected for the presence of Ia antigen and KLH-specific augmenting activity of their extracts in the secondary antibody response. The detailed phenotypic and functional analysis of 1 of these clones, FL10, is reported here. The hybrid was positive for both Thy1.1 and Thy1.2 antigens and possessed the Lyt-1+,2-,3- phenotype. Both VH and Ia determinants were detected on their cell surface. The IA locus was mapped in the I-A subregion, but the Ia specificities were serologically distinct from those of B cell Ia antigen. This was demonstrated by the fact that anti-Ia antiserum preabsorbed with B cells could react with the hybrid cells, whereas none of the monoclonal anti-Ia specific for private and public determinations of Iak could. The extract from the cell line specifically augmented the in vitro secondary antibody response against dinitrophenylated KLH, and this activity was removed by absorption with antigen and conventional anti-Ia antisera. The results indicate that the cell line, FL10, carries Ia antigen unique to the T cell, which is associated with the antigen-specific augmenting molecule.  相似文献   
27.
The direct staining of BUdR-substituted Chinese hamster chromosomes in a 4Na-EDTA-Giemsa solution resulted in a B-dark type of sister chromatid differential staining (SCD) in which bifilarly substituted chromatids stained dark. On the other hand, when BUdR-substituted chromosomes were pretreated with a 4Na-EDTA solution and then stained with Giemsa, a B-light type SCD was obtained in which bifilarly substituted chromatids stained light.  相似文献   
28.
A new inherited variant of carbonic anhydrase I (CA I), designated CA INagasaki 1 (CA INGS 1), was discovered during a survey of hemolysates from 5852 individuals from the cities of Hiroshima and Nagasaki in Japan. Analysis of the amino acid composition of a tryptic peptide from the CA INGS 1 variant indicated that a glutaminyl residue was substituted for an arginyl residue at position 76. Heat degradation studies showed that the CA INGS 1 variant was less stable than normal CA I. The CO2 hydrase and esterase activities of the normal and variant carbonic anhydrases I, as well as the relative amounts of the two enzymes in heterozygotes, were similar.This work was supported in part by Contract E(11-1)-1552 with the Energy Research and Development Administration, Washington, D.C. (to J. V. Neel), and by U.S. Public Health Service Grant GM-24681.  相似文献   
29.
The component aldehydes in dialdehyde fragments formed by periodate oxidation of oligosaccharides were converted quantitatively into the corresponding (2,4-dinitrophenyl)hydrazones by the simple procedure of treatment with excess (2,4-dinitrophenyl)hydrazine hydrochloride in 1,2-dimethoxyethane. Then, by chromatographic separation of the hydrazones on a small column of silica gel and subsequent spectrophotometric analysis, it was possible to determine the position of glycosidic substitution in μmolar amounts of various types of glucobioses, oligosaccharides of senega, and some synthetic (1→6)-β-D-gluco-oligosaccharides.  相似文献   
30.
Outer membranes, almost free from peptidoglycan components, were prepared from a moderately halophilic gram-negative bacterium grown in a medium containing 2 M NaCl. The outer membrane was easily released, leaving mureinoplasts, by mild desalting in a 20% sucrose solution containing 50 mM tris(hydroxymethyl)aminomethane-HCl buffer, pH 7.8. The membrane was recovered by treatment with DNase I and CsCl buoyant density centrifugation. Chemical analyses revealed that the outer membrane was mainly composed of 31% protein, about 20% extractable lipids (mainly phospholipids), and lipopolysaccharides. The proteins had about 18 mol % excess of acidic over basic amino acids. The phospholipids comprised phosphatidyl ethanolamine, phosphatidyl glycerol, cardiolipin, and an unidentified phospholipid containing glucose, which seemed mainly associated with the outer membrane. The content of lipopolysaccharides in the outer membrane was calculated arbitrarily as 30% from the heptose content. A unique feature of these lipopolysaccharides seemed to be higher lipid content than found in lipopolysaccharides of other gram-negative bacteria. The major fatty acids of bound lipids of the outer membrane resembled those of the lipopolysaccharides obtained from cell envelope preparation and contained high concentrations of 3-hydroxy lauric acid.  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