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   1889篇
  免费   123篇
  2022年   8篇
  2021年   19篇
  2020年   9篇
  2019年   10篇
  2018年   20篇
  2017年   26篇
  2016年   27篇
  2015年   54篇
  2014年   61篇
  2013年   141篇
  2012年   95篇
  2011年   101篇
  2010年   58篇
  2009年   71篇
  2008年   118篇
  2007年   113篇
  2006年   111篇
  2005年   83篇
  2004年   101篇
  2003年   108篇
  2002年   111篇
  2001年   43篇
  2000年   49篇
  1999年   50篇
  1998年   32篇
  1997年   17篇
  1996年   26篇
  1995年   24篇
  1994年   16篇
  1993年   24篇
  1992年   23篇
  1991年   30篇
  1990年   23篇
  1989年   26篇
  1988年   15篇
  1987年   21篇
  1986年   13篇
  1985年   12篇
  1984年   17篇
  1983年   15篇
  1982年   6篇
  1981年   6篇
  1980年   16篇
  1979年   9篇
  1978年   6篇
  1977年   7篇
  1975年   10篇
  1971年   3篇
  1970年   5篇
  1967年   4篇
排序方式: 共有2012条查询结果,搜索用时 15 毫秒
21.
22.
A highly sensitive chemiluminescent assay for NAD(P)H have been developed. The principle of the method is as follows; NAD(P)H reduces molecular oxygen to superoxide anion (O) and hydrogen peroxide (H2O2) in the presence of 1-methoxy-5-methylphenazinium methyl sulphate (1-MPMS) as electron mediator. The produced O and H2O2 can be measured by chemiluminescent reaction using isoluminol (IL) and microperoxidase (m-POD). A linear relationship between chemiluminescence intensity and NAD(P)H concentration (log/log) was obtained ranged from 10?9 mol/I to 10?5 mol/I. This chemiluminescent reaction has been coupled to the assay of glucose-6-phosphate dehydrogenase (G6PDH), β-D -galactosidase (β-Gal) and alkaline phosphatase (ALP). The detection limits of G6PDH, β-Gal and ALP were 10?18 mol, 10?20 mol and 10?18 mol per assay, respectively. The chemiluminescent assay of these enzymes applied to chemiluminescent enzyme immunoassay for 17α-hydroxy-progesterone and DNA hybridization assay using these enzymes as label.  相似文献   
23.
Angiokeratoma corporis diffusum (Fabry's disease) is an X-linked disorder of glycosphingolipid catabolism. Heterozygous females, although usually asymptomatic, are occasionally as severely afflicted as hemizygous males; recently we identified a heterozygous patient with cardiomyopathy and severe pain in the extremities. In order to elucidate the difference of the clinical features, we analyzed the glycolipid composition of the heart, liver, and kidney obtained from the patient and from a hemizygote. Gas-liquid chromatography revealed that globotriaosylceramide (Gb3) was markedly increased in the heart (32.4 times higher than control) and increased to a lesser extent in the liver and kidney (3.74 and 6.79 times, respectively). The pattern of Gb3 accumulation in the heterozygote, where the highest increases were seen in the heart, was distinct from that in the hemizygote, where elevated levels of Gb3 and Ga2 were found in the kidney. Furthermore, the alpha-galactosidase activity in the heart, liver, and kidney of the heterozygote was 17%, 26%, and 36%, respectively, of normal controls, which correlated well with the accumulation of glycosphingolipid in the heart and with the disease's clinical manifestations. Two other hemizygotic patients, who were identified by low alpha-galactosidase activities, demonstrated the cardiac involvement.  相似文献   
24.
Summary For the production of a herbicide, 5-amino-levulinic acid (ALA), from anaerobic digestion liquor, the utilization of the photosynthetic bacterium, Rhodobacter sphaeroides was examined. This bacterium could produce ALA extracelularly from this liquor with the addition of levulinic acid (LA), an inhibitor of ALA dehydratase (ALAD), and glycine, a precursor of ALA biosynthesis in the Shemin pathway. Succinate (another precursor) addition was unnecessary for ALA production. When repeated additions of LA were made together with glycine ALA production was significantly enhanced. However, above three additions of LA, ALA production was not further enhanced. The maximum value of ALA production attained was 4.2 mM (0.63 g/ 1), which was over double that of other ALA producers such as Chlorella vulgaris. Propionic acid was predominantly utilized compared with other lower fatty acids, suggesting that this might be converted to ALA via succinyl-coenzyme A (CoA) in the methylmalonyl-CoA pathway.Offprint requests to: Y. Nishizawa  相似文献   
25.
Summary The effects of brefeldin A (BFA) on the secretion of acid phosphatase (APase) by tobacco protoplasts were investigated. Secretion of APase was inhibited by BFA in a dose-dependent manner, with a concomitant intracellular accumulation of the enzyme. The secreted APase was composed of two isoforms. BFA (10/ g/ml) inhibited the secretion of one of the isoforms without inhibiting that of the other, and this phenomenon explains the partial inhibition of APase secretion as a whole. The inhibition of APase secretion was accompanied by changes in the morphology of the Golgi apparatus and also by an increment in massdensity of cells.Abbreviations APase acid phosphatase - BFA brefeldin A - CHX cycloheximide - PAGE polyacrylamide gel electrophoresis  相似文献   
26.
The purpose of this study was to determine the extent of aluminum (Al) accumulation in the human aorta and cerebral arteries. The Al contents in the aortae and in the cerebral arteries from 23 human subjects was determined by inductively coupled plasma atomic emission spectrophotometry (ICP-AES). The subjects' age range was 45–99-yr-old; 15 of the subjects were males and 8 were females. Al was detected in twelve aortae and in six cerebral arteries, when the entire specimen was analyzed. Two specimens where Al was found in the cerebral arteries contained no Al in the aorta. No relationship to the subject's sex was found. When related to age, two groups were established. Group L (45–75 yr old) and group H (>75 yr old), which exhibited aortal Al concentrations of 33.3 and 72.7%, respectively. When the aortic wall was dissected into the tunica intima, media, and adventitia, Al was found mainly in the tunica media. In the aorta, significant relationships were found between Al and phosphorus (P) levels (r=0.801,p<0.01) and between Al and calcium (Ca) (r=0.661,p<0.05). We have concluded that Al accumulation is age-dependent and that it occurs both in the aorta and in the cerebral artery. In the aorta, accumulation occurs mainly in the tunica media. Both P and Ca appear to enhance aortal Al accumulation.  相似文献   
27.
Vertebrate lens tissues contain several species of acidic andneutral glycosphingolipids in relatively high amounts. However,the epithelia with capsule from dog and rhesus monkey lenseshad a simpler composition and lower content of glycosphingolipidsthan whole lenses. Gangliosides and neutral glycosphingolipidsin monolayer cultures of lens epithelial cells were also differentfrom those in whole lenses. Although -galactosyl (Gal1-3Ga1-R)or Lewisx (Galß1-4[Fuc1-3]GlcNAc-R) epitopes werefound in glycosphingolipids from whole lenses, they were notdetected in those from monolayer cultures of dog and rhesusmonkey lens cells. In addition, significant changes in ganglio-seriesgangliosides were induced in monolayer cultures of both cells,where GM3 and GD3 were predominant. Immunofluorescence studyrevealed a characteristic distribution of cell surface gangliosidesin confluent monolayers. These findings suggest that glycosphingolipidsynthesis in lens epithelia is intrinsically different fromthat in cortical and nuclear fibres, and that the expressionof Lewisx and -galactosyl epitopes in glycosphingolipids appearsto be associated with the differentiation of epithelial cellsto fibres. gangliosides glycosphingolipids lens epithelial cells Lewisx rhesus monkey.  相似文献   
28.
Kanazawa  K.  Mihashi  S.  Nishizawa  N. K.  Chino  M.  Mori  S. 《Plant and Soil》1993,155(1):103-105
A new assay system for the detection of nicotianamine amino-transferase activity was developed. The activity of nicotianamine amino-transferase which participated in biosynthetic pathway of MAs from methionine in graminaceous plants was induced by the iron deficiency treatment.  相似文献   
29.
The structural damage to and leakage of internal substances from Saccharomyces cerevisiae 0–39 cells induced by hydrostatic pressure were investigated. By scanning electron microscopy, yeast cells treated at room temperature with pressuresbellw 400 MPa for 10 min showed a slight alteration in outer shape. Transmission electron microscopy, however, showed that the inner structure of the cell began to be affected, especially the nuclear membrane, when treated with hydrostatic pressure around 100 MPa at room temperature for 10 min; at more than 400–600 MPa, further alterations appeared in the mitochondria and cytoplasm. Furthermore, when high pressure treatment was carried out at — 20° C, the inner structure of the cells was severely damaged even at 200 MPa, and almost all of the nuclear membrane disappeared, although the fluorescent nucleus in the cytoplasm was visible by 4,6-diamidino-2-phenylindole (DAPI) staining. The structural damage of pressure-treated cells was accompanied by the leakage of internal substances. The efflux of UV-absorbing substances including amino acid pools, peptides, and metal ions increased with increase in pressure up to 600 MPa. In particular, amounts of individual metal ion release varied with the magnitude of hydrostatic pressures over 300 MPa, which suggests that the ions can be removed from the yeast cells separately by hydrostatic pressure treatment. Correspondence to: S. Shimada  相似文献   
30.
Abstract The blood cells of a solitary ascidian, Halocynthia roretzi, were examined by electron microscopy (EM) with reference to their appearance by light microscopy (LM). In addition, their movement and stainability by vital dyes was observed by phase-contrast microscopy, and their stainability by Giemsa was also examined. Nine cell types were recognized: vacuolated cells, hyaline amoebocytes, small amoebocytes, granular amoebocytes, macrogranular cells, globular cells, lymphocyte-like cells, large basophilic cells and large granular cells. Vacuolated cells were found to possess various numbers of vacuoles containing strongly electron-dense materials and could be divided into at least three subgroups. Granular amoebocytes contained microfilaments and many granules of uniform size. Hyaline amoebocytes and small amoebocytes seemed to be specialized as phagocytes. Macrogranular cells and globular cells were not well characterized. In the blood of adult individuals, hemoblasts were rarely found, although lymphocyte-like cells were present. Each of two large cells, large basophilic cells and large granular cells, possessed novel granules or vacuoles, whose functions remain to be elucidated. The possible functions and relationships of these cells among various ascidian species are discussed.  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