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   2056篇
  免费   122篇
  国内免费   95篇
  2273篇
  2023年   23篇
  2022年   47篇
  2021年   91篇
  2020年   51篇
  2019年   56篇
  2018年   56篇
  2017年   51篇
  2016年   70篇
  2015年   141篇
  2014年   105篇
  2013年   144篇
  2012年   190篇
  2011年   172篇
  2010年   100篇
  2009年   68篇
  2008年   122篇
  2007年   96篇
  2006年   82篇
  2005年   76篇
  2004年   57篇
  2003年   65篇
  2002年   43篇
  2001年   57篇
  2000年   38篇
  1999年   51篇
  1998年   16篇
  1997年   13篇
  1996年   13篇
  1995年   12篇
  1994年   10篇
  1993年   7篇
  1992年   20篇
  1991年   15篇
  1990年   20篇
  1989年   22篇
  1988年   6篇
  1987年   5篇
  1986年   6篇
  1985年   6篇
  1983年   3篇
  1979年   3篇
  1978年   5篇
  1975年   3篇
  1974年   3篇
  1972年   3篇
  1971年   3篇
  1970年   5篇
  1967年   2篇
  1966年   2篇
  1956年   2篇
排序方式: 共有2273条查询结果,搜索用时 0 毫秒
1.
2.
To establish an animal model of intracranial sparganosis, the fate and behavior of the experimentally inoculated spargana were observed. A total of 102 scolices of spargana were injected into 22 cat brains, and the cats were sacrificed at 2 weeks, 1 month, 3 months and 6 months after the inoculation. Neurosparganosis was established in 77% of the cats. Of 43 recovered worms, 19 (44%) were located in the subdural or subarachnoid space, 16 (37%) in the brain parenchyme, and 2 (5%) in the lateral ventricle. One was detected at the diploic space of the skull and 5 were outside the cranial cavity. All but one were alive, and had grown tails. They were distributed in the brain parenchyme randomly. There was no place which they could not invade. No adult was found in the intestine. Cerebrospinal fluid (CSF) was collected before inoculation, 1 week, 2 weeks, 1 month, 3 months and 6 months after inoculation. The level of anti-sparganum IgG antibody in CSF measured by ELISA began to increase above the criteria of positivity 1 month after inoculation. Three months after inoculation, the values markedly increased. The present findings reveal that intracranial inoculation of spargana into the brains of cats would be a good animal model of experimental neurosparganosis.  相似文献   
3.
The present study is intended to observe the chronologic changes of experimental sparganosis by histopathological observation and detection of circulating anti-sparganum IgG antibody using ELISA. Each of 25 mice was infected with five spargana, and they were examined after 1, 2, 4, 10 weeks or 6 months from infection. The followings are summarized results. 1. The plerocercoids were detected in the subcutaneous tissue of the trunk, neck or axilla, but a few often extended into the skeletal muscle. The recovery rates were 72% at the first week, 80% at the second week, 95% at the fourth week, 92% at the tenth week and 100% at the sixth month. The larvae grew slowly in both length and weight until 6 months. 2. Histopathologically, most of the larvae were observed alive in the soft tissue or skeletal muscle. Numerous eosinophils, neutrophils, lymphocytes and plasma cells were infiltrated focally around the worms by the second week, but they surrounded the worms to form a layer of inflammatory reaction after 4 weeks of infection. Also histiocytes and fibroblasts began to appear around the inflammatory cells at 4 weeks. After 10 weeks, the worms encircled by a thin fibrous layer were found. After 6 months, the worms were surrounded by either fibrous tissue or active inflammatory cells. The inflammation looked more severe in the tracks left by the worms, rather than around the worms. 3. The level of anti-sparganum IgG antibody in the serum showed an increase by the fourth week, and a rapid and continuous increase was observed thereafter by the tenth week after infection.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
4.
Summary The electrochemical effect of a charged dextran derivative and the hydrophobic effect of hydrophobic chain PEG derivative on partitioning of six types of proteins in PEG/dextran aqueous two-phase systems were investigated- When 1. 6%(w/w)DEAE-dextran was present in the system,the partition coefficient decreased quickly with increasing pH value;when 0. 4% (w/w)PEG pentadecanoic acid ester was present in the system, the partition coefficient of protein with strong hydrophobicity was greatly increased. The experimental results show that the influence of hydrocarbon chain PEG derivative on partition coefficient is closely related to the hydrophobicity of proteins.  相似文献   
5.
6.
The neoglycolipid technology comprises several microproceduresinvolving the generation of lipid-linked oligosaccharide probesfor carbohydrate recognition studies in conjunction with oligosaccharidesequence determination by mass spectrometry. Although applicableto any desired oilgosaccharides, procedures are greatly facilitatedif the ohgosaccharides are nonreduced, as conjugation is byreductive amination of a reducing end aldehyde to a phosphatidylethanolamine.Using bovine submaxillary mucin as a model for release of O-glycansin the reducing state, and based on yields of neoglycolipidsand side-products from "peeling" reactions and degradation,aqueous ethylamine 70% w/v at 22°C for 48 h has been selectedin preference to other conditions, triethylainine, sodium hydroxide,and bydrazine. The integrity of the main acidic and neutraloligosaccharides released under these conditions, di- to octasaccharides,was established by analyses of free oligosaccharides by liquidsecondary ion mass spectrometry (LSIMS) and of the derived neoglycolipidsby TLCLSIMS; the repertoire compared favorably with that ofthe oligosaccharide alditols generated by conventional reductivealkaline borohydride treatment. More forcing conditions of ethylamine70% w/v at 65°C for 6 h were required to release oligosaccharidesfrom porcine gastric mucin; di- to nonasaccharides were obtainedof which about one-third had an intact core GalNAc. Relativeto yields after reductive alkaline hydrolysis, the overall yieldsfor these two glycoproteins were 20% and 40–50% for acidicand neutral oligosaccharides, respectively. Among O-glycansreleased from an ovarian cystadenoma glycoprotein using ethylamine,three variants of the sulfated Lea/x sequences were identifiedas ligands for the endothelial adhesion molecule E-selectin,one of which is based on the unusual backbone Gal-3/4GlcNAc-3Gal-3Gal. mucins O-linked oligosaccharides TLC-LSIMS neoglycolipids E-selectin  相似文献   
7.
诺卡氏菌对油酸的羟基化作用   总被引:1,自引:0,他引:1  
诺卡氏菌(Nocardia sp.N13)休止细胞对油酸(顾-9-十八碳烯酸)进行羟基化作用。用休止细胞转化时最适温度为30℃,最适pH为6.5,当菌体(干菌)与底物的最适比例为20 :1对,对油酸的转化率为83.4%,不同的表面活性剂影响转化的效果。N13休止细胞在磷酸缓冲液中重复转化3次仍可保持50%左右的转化率。红外光谱、质谱、棱磁共振鉴定产物为10-羟基硬脂酸。  相似文献   
8.
Extraction of the white matter of pig brain with EDTA, lysolecithin or Triton X-100 gave poor yields of soluble acetylcholinesterase although these agents had proved effective at solubilizing the enzyme in the grey matter. This finding, together with the observation that the strong detergent sodium deoxycholate, was needed to solubilize the enzyme, shows that it is more difficult to remove acetylcholinesterase from the white matter of brain than from the grey. This could mean that the enzyme in the white matter is more firmly bound to the membrane than the enzyme in the grey matter.The difference in binding of the enzyme from the two regions of the brain is also reflected in the affinity chromatography experiments which showed a lower recovery for the acetylcholinesterase of white matter compared with the enzyme from grey matter.Starch-block electrophoresis of acetylcholinesterase showed a single negatively charged peak of activity for both the naturally soluble and the deoxycholate solubilized preparations. The presence of only one form on electrophoresis suggests that the molecular species of acetylcholinesterase do not arise from differences in charge.Sucrose density gradient centrifugation of the two preparations from white matter gave a single peak of activity with a sedimentation constant of about 10 S. This corresponds closely to the major species of molecular weight 260,000 detected by gradient gel electrophoresis. Other forms detected in both enzyme preparations by gradient gel electrophoresis were species with molecular weights of 660,000, 180,000, 130,000 and 115,000. The significance of these species in terms of the formation of oligomers is discussed.A comparison was made with the corresponding preparations of acetylcholinesterase from the grey matter and the results showed that acetylcholinesterase from the white and grey matter of pig brain were very similar. The exception to this was the species with a molecular weight of 68,000 which was present in the grey but not the white matter of pig brain.  相似文献   
9.
10.
Binding specificity of the major surfactant protein SP-A from human and dog lung has been investigated. Radiobinding experiments have shown that both proteins bind in a Ca(2+)-dependent manner to galactose, mannose, fucose, and glucose linked to bovine serum albumin. These results are in accord with a previous study in which monosaccharides were linked to agarose (Haagsman, H. P., Hawgood, S., Sargeant, T., Buckley, D., White, R. T., Drickamer, K., and Benson, B. J. (1987) J. Biol. Chem. 262, 13877-13880). Chromatogram overlays in conjunction with in situ liquid secondary ion mass spectrometry (TLC-LSIMS) of several purified glycosphingolipids and neoglycolipids as well as binding assays with glycolipids immobilized on plastic wells, demonstrate recognition of galactose (human and dog SP-A), glucose, and lactose (human SP-A) in association with specific lipids. In addition, the occurrence of several neutral and acidic glycosphingolipids in human and rat extracellular surfactants and rat alveolar type II cells is described. Selected components among the neutral glycolipids are bound by radiolabeled human SP-A; these are identified by TLC-LSIMS as predominantly ceramide mono- and disaccharides (human surfactant) and ceramide tri- and tetrasaccharides (rat surfactant and type II cells). A recombinant carbohydrate recognition domain (CRD) of human SP-A inhibits the binding of human SP-A to galactosyl ceramide and to galactose- and mannose-bovine serum albumin, indicating that the CRD is directly involved in the binding of SP-A to these ligands. These results provide evidence for a novel type of binding specificity for proteins that have Ca(2+)-dependent CRDs and raise the possibility that glycosphingolipids are endogenous ligands for SP-A.  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