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   161篇
  免费   22篇
  2023年   3篇
  2015年   3篇
  2014年   3篇
  2013年   5篇
  2012年   2篇
  2011年   8篇
  2010年   2篇
  2009年   10篇
  2008年   9篇
  2007年   5篇
  2006年   2篇
  2005年   7篇
  2004年   8篇
  2003年   5篇
  2002年   2篇
  2001年   3篇
  2000年   3篇
  1999年   8篇
  1998年   4篇
  1997年   4篇
  1996年   3篇
  1995年   6篇
  1992年   4篇
  1991年   3篇
  1990年   3篇
  1987年   5篇
  1986年   4篇
  1985年   2篇
  1984年   4篇
  1983年   2篇
  1982年   3篇
  1981年   3篇
  1979年   4篇
  1978年   2篇
  1977年   2篇
  1976年   2篇
  1975年   4篇
  1974年   4篇
  1973年   4篇
  1971年   1篇
  1970年   3篇
  1969年   1篇
  1965年   2篇
  1963年   1篇
  1959年   1篇
  1958年   1篇
  1957年   2篇
  1953年   1篇
  1924年   1篇
  1905年   1篇
排序方式: 共有183条查询结果,搜索用时 15 毫秒
1.
First appearing in 2000, and with 20,000 copies sold as it entered its sixth printing in 2004, Richard Trudgen's Why Warriors Lie down and Die is a minor publishing phenomenon. Although scholarly forums have generally ignored the book, Christian media outlets, the popular press and neo‐conservative political activists have enthusiastically received and promoted it. An examination of the merits of Why Warriors Lie down and Die suggests that its popularity is only partly explained by original observations or insights on the part of the author. The most important explanation, and implication, of the book's remarkable take‐up lies in the opportune way in which it corresponds with now ascendant neo‐conservative political perspectives on indigenous policy.  相似文献   
2.
S L Mowbray  D E Koshland 《Cell》1987,50(2):171-180
The aspartate and maltose responses of E. coli are mediated through a single membrane receptor, yet the responses are independent and additive. Both stimuli cause methylation of the same 4 glutamic acid residues. More extensive methylation occurs when a cell that has adapted to one stimulus is exposed to the second, or when both stimuli are added simultaneously. The degree of methylation, as well as receptor migration on two-dimensional gels, demonstrates that only one type of protein is involved, rather than two different receptors arising from differential processing of a single gene. A conformational "push-pull" mechanism in which binding of stimulus and covalent modification, producing opposing stresses, can explain these diverse results.  相似文献   
3.
Ribose-binding protein is a bifunctional soluble receptor found in the periplasm of Escherichia coli. Interaction of liganded binding protein with the ribose high affinity transport complex results in the transfer of ribose across the cytoplasmic membrane. Alternatively, interaction of liganded binding protein with a chemotactic signal transducer, Trg, initiates taxis toward ribose. We have generated a functional map of the surface of ribose-binding protein by creating and analyzing directed mutations of exposed residues. Residues in an area on the cleft side of the molecule including both domains have effects on transport. A portion of the area involved in transport is also essential to chemotactic function. On the opposite face of the protein, mutations in residues near the hinge are shown to affect chemotaxis specifically.  相似文献   
4.
The effects of the trichothecene mycotoxins (acetyl T-2 toxin, T-2 toxin, HT-2 toxin, palmityl T-2 toxin, diacetoxyscirpenol (DAS), deoxynivalenol (DON), and T-2 tetraol) on bovine platelet function were examined in homologous plasma stimulated with platelet activating factor (PAF). The mycotoxins inhibited platelet function with the following order of potency: acetyl T-2 toxin > palmityl T-2 toxin = DAS > HT-2 toxin = T-2 toxin. While T-2 tetraol was completely ineffective as an inhibitor, DON exhibited minimal inhibitory activity at concentrations above 10×10?4M. The stability of the platelet aggregates formed was significantly reduced in all mycotoxin treated platelets compared to that of the untreated PAF controls. It is suggested that the increased sensitivity of PAF stimulated bovine platelets to the more lipophilic mycotoxins may be related to their more efficient partitioning into the platelet membrane compared to the more hydrophilic compounds.  相似文献   
5.
Skeletons of chimpanzees with recorded life stories allow assessment of the potential relationships among hard tissue features and expressed behaviors. We analyze bone size, weight, and mineralization to assess osteological characters for identification of laterality of expressed behaviors involving the upper body. Results show that associations are not yet clearly defined.  相似文献   
6.
During the period of COVID-19, the occurrences of mucormycosis in immunocompromised patients have increased significantly. Mucormycosis (black fungus) is a rare and rapidly progressing fungal infection associated with high mortality and morbidity in India as well as globally. The causative agents for this infection are collectively called mucoromycetes which are the members of the order Mucorales. The diagnosis of the infection needs to be performed as soon as the occurrence of clinical symptoms which differs with types of Mucorales infection. Imaging techniques magnetic resonance imaging or computed tomography scan, culture testing, and microscopy are the approaches for the diagnosis. After the diagnosis of the infection is confirmed, rapid action is needed for the treatment in the form of antifungal therapy or surgery depending upon the severity of the infection. Delaying in treatment declines the chances of survival. In antifungal therapy, there are two approaches first-line therapy (monotherapy) and combination therapy. Amphotericin B ( 1 ) and isavuconazole ( 2 ) are the drugs of choice for first-line therapy in the treatment of mucormycosis. Salvage therapy with posaconazole ( 3 ) and deferasirox ( 4 ) is another approach for patients who are not responsible for any other therapy. Adjunctive therapy is also used in the treatment of mucormycosis along with first-line therapy, which involves hyperbaric oxygen and cytokine therapy. There are some drugs like VT-1161 ( 5 ) and APX001A ( 6 ), Colistin, SCH 42427, and PC1244 that are under clinical trials. Despite all these approaches, none can be 100% successful in giving results. Therefore, new medications with favorable or little side effects are required for the treatment of mucormycosis.  相似文献   
7.
1. The contents of the major purine nucleotides in the isolated non-working perfused rat heart varied systematically during 80min of perfusion. In particular the amounts of ATP, ADP, GTP, cyclic AMP and cyclic GMP in the well-oxygenated myocardium showed changes ranging from 25 to 60% of the mean concentrations. The apparent periodicity was about 30min for some and about 60min for other nucleotides. 2. These data are in contrast with measurements of parameters reflecting heart performance, which remained constant over this period of perfusion. 3. The ATP/ADP ratio, the cyclic AMP content, the GTP content and the GTP/GDP ratio in the tissue bore a constant relationship to one another, and all showed the same temporal variation. 4. Increasing the energy demand on the heart by administration of bovine somatotropin (1μg/ml) tended to damp the variations, and generally lower the content of all the nucleotides. 5. The total extractable adenine nucleotide pool also showed systematic temporal variations of as much as 1.3μmol/g wet wt. of tissue within 10min. 6. These variations could not be accounted for as inter-conversion with adenosine, other purine nucleotides, nucleosides or purine-degradation products either in the tissue or in the perfusion medium. No evidence was found in this preparation of the purine nucleotide oscillations described by Lowenstein and his co-workers [see Tornheim & Lowenstein (1975) J. Biol. Chem. 250, 6304–6314]. 7. Further, the pool size increases cannot be satisfactorily explained by either synthesis de novo or the breakdown of any purine macromolecular species in the cell. Thus it is suggested that an unsuspected substantial storage form of purine nucleotide may exist in heart.  相似文献   
8.
The X-ray structure of the periplasmic ribose receptor (binding protein) of Escherichia coli (RBP) was solved at 3 A resolution by the method of multiple isomorphous replacement. Alternating cycles of refitting and refinement have resulted in a model structure with an R-factor of 18.7% for 27,526 reflections from 7.5 to 1.7 A resolution (96% of the data). The model contains 2228 non-hydrogen atoms, including all 271 residues of the amino acid sequence, 220 solvent atoms and beta-D-ribose. The protein consists of two highly similar structural domains, each of which is composed of a core of parallel beta-sheet flanked on both sides by alpha-helices. The two domains are related to each other by an almost perfect 2-fold axis of rotation, with the C termini of the beta-strands of each sheet pointing toward the center of the molecule. Three short stretches of amino acid chain (from symmetrically related portions of the protein) link these two domains, and presumably act as a hinge to allow relative movement of the domains in functionally important conformational changes. Two water molecules are also an intrinsic part of the hinge, allowing crucial flexibility in the structure. The ligand beta-D-ribose (in the pyranose form) is bound between the domains, held by interactions with side-chains of the interior loops. The binding site is precisely tailored, with a combination of hydrogen bonding, hydrophobic and steric effects giving rise to tight binding (0.1 microM for ribose) and high specificity. Four out of seven binding-site residues are charged (2 each of aspartate and arginine) and contribute two hydrogen bonds each. The remaining hydrogen bonds are contributed by asparagine and glutamine residues. Three phenylalanine residues supply the hydrophobic component, packing against both faces of the sugar molecule. The arrangement of these hydrogen bonding and hydrophobic residues results in an enclosed binding site with the exact shape of the allowed sugar molecules; in the process of binding, the ligand loses all of its surface-accessible area. The sites of two mutations that affect the rate of folding of the ribose receptor are shown to be located near small cavities in the wild-type protein. The cavities thus allow the incorporation of the larger residues in the mutant proteins. Since these alterations would seriously affect the ability of the protein to build the first portion of the hydrophobic core in the first domain, it is proposed that this process is the rate-limiting step in folding of the ribose receptor.  相似文献   
9.
Perfusion with [8-14C]adenosine demonstrated the likely existence in rat liver of oligophosphoglyceroyl-ATP (OPG-ATP). Purification followed by assay with a new specific 3' phosphodiesterase confirmed this. The quantities present were 5-10-fold those found previously and comparable to total soluble nucleotides. OPG-ATP was also purified from the mitochondrial fraction, shown to co-distribute with succinate dehydrogenase and can be co-purified with an enzyme confined to intermembrane space.  相似文献   
10.
AR Boobis  MB Slade  C Stern  KM Lewis  DS Davies 《Life sciences》1981,29(14):1443-1448
Cytochrome P-448 (mol wt 55,000 Daltons) from rabbit liver was purified to a specific content of 16.6 nmol/mg. Mice were immunised with this preparation, their spleens removed and dissociated lymphocytes hybridised with myeloma cells. Four monoclonal antibodies against cytochrome P-448 were raised and partially characterised. All four antibodies interacted with cytochrome P-448 in intact microsomal fractions and selectively immunoadsorbed cytochrome P-448 from solubilised microsomal preparations. One of the antibodies inhibited benzo[a] pyrene hydroxylase activity in a reconstituted system, one had no effect on activity and two increased activity. The possible applications of such antibodies 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