全文获取类型
收费全文 | 3587篇 |
免费 | 241篇 |
国内免费 | 1篇 |
专业分类
3829篇 |
出版年
2023年 | 21篇 |
2022年 | 36篇 |
2021年 | 83篇 |
2020年 | 30篇 |
2019年 | 52篇 |
2018年 | 47篇 |
2017年 | 48篇 |
2016年 | 70篇 |
2015年 | 166篇 |
2014年 | 193篇 |
2013年 | 254篇 |
2012年 | 262篇 |
2011年 | 290篇 |
2010年 | 180篇 |
2009年 | 158篇 |
2008年 | 215篇 |
2007年 | 241篇 |
2006年 | 227篇 |
2005年 | 192篇 |
2004年 | 214篇 |
2003年 | 173篇 |
2002年 | 149篇 |
2001年 | 27篇 |
2000年 | 24篇 |
1999年 | 24篇 |
1998年 | 31篇 |
1997年 | 35篇 |
1996年 | 17篇 |
1995年 | 21篇 |
1994年 | 23篇 |
1993年 | 19篇 |
1992年 | 26篇 |
1991年 | 17篇 |
1990年 | 20篇 |
1989年 | 18篇 |
1988年 | 15篇 |
1987年 | 14篇 |
1986年 | 10篇 |
1985年 | 11篇 |
1984年 | 16篇 |
1983年 | 12篇 |
1982年 | 26篇 |
1981年 | 21篇 |
1980年 | 17篇 |
1979年 | 12篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1974年 | 7篇 |
排序方式: 共有3829条查询结果,搜索用时 15 毫秒
71.
Rational design of Salmonella-based vaccination strategies 总被引:3,自引:0,他引:3
A permanently growing body of information is becoming available about the quality of protective immune responses induced by mucosal immunization. Attenuated live bacterial vaccines can be administered orally and induce long-lasting protective immunity in humans without causing major side effects. An attenuated Salmonella enterica serovar Typhi strain is registered as live oral vaccine against typhoid fever and has been in use for more than two decades. Recombinant attenuated Salmonella strains are also an attractive means of delivering heterologous antigens to the immune system, thereby, stimulating strong mucosal and systemic immune responses and consequently provide an efficient platform technology to design novel vaccination strategies. This includes the choice of heterologous protective antigens and their expression under the control of appropriate promoters within the carrier strain. The availability of well-characterized attenuated mutants of Salmonella concomitantly supports fine tuning of immune response triggered against heterologous antigens. Exploring different mucosal sites as a potential route of immunization has to be taken into account as an additional important way to modulate immune responses according to clinical requirements. This article focuses on the rational design of strategies to modulate appropriate immunological effector functions on the basis of selection of (i) attenuating mutations of the Salmonella strains, (ii) specific expression systems for the heterologous antigens, and (iii) route of mucosal administration. 相似文献
72.
Anion-exchange high-performance liquid chromatographic analysis of inositol phosphates 总被引:1,自引:0,他引:1
The analysis of inositol phosphates by anion-exchange HPLC is described. The method employs a citrate buffer gradient to resolve several inositol phosphates including inositol 1-phosphate, inositol 1,4-bisphosphate (IP2), and inositol 1,4,5-trisphosphate (IP3), as well as some of the isomers of these compounds. Since the buffer system does not contain any phosphate, we can use a phosphate assay to examine the chromatographic behavior of phosphate-containing compounds. The method shows good resolution and recovery (greater than 95% for IP2 and IP3). Total analysis time, including reequilibration, is about 90 min. In addition, an isocratic system that can rapidly (less than 10 min) measure IP3 is described. The HPLC system was used to characterize inositol phosphate turnover in thrombin-stimulated platelets and formylmethionyl-leucyl-phenylalanine-stimulated HL-60 cells. 相似文献
73.
Catherin Niemann Volker Brinkmann Eva Spitzer Guido Hartmann Martin Sachs Helga Naundorf Walter Birchmeier 《The Journal of cell biology》1998,143(2):533-545
We have established a cell culture system that reproduces morphogenic processes in the developing mammary gland. EpH4 mouse mammary epithelial cells cultured in matrigel form branched tubules in the presence of hepatocyte growth factor/scatter factor (HGF/SF), the ligand of the c-met tyrosine kinase receptor. In contrast, alveolar structures are formed in the presence of neuregulin, a ligand of c-erbB tyrosine kinase receptors. These distinct morphogenic responses can also be observed with selected human mammary carcinoma tissue in explant culture. HGF/SF-induced branching was abrogated by the PI3 kinase inhibitors wortmannin and . In contrast, neuregulin- induced alveolar morphogenesis was inhibited by the MAPK kinase inhibitor PD98059. The c-met–mediated response could also be evoked by transfection of a c-met specific substrate, Gab1, which can activate the PI3 kinase pathway. An activated hybrid receptor that contained the intracellular domain of c-erbB2 receptor suffices to induce alveolar morphogenesis, and was observed in the presence of tyrosine residues Y1028, Y1144, Y1201, and Y1226/27 in the substrate-binding domain of c-erbB2. Our data demonstrate that c-met and c-erbB2 signaling elicit distinct morphogenic programs in mammary epithelial cells: formation of branched tubules relies on a pathway involving PI3 kinase, whereas alveolar morphogenesis requires MAPK kinase. LY294002相似文献
74.
Dario Cremaschi Giuliano Meyer Guido Bottà Carlo Rossetti 《The Journal of membrane biology》1987,95(3):219-228
Summary In the epithelium of rabbit gallbladder, in the nominal absence of bicarbonate, intracellular Cl– activity is about 25mm, about 4 times higher than intracellular Cl– activity at the electrochemical equilibrium. It is essentially not affected by 10–4
m acetazolamide and 10–4
m 4-acetamido-4-isothiocyanostilbene-2,2-disulfonate (SITS) even during prolonged exposures; it falls to the equilibrium value by removal of Na+ from the lumen without significant changes of the apical membrane potential difference. Both intracellular Cl– and Na+ activities are decreased by luminal treatment with 25mm SCN–; the initial rates of change are not significantly different. In addition, the initial rates of change of intracellular Cl– activity are not significantly different upon Na+ or Cl– entry block by the appropriate reduction of the concentration of either ion in the luminal solution. Luminal K+ removal or 10–5
m bumetanide do not affect intracellular Cl– and Na+ activities or Cl– influx through the apical membrane. It is concluded that in the absence of bicarbonate NaCl entry is entirely due to a Na+–Cl– symport on a single carrier which, at least under the conditions tested, does not cotransport K+. 相似文献
75.
Salis A Svensson I Monduzzi M Solinas V Adlercreutz P 《Biochimica et biophysica acta》2003,1646(1-2):145-151
Candida antarctica lipase B (CALB) and Thermomyces lanuginosa lipase (TLL) were evaluated as catalysts in different reaction media using hydrolysis of tributyrin as model reaction. In o/w emulsions, the enzymes were used in the free form and for use in monophasic organic media, the lipases were adsorbed on porous polypropylene (Accurel EP-100). In monophasic organic media, the highest specific activity of both lipases was obtained in pure tributyrin at a water activity of >0.5 and at an enzyme loading of 10 mg/g support. With tributyrin emulsified in water, the specific activities were 2780 micromol min(-1) mg(-1) for TLL and 535 micromol min(-1) mg(-1) for CALB. Under optimal conditions in pure tributyrin, CALB expressed 49% of the activity in emulsion (264 micromol min(-1) mg(-1)) while TLL expressed only 9.2% (256 micromol min(-1) mg(-1)) of its activity in emulsion. This large decrease is probably due to the structure of TLL, which is a typical lipase with a large lid domain. Conversion between open and closed conformers of TLL involves large internal movements and catalysis probably requires more protein mobility in TLL than in CALB, which does not have a typical lid region. Furthermore, TLL lost more activity than CALB when the water activity was reduced below 0.5, which could be due to further reduction in protein mobility. 相似文献
76.
Massimo Aureli Valentina Murdica Nicoletta Loberto Maura Samarani Alessandro Prinetti Rosaria Bassi Sandro Sonnino 《Glycoconjugate journal》2014,31(6-7):449-459
The aim of radiotherapy is to eradicate cancer cells with ionizing radiation; tumor cell death following irradiation can be induced by several signaling pathways, most of which are triggered as a consequence of DNA damage, the primary and major relevant cell response to radiation. Several lines of evidence demonstrated that ceramide, a crucial sensor and/or effector of different signalling pathways promoting cell cycle arrest, death and differentiation, is directly involved in the molecular mechanisms underlying cellular response to irradiation. Most of the studies strongly support a direct relationship between ceramide accumulation and radiation-induced cell death, mainly apoptosis; for this reason, defining the contribution of the multiple metabolic pathways leading to ceramide formation and the causes of its dysregulated metabolism represent the main goal in order to elucidate the ceramide-mediated signaling in radiotherapy. In this review, we summarize the current knowledge concerning the different routes leading to ceramide accumulation in radiation-induced cell response with particular regard to the role of the enzymes involved in both ceramide neogenesis and catabolism. Emphasis is placed on sphingolipid breakdown as mechanism of ceramide generation activated following cell irradiation; the functional relevance of this pathway, and the role of glycosphingolipid glycohydrolases as direct targets of ionizing radiation are also discussed. These new findings add a further attractive point of investigation to better define the complex interplay between sphingolipid metabolism and radiation therapy. 相似文献
77.
78.
Evidence for two waves of induction of DNA enzymes in stimulated human lymphocytes 总被引:2,自引:3,他引:2 下载免费PDF全文
Guido C. F. Pedrali Noy Leda Dalpra Antonia M. Pedrini Giovanni Ciarrocchi Elena Giulotto Fiorella Nuzzo Arturo Falaschi 《Nucleic acids research》1974,1(9):1183-1199
The stimulation of human lymphocytes with phytohaemoagglutinin induces the appearance or increase of several enzymes of DNA metabolism [Pedrini etal., Biochem. Biophys. Res. Comm., 47:1221(1972)]. With long times of stimulation, two phenomena are observed; an increase in the levels of DNA polymerase, of a DNase acting on single-stranded DNA, and of an endonuclease, occurring between the third and fourth day, in parallel with a wave of DNA synthesis;a second wave of increase of the same enzymes and of DNA ligase,occurring between the fifth and eight day when the DNA replication rate, as measured by thymidine-pulses, has decreased to values close to the background. 相似文献
79.
Monica Gomaraschi Alice Ossoli Silvia Pozzi Peter Nilsson Angelo B. Cefalù Maurizio Averna Jan Albert Kuivenhoven G. Kees Hovingh Fabrizio Veglia Guido Franceschini Laura Calabresi 《PloS one》2014,9(5)
Mutations in the CETP gene resulting in defective CETP activity have been shown to cause remarkable elevations of plasma HDL-C levels, with the accumulation in plasma of large, buoyant HDL particles enriched in apolipoprotein E. Genetic CETP deficiency thus represents a unique tool to evaluate how structural alterations of HDL impact on HDL atheroprotective functions. Aim of the present study was to assess the ability of HDL obtained from CETP-deficient subjects to protect endothelial cells from the development of endothelial dysfunction. HDL isolated from one homozygous and seven heterozygous carriers of CETP null mutations were evaluated for their ability to down-regulate cytokine-induced cell adhesion molecule expression and to promote NO production in cultured endothelial cells. When compared at the same protein concentration, HDL and HDL3 from carriers proved to be as effective as control HDL and HDL3 in down-regulating cytokine-induced VCAM-1, while carrier HDL2 were more effective than control HDL2 in inhibiting VCAM-1 expression. On the other hand, HDL and HDL fractions from carriers of CETP deficiency were significantly less effective than control HDL and HDL fractions in stimulating NO production, due to a reduced eNOS activating capacity, likely because of a reduced S1P content. In conclusion, the present findings support the notion that genetic CETP deficiency, by affecting HDL particle structure, impacts on HDL vasculoprotective functions. Understanding of these effects might be important for predicting the outcomes of pharmacological CETP inhibition. 相似文献
80.
Jan-Peter Sowa ?zgür Atmaca Alisan Kahraman Martin Schlattjan Marion Lindner Svenja Sydor Norbert Scherbaum Karoline Lackner Guido Gerken Dominik Heider Gavin E. Arteel Yesim Erim Ali Canbay 《PloS one》2014,9(7)