全文获取类型
收费全文 | 1644篇 |
免费 | 134篇 |
出版年
2023年 | 15篇 |
2022年 | 8篇 |
2021年 | 38篇 |
2020年 | 25篇 |
2019年 | 33篇 |
2018年 | 51篇 |
2017年 | 34篇 |
2016年 | 61篇 |
2015年 | 84篇 |
2014年 | 91篇 |
2013年 | 127篇 |
2012年 | 139篇 |
2011年 | 128篇 |
2010年 | 92篇 |
2009年 | 74篇 |
2008年 | 103篇 |
2007年 | 89篇 |
2006年 | 92篇 |
2005年 | 88篇 |
2004年 | 69篇 |
2003年 | 75篇 |
2002年 | 72篇 |
2001年 | 14篇 |
2000年 | 8篇 |
1999年 | 15篇 |
1998年 | 22篇 |
1997年 | 10篇 |
1996年 | 13篇 |
1995年 | 13篇 |
1994年 | 11篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 9篇 |
1988年 | 7篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 14篇 |
1983年 | 1篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有1778条查询结果,搜索用时 15 毫秒
91.
92.
Brandolini L Allegretti M Berdini V Cervellera MN Mascagni P Rinaldi M Melillo G Ghezzi P Mengozzi M Bertini R 《European cytokine network》2003,14(1):20-26
Carbocysteine lysine salt monohydrate (SCMC-Lys) is a well-known mucoactive drug whose therapeutic efficacy is commonly related to the ability of SCMC-Lys to replace fucomucins by sialomucins. The aim of this study was to determine if SCMC-Lys could exert an anti-oxidant action by scavenging reactive oxygen intermediates (ROIs). Our results show that SCMC-Lys proved effective as a selective scavenger of hypochlorous acid (HOCl) and hydroxyl radical (OH.), this effect being related to the reactivity of the SCMC tioether group. The scavenger activity of SCMC-Lys was observed in free cellular system as well as in activated human polymorphonuclear neutrophils (PMNs). SCMC-Lys scavenger activity on HOCl was paralleled by a powerful protection from HOCl-mediated inactivation of alpha1-antitripsin (alpha1-AT) inhibitor, the main serum protease inhibitor. Production of interleukin-(IL-)8, a major mediator of PMN recruitment in inflammatory diseases, is known to be mediated by intracellular OH. SCMC-Lys significantly reduced IL-8 production on stimulated human peripheral blood mononuclear cells (PBMCs) in the same range of concentrations affecting OH. activity. It is concluded that SCMC-Lys could exert, in addition to its mucoactive capacity, an anti-oxidant action, thus contributing to the therapeutic efficacy of SCMC-Lys. 相似文献
93.
Baratto MC Tattini M Galardi C Pinelli P Romani A Visioli F Basosi R Pogni R 《Free radical research》2003,37(4):405-412
The antioxidant properties of galloyl quinic derivatives isolated from Pistacia lentiscus L. leaves have been investigated by means of Electron Paramagnetic Resonance spectroscopy (EPR) and UV-Vis spectrophotometry. Antioxidant properties have been also estimated using the biologically relevant LDL test. The scavenger activities of gallic acid, 5- O -galloyl, 3,5- O -digalloyl, 3,4,5- O -trigalloyl quinic acid derivatives, have been estimated against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, superoxide ( O 2 - ) radical, and hydroxyl (OH) radical. On the whole, the scavenger activity raised as the number of galloyl groups on the quinic acid skeleton increased. The half-inhibition concentrations (IC 50 ) of di- and tri-galloyl derivatives did not exceed 30 μM for all the tested free radicals. All the tested metabolites strongly reduced the oxidation of low-density lipoproteins (LDL), following a trend similar to that observed for the scavenger ability against OH radical. 相似文献
94.
Onori L Aggio A Taddei G Loreto MF Ciccocioppo R Vicini R Tonini M 《American journal of physiology. Gastrointestinal and liver physiology》2003,285(2):G325-G331
In the gastrointestinal tract, tachykinin NK1 receptors are widely distributed in a number of neuronal and nonneuronal cells involved in the control of gut motor activity. In particular, in the rabbit isolated distal colon, which is a suitable model system to investigate the contribution of tachykinins as noncholinergic excitatory transmitters, the influence of NK1 receptors in the regulation of peristalsis is not known. The selective NK1-receptor antagonists SR-140333 (0.3 and 1 nM) and MEN-10930 (0.3-10 nM) significantly enhanced the velocity of rabbit colonic propulsion to submaximal stimulation. The prokinetic effect of SR-140333 was prevented by N(omega)-nitro-L-arginine (L-NNA), a nitric oxide synthase inhibitor, indicating that NK1 receptors located on nitrergic innervation exert a functional inhibitory restraint on the circular muscle and probably on descending excitatory and inhibitory pathways during propulsion. Conversely, the selective NK1-receptor agonist septide (3-10 nM) significantly inhibited colonic propulsion. In the presence of L-NNA, the inhibitory effect of septide was reverted into a prokinetic effect, which is probably mediated by the activation of postjunctional excitatory NK1 receptors. 相似文献
95.
Horiuchi K Weskamp G Lum L Hammes HP Cai H Brodie TA Ludwig T Chiusaroli R Baron R Preissner KT Manova K Blobel CP 《Molecular and cellular biology》2003,23(16):5614-5624
ADAM15 (named for a disintegrin and metalloprotease 15, metargidin) is a membrane-anchored glycoprotein that has been implicated in cell-cell or cell-matrix interactions and in the proteolysis of molecules on the cell surface or extracellular matrix. To characterize the potential roles of ADAM15 during development and in adult mice, we analyzed its expression pattern by mRNA in situ hybridization and generated mice carrying a targeted deletion of ADAM15 (adam15(-/-) mice). A high level of expression of ADAM15 was found in vascular cells, the endocardium, hypertrophic cells in developing bone, and specific areas of the hippocampus and cerebellum. However, despite the pronounced expression of ADAM15 in these tissues, no major developmental defects or pathological phenotypes were evident in adam15(-/-) mice. The elevated levels of ADAM15 in endothelial cells prompted an evaluation of its role in neovascularization. In a mouse model for retinopathy of prematurity, adam15(-/-) mice had a major reduction in neovascularization compared to wild-type controls. Furthermore, the size of tumors resulting from implanted B16F0 mouse melanoma cells was significantly smaller in adam15(-/-) mice than in wild-type controls. Since ADAM15 does not appear to be required for developmental angiogenesis or for adult homeostasis, it may represent a novel target for the design of inhibitors of pathological neovascularization. 相似文献
96.
Potential of Unicellular Cyanobacteria from Saline Environments as Exopolysaccharide Producers 总被引:3,自引:1,他引:2 下载免费PDF全文
Roberto De Philippis Maria Cristina Margheri Riccardo Materassi Massimo Vincenzini 《Applied microbiology》1998,64(3):1130-1132
Fifteen Cyanothece strains isolated from saline environments have been characterized with regard to exopolysaccharide (EPS) production. The polymers contained six to eight monosaccharides, with one or two acidic sugars. In some EPS samples, the additional presence of acetyl, pyruvyl, and/or sulfate groups was also detected. 相似文献
97.
98.
Riccardo A.A Muzzarelli Viviana Ramos Vesna Stanic Bruno Dubini Monica Mattioli-Belmonte Giorgio Tosi Roberto Giardino 《Carbohydrate polymers》1998,36(4):267-276
The effects of N,N-dicarboxymethyl chitosan (DCMC) on the precipitation of insoluble calcium salts, namely phosphate, sulfate, oxalate, carbonate, bicarbonate and fluoride, and magnesium salts, namely phosphate and carbonate, were studied. Results indicated that the chelating ability of DCMC interfered effectively with the well-known physico-chemical behaviour of magnesium and calcium salts. Dicarboxymethyl chitosan formed self-sustaining gels upon mixing with calcium acetate, as a consequence of calcium chelation. DCMC mixed with calcium acetate and with disodium hydrogen phosphate in appropriate ratios (molar ratio Ca/DCMC close to 2.4) yielded a clear solution, from which, after dialysis and freeze-drying, an amorphous material was isolated containing an inorganic component about one half its weight. This compound was used for the treatment of bone lesions in experimental surgery and in dentistry. Bone tissue regeneration was promoted in sheep, leading to complete healing of otherwise non-healing surgical defects. Radiographic evidence of bone regeneration was observed in human patients undergoing apicectomies and avulsions. The DCMC–CaP chelate favoured osteogenesis while promoting bone mineralization. 相似文献
99.
A method for monitoring low-density lipoprotein (LDL) oxidation by low-level chemiluminescence (LL-CL) is described in this study. The kinetic indices obtained with this procedure, in particular lag-time and K value (related to prooxidant activity of Cu2+ bound to LDL) are compared with those of the established UV-absorbing conjugated diene assay. The correlation of lag-time values obtained by LL-CL and conjugated diene assay was very high both in the case of Cu2+- and peroxyl-radical-mediated oxidation (r = 0.99). By using the transient free radical scavenging activity of butylated hydroxytoluene, a calibration of LL-CL for lipid peroxyl radical and termination rate was obtained. The spectral analysis of LL-CL from oxidizing LDL shows a maximum peak between 420 and 500 nm, corresponding to the emission of triplet carbonyl compounds. LL-CL allows continuous and direct monitoring of LDL oxidation as extraction and derivatization of lipid peroxidation products are not required. Moreover, some limitations of UV spectroscopy such as by absorbing compounds need not be considered. Therefore, the present procedure represents a simple and convenient tool for continuous monitoring of LDL oxidation which may be applied to mechanistic and clinical studies. 相似文献
100.
Long Tree-Ring Chronologies Provide Evidence of Recent Tree Growth Decrease in a Central African Tropical Forest 总被引:1,自引:0,他引:1
Giovanna Battipaglia Enrica Zalloni Simona Castaldi Fabio Marzaioli Roberto Cazzolla- Gatti Bruno Lasserre Roberto Tognetti Marco Marchetti Riccardo Valentini 《PloS one》2015,10(3)
It is still unclear whether the exponential rise of atmospheric CO2 concentration has produced a fertilization effect on tropical forests, thus incrementing their growth rate, in the last two centuries. As many factors affect tree growth patterns, short -term studies might be influenced by the confounding effect of several interacting environmental variables on plant growth. Long-term analyses of tree growth can elucidate long-term trends of plant growth response to dominant drivers. The study of annual rings, applied to long tree-ring chronologies in tropical forest trees enables such analysis. Long-term tree-ring chronologies of three widespread African species were measured in Central Africa to analyze the growth of trees over the last two centuries. Growth trends were correlated to changes in global atmospheric CO2 concentration and local variations in the main climatic drivers, temperature and rainfall. Our results provided no evidence for a fertilization effect of CO2 on tree growth. On the contrary, an overall growth decline was observed for all three species in the last century, which appears to be significantly correlated to the increase in local temperature. These findings provide additional support to the global observations of a slowing down of C sequestration in the trunks of forest trees in recent decades. Data indicate that the CO2 increase alone has not been sufficient to obtain a tree growth increase in tropical trees. The effect of other changing environmental factors, like temperature, may have overridden the fertilization effect of CO2. 相似文献