全文获取类型
收费全文 | 6302篇 |
免费 | 486篇 |
国内免费 | 2篇 |
专业分类
6790篇 |
出版年
2023年 | 31篇 |
2022年 | 92篇 |
2021年 | 157篇 |
2020年 | 106篇 |
2019年 | 126篇 |
2018年 | 159篇 |
2017年 | 140篇 |
2016年 | 224篇 |
2015年 | 330篇 |
2014年 | 328篇 |
2013年 | 556篇 |
2012年 | 563篇 |
2011年 | 498篇 |
2010年 | 332篇 |
2009年 | 254篇 |
2008年 | 401篇 |
2007年 | 395篇 |
2006年 | 362篇 |
2005年 | 267篇 |
2004年 | 276篇 |
2003年 | 262篇 |
2002年 | 236篇 |
2001年 | 49篇 |
2000年 | 34篇 |
1999年 | 55篇 |
1998年 | 57篇 |
1997年 | 51篇 |
1996年 | 45篇 |
1995年 | 29篇 |
1994年 | 40篇 |
1993年 | 42篇 |
1992年 | 28篇 |
1991年 | 21篇 |
1990年 | 22篇 |
1989年 | 13篇 |
1988年 | 14篇 |
1987年 | 16篇 |
1986年 | 12篇 |
1985年 | 10篇 |
1984年 | 18篇 |
1983年 | 15篇 |
1982年 | 18篇 |
1981年 | 17篇 |
1980年 | 7篇 |
1978年 | 13篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1974年 | 7篇 |
1973年 | 7篇 |
1972年 | 6篇 |
排序方式: 共有6790条查询结果,搜索用时 0 毫秒
991.
New Treatment of Medullary and Papillary Human Thyroid Cancer: Biological Effects of Hyaluronic Acid Hydrogel Loaded With Quercetin Alone or in Combination to an Inhibitor of Aurora Kinase 下载免费PDF全文
992.
993.
994.
995.
Rolf Frischknecht Peter Fantke Laura Tschümperlin Monia Niero Assumpció Antón Jane Bare Anne-Marie Boulay Francesco Cherubini Michael Z. Hauschild Andrew Henderson Annie Levasseur Thomas E. McKone Ottar Michelsen Llorenç Milà i Canals Stephan Pfister Brad Ridoutt Ralph K. Rosenbaum Francesca Verones Bruce Vigon Olivier Jolliet 《The International Journal of Life Cycle Assessment》2016,21(3):429-442
996.
Bradley G. Ridoutt Stephan Pfister Alessandro Manzardo Jane Bare Anne-Marie Boulay Francesco Cherubini Peter Fantke Rolf Frischknecht Michael Hauschild Andrew Henderson Olivier Jolliet Annie Levasseur Manuele Margni Thomas McKone Ottar Michelsen Llorenç Milà i Canals Girija Page Rana Pant Marco Raugei Serenella Sala Francesca Verones 《The International Journal of Life Cycle Assessment》2016,21(2):276-280
997.
Basili S Bergen A Dall'Acqua F Faccio A Granzhan A Ihmels H Moro S Viola G 《Biochemistry》2007,46(44):12721-12736
The association of dicationic polycyclic ligands, namely, four diazoniapentaphene derivatives, three diazoniaanthra[1,2-a]anthracenes, diazoniahexaphene, and a partly saturated hydroxy-substituted diazoniapentaphene with double-stranded and triple-helical DNA, was investigated by spectrophotometric and viscosimetric titrations, CD and LD spectroscopy, DNA melting experiments, and molecular modeling studies. All experimental and theoretical data reveal an intercalative DNA-binding mode of the diazoniapentaphenes and diazoniaanthra[1,2-a]anthracenes; the latter have approximately 10-fold higher affinity for the DNA duplex. CD spectroscopic investigations and molecular modeling studies show that only one azonianaphthalene part of the ligand is intercalated between the DNA base pairs, whereas the remaining part of the ligand points outside the intercalation pocket. In contrast, the diazoniahexaphene is a DNA groove binder, which binds selectively to [poly(dAdT)]2. At low ligand-to-DNA ratios (r < 0.15), the diazoniahexaphene also behaves as an intercalator; however, all spectroscopic and viscosimetric data are consistent with significant groove binding of this ligand at r > 0.2. Studies of the interaction of diazoniapolycyclic ions with triplex DNA reveal a preferential binding of both diazoniapentaphenes and diazoniaanthra[1,2-a]anthracenes to the triplex and stabilization thereof. These properties are more pronounced in the case of the hexacyclic diazoniaanthra[1,2-a]anthracenes; however, the diazoniahexaphene shows no preferential binding to the triplex. The DNA binding properties of the diazoniapentaphene derivatives remain essentially the same upon variation of the positions of nitrogen atoms or substitution with methyl groups. In contrast, the interactions of the diazoniaanthra[1,2-a]anthracence isomers with triplex DNA are slightly different. Notably, the 14a,16a-diazoniaanthra[1,2-a]anthracene is among the most efficient triplex stabilizers, with a 9-fold larger binding affinity for the triplex than for the DNA duplex. Moreover, the diazoniapentaphene and diazoniaanthra[1,2-a]anthracene derivatives represent the first examples of triplex-DNA binders that do not require additional aminoalkyl side chains for efficient triplex stabilization. 相似文献
998.
Nickel is a fundamental micronutrient for cellular life, but it is toxic in soluble form at nonphysiological concentrations. Such potentially contradictory features required living organisms to develop efficient systems for nickel utilization and homeostasis. This is the case for incorporation of nickel into the active site of urease, a multistep, tightly regulated process, requiring the interplay of various accessory proteins. The understanding of this activation mechanism may find medical applications against ureolytic bacteria, among which Mycobacterium tuberculosis is a deadly pathogen for humans. The topic of this study is UreG, an essential chaperone in the in vivo activation of urease upon insertion of Ni2+ into the active site. The protein was examined using both experimental and computational approaches. In particular, the soluble M. tuberculosis UreG (MtUreG) was overexpressed in Escherichia coli and purified to homogeneity. The identity of the isolated protein was established by mass spectrometry. On-line size-exclusion chromatography and light scattering indicated that MtUreG exists as a dimeric form in solution. Determination of the free thiol concentration revealed that a disulfide bond is present in the dimer. The isolated MtUreG shows low GTPase activity under native conditions, with a kcat of 0.01 min-1. Circular dichroism spectroscopy demonstrated the presence of a well-defined secondary structure (8% alpha-helices, 29% beta-strands) in MtUreG, whereas NMR spectroscopy indicated that this protein does not behave as a rigid three-dimensional fold and thus can be assigned to the class of intrinsically unstructured polypeptides. The molecular model of MtUreG in the fully folded and functional form was built using fold recognition algorithms. An extensive similarity search was performed to determine conservation patterns in all known bacterial UreG sequences. The generation of a multiple-sequence alignment and the related phylogenetic tree allowed us to recognize key residues and motifs that are likely important for protein function. A structural database containing the homology-built models of the most representative UreG proteins was created, confirming the structural analogies among the UreG family. A flexible region, likely to be important for protein function, is identified. The structural conservation among this class of GTPases is discussed on the basis of their function in the urease assembly process. 相似文献
999.
1000.
De Simone F Guzzi R Sportelli L Marsh D Bartucci R 《Biochimica et biophysica acta》2007,1768(6):1541-1549
Human serum albumin (HSA) is an abundant plasma protein that transports fatty acids and also binds a wide variety of hydrophobic pharmacores. Echo-detected (ED) EPR spectra and D(2)O-electron spin echo envelope modulation (ESEEM) Fourier-transform spectra of spin-labelled free fatty acids and phospholipids were used jointly to investigate the binding of stearic acid to HSA and the adsorption of the protein on dipalmitoyl phosphatidylcholine (DPPC) membranes. In membranes, torsional librations are detected in the ED-spectra, the intensity of which depends on chain position at low temperature. Water penetration into the membrane is seen in the D(2)O-ESEEM spectra, the intensity of which decreases greatly at the middle of the membrane. Both the chain librational motion and the water penetration are only little affected by adsorption of serum albumin at the DPPC membrane surface. In contrast, both the librational motion and the accessibility of the chains to water are very different in the hydrophobic fatty acid binding sites of HSA from those in membranes. Indeed, the librational motion of bound fatty acids is suppressed at low temperature, and is similar for the different chain positions, at all temperatures. Correspondingly, all segments of the bound chains are accessible to water, to rather similar extents. 相似文献