全文获取类型
收费全文 | 845篇 |
免费 | 58篇 |
出版年
2023年 | 2篇 |
2022年 | 9篇 |
2021年 | 12篇 |
2020年 | 6篇 |
2019年 | 11篇 |
2018年 | 12篇 |
2017年 | 21篇 |
2016年 | 24篇 |
2015年 | 25篇 |
2014年 | 44篇 |
2013年 | 56篇 |
2012年 | 48篇 |
2011年 | 58篇 |
2010年 | 46篇 |
2009年 | 35篇 |
2008年 | 40篇 |
2007年 | 50篇 |
2006年 | 48篇 |
2005年 | 36篇 |
2004年 | 43篇 |
2003年 | 37篇 |
2002年 | 29篇 |
2001年 | 16篇 |
2000年 | 16篇 |
1999年 | 15篇 |
1998年 | 14篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 7篇 |
1994年 | 10篇 |
1993年 | 7篇 |
1992年 | 9篇 |
1991年 | 19篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 10篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1979年 | 8篇 |
1977年 | 2篇 |
1976年 | 6篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1967年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有903条查询结果,搜索用时 171 毫秒
81.
82.
Garavelli L Cerruti-Mainardi P Virdis R Pedori S Pastore G Godi M Provera S Rauch A Zweier C Zollino M Banchini G Longo N Mowat D Neri G Bernasconi S 《Hormone research》2005,63(4):187-192
Hypospadias, when the urethra opens on the ventral side of the penis, is a common malformation seen in about 3 per 1,000 male births. It is a complex disorder associated with genetic and environmental factors and can be part of genetic syndromes. Mowat-Wilson syndrome (MWS) is a multiple congenital anomaly syndrome characterized by a distinct facial phenotype, Hirschsprung disease, microcephaly and mental retardation. It is caused by mutations in the zinc finger homeo box 1B gene, ZFHX1B (SIP1). To date, 68 deletion/mutation-positive cases have been reported. Genitourinary anomalies are common in MWS. Here we report that hypospadias is common in males with this syndrome. In 39 patients where this information was available, hypospadias was present in 46% of patients (18/39). In the 3 Italian male cases reported here, hypospadias was always present. MWS should be considered by endocrinologists in patients with hypospadias associated with developmental delays/mental retardation, in particular in the presence of a distinct facial phenotype. 相似文献
83.
Ferreira VS Rêgo IN Pastore F Mandai MM Mendes LS Santos KA Rubim JC Suarez PA 《Bioresource technology》2005,96(5):605-609
A comparative study of rubber sheets obtained using formic, acetic, and smoke acid as coagulants is shown for latex obtained from native Amazonian trees and also from commercial cultivated trees. The evaluation of both processes of coagulation was carried out by spectroscopic and physical-chemical analysis, showing no differences in the rubber sheets obtained. This new method of rubber sheet preparation was introduced into Amazonian rainforest rubber tapper communities, which are actually producing in large scale. The physical-mechanical properties were similar among a large sheets made by different rubber tapper communities using this new method. 相似文献
84.
One of the most important outcomes of modern biology has been the demonstration of the unity of life. All living beings are in fact descendants of a unique ancestor commonly referred to as Luca (the Last universal common ancestor). The discovery - nearly 30 years ago by Carl Woese - that present-day life on our planet can be assigned to only three domains: two of prokaryotic nature (Archaea and Bacteria), and one eukaryoyic (Eucarya), has given birth to a new field of investigation aimed at determining the nature of Luca. Today, thanks to the accumulation of genomic data, we can loop back into the past and infer a few characters of Luca by comparing what present-day organisms have in common. For example, it is now clear that Luca was a cellular organism provided with a cytoplasmic membrane, and that it harboured already a quite sophisticated translation apparatus. However, the inference of other characters of Luca from comparative genomics is less straightforward: for instance, a few key molecular mechanisms for DNA replication are non-homologous across the three domains and their distribution is often puzzling. This evidence has been embraced by proponents of the hypothesis that Luca harboured an RNA genome and that its replacement by DNA and the appearance of the corresponding molecular systems would have occurred independently in the three life domains after their divergence. However, an equally likely scenario would be that of a Luca with a DNA genome and of a subsequent replacement of its DNA-replication systems by non-homologous counterparts either in the bacterial or in the archaeal/eukaroytic branch. Nevertheless, including the viral world into the picture of the tree of life may thus provide us with precious insights into our most distant past since the invention and spread potential of viruses may have played a key role in early evolution. 相似文献
85.
Alcaro S Arena A Di Bella R Neri S Ottanà R Ortuso F Pavone B Trincone A Vigorita MG 《Bioorganic & medicinal chemistry》2005,13(10):3371-3378
In pursuing research on the antiviral, interferon (IFN)-inducing tilorone congeners, a new series of fluoren-carboxyhydroxyesters has been prepared and biologically explored. These esters have subsequently been used as sugar acceptors in the enzymatic transglycosylation reaction using the 'retaining' beta-glycosidase from the archaeon Sulfolobus solfataricus (Ssbeta-Gly). Both aglycones (1-6) and corresponding beta-glucosides (beta-glu 1-beta-glu 6) have been screened for cytotoxicity, interferon-stimulating and antiviral properties against HSV-2. It was found that the addition of compounds beta-glu 5, beta-glu 6 and beta-glu 4 to HSV-2 infected U937 cells downregulates viral replication and triggers cells to release IFN-alpha/beta. Taken together, the results showed improved pharmacological profiles as a consequence of glycosylation. A molecular modelling study carried out on this series of compounds completed the structural characterisation of the novel compounds. 相似文献
86.
Nanoarchaea: representatives of a novel archaeal phylum or a fast-evolving euryarchaeal lineage related to Thermococcales? 总被引:7,自引:2,他引:5
Background
Cultivable archaeal species are assigned to two phyla - the Crenarchaeota and the Euryarchaeota - by a number of important genetic differences, and this ancient split is strongly supported by phylogenetic analysis. The recently described hyperthermophile Nanoarchaeum equitans, harboring the smallest cellular genome ever sequenced (480 kb), has been suggested as the representative of a new phylum - the Nanoarchaeota - that would have diverged before the Crenarchaeota/Euryarchaeota split. Confirming the phylogenetic position of N. equitans is thus crucial for deciphering the history of the archaeal domain. 相似文献87.
88.
The ability to visualize plasmid DNA entrapment in muscle cells undergoing an "in vivo" electroporation treatment was investigated on BALB/c mice using a 7-T magnetic resonance imaging (MRI) scanner using the paramagnetic Gd-DOTA-spd complex as imaging reporter. Gd-DOTA-spd bears a tripositively charged spermidine residue that yields a strong binding affinity toward the negatively charged DNA chain (6.4 kb, K(a) = 2.2 x 10(3) M(-1) for approximately 2500 +/- 500 binding sites). Cellular colocalization of Gd-DOTA-spd and plasmid DNA has been validated by histological analysis of excised treated muscle. In vivo MRI visualization of Gd-DOTA-spd distribution provides an excellent route to access the cellular entrapment of plasmid DNA upon applying an electroporation pulse. 相似文献
89.
Pedone E Saviano M Bartolucci S Rossi M Ausili A Scirè A Bertoli E Tanfani F 《Journal of proteome research》2005,4(6):1972-1980
The effect of SDS, pD, and temperature on the structure and stability of the protein disulfide oxidoreductase from Pyrococcus furiosus (PfPDO) was investigated by molecular dynamic (MD) simulations and FT-IR spectroscopy. pD affects the thermostability of alpha-helices and beta-sheets differently, and 0.5% or higher SDS concentration influences the structure significantly. The experiments allowed us to detect a secondary structural reorganization at a definite temperature and pD which may correlate with a high ATPase activity of the protein. The MD simulations supported the infrared data and revealed the different behavior of the N and C terminal segments, as well as of the two active sites. 相似文献
90.
Ilari A Latella MC Ceci P Ribacchi F Su M Giangiacomo L Stefanini S Chasteen ND Chiancone E 《Biochemistry》2005,44(15):5579-5587
The role of the ferroxidase center in iron uptake and hydrogen peroxide detoxification was investigated in Listeria innocua Dps by substituting the iron ligands His31, His43, and Asp58 with glycine or alanine residues either individually or in combination. The X-ray crystal structures of the variants reveal only small alterations in the ferroxidase center region compared to the native protein. Quenching of the protein fluorescence was exploited to assess stoichiometry and affinity of metal binding. Substitution of either His31 or His43 decreases Fe(II) affinity significantly with respect to wt L. innocua Dps (K approximately 10(5) vs approximately 10(7) M(-)(1)) but does not alter the binding stoichiometry [12 Fe(II)/dodecamer]. In the H31G-H43G and H31G-H43G-D58A variants, binding of Fe(II) does not take place with measurable affinity. Oxidation of protein-bound Fe(II) increases the binding stoichiometry to 24 Fe(III)/dodecamer. However, the extent of fluorescence quenching upon Fe(III) binding decreases, and the end point near 24 Fe(III)/dodecamer becomes less distinct with increase in the number of mutated residues. In the presence of dioxygen, the mutations have little or no effect on the kinetics of iron uptake and in the formation of micelles inside the protein shell. In contrast, in the presence of hydrogen peroxide, with increase in the number of substitutions the rate of iron oxidation and the capacity to inhibit Fenton chemistry, thereby protecting DNA from oxidative damage, appear increasingly compromised, a further indication of the role of ferroxidation in conferring peroxide tolerance to the bacterium. 相似文献