全文获取类型
收费全文 | 30398篇 |
免费 | 3559篇 |
国内免费 | 12246篇 |
出版年
2024年 | 254篇 |
2023年 | 778篇 |
2022年 | 1255篇 |
2021年 | 1438篇 |
2020年 | 1295篇 |
2019年 | 1480篇 |
2018年 | 1135篇 |
2017年 | 1047篇 |
2016年 | 1146篇 |
2015年 | 1603篇 |
2014年 | 2166篇 |
2013年 | 2129篇 |
2012年 | 2737篇 |
2011年 | 2671篇 |
2010年 | 2150篇 |
2009年 | 2098篇 |
2008年 | 2443篇 |
2007年 | 2348篇 |
2006年 | 2290篇 |
2005年 | 1882篇 |
2004年 | 1610篇 |
2003年 | 1494篇 |
2002年 | 1342篇 |
2001年 | 1241篇 |
2000年 | 1156篇 |
1999年 | 877篇 |
1998年 | 407篇 |
1997年 | 268篇 |
1996年 | 221篇 |
1995年 | 150篇 |
1994年 | 181篇 |
1993年 | 140篇 |
1992年 | 233篇 |
1991年 | 239篇 |
1990年 | 198篇 |
1989年 | 216篇 |
1988年 | 188篇 |
1987年 | 149篇 |
1986年 | 147篇 |
1985年 | 146篇 |
1984年 | 112篇 |
1983年 | 98篇 |
1982年 | 102篇 |
1981年 | 61篇 |
1979年 | 59篇 |
1977年 | 80篇 |
1976年 | 50篇 |
1975年 | 52篇 |
1974年 | 67篇 |
1971年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
11.
The elucidation of the multiple signaling cascades coupled to the TSH receptor has offered new approaches in the understanding of the pathogenesis of Graves' disease. Here we review findings showing that immunoglobulins from Graves' patients are heterogeneous, bind to different epitopes and, similarly to TSH, activate different signaling pathways, including adenylyl cyclase, phospholipase C and phospholipase A2. Evidence that the multiplicity of signals correlates with the different manifestations of the disease is also summarized. We believe that the dissection of the molecular mechanisms involved in the pathogenesis of Graves' disease offers the basis for developing novel therapeutical approaches to this disease. 相似文献
12.
13.
14.
Gabrielle C. Winters Gianluca Polese Anna Di Cosmo Leonid L. Moroz 《Journal of morphology》2020,281(7):790-801
Neuropeptide Y (NPY) is an evolutionarily conserved neurosecretory molecule implicated in a diverse complement of functions across taxa and in regulating feeding behavior and reproductive maturation in Octopus. However, little is known about the precise molecular circuitry of NPY-mediated behaviors and physiological processes, which likely involve a complex interaction of multiple signal molecules in specific brain regions. Here, we examined the expression of NPY throughout the Octopus central nervous system. The sequence analysis of Octopus NPY precursor confirmed the presence of both, signal peptide and putative active peptides, which are highly conserved across bilaterians. In situ hybridization revealed distinct expression of NPY in specialized compartments, including potential “integration centers,” where visual, tactile, and other behavioral circuitries converge. These centers integrating separate circuits may maintain and modulate learning and memory or other behaviors not yet attributed to NPY-dependent modulation in Octopus. Extrasomatic localization of NPY mRNA in the neurites of specific neuron populations in the brain suggests a potential demand for immediate translation at synapses and a crucial temporal role for NPY in these cell populations. We also documented the presence of NPY mRNA in a small cell population in the olfactory lobe, which is a component of the Octopus feeding and reproductive control centers. However, the molecular mapping of NPY expression only partially overlapped with that produced by immunohistochemistry in previous studies. Our study provides a precise molecular map of NPY mRNA expression that can be used to design and test future hypotheses about molecular signaling in various Octopus behaviors. 相似文献
15.
Francesca Passaretta Domenico Bosco Lucia Centurione Maria Antonietta Centurione Fabio Marongiu Roberta Di Pietro 《Journal of cellular and molecular medicine》2020,24(7):4350-4355
Human Amniotic Epithelial Cells (hAEC) isolated from term placenta are a promising source for regenerative medicine. However, it has long been debated whether the hAEC population consists of heterogeneous or homogeneous cells. In a previous study, we investigated the characteristics of hAEC isolated from four different regions of the amniotic membrane finding significant heterogeneity. The aim of this study was to evaluate the hepatic differentiation capability of hAEC isolated from these four regions. Human term placentae were collected after caesarean section and hAEC were isolated from four regions of the amniotic membrane (R1-R4, according to their relative distance from the umbilical cord) and treated in hepatic differentiation conditions for 14 days. hAEC-derived hepatocyte-like cells showed marked differences in the expression of hepatic markers: R4 showed higher levels of Albumin and Hepatocyte Nuclear Factor (HNF) 4α whereas R1 expressed higher Cytochrome P450 enzymes, both at the gene and protein level. These preliminary results suggest that hAEC isolated from R1 and R4 of the amniotic membrane are more prone to hepatic differentiation. Therefore, the use of hAEC from a specific region of the amniotic membrane should be taken into consideration as it could have an impact on the outcome of therapeutic applications. 相似文献
16.
The DNA of fifteen Italian cultivars of durum wheat (Triticum turgidum L. ssp. durum) were analyzed by in fluorescence amplified fragment length polymorphism (fAFLP) in order to obtain the characteristic fingerprintings
of genotypes and assess their genetic relatedness. Among 64 combinations of fluorescence labelled primers, three different
combinations were chosen as producing a total of 6630 AFLP fragments, 2277 (34.3 %) of them being polymorphic. By using this
fAFLP methodology a DNA fingerprinting of each durum wheat cultivar was generated for genotype identification. Analysis of
the genetic relationships show the low variability among durum wheat cultivars. 相似文献
17.
18.
Energy metabolism and lipid peroxidation of human erythrocytes as a function of increased oxidative stress. 总被引:5,自引:0,他引:5
B Tavazzi D Di Pierro A M Amorini G Fazzina M Tuttobene B Giardina G Lazzarino 《European journal of biochemistry》2000,267(3):684-689
To study the influence of oxidative stress on energy metabolism and lipid peroxidation in erythrocytes, cells were incubated with increasing concentrations (0.5-10 mM) of hydrogen peroxide for 1 h at 37 degrees C and the main substances of energy metabolism (ATP, AMP, GTP and IMP) and one index of lipid peroxidation (malondialdehyde) were determined by HPLC on cell extracts. Using the same incubation conditions, the activity of AMP-deaminase was also determined. Under nonhaemolysing conditions (at up to 4 mM H2O2), oxidative stress produced, starting from 1 mM H2O2, progressive ATP depletion and a net decrease in the intracellular sum of adenine nucleotides (ATP + ADP + AMP), which were not paralleled by AMP formation. Concomitantly, the IMP level increased by up to 20-fold with respect to the value determined in control erythrocytes, when cells were challenged with the highest nonhaemolysing H2O2 concentration (4 mM). Efflux of inosine, hypoxanthine, xanthine and uric acid towards the extracellular medium was observed. The metabolic imbalance of erythrocytes following oxidative stress was due to a dramatic and unexpected activation of AMP-deaminase (a twofold increase of activity with respect to controls) that was already evident at the lowest dose of H2O2 used; this enzymatic activity increased with increasing H2O2 in the medium, and reached its maximum at 4 mM H2O2-treated erythrocytes (10-fold higher activity than controls). Generation of malondialdehyde was strictly related to the dose of H2O2, being detectable at the lowest H2O2 concentration and increasing without appreciable haemolysis up to 4 mM H2O2. Besides demonstrating a close relationship between lipid peroxidation and haemolysis, these data suggest that glycolytic enzymes are moderately affected by oxygen radical action and strongly indicate, in the change of AMP-deaminase activity, a highly sensitive enzymatic site responsible for a profound modification of erythrocyte energy metabolism during oxidative stress. 相似文献
19.
20.
Sonia Coni Silvia Maria Serrao Zuleyha Nihan Yurtsever Laura Di Magno Rosa Bordone Camilla Bertani Valerio Licursi Zaira Ianniello Paola Infante Marta Moretti Marialaura Petroni Francesca Guerrieri Alessandro Fatica Alberto Macone Enrico De Smaele Lucia Di Marcotullio Giuseppe Giannini Marella Maroder Enzo Agostinelli Gianluca Canettieri 《Cell death & disease》2020,11(12)