全文获取类型
收费全文 | 1381篇 |
免费 | 67篇 |
出版年
2022年 | 5篇 |
2021年 | 31篇 |
2020年 | 15篇 |
2019年 | 12篇 |
2018年 | 27篇 |
2017年 | 20篇 |
2016年 | 42篇 |
2015年 | 72篇 |
2014年 | 77篇 |
2013年 | 107篇 |
2012年 | 112篇 |
2011年 | 109篇 |
2010年 | 59篇 |
2009年 | 45篇 |
2008年 | 82篇 |
2007年 | 84篇 |
2006年 | 65篇 |
2005年 | 65篇 |
2004年 | 63篇 |
2003年 | 44篇 |
2002年 | 50篇 |
2001年 | 18篇 |
2000年 | 19篇 |
1999年 | 9篇 |
1998年 | 16篇 |
1997年 | 10篇 |
1996年 | 14篇 |
1995年 | 4篇 |
1994年 | 7篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 17篇 |
1990年 | 8篇 |
1989年 | 11篇 |
1988年 | 7篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 14篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1949年 | 3篇 |
1934年 | 2篇 |
1919年 | 2篇 |
排序方式: 共有1448条查询结果,搜索用时 93 毫秒
1.
Here we present an analytical technique for the measurement and evaluation of changes in chronologically sequenced assemblages. To illustrate the method, we studied the cultural evolution of European cooking as revealed in seven cook books dispersed over the past 800 years. We investigated if changes in the set of commonly used ingredients were mainly gradual or subject to fashion fluctuations. Applying our method to the data from the cook books revealed that overall, there is a clear continuity in cooking over the ages – cooking is knowledge that is passed down through generations, not something (re-)invented by each generation on its own. Looking at three main categories of ingredients separately (spices, animal products and vegetables), however, disclosed that all ingredients do not change according to the same pattern. While choice of animal products was very conservative, changing completely sequentially, changes in the choices of spices, but also of vegetables, were more unbounded. We hypothesize that this may be due a combination of fashion fluctuations and changes in availability due to contact with the Americas during our study time period. The presented method is also usable on other assemblage type data, and can thus be of utility for analyzing sequential archaeological data from the same area or other similarly organized material. 相似文献
2.
3.
Maria Ida De Michelis Antonella Camelli Franca Rasi-Caldogno 《Plant biology (Stuttgart, Germany)》1993,106(1):20-25
The transport and hydrolytic activities of the plasma membrane (PM) Ca2+ pump were characterized in a PM fraction purified from seedlings of Arabidopsis thaliana by the aqueous two-phase partitioning technique. Ca2+ uptake could be energized by ATP and by ITP (at about 70% the rate sustained by ATP). This characteristic was used to measure the hydrolytic activity of the enzyme as Ca2+-dependent ITPase activity. The PM Ca2+ pump displayed a broad pH optimum around pH 7.2, was drastically inhibited by erythrosin B (EB), and was half-saturated by 60 μM ITP. It was stimulated by CaM, specially at low, non-saturating Ca2+ concentrations. All of these characteristics closely resemble those of the PM Ca2+ pump in other plant materials. Analysis of the effects of EB and other fluorescein derivatives (eosin Y and rose bengal) showed that: i) EB behaved as a competitive inhibitor with respect to ITP; ii) the PM Ca2+ pump was drastically inhibited by concentrations of fluorescein derivatives (submicromolar), much lower than those required to inhibit the PM H+-ATPase; iii) the different fluorescein derivatives were diversely efficient in inhibiting the activities of the Ca2+ pump and of the H+-ATPase of the PM (eosin Y was about 10000-fold, EB 1000-fold and rose bengal only 50-fold more active on the Ca2+ pump than on the H+-ATPase); and iv) the effectiveness of EB in inhibiting the Ca2+ pump was strongly affected by the protein concentration in the assay medium. 相似文献
4.
5.
The assembly of a large physical map of genomes requires simultaneous analysis of many cosmid clones for overlapping regions. The search for overlapping regions may be achieved by various means. High-performance liquid chromatography (HPLC) provides an alternative to gel electrophoresis since microgram amounts of each DNA fragment may be collected into individual test tubes for further analysis. HPLC has been used to identify overlapping cosmid clones from a pool of cosmid DNA containing the terminal portion of the long arm of the human X chromosome (Xq24-qter). Among 400 cosmids analyzed, 3 were shown to overlap. 相似文献
6.
Ida Mann 《BMJ (Clinical research ed.)》1943,2(4319):482-483
7.
Human PARP family consists of 17 members of which PARP-1 is a prominent member and plays a key role in DNA repair pathways. It has an N-terminal DNA-binding domain (DBD) encompassing the nuclear localisation signal (NLS), central automodification domain and C-terminal catalytic domain. PARP-1 accounts for majority of poly-(ADP-ribose) polymer synthesis that upon binding to numerous proteins including PARP itself modulates their activity. Reduced PARP-1 activity in ageing human samples and its deficiency leading to telomere shortening has been reported. Hence for cell survival, maintenance of genomic integrity and longevity presence of intact PARP-1 in the nucleus is paramount. Although localisation of full-length and truncated PARP-1 in PARP-1 proficient cells is well documented, subcellular distribution of PARP-1 fragments in the absence of endogenous PARP-1 is not known. Here we report the differential localisation of PARP-1 N-terminal fragment encompassing NLS in PARP-1+/+ and PARP-1−/− mouse embryo fibroblasts by live imaging of cells transiently expressing EGFP tagged fragment. In PARP-1+/+ cells the fragment localises to the nuclei presenting a granular pattern. Furthermore, it is densely packaged in the midsections of the nucleus. In contrast, the fragment localises exclusively to the cytoplasm in PARP-1−/− cells. Flourescence intensity analysis further confirmed this observation indicating that the N-terminal fragment requires endogenous PARP-1 for its nuclear transport. Our study illustrates the trafficking role of PARP-1 independently of its enzymatic activity and highlights the possibility that full-length PARP-1 may play a key role in the nuclear transport of its siblings and other molecules. 相似文献
8.
Kirsti Greiff John Reidar Mathiassen Ekrem Misimi Margrethe Hersleth Ida G. Aursand 《PloS one》2015,10(9)
The European diet today generally contains too much sodium (Na+). A partial substitution of NaCl by KCl has shown to be a promising method for reducing sodium content. The aim of this work was to investigate the sensorial changes of cooked ham with reduced sodium content. Traditional sensorial evaluation and objective multimodal machine vision were used. The salt content in the hams was decreased from 3.4% to 1.4%, and 25% of the Na+ was replaced by K+. The salt reduction had highest influence on the sensory attributes salty taste, after taste, tenderness, hardness and color hue. The multimodal machine vision system showed changes in lightness, as a function of reduced salt content. Compared to the reference ham (3.4% salt), a replacement of Na+-ions by K+-ions of 25% gave no significant changes in WHC, moisture, pH, expressed moisture, the sensory profile attributes or the surface lightness and shininess. A further reduction of salt down to 1.7–1.4% salt, led to a decrease in WHC and an increase in expressible moisture. 相似文献
9.
Petra Suchankova Pia Steensland Ida Fredriksson J?rgen A. Engel Elisabet Jerlhag 《PloS one》2013,8(8)
Alcohol dependence is a heterogeneous disorder where several signalling systems play important roles. Recent studies implicate that the gut-brain hormone ghrelin, an orexigenic peptide, is a potential mediator of alcohol related behaviours. Ghrelin increases whereas a ghrelin receptor (GHS-R1A) antagonist decreases alcohol consumption as well as operant self-administration of alcohol in rodents that have consumed alcohol for twelve weeks. In the present study we aimed at investigating the effect of acute and repeated treatment with the GHS-R1A antagonist JMV2959 on alcohol intake in a group of rats following voluntarily alcohol consumption for two, five and eight months. After approximately ten months of voluntary alcohol consumption the expression of the GHS-R1A gene (Ghsr) as well as the degree of methylation of a CpG island found in Ghsr was examined in reward related brain areas. In a separate group of rats, we examined the effect of the JMV2959 on alcohol relapse using the alcohol deprivation paradigm. Acute JMV2959 treatment was found to decrease alcohol intake and the effect was more pronounced after five, compared to two months of alcohol exposure. In addition, repeated JMV2959 treatment decreased alcohol intake without inducing tolerance or rebound increase in alcohol intake after the treatment. The GHS-R1A antagonist prevented the alcohol deprivation effect in rats. There was a significant down-regulation of the Ghsr expression in the ventral tegmental area (VTA) in high- compared to low-alcohol consuming rats after approximately ten months of voluntary alcohol consumption. Further analysis revealed a negative correlation between Ghsr expression in the VTA and alcohol intake. No differences in methylation degree were found between high- compared to low-alcohol consuming rats. These findings support previous studies showing that the ghrelin signalling system may constitute a potential target for development of novel treatment strategies for alcohol dependence. 相似文献
10.
Michelle de C. S. Azevedo Patricia S. Rosa Cleverson T. Soares Luciana R. V. Fachin Ida Maria F. D. Baptista William J. Woods Gustavo P. Garlet Ana Paula F. Trombone Andrea de F. F. Belone 《PloS one》2015,10(12)
Jorge Lobo’s disease (JLD) is a chronic infection that affects the skin and subcutaneous tissues. Its etiologic agent is the fungus Lacazia loboi. Lesions are classified as localized, multifocal, or disseminated, depending on their location. Early diagnosis and the surgical removal of lesions are the best therapeutic options currently available for JLD. The few studies that evaluate the immunological response of JLD patients show a predominance of Th2 response, as well as a high frequency of TGF-β and IL-10 positive cells in the lesions; however, the overall immunological status of the lesions in terms of their T cell phenotype has yet to be determined. Therefore, the objective of this study was to evaluate the pattern of Th1, Th2, Th17 and regulatory T cell (Treg) markers mRNA in JLD patients by means of real-time PCR. Biopsies of JLD lesions (N = 102) were classified according to their clinical and histopathological features and then analyzed using real-time PCR in order to determine the expression levels of TGF-β1, FoxP3, CTLA4, IKZF2, IL-10, T-bet, IFN-γ, GATA3, IL-4, IL-5, IL-13, IL-33, RORC, IL-17A, IL-17F, and IL-22 and to compare these levels to those of healthy control skin (N = 12). The results showed an increased expression of FoxP3, CTLA4, TGF-β1, IL-10, T-bet, IL-17F, and IL-17A in lesions, while GATA3 and IL-4 levels were found to be lower in diseased skin than in the control group. When the clinical forms were compared, TGF-β1 was found to be highly expressed in patients with a single localized lesion while IL-5 and IL-17A levels were higher in patients with multiple/disseminated lesions. These results demonstrate the occurrence of mixed T helper responses and suggest the dominance of regulatory T cell activity, which could inhibit Th-dependent protective responses to intracellular fungi such as L. loboi. Therefore, Tregs may play a key role in JLD pathogenesis. 相似文献