全文获取类型
收费全文 | 1860篇 |
免费 | 82篇 |
国内免费 | 11篇 |
专业分类
化学 | 1200篇 |
晶体学 | 5篇 |
力学 | 85篇 |
数学 | 332篇 |
物理学 | 331篇 |
出版年
2023年 | 15篇 |
2022年 | 49篇 |
2021年 | 48篇 |
2020年 | 38篇 |
2019年 | 39篇 |
2018年 | 32篇 |
2017年 | 19篇 |
2016年 | 73篇 |
2015年 | 65篇 |
2014年 | 85篇 |
2013年 | 109篇 |
2012年 | 126篇 |
2011年 | 145篇 |
2010年 | 91篇 |
2009年 | 63篇 |
2008年 | 114篇 |
2007年 | 110篇 |
2006年 | 107篇 |
2005年 | 112篇 |
2004年 | 91篇 |
2003年 | 78篇 |
2002年 | 52篇 |
2001年 | 27篇 |
2000年 | 16篇 |
1999年 | 19篇 |
1998年 | 11篇 |
1997年 | 16篇 |
1996年 | 22篇 |
1995年 | 14篇 |
1994年 | 14篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 14篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1985年 | 6篇 |
1984年 | 14篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1973年 | 5篇 |
1921年 | 2篇 |
排序方式: 共有1953条查询结果,搜索用时 0 毫秒
91.
Hualong Song Simon J. Allison Viktor Brabec Hannah E. Bridgewater Jana Kasparkova Hana Kostrhunova Vojtech Novohradsky Roger M. Phillips Jitka Pracharova Nicola J. Rogers Samantha L. Shepherd Peter Scott 《Angewandte Chemie (International ed. in English)》2020,59(34):14677-14685
Monosaccharides are added to the hydrophilic face of a self‐assembled asymmetric FeII metallohelix, using CuAAC chemistry. The sixteen resulting architectures are water‐stable and optically pure, and exhibit improved antiproliferative selectivity against colon cancer cells (HCT116 p53+/+) with respect to the non‐cancerous ARPE‐19 cell line. While the most selective compound is a glucose‐appended enantiomer, its cellular entry is not mainly glucose transporter‐mediated. Glucose conjugation nevertheless increases nuclear delivery ca 2.5‐fold, and a non‐destructive interaction with DNA is indicated. Addition of the glucose units affects the binding orientation of the metallohelix to naked DNA, but does not substantially alter the overall affinity. In a mouse model, the glucose conjugated compound was far better tolerated, and tumour growth delays for the parent compound (2.6 d) were improved to 4.3 d; performance as good as cisplatin but with the advantage of no weight loss in the subjects. 相似文献
92.
93.
Sara Basile Natale Badalamenti Ornella Riccobono Salvatore Guarino Vincenzo Ilardi Maurizio Bruno Ezio Peri 《Molecules (Basel, Switzerland)》2022,27(3)
The problems of the environment and human health related to the use of synthetic and broad-spectrum insecticides have increasingly motivated scientific research on different alternatives and among these, the use of green systems, such as essential oils, have been explored. Several species of the Apiaceae and Asteraceae families, aromatic herbs rich in secondary bioactive metabolites, are used in the industrial field for pharmaceutical, cosmetic, and food purposes. Different essential oils extracted from some species of these families have shown acute toxicity and attractive and/or repellent effects towards different insects. In our work, we investigated the toxic potential of Calendula incana subsp. maritima and Laserpitium siler subsp. siculum essential oils against four insect species, Sitophilus oryzae, Lasioderma serricorne, Necrobia rufipes, and Rhyzoperta dominica, which are common pests of stored products. The composition of both oils, extracted by hydrodistillation from the aerial parts of the two plants, was evaluated by GC×GC-MS. Calendula incana subsp. maritima essential oil was rich in oxygenated sesquiterpenoids, such as cubebol (35.39%), 4-epi-cubebol (22.99%), and cubenol (12.77%), while the Laserpitium siler subsp. siculum essential oil was composed mainly of monoterpene hydrocarbons, such as β-phellandrene (42.16%), limonene (23.87%), and β-terpinene (11.80%). The toxicity Petri dish bioassays indicated that C. maritima oil killed a mean of 65.50% of S. oryzae and 44.00% of R. dominica adults, indicating a higher biocidal activity in comparison with L. siculum oil, while toward the other species, no significant differences in mortality were recorded. Calendula maritima oil could be, then, considered a promising candidate for further tests as an alternative biocide toward S. oryzae and R. dominica. The possibility that the relatively high content of oxygenated sesquiterpenoids in C. maritima essential oil determines its higher biocidal activity is discussed. 相似文献
94.
In this work we investigate whether information theory measures like mutual information and transfer entropy, extracted from a bank network, Granger cause financial stress indexes like LIBOR-OIS (London Interbank Offered Rate-Overnight Index Swap) spread, STLFSI (St. Louis Fed Financial Stress Index) and USD/CHF (USA Dollar/Swiss Franc) exchange rate. The information theory measures are extracted from a Gaussian Graphical Model constructed from daily stock time series of the top 74 listed US banks. The graphical model is calculated with a recently developed algorithm (LoGo) which provides very fast inference model that allows us to update the graphical model each market day. We therefore can generate daily time series of mutual information and transfer entropy for each bank of the network. The Granger causality between the bank related measures and the financial stress indexes is investigated with both standard Granger-causality and Partial Granger-causality conditioned on control measures representative of the general economy conditions. 相似文献
95.
96.
97.
Gianfranco Denti Scolastica Serroni Giovanni Sindona Nicola Uccella 《Journal of the American Society for Mass Spectrometry》1993,4(4):306-311
Fast-atom bombardment (FAB) mass spectrometry in the negative ionization mode enables the sputtering into the gas phase of the ruthenium complexes [Ru(2,2′-bipyridine[bpy])2(2,5-bis) (pyrydil)pyrazine[dpp])](PF6)2; [Ru(bpy)2,(2,3dpp)](PF6)2;[Ru(bpy)2,(2,3-dpp-Me)]( PF6)3; and [Ru(bpy)2(?-2,3-dpp)]2 RuCl2(PF6)4 as intact radical anions. These data, combined with those avaiiable from the positive FAB spectra allow a full characterization of the analytes. 相似文献
98.
Herman Bachelard Peter Morris Andrew Taylor Nicola Thatcher 《Magnetic resonance imaging》1995,13(8):1223-1226
We are applying multi-nuclear high-field (500 MHz) MR spectroscopy of metabolising whole tissue preparations of the mammalian brain to studies on individual components of convulsions, which include prolonged depolarization, metabolic deprivation, and the effects of excitotoxins. The responses of glial cells and neurones can be partially distinguished by following labelling patterns of metabolic intermediates from 13C-labelled glucose or acetate (which enters only glial cells). This approach clearly confirmed our earlier indications that the metabolic response to depolarization (40 mM extracellular K+) occurs essentially in glial cells. Some evidence for metabolic shuttling between glia and neurones was obtained from the changes in C3/C4 ratios of glutamate and glutamine, and the C2/C3 of GABA. Mechanisms for metabolic support of neurones by glia may be of importance in neuronal protection under such metabolic stress as occurs in epilepsy. Changes in free intracellular divalent cations ([Ca2+]i and [Zn2+]i) were monitored using the 19F-MRS indicator, 5FBAPTA. Large increases in [Ca2+]i and decreases in PCr were produced by excitotoxins (glutamate and NMDA), depolarization or ischaemia, but intracellular Zn2+ appeared only after exposure to the excitotoxins. The NMDA receptor blocker, MK801, removed all of the responses to NMDA, but only prevented the appearance of Zn2+ observed with glutamate. These results indicate that the damage caused to neurones by such insults as convulsions is not due simply to the presence of excessive excitotoxic glutamate. 相似文献
99.
Eric Mayer-Santos Tatjana Maravic Allegra Comba Patricia Moreira Freitas Giovanna Bueno Marinho Claudia Mazzitelli Edoardo Mancuso Nicola Scotti Federica Florenzano Lorenzo Breschi Annalisa Mazzoni 《Molecules (Basel, Switzerland)》2022,27(5)
This study aimed to investigate matrix metalloproteinase (MMP) activity in human dentin using in-situ and gelatin zymography, after at-home and in-office bleaching, related to their clinical exposure times. Dentin specimens (n = 5) were treated with 35% hydrogen peroxide (50 min per session/4 sessions), 10% carbamide peroxide (180 min/21 sessions), or no treatment. All were subjected to in-situ zymography. Dentin slices were, subsequently, obtained, covered with fluorescein-conjugated gelatin, and examined with confocal laser-scanning microscopy. The fluorescence intensity was quantified and statistically analyzed using one-way ANOVA and Bonferroni tests (α = 0.05). Furthermore, gelatin zymography was performed on protein extracts obtained from dentin powder (N = 8 teeth), treated with hydrogen peroxide or carbamide peroxide, with different exposure times (10/50 min for hydrogen peroxide; 252/1260 min for carbamide peroxide). The results of the in-situ zymography showed no statistical differences between the bleached specimens and the control group, with a medium level of gelatinolytic activity expressed in the dentin tubules. The results of gelatin zymography showed an increased expression of pro-MMP-9 in carbamide peroxide groups. The expression of pro-MMP-2 decreased in all the experimental groups. The bleaching treatments performed on the enamel of sound teeth do not influence dentinal enzymatic activity. However, when unprotected dentin tissue is bleached, matrix metalloproteinases are more expressed, particularly when carbamide peroxide is used, proportional to the exposure time. 相似文献
100.