全文获取类型
收费全文 | 1028篇 |
免费 | 50篇 |
国内免费 | 2篇 |
专业分类
化学 | 859篇 |
晶体学 | 5篇 |
力学 | 9篇 |
数学 | 100篇 |
物理学 | 107篇 |
出版年
2023年 | 17篇 |
2022年 | 40篇 |
2021年 | 40篇 |
2020年 | 25篇 |
2019年 | 30篇 |
2018年 | 15篇 |
2017年 | 10篇 |
2016年 | 48篇 |
2015年 | 42篇 |
2014年 | 33篇 |
2013年 | 60篇 |
2012年 | 68篇 |
2011年 | 90篇 |
2010年 | 52篇 |
2009年 | 49篇 |
2008年 | 61篇 |
2007年 | 62篇 |
2006年 | 53篇 |
2005年 | 51篇 |
2004年 | 39篇 |
2003年 | 35篇 |
2002年 | 22篇 |
2001年 | 12篇 |
2000年 | 5篇 |
1999年 | 8篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 14篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1986年 | 7篇 |
1985年 | 10篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1977年 | 2篇 |
1975年 | 3篇 |
1973年 | 3篇 |
1909年 | 1篇 |
1908年 | 2篇 |
1858年 | 1篇 |
排序方式: 共有1080条查询结果,搜索用时 15 毫秒
61.
Hideyuki Tatsuno Kasper S. Kjr Kristjan Kunnus Tobias C. B. Harlang Cornelia Timm Meiyuan Guo Pavel Chbera Lisa A. Fredin Robert W. Hartsock Marco E. Reinhard Sergey Koroidov Lin Li Amy A. Cordones Olga Gordivska Om Prakash Yizhu Liu Mads G. Laursen Elisa Biasin Frederik B. Hansen Peter Vester Morten Christensen Kristoffer Haldrup Zoltn Nmeth Dorottya Srosin Szemes va Bajnczi Gyrgy Vank Tim B. Van Driel Roberto Alonso‐Mori James M. Glownia Silke Nelson Marcin Sikorski Henrik T. Lemke Dimosthenis Sokaras Sophie E. Canton Asmus O. Dohn Klaus B. Mller Martin M. Nielsen Kelly J. Gaffney Kenneth Wrnmark Villy Sundstrm Petter Persson Jens Uhlig 《Angewandte Chemie (International ed. in English)》2020,59(1):364-372
Iron N‐heterocyclic carbene (NHC) complexes have received a great deal of attention recently because of their growing potential as light sensitizers or photocatalysts. We present a sub‐ps X‐ray spectroscopy study of an FeIINHC complex that identifies and quantifies the states involved in the deactivation cascade after light absorption. Excited molecules relax back to the ground state along two pathways: After population of a hot 3MLCT state, from the initially excited 1MLCT state, 30 % of the molecules undergo ultrafast (150 fs) relaxation to the 3MC state, in competition with vibrational relaxation and cooling to the relaxed 3MLCT state. The relaxed 3MLCT state then decays much more slowly (7.6 ps) to the 3MC state. The 3MC state is rapidly (2.2 ps) deactivated to the ground state. The 5MC state is not involved in the deactivation pathway. The ultrafast partial deactivation of the 3MLCT state constitutes a loss channel from the point of view of photochemical efficiency and highlights the necessity to screen transition‐metal complexes for similar ultrafast decays to optimize photochemical performance. 相似文献
62.
Elisa Roda Fabrizio De Luca Carlo Alessandro Locatelli Daniela Ratto Carmine Di Iorio Elena Savino Maria Grazia Bottone Paola Rossi 《Molecules (Basel, Switzerland)》2020,25(22)
Bioactive metabolites isolated from medicinal mushrooms (MM) used as supportive treatment in conventional oncology have recently gained interest. Acting as anticancer agents, they interfere with tumor cells and microenvironment (TME), disturbing cancer development/progression. Nonetheless, their action mechanisms still need to be elucidated. Recently, using a 4T1 triple-negative mouse BC model, we demonstrated that supplementation with Micotherapy U-Care, a MM blend, produced a striking reduction of lung metastases density/number, paralleled by decreased inflammation and oxidative stress both in TME and metastases, together with QoL amelioration. We hypothesized that these effects could be due to either a direct anticancer effect and/or to a secondary/indirect impact of Micotherapy U-Care on systemic inflammation/immunomodulation. To address this question, we presently focused on apoptosis/proliferation, investigating specific molecules, i.e., PARP1, p53, BAX, Bcl2, and PCNA, whose critical role in BC is well recognized. We revealed that Micotherapy U-Care is effective to influence balance between cell death and proliferation, which appeared strictly interconnected and inversely related (p53/Bax vs. Bcl2/PARP1/PCNA expression trends). MM blend displayed a direct effect, with different efficacy extent on cancer cells and TME, forcing tumor cells to apoptosis. Yet again, this study supports the potential of MM extracts, as adjuvant supplement in the TNBC management. 相似文献
63.
IRMPD Spectra of Protonated Hydroxybenzaldehydes: Evidence of Torsional Barriers in Carboxonium Ions
Prof. Barbara Chiavarino Prof. Otto Dopfer Prof. Maria Elisa Crestoni Dr. Davide Corinti Dr. Philippe Maître Prof. Simonetta Fornarini 《Chemphyschem》2020,21(8):749-761
Protonation at the formyl oxygen atom of benzaldehydes leading to the formation of carboxonium ions yields two distinct isomers, depending on the relative orientation of the proton either cis or trans with respect to the hydrogen atom on the adjacent carbon. In this context, the IR multiple photon dissociation (IRMPD) spectra of protonated ortho, meta, and para-hydroxybenzaldehydes ( OH−BZH+ ), delivered into the gas phase by electrospray ionization of hydro-alcoholic solutions, are reported in the 3200–3700 cm−1 spectral range. This range is characteristic of O−H stretching modes and thus able to differentiate cis and trans carboxonium isomers. Comparison between IRMPD spectra and DFT calculations at the B3LYP/6-311++G(2df2p) level suggests that for both p- OH−BZH+ and m- OH−BZH+ only cis conformers are present in the ion population analyzed. For o- OH−BZH+ , IRMPD spectroscopy points to a mixture comprising one trans and more than one cis conformers. The energy barrier for cis–trans isomerization calculated for each OH−BZH+ isomer is a measure of the degree of π-electron delocalization. Furthermore, IRMPD spectra of p- OH−BZH+ , m- OH−BZH+ and protonated phenol (this last used as reference) were recorded also in the fingerprint range. Both the observed C−O and O−H stretching vibrations appear to be a measure of π-electron delocalization in the ions. 相似文献
64.
Elisa E. Greciano Joaquín Calbo Enrique Ortí Luis Snchez 《Angewandte Chemie (International ed. in English)》2020,59(40):17759-17759
65.
Maria Michela Salvatore Ilaria Di Lelio Marina DellaGreca Rosario Nicoletti Francesco Salvatore Elia Russo Gennaro Volpe Andrea Becchimanzi Alla Eddine Mahamedi Akila Berraf-Tebbal Anna Andolfi 《Molecules (Basel, Switzerland)》2022,27(7)
An undescribed 5,6-dihydropyran-2-one, namely diplopyrone C, was isolated and characterized from the cultures of an isolate of the fungus Diplodia corticola recovered from Quercus suber in Algeria. The structure and relative stereostructure of (5S,6S,7Z,9S,10S)-5-hydroxy-6-(2-(3-methyloxiran-2-yl)vinyl)-5,6-dihydro-2H-pyran-2-one were assigned essentially based on NMR and MS data. Furthermore, ten known compounds were isolated and identified in the same cultures. The most abundant product, the tetracyclic pimarane diterpene sphaeropsidin A, was tested for insecticidal effects against the model sucking aphid, Acyrthosiphon pisum. Results showed a toxic dose-dependent oral activity of sphaeropsidin A, with an LC50 of 9.64 mM. 相似文献
66.
Investigation of anthropic effects connected with metal ions concentration, organic matter and grain size in Bormida river sediments 总被引:9,自引:0,他引:9
Emilio Marengo Maria Carla Gennaro Elisa Robotti Piero Rossanigo Caterina Rinaudo Manuela Roz-Gastaldi 《Analytica chimica acta》2006,560(1-2):172-183
An investigation on the sediment composition and grain size was carried out along the Bormida river (Piedmont, Northern Italy). The samples were taken both in the riverbed and on its banks. Multivariate statistical exploratory methods permitted to identify possible sources of primary pollution. In particular, principal component analysis (PCA) showed that there are probably at least three anthropogenic main causes of pollution, one connected with Cr, Ni and Sn, the second with cadmium and the last one with mercury. Some correlations were found between heavy metal ion concentrations and organic matter and/or the sediment grain size. Differences between the samples collected in the riverbed and on the banks were identified and the relationships between the principal components and the distance of the samples from the riverbed and from the hot spot represented by the ACNA industrial site were also analyzed. 相似文献
67.
Riet Dams Elena Bernabe Anna Nicoletti Claudio Loda Luca Martini Damiano Papini 《Rapid communications in mass spectrometry : RCM》2010,24(17):2650-2654
The introduction of Quality by Design (QbD) in Drug Development has resulted in a greater emphasis on chemical process understanding, in particular on the origin and fate of impurities. Therefore, the identification and quantitation of low level impurities in new Active Pharmaceutical Ingredients (APIs) play a crucial role in project progression and this has created a greater need for sensitive and selective analytical methodology. Consequently, scientists are constantly challenged to look for new applications of traditional analytical techniques. In this context a normal‐phase liquid chromatography/electrospray ionization mass spectrometry (LC/ESI‐MS) method was developed to determine the amount of a de‐fluorinated analogue impurity in Casopitant Mesylate, a new API under development in GlaxoSmithKline, Verona. Normal‐phase LC provided the selectivity needed between our target analyte and Casopitant, while a single quadrupole mass spectrometer was used to ensure the sensitivity needed to detect the impurity at <0.05%w/w. Standard solutions and samples were prepared in heptane/ethanol (50:50, v/v) containing 1% of 2 M NH3 in ethanol; the mobile phase consisted of heptane/ethanol (95:5, v/v) with isocratic elution (flow rate: 1.0 mL/min, total run time: 23 min). To allow the formation of ions in solutions under normal‐phase (apolar) conditions, a post‐column infusion of a solution of 0.1% v/v of formic acid in methanol was applied (flow rate: 200 µL/min). The analysis was carried out in positive ion mode, monitoring the impurity by single ion monitoring (SIM). The method was fully validated and its applicability was demonstrated by the analysis of real‐life samples. This work is an example of the need for selective and accurate methodology during the development of a new chemical entity in order to develop an appropriate control strategy for impurities to ultimately ensure patient safety. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
68.
69.
Enzo Giannetti Giuseppe Martino Nicoletti Romano Mazzocchi 《Journal of polymer science. Part A, Polymer chemistry》1985,23(8):2117-2134
Homogeneous Ziegler-Natta systems for the ethylene polymerization, deriving from R2R2′M complexes (R = cyclopentadienyl; R′ = alkyl, aryl; M = Ti, Zr, Hf) and oligomeric oxoalane compounds, were studied. Further results concerning the methyl aluminoxane synthesis and the related chemistry are reported. On the basis of spectroscopic data a delocalized electronic structure could be inferred for these compounds. Results from polymerization experiments showed that the highest productivities are obtained only by oxoalane cocatalysts having a high degree of oligomerization. The catalytic activity of the systems under investigation was strongly affected also by changing both the σ-alkyl and the π-cyclo-pentadienyl ligands. Furthermore, it was found that in the presence of methyl aluminoxane, the homoleptic σ-alkyl derivatives of IVB transition metals, such as Zr(CH2C6H5)4, are also able to polymerize ethylene with a fairly high productivity. Active species containing Zr? O? Al bonds have been postulated. 相似文献
70.