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581.
582.
Katsinis Dimitrios Mitsoulas Ioannis Pastras Georgios 《The European Physical Journal C - Particles and Fields》2018,78(8):1-9
The European Physical Journal C - We discuss the possible existence of the fully-heavy tetraquarks. We calculate the ground-state energy of the $$bb {\bar{b}} {\bar{b}}$$ bound state, where b... 相似文献
583.
Transition states (index-1 saddle points) play a crucial role in determining the rates of chemical transformations but their reliable identification remains challenging in many applications. Deterministic global optimization methods have previously been employed for the location of transition states (TSs) by initially finding all stationary points and then identifying the TSs among the set of solutions. We propose several regional tests, applicable to general nonlinear, twice continuously differentiable functions, to accelerate the convergence of such approaches by identifying areas that do not contain any TS or that may contain a unique TS. The tests are based on the application of the interval extension of theorems from linear algebra to an interval Hessian matrix. They can be used within the framework of global optimization methods with the potential of reducing the computational time for TS location. We present the theory behind the tests, discuss their algorithmic complexity and show via a few examples that significant gains in computational time can be achieved by using these tests. 相似文献
584.
Takahito Kasahara Young Jin Jang Lanne Racicot Dimitrios Panagopoulos Steven H. Liang Marco A. Ciufolini 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(36):9791-9793
A metathesis reaction occurs when a diaryliodonium triflate is heated with an aryl iodide, resulting in the formation of a new diaryliodonium triflate. 相似文献
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Ramona Pristavita Norma-Yadira Mendoza-Gonzalez Jean-Luc Meunier Dimitrios Berk 《Plasma Chemistry and Plasma Processing》2011,31(6):851-866
The process control for reproducibility, uniformity, and achievement of desired structures for carbon black generated in thermal
plasma devices is studied in this paper through modeling, and correlated with experimental results. A numerical simulation
of the flow and energy fields, stream function lines and the quench rates of the plasma gas in a conical shape reactor at
different pressures was made. An argon plasma is used with highly diluted methane (0.6–7%) as the carbon precursor. The quench
rates were studied in order to observe the flow development and hence the thermal history of particle nucleation. Three pressure
cases of 20.7, 55.2 and 101.3 kPa and two plasma powers cases of 10 and 20 kW were studied. The modeling results enabled carbon
nanoflakes production in the experimental tests performed on an inductively coupled thermal plasma system. Results indicate
a robust process control enabling very little particle morphology variation over this wide range of reactor pressure values
and varying plasma power, and a very high reproducibility of the particle morphologies obtained. 相似文献
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Chiara Pelosi Francesca Saitta Caterina Zerino Giovanni Canil Tarita Biver Alessandro Pratesi Celia Duce Dimitrios Fessas Chiara Gabbiani Maria Rosaria Tin 《Molecules (Basel, Switzerland)》2021,26(8)
In this work, we have analysed the binding of the Pt(II) complexes ([PtCl(4′-phenyl-2,2′:6′,2″-terpyridine)](CF3SO3) (1), [PtI(4′-phenyl-2,2′:6′,2″-terpyridine)](CF3SO3) (2) and [PtCl(1,3-di(2-pyridyl)benzene) (3)] with selected model proteins (hen egg-white lysozyme, HEWL, and ribonuclease A, RNase A). Platinum coordination compounds are intensively studied to develop improved anticancer agents. In this regard, a critical issue is the possible role of Pt-protein interactions in their mechanisms of action. Multiple techniques such as differential scanning calorimetry (DSC), electrospray ionization mass spectrometry (ESI-MS) and UV-Vis absorbance titrations were used to enlighten the details of the binding to the different biosubstrates. On the one hand, it may be concluded that the affinity of 3 for the proteins is low. On the other hand, 1 and 2 strongly bind them, but with major binding mode differences when switching from HEWL to RNase A. Both 1 and 2 bind to HEWL with a non-specific (DSC) and non-covalent (ESI-MS) binding mode, dominated by a 1:1 binding stoichiometry (UV-Vis). ESI-MS data indicate a protein-driven chloride loss that does not convert into a covalent bond, likely due to the unfavourable complexes’ geometries and steric hindrance. This result, together with the significant changes of the absorbance profiles of the complex upon interaction, suggest an electrostatic binding mode supported by some stacking interaction of the aromatic ligand. Very differently, in the case of RNase A, slow formation of covalent adducts occurs (DSC, ESI-MS). The reactivity is higher for the iodo-compound 2, in agreement with iodine lability higher than chlorine. 相似文献
590.
Derivatization of amino acids by 2 M HCl/CH3OH (60 min, 80 °C) followed by derivatization of the intermediate methyl esters with pentafluoropropionic anhydride (PFPA) in ethyl acetate (30 min, 65 °C) is a useful two-step derivatization procedure (procedure A) for their quantitative measurement in biological samples by gas chromatography-mass spectrometry (GC-MS) as methyl ester pentafluoropropionic (PFP) derivatives, (Me)m-(PFP)n. This procedure allows in situ preparation of trideutero-methyl esters PFP derivatives, (d3Me)m-(PFP)n, from synthetic amino acids and 2 M HCl/CD3OD for use as internal standards. However, procedure A converts citrulline (Cit) to ornithine (Orn) and homocitrulline (hCit) to lysine (Lys) due to the instability of their carbamide groups under the acidic conditions of the esterification step. In the present study, we investigated whether reversing the order of the two-step derivatization may allow discrimination and simultaneous analysis of these amino acids. Pentafluoropropionylation (30 min, 65 °C) and subsequent methyl esterification (30 min, 80 °C), i.e., procedure B, of Cit resulted in the formation of six open and cyclic reaction products. The most abundant product is likely to be N5-Carboxy-Orn. The second most abundant product was confirmed to be Orn. The most abundant reaction product of hCit was confirmed to be Lys, with the minor reaction product likely being N6-Carboxy-Lys. Mechanisms are proposed for the formation of the reaction products of Cit and hCit via procedure B. It is assumed that at the first derivatization step, amino acids form (N,O)-PFP derivatives including mixed anhydrides. At the second derivatization step, the Cit-(PFP)4 and hCit-(PFP)4 are esterified on their C1-Carboxylic groups and on their activated Nureido groups. Procedure B also allows in situ preparation of (d3Me)m-(PFP)n from synthetic amino acids for use as internal standards. It is demonstrated that the derivatization procedure B enables discrimination between Cit and Orn, and between hCit and Lys. The utility of procedure B to measure simultaneously these amino acids in biological samples such as plasma and urine remains to be demonstrated. Further work is required to optimize the derivatization conditions of procedure B for biological amino acids. 相似文献