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841.
Ghorai Santu Chakraborty Priyanka Poria Swarup Bairagi Nandadulal 《Nonlinear dynamics》2020,100(1):749-762
Nonlinear Dynamics - Dispersal-induced pattern formation is important from both fundamental and application points of view. Spatial pattern in an ecological system can strongly depend on exogenous... 相似文献
842.
In the most general practice of asymmetric catalysis, a chiral catalyst, typically bearing a center or an axis of chirality, is employed as the chiral source for imparting enantiocontrol over the developing product. Given the current interest toward optically pure compounds, various forms of chiral induction enabled by diverse chiral sources as well as the use of multiple catalysts under one-pot conditions have been in focus. In one such promising development, an achiral N-sulfonamide protected 1,6-amino allyl alcohol (NaphSO2NHCH2C(Ph)2CH2CH CHCH2OH) was subjected to Tsuji–Trost activation and an intramolecular amination to form important chiral pyrrolidine frameworks. A dual catalytic system comprising Pd(PPh3)4 and DAPCy (β-cyclohexyl substituted double axially chiral phosphoric acid derived from two homocoupled BINOL backbones with a dynamic central chiral axis) under mild conditions was reported to offer quantitative conversion with an ee of 95%. Here, we provide molecular insights into the origin of chiral induction by DAPCy, as obtained through a comprehensive density functional theory (SMD(toluene)/B3LYP-D3/6-31G**,Pd(SDD)) investigation. Two key steps in the mechanism are identified to involve a cooperative mode of activation of the Pd-bound allyl alcohol in the form of a Pd-π-allyl moiety at one end of the substrate, followed by an intramolecular nucleophilic addition of N-sulfonamide from the other end to yield a pyrrolidine derivative bearing an α-vinyl stereogenic center. (S,R,S)-DAPCy is found to steer the dehydroxylation to yield a Pd-π-allyl intermediate with a suitably poised si prochiral face for the nucleophilic addition. In the enantiocontrolled (as well as the turn-over determining step) nucleophilic addition, the chiral catalyst is identified to serve as a chiral phosphate counterion. The chiral induction is facilitated by a series of N–H⋯O, C–H⋯O, C–H⋯π, lone pair (lp)⋯π, O–H⋯O, O–H⋯π, and π⋯π noncovalent interactions, which is noted as more effective in the lower energy C–N bond formation transition state through the si prochiral face of the Pd-π-allyl moiety. These insights into the novel dynamic axially double chiral catalyst could be valuable toward exploiting such modes of stereoinduction.The origin of enantiocontrol in an intramolecular amination involving Pd(PPh3)4 and a double axially chiral phosphoric acid (DAPCy) dual catalytic system is traced to a more effective series of noncovalent interactions in the lower energy C–N bond formation transition state. 相似文献
843.
Debsena Chakraborty Rupak Saha Jack K. Clegg Partha Sarathi Mukherjee 《Chemical science》2022,13(40):11764
Polycyclic aromatic hydrocarbons (PAHs) find multiple applications ranging from fabric dyes to optoelectronic materials. Hydrogenation of PAHs is often employed for their purification or derivatization. However, separation of PAHs from their hydrogenated analogues is challenging because of their similar physical properties. An example of such is the separation of 9,10-dihydroanthracene from phenanthrene/anthracene which requires fractional distillation at high temperature (∼340 °C) to obtain pure anthracene/phenanthrene in coal industry. Herein we demonstrate a new approach for this separation at room temperature using a water-soluble interlocked cage (1) as extracting agent by host–guest chemistry. The cage was obtained by self-assembly of a triimidazole donor L·HNO3 with cis-[(tmeda)Pd(NO3)2] (M) [tmeda = N,N,N′,N′-tetramethylethane-1,2-diamine]. 1 has a triply interlocked structure with an inner cavity capable of selectively binding planar aromatic guests.We report here a triply interlocked cage with the ability to encapsulate planar guests in aqueous medium. This property was then employed to efficiently separate planar and non-planar aromatic hydrocarbons by aqueous extraction. 相似文献
844.
A bubble expands adiabatically in an incompressible, inviscid liquid. The variation of its radiusR with time is given by the Rayleigh’s equation. We find that the bubble is stable at the equilibrium point in this model. 相似文献
845.
Atasi Patra Maiti Arun Chakraborty 《Mathematical Methods in the Applied Sciences》2020,43(12):7397-7423
In this article, a nutrient-autotroph-herbivore model with nutrient recycling is constructed. Holling type-II functional response for the relation between nutrient and autotroph while Beddington-DeAngelis-type functional response for autotroph and herbivore relation are considered here. It is plausible that the conversion of nutrient from dead biomass (autotroph and herbivore) by decomposers (i.e., bacteria and fungi) are not instantaneous, which takes times. Hereby, two different discrete time delays for the decomposition process are introduced. The local and global stability behaviours of both nondelayed and delayed models are analysed around the equilibrium points. The stability and direction of Hopf-bifurcation using normal form theory and centre manifold theorem by taking one delay as a bifurcation parameter while keeping the other one fixed in the stable interval are discussed. It is observed that if the delay increases, the system loses its stability and hence becomes unstable. It is analysed how autotroph-herbivore ecosystem can be affected by the quantity of input nutrient and the properties of delays. The quantity of nutrient and the length of delays play significant roles in determining the stability of the system since a sufficiently small amount of nutrients or a long enough delay leads to the extinction of a species. 相似文献
846.
Madhubani Mukherjee Soumi Haldar Achintya K. Dutta 《International journal of quantum chemistry》2020,120(6):e26127
In the present work, we investigate the effect of aqueous environment on the vertical ionization potential (VIP) of adenine-thymine (AT) base pair using a multilayer equation of the motion-coupled cluster method. The microsolvation can cause both blue-shift and red-shit of the IP values. However, the bulk water environment always results in the red-shift of the vertical ionization potential. Our study shows that the correct treatment of the short-range interaction plays an essential role in determining the magnitude of the red-shift. We have developed a biased sampling scheme based on Koopmans' energy, which can significantly speed up the convergence with respect to the number of solvent-solute configurations. 相似文献
847.
Dr. Sourav Chakraborty Dr. Alessandro Aliprandi Prof. Luisa De Cola 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(48):11007-11012
The self-assembly of platinum complexes is a well-documented process that leads to interesting changes of the photophysical and electrochemical behavior as well as to a change in reactivity of the complexes. However, it is still not clear how many metal units must interact in order to achieve the desired properties of a large assembly. This work aimed to clarify the role of the number of interacting PtII units leading to an enhancement of the spectroscopic properties and how to address inter- versus intramolecular processes. Therefore, a series of neutral multinuclear PtII complexes were synthesized and characterized, and their photophysical properties at different concentration were studied. Going from the monomer to dimers, the growth of a new emission band and the enhancement of the emission properties were observed. Upon increasing the platinum units up to three, the monomeric blue emission could not be detected anymore and a concentration independent bright-yellow/orange emission, due to the establishment of intramolecular metallophilic interactions, was observed. 相似文献
848.
Czechoslovak Mathematical Journal - We examine an arithmetical function defined by recursion relations on the sequence {f(pk)}k∈? and obtain sufficient condition(s) for the sequence to... 相似文献
849.
To maximize the production of esters (E), keto (K) and keto-ester (KE) by esterification and ketalization of levulinic acid (LA) has been reacted using diols such as 1,2-propane diol (PDOL),1,2-ethane diol (EDOL), and 1,2,3-propane triol or glycerol (TRIOL) with desilicated Hβ. This work aims to assess the conversion and selectivity for the production of esters using conventional and microwave-irradiated (MWI) reactors. Catalysts characterizations were performed using NH3-temperature programme desorption, Brunauer, Emmett and Teller surface area (BET), Barrett, Joyner, and Halenda (BJH), scanning electron microscope, transmission electron microscope, and dynamic light scattering. Operating parameters such as reaction temperature (170–180°C), reaction time (20–80 min), feed composition (LA:PDOL/EDOL/TRIOL, 1:8/10/12), and microwave energy (300–500 watt) have been systematically investigated. Note that 99–100% conversion was achieved with the product selectivity of E (40%), K (30%), and KE (30%) with1,2-EDOL; E (56%), K (2%), and KE (17%) with 1,2-PDOL; E (69%), K(0%), and KE (22%) with TRIOL using D-Hβ as a solid catalyst in an MWI reactor. Reaction paths and kinetics were studied using pseudo-homogeneous (PH) model. 相似文献
850.