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161.
162.
163.
Alfred D. French 《Cellulose (London, England)》2011,18(4):889-896
Thorough conformational study of cellobiose requires consideration of numerous arrangements of the exocyclic groups. Therefore,
it is customary to prepare a number of structures with different arrangements of hydroxyl and hydroxymethyl groups. These
“starting geometries” are then given different values of the glycosidic linkage torsion angles ϕ and ψ. At each increment
of ϕ and ψ, the energy is calculated. Usually, the final product is an “adiabatic” contour plot of the lowest energy at each
ϕ/ψ point after considering all of the starting geometries. The present paper advocates for adiabatic maps despite the statement
by Schnupf and Momany (preceding paper) that adiabatic maps are not of interest because they contain sparse details about
the structures at each minimum. Similar information is computed by their method and adiabatic mapping, and comparable details
can be provided from adiabatic studies. Although Schnupf and Momany presented maps from calculations in vacuum and in water
that considered all of their calculated energies, they favored the presentation of two to four maps for each of 36 individual
minima, each with its own zero of relative energy. However, previous work showed that more structures are needed to provide
the lowest energies at each point in ϕ/ψ space. Following their preferred strategy would result in even more maps when the
added structures are considered. The need to map individual minima can be avoided by starting calculations with the same exocyclic
orientations at each ϕ/ψ point instead of using the preceding optimized structure to start the next energy minimization. Using
the same orientations at each point allows periodic maps that depict barriers between minima. 相似文献
164.
Ragab AE Grüschow S Tromans DR Goss RJ 《Journal of the American Chemical Society》2011,133(39):15288-15291
The pacidamycins belong to a class of antimicrobial nucleoside antibiotics that act by inhibiting the clinically unexploited target translocase I, a key enzyme in peptidoglycan assembly. As with other nucleoside antibiotics, the pacidamycin 4',5'-dehydronucleoside portion is an essential pharmacophore. Here we show that the biosynthesis of the pacidamycin nucleoside in Streptomyces coeruleorubidus proceeds through three steps from uridine. The transformations involve oxidation of the 5'-alcohol by Pac11, transamination of the resulting aldehyde by Pac5, and dehydration by the Cupin-domain protein Pac13. 相似文献
165.
The gas-phase fluorescence excitation, emission and photodissociation characteristics of three xanthene dyes (rhodamine 575,
rhodamine 590, and rhodamine 6G) have been investigated in a quadrupole ion trap mass spectrometer. Measured gas-phase excitation
and dispersed emission spectra are compared with solution-phase spectra and computations. The excitation and emission maxima
for all three protonated dyes lie at higher energy in the gas phase than in solution. The measured Stokes shifts are significantly
smaller for the isolated gaseous ions than the solvated ions. Laser power-dependence measurements indicate that absorption
of multiple photons is required for photodissociation. Redshifts and broadening of the dispersed fluorescence spectra at high
excitation laser power provide evidence of gradual heating of the ion population, pointing to a mechanism of sequential multiple-photon
activation through absorption/emission cycling. The relative brightness in the gas phase follows the order R575(1.00) < R590(1.15) < R6G(1.29).
Fluorescence emission from several mass-selected product ions has been measured. 相似文献
166.
Liu S Yu Z Yu X Huang SX Luo Y Wu L Shen W Yang Z Wang L Gunawan AM Chan RJ Shen B Zhang ZY 《Chemistry & biology》2011,18(1):101-110
SHP2 phosphatase is a positive transducer of growth factor and cytokine signaling. SHP2 is also a bona fide oncogene; gain-of-function SHP2 mutations leading to increased phosphatase activity cause Noonan syndrome, as well as multiple forms of leukemia and solid tumors. We report that tautomycetin (TTN), an immunosuppressor in organ transplantation, and its engineered analog TTN D-1 are potent SHP2 inhibitors. TTN and TTN D-1 block T?cell receptor-mediated tyrosine phosphorylation and ERK activation and gain-of-function mutant SHP2-induced hematopoietic progenitor hyperproliferation and monocytic differentiation. Crystal structure of the SHP2?TTN D-1 complex reveals that TTN D-1 occupies the SHP2 active site in a manner similar to that of a peptide substrate. Collectively, the data support the notion that SHP2 is a cellular target for TTN and provide a potential mechanism for the immunosuppressive activity of TTN. Moreover, the structure furnishes molecular insights upon which therapeutics targeting SHP2 can be developed on the basis of the TTN scaffold. 相似文献
167.
Altun M Kramer HB Willems LI McDermott JL Leach CA Goldenberg SJ Kumar KG Konietzny R Fischer R Kogan E Mackeen MM McGouran J Khoronenkova SV Parsons JL Dianov GL Nicholson B Kessler BM 《Chemistry & biology》2011,18(11):1401-1412
Converting lead compounds into drug candidates is a crucial step in drug development, requiring early assessment of potency, selectivity, and off-target effects. We have utilized activity-based chemical proteomics to determine the potency and selectivity of deubiquitylating enzyme (DUB) inhibitors in cell culture models. Importantly, we characterized the small molecule PR-619 as a broad-range DUB inhibitor, and P22077 as a USP7 inhibitor with potential for further development as a chemotherapeutic agent in cancer therapy. A striking accumulation of polyubiquitylated proteins was observed after both selective and general inhibition of cellular DUB activity without direct impairment of proteasomal proteolysis. The repertoire of ubiquitylated substrates was analyzed by tandem mass spectrometry, identifying distinct subsets for general or specific inhibition of DUBs. This enabled identification of previously unknown functional links between USP7 and enzymes involved in DNA repair. 相似文献
168.
Obenchain DA Bills BJ Christenholz CL Elmuti LF Peebles RA Peebles SA Neill JL Steber AL 《The journal of physical chemistry. A》2011,115(44):12228-12234
The microwave spectra of four isotopologues of the CHBrF(2)···HCCH weakly bound dimer have been measured in the 6-18 GHz region using chirped-pulse and Balle-Flygare Fourier-transform microwave spectroscopy. Spectra of (13)CH(79)BrF(2) and (13)CH(81)BrF(2) monomers have also been measured, and spectroscopic constants are reported. Measurement of spectra for the (79)Br and (81)Br isotopologues of CHBrF(2) complexed with both (12)C(2)H(2) and (13)C(2)H(2) have allowed the determination of a structure with C(s) symmetry for this complex. CHBrF(2) interacts with the triple bond of acetylene via a C-H···π contact (R(H···π) = 2.670(8) ?) with the Br atom lying in the ab plane, located 3.293(40) ? from a hydrogen atom of the HCCH molecule. The structure of CHBrF(2)···HCCH has been compared with recently studied related acetylene complexes, including a comparison with (and further structural analysis of) the CHClF(2)···HCCH complex. 相似文献
169.
Baker ML Bianchi A Carretta S Collison D Docherty RJ McLnnes EJ McRobbie A Muryn CA Mutka H Piligkos S Rancan M Santini P Timco GA Tregenna-Piggott PL Tuna F Güdel HU Winpenny RE 《Dalton transactions (Cambridge, England : 2003)》2011,40(12):2725-2734
We report a detailed physical analysis on a family of isolated, antiferro-magnetically (AF) coupled, chromium(III) finite chains, of general formula (Cr(RCO(2))(2)F)(n) where the chain length n = 6 or 7. Additionally, the chains are capped with a selection of possible terminating ligands, including hfac (= l,l,l,5,5,5-hexafluoropentane-2,4-dionate(l-)), acac (= pentane-2,4-dionate(l-)) or (F)(3). Measurements by inelastic neutron scattering (INS), magnetometery and electron paramagnetic resonance (EPR) spectroscopy have been used to study how the electronic properties are affected by n and capping ligand type. These comparisons allowed the subtle electronic effects the choice of capping ligand makes for odd member spin 3/2 ground state and even membered spin 0 ground state chains to be investigated. For this investigation full characterisation of physical properties have been performed with spin Hamiltonian parameterisation, including the determination of Heisenberg exchange coupling constants and single ion axial and rhombic anisotropy. We reveal how the quantum spin energy levels of odd or even membered chains can be modified by the type of capping ligand terminating the chain. Choice of capping ligands enables Cr-Cr exchange coupling to be adjusted by 0, 4 or 24%, relative to Cr-Cr exchange coupling within the body of the chain, by the substitution of hfac, acac or (F)(3) capping ligands to the ends of the chain, respectively. The manipulation of quantum spin levels via ligands which play no role in super-exchange, is of general interest to the practise of spin Hamilton modelling, where such second order effects are generally not considered of relevance to magnetic properties. 相似文献
170.
Uppal BS Booth RK Ali N Lockwood C Rice CR Elliott PI 《Dalton transactions (Cambridge, England : 2003)》2011,40(29):7610-7616
A series of 1-alkyl-4-aryl-1,2,3-triazoles (1-methyl-4-phenyl-1,2,3-triazole (1a); 1-propyl-4-phenyl-1,2,3-triazole (1b); 1-benzyl-4-phenyl-1,2,3-triazole (1c); 1-propyl-4-p-tolyl-1,2,3-triazole (1d)) have been prepared through a one-pot procedure involving in situ generation of the alkyl azide from a halide precursor followed by copper catalysed alkyne/azide cycloaddition (CuAAC) with the appropriate aryl alkyne. Cationic Re(I) complexes [Re(bpy)(CO)(3)(1a-d)]PF(6) (2a-d) were then prepared by stirring [Re(bpy)(CO)(3)Cl] with AgPF(6) in dichloromethane in the presence of ligands 1a-d. X-ray crystal structures were obtained for 2a and 2b. In the solid state, 2a adopts a highly distorted geometry, which is not seen for 2b, in which the plane of the triazole ligand tilts by 13° with respect to the Re-N bond as a result of a π-stacking interaction between the Ph substituent and one of the rings of the bpy ligand. This π-stacking interaction also results in severe twisting of the bpy ligand. Infrared spectra of 2a-d exhibit ν(CO) bands at ~2035 and ~1926 cm(-1) suggesting that these ligands are marginally better donors than pyridine (ν(CO) = 2037, 1932 cm(-1)). The complexes are luminescent in aerated dichloromethane at room temperature with emission maxima at 542 to 552 nm comparable to that of the pyridine analogue (549 nm) and blue shifted relative to the parent chloride complex. Long luminescent lifetimes are observed for the triazole complexes (475 to 513 ns) in aerated dichloromethane solutions at room temperature. 相似文献