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941.
Moriou C Thomas M Adeline MT Martin MT Chiaroni A Pochet S Fourrey JL Favre A Clivio P 《The Journal of organic chemistry》2007,72(1):43-50
The 3'-N-sulfamate analogue of thymidylyl(3'-5')thymidine (TnsoT, 1) exhibits a preference for a C3'-endo conformation in the solution and solid states. Its photochemical behavior in solution is compared to that of its natural counterpart, thymidylyl(3'-5')thymidine (TpT, 2), to get further insight into the significance of the C3'-endo conformation on the photoproduct formation at the single-stranded dinucleotide level. Irradiation at 254 nm of 1 led to the same type of photoproducts as observed with 2. However, 1 was significantly more photoreactive than 2, and accordingly, the initial rate of photoproduct formation was enhanced in accordance with its propensity to base stack compared to 2. The corresponding quantum yields were determined and showed that the enhancement factor (1 compared to 2) is moderate for the cyclobutane pyrimidine dimer (CPD) (1.26) and much higher for the (6-4) photoproduct (1.8). These data strongly suggest that the CPD and (6-4) photoproduct arise from distinct minor stacked conformations. 相似文献
942.
Härtl A Garrido JA Nowy S Zimmermann R Werner C Horinek D Netz R Stutzmann M 《Journal of the American Chemical Society》2007,129(5):1287-1292
Charge build-up at the solid/aqueous interface is a ubiquitous phenomenon that determines the properties of interfacial electrical double layers. Due to its unique properties, the surface of diamond offers an attractive platform to investigate charging mechanisms in aqueous solutions. We investigate the surface charge by studying the ion sensitivity of H-terminated single crystalline diamond surface conductive layers. The effect of monovalent and divalent salts has been probed at different pH values. For a pH above 3.5, increasing the ionic strength results in a decrease of the surface conductivity, in contrast to the results obtained for pH below 3.5. Electrokinetic experiments are in good agreement with the surface conductivity measurements, showing an isoelectric point at pH 3.5 for the H-terminated diamond surface. We discuss the results in terms of the Coulombic screening by electrolyte ions of the surface potential, which is induced by a pH-dependent surface charge. The origin of this surface charge is discussed in terms of charge regulation by amphoteric hydroxyl surface groups and unsymmetrical adsorption of hydroxide and hydronium ions induced by the hydrophobic nature of the H-terminated diamond surface. This surface charge can have important consequences for processes governed by the diamond/aqueous interface, such as electron transfer to charged redox molecules, adsorption of charged molecules and proteins, and ion sensitivity. 相似文献
943.
944.
E. V. Agina N. I. Boiko R. M. Richardson B. I. Ostrovskii V. P. Shibaev E. A. Rebrov A. M. Muzafarov 《Polymer Science Series A》2007,49(4):412-424
Two series of carbosilane LC dendrimers with terminal protonated and deuterated butoxyphenylbenzoate mesogenic groups linked to carbosilane dendritic matrices of the first to fifth generations via an undecylene spacer have been synthesized. The chemical structure of new dendrimers has been studied by 1H NMR spectroscopy and gel-permeation chromatography. The dendrimers of first-fourth generations are characterized by formation of the smectic C mesophase in a wide temperature range, whereas much more complex columnar supramolecular structures are formed in dendrimers of the fifth generation. Structural studied of mesophases by X-ray diffraction and small-angle neutron scattering show that segregation takes place in mixtures of deuterated and protonated LC dendrimers; as a result, huge aggregates composed of hundreds of chemically unbound molecules develop and the sizes of these aggregates reversibly change with temperature. 相似文献
945.
Bolm C Martin M Gescheidt G Palivan C Stanoeva T Bertagnolli H Feth M Schweiger A Mitrikas G Harmer J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(6):1842-1850
The initial steps of an enantioselective Diels-Alder reaction catalyzed by a CuII-bissulfoximine complex were followed by EXAFS (EXAFS=extended X-ray absorption fine structure), EPR (EPR=electron paramagnetic resonance) spectroscopy (CW-EPR, FID-detected EPR, pulse ENDOR, HYSCORE; CW=continuous wave; ENDOR=electron nuclear double resonance; HYSCORE=hyperfine sublevel correlation; FID=free induction decay), and UV-visible spectroscopy. The complexes formed between the parent CuX2 (X=Cl-, Br-, TfO-, SbF6-) salts, the chiral bissulfoximine ligand (S,S)-1, and N-(1-oxoprop-2-en-1-yl)oxazolidin-2-one (2) as the substrate in CH2Cl2 were investigated in frozen and fluid solution. In all cases, penta- or hexacoordinated CuII centers were established. The complexes with counterions indicating high stereoselectivity (TfO- and SbF6-) reveal one unique species in which substrate 2 binds to pseudoequatorial positions (via O atoms), shifting the counterions to axial locations. On the other hand, those lacking stereoselectivity (X=Cl- and Br-) form two species in which the parent halogen anions remain at equatorial positions preventing the formation of geometries compatible with those found for X=TfO- and SbF6-. 相似文献
946.
The molecular structure of trichloronitromethane has been studied in the gas phase using electron diffraction data. The molecules are found to undergo low barrier rotation about the CN bond with a planar CNO2 moiety in agreement with HF/MP2/B3LYP/6-311G(d,p) calculations. The experimental data are consistent with a dynamic model using a potential function for the torsion of V = (V6/2)(1 − cos 6τ). The major geometrical parameters (rg and ) for the eclipsed form, obtained from least squares analysis of the data are as follows: r(NO3) = r(NO4) = 1.213(2) Å, r(CN) = 1.592(6) Å, r(CCl)av = 1.749(1) Å, Cl5CN/Cl6CN = 109. 6°/106.3°(2), O3NC/O4NC = 117. 6°/114.1°(4), τCl5C1N2O3 = 0.0°, and V6 = 0.20(25) kcal/mol. 相似文献
947.
The relation between thermochromism and thermal motion of aromatic rings on model bithiophene and 3-butylbithiophene molecules was studied by molecular dynamics (MD) simulations based on semiempirical AM1 hamiltonian. Theoretical optical spectra at various temperatures are generated from the conformations obtained from MD calculations. Alkyl chains have a tendency to tilt bithiophene fragments from co-planarity (connected with blue shift) whereas the unsubstituted systems prefer the higher degree of planarity (connected with red shift) upon the temperature increase. The slope of the linear temperature dependence of the reciprocal maximal wavelengths consists of the above electronic and of the vibrational contribution that (according to Wien’s displacement law) causes always the increase of the above mentioned slope by reciprocal Wien’s constant. This model explains the temperature dependence of experimental UV–vis spectra for dibutylheptathiophene and 3′,3,4′,4-tetrahexylhexathiophene. 相似文献
948.
Bubble pressure points of ethanol–1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea refrigerant) mixtures from the third Industrial Fluid Properties Simulation Challenge are computed using publicly available molecular simulation software. Several published force fields are compared against the known answers provided in the contest guidelines and the best force fields are used to make predictions for the unknown results. 相似文献
949.
DeNicola Cafferky K Thompson RL Richardson DD Caruso JA 《Analytical and bioanalytical chemistry》2007,387(6):2037-2043
Metals and metal-containing compounds are known to play important roles in many biological processes, including metabolic
and detoxification pathways and the formation and function of proteins. Like all organisms, viruses are expected to contain
different metals. These metals, either by themselves or in the form of metalloproteins, may be involved in the virus’s ability
to infect healthy cells and replicate within them. Identification and speciation of metals in control cells and in cells affected
by a virus could be helpful in elucidating infection and replication mechanisms; these might, in turn, be vital to the development
of more effective treatments. There has, however, been no extensive investigation of the metals specific viruses contain or
affect. The objective of this study was to investigate changes in cellular metal content resulting from herpes simplex virus
1 (HSV-1) infection. Inductively coupled plasma mass spectrometry was used to identify differences between metal concentrations
in uninfected and HSV-1-infected mammalian cells. Although it can be assumed that decreases in metal content are a result
of cellular response to the virus, increases can be attributed either to cellular response or to the HSV-1 virus itself. Microwave
digestion and flow injection methods suitable for small sample volumes were used, and the effects of different virus inactivation
procedures were explored. This work is the first step in the identification of metals pertinent to HSV-1 infection and lays
the foundation for future studies concentrating on characterization of these metal-associated or containing molecules. 相似文献
950.
Cécile Machut-Binkowski Frédéric Hapiot Roméo Cecchelli Patrick Martin Eric Monflier 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):567-572
For many commercial drugs, reaching the central nervous system in large amount without damaging the blood-brain-barrier (BBB)
remains a challenging task. We present here a supramolecular strategy aiming at using a well-defined cyclodextrin-coated liposomes
as drug carrier and adamantoyl saccharides as BBB-interacting ligands. In this study, the liposome is constituted of n-alkyldimethylammoniumcyclodextrins incorporated in the lipid bilayer of a 3/7 cholesterol/dipalmitoylphosphatidylcholine
mixture and the ligand is constituted of an adamantoylglucose molecule whose adamantoyl moiety can be included in the CD cavity.
The whole supramolecular assembly has been characterized by light-scattering and 31P NMR measurements. Toxicity and permeability studies on an in vitro model of the BBB clearly demonstrated a 5-fold improved
ability of the modified liposome to enter the BBB-endothelial cells compared to the non-coated liposome. Fluorescence labelling
of these liposomes is also displayed with DiI as a fluorescent probe. 相似文献