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201.
N-[3-(Trifluoromethyl)homoallyl]sulfonamides, prepared via ring opening of (S)-glycidyl ethers or 2-aryloxiranes with 1-(trifluoromethyl)vinyllithium, underwent intramolecular addition or S(N)2'-type reaction in the normally disfavored 5-endo-trig fashion, leading to 2-substituted 4-(trifluoromethyl)- or 4-(difluoromethylene)pyrrolidines. Both alpha- and beta-face-selective hydrogenation of the 4-difluoromethylene group afforded syn- and anti-4-(difluoromethyl)pyrrolidines, respectively. These sequences, followed by the oxidation of a 2-hydroxymethyl or 2-aryl group, successfully provided prolines with a trifluoromethyl, difluoromethylene, or difluoromethyl group at the 4-position, including optically active prolines. 相似文献
202.
A novel approach is presented for studying the kinetics of specific protein-DNA interactions by NMR exchange spectroscopy. The experimental design involves the direct observation of translocation of a homeodomain between cognate sites on two oligonucleotide duplexes, differing by only a single base pair at the edge of the DNA recognition sequence. The single base-pair change perturbs the 1H-15N correlation spectrum of a number of residues, while leaving the affinity for the DNA unchanged. The exchange process has apparent rate constants in the 5-20 s-1 range which are linearly dependent upon the concentration of free DNA. These rates are about 3 orders of magnitude larger than the dissociation rate constant determined by gel shift assays at nanomolar DNA concentrations. The complete NMR exchange data set, comprising auto- and cross-peak intensities as a function of mixing time at five concentrations of free DNA, can be fit simultaneously to a simple model in which protein translocation between DNA duplexes occurs via a second-order process (with rate constants of approximately 6 x 104 M-1 s-1) involving direct collision of a protein-DNA complex with free DNA. This is akin to intersegmental transfer, and a physical model for the process is discussed. Rapid translocation at high concentrations of free DNA observed directly by NMR exchange spectroscopy reconciles the long half-lives of protein-DNA complexes measured by biochemical analysis in vitro with the highly dynamic behavior of such complexes observed in vivo. The relevance of this mechanism to the kinetics of protein-DNA interactions within the cell is discussed. 相似文献
203.
Tokuyama E Shibasaki T Kawabe H Mukai J Okada S Uchida T 《Chemical & pharmaceutical bulletin》2006,54(9):1288-1292
The purpose of the present study was to evaluate the bitterness-suppressing effect of L-ornithine (L-Orn) on single or mixed solutions of branched-chain amino acids (BCAAs) using human gustatory sensation tests and an artificial taste sensor. The BCAAs tested (L-isoleucine (L-Ile), L-leucine (L-Leu), and L-valine (L-Val)) are the main components of various enteral nutrients or supplements. The bitterness-suppression effect of L-Orn was also compared with the effect of L-Arg. L-Orn was effective in suppressing the bitterness of single or mixed solutions of BCAAs in human gustatory sensation tests, the effect being similar to or greater than that of L-Arg. The artificial taste sensor was able to predict the bitterness-suppressing effects of L-Orn and L-Arg. The response electric potential patterns of L-Val, L-Leu and L-Ile solutions to which 100 mM L-Arg had been added were quite similar to the sensor response patterns of the 100 mM L-Arg solutions alone. The relative response electric potential patterns of L-Val, L-Leu or L-Ile solutions containing 100 mM L-Orn in channels 5-8 (positively charged) are similar to that of single solution of 100 mM L-Orn. 相似文献
204.
Hayakawa T Goseki R Kakimoto MA Tokita M Watanabe J Liao Y Horiuchi S 《Organic letters》2006,8(24):5453-5456
Wholly aromatic rod-rod type di- and triblock molecules, oligo(ether sulfone)-b-oligo(ether ketone)s (OES-OEK), were synthesized to study a solid-state self-assembled nanostructure. The OES and OEK segments in the block molecules form segregated crystalline domains. The energy-filtering transmission electron microscopy images revealed that the di- and triblock OES-OEK co-oligomers formed lamellar nanostructures with a periodicity of approximately 9 and 13 nm, respectively. [structure: see text]. 相似文献
205.
206.
Elucidation of codoping effects on the solubility enhancement of Er3+ in SiO2 glass: striking difference between Al and P codoping 总被引:1,自引:0,他引:1
Saitoh A Matsuishi S Se-Weon C Nishii J Oto M Hirano M Hosono H 《The journal of physical chemistry. B》2006,110(15):7617-7620
The codoping effect mechanism of Al and P on the solubility enhancement of Er(3+) ion in SiO(2) glass was clarified by electron spin-echo envelope modulation spectroscopy. It turned out that doped P ions preferentially coordinate to the Er(3+) ion to form a "solvation shell structure", and the environment is similar to that in phosphate glass, while doped Al ions do not form such a selective solvation structure, taking octahedral coordination. This striking difference indicates that the primary roles of the P-doping and the Al-doping are attributed to "enthalpy of mixing" and to "entropy of mixing", respectively. 相似文献
207.
Yamauchi Junji Shibayama Jun Nakano Hisamatsu 《Optical and Quantum Electronics》1999,31(9-10):675-687
The generalized Douglas (GD) scheme is applied to the analysis of various optical waveguides. The GD scheme has an advantage over the conventional finite-difference scheme in that the truncation error can be reduced, while maintaining a tridiagonal matrix. To demonstrate fourth-order accuracy for a three-dimensional problem, a graded-index fiber is analyzed. Furthermore, the coupling length of a rib waveguide directional coupler is analyzed and its convergence behavior is discussed. Application of the GD scheme to a time-domain analysis is also presented. 相似文献
208.
The conjugate reduction of α,β-unsaturated esters such as acrylates, crotonate, and cinnamates followed by Mannich-type coupling toward aldimines was efficiently promoted by rhodium-bis(oxazolinyl)phenyl catalyst and alkoxyhydrosilanes to show high anti-selectivity up to 99. 相似文献
209.
210.
Atsushi?SatsumaEmail author Junji?Shibata Ken-ichi?Shimizu Tadashi?Hattori 《Catalysis Surveys from Asia》2005,9(2):75-85
The addition of hydrogen in the reaction atmosphere is effective in promoting the activity of Ag/alumina and Ag-zeolites on the selective reduction of NO by hydrocarbons (HC-SCR) at low temperatures. The increment of NO conversion over Ag-MFI corresponds to the periodic addition of hydrogen into C3H8-SCR conditions. The UV–VIS spectra of Ag-MFI have revealed that the addition of hydrogen results in the formation of Agnδ+ clusters due to partial reduction and agglomeration of Ag species. The coincidence of the formation of the Agnδ+ clusters and the increment of NO conversion suggests that Agnδ+ clusters are the highly active species for HC-SCR. From analysis by H2-TPR, UV–VIS, and EXAFS, the structure of Agnδ+ clusters on Ag-MFI is identified as being Ag42+ on average. The formation of Ag clusters was strongly affected by the type of zeolites: The major Ag species are Ag+ ions for MOR, Agnδ+ clusters for MFI and BEA, and relatively large metallic Agmparticles for Y. The sequence of Ag agglomeration (MOR < MFI < BEA < Y) is in accordance with the strength of the acid sites of zeolites. It can be expected that the interaction between the positive charge of Agnδ+ clusters and acid sites, i.e., the ion-exchange site of zeolites, stabilizes Agnδ+ clusters. The type of Ag species under HC-SCR conditions depends on the concentration of gas-phase oxidants (NO, O2) and reductants (H2, HC), and also on the number and strength of the zeolite acid sites. 相似文献