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201.
A highly simplified approach for the generation of substituted pyrimido[2,1-b]quinazoline core from the primary allyl amines afforded from the Baylis–Hillman adducts is described. Sequential reductive alkylation of the primary allyl amine with 2-nitrobenzaldehyde, reduction of the aromatic nitro group with In, CNBr-promoted intramolecular cyclization followed by NaOMe-mediated another intramolecular cyclization furnish the title compounds. 相似文献
202.
Molecular dynamics simulations of dilute and concentrated aqueous NaCl solutions are carried out to investigate the changes
of the hydrogen bonded structures in the vicinity of ions for different ion concentrations. An analysis of the hydrogen bond
population in the first and second solvation shells of the ions and in the bulk water is done. Although essentially no effect
of ions on the hydrogen bonding is observed beyond the first solvation shell of the ions for the dilute solutions, for the
concentrated solutions a noticeable change in the average number of water-water hydrogen bonds is observed in the second solvation
shells of the ions and even beyond. However, the changes in the average number of hydrogen bonds are found to be relatively
less when both water-water and ion-water hydrogen bonds are counted. Thus, the changes in the total number of hydrogen bonds
per water are not very dramatic beyond the first solvation shell even for concentrated solutions. 相似文献
203.
The lanthanide(III) complexes [Ln(LH2)(NO3)3] 1-11(La-Er), 15(Y) and [Ln(LH2)(NO3)2(H2O)](NO3) 12-14 (Tm-Lu) of the tetraiminodiphenolate macrocycle L2- have been prepared by the transmetallation reaction between [Pb(LH2)(NO3)2] and Ln(NO3)3.nH2O. In these compounds, the uncoordinated imino nitrogens are protonated and are hydrogen bonded to the phenolate oxygens. The X-ray crystal structures of the La (1), Ho (10) and Lu (14) compounds have been determined. Compounds 1 and 10, in which all the three nitrates are bound in bidentate fashion, are isostructural with distorted bicapped square antiprism geometry for the metal centre. In [Lu(LH2)(NO3)2(H2O)](NO3) 14, of the two metal bound nitrates one is bidentate and the other is unidentate, while the metal centre obtains a distorted square antiprism coordination environment. Proton NMR spectra of the paramagnetic lanthanide complexes have been studied in detail. Contributions of contact and pseudo-contact shifts to the lanthanide induced isotropic shifts (LIS) of the macrocycle protons have been separated and good agreement has been obtained between the calculated LIS values and the experimentally observed values. Analysis of the NMR data has led us to conclude that all the complexes in dimethyl sulfoxide solution attain similar configurations. The absorption and emission spectral characteristic of several compounds have been investigated. The complexes of samarium (5) and europium (6) on photoexcitation at 400 nm exhibit well-resolved luminescence spectra at 77 K both in the solid state and a methanol-ethanol (1 : 4) glassy matrix. For the terbium (8) and dysprosium (9) complexes, however, the observed luminescence peaks are less resolved and weak in intensity. 相似文献
204.
Heather D. Agnew Rosemary D. Rohde Steven W. Millward Dr. Arundhati Nag Woon‐Seok Yeo Dr. Jason E. Hein Dr. Suresh M. Pitram Dr. Abdul Ahad Tariq Vanessa M. Burns Russell J. Krom Valery V. Fokin Prof. K. Barry Sharpless Prof. James R. Heath Prof. 《Angewandte Chemie (International ed. in English)》2009,48(27):4944-4948
Special agents for protein capture : Iterative in situ click chemistry (see scheme for the tertiary ligand screen) and the one‐bead–one‐compound method for the creation of a peptide library enable the fragment‐based assembly of selective high‐affinity protein‐capture agents. The resulting ligands are water‐soluble and stable chemically, biochemically, and thermally. They can be produced in gram quantities through copper(I)‐catalyzed cycloaddition.
205.
Vision is hampered in aging and diseases, such as age-related macular degeneration, retinitis pigmentosa, diabetic retinopathy and glaucoma. This review collates the fine structural alterations of the human retina in aging and various pathological situations and their links to the disease pathogenesis. It transpires that most changes occur at the level of the retinal pigment epithelium -Bruch's membrane and the photoreceptor layer, causing visual problems to the sufferers. These changes include loss of normal, essential features of these cells and their gradual disappearance. It is important to understand in depth the selective vulnerability of this retinal region to alterations in aging and diseases. Evidence indicates that some of these changes may be mediated by the effects of oxidative stress, inflammation, and chronic light exposure. There are changes also in the inner retinal layers, wherein hypertension, auto-immunity, hypoxia and ischemia could play significant roles in disease pathogenesis. Results of extensive research utilizing animal models have broadened our idea about photoreceptor pathology. However, equivalent knowledge on various changes in aging human retina and in dystrophies that affect the macula is not complete. Since cone photoreceptor and ganglion cell death are a potential problem, it is imperative to know about the basic facts on how they are affected and the mechanisms involved in their death. Thus, prevention of cone and ganglion cell loss should be the target of choice. This review also highlights the significant role played by electron microscopy in understanding such ultrastructural changes and future strategies utilizing it and other techniques to fill some of the existing lacunae and advance our knowledge. 相似文献
206.
Davon W. Ferrara Evan R. MacQuarrie Victor Diez-Blanco Joyeeta Nag Anthony B. Kaye Richard F. Haglund Jr. 《Applied Physics A: Materials Science & Processing》2012,108(2):255-261
Nanocomposites consisting of gold nanoparticle (NP) arrays and vanadium dioxide (VO2) thin films are noteworthy for the tunability of both their thermal and optical properties. The localized surface plasmon resonance (LSPR) of the Au can be tuned when its dielectric environment is modulated by the semiconducting-to-metal phase transition (SMT) of the VO2; the LSPR itself can be altered by changing the shape of the NPs and the pitch of the NP array. In principle, then it should be possible to choose a combination of VO2 film and Au LSPR properties that maximizes the overall optical response of the nanocomposite. To demonstrate this effect, transient transmission measurements were conducted on lithographically fabricated arrays of Au NPs of diameter 140?nm, array spacing 350 nm, and covered with a 60?nm thick films of VO2 via pulsed laser deposition. Both Au::VO2 nanocomposites and bare VO2 film were irradiated with a shuttered 785?nm pump laser, and their optical response was probed at 1550?nm by a fixed-frequency diode laser. The Au::VO2 nanocomposite exhibited an increased effective absorption coefficient 1.5 times that of the plain film and required 37?% less laser power to induce the SMT. The time-dependent temperature rise in the film as a function of laser intensity was calculated from these measurements and compared with both analytic and finite-element models. Our results suggest that Au::VO2 nanocomposites may be useful in applications such as thermal-management coatings for energy efficient ??smart?? windows. 相似文献
207.
Sajid Saikia Animesh Ghosh Angshuman Nag 《Angewandte Chemie (International ed. in English)》2023,62(33):e202307689
A phosphor emitting both white light and broad near-infrared (NIR) radiation can simultaneously provide visual inspection and early signs of rotting of food products. The broad NIR emission is absorbed by the vibrational overtones of water molecules present in food items, providing the non-invasive image contrast to assess the food freshness. Here we design a phosphor, namely, Cr3+-Bi3+-codoped Cs2Ag0.6Na0.4InCl6, that simultaneously emit warm white light and broad NIR (1000 nm) radiation with quantum yield 27 %. This dual emitter is designed by combining the features of s2-electron (Bi3+) and d3-electron (Cr3+) doping in a weak crystal field of the halide perovskite host. excitation of Bi3+, using a commercial 370 nm ultraviolet light-emitting-diodes (UV-LED), yields both the emissions. A fraction of the excited Bi3+ dopants emit the warm white light, and the other fraction transfers its energy non-radiatively to Cr3+. Then the Cr3+ de-excites emitting broad NIR emission. Temperature dependent (6.4–300 K) photoluminescence in combination with Tanabe-Sugano diagram show that the Cr3+ experiences a weak crystal field ( =2.2), yielding the NIR emission. As a proof of concept, we fabricated a panel containing 122 phosphor-converted LEDs, demonstrating its capability to inspect food products. 相似文献