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121.
Rojo I Teixidor F Viñas C Kivekäs R Sillanpää R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(21):5376-5385
The anionic chelating ligand [1,1'-(PPh2)2-3,3'-Co(1,2-C2B9H10)2]- has been synthesized from [3,3'-Co(1,2-C2B9H11)2]- in very good yield in a one-pot process with an easy work-up procedure. The coordinating ability of this ligand has been studied with Group 11 metal ions (Ag, Au) and with transition-metal ions (Pd, Rh). The two dicarbollide halves of the [1,1'-(PPh2)2-3,3'-Co(1,2-C2B9H10)2]- ligand can swing about one axis in a manner analogous to the constituent parts of BINAP and ferrocenyl phosphine derivatives. All these ligands function as hinges, with the most important property in relation to the coordination requirements of the metal being the PP distance. [1,1'-(PPh2)2-3,3'-Co(1,2-C2B9H10)2]-, BINAP, ferrocenyl phosphine derivatives, and other hinge ligands present a range of different PP separations, and consequently different coordination spheres and dispositions around metal cations. To account for these differences, the equation Dphi2 = D02 + 4 R2cos2(90-phi/2) has been developed. It relates the PP distance (Dphi) in a complex with the minimum PP distance (D0) that is characteristic of the hinge-type ligand. 相似文献
122.
Teresa M. V. D. Pinho e Melo Clara S. B. Gomes Maria I. L. Soares Antanio M. d'A Rocha Gonsalves Jos A. Paixo Ana M. Beja Manuela Ramos Silva 《Journal of heterocyclic chemistry》2004,41(4):493-497
3‐Carbethoxy‐5‐phenyl‐5H,7H‐thiazolo[3,4‐c]oxazol‐4‐ium‐1‐olate was generated from (2R,4R)‐N‐ethoxyoxalyl‐2‐phenylthiazolidine‐4‐carboxylic acid and its reactivity studied. This münchnone showed low reactivity as dipole although from the reaction with dimethyl acetylenedicarboxylate the corresponding (3R)‐3‐phenyl‐17H,3H‐pyrrolo[1,2‐c]thiazole‐5,6,7‐tricarboxylate could be isolated. The thermolysis of (2R,4R)‐N‐ethoxyoxalyl‐2‐phenylthiazolidine‐4‐carboxylic acid in refluxing acetic anhydride led to the synthesis of N‐(1‐ethoxycarbonyl‐2‐phenylvinyl)‐2‐phenyl‐4‐thioxo‐1,3‐thiazolidine. The structure of methyl (2R,4R)‐N‐ethoxyoxalyl‐2‐phenylthiazoliddine‐4‐carboxylate was determined by X‐ray crystallography. 相似文献
123.
124.
Choi CY Schneider EL Kim JM Gluzman IY Goldberg DE Ellman JA Marletta MA 《Chemistry & biology》2002,9(8):881-889
The erythrocytic growth stage of Plasmodium falciparum involves hemoglobin proteolysis as the primary nutrient source with the concomitant release of free heme. The liberated heme is processed by the parasite into hemozoin, a polymeric porphyrin dimer. Histidine-rich protein binds heme and mediates the formation of hemozoin, which is inhibited by the antimalarial drug chloroquine. Interference with heme binding was determined using a microtiterplate assay. Combinatorial libraries were screened and tested against parasite growth, revealing a good correlation between heme binding interference and the inhibition of parasite growth. Several of these compounds retain their potency against a chloroquine-resistant strain of Plasmodium falciparum. The most potent compounds have IC(50) values less than or equal to 50 nM against chloroquine-resistant and chloroquine-sensitive parasites. 相似文献
125.
Clara Grosso Ana Cristina Figueiredo Jesus Burillo Ana M. Mainar José S. Urieta José G. Barroso José A. Coelho António M. F. Palavra 《Journal of separation science》2010,33(14):2211-2218
Supercritical fluid extraction (SFE) of the volatile oil from Thymus vulgaris L. aerial flowering parts was performed under different conditions of pressure, temperature, mean particle size and CO2 flow rate and the correspondent yield and composition were compared with those of the essential oil isolated by hydrodistillation (HD). Both the oils were analyzed by GC and GC‐MS and 52 components were identified. The main volatile components obtained were p‐cymene (10.0–42.6% for SFE and 28.9–34.8% for HD), γ‐terpinene (0.8–6.9% for SFE and 5.1–7.0% for HD), linalool (2.3–5.3% for SFE and 2.8–3.1% for HD), thymol (19.5–40.8% for SFE and 35.4–41.6% for HD), and carvacrol (1.4–3.1% for SFE and 2.6–3.1% for HD). The main difference was found to be the relative percentage of thymoquinone (not found in the essential oil) and carvacryl methyl ether (1.0–1.2% for HD versus t?0.4 for SFE) which can explain the higher antioxidant activity, assessed by Rancimat test, of the SFE volatiles when compared with HD. Thymoquinone is considered a strong antioxidant compound. 相似文献
126.
Francisco A. Macías José O. Guerra Ana M. Simonet Andy J. Pérez Clara Nogueiras 《Magnetic resonance in chemistry : MRC》2010,48(5):350-355
A careful NMR analysis, especially by 1D TOCSY and 1D ROESY, of a refined saponin fraction allowed us to determine the structure of three saponins from a polar extract of Agave brittoniana Trel. spp. Brachypus leaves. The use of 1D DOSY for the suppression of the solvent signal was useful to obtain the chemical shifts of anomeric signals. A full assignment of the 1H and 13C spectral data for the new saponins, agabrittonosides E–F (1–2) and the well‐known Karatavioside C (3) and their methoxyl derivatives, is reported. The structures were established using a combination of 1D and 2D (1H, 1H‐COSY, TOCSY, ROESY, g‐HSQC, g‐HMBC and g‐HSQC‐TOCSY) NMR techniques and ESI–MS. In addition, the methoxylation of these furostane saponins in the presence of MeOH was studied. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
127.
Fabio Fenili Clara Rigamonti Alberto Bossi Paolo Ferruti Amedea Manfredi Stefano Maiorana Clara Baldoli Silvia Cauteruccio Emanuela Licandro Elisabetta Ranucci 《Journal of polymer science. Part A, Polymer chemistry》2010,48(21):4704-4710
A tetrathia‐[7]‐helicene bearing in the 2 and 13 positions cyanovinyl groups was used as comonomer in the Michael‐type polyaddition reaction with N,N′‐bis(β‐mercaptoethyl)piperazine. This led to a new polymer bearing tetrathia‐[7]‐helicene units regularly distributed along the polymer backbone, which may be regarded as the first example of a new family of potentially useful nonlinear optical materials. All products were structurally characterized by 1H and 13C NMR spectroscopy. Differential scanning calorimetry characterizations revealed the presence, in both monomeric and polymeric helicenes, of glass‐transition like temperatures, associated to some conformational variation of the helicene units. The optical properties, the film formation and the morphology of the polymer‐containing tetratia‐[7]‐helicenes were also investigated. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 相似文献
128.
Clara D. Christ Alan E. Mark Wilfred F. van Gunsteren 《Journal of computational chemistry》2010,31(8):1569-1582
Methods to compute free energy differences between different states of a molecular system are reviewed with the aim of identifying their basic ingredients and their utility when applied in practice to biomolecular systems. A free energy calculation is comprised of three basic components: (i) a suitable model or Hamiltonian, (ii) a sampling protocol with which one can generate a representative ensemble of molecular configurations, and (iii) an estimator of the free energy difference itself. Alternative sampling protocols can be distinguished according to whether one or more states are to be sampled. In cases where only a single state is considered, six alternative techniques could be distinguished: (i) changing the dynamics, (ii) deforming the energy surface, (iii) extending the dimensionality, (iv) perturbing the forces, (v) reducing the number of degrees of freedom, and (vi) multi‐copy approaches. In cases where multiple states are to be sampled, the three primary techniques are staging, importance sampling, and adiabatic decoupling. Estimators of the free energy can be classified as global methods that either count the number of times a given state is sampled or use energy differences. Or, they can be classified as local methods that either make use of the force or are based on transition probabilities. Finally, this overview of the available techniques and how they can be best used in a practical context is aimed at helping the reader choose the most appropriate combination of approaches for the biomolecular system, Hamiltonian and free energy difference of interest. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 相似文献
129.
M. Clara Gonçalves Luis M. Fortes Rui M. Almeida Alessandro Chiasera Andrea Chiappini Maurizio Ferrari Shivakiran Bhaktha 《Journal of Sol-Gel Science and Technology》2010,55(1):52-58
Er3+ photoluminescence (PL) and Yb3+ → Er3+ energy transfer (ET) phenomena in the near infrared (NIR) have been studied in three-dimensional (3-D) inverse opal (IO)
structures synthesized by a colloidal/sol–gel route, starting with the deposition of polystyrene microsphere (235 nm and 460 nm
diameter) direct opal templates by convective self-assembly, followed by infiltration of the interstices with Er3+/Yb3+-doped silica, titania and silica-titania sols and heat-removal of the polymeric template material. The crystalline quality
of the IOs has been optimized through suitable substrate treatments, plus the control of temperature and humidity during deposition
of the templates. The structural and optical properties of the 3-D opal and IO structures have been studied by field emission
scanning electron microscopy and visible-NIR reflection spectroscopy, in order to assess the relationship between microstructure
and the photonic properties obtained. Photonic bandgaps have been evidenced by the corresponding stop bands in the reflection
spectra. The shape and the intensity of the Er3+
4I13/2 → 4I15/2 transition at ~1.5 μm were modified in most IOs relatively to similar matrix deposits without a photonic crystal structure,
particularly in the case of pure silica and titania IOs, where the PL peak narrowed and intensified. It was not possible at
this stage to detect Yb3+ → Er3+ ET phenomena in the IOs structures. 相似文献
130.
We present some results whose central theme is the phenomenon of the first eigenvalue of the Laplacian and conductance of
the dynamical system. Our main tool is a method for studying how the hyperbolic metric on a Riemann surface behaves under
deformation of the surface. With this model, we show that there are variation of the first eigenvalue of the laplacian and
the conductance of the dynamical system, with the Fenchel–Nielsen coordinates, that characterize the surface. 相似文献