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991.
The effect of an acidic surfactant, perfluorotetradecanoic acid (PFTDA), on the gelation of octadecyltrimethoxysilane (ODTMS) monolayers at the air/water interface was investigated using a Langmuir film balance, attenuated total reflection (ATR) infrared spectroscopy, and atomic force microscopy (AFM). The gelation of ODTMS was greatly accelerated by adding only 2 mol % PFTDA into the monolayer; in this case, the hydrolysis of ODTMS was completed within a few minutes, whereas otherwise it took 18 h. ATR-IR spectroscopy clearly demonstrated that the gelation of a 49:1 ODTMS/PFTDA monolayer proceeded on a pure water subphase mainly via hydrolysis followed by condensation. In the presence of PFTDA, the local acidity at specific sites is presumed to be very high, catalyzing the hydrolysis of ODTMS. The extremely fast rate is attributed not only to the lateral diffusion of PFTDA in the mixed monolayer but also to proton propagation where the proton(s) involved in the initial hydrolysis are transposed rapidly to the nearby methoxy groups for subsequent hydrolysis. The catalytic activity of PFTDA can be neutralized, however, simply by the addition of multivalent metallic ions such as Cd2+ to form saltlike complexes with PFTDA; the rate of 2-D sol-gel processes can thus be easily regulated by a minute amount of PFTDA and/or Cd2+ added into the reaction system. 相似文献
992.
Tai HC Khidekel N Ficarro SB Peters EC Hsieh-Wilson LC 《Journal of the American Chemical Society》2004,126(34):10500-10501
We report a new strategy for the parallel identification of O-GlcNAc-glycosylated proteins from cell lysates. The approach permits specific proteins of interest to be rapidly interrogated for the modification in any tissue or cell type and can be extended to peptides to facilitate the mapping of glycosylation sites. As an illustration of the approach, we identified four new O-GlcNAc-glycosylated proteins of low cellular abundance (c-Fos, c-Jun, ATF-1, and CBP) and two short regions of glycosylation in the enzyme O-GlcNAc transferase (OGT). The ability to target specific proteins across various tissue or cell types complements emerging proteomic technologies and should advance our understanding of this important posttranslational modification. 相似文献
993.
Tai K Murdock S Wu B Ng MH Johnston S Fangohr H Cox SJ Jeffreys P Essex JW Sansom MS 《Organic & biomolecular chemistry》2004,2(22):3219-3221
BioSimGrid is a database for biomolecular simulations, or, a "Protein Data Bank extended in time" for molecular dynamics trajectories. We describe the implementation details: architecture, data schema, deposition, and analysis modules. We encourage the simulation community to explore BioSimGrid and work towards a common trajectory exchange format. 相似文献
994.
Tosyl-o-allylaniline 1 undergoes oxidative cyclization to produce tetracycle 2 upon treatment with Cu(OAc)(2) and Cs(2)CO(3) at 120 degrees C. The scope of the reaction was extended to other N-sulfonylated aromatic systems. 相似文献
995.
Jun Lin Yuan Xiao Jun Wang Ding Bang Xiong Cheng Jun Duan Jing Tai Zhao Yi Bing Fu Chao Shu Shi 《Journal of luminescence》2007,126(1):130-134
Spectroscopic properties of Ce3+ and Pr3+-doped AREP2O7-type alkali rare earth diphosphates (A=Na, K, Rb, Cs; RE=Y, Lu) have been investigated using VUV spectroscopy technique. Ce3+-doped samples show typical Ce3+ emission in the range of 325-450 nm. The strong host absorption band starting at around 160 nm indicates that the optical band gap of AREP2O7 hosts is at least 7.7 eV, and the host→Ce3+ energy transfer process is rather efficient. However, AREP2O7:Pr3+ samples show less efficient host→Pr3+ energy transfer. The direct Pr3+ 4f2→4f15d1 excitation, which are 12160±640 cm−1 higher respect to that of Ce3+, leads to strong 4f15d1→4f2 emission bands in the range of 230-325 nm but no obvious 4f2→4f2 emission lines. 相似文献
996.
The partial neglect of differential overlap (PNDO) method has been applied to the heterocycles in the title to obtain total charge distributions. These have then been used to construct (semi-empirical) molecular cores, which have been used in the VESCF treatment of the -systems. Configuration interaction treatments have then been carried out using the ground configuration, and all singly- and doubly-excited configurations. While the treatment is a semiempirical one, care has been taken to introduce no parameters which would be inconsistent with our earlier treatments of hydrocarbons and carbonyl compounds by the same methods. The results indicate that following this kind of scheme, it will probably be finally possible to calculate in a general a priori way the electronic spectra of -systems of heterocycles, as well as hydrocarbons and carbonyl compounds, with an accuracy comparable with that of experiment.
This research was supported by Research Grant GP 6763 from the National Science Foundation. 相似文献
Zusammenfassung Die Methode der teilweisen Vernachlässigung der differentiellen Überlappung (PNDO) wurde auf die im Titel genannten Heterozyklen angewandt, um totale Ladungsverteilungen zu erhalten. Diese wurden benutzt, um (halb-empirisch) molekulare Kerne zu konstruieren, die bei der VESCF Behandlung von -Systemen benötigt wurden. CI-Verfahren wurden dann durchgeführt unter Verwendung der Grundkonfiguration und aller einfach und doppelt angeregten Konfigurationen. Da das Verfahren semiempirisch ist, muß man darauf achten, keine Parameter einzuführen, die inkonsistent sind mit unseren früheren Behandlungen von Kohlenwasserstoffen und Carbonylverbindungen mittels derselben Methoden. Die Resultate zeigen an, daß bei Verfolgung dieser Art von Schema, es wahrscheinlich endgültig möglich sein wird, auf einem allgemeinen a priori Weg die Elektronenspektren von -Systemen bei Heterozyklen ebenso wie bei Kohlenwasserstoffen und Carbonylverbindungen mit einer dem Experiment vergleichbaren Genauigkeit auszurechnen.
Résumé La méthode du recouvrement différentiel partiellement nul (PNDO) a été appliquée aux hétérocycles afin d'obtenir des distributions de charge totale. Celles ci on été ensuite utilisées pour construire des squelettes moléculaires (semi-empiriques), employés dans la traitement VESCF des systèmes d'électrons . L'interaction de configurations a été réalisée en utilisant toutes les configurations mono et di-excitées. Malgré le caractère semi-empirique de ce traitement, on a pris la précaution de ne pas introduire de paramètres qui présenteraient une incohérence avec notre traitement analogue des hydrocarbures et des composés carbonyles. Les résultats obtenus montrent qu'en suivant un tel schéma de calcul il serait probablement possible de calculer d'une manière générale à priori les spectres électroniques des systèmes des hétérocycles, des hydrocarbures et des composés carbonyles, à la précision expérimentale.
This research was supported by Research Grant GP 6763 from the National Science Foundation. 相似文献
997.
From the basic entropy of information, the information leakage through a passive coherent channel is calculated. In the course of the derivation, the optical channel is decomposed into a series of cascaded subchannels. It is shown that the amount of information decreases as the information flows through the cascaded channels. The best a passive channel can achieve, in principle, is to preserve the entire input information. It is possible to obtain at the output an amount of information greater than the input, but only through the use of active channels. However, an active channel requires an external source of energy which in some cases could lead to an enormous amount of energy. 相似文献
998.
999.
Tai K Shen T Henchman RH Bourne Y Marchot P McCammon JA 《Journal of the American Chemical Society》2002,124(21):6153-6161
Our previous molecular dynamics simulation (10 ns) of mouse acetylcholinesterase (EC 3.1.1.7) revealed complex fluctuation of the enzyme active site gorge. Now we report a 5-ns simulation of acetylcholinesterase complexed with fasciculin 2. Fasciculin 2 binds to the gorge entrance of acetylcholinesterase with excellent complementarity and many polar and hydrophobic interactions. In this simulation of the protein-protein complex, where fasciculin 2 appears to sterically block access of ligands to the gorge, again we observe a two-peaked probability distribution of the gorge width. When fasciculin is present, the gorge width distribution is altered such that the gorge is more likely to be narrow. Moreover, there are large increases in the opening of alternative passages, namely, the side door (near Thr 75) and the back door (near Tyr 449). Finally, the catalytic triad arrangement in the acetylcholinesterase active site is disrupted with fasciculin bound. These data support that, in addition to the steric obstruction seen in the crystal structure, fasciculin may inhibit acetylcholinesterase by combined allosteric and dynamical means. Additional data from these simulations can be found at http://mccammon.ucsd.edu/. 相似文献
1000.
A homogeneous series of heterobimetallic complexes of [R-Fc(4-py)Ru(NH3)5](PF6)2 (R = H, Et, Br, acetyl; Fc(4-py) = 4-ferrocenylpyridine) have been prepared and characterized. The mixed-valence species generated in situ using ferrocenium hexafluorophosphate as the oxidant show class II behavior, and the oxidized sites are ruthenium centered. deltaE(1/2), E(1/2)(Fe(III)/Fe(II)) - E(1/2)(Ru(III)/Ru(II)), an upper limit for deltaGo that is an energetic difference between the donor and acceptor sites, changes sharply and linearly with Gutmann solvent donor number (DN) and Hammett substituent constants (sigma). The solvent-dependent and substituent-dependent intervalence transfer bands were found to vary almost exclusively with deltaE(1/2). The activation energy for the optical electron transfer versus deltaE(1/2) plot yields a common nuclear reorganization energy (lambda) of 0.74 +/- 0.04 eV for this series. The equation that allows one to incorporate the effect of both solvent donicity and substituents on optical electron transfer is Eop = lambda + deltaGo, where deltaGo = (deltaGo)intrinsic + (deltaGo)solvent donicity + (deltaGo)substituent effect (deltaGo )intinnsic with a numerical value of 0.083 +/- 0.045 eV was obtained from the intercept of the deltaE(1/2) of [H-Fc(4-py)Ru(NH3)5]2+,3+,4+ versus DN plot. (deltaGo)solvent donicity was obtained from the average slopes of the deltaE(1/2) of [R-Fc-(4-py)Ru(NH3)5]2+,3+,4+ versus DN plot, and (deltaGo)substituent effect was obtained from the average slopes of the corresponding deltaE(1/2) versus sigma plot. The empirical equation allows one to finely tune Eop of this series to Eop = 0.82 + 0.019(DN) + 0.44sigma eV at 298 K, and the discrepancy between the calculated and experimental data is less than 6%. 相似文献