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991.
Trialkylsiloxy-modified Ta(v) centers on mesoporous silica exhibit excellent selectivity for epoxide formation (>98% after 2 h) in the oxidation of cyclohexene using aqueous H2O2 as the oxidant; the modified catalysts exhibit an increased lifetime, retaining high selectivity after 6 h of reaction (>95% epoxide). 相似文献
992.
Olsson D Arunachalampillai A Wendt OF 《Dalton transactions (Cambridge, England : 2003)》2007,(46):5427-5433
New and improved preparative routes to the previously known PCP ligands cis-1,3-bis(di-isopropylphosphinito)cyclohexane and cis-1,3-bis[(di-tert-butylphosphino)methyl]cyclohexane are reported. They react with 1 equivalent of dichloro(1,5-cyclooctadiene)platinum(II) [(COD)PtCl2] to give the cis coordinated complex cis-[PtCl2{cis-1,3-bis(di-isopropylphosphinito)}cyclohexane] and the C(sp3)-H activated complex trans-[PtCl{cis-1,3-bis(di-tert-butylphosphino)}cyclohexane]. The new PCP ligand cis-1,3-bis(di-tert-butylphosphinito)cyclohexane was synthesised and reacts with [(COD)PtCl2] giving the di-nuclear trans-[PtCl2{cis-1,3-bis(di-tert-butylphosphinito)cyclohexane}]2, which is highly insoluble. All metal complexes were characterised with X-ray crystallography. DFT calculations indicate that the inability of the phosphinite ligands to cyclometallate is due to a kinetic barrier, possibly involving an axial-equatorial conformational change necessary for the C-H activation process. 相似文献
993.
Milon J Daniel MC Kaiba A Guionneau P Brandès S Sutter JP 《Journal of the American Chemical Society》2007,129(45):13872-13878
Molecule-based solids represent a rare opportunity to combine, adjust, and interrelate structural and physical functionalities to develop multifunctional materials. Here we report on a series of porous supramolecular magnets whose magnetic properties are related to their sorption state. A family of magnets of the formula [{Mn(HL)(H2O)}2Mn{Mo(CN)7}2].2H2O have been obtained by assembling the heptacyano-metalate building unit {Mo(CN)7}4- with Mn(II) in the presence of protonated N,N-dimethylalaninol (L) as ligand, the latter being either as a racemic mixture or as a chiral R- or S-enantiomer. The resulting magnets possess an open framework structure and exhibit a TC with a switching behavior (TC = 85 K <--> 106 K) as a function of the hydration state. Moreover, chiral magnets are formed with the optically active ligands. The H2O and gas (N2, CO2, CO) sorption features, the magnetic behavior of both the hydrated and dehydrated magnets, and the crystal structures of the hydrated chiral (S) and racemic magnets are described. 相似文献
994.
995.
Two liquid chromatography mass spectrometric techniques, i.e. ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry (UPLC/Q-Tof MS) and high-performance liquid chromatography/tandem mass spectrometry (LC/MS/MS), were used for quantification, confirmation or identification of six macrolide antibiotic residues and/or their degradation products in eggs, raw milk, and/or honey. Macrolides were extracted from food samples by acetonitrile or phosphate buffer (0.1 M, pH 8.0), and sample extracts were further cleaned up using solid-phase extraction cartridges. UPLC/Q-Tof data were acquired in Tof MS full scan mode that allowed both quantification and confirmation of macrolides, and identification of their degradation products. LC/MS/MS data acquisition was achieved using multiple reaction monitoring (MRM), i.e. two transitions, to provide a high degree of sensitivity and repeatability. Matrix-matched standard calibration curves with the use of roxithromycin as an internal standard were utilized to achieve the best accuracy of the method. Both techniques demonstrated good quantitative performance in terms of accuracy and repeatability. LC/MS/MS had advantages over UPLC/Q-Tof MS in that its limits of detection were lower and repeatability was somewhat better. UPLC/Q-Tof provided ultimate and unequivocal confirmation of positive findings, and allowed degradation product identification based on accurate mass. The combination of the two techniques can be very beneficial or complementary in routine analysis of macrolide antibiotic residues and their degradation products in food matrices to ensure the safety of food supply. 相似文献
996.
Daniel Wright Mariagioia Zampagni Elisa Evangelisti Simona Conti Giampiero D'Adamio Andrea Goti Matteo Becatti Claudia Fiorillo Niccolò Taddei Gianfranco Liguri 《Photochemistry and photobiology》2013,89(2):442-452
UV‐induced toxicity is characterized by marked oxidative stress, accompanied by the depletion of key cellular antioxidants, particularly glutathione (GSH). Replenishing cellular GSH may represent a means of counteracting UV‐induced toxicity: however, treatment with free GSH is not therapeutically effective due to its unfavorable pharmacokinetic properties. In this study, we show that S‐acyl‐glutathione (acyl‐SG) derivatives, which consist of an acyl chain (of variable length and saturation) linked via a thioester bond to GSH, increase intracellular levels of reduced GSH in primary skin fibroblasts, adenocarcinoma HeLa and neuroblastoma SH‐SY5Y cells. Consistent with this, acyl‐SG derivatives protect against UV‐induced reactive oxygen species (ROS) production and UV‐B/C‐mediated lipid peroxidation and caspase‐3 activation in the analyzed cell lines, with unsaturated thioesters displaying a significantly greater protective effect. Taken together, our findings suggest that acyl‐SG thioesters may be therapeutically effective in the treatment of UV‐related skin disorders and oxidative stress‐mediated conditions in general. 相似文献
997.
Wang Mei Miguel Daniel Riera Víctor Bois Claudette Jeannin Yves 《Transition Metal Chemistry》2001,26(4-5):566-569
A novel dimolybdenum complex [(3-C3H5)(CO)2Mo(-S2CPCy3)Mo(3-CH2CMeCH2)(CO)2], obtained by reacting the [(CO)2(3-C3H5)Mo(-S2CPCy3)Mo(CO)3]– anion with an excess of ClCH2CMe=CH2, has been characterized by i.r., 31P{1H}, 1H- and 13C-n.m.r. spectroscopy and by elemental analysis. The crystal structure of the complex, determined by X-ray diffraction, shows a definite preference for the central carbon of the S2CPCy3 bridge to bind to the Mo(2) atom coordinated by 3-2-methylallyl, rather than the Mo(1) atom attached to unsubstituted 3-allyl ligand. 相似文献
998.
In situ-generated (bis-DPPMB)-Cu(OTf)2 complex has been examined to catalyze a tandem olefin migration and Prins cyclization of an alkenol with various aldehydes. The reaction proceeded with electron-rich aromatic aldehydes at room temperature and provided functionalized tetrahydropyrans in good yields. An efficient synthesis of the bis-DPPMB ligand has also been described. 相似文献
999.
April D. Jewell Samuel J. Kyran Prof. Daniel Rabinovich Prof. E. Charles H. Sykes 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(23):7169-7178
Surface molecular self‐assembly is a fast advancing field with broad applications in sensing, patterning, device assembly, and biochemical applications. A vast number of practical systems utilize alkane thiols supported on gold surfaces. Whereas a strong Au? S bond facilitates robust self‐assembly, the interaction is so strong that the surface is reconstructed, leaving etch pits that render the monolayers susceptible to degradation. By using different head group elements to adcust the molecule–surface interaction, a vast array of new systems with novel properties may be formed. In this paper we use a carefully chosen set of molecules to make a direct comparison of the self‐assembly of thioether, selenoether, and phosphine species on Au(111). Using the herringbone reconstruction of gold as a sensitive readout of molecule–surface interaction strength, we correlate head‐group chemistry with monolayer (ML) properties. It is demonstrated that the hard/soft rules of inorganic chemistry can be used to rationalize the observed trend of molecular interaction strengths with the soft gold surface, that is, P>Se>S. We find that the structure of the monolayers can be explained by the geometry of the molecules in terms of dipolar, quadrupolar, or van der Waals interactions between neighboring species driving the assembly of distinct ordered arrays. As this study directly compares one element with another in simple systems, it may serve as a guide for the design of self‐assembled monolayers with novel structures and properties. 相似文献
1000.
Benjamin Schulze Dr. Daniel Escudero Christian Friebe Dr. Ronald Siebert Dr. Helmar Görls Stephan Sinn Martin Thomas Sebastian Mai Prof. Dr. Jürgen Popp Prof. Dr. Benjamin Dietzek Prof. Dr. Leticia González Prof. Dr. Ulrich S. Schubert 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(13):4010-4025
A systematic series of heteroleptic bis(tridentate)ruthenium(II) complexes of click‐derived 1,3‐bis(1,2,3‐triazol‐4‐yl)benzene N^C^N‐coordinating ligands was synthesized, analyzed by single crystal X‐ray diffraction, investigated photophysically and electrochemically, and studied by computational methods. The presented comprehensive characterization allows a more detailed understanding of the radiationless deactivation mechanisms. Furthermore, we provide a fully optimized synthesis and systematic variations towards redox‐matched, broadly and intensely absorbing, cyclometalated ruthenium(II) complexes. Most of them show a weak room‐temperature emission and a prolonged excited‐state lifetime. They display a broad absorption up to 700 nm and high molar extinction coefficients up to 20 000 M ?1 cm?1 of the metal‐to‐ligand charge transfer bands, resulting in a black color. Thus, the complexes reveal great potential for dye‐sensitized solar‐cell applications. 相似文献