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991.
Frederick W. King 《International journal of quantum chemistry》2013,113(23):2534-2539
High‐precision Hylleraas‐type calculations of the hyperfine constants for the four lowest excited 1s2sns 4Se (n = 3–6) levels of the lithium atom are reported. The transition energies from the lowest 4Po term to the 1s2sns 4Se (n = 3–6) levels for the stable isotopes 6Li and 7Li are evaluated. A number of addition expectation values for the four levels studied are also reported, including some moments of the electron–nuclear separation, the electron–electron separation, and the specific mass‐shift operator. © 2013 Wiley Periodicals, Inc. 相似文献
992.
Dr. Andrey E. Sheshenev Dr. Ekaterina V. Boltukhina Anastasiya A. Grishina Dr. Ivana Cisa?ova Dr. Ilya M. Lyapkalo Dr. King Kuok Hii 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(25):8136-8143
A family of new chiral zwitterionic phosphorus‐containing heterocycles (zPHC) have been derived from methylene‐bridged bis(imidazolines). These structures were unambiguously determined, including single‐crystal XRD analysis for two compounds. The stability, acid/base and electronic properties of these dipolar phosphorus heterocycles were subsequently investigated. zPHCs can be successfully employed as a new class of chiral solvating agents for the enantiodifferentiation of chiral carboxylic and sulfonic acids by NMR spectroscopy. The stoichiometry and binding constants for the donor–acceptor complexes formed were established by NMR titration methods. 相似文献
993.
Agnes M. Stepan Alistair W. T. King Tia Kakko Guillermo Toriz Ilkka Kilpeläinen Paul Gatenholm 《Cellulose (London, England)》2013,20(6):2813-2824
In this study high molecular weight pure rye arabinoxylan and spruce arabinoglucuronoxylan were acetylated in ionic liquid (IL) systems. Two different ILs were used in our study. In both IL, using optimized procedures, it was possible to achieve acetylation within 5 min. The first system involved direct dissolution into 1-ethyl-3-methylimidazolium dimethylphosphate ([emim][Me2PO4]), followed by addition of acetyl chloride/pyridine (AcCl/Pyr) and additional chloroform (CHCl3), as co-solvent. The other system involved direct dissolution into the novel protic IL 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH][OAc]), followed by acetic anhydride/1,5-diazabicyclo[4.3.0]non-5-ene (Ac2O/DBN) and no co-solvent added. The full acetyl substitution of the xylans was confirmed by FT IR and 1H NMR. The acetylated xylans maintained a high molecular weight, which was confirmed by gel permeation chromatography. The products were soluble in CHCl3 and dimethyl carbonate, which is considered as a ‘green’ reagent or solvent. This allowed for the casting of the materials into clear transparent films, opening opportunity for further processing and evaluation of these materials. 相似文献
994.
Martin J. Duffy Orla Kelly Christopher R. Calvert Raymond B. King Louise Belshaw Thomas J. Kelly John T. Costello David J. Timson William A. Bryan Thomas Kierspel I. C. Edmond Turcu Cephise M. Cacho Emma Springate Ian D. Williams Jason B. Greenwood 《Journal of the American Society for Mass Spectrometry》2013,24(9):1366-1375
High power femtosecond laser pulses have unique properties that could lead to their application as ionization or activation sources in mass spectrometry. By concentrating many photons into pulse lengths approaching the timescales associated with atomic motion, very strong electric field strengths are generated, which can efficiently ionize and fragment molecules without the need for resonant absorption. However, the complex interaction between these pulses and biomolecular species is not well understood. To address this issue, we have studied the interaction of intense, femtosecond pulses with a number of amino acids and small peptides. Unlike previous studies, we have used neutral forms of these molecular targets, which allowed us to investigate dissociation of radical cations without the spectra being complicated by the action of mobile protons. We found fragmentation was dominated by fast, radical-initiated dissociation close to the charge site generated by the initial ionization or from subsequent ultrafast migration of this charge. Fragments with lower yields, which are useful for structural determinations, were also observed and attributed to radical migration caused by hydrogen atom transfer within the molecule. Figure
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995.
Ming‐Yi Hsu Dr. Po‐Yu Tsai Zheng‐Rong Wei Meng‐Hsuan Chao Prof. Bing Zhang Prof. Toshio Kasai Prof. King‐Chuen Lin 《Chemphyschem》2013,14(5):936-945
Competitive bond dissociation mechanisms for bromoacetyl chloride and 2‐ and 3‐bromopropionyl chloride following the 1[n(O)→π*(C?O)] transition at 234–235 nm are investigated. Branching ratios for C? Br/C? Cl bond fission are found by using the (2+1) resonance‐enhanced multiphoton ionization (REMPI) technique coupled with velocity ion imaging. The fragment branching ratios depend mainly on the dissociation pathways and the distances between the orbitals of Br and the C?O chromophore. C? Cl bond fission is anticipated to follow an adiabatic potential surface for a strong diabatic coupling between the n(O)π*(C?O) and np(Cl)σ*(C? Cl) bands. In contrast, C? Br bond fission is subject to much weaker coupling between n(O)π*(C?O) and np(Br)σ*(C? Br). Thus, a diabatic pathway is preferred for bromoacetyl chloride and 2‐bromopropionyl chloride, which leads to excited‐state products. For 3‐bromopropionyl chloride, the available energy is not high enough to reach the excited‐state products such that C? Br bond fission must proceed through an adiabatic pathway with severe suppression by nonadiabatic coupling. The fragment translational energies and anisotropy parameters for the three molecules are also analyzed and appropriately interpreted. 相似文献
996.
Sierra C. Marker A. Paden King Robert V. Swanda Brett Vaughn Eszter Boros Shu‐Bing Qian Justin J. Wilson 《Angewandte Chemie (International ed. in English)》2020,59(32):13391-13400
Rhenium tricarbonyl complexes have been recently investigated as novel anticancer agents. However, little is understood about their mechanisms of action, as well as the means by which cancer cells respond to chronic exposure to these compounds. To gain a deeper mechanistic insight into these rhenium anticancer agents, we developed and characterized an ovarian cancer cell line that is resistant to a previously studied compound [Re(CO)3(dmphen)(ptolICN)]+, where dmphen=2,9‐dimethyl‐1,10‐phenanthroline and ptolICN=para‐tolyl isonitrile, called TRIP. This TRIP‐resistant ovarian cancer cell line, A2780TR, was found to be 9 times less sensitive to TRIP compared to the wild‐type A2780 ovarian cancer cell line. Furthermore, the cytotoxicities of established drugs and other rhenium anticancer agents in the TRIP‐resistant cell line were determined. Notably, the drug taxol was found to exhibit a 184‐fold decrease in activity in the A2780TR cell line, suggesting that mechanisms of resistance towards TRIP and this drug are similar. Accordingly, expression levels of the ATP‐binding cassette transporter P‐glycoprotein, an efflux transporter known to detoxify taxol, were found to be elevated in the A2780TR cell line. Additionally, a gene expression analysis using the National Cancer Institute 60 cell line panel identified the MT1E gene to be overexpressed in cells that are less sensitive to TRIP. Because this gene encodes for metallothioneins, this result suggests that detoxification by this class of proteins is another mechanism for resistance to TRIP. The importance of this gene in the A2780TR cell line was assessed, confirming that its expression is elevated in this cell line as well. As the first study to investigate and identify the cancer cell resistance pathways in response to a rhenium complex, this report highlights important similarities and differences in the resistance responses of ovarian cancer cells to TRIP and conventional drugs. 相似文献
997.
The kinetics of the reactions of the atoms O(3P), S(3P), Se(3P), and Te(3P) with a series of alkenes are examined for correlations relating the logarithms of the rate coefficients to the energies of the highest occupied molecular orbitals (HOMOs) of the alkenes. These correlations may be employed to predict rate coefficients from the calculated HOMO energy of any other alkene of interest. The rate coefficients obtained from the correlations were used to © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 351–356, 2006 相似文献
998.
King Wai Lau Sarah R. Hart Jennifer A. Lynch Stephen C. C. Wong Simon J. Hubbard Simon J. Gaskell 《Rapid communications in mass spectrometry : RCM》2009,23(10):1508-1514
Tandem mass spectrometric data from peptides are routinely used in an unsupervised manner to infer product ion sequence and hence the identity of their parent protein. However, significant variability in relative signal intensity of product ions within peptide tandem mass spectra is commonly observed. Furthermore, instrument‐specific patterns of fragmentation are observed, even where a common mechanism of ion heating is responsible for generation of the product ions. This information is currently not fully exploited within database searching strategies; this motivated the present study to examine a large dataset of tandem mass spectra derived from multiple instrumental platforms. Here, we report marked global differences in the product ion spectra of protonated tryptic peptides generated from two of the most common proteomic platforms, namely tandem quadrupole‐time‐of‐flight and quadrupole ion trap instruments. Specifically, quadrupole‐time‐of‐flight tandem mass spectra show a significant under‐representation of N‐terminal b‐type fragments in comparison to quadrupole ion trap product ion spectra. Energy‐resolved mass spectrometry experiments conducted upon test tryptic peptides clarify this disparity; b‐type ions are significantly less stable than their y‐type N‐terminal counterparts, which contain strongly basic residues. Secondary fragmentation processes which occur within the tandem quadrupole‐time‐of‐flight device account for the observed differences, whereas this secondary product ion generation does not occur to a significant extent from resonant excitation performed within the quadrupole ion trap. We suggest that incorporation of this stability information in database searching strategies has the potential to significantly improve the veracity of peptide ion identifications as made by conventional database searching strategies. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
999.
1000.
B King 《Accreditation and quality assurance》1999,4(1-2):27-30
In some cases the compliance of a measurement result with a limit value will be unclear and a 'judgment' is required based
on agreed criteria. Recent developments in the estimation of measurement uncertainty have opened up the possibility of a more
rational approach to such problems. This paper briefly reviews some of the issues and current practices and suggests a pragmatic
way forward.
Received: 26 August 1998 · Accepted: 31 August 1998 相似文献