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211.
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Barry K. Carpenter 《Angewandte Chemie (International ed. in English)》1998,37(24):3340-3350
An unexpected yes is the answer the author gives to the following questions: If a reactive intermediate was faced with two equally high energy barriers to product formation, could the kinetic product ratio ever be anything other than 1:1? If the two barriers were of unequal height, could there ever be a preference to form the product that corresponds to the higher barrier pathway? The basis for this yes are the results from molecular dynamics simulations and experiments that suggest that the interpretation of reaction mechanisms by statistical models is not always correct. 相似文献
214.
Synthesis and Characterization of a Cu14 Hydride Cluster Supported by Neutral Donor Ligands 下载免费PDF全文
Thuy‐Ai D. Nguyen Bryan R. Goldsmith Homaira T. Zaman Dr. Guang Wu Prof. Dr. Baron Peters Prof. Dr. Trevor W. Hayton 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(14):5341-5344
The copper hydride clusters [Cu14H12(phen)6(PPh3)4][X]2 (X=Cl or OTf; OTf=trifluoromethanesulfonate, phen=1,10‐phenanthroline) are obtained in good yields by the reaction of [(Ph3P)CuH]6 with phen, in the presence of a halide or pseudohalide source. The complex [Cu14H12(phen)6(PPh3)4][Cl]2 reacts with CO2 in CH2Cl2, in the presence of excess Ph3P, to form the formate complex [(Ph3P)2Cu(κ2‐O2CH)], along with [(phen)(Ph3P)CuCl]. 相似文献
215.
Vladimir Martis Martin Martis John Lipp Dirk Detollenaere Trevor Rayment Gopinathan Sankar Wim Bras 《Journal of synchrotron radiation》2014,21(4):744-750
Energy‐resolved electron‐yield X‐ray absorption spectroscopy is a promising technique for probing the near‐surface structure of nanomaterials because of its ability to discriminate between the near‐surface and bulk of materials. So far, the technique has only been used in model systems. Here, the local structural characterization of nanoporous cobalt‐substituted aluminophosphates is reported and it is shown that the technique can be employed for the study of open‐framework catalytically active systems. Evidence that the cobalt ions on the surface of the crystals react differently to those in the bulk is found. 相似文献
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217.
Dr. Aron J. Huckaba Dr. Aswani Yella Dr. Louis E. McNamara April E. Steen J. Scott Murphy Casey A. Carpenter George D. Puneky Prof. Nathan I. Hammer Prof. Mohammad Khaja Nazeeruddin Prof. Michael Grätzel Prof. Jared H. Delcamp 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(43):15536-15542
Desirable components for dye‐sensitzed solar cell (DSC) sensitizers and fluorescent imaging dyes include strong donating building blocks coupled with well‐balanced acceptor functionalities for absorption beyond the visible range. We have evaluated the effects of increasing acceptor strengths and incorporation of dye morphology controlling groups on molar absorptivity and absorption breadth with indolizine donor‐based dyes. Indolizine‐based D –A and D –π–A sensitizers incorporating bis‐rhodanine, tricyanofuran (TCF), and cyanoacrylic acid functionalities were analyzed for performance in DSC devices. The TCF derivatives were also evaluated as near‐infrared (NIR)‐emissive materials with the AH25 emissions extending past 1000 nm. 相似文献
218.
Yumeng Xi Trevor W. Butcher Jing Zhang John F. Hartwig 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2016,128(2):786-790
We report the regioselective and enantioselective formal hydroamination of unsymmetrical internal alkenes catalyzed by a copper catalyst ligated by DTBM‐SEGPHOS. The regioselectivity of the reaction is controlled by the electronic effects of ether, ester, and sulfonamide groups in the homoallylic position. The observed selectivity underscores the influence of inductive effects of remote substituents on the selectivity of catalytic processes occurring at hydrocarbyl groups, and the method provides direct access to various 1,3‐aminoalcohol derivatives with high enantioselectivity. 相似文献
219.
The effect of sodium interference on the analytical performance of inductively-coupled plasma/atomic emission spectrometry is evaluated. A suitable response function based on the square of the percentage interference was used for multi-element simplex optimization to locate a minimum interference zone in the argon plasma. The plasma was optimized for minimum easily ionizable element interference for Tl, Mn, Mg and Sr. Interferences could be removed completely at the cost of losing sensitivity by up to a factor of 4. The optimization correctly identified an interference-free zone in the plasma. Stability of the injector gas flow rate was found to be vital for accurate location and long-term stability of this zone. Pressure fluctuations during nebulization were shown to be the major cause of high-frequency fluctuations of this zone. 相似文献
220.
Andrew P. Mendham Trevor J. Dines M. J. Snowden Robert Withnall Babur Z. Chowdhry 《Journal of Raman spectroscopy : JRS》2009,40(11):1508-1520
B3‐LYP/cc‐pVDZ calculations of the gas‐phase structure and vibrational spectra of the isolated molecule cyclo(L ‐Ser‐L ‐Ser), a cyclic di‐amino acid peptide (CDAP), were carried out by assuming C2 symmetry. It is predicted that the minimum‐energy structure is a boat conformation for the diketopiperazine (DKP) ring with both L ‐seryl side chains being folded slightly above the ring. An additional structure of higher energy (15.16 kJ mol−1) has been calculated for a DKP ring with a planar geometry, although in this case two fundamental vibrations have been calculated with imaginary wavenumbers. The reported X‐ray crystallographic structure of cyclo(L ‐Ser‐L ‐Ser), shows that the DKP ring displays a near‐planar conformation, with both the two L ‐seryl side chains being folded above the ring. It is hypothesized that the crystal packing forces constrain the DKP ring in a planar conformation and it is probable that the lower energy boat conformation may prevail in the aqueous environment. Raman scattering and Fourier‐transform infrared (FT‐IR) spectra of solid state and aqueous solution samples of cyclo(L ‐Ser‐L ‐Ser) are reported and discussed. Vibrational band assignments have been made on the basis of comparisons with the calculated vibrational spectra and band wavenumber shifts upon deuteration of labile protons. The experimental Raman and IR results for solid‐state samples show characteristic amide I vibrations which are split (Raman: 1661 and 1687 cm−1, IR: 1666 and 1680 cm−1), possibly due to interactions between molecules in a crystallographic unit cell. The cis amide I band is differentiated by its deuterium shift of ∼30 cm−1, which is larger than that previously reported for trans amide I deuterium shifts. A cis amide II mode has been assigned to a Raman band located at 1520 cm−1. The occurrence of this cis amide II mode at a wavenumber above 1500 cm−1 concurs with results of previously examined CDAP molecules with low molecular weight substituents on the Cα atoms, and is also indicative of a relatively unstrained DKP ring. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献