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141.
An efficient coupling route to novel pi-conjugated comonomers consisting of pyrimidine, thiophene, and bithiophene units was developed. The novel pi-donor-acceptor-donor and pi-donor-acceptor-acceptor-donor conjugated compounds were prepared by Suzuki heterocoupling and Ni(0)-mediated Ullman homocoupling reactions. Photophysical investigation of these alternating pi-donor and acceptor compounds indicated that the deactivation of their singlet excited state proceeds predominately by fluorescence and results in high fluorescence quantum yields. Intersystem crossing to the triplet state was also present in ca. 10%. Quantification of the triplet manifold by laser flash photolysis further revealed that bithiophene produced its triplet state in only 31%. Cyclic voltammetry studies showed that the comonomers undergo both oxidation and reduction leading to their radical cations and radical anions, respectively. The radical cations are highly reactive and undergo anodic polymerization resulting in mutual p- and n-type dopable polymers. The extended conjugation resulting from polymer formation was confirmed by both absorbance and fluorescence spectroscopy and by GPC. Ruthenium binding with the conjugated homocoupled ligand was also found resulting in a hybrid alternating copolymer with significantly different spectroscopic and electrochemical properties relative to its metal-free counterpart. 相似文献
142.
Fabien J. T. Talbot Dr. Quentin Dherbassy Dr. Srimanta Manna Dr. Chunling Shi Shibo Zhang Dr. Gareth P. Howell Dr. Gregory J. P. Perry Prof. Dr. David J. Procter 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(46):20454-20465
Copper-catalyzed borylative multicomponent reactions (MCRs) involving olefins and C−N electrophiles are a powerful tool to rapidly build up molecular complexity. The products from these reactions contain multiple functionalities, such as amino, cyano and boronate groups, that are ubiquitous in medicinal and process chemistry programs. Copper-catalyzed MCRs are particularly attractive because they use a relatively abundant and non-toxic catalyst to selectively deliver high-value products from simple feedstocks such as olefins. In this Minireview, we explore this rapidly emerging field and survey the borylative union of allenes, dienes, styrenes and other olefins, with imines, nitriles and related C−N electrophiles. 相似文献
143.
Milman G Barnes AJ Schwope DM Schwilke EW Goodwin RS Kelly DL Gorelick DA Huestis MA 《Analytical and bioanalytical chemistry》2011,401(2):599-607
Oral fluid (OF) is an increasingly accepted matrix for drug testing programs, but questions remain about its usefulness for
monitoring cannabinoids. Expectorated OF specimens (n = 360) were obtained from 10 adult daily cannabis smokers before, during, and after 37 20-mg oral Δ9-tetrahydrocannabinol (THC) doses over 9 days to characterize cannabinoid disposition in this matrix. Specimens were extracted
and analyzed by gas chromatography–mass spectrometry with electron-impact ionization for THC, 11-hydroxy-THC, cannabidiol,
and cannabinol, and negative chemical ionization for 11-nor-9-carboxy-THC (THCCOOH). Linear ranges for THC, 11-hydroxy-THC,
and cannabidiol were 0.25–50 ng/mL; cannabinol 1–50 ng/mL; and THCCOOH 5–500 pg/mL. THCCOOH was the most prevalent analyte
in 344 specimens (96.9%), with concentrations up to 1,390.3 pg/mL. 11-hydroxy-THC, cannabidiol, and cannabinol were detected
in 1, 1, and 3 specimens, respectively. THC was detected in only 13.8% of specimens. The highest THC concentrations were obtained
at admission (median 1.4 ng/mL, range 0.3–113.6) from previously self-administered smoked cannabis. A total of 2.5 and 3.7%
of specimens were THC-positive at the recommended Substance Abuse and Mental Health Services Administration (2 ng/mL) and
Driving Under the Influence of Drugs, Alcohol and Medicines (DRUID) (1 ng/mL) confirmation cutoffs, respectively. THC is currently
the only analyte for monitoring cannabis exposure in OF; however, these data indicate chronic therapeutic oral THC administration
and illicit oral THC use are unlikely to be identified with current guidelines. Measurement of THCCOOH may improve the detection
and interpretation of OF cannabinoid tests and minimize the possibility of OF contamination from passive inhalation of cannabis
smoke. 相似文献
144.
Bangerter NK Cukur T Hargreaves BA Hu BS Brittain JH Park D Gold GE Nishimura DG 《Magnetic resonance imaging》2011,29(8):1119-1124
Accurate depiction of the vessels of the lower leg, foot or hand benefits from suppression of bright MR signal from lipid (such as bone marrow) and long-T1 fluid (such as synovial fluid and edema). Signal independence of blood flow velocities, good arterial/muscle contrast and arterial/venous separation are also desirable. The high SNR, short scan times and flow properties of balanced steady-state free precession (SSFP) make it an excellent candidate for flow-independent angiography. In this work, a new magnetization-prepared 3D SSFP sequence for flow-independent peripheral angiography is presented. The technique combines a number of component techniques (phase-sensitive fat detection, inversion recovery, T2-preparation and square-spiral phase-encode ordering) to achieve high-contrast peripheral angiograms at only a modest scan time penalty over simple 3D SSFP. The technique is described in detail, a parameter optimization performed and preliminary results presented achieving high contrast and 1-mm isotropic resolution in a normal foot. 相似文献
145.
The spin-1/2 Cu(2+) ions of LiCuVO(4) form one-dimensional chains along the b direction, and the spin frustration in LiCuVO(4) is described in terms of the nearest-neighbor ferromagnetic exchange J(1) and the next-nearest-neighbor antiferromagnetic exchange J(2) in these chains. Recently, it has become controversial whether or not J(1) is stronger in magnitude than J(2). To resolve this controversy, we determined the crystal structure of LiCuVO(4) at 1.6 K by neutron diffraction, analyzed the magnetic susceptibility of LiCuVO(4) to deduce the Curie-Weiss temperature θ and the J(2)/J(1) ratio, and finally extracted the spin exchange constants of LiCuVO(4) on the basis of density functional calculations. Our work shows unambiguously that the Curie-Weiss temperature θ of LiCuVO(4) is negative in the range of -20 K, so that J(2) is substantially stronger in magnitude than J(1). 相似文献
146.
The reduction of unactivated esters using samarium diiodide is reported for the first time. The optimised protocol allows for the reduction of primary, secondary and tertiary alkyl esters in excellent yields and is competitive with reductions mediated by metal hydrides and alkali metals. 相似文献
147.
Ford SJ Delamore OJ Evans JS McIntyre GJ Johnson MR Radosavljević Evans I 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(52):14942-14951
Deuterated 3,5‐pyridinedicarboxylic acid exhibits reversible temperature‐induced deuteron migration of a magnitude unprecedented in this class of compounds. We used a combination of variable‐temperature powder and single‐crystal neutron diffraction and density functional theory (DFT)‐based computational methods to elucidate the origin of this remarkable behaviour. Single‐crystal neutron diffraction shows that between 15 and 300 K, the deuteron moves by 0.32(1) Å and the structure changes from a low‐temperature N? D???O form to a high‐temperature N???D? O form. Variable‐temperature powder neutron‐diffraction data, which was fitted by using parametric Rietveld refinement, show that this deuteron migration is due to an isosymmetric, first‐order phase transition that occurs by growth of the daughter phase in the parent‐phase matrix. Similar phase transitions are observed in two selectively deuterated forms of the material. DFT calculations demonstrate the role of phonons and show that vibrational free‐energy stabilisation, which plays a key role in the observed structural phase transitions, is more pronounced in the fully deuterated material and proportional to the mass of the molecule, that is, the level of deuteration. This is consistent with our experimental work, for which distinct crystallographic phase transitions were clearly observed for the three deuterated systems, but not for the fully protonated material. 相似文献
148.
Garry Kerch Alexander Glonin Janis Zicans Remo Merijs Meri 《Journal of Thermal Analysis and Calorimetry》2012,108(1):185-189
The effect of bread making methods on bound water migration from crumb to crust and moisture redistribution during bread storage
at room temperature was studied. Comparative analysis of water behavior in bread crusts and crumbs was performed using differential
scanning calorimetry method. Water vaporization enthalpies and temperatures of water vaporization peaks were determined and
compared for bread produced by a single stage, straight dough method and bread produced by a two stage, sponge-and-dough method.
The effect of chitosan on the crust and the crumb properties was analyzed for the breads produced by both methods. 相似文献
149.
Samarium(II) iodide (SmI(2)) is one of the most important reducing agents in organic synthesis. Synthetic chemistry promoted by SmI(2) depends on the efficient and reliable preparation of the reagent. Unfortunately, users can experience difficulties preparing the reagent, and this has prevented realization of the full synthetic potential of SmI(2). To provide synthetic chemists with general and reliable methods for the preparation of SmI(2), a systematic evaluation of the factors involved in its synthesis has been carried out. Our studies confirm that SmI(2) is a user-friendly reagent. Factors such as water, oxygen, and peroxide content in THF have little influence on the synthesis of SmI(2). In addition, the use of specialized glovebox equipment or Schlenk techniques is not required for the preparation of SmI(2). However, our studies suggest that the quality of samarium metal is an important factor and that the use of low quality metal is the main cause of failed preparations of the reagent. Accordingly, we report a straightforward method for activation of "inactive" samarium metal and demonstrate the broad utility of this protocol through the electron transfer reductions of a range of substrates using SmI(2) prepared from otherwise "inactive" metal. An investigation into the stability of SmI(2) solutions and an evaluation of commercially available solutions of the reagent is also reported. 相似文献
150.
In this paper, we present a method for “super-resolved” Raman spectroscopy which improves the resolution of obtained spectra. Experimental investigations were carried out on the spectra of toluene and a toluene–chlorobenzene mixture. A tunable Fabry–Perot filter is added to the detection channel and by measuring the spectra for several states of the filter a spectrum of higher resolution can be obtained after a decoding process. We demonstrate both a reduced linewidth in the pure toluene spectra and partial separation of the two overlapping peaks in the mixture. 相似文献