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81.
The dynamic covalent synthesis, structure and conformational dynamics of a chiral polyimine nanocapsule 1a are reported. Reaction of four tetraformyl cavitands and eight H(2)N(CH(2))(2)NH(2) yields quantitatively 1a, which has a compact, asymmetrically folded, pseudo-C(2)-symmetric structure, as determined by X-ray crystallography, and encapsulates four CHCl(3) and three CH(3)OH guests in the solid state. In solution, 1a enantiomerizes by passing over a barrier of ΔG(298)(double dagger) = 21.5 ± 0.7 kcal mol(-1) via a refolding process. 相似文献
82.
Ralf Freund Siavosh Mahboobi Klaus Noack Peter Schonhlzer Karl Bernauer 《Helvetica chimica acta》1990,73(2):439-454
C-(Alkoxycarbonyl)formimines of type 15–18 were derived from the 2-substituted tryptamines 2 , 9 , 10 , and 11 and transformed with tosyl chloride into tricyclic 3-spiroindoles of types 19–22 (Scheme 3). The influence of the homochiral alkoxy moieties A–D on the stereochemical outcome of this reaction was studied. Good-to-excellent diastereoselectivities were observed with the (?)-8-(phenylmenth-3-yl)oxy group ( B ) as homochiral auxiliary. The structures of the tricycles 4 , (2′R,3S)- 19B , and (2′S,3R) 20C were established by X-ray analysis, the structures of the others by NOE and CD studies, and by chemical correlation. Possibilities to explain the steric course of the spirocyclizations are discussed. 相似文献
83.
P. Aufmuth A. Bernard M. Deckwer E. -G. Kopp A. Steudel 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1992,23(1):19-27
The high resolution laser-atomic-beam technique was used to investigate the hyperfine structure in Nd I 4f 46s 2 5 I,5 F,5 S and 4f 45d6s 7 L,7 K,7 I,7 H. The metastable states were populated by an arc discharge burning in the atomic beam. The measured hyperfine constantsA andB of the levels of 4f 46s 2 and 4f 45d6s allow a parametric analysis to be performed using the effective tensor operator formalism. The experimental radial integrals of the 4f and 5d electrons fit with those of the other lanthanides. The 4f radial integrals are in agreement with values of optimized Hartree-Fock-Slater calculations. The spectroscopic quadrupole moments of143Nd and145Nd are deduced from the 4f parameters:Q I =?0.610(21) b and ?0.314(12) b, respectively. TheQ I resulting from the 5d parameter are in satisfactory agreement with these values. The hyperfine anomaly due to thes electron in 4f 45d 6s amounts to about 1%. 相似文献
84.
H. Brüggemeyer H. Esrom V. Pfeufer A. Steudel J. Bauche 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1986,1(1):55-64
High-resolution laser atomic beam spectroscopy has been applied to studyJ and term dependences in the isotope shift of the levels 4f 75d6s a 10 D J ,a 8 D J of Eu I. A parametric analysis of the isotope shift has been performed. TheJ dependence is interpreted through two term-dependent parametersz 5d , and the term dependence through one parameterΔT:z 5d (a 10 D)=44.1 (2.6) MHz,z 5d (a 8 D)=55.9 (2.3) MHz,ΔT=408.5 (3.2) MHz. Ab initio Hartree-Fock and Dirac-Fock calculations have been made to interpret these parameters. Within the accuracy of the calculations the parameters can be attributed to field shift effects. 相似文献
85.
Kerdelhué JL Langenwalter KJ Warmuth R 《Journal of the American Chemical Society》2003,125(4):973-986
Photolysis of p-tolyldiazirine (6) in the inner phase of a hemicarcerand with four butane-1,4-dioxy linker groups (5) in C(6)D(5)CD(3) at 77 K yields the 5-methylcycloheptatetraene hemicarceplex 5 circle 3b in 41% together with innermolecular reaction products resulting from an insertion of transient p-tolylcarbene (1b) into an acetal C-H or linker C-O bond of 5 and from the addition of 1b to an aryl unit of 5. The yield of incarcerated 3b increased up to 67% if 6 is photolyzed inside a hemicarcerand with deuterated spanners and butane-1,4-dioxy linker groups (d(48)-5). Hemicarceplex 5 circle 3b is not formed if the photolysis is carried out in CDCl(3). Incarcerated 3b is stable at room temperature in the absence of oxygen and is characterized by 1D and 2D NMR spectroscopy. In the presence of oxygen, 3b reacts quantitatively to yield toluene and CO(2). Upon heating solutions of d(48)-5 circle 3b in C(6)D(5)CD(3), 3b rearranges to 1b and m-tolylcarbene (18). Both tolylcarbenes immediately react with the surrounding host. From a product analysis and the measured rate constants for the thermal decomposition of d(48)-5 circle 3b in the temperature range 70-102 degrees C, the activation parameters for the 3b to 1b and 3b to 18 rearrangements are calculated (3b to 1b: DeltaG(373)++ = 27.3 +/- 1.4 kcal/mol, DeltaH(373)++ = 26.4 +/- 1.0 kcal/mol, TDeltaS(373)++ = -0.9 +/- 1.0 kcal/mol; 3b to 18: DeltaG(373)++ = 27.8 +/- 1.4 kcal/mol, DeltaH(373)++ = 19.7 +/- 1.0 kcal/mol, TDeltaS(373)++ = 8.1 +/- 1.0 kcal/mol). These values are compared with those calculated by Geise and Hadad at the B3LYP/6-311+G** level of theory (Geise, C. M.; Hadad, C. M. J. Org. Chem. 2002, 67, 2532-2540). The slightly higher inner phase activation free energy of the 3b to 18 rearrangement is explained through steric constraints imposed by the surrounding hemicarcerand on the transition state. The enthalpy-entropy compensation observed for the 3b to 18 rearrangement is discussed and interpreted as a result of a hemicarcerand and solvent reorganization along the reaction coordinate. It is taken as indirect evidence for the intermediacy of 2-methylbicyclo[4.1.0]hepta-2,4,6-triene in the 3b to 18 rearrangement. 相似文献
86.
87.
Soft single-photon ionisation (SPI)–time-of-flight mass spectrometry (TOFMS) has been used to investigate the effect of different
cigarette-lighting devices on the chemical composition of the mainstream smoke from the first cigarette puff. Lighting devices
examined were a Borgwaldt electric lighter, a propane/butane gas lighter, a match, a candle, and the burning zone of another
cigarette. To eliminate the effects of the different masses of tobacco burnt by use of the different lighting methods a normalisation
procedure was performed which enabled investigation of changes in the chemical patterns of the resulting smoke. When another
cigarette was used as the lighting device, elevated levels of ammonia and other nitrogen-containing substances were observed.
These are high in the sidestream smoke of the cigarette used for lighting and would be drawn into the mainstream smoke of
the cigarette being lit. In contrast, smoke from the cigarette lit by the electric lighter contained slightly higher normalised
amounts of isoprene. Lighting the cigarette by use of a candle resulted in larger amounts of substances, e.g. benzene, which
most probably originated from thermal decomposition of wax. The composition of the first puff of smoke obtained by use of
the three lighting methods with open flames (gas lighter, match, and candle) was usually similar whereas the composition of
the smoke produced by use of the electric lighter and the cigarette as the lighter were more unique. The chemical patterns
generated by the different lighting devices could, however, be separated by principal-component analyses. Two additional test
series were also studied. In the first the cigarette was lit with an electric lighter, then extinguished, the ash was cut
off, and the cigarette was re-lit. In the second the cigarette was heated in an oven to 80 °C for 5 min before being lit.
These treatments did not result in changes in the chemical composition compared with cigarettes lit in the ordinary way.
Figure Time-of-flight mass spectrometry (TOFMS) has been used to investigate the effect of different cigarette-lighting devices on
the chemical composition of the mainstream smoke from the first cigarette puff 相似文献
88.
Two-dimensional electrophoresis of membrane proteins 总被引:1,自引:0,他引:1
One third of all genes of various organisms encode membrane proteins, emphasizing their crucial cellular role. However, due
to their high hydrophobicity, membrane proteins demonstrate low solubility and a high tendency for aggregation. Indeed, conventional
two-dimensional gel electrophoresis (2-DE), a powerful electrophoretic method for the separation of complex protein samples
that applies isoelectric focusing (IEF) in the first dimension and sodium dodecyl sulfate polyacrylamide gel electrophoresis
(SDS-PAGE) in the second dimension, has a strong bias against membrane proteins. This review describes two-dimensional electrophoretic
techniques that can be used to separate membrane proteins. Alternative methods for performing conventional 2-DE are highlighted;
these involve replacing the IEF with electrophoresis using cationic detergents, namely 16-benzyldimethyl-n-hexadecylammonium chloride (16-BAC) and cetyl trimethyl ammonium bromide (CTAB), or the anionic detergent SDS. Finally, the
separation of native membrane protein complexes through the application of blue and clear native gel electrophoresis (BN/CN-PAGE)
is reviewed, as well as the free-flow electrophoresis (FFE) of membranes. 相似文献
89.
Sequential Hydroformylation/Diels–Alder Processes: One‐Pot Synthesis of Polysubstituted Cyclohexenes,Cyclohexadienes, and Phthalates from Alkynes 下载免费PDF全文
Xianjie Fang Dr. Ralf Jackstell Prof. Dr. Matthias Beller 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(26):7939-7942
A novel, one‐pot hydroformylation/Diels–Alder sequence for the synthesis of multisubstituted cyclohexenes, cyclohexadienes, and phthalates has been developed. Various alkynes were efficiently converted into the corresponding products in good yields and with excellent diastereoselectivity through palladium‐catalyzed hydroformylation followed by an AAD‐type reaction (AAD: Amides–Aldehydes–Dienophiles). In view of the availability of the substrates, the atom‐efficiency of the overall process, and the convenient introduction of substituents in the cyclohexene ring, this method complements current methods for the preparation of polysubstituted cyclohexane derivatives. 相似文献
90.
An analytical method has been developed for the simultaneous extraction and determination of trace tertiary octylphenol (t-OP), technical nonylphenol isomers (NP), nonylphenol monoethoxylate isomers (NP1EO) and seven phthalates in the atmosphere using gas chromatography-mass spectrometry (GC-MS). High volume samples were collected using a high-volume pump equipped with a PUF/XAD-2 column for air and glass fiber filter for particles. The detection limits of the method for alkylphenols (APs) and the phthalates ranged from 0.0006 to 0.034 ng m−3 in air. The recoveries of t-OP, NP, NP1EO and the phthalates for the entire procedure were satisfactory (>69%). The method was successfully applied to the determination of the analytes in the atmosphere samples collected over land and the ocean. The concentrations of t-OP, NP, NP1EO showed decline trends from land to the open sea, and the phthalates present over land and the North Sea were comparable. It is suggested that the atmosphere is a significant pathway for the transport of alkylphenols and the phthalates in the environment. 相似文献