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991.
Peter M. Tolstoy Sergei N. Smirnov Ilya G. Shenderovich Nikolai S. Golubev Gleb S. Denisov Hans-Heinrich Limbach 《Journal of Molecular Structure》2004,700(1-3):19-27
1H and 15N NMR spectra of 10 complexes exhibiting strong OHN hydrogen bonds formed by 15N-labeled collidine and different proton donors, partially deuterated in mobile proton sites, have been observed by low-temperature NMR spectroscopy using a low-freezing CDF3/CDF2Cl mixture as polar aprotic solvent. The following proton donors have been used: HCl, formic acid, acetic acid, various substituted benzoic acids and HBF4. The slow hydrogen bond exchange regime could be reached below 140 K, which allowed us to resolve 15N signal splittings due to H/D isotopic substitution. The valence bond order model is used to link the observed NMR parameters to hydrogen bond geometries. The results are compared to those obtained previously [Magn. Reson. Chem. 39 (2001) S18] for the same complexes in the organic solids. The increase of the dielectric constant from the organic solids to the solution (30 at 130 K) leads to a change of the hydrogen bond geometries along the geometric correlation line towards the zwitterionic structures, where the proton is partially transferred from oxygen to nitrogen. Whereas the changes of spectroscopic and, hence, geometric parameters are small for the systems which are already zwitterionic in the solid state, large changes are observed for molecular complexes which exhibit almost a full proton transfer from oxygen to nitrogen in the polar liquid solvent. 相似文献
992.
Three new metabolites, kunzeanones A (1), B (2), and C (3), along with three known compounds, cryptostrobin (4), (+)-spathulenol (5), and (−)-globulol (6), were isolated from the non-polar fraction of the dried leaves of Kunzea ambigua (Myrtaceae), which shows ichthyotoxicity toward a small fish, medaka. The structures of these new compounds were elucidated as condensates of alkylated phloroglucinol with methylflavanone and germacrane-type sesquiterpene, respectively, on the basis of spectral analyses including 1-D and 2-D NMR spectra. The stereochemistries of kunzeanones A and B were determined by X-ray crystallographic analysis. A sesquiterpene, (+)-spathulenol (5), among the isolates was characterized as the ichthyotoxic principle of the extract. 相似文献
993.
Koridze A. A. Zdanovich V. I. Lagunova V. Yu. Petukhova I. I. Dolgushin F. M. Starikova Z. A. Ezernitskaya M. G. Petrovskii P. V. 《Russian Chemical Bulletin》2002,51(5):876-886
The thermal reaction of Ru3(CO)10(-Ph2PCH2PPh2) (1) with enyne PhCH=CHCCPh afforded the trinuclear ruthenium clusters Ru3(CO)6{3-P(Ph)CH2PPh2}{3-C(Ph)=CHCC(Ph)(1,2-C6H4)C(=0)} (2), Ru3(-H)(CO)5{3-P(Ph)CH2PPh2}{3-C(Ph)=CHCC(Ph)(1,2-C6H4)C(—0)} (3), and Ru3(CO)6(-CO){3-P(Ph)CH2PPh2}{3-C(C=CPh2)CH=C(H)Ph} (4) and also two isomers of Ru3(CO)5(-CO)(-Ph2PCH2PPh2){3-C4Ph2(CH=CHPh)2} (5a and 5b). Clusters 2, 3, and 4 were characterized by IR spectroscopy, 1H and 31P NMR spectroscopy, and X-ray diffraction analysis. The reaction of complex 1 with enyne FcCH=CHCCFc gave rise to the Ru3(CO)6{3-P(Ph)CH2PPh2}{3-C(Fc)=CHCC(Fc)(1,2-C6H4)C(=0)} (6) and Ru3(-H)(CO)5{3-P(Ph)CH2PPh2}{3-C(Fc)=CHCC(Fc)(1,2-C6H4)C(—0)} (7) clusters. According to the spectral data, the latter compounds are isostructural to complexes 2 and 3, respectively. 相似文献
994.
Although known since the 1950s, free-radical carbonylation has not received much attention until only recently. In the last few years the application of modern free-radical techniques has revealed the high synthetic potential of this reaction as a tool for introducing CO into organic molecules. Clearly now is the time for a renaissance of this chemistry. Under standard conditions (tributyltin hydride/CO) primary, secondary, as well as tertiary alkyl bromides and iodides can be efficiently converted into the corresponding aldehydes. Aromatic and α,β-unsaturated aldehydes can also be prepared from the parent aromatic and vinylic iodides. If the reaction is carried out in the presence of alkenes containing an electron-withdrawing substituent, the initially formed acyl radical subsequently adds to the alkene, leading to a general method for the synthesis of unsymmetrical ketones. This three-component coupling reaction can be extended successfully to allyltin-mediated reactions. Thus, β,γ-enones can be prepared from organic halides, CO, and allyltributylstannanes. In a remarkable one-pot procedure alkyl halides can be treated with a mixture of alkene, allyltributylstannane, and carbon monoxide in a four-component coupling reaction that provides β-functionalized δ,?-unsaturated ketones by the formation of three new C? C bonds. The reaction of 4-pentenyl radicals with CO leads to acyl radical cyclization, which provides a useful method for the synthesis of cyclopentanones. Certain useful one-electron oxidations can be combined efficiently with free-radical carbonylations. These findings and others discussed in this article clearly demonstrate that free-radical carbonylation can now be considered a practical alternative to transition metal mediated carbonylation. 相似文献
995.
996.
997.
Shoichi Katsuta Tokutaro Kimura Yoshihiro Kudo Ryozo Nakagawa Yasuyuki Takeda Mikio Ouchi 《Journal of inclusion phenomena and macrocyclic chemistry》1998,31(2):89-98
The overall extraction constants (Kex) of uni- andbivalent metal picrates with 15-(2,5-dioxahexyl)-15-methyl-16-crown-5(L16C5) were determined between benzene and water at 25°C. TheKex values were analyzed into the constituent equilibriumconstants, i.e., the extraction constant of picric acid, the distributionconstant of the crown ether, the stability constant of the metalion–crown ether complex in water, and the ion-pair extraction constantof the complex cation with the picrate anion. The Kex valuedecreases in the orders Ag+ > Na+ >Tl+ > K+ > Li+ andPb2+ > Ba2+ > Sr2+ for theuni- and bivalent metals, respectively, which are the same as those observedfor 16C5. The extraction selectivity was found to be governed by theselectivity of the ion-pair extraction of the L16C5–metal picratecomplex rather than by that of the complex formation in water. Theextraction ability of L16C5 is smaller for all the metals than that of 16C5,which is mostly attributed to the higher lipophilicity of L16C5. Differencesin the extraction selectivity between L16C5 and 16C5 were observed for thebivalent metals but little for the univalent metals. The side-arm effect onthe extraction selectivity was interpreted on the basis of the negativecorrelation between the effect on the complex stability constant in waterand that on the ion-pair extraction constant. 相似文献
998.
Elena Junquera Emilio Aicart 《Journal of inclusion phenomena and macrocyclic chemistry》1997,29(2):119-136
The encapsulation of the acid/base conjugated system salicylic acid(HSA)/salicylate (SA-) by hydroxypropyl--cyclodextrin (HPBCD) has beenstudied through fluorescence emission enhancement measurements in aqueoussolutions at 25 °C. With the aim of analyzing the crucial importance ofa proper and cautious choice of the pH of the medium (i.e. choice of thebuffer), the study has been carried out at pH = 1, 2, 4 and 7. Since the pKa of the HSA/SA- system is 2.95 at 25 °C, the presence of the protonated(HSA) and non-protonated (SA-) forms suitable for inclusion by cyclodextrinvary appreciably within the different pH conditions: 99% HSA,1% SA- at pH = 1, 90% HSA, 10% SA- at pH = 2,10% HSA, 90% SA- at pH = 4, and 0% HSA,100% SA- at pH =7. The association constants K CD : HSA and K CD: SA- have been determined in all cases by using a nonlinear regressionanalysis of the experimental data at three different em. The effectof the pH of the medium on all the equilibria involved as well as in the Kvalues is fully discussed. The 8-anilino-1-naphthalene sulfonate (ANS) +-cyclodextrin (-CD) system, widely reported in literature, hasinitially been studied to check the experimental protocol and the numericalmethod. 相似文献
999.
Ab initio calculations were performed on 18 fluorinated and unfluorinated alcohols at the B3LYP and HF levels with the 6-311G∗∗ basis set. Molar volumes of the alcohols were computed at each level and averaged to produce a scale of relative size. From this, various isosteric replacements of potential use in drug design were suggested: ethyl by FCH2CH2 or HCF2CH2, propyl by CF3CH2, isopropyl by CF3(CH3)CH or (FCH2)2CH, isobutyl or t-butyl by (CF3)2CH, and 3-methyl-2-butyl by CF3(CH3)2C. Calculation of the charge on oxygen and the Wiberg index of the CO bond allowed an electronegativity scale to be constructed for the fluoroalkyl groups. Electronegativity decreased in the order: (CF3)3C>(CF3)2CH>C2F5CH2>CF3CH2>CH3(CF3)2C>HCF2CH2>CF3(CH3)CH>(FCH2)2CH>FCH2CH2>CF3(CH3)2C. This ranking agreed with literature acid dissociation data for the alcohols studied. 相似文献
1000.
Masaki Shimizu Prof. Dr. Takuya Kurahashi Dr. Katsuhiro Shimono Dr. Kei Tanaka Ikuhiro Nagao Shin‐ichi Kiyomoto Tamejiro Hiyama Prof. Dr. 《化学:亚洲杂志》2007,2(11):1400-1408
Treatment of 1,1‐bis(pinacolatoboryl)ethene with an excess of 1‐bromo‐1‐lithioethene gave 2,3‐bis(pinacolatoboryl)‐1,3‐butadiene in high yield. Palladium‐catalyzed cross‐coupling of the resulting diborylbutadiene with aryl iodides took place smoothly in the presence of a catalytic amount of Pd(OAc)2/PPh3 and aqueous KOH to give 2,3‐diaryl‐1,3‐butadienes in good yields. The coupling reaction with commercially available 4‐acetoxyphenylmethyl chloride under the same conditions followed by hydrolysis of the acetyl groups gave anolignan B in a one‐pot manner. A variety of [3]‐ to [6]dendralenes were synthesized by palladium‐catalyzed coupling of the diene or 1,1‐bis(pinacolato)borylethene with alkenyl or dienyl halides, respectively, in good yields. 相似文献