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991.
Marie-Paule Foloppe Pascal Sonnet Isabelle Bureau Sylvain Rault Max Robba 《Journal of heterocyclic chemistry》1996,33(1):75-80
Pyrrolo[1,2-a]thieno[3,2-f][1,4]diazepines were obtained in an original one step synthesis by treatment of imines 1 with paraformaldehyde in refluxing ethanol. The intermediate Mannich bases were also converted into the thienooxadiazocines 12 and the diazepine N-oxide 13 . 相似文献
992.
Koszinowski K Schröder D Schwarz H Holthausen MC Sauer J Koizumi H Armentrout PB 《Inorganic chemistry》2002,41(22):5882-5890
The bond dissociation energies of CuNO(+), Cu(NO)(2)(+), and CuAr(+) are determined by means of guided ion beam mass spectrometry and quantum chemical calculations. From the experiment, the values D(0)(Cu(+)-NO) = 1.13 +/- 0.05, D(0)(ONCu(+)-NO) = 1.12 +/- 0.06, D(0)(Cu(+)-Ar) = 0.50 +/- 0.07, and D(0)(Cu(+)-Xe) = 1.02 +/- 0.06 eV are obtained. The computational approaches corroborate these results and provide additional structural data. The relative values of D(0)(Cu(+)-NO) and D(0)(Cu(+)-Xe) are consistent with the approximately thermoneutral formation of CuXe(+) upon interacting CuNO(+) with xenon. The sequential bond dissociation energies of Cu(NO)(2)(+) exhibit a trend similar to those of other Cu(I) complexes described in the literature. Although metathesis of nitric oxide to N(2) and O(2) is of considerable interest, no evidence for N-N- or O-O-bond formations in Cu(NO)(n)(+) ions (with n up to 3) is obtained within the energy range studied experimentally. 相似文献
993.
Yersin H Donges D Humbs W Strasser J Sitters R Glasbeek M 《Inorganic chemistry》2002,41(19):4915-4922
The emitting triplet state of cyclometalated Pt(thpy)(CO)(Cl) monomers ((thpy)(-) = 2-(2'-thienylpyridinate), frequently also abbreviated as (2-thpy)(-)) is investigated at T = 1.2 K (typically) by use of the complementary methods of high-resolution optical spectroscopy and of optically detected magnetic resonance (ODMR) spectroscopy. Such a complimentary investigation is carried out for the first time for a Pt(II) compound. In solution, oligomer or short linear chain formation is also observed. However, the monomers can be investigated selectively, when they are dissolved in a relatively inert n-octane matrix (Shpol'skii matrix). This allows us to determine the energies of the T(1) triplet substates I, II, and III relative to the electronic ground state S(0)(0), the zero-field splittings (ZFSs) of T(1), and emission decay time constants (I/II <--> 0, 18012.5 cm(-1); III <--> 0, 18016.3 cm(-1); DeltaE(I,II) = 0.05437 cm(-1) (1.631 GHz), DeltaE(I,III) = 3.8 cm(-1) (114 GHz); tau(I) = 120 micros, tau(II) = 45 micros, tau(III) = 35 micros; spin-lattice relaxation time for the processes III --->I/II, tau(SLR) = 3.0 micros). The vibrational satellite structure observed in the emission of the T(1) state to the singlet ground state S(0) is also discussed. Moreover, it is possible to estimate the intersystem crossing time from the excited singlet state S(1) at 22952 cm(-1) to the triplet state T(1) to approximately 5 ps. The T(1) state is assigned as a thpy-ligand-centered (3)pipi* state with small metal-to-ligand charge-transfer (MLCT) admixtures. A comparison of Pt(thpy)(CO)(Cl) to a series of other organometallic Pt(II) compounds, such as heteroleptic Pt(ppy)(CO)(Cl) ((ppy)(-) = phenylpyridinate), Pt(dppy)(CO) ((dppy)(2-) = diphenylpyridinate), and Pt(i-biq)(CN)(2) (i-biq = 2,2'-bisisoquinoline) and homoleptic Pt(thpy)(2) and Pt(ppy)(2), is carried out. (The structures are shown in Figure 7.) Trends of photophysical properties are discussed. In particular, by chelation of two equal ligands the pattern of ZFS is strongly altered, resulting in a significant increase of the MLCT participation in the lowest triplet state of these organometallic compounds. This new observation represents an interesting further step concerning chemical tunability of photophysical properties. 相似文献
994.
Abhoy N. Ganguly Pradip K. Sengupta Jost H. Bieri Max Viscontini 《Helvetica chimica acta》1980,63(2):395-401
On the Pathway of the Catalytic Reduction of 7-Methylpterin The catalytic hydrogenation of 7-methylpterin (VII) in a neutral solution occurs first by the reduction of the 7,8-double bond (thermodynamically-controlled reaction) followed by the reduction of the 5,6-double bond. On the contrary, in an acidic medium like CF3COOH, the 5,6-double bond is reduced first (kinetically-controlled reaction). The dihydro-intermediate then undergoes a [1,2]-H-rearrangement leading to the formation of the thermodynamically more stable 7-methyl-7,8-dihydropterin (XV) which on further reduction gives 7-methyl-5,6,7,8-tetrahydropterin (VIII). The catalytic reduction of 7-methyl-7,8-dihydropterin (XV) with deuterium gives stereoselectively a sole product with D at C(6) in the equatorial position. 相似文献
995.
Max Iseli Georges Wagnire J. Georges Brahms Sabine Brahms 《Helvetica chimica acta》1979,62(4):921-931
The wavelength range of the CD. spectra of some cyclohexapeptides containing different sequences of glycine, L - and D -alanine is extended down to 170 nm. This allows a relatively complete recording of the (n ? π*) and (π° ? π*) Cotton effects. Some striking spectral changes are observed on going from one molecule to another. The relative influence of L - and D -alanyl residues is discussed: Some spectra may be qualitatively related to each other by considering the effect of an L -residue at position q in the ring to cancel partially with the effect of a D -residue at position q ± 3. Assuming these cyclopeptides to occur in a hydrogen-bonded pleated sheet structure, certain dominant changes in the spectra are interpreted as reflecting a transition of the overall backbone conformation from one which is closer to the (optically inactive) symmetry Ci to another which is closer to the (optically active) symmetry C2. An attempt is made to relate the influence of L - and D -substituents within hairpin bends of the pleated sheet structure to an amide sector rule. 相似文献
996.
Teubner M 《The Journal of chemical physics》2005,123(17):174107
Impulsive linear collisions between a string oscillator (a one-dimensional particle in a box) and a mass point are studied quantum mechanically. In the limit of a very heavy mass point (which corresponds classically to many collisions during a single encounter) the transition probabilities are determined exactly. The result permits a discussion of the mixed quantum-classical regime where the collider becomes almost classical while the oscillator remains quantum mechanical. While the average transition probabilities P(m-->n) are well reproduced by the Ehrenfest mean-field approximation, the prediction for the superimposed high-frequency resonance structure is qualitatively wrong for a genuine quantum oscillator. Only if the oscillator is also almost classical and if (m-n)2 square root(mu) < m, where mu is the mass ratio collider/oscillator, this structure is correctly predicted by the Ehrenfest approximation. 相似文献
997.
The full details of investigations into the cobalt(I)-catalyzed ene type reaction of epsilon-acetylenic beta-keto esters to form highly functionalized methylenecyclopentanes are described. The observed regio-, chemo-, and stereoselectivities support a process of cycloisomerization which controls the relative stereochemistry of two contiguous stereogenic centers. An efficient route to the basic skeleton of the phyllocladane family has been achieved via a one-pot sequence of cyclizations: ene type, [2 + 2 + 2], [4 + 2]. This new cascade created six carbon-carbon bonds and four rings in a totally stereoselective manner from an easily accessible acyclic polyunsaturated precursor. 相似文献
998.
This tutorial review aims at presenting recent contributions dealing with organic chemistry of organophosphorus radicals. The first part briefly lays out the physical organic background of such intermediates. In a second part the use of organophosphorus radicals possessing a P-H bond that can undergo homolytic cleavage as alternative mediators is detailed. The third part is focused on radical additions of phosphorus-centered radicals to unsaturated compounds, an old reaction that is being rejuvenated. Lastly, radical eliminations of phosphorus-centered radical are introduced in the fourth part. Most of the latter are relatively novel reactions, and have never been reviewed previously. 相似文献
999.
Bernd Wrackmeyer Heidi E. Maisel Oleg L. Tok Wolfgang Milius Max Herberhold 《无机化学与普通化学杂志》2004,630(12):2106-2109
Isocyanoferrocene ( 1 ) and 1, 1′‐diisocyanoferrocene ( 2 ) were prepared and studied by 1H, 13C, 14N and 57Fe NMR spectroscopy in order to gain a more complete data set. The NMR data of 1 (chemical shifts and coupling constants) were calculated by DFT methods [B3LYP/6‐311+G(d, p)] and compare favourably with experimental data. The molecular structure of 1 was determined by X‐ray structural analysis, and an almost undistorted ferrocene‐like geometry was found. 相似文献
1000.
We derive an upper limit, imposed by kinematic constraints, for the ratio of the average density function relative to the
local density function for a freely rotating right circular cylindrical domain made of right circular spherocylindrical molecules.
The derivation is made under the assumption that the molecules are rigid, that they are close packed and that their molecular
axes are perpendicular to the base of the domain. For domains containing more than 100 molecules, the average density, evaluated
as a function of domain size, is well approximated by a simple smooth analytical expression. For smaller domains, on the other
hand, the boundary effects lead to an average density that varies erratically with the size of the domain. The contribution
of the boundary effects to the difference between the local density on the average domain density, increases with decreasing
domain size. It is negligible for very large domain, it is about 2.5% for domains containing around 10 000 molecules, and
it can be as high as 20% for very small domains. The theoretical results obtained here are consistent with the reported discrepancy
between the value of the molecular area obtained from pressure area measurements and that obtained from X‐ray measurements.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献