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101.
Adolph B. Bolotin Victor A. Bolotin Victoria L. Gineityte 《International journal of quantum chemistry》1979,16(4):839-845
Rotational isomerization of bipyridines C5H4N? C5H4N was studied by CNDO /2, PPP /CI , and CNDO /CI methods. It is shown that CNDO /2 overestimates the angle of rotation ? between the pyridine rings ca. two times. The angle ? was determined for 2,2′-bipyridine by means of correlation of the theoretical (CNDO /2) and experimental dipole moment. It was also found from the correlation between the theoretical and experimental UV spectra. It is shown that there is an explicit dependence of the results upon the distance between heteroatoms (PPP /CI ). It has been found that the CNDO /CI method correctly predicts the value of the rotational angles and their sequence in bipyridines. 相似文献
102.
High resolution 13C and 15N NMR spectra have been obtained for powdered CH3CN. The presence of resolved dipolar structure in the 13C spectra permits the conclusion that the symmetry axis of the 13C shielding tensor lies along the CN bond direction. 相似文献
103.
John Philip Tarburton Cynthia S. Day Victor W. Day Iraj Tavaniepour Norman H. Cromwell 《Journal of heterocyclic chemistry》1986,23(2):433-441
Solid-state structures have been determined for cis- and trans-1-cyclohexyl-2-phenyl-3-(p-toluyl)aziridines using single-crystal X-ray diffraction techniques. The cis isomer crystallizes in the centrosymmetric monoclinic space group P21/c (No. 14), with a = 18.669(3)Å, b = 5.709(1)Å, c = 17.412(2)Å, β = 96.29(1)° and Z = 4; the trans isomer crystallizes in the noncentrosymmetric orthorhombic space group Pna21 (No. 33), with a = 17.089(2)Å, b = 18.729(3)Å, c = 5.749(1)Å and Z = 4. Full-matrix least-squares refinement of the structural parameters led to the following final agreement factors: R1 (unweighted, based on F) = 0.040 and R2 (weighted, based on F) = 0.054 for the 2592 independent reflections of the cis isomer having 2θMoK¯α <55° and I>3σ1, and R1 = 0.033 and R2 = 0.031 for the 1504 independent reflections of the trans isomer having 2θMoK¯α <55° and I>3σ1. The statistically significant differences that exist between the two isomers for two bond lengths and ten bond angles (p < 0.05) appear to be the direct result of the p-toluyl group orientation with respect to the cyclohexyl and phenyl substituents. In the cis isomer it is anti with respect to the N-cyclohexyl group and cis with respect to the phenyl group, whereas in the trans isomer it is syn with respect to the N-cyclohexyl and trans with respect to the phenyl group. Three-ring to carbonyl hyperconjugation is correlated with stereoelectronic interactions in the trans isomer. Bonding, determined by X-ray and nmr studies, is discussed for the three-membered aziridine ring proper; while bonding, determined by X-ray studies, is discussed for substituents of the aziridine ring. These aziridinyl ketone compounds are of importance as potential mammalian DNA alkylating anti-tumor agents in solid-state solid-state systems. To date only a trans isomer has demonstrated this biological activity in tumor-bearing rats. 相似文献
104.
Dale F Shellhamer David C Gleason Andrew J Ryan Victor L Heasley 《Journal of fluorine chemistry》2003,123(2):171-176
Ionic and photochemical reaction of chlorine (Cl2), bromine (Br2) and iodine monochloride (ICl) to hexafluoro-1,3-butadiene (1) and 1,3-butadiene (2) were carried out under conditions that would provide product distributions under controlled ionic or free-radical conditions. Product distributions for ionic reaction of Cl2 and Br2 with 1 are similar and suggest a weakly-bridged halonium ion species. Theoretical calculations support weakly-bridged chloronium and bromonium ions for both dienes 1 and 2. There are more of the 1,4-dihalo-2-butene products from ionic halogenation of 1 than 2 which correlates with the greater charge density on carbon-4 of halonium ions from 1. Ionic and free-radical reactions of ICl with 1 give 8 and 2% of 3-chloro-4-iodohexafluoro-1-butene and 4-chloro-3-iodohexafluoro-1-butene, respectively. The minor cis-1,4-dihalo-2-butene products from 1 and 2 are reported when formed. 相似文献
105.
Borovkov VV Lintuluoto JM Sugeta H Fujiki M Arakawa R Inoue Y 《Journal of the American Chemical Society》2002,124(12):2993-3006
Complexation mechanism, binding properties and thermodynamic parameters of supramolecular chirality induction in the achiral host molecule, syn (face-to-face conformation) ethane-bridged bis(zinc porphyrin), upon interaction with chiral monoamine and monoalcohol guests have been studied by means of the UV-vis, CD, (1)H NMR, and ESI MS techniques. It was found that the chirogenesis process includes three major equilibria steps: the first guest ligation to a zinc porphyrin subunit of the host (K(1)), syn to anti conformational switching (K(S)), and further ligation by a second guest molecule to the remaining ligand-free zinc porphyrin subunit (K(2)), thus forming the final bis-ligated species possessing supramolecular chirality. The validity of this equilibria model is confirmed by the excellent match between the calculated and experimentally observed spectral parameters of the bis-ligated species. The second ligation proceeds in a cooperative manner as K(2) > K(1) for all supramolecular systems studied, regardless of the structure of the chiral ligand used. The binding properties are highly dependent on the nature of the functional group (amines are stronger binders than alcohols) and on the structure of the chiral guests (primary and aliphatic amines have overall binding constant values greater than those of secondary and aromatic amines, respectively). 相似文献
106.
Gold(III) can be separated from Cd, In. Zn, Ni, Cu(II), Mn(II), Co(II), Mg, Ca, Al, Fe(III), Ga and U(VI) by adsorbing these elements on a column of AG50W-X8 sulphonated polystyrene cation-exchange resin from 0.1M HCl containing 60% v v acetone, while Au(III) passes through and can be eluted with the same reagent. Separations are sharp and quantitative. The amounts of gold retained by the resin are between 1 and 2 orders of magnitude lower than encountered during adsorption from aqueous 0.1M HCl. Recoveries for mg amounts of gold are 99.9% or better and for ng amounts are still better than 99%, as shown by radioactive tracer methods. Hg(II), Bi, Sn(IV), the platinum metals and some elements which tend to form oxy-anions in dilute acid accompany gold. All other elements, though not investigated in detail, should be retained, according to their known distribution coefficients. Relevant elution curves, results of quantitative separations of binary mixtures and of recovery tests are presented. 相似文献
107.
Toeplitz operators in n-dimensions 总被引:2,自引:0,他引:2
Victor Guillemin 《Integral Equations and Operator Theory》1984,7(2):145-205
The interplay between the theory of Toeplitz operators on the circle and the theory of pseudodifferential operators on the line (i. e. Wiener-Hopf operators) is by now well-known and well-understood. In this article we show that there is a parallel situation in higher dimensions. To begin with, by using pseudodifferential multipliers, one can simplify the composition rules for Toeplitz operators, (§ 3), and describe precisely how Toeplitz operators of Bergmann type are related to Toeplitz operators of Szegö type (§ 9). Furthermore, it turns out that the ring of pseudodifferential operators on a compact manifold, M, is isomorphic with the ring of Toeplitz operators on an appropriate Grauert tube about M (§ § 4–6), and the ring of Weyl operators on n is isomorphic with the ring of Toeplitz operators on the complex ball in n (§ § 7–10). 相似文献
108.
Isaac B. Bersuker Natalia N. Gorinchoi Victor Z. Polinger 《Theoretical chemistry accounts》1984,66(3-4):161-172
The vibronic origin of dynamic instability of molecular systems considered earlier, is here given a more complete and rigorous treatment. It is shown that the nonvibronic contribution to the curvature of the adiabatic potential arising due to nuclear displacements under fixed electronic density distribution, is always positive, and hence the only reason for dynamic instability is the pseudo Jahn-Teller effect. For some examples of special interest (planar equilateral NH3, planar square CH4 and linear H
3
+
) the molecular excited states, responsible for the instability of the ground state, are revealed by means of ab initio calculations. 相似文献
109.
Millar AJ Doonan CJ Smith PD Nemykin VN Basu P Young CG 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(11):3255-3267
Intermediates in the oxygen atom transfer from Mo(VI) to P(III), [Tp(iPr)MoOX(OPR3)] (Tp(iPr) = hydrotris(3-isopropylpyrazol-1-yl)borate; X = Cl-, phenolates, thiolates), have been isolated from the reactions of [Tp(iPr)MoO2X] with phosphines (PEt3, PMePh2, PPh3). The green, diamagnetic oxomolybdenum(IV) complexes possess local C(1) symmetry (by NMR spectroscopy) and exhibit IR bands assigned to nu(Mo==O) (approximately 950 cm(-1)) and nu(P==O) (1140-1083 cm(-1)) vibrations. The X-ray crystal structures of [Tp(iPr)MoOX(OPEt3)] (X = OC6H4-2-sBu, SnBu), [Tp(iPr)MoO(OPh)(OPMePh2)], and [Tp(iPr)MoOCl(OPPh3)] have been determined. The monomeric complexes exhibit distorted octahedral geometries, with coordination spheres composed of tridentate fac-Tp(iPr) and mutually cis monodentate terminal oxo, phosphoryl (phosphine oxide), and monoanionic X ligands. The electronic structures and stabilities of the complexes have been probed by computational methods, with the three-dimensional energy surfaces confirming the existence of a low-energy steric pocket that restricts the conformational freedom of the phosphoryl ligand and inhibits complete oxygen atom transfer. The reactivity of the complexes is also briefly described. 相似文献
110.
A versatile microfabricated platform for electrophoresis of double- and single-stranded DNA 总被引:1,自引:0,他引:1
We demonstrate a versatile microfabricated electrophoresis platform, incorporating arrays of integrated on-chip electrodes, heaters, and temperature sensors. This design allows a range of different sieving gels to be used within the same device to perform separations involving both single- and double-stranded DNA over distances on the order of 1 cm. We use this device to compare linear and cross-linked polyacrylamide, agarose, and thermo-reversible Pluronic-F127 gels on the basis of gel casting ease, reusability, and overall separation performance using a 100 base pair double-stranded DNA ladder as a standard sample. While cross-linked polyacrylamide matrices provide consistently high-quality separations in our system over a wide range of DNA fragment sizes, Pluronic gels also offer compelling advantages in terms of the ability to remove and reload the gel. Agarose gels offer good separation performance, however, additional care must be exercised to ensure consistent gel properties as a consequence of the need for elevated gel loading temperatures. We also demonstrate the use of denaturing cross-linked polyacrylamide gels at concentrations up to 19% to separate single-stranded DNA fragments ranging in size from 18 to 400 bases in length. Primers differing by 4 bases at a read length of 30 bases can be separated with a resolution of 0.9-1.0 in under 20 min. This level of performance is sufficient to conduct a variety of genotyping assays including the rapid detection of single nucleotide polymorphisms (SNPs) in a microfabricated platform. The ability to use a single microelectrophoresis system to satisfy a wide range of separation applications offers molecular biologists an unprecedented level of flexibility in a portable and inexpensive format. 相似文献