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991.
Brumshtein B Aguilar-Moncayo M Benito JM García Fernandez JM Silman I Shaaltiel Y Aviezer D Sussman JL Futerman AH Ortiz Mellet C 《Organic & biomolecular chemistry》2011,9(11):4160-4167
Cyclodextrin-based host-guest chemistry has been exploited to facilitate co-crystallization of recombinant human acid β-glucosidase (β-glucocerebrosidase, GlcCerase) with amphiphilic bicyclic nojirimycin analogues of the sp(2)-iminosugar type. Attempts to co-crystallize GlcCerase with 5-N,6-O-[N'-(n-octyl)iminomethylidene]nojirimycin (NOI-NJ) or with 5-N,6-S-[N'-(n-octyl)iminomethylidene]-6-thionojirimycin (6S-NOI-NJ), two potent inhibitors of the enzyme with promising pharmacological chaperone activity for several Gaucher disease-associated mutations, were unsuccessful probably due to the formation of aggregates that increase the heterogeneity of the sample and affect nucleation and growth of crystals. Cyclomaltoheptaose (β-cyclodextrin, βCD) efficiently captures NOI-NJ and 6S-NOI-NJ in aqueous media to form inclusion complexes in which the lipophilic tail is accommodated in the hydrophobic cavity of the cyclooligosaccharide. The dissociation constant of the complex of the amphiphilic sp(2)-iminosugars with βCD is two orders of magnitude higher than that of the corresponding complex with GlcCerase, allowing the efficient transfer of the inhibitor from the βCD cavity to the GlcCerase active site. Enzyme-inhibitor complexes suitable for X-ray analysis were thus grown in the presence of βCD. In contrast to what was previously observed for the complex of GlcCerase with the more basic derivative, 6-amino-6-deoxy-5-N,6-N-[N'-(n-octyl)iminomethylidene]nojirimycin (6N-NOI-NJ), the β-anomers of both NOI-NJ and 6S-NOI-NJ were seen in the active site, even though the α-anomer was exclusively detected both in aqueous solution and in the corresponding βCD:sp(2)-iminosugar complexes. Our results further suggest that cyclodextrin derivatives might serve as suitable delivery systems of amphiphilic glycosidase inhibitors in a biomedical context. 相似文献
992.
Butenschön H Ma J Daniliuc CG Nowik I Herber RH 《Dalton transactions (Cambridge, England : 2003)》2011,40(14):3671-3676
The title compound 2 was prepared and its crystal structure was determined at 100 K. The neat solid was examined by temperature dependent (57)Fe M?ssbauer effect (ME) spectroscopy over the interval 92 < T < 318 K, and evidences two diamagnetic Fe(II) sites and one paramagnetic Fe(III) site. The latter shows spin-lattice relaxation, but there is no evidence of electron delocalization among the three iron sites in the above temperature interval. The mean-square-amplitude-of-vibration of the diamagnetic iron site has been determined from the recoil-free fraction ME resonance, and compared to the neutral Fc(3)COH homologue (1). The ME dynamical data are in good agreement with the U(i,j) value at 100 K extracted from the crystallographic results. The ME parameters at 5 K have also been determined with the sample compound embedded in a paraffin wax matrix as well as pelletized with BN. 相似文献
993.
DFT calculations predict that the [8 + 2] cycloaddition reaction between ketenes and 8-azaheptafulvenes occurs stepwise through antiaromatic zwitterionic intermediates. With adequate modifications of both the electronic properties of the ketene and the reaction conditions, these elusive intermediates have been successfully trapped and fully characterized (X-ray), thus confirming the predicted stepwise nature of the transformation. 相似文献
994.
Sequential aldol condensation of aldehydes with methyl ketones followed by transition metal-catalyzed addition reactions of arylboronic acids to form β-substituted ketones is described. By using the 1,1'-spirobiindane-7,7'-diol (SPINOL)-based phosphite, an asymmetric version of this type of sequential reaction, with up to 92% ee, was also realized. Our study provided an efficient method to access β-substituted ketones and might lead to the development of other sequential/tandem reactions with transition metal-catalyzed addition reactions as the key step. 相似文献
995.
Chlorinated compounds are important environmental pollutants whose biodegradation may be limited by inefficient dechlorinating enzymes. Dictyostelium amoebae produce a chlorinated alkyl phenone called DIF which induces stalk cell differentiation during their multicellular development. Here we describe the identification of DIF dechlorinase. DIF dechlorinase is active when expressed in bacteria, and activity is lost from Dictyostelium cells when its gene, drcA, is knocked out. It has a K(m) for DIF of 88 nM and K(cat) of 6.7 s(-1). DrcA is related to glutathione S-transferases, but with a key asparagine-to-cysteine substitution in the catalytic pocket. When this change is reversed, the enzyme reverts to a glutathione S-transferase, thus suggesting a catalytic mechanism. DrcA offers new possibilities for the rational design of bioremediation strategies. 相似文献
996.
The [Ni-(H(2)O)(n)](2+)(H(2)O)(m) (n ≤ 6, m ≤ 18) complexes were studied by means of first-principles all-electron calculations performed with the BPW91 gradient corrected functional and the 6-311+G(d,p) basis sets for the H, O, and Ni atoms. Triplet states were found as low-lying states for each (n, m) combination. The estimated Ni(2+)-(H(2)O)(n) binding energies (112.8-57.4 kcal/mol for the first layer and 52.0-23.0 kcal/mol for the second one) decreases and the Ni(2+)-OH(2) bond lengths lengthen as n + m increases. With six H(2)O moieties the Ni(2+) ion furnishes its first coordination sphere of octahedral geometry. Further water addition renders the formation of the second layer. The effect of Ni(2+) on the (H(2)O)(n)···(H(2)O)(m) hydrogen bond formation for several "n" and "m" combinations was studied, revealing an enhancement of this kind of bonding, which is of key importance for the stabilization and growth of the clusters. For some n + m isomers the second layer appears before the first octahedral layer is fully formed. For example, the square planar Ni(2+)-(H(2)O)(4) core originates two-dimensional 4 + 2 and 4 + 4 isomers, where each outer water molecule accepts two H-bonds, lying 2.0 kcal/mol above the 6 and 6 + 2 ground states. The clusters were also studied by IR spectra; the OH stretching vibrational frequencies allowed us to identify the outer solvation shells by the presence of red-shifted hydrogen bond regions. 相似文献
997.
We extend (and somewhat simplify) the algebraic proof technique of Guth and Katz (2010) [9], to obtain several sharp bounds on the number of incidences between lines and points in three dimensions. Specifically, we show: (i) The maximum possible number of incidences between n lines in R3 and m of their joints (points incident to at least three non-coplanar lines) is Θ(m1/3n) for m?n, and Θ(m2/3n2/3+m+n) for m?n. (ii) In particular, the number of such incidences cannot exceed O(n3/2). (iii) The bound in (i) also holds for incidences between n lines and m arbitrary points (not necessarily joints), provided that no plane contains more than O(n) points and each point is incident to at least three lines. As a preliminary step, we give a simpler proof of (an extension of) the bound O(n3/2), established by Guth and Katz, on the number of joints in a set of n lines in R3. We also present some further extensions of these bounds, and give a trivial proof of Bourgain's conjecture on incidences between points and lines in 3-space, which is an immediate consequence of our incidence bounds, and which constitutes a much simpler alternative to the proof of Guth and Katz (2010) [9]. 相似文献
998.
In a randomized incremental construction of the minimization diagram of a collection of n hyperplanes in ℝ
d
, for d≥2, the hyperplanes are inserted one by one, in a random order, and the minimization diagram is updated after each insertion.
We show that if we retain all the versions of the diagram, without removing any old feature that is now replaced by new features,
the expected combinatorial complexity of the resulting overlay does not grow significantly. Specifically, this complexity
is O(n
⌊d/2⌋log n), for d odd, and O(n
⌊d/2⌋), for d even. The bound is asymptotically tight in the worst case for d even, and we show that this is also the case for d=3. Several implications of this bound, mainly its relation to approximate halfspace range counting, are also discussed. 相似文献
999.
Israel Arias-González Joel Reza Arturo Trejo 《The Journal of chemical thermodynamics》2010,42(11):1386-1392
The solubility of anthracene was measured in pure water and in sodium chloride aqueous solution (salt concentration, m/mol · kg?1 = 0.1006, 0.5056, and 0.6082) at temperatures between (278 and 333) K. Solubility of anthracene in pure water agrees fairly well with values reported in earlier similar studies. Solubility of anthracene in sodium chloride aqueous solutions ranged from (6 · 10?8 to 143 · 10?8) mol · kg?1. Sodium chloride had a salting-out effect on the solubility of anthracene. The salting-out coefficients did not vary significantly with temperature over the range studied. The average salting-out coefficient for anthracene was 0.256 kg · mol?1.The standard molar Gibbs free energies, ΔtrG°, enthalpies, ΔtrH°, and entropies, ΔtrS°, for the transfer of anthracene from pure water to sodium chloride aqueous solutions were also estimated. Most of the estimated ΔtrG° values were positive [(20 to 1230) J · mol?1]. The analysis of the thermodynamic parameters shows that the transfer of anthracene from pure water to sodium chloride aqueous solution is thermodynamically unfavorable, and that this unfavorable condition is caused by a decrease in entropy. 相似文献
1000.
Syed Zafar Ilyas S.M. Nasir Yuksel Kaplan 《Mathematical and Computer Modelling》2009,50(9-10):1495-1497
A Gaussian trend for humidity versus temperature is confirmed by a theoretical fit, i.e., where T0 and H0 are the experimental values of the temperature and humidity, respectively and K is a constant. 相似文献