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141.
Bruno Jean Georges Bokias Lay-Theng Lee Ilias Iliopoulos Bernard Cabane 《Colloid and polymer science》2002,280(10):908-914
The structures of aqueous copolymer solutions have been examined through small angle neutron scattering. The copolymers contained mostly N-isopropylacrylamide (NIPAM) monomers. Poly (NIPAM) solutions have a lower critical solution temperature (LCST), above which the macromolecules separate from water. A small fraction of ionizable N,N-[(dimethylamino) propyl] methacrylamide (MADAP) monomers was introduced into the macromolecules. This had dramatic consequences on the solution behavior at temperatures above the LCST of PNIPAM, where phase separation would have been expected for the homopolymer. When all MADAP monomers were ionized, it was found that the solutions resisted the phase separation. At short spatial scales, the chains were collapsed but at large scales they formed branched aggregates that did not separate out of water. When only half of the MADAP monomers are ionized, the electrical charges were able to redistribute themselves along the chains. In this case, the rise in temperature caused a microphase separation where the electrical charges were relocated on a fraction of the chains that remained in solution.The other chains (or section of chains) formed large nodules of a polymer rich phase. 相似文献
142.
Sylvie Malo Antoine Maignan Sylvain Marinel Maryvonne Hervieu Kenneth R. Poeppelmeier Bernard Raveau 《Solid State Sciences》2005,7(12):1492
Recently, the ferroelectromagnet YMnO3 has been the focus of interest because it exhibits both antiferromagnetism (Néel temperature 80 K) and ferroelectricity (Curie temperature 914 K). There have been no reports of complete YMn1−xMxO3 solid solutions in which substitution of the foreign M cation preserves the hexagonal P63cm structure. In contrast there exist several homeotypic phases with the general formula, Ln1+nCunMO3+3n (n=1 (M=Ti), 2 (M=V) and 3 (M=Mo); Ln: lanthanide). Several YMn1−x(Cu3/4Mo1/4)xO3 compounds have been synthesized. The solid solution, from YMnO3 (x=0) to YCu3/4Mo1/4O3 (x=1) has been characterized by X-ray diffraction and transmission electron microscopy study. For 0<x<0.9, the compounds are found to crystallize in the non-centrosymmetric structure, space group P63cm, of YMnO3. The Mn-free end member, x=1, crystallizes in a complex multiple cell, the superstructure being associated to Cu3+/Mo6+ cationic ordering. Dilution of the Mn3+ magnetic array by the paramagnetic (Cu2+) and diamagnetic (Mo6+) cations is found to decrease the antiferromagnetic ordering temperature and it becomes undetectable for x0.5 compositions. 相似文献
143.
We report here our findings on a new and highly efficient strategy for the synthesis of β-amino acids involving the addition of bis(O-silyl) ketene acetals on Mannich type iminium electrophiles. 相似文献
144.
A non-empirical SCF calculation on the cyclic dimer of formamide in two different GTF basis sets has been performed and is compared to a similar calculation for the isolated monomer. The energy gain per H-bond is reasonable. Both the proton-donor and proton-acceptor show a global gain in electrons at the expense of the hydrogen of the bridge and of the C atoms. This gross changes in charge are reflected in the
1s
values. They cover a gain for nitrogen and a loss for oxygen which are studied in detail on the difference density maps in the molecular plane. The covalent character of the H bond appears very small. Both basis sets yield similar conclusions.
This work was supported by grant n CR 66-236 of the Institut National de la Santé et de la Recherche Médicale (Comité Cancer et Leucémie). 相似文献
Zusammenfassung Eine SCF-Rechnung mit nicht empirischen Parametern wurde mit zwei verschiedenen aus Gauß aufgebauten Basissätzen für das zyklische Dimere und das Monomere des Formamid durchgeführt. Der Energiegewinn ist beträchtlich. Sowohl der Protonendonor als auch der -acceptor zeigen insgesamt einen Elektronengewinn auf Kosten des Brückenwasserstoffs und des Kohlenstoffatoms. Diese Änderung zeigt sich auch in den 1s -Werten. Der Gewinn und Verlust an -Elektronen für Stickstoff bzw. Sauerstoff wird an Hand von Elektronendichtekonturen untersucht. Der kovalente Charakter der Wasserstoffbrückenbindung ist sehr klein. Die beiden Basissätze führen zu ähnlichen Ergebnissen.
Résumé Un calcul SCF non-empirique du dimère cyclique de la formamide a été fait dans deux bases de fonctions gaussiennes différentes et comparaison est faite avec le monomère isolé. Le gain d'énergie par liaison H est d'un ordre de grandeur raisonnable. Le donneur et l'accepteur de proton gagnent au total des électrons alors que l'hydrogène de la liaison H en perd ainsi que le carbone central; ces déplacements globaux se reflètent dans les valeurs des 1s correspondants. Ils couvrent un gain pour l'azote et une perte pour l'oxygène qui sont étudiés en détails sur les courbes d'isodensité différentielle dans le plan moléculaire. La liaison H apparait peu ou pas covalente. Les deux bases de gaussiennes choisies donnent les mêmes conclusions qualitatives.
This work was supported by grant n CR 66-236 of the Institut National de la Santé et de la Recherche Médicale (Comité Cancer et Leucémie). 相似文献
145.
P. Netchitailo Bernard Decroix Jean Morel Paul Pastour 《Journal of heterocyclic chemistry》1978,15(2):337-342
We describe the first synthesis of 2-arylbenzo[4,5]thieno-[2,3-b]pyran-4-one and of 2-arylbenzo [4,5] thieno [3,2-b] pyran-4-one, from benzo [4,5] thiophene and we have extended these cyclizations to obtain the heterocyclic analogs of the xanthones. 相似文献
146.
Michael Aizenman FranÇois Delyon Bernard Souillard 《Journal of statistical physics》1980,23(3):267-280
We rigorously prove that the probabilityP
n
that the origin of ad-dimensional lattice belongs to a cluster of exactlyn sites satisfiesP
n
> exp(–n
(d–1)/d
) whenever percolation occurs. This holds for the usual (noninteracting) percolation models for any concentrationp > p
c
, as well as for the equilibrium states of lattice spin systems with quite general interactions. Such a lower bound applies also if no percolation occurs, but if it appears in some other phase of the system. 相似文献
147.
Bernard S. Kay 《Communications in Mathematical Physics》1980,71(1):29-46
The quantum theory of both linear, and interacting fields on curved space-times is discussed. It is argued that generic curved space-time situations force the adoption of the algebraic approach to quantum field theory: and a suitable formalism is presented for handling an arbitrary quasi-free state in an arbitrary globally hyperbolic space-time.For the interacting case, these quasi-free states are taken as suitable starting points, in terms of which expectation values of field operator products may be calculated to arbitrary order in perturbation theory. The formal treatment of interacting fields in perturbation theory is reduced to a treatment of free quantum fields interacting with external sources.Central to the approach is the so-called two-current operator, which characterises the effect of external sources in terms of purely algebraic (i.e. representation free) properties of the source-free theory.The paper ends with a set of Feynman rules which seems particularly appropriate to curved space-times in that it takes care of those aspects of the problem which are specific to curved space-times (and independent of interaction). Heuristically, the scheme calculates in-in rather than in-out matrix elements. Renormalization problems are discussed but not treated.Work partly supported by the Schweizerische Nationalfonds 相似文献
148.
T. Bernard Tate 《The Journal of the Operational Research Society》1977,28(4):765-779
Good technique, i.e. competence in carrying out operational research, is as vital for the practitioner to acquire as competence in the traditional ‘techniques’. It is suggested that universities should teach students how to conduct simple projects prior to alerting them to more sophisticated methodological issues.As an aid to this task, the traditional five or six parts of an operational research project are broken down and extended into 39 steps, and regrouped into three phases. Also, five skills are identified as being conceptually essential to "good" operational research, which students can develop through tackling suitable case studies. 相似文献
149.
Almeida CM Vasconcelos MT Barbaste M Medina B 《Analytical and bioanalytical chemistry》2002,374(2):314-322
A comparison of the performance of the methodologies used in two distinct laboratories (Lab A and Lab B) for multi-element analysis in different wines was carried out. ICP-MS apparatus (quadrupole mass analyzers) of different brands as well as different wine pre-treatments were used. At Lab A, a pre-treatment by UV-irradiation was performed. At Lab B, a micro-concentric nebulizer was used for direct analysis of the wine. Twenty-six elements (Li, V, Co, Ni, Cu, Zn, Ga, As, Rb, Sr, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Pb) were measured in common at the two labs in three different wine samples (red and white Bordeaux table wines and Port wine) and the results were compared. The two methodologies provided similar LODs and similar precisions, with RSDs of 0.5-5%, for most of the elements. The recovery percentages were 85-120% at Lab A for the three wines, and 78-119% at Lab B for the Bordeaux wines, validating the accuracy of the methods used. Comparable results were obtained at both labs for ten elements (Li, V, Co, Ni, Cu, Zn, Rb, Sr, Ba, and Pb) in the three selected wines; the differences were lower than 10% in most cases. For REEs, the differences observed were slightly higher, but still in the acceptable range due to the sub-ppb levels involved. The results obtained for As and Ga were not comparable, due to methodological influence. A comparison through linear least-squares adjustment indicated that the results obtained by the two labs were linearly correlated (correlation coefficient =0.997) but statistically different as the slope was slightly, but significantly different from one, for a confidence level of 95% (the intercept was statistically identical to zero in any case). In the future, strictly more identical results can be achieved by using a reference wine sample. 相似文献
150.
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