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101.
Julien Labaune J. Bianca Jackson Kaori Fukunaga Jeffrey White Laura d’Alessandro Alison Whyte Michel Menu Gerard Mourou 《Applied Physics A: Materials Science & Processing》2011,105(1):5-9
Terahertz Time Domain Imaging has been used in the last few years for the investigation of cultural heritage. In this article,
the authors demonstrate the possibility to apply it for the investigation of clay artifacts. Tomographic images were obtained
of a model in reflection, and an Egyptian vessel in transmission. 相似文献
102.
Gerard van Doremaele Martin van Duin Maxence Valla Alexandra Berthoud 《Journal of polymer science. Part A, Polymer chemistry》2017,55(18):2877-2891
ARLANXEO Elastomers has developed and commercialized Keltan ACE™ technology, a class of half-sandwich cyclopentadienyl κ1-amidinate metal complexes, which are extremely active for the production of first-class ethylene/propylene/diene copolymers (EPDM). In this review, the development and some of the key features of the Keltan ACE™ catalyst system are presented. Many different ACE catalysts have been synthesized over the past years, including bridged and bimetallic catalysts. With Keltan ACE™, a complete range of EPDM products with similar polymer characteristics as their Ziegler–Natta (ZN) counterparts can be produced, including variations containing very high 5-ethylidene-2-norbornene (ENB) contents, controlled long chain branching, very high molecular weight, as well as oil-extended products. Moreover, other EPDM structures can be polymerized. The Keltan ACE™ catalyst technology also allows the production of EPDMs with very high amounts of dicyclopentadiene (DCPD) or 5-vinyl 2-norbornene (VNB) without excessive gelation and reactor fouling, that is, products that cannot or are extremely difficult to obtain via classical ZN catalysis. In a next step, high-VNB-EPDM can be postreactor modified, for example, via metathesis chemistry. In addition, EPDM polymers with a very broad or even bimodal molecular weight distribution can be obtained in a single reactor with certain ACE catalyst structures at particular activator/precatalyst ratios. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2877–2891 相似文献
103.
Unusually Facile Thermal Homodienyl‐[1,5]‐Hydrogen Shift Reactions in Photochemically Generated Vinyl Aziridines 下载免费PDF全文
Dr. Jonathan P. Knowles Prof. Dr. Kevin I. Booker‐Milburn 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(32):11429-11434
A range of photochemically generated tri‐ and tetracyclic vinyl aziridines have been found to undergo a general and surprisingly low temperature ring opening through a [1,5]‐hydrogen shift reaction. The rate of the process was found to be highly dependent on the structure and substitution around the azirdine ring and the alkene terminus, with some substrates being observed to undergo ring opening at temperatures as low as 25 °C. The rigid nature of these polycyclic systems precludes a conformational explanation of these rate differences, and an Eyring study confirmed a negligible entropic barrier to the reaction. However, the Eyring plots for two different aziridines systems showed a significant difference in their enthalpies of activation. It is therefore believed that the levels of aziridine ring strain, as well as electronic effects, are the dominant factors in this sequence. 相似文献
104.
Gerard R. Richter. 《Mathematics of Computation》2002,71(238):527-535
We consider a family of tensor product finite element methods for hyperbolic equations in , , which are explicit and generate a continuous approximate solution. The base case (an extension of the box scheme to higher order) is due to Winther, who proved stability and optimal order convergence. By means of a simple counterexample, we show that, for linear approximation with , the corresponding methods are unstable.
105.
Based on our analysis of the hopcount of the shortest path between two arbitrary nodes in the class G
p
(N) of random graphs, the corresponding flooding time is investigated. The flooding time T
N
(p) is the minimum time needed to reach all other nodes from one node. We show that, after scaling, the flooding time T
N
(p) converges in distribution to the two-fold convolution (2*) of the Gumbel distribution function (z)=exp (–e
–z
), when the link density p
N
satisfies Np
N
/(log N)3 if N . 相似文献
106.
A key contact in the active site of an aminoglycoside phosphotransferase enzyme (APH(3')-IIIa) is a pi-pi stacking interaction between Tyr42 and the adenine ring of bound nucleotides. We investigated the prevalence of similar Tyr-adenine contacts and found that many different protein systems employ Tyr residues in the recognition of the adenine ring. The geometry of these stacking interactions suggests that electrostatics play a role in the attraction between these aromatic systems. Kinetic and calorimetric experiments on wild-type and mutant forms of APH(3')-IIIa yielded further experimental evidence of the importance of electrostatics in the adenine binding region and suggested that the stacking interaction contributes approximately 2 kcal/mol of binding energy. This type of information concerning the forces that govern nucleotide binding in APH(3')-IIIa will facilitate inhibitor design strategies that target the nucleotide binding site of APH-type enzymes. 相似文献
107.
Farrington EJ Martinez Viviente E Williams BS van Koten G Brown JM 《Chemical communications (Cambridge, England)》2002,(4):308-309
The 1,3-bis(diphosphinomethyl)ferrocene 3 readily reacts with [(C2H4)2RhCl]2 to form an equilibrating pair of diastereomers 8a and 8b by C-H insertion into the ferrocene. 相似文献
108.
Studies on square planar iridium complexes of the type trans-Ir(PR(3))(2)(CO)Cl, where PR(3) is PhP[(C(5)Me(4))](2), PhP[Me(2)C(4)H(6)], or PhP[Pr(i)(2)C(4)H(6)], demonstrate that monodentate chiral phosphines impart exceptional degrees of diastereoselectivity in the oxidative addition of H(2). Thus, the oxidative addition of H(2) to the two faces of the meso isomer (R,S)-trans-Ir(PR(3))(2)(CO)Cl proceeds with a kinetic diastereoselectivity which exceeds that for related square planar iridium complexes employing bidentate chiral phosphine ligands. Furthermore, the kinetically favored dihydride is not favored thermodynamically, and the magnitude of the inversion of the kinetic and thermodynamic selectivities is greater than has previously been observed using bidentate phosphines. 相似文献
109.
A neutral polar molecule experiences a force in an inhomogeneous electric field. This electric field can be designed such that a beam of polar molecules is exposed to a harmonic potential in the forward direction. In this potential the longitudinal phase-space distribution of the ensemble of molecules is rotated uniformly. This property is used to longitudinally focus a pulsed beam of ammonia molecules and to produce a beam with a longitudinal velocity spread of 0.76 m/s, corresponding to a temperature of 250 mu K. 相似文献
110.
Niobium and tantalum carbide clusters have been isolated in the gas phase and irradiated with intense tunable infrared (IR) light. Stable neutral clusters are selectively ionized and subsequently detected in a mass spectrometer. By tuning the IR frequency, infrared multiphoton absorption spectra are obtained for a whole range of clusters. These mass-selective IR spectra lead to insights into the structures of small niobium and tantalum carbide clusters and nanocrystals. 相似文献