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151.
M. Sc. Michael Stadlmeier M. Sc. Jana Bogena M. Sc. Miriam Wallner Prof. Dr. Martin Wühr Prof. Dr. Thomas Carell 《Angewandte Chemie (International ed. in English)》2018,57(11):2958-2962
Modern proteomics requires reagents for exact quantification of peptides in complex mixtures. Peptide labelling is most typically achieved with isobaric tags that consist of a balancer and a reporter part that separate in the gas phase. An ingenious distribution of stable isotopes provides multiple reagents with identical molecular weight but a different mass of the reporter groups, allowing relative quantification of multiple samples in one measurement. Here we report a new isobaric labelling reagent, where the balancer and the reporter are linked by a sulfoxide group, which, based on the sulfoxide pyrolysis, leads to easy and asymmetric cleavage at low fragmentation energy. The fragmentation of our new design is significantly improved, yielding more intense complementary ion signals, allowing complementary ion cluster analysis as well. 相似文献
152.
The two major fundamental obstacles which so far have prevented theisolation of stable silynes, RSiCR (1), are: (a)the existence of more stable isomers, e.g., RRC=Si: (2) and(b) their extremely facile (exothermic) dimerication. The steric andelectronic effects of various substituents R and R (R = alkoxy,alkyl, aryl and silyl; R = alkyl and aryl groups) on the stability ofRSiCR relative to the isomeric RRC=Si:(E(1-2)), and on the energy of dimerization tothe corresponding 1,3-disilacyclobutadienes (E(D)), werestudied computationally using density functional theory (DFT) and theONIOM method. The goal was to find a combination of substituents thatwill make RSiCR more stable than RRC=Si: and whichwill also prevent its dimerization. For R = R = H,E(1-2)) = 40.7 kcal/mol (i.e., 2 islower in energy than 1), and E(D) = –104.0kcal/mol. 1, R = OH, R = m-Tbt 2,6-bis[bis(silyl)methyl]phenyl, is by 11.1 kcal/mol morestable than the isomeric silylidene 2. However, thedimerization of 1, R = OH, R = m-Tbt remains highlyexothermic (by 101 kcal/mol). 1, R = R = m-Tbt and1, R = (t-Bu)3Si, R = m-Tbt, are by 5.8 and 2.0kcal/mol, respectively, less stable than the corresponding 2.However, the dimerization of 1, R = (t-Bu)3Si, = m-Tbt is exothermic by only 12 kcal/mol. For1, R = (t-Bu)3Si, and R = Tbt 2,6-bis[bis(trimethylsilyl)methyl]phenyl, the corresponding1,3-disilacyclobutadiene dimer 3, dissociates spontaneously.Thus, (t-Bu3Si)SiCTbt is predicted to be kineticallystable towards both, isomerization to (t-Bu3Si)TbtC=Si: anddimerization to 3, making it a viable synthetic target. Thereported energies were calculated atB3LYP/6-31G**//B3LYP/3-21G*; good agreement is found betweenthe DFT and the ONIOM results. 相似文献
153.
Actions of Commutative Hopf Algebras 总被引:3,自引:0,他引:3
We show that actions of finite-dimensional semisimple commutativeHopf algebras H on H-module algebras A are essentially group-gradings.Moreover we show that the centralizer of H in the smash productA # H equals AH H. Using these we invoke results about groupgraded algebras and results about centralizers of separablesubalgebras to give connections between the ideal structureof A, AH and A # H. Examples of the above occur naturally when one considers: (1) finite abelian groups G of automorphisms of an algebra Awith | G |1 A; (2) G-graded algebras, for finite groups G; (3) finite-dimensional restricted Lie algebras L, with semisimplerestricted enveloping algebra u(L), acting as derivations onan algebra A. 相似文献
154.
Seo YS Samuilov VA Sokolov J Rafailovich M Tinland B Kim J Chu B 《Electrophoresis》2002,23(16):2618-2625
We demonstrate that it is possible to separate a broad band of DNA on a solid substrate without topological obstacles. The mobility was found to scale with molecular size (N) as N(-0.25), while the resolution scaled as N(0.75) indicating that diffusivity on this substrate was minimal. By varying the buffer concentration we were able to show that the mobility for a given chain length scaled with the persistent length (p) as p(1/2). This could be shown to be related to the Gaussian conformation of the chains adsorbed on the surface. A two-dimensional corrugated surface of nonporous silica beads was produced using a self-assembling process at the air/water interface. Even though the surface corrugations were comparable to persistence length we show that they do not affect the mobility, indicating that surface friction rather than topological constraints are the predominant mechanism of separation on a surface. 相似文献
155.
Glòria Sanclimens Laia CrespoMiquel Pons Ernest Giralt Fernando Albericio Miriam Royo 《Tetrahedron letters》2003,44(9):1751-1754
Although the solid-phase mode is an excellent strategy for the preparation of both biomolecules and small molecules, the synthesis of polyproline-based dendrimers has provided evidence that the capacity of the bead is limited. This phenomenon, which can be interpreted as saturation or stress of the resin, can lead to a complete breakdown of the bead structure. 相似文献
156.
2-Oxopiperazine-based gamma-turn conformationally constrained peptides: synthesis of CCK-4 analogues
Herrero S García-López MT Latorre M Cenarruzabeitia E Del Río J Herranz R 《The Journal of organic chemistry》2002,67(11):3866-3873
2-Oxopiperazine derivatives 1 have been designed as mimetics of gamma-turn conformationally constrained tripeptides. The synthetic pathway devised for the preparation of both epimers of 1 at C(5) involves a reductive amination of cyanomethyleneamino pseudopeptides with amino acid derivatives, followed by regiospecific lactamization of the resulting C-backbone branched pseudopeptides. The versatility of this methodology is illustrated in the synthesis of analogues of the tetrapeptides Boc-[Nle(31)]-CCK-4 and Boc-[Lys(o-tolylaminocarbonyl)(31)]-CCK-4. The introduction of the new conformational restriction into these Boc-CCK-4 analogues led to a loss of 2 or 3 orders of magnitude in the affinity at CCK receptors. These results suggest the absence of a gamma-turn in the bioactive conformation of the C-terminal tripeptide of CCK-4. 相似文献
157.
Andrea?TuroňováEmail author Miriam?Gálová Magdaléna??upicová Ladislav?Lux 《Journal of Solid State Electrochemistry》2003,7(10):689-693
The composition of a two-component Ni-Cu coating and the efficiency of its electrochemical deposition on Fe powder was studied
by constant current electrolysis. A fluidized bed arrangement was applied. The variable parameters were: the particle size
fraction, the density of the suspension of the Fe powder in the plating bath, and the intensity of the stirring of the fluidized
bed. Both the Cu and Ni contents in the deposit decrease with increase in the particle size, and with decrease in the suspension
density. Thus, the surface area available for the electrochemical process proved to be of high importance. Another important
factor is the quality of the contacts of the powder particles with the current carrying compact electrode during which the
deposition of Ni is preferred. This influence is manifested in a decrease of the Ni-Cu ratio in the deposit with an increase
in the particle size and rotation speed and, consequently, with a decrease in the suspension density. The current efficiency
values on the powder for optimum conditions reached 80%. 相似文献
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