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191.
A family of of open subsets of the real line is called an ω-cover of a set X iff every finite subset of X is contained in an element of . A set of reals X is a γ-set iff for every ω-cover of X there exists such that In this paper we show that assuming Martin's axiom there is a γ-set X of cardinality the continuum. 相似文献
192.
Silica gel impregnated with poly(ethylene glycol) of different molecular mass (400, 1000, 1540, 4000, and 5500) was investigated for salting-out thin-layer chromatography of 15 mixed aminocarboxylato Co(III) complexes using eight ammonium sulphate solutions as mobile phases. Regularities established earlier for non-impregnated adsorbents are also valid in this work. Poly(ethylene glycol) of high molecular mass increases the hydrophobicity of the adsorbent. Positive linear dependence of RM values and of salting-out efficiency on average poly(ethylene glycol) molecular mass was usually observed. In contrast with non-impregnated silica gel, separation was achieved between complexes with the smallest hydrocarbon groups. 相似文献
193.
194.
Mavroudis A Demertzis 《Analytica chimica acta》2004,505(1):73-76
An efficient, more sensitive and accurate spectrophotometric process is possible and can be used to obtain qualitative or quantitative results for analytes at limiting concentrations lower than usual. Transmission measurements (incident light power, P0, or transmitted, P) are performed with a fluorescence spectrometer. One cell only is used to measure standards or unknown solutions, placed between the standard holder cuvette and the emission monochromator of the instrument. The source of the radiant power (P0) is not the xenon lamp but the fluorescence or scattered radiation from the holder cuvette filled with an appropriate solution. The analyte concentration is found from a calibration graph, based upon Beer’s law or the approximate formula P0−P=2.303P0εbc, which is valid for dilute solutions. Determination of iron in a reference material, using 1,10-phenanthroline as the chromogenic reagent, was chosen as an example to demonstrate the suitability of the proposed method and clarify several important statistical questions. Also discussed is why and to what extent molecular fluorescence methods are more sensitive than molecular absorption methods. 相似文献
195.
196.
Z. Guennoun A. Coupeaud I. Couturier-Tamburelli N. Pitri S. Coussan J.-P. Aycard 《Chemical physics》2004,300(1-3):143-151
The structures and energies of the 1:1 acetylene/cyanoacetylene, acetylene/dicyanoacetylene and cyanoacetylene/dicyanoacetylene complexes in solid argon matrices have been investigated using FT-IR spectroscopy and ab initio calculations, at the B3LYP/6-31G** level of theory. For the three complexes, predicted frequency shifts for the L shaped structures, characterized by a hydrogen bond between the nitrogen of the cyano group and the acetylenic proton, were found to be in good agreement with those experimental. Only in the case of acetylene/cyanoacetylene complex, we obtained a second minimum with a T shaped structure characterized by an interaction between the proton of cyanoacetylene and the Π system of acetylene. It appears clearly that HC3N acts as an electrophile or as a nucleophile in these complexes. 相似文献
197.
LetA be anM-matrix in standard lower block triangular form, with diagonal blocksA
ii irreducible. LetS be the set of indices such that the diagonal blockA
is singular. We define the singular graph ofA to be the setS with partial order defined by > if there exists a chain of non-zero blocksA
i, Aij, , Al.Let 1 be the set of maximal elements ofS, and define thep-th level
p
,p = 2, 3, , inductively as the set of maximal elements ofS
\(
1
p-1). Denote by
p
the number of elements in
p
. The Weyr characteristic (associated with 0) ofA is defined to be (A) = (
1, 2,,
h
), where
1 + +
p
= dim KerA
p
,p = 1, 2, , and
h > 0, h+1 = 0.Using a special type of basis, called anS-basis, for the generalized eigenspaceE(A) of 0 ofA, we associate a matrixD withA. We show that(A) = (
1, , h) if and only if certain submatricesD
p,p+1
,p = 1, , h – 1, ofD have full column rank. This condition is also necessary and sufficient forE(A) to have a basis consisting of non-negative vectors, which is a Jordan basis for –A.
We also consider a given finite partially ordered setS, and we find a necessary and sufficient condition that allM-matricesA with singular graphS have(A) = (
1, , h). This condition is satisfied ifS is a rooted forest.The work of the second-named author was partly supported by the National Science Foundation, under grant MPS-08618 A02. 相似文献
198.
Guey‐Sheng Liou Sheng‐Huei Hsiao 《Journal of polymer science. Part A, Polymer chemistry》2002,40(4):459-470
Two series of phosphorus‐containing aromatic poly(ester amide)s with inherent viscosities of 0.46–3.20 dL/g were prepared by low‐temperature solution polycondensation from 1,4‐bis(3‐aminobenzoyloxy)‐2‐(6‐oxido‐6H‐dibenz〈c,e〉〈1,2〉oxaphosphorin‐6‐yl)naphthalene and 1,4‐bis(4‐aminobenzoyloxy)‐2‐(6‐oxido‐6H‐dibenz〈c,e〉〈1,2〉oxaphosphorin‐6‐yl)naphthalene with various aromatic diacid chlorides. All the poly(ester amide)s were amorphous and readily soluble in many organic solvents, such as N,N‐dimethylformamide, N,N‐dimethylacetamide (DMAc), and N‐methyl‐2‐pyrrolidone (NMP). Transparent, tough, and flexible films of these polymers were cast from DMAc and NMP solutions. Their casting films had tensile strengths of 71–214 MPa, elongations to break of 5–10%, and initial moduli of 2.3–6.0 GPa. These poly(ester amide)s had glass‐transition temperatures of 209–239 °C (m‐series) and 222–267 °C (p‐series). The degradation temperatures at 10% weight loss in nitrogen for these polymers ranged from 462 to 489 °C, and the char yields at 800 °C were 55–63%. Most of the poly(ester amide)s also showed a high char yield of 35–45%, even at 800 °C under a flow of air. The limited oxygen indices of these poly(ester amide)s were 35–46. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 459–470, 2002; DOI 10.1002/pola.10129 相似文献
199.
200.
Low-temperature heat capacities of the compound Na(C4H7O5)·H2O(s) have been measured with an automated adiabatic calorimeter. A solid-solid phase transition and dehydration occur at 290-318 K and 367-373 K, respectively. The enthalpy and entropy of the solid-solid transition are ΔtransHm = (5.75 ± 0.01) kJ mol−1 and ΔtransSm = (18.47 ± 0.02) J K−1 mol−1. The enthalpy and entropy of the dehydration are ΔdHm = (15.35 ± 0.03) kJ mol−1 and ΔdSm = (41.35 ± 0.08) J K−1 mol−1. Experimental values of heat capacities for the solids (I and II) and the solid-liquid mixture (III) have been fitted to polynomial equations. 相似文献