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71.
P. N. Kogerman G. Egloff J. C. Morrell Ch. Wirth III G. B. Murphy 《Analytical and bioanalytical chemistry》1935,100(5-6):238-238
72.
73.
E. N. Brown R. B. Willms G. T. Gray III P. J. Rae C. M. Cady K. S. Vecchio J. Flowers M. Y. Martinez 《Experimental Mechanics》2007,47(3):381-393
The current work presents the characterization and comparison of the mechanical response of three different industrial forms
of polyethylene. Specifically, high-density polyethylene (HDPE), ultra high molecular weight polyethylene (UHMWPE), and cross-linked
polyethylene (PEX) were tested in compression as a function of temperature (−75 to 100°C) and strain-rate (10−4 to 2,600 s−1). The responses of UHMWPE and PEX are very similar, whereas HDPE exhibits some differences. The HDPE samples display a significantly
higher yield stress followed by a flat flow behavior. Conversely UHMWPE and PEX both exhibit significant strain hardening
after yield. The temperature and strain-rate dependence are captured by simple linear and logarithmic fits over the full range
of conditions investigated. The yield behavior is presented in terms of an empirical mapping function that is extended to
analytically solve for the mapping constant. The power-law dependence on strain-rate observed in some polymers is explained
using this mapping function. 相似文献
74.
Guoliang Li Ioan Silaghi-Dumitrescu R. Bruce King Henry F. Schaefer III 《Journal of organometallic chemistry》2010,695(6):804-808
Density functional theory studies on a series of Cp2Co2E2 derivatives (E = S and PX; X = H, Cl, OH, OMe, NH2, NMe2) predict global minimum butterfly structures with one Co-Co bond for the “body” of the butterfly and four Co-E bonds at the edges of the “wings” of the butterfly. Tetrahedrane structures with both Co-Co and E-E bonds are higher in energy for Cp2Co2S2 and Cp2Co2(PH)2 and are not found in the other systems. This differs from the corresponding Fe2(CO)6S2 and Fe2(CO)6(PX)2 derivatives where tetrahedrane structures are predicted to be the lowest energy structures for all cases except X = NR2 and OH and such a tetrahedrane structure is found experimentally for Fe2(CO)6S2. The butterfly structures for the Cp2Co2E2 derivatives are of two types. For Cp2Co2(PX)2 (X = H, OH, OMe, NH2, NMe2) the lowest energy structures are unsymmetrical butterflies Cp2Co2(P)(PX2) with two X groups on one phosphorus atom and a lone pair on the other (naked) phosphorus atom. Related low-energy unsymmetrical butterfly Fe2(CO)6(P)(PX2) structures, not observed in previous theoretical studies, are now found for the corresponding Fe2(CO)6(PX)2 derivatives. Symmetrical butterfly singlet diradical structures with one X group on each phosphorus atom in relative cis or trans positions are also found for the Cp2Co2(PX)2 derivatives and are the global minima for Cp2Co2(PCl)2 as well as Cp2Co2S2. In all cases the cis structures are of lower energy than the corresponding trans structures. Rhombus structures having neither Co-Co nor E-E bonds are also found for all of the Cp2Co2(PX)2 derivatives but always at higher energies than the butterfly structures, ranging from 17 to 29 kcal/mol above the global minima. 相似文献
75.
Bobby G. Poe III Ciarán F. Duffy Michael A. Greminger Bradley J. Nelson Edgar A. Arriaga 《Analytical and bioanalytical chemistry》2010,397(8):3397-3407
Mitochondrial DNA (mtDNA) mutations have been associated with disease and aging. Since each cell has thousands of mtDNA copies,
clustered into nucleoids of five to ten mtDNA molecules each, determining the effects of a given mtDNA mutation and their
connection with disease phenotype is not straightforward. It has been postulated that heteroplasmy (coexistence of mutated
and wild-type DNA) follows simple probability rules dictated by the random distribution of mtDNA molecules at the nucleoid
level. This model has been used to explain how mutation levels correlate with the onset of disease phenotype and loss of cellular
function. Nonetheless, experimental evidence of heteroplasmy at the nucleoid level is scarce. Here, we report a new method
to determine heteroplasmy of individual mitochondrial particles containing one or more nucleoids. The method uses capillary
cytometry with laser-induced fluorescence detection to detect individual mitochondrial particles stained with PicoGreen, which
makes it possible to quantify the mtDNA copy number of each particle. After detection, one or more particles are collected
into polymerase chain reaction (PCR) wells and then subjected to real-time multiplexed PCR amplification. This PCR strategy
is suitable to obtain the relative abundance of mutated and wild-type mtDNA. The results obtained here indicate that individual
mitochondrial particles and nucleoids contained within these particles are not heteroplasmic. The results presented here suggest
that current models of mtDNA segregation and distribution (i.e., heteroplasmic nucleoids) need further consideration. 相似文献
76.
Mark E. Erupe Allegra Liberman-Martin Philip J. Silva Quentin G.J. Malloy Naomi Yonis David R. Cocker III Kathleen L. Purvis-Roberts 《Journal of chromatography. A》2010,1217(13):2070-2073
An ion chromatography method with non-suppressed conductivity detection was developed for the simultaneous determination of methylamines (methylamine, dimethylamine, trimethylamine) and trimethylamine-N-oxide in particulate matter air samples. The analytes were well separated by means of cation-exchange chromatography using a 3 mM nitric acid/3.5% acetonitrile (v/v) eluent solution and a Metrosep C 2 250 (250 mm × 4 mm i.d.) separation column. The effects of the different chromatographic parameters on the separation were also investigated. Detection limits of methylamine, dimethylamine, trimethylamine, and trimethylamine-N-oxide were 43, 46, 76 and 72 μg/L, respectively. The relative standard deviations of the retention times were between 0.42% and 1.14% while the recoveries were between 78.8% and 88.3%. The method is suitable for determining if methylamines and trimethylamine-N-oxide are a significant component of organic nitrogen aerosol in areas with high concentration of these species. 相似文献
77.
Given a non-compact, simply connected homogeneous three-manifold X and a sequence {Ωn}n of isoperimetric domains in X with volumes tending to infinity, we prove that, as n→∞:
- (1)
- The radii of the Ωn tend to infinity. 相似文献
78.
79.
80.
We prove that if the quotient surface of a properly embedded doubly–periodic minimal surface in ℝ3 has genus zero, then the surface is one of the classical Scherk examples.
Oblatum 30-IX-1998 & 18-II-2000?Published online: 30 October 2000 相似文献