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111.
从TGEV 3CL蛋白酶二聚体结构出发,研究了TGEV 3CL蛋白酶二聚体单体之间的静电和疏水相互作用.蛋白质的静电相互作用通过有限差分方法求解Poisson-Boltzmann方程得到,疏水相互作用通过分析溶剂可及性表面模型得到.考察了不同pH值对TGEV 3CL蛋白酶二聚体静电和疏水相互作用的影响,在pH值为5.5~8.5时,二聚体静电相互作用能、静电去溶剂化能和疏水自由能都较小,表明在该条件下静电和疏水相互作用有利于二聚体的稳定存在,这符合实验结晶所需条件.pH值对静电去溶剂化能的影响大于疏水自由能,表明静电作用是造成强酸或强碱条件下二聚体不能稳定存在的主要原因. 相似文献
112.
The composition range and (composite modulated) structure of compounds within the wide range non-stoichiometric LaSb2Snx, 0.1?x?0.75, solid solution is carefully investigated via a combined electron diffraction, XRD and electron probe microanalysis study. Evidence for metastability of the LaSb2Snx phase at the low x composition end of the solid solution is presented. Direct evidence is found for a reasonably (although by no means perfectly) well ordered Sn sub-structure which is, in general, mutually incommensurable with respect to a very well ordered underlying LaSb2 sub-structure along both a and c directions. The overall (3+2)-d superspace group symmetry is given along with a discussion of the consequences as regards the arrangement of the Sn atoms. The Sn sub-structure c-axis cell dimension shows very little variation with composition x providing direct experimental evidence of the importance of Sn-Sn metallic bonding (along one-dimensional [001] Sn strings) for the stability of the phase. 相似文献
113.
Rudolf Sobczak 《Monatshefte für Chemie / Chemical Monthly》1979,110(3):721-727
Magnetic measurements onHeusler alloys (Co,T)2
XY (field and temperature dependence) are performed around theCurie points (temperature range:T
C–50 toT
C+50). A method otherwise used to get rid of ferromagnetic impurities only (
g
versus 1/H plot) is applied to pure ferromagnets and yields completely new
g
(extrap.) versusT curves with a maximumT
max>
T
C. The method was applied to pure gadolinium first which has aCurie point within the accessible region of the susceptibility measuring device. 相似文献
114.
E.?DesimoniEmail author B.?Brunetti R.?Cattaneo 《Accreditation and quality assurance》2004,9(8):445-449
Considering the uncertainty of measurement when assessing compliance with reference values given in compositional specifications and statutory limits is still a controversial matter. In theory, assessing compliance requires considering both type I (false positive) and type II (false negative) errors. The more the concentration of the analyte in the sample under investigation is close to the allowed concentration limit, the more critical it is to consider both types of errors. This paper describes how this could be done. The matter is discussed in the light of the most recent literature information. 相似文献
115.
Lei Wang Guang-ming Zhu Yue-zhong Meng Chun-mei Gao 《高分子科学》2007,(4):419-426
A novel sulfonated poly(arylene ether) containing triphenylmethane moieties was synthesized by the sulfonation of a designed parent polymer using chlorosulfonic acid as sulfonation agent. The sulfonation took place at the para position of the pendant phenyl rings because of the specially designed parent polymer. The position and degree of sulfonation were characterized by ^1H-NMR and elemental analysis. The sulfonated polymers are highly soluble in common organic solvents, such as dimethylsulfoxide, N,N'-dimethylacetamide, dimethylformamide, ethylene glycol monomethyl ether, and can be readily cast into tough and smooth films from solutions. The films showed good thermal and hydrolysis stabilities. Moreover, Fenton's reagent test revealed that the films exhibited superior stability to oxidation. The proton conductivities of the films were comparable with Nation 117 under same conditions. The membrane electrode assembly (MEA) prepared with the asmade film (706 EW, 100 μm dry thickness) shows better cell performance than Nation 115-MEA in the whole current density range. 相似文献
116.
An expectation value approach to calculations of first-order properties using the non-iterative, triple-excitation amplitudes
in the coupled cluster wave function is exploited. Three methods are suggested and analysed using the many body perturbation
theory (MBPT) expansion arguments. The first method, in which non-iterative triple-excitation amplitudes are used in the expression
for the expectation values, makes the wave function accurate through the second order of MBPT. In the second method, which
is an extension of the first, effects of triple-excitation amplitudes are coupled with single- and double-excitation amplitudes.
The correlated density matrix equivalent through the fourth order to that obtained when CCSDT-la amplitudes are used is employed
in the third method. The suggested methods are tested on dipole moment and polarizability calculations for several diatomic
closed-shell molecules and are compared to other related approaches.
Received: 15 May 1997 / Accepted: 5 June 1997 相似文献
117.
Siu Kay Wong 《Accreditation and quality assurance》2005,10(8):409-414
Proficiency testing (PT) is an essential tool used by laboratory accreditation bodies to assess the competency of laboratories.
Because of limited resources of PT providers or for other reasons, the assigned reference value used in the calculation of
z-score values has usually been derived from some sort of consensus value obtained by central tendency estimators such as the
arithmetic mean or robust mean. However, if the assigned reference value deviates significantly from the ‘true value’ of the
analyte in the test material, laboratories’ performance will be evaluated incorrectly. This paper evaluates the use of consensus
values in proficiency testing programmes using the Monte Carlo simulation technique. The results indicated that the deviation
of the assigned value from the true value could be as large as 40%, depending on the parameters of the proficiency testing
programmes under investigation such as sample homogeneity, number of participant laboratories, concentration level, method
precision and laboratory bias. To study how these parameters affect the degree of discrepancy between the consensus value
and the true value, a fractional factorial design was also applied. The findings indicate that the number of participating
laboratories and the distribution of laboratory bias were the prime two factors affecting the deviation of the consensus value
from the true value. 相似文献
118.
David W. Schwenke Steven L. Mielke Donald G. Truhlar 《Theoretical chemistry accounts》1991,79(3-4):241-269
Summary We have developed efficient and accurate techniques for the calculation of quantum mechanical reaction probabilities of atom-diatom exchange reactions in the gas phase, and we have optimized a computer code employing these techniques and applied it sucessfully to several systems. In this paper we consider further strategies for improving the algorithm to allow even more demanding applications. In this context, improvement means that equivalent results can be obtained using fewer computational resources (computer time or storage) or that an equivalent expenditure of resources can yield higher accuracy. The new strategies discussed here lead to improvement in both of these areas. Two areas of special focus in the present paper are (i) the finite difference boundary value method used for calculating distorted wave Green's functions and regular solutions for scattering by the distortion potential and (ii) the choice of the distortion potential itself. Among other results included here is the first application of the outgoing wave or scattered wave variational principle to reactive scattering. 相似文献
119.
Dip Singh Gill 《Journal of solution chemistry》1979,8(10):691-699
Precise conductances for tetrabutylammonium tetrabutylboride (Bu4NBBu4) at 25°C have been measured in a number of nonaqueous solvents, and the data have been analyzed by the 1957 Fuoss-Onsager conductance equation. Limiting ion conductances for the Bu4N+ ion at infinite dilution 0(Bu
4
N
+) in various solvents have been evaluated by dividing 0 values of the salt into two equal parts. The 0(Bu
4
N
+) values so obtained are in fairly good agreement (within±0.1–3.5%) with the corresponding values determined from direct transference number measurements in these solvents. 相似文献
120.
Peter Schramel 《Mikrochimica acta》1989,99(3-6):355-364
The most sensitive emission lines for the elements B, Be, Co and Mo are strongly influenced by disturbing emission lines of Fe using normal optical resolution. The advantages of high resolution, applying the new ICP-spectrometer JY 38 Plus (Jobin-Yvon, France) with the 2400 lines/mm grating measuring in the 1st and 2nd order will be discussed. Beside the concentrations in soils, sediments and sludges, applying aqua regia and HF decomposition methods, the detection limits in these matrices will be given. The possibilities of ICP-spectrometry for the determination of the above-mentioned elements are shown at the examples of SRMs (standard reference materials). The materials used here were three soils and three sludges from the BCR (Community Bureau of Reference, European Communities) and one sediment from NBS (National Bureau of Standards, USA). For example, the most sensitive and normally used line for the determination of boron at 249.7733 nm cannot be used in case of this type of matrix due to normally high Fe-concentrations and due to a strong Fe-interference. Therefore, it is necessary to use the line at 249.6778 nm, where an interference-free measurement can be achieved in case of high optical resolution. The measured B-contents in these samples are in the range of 20 to 60 g/g, for Co in the 10 g/g region, for Be well below 1 g/g, for Sn between 3 and 400 g/g. Mo was only detectable in the sludge samples (limit of determination 0.5 g/g).Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, Austria 相似文献