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991.
过渡金属酞等配合物(MPC)用手均相液相氧化中作催化剂已有不少报导,象许多均相催化剂一样,MPC用于均相反应存在着难于从反应体系中分离出来的问题.把均相配合物催化剂固载在无机氧化物如硅股或有机高分子载体上是解决这一问题的一种方法.我们曾尝试把MP。固载在分子筛载体和硅胶载体上,并用ESR研究其对O2的活化作用[1,2].本文报导MPc通过共价键键联固载在SiO2上,并研究其对O2的活化作用.1实验部分1.1试剂HSIC13为日本东京化成株式会社产品,二级试剂·发烟硫酸(SO。质量分数大于20%)为分析纯试剂.PCl5为化学纯试… 相似文献
992.
For many applications poly(styrene) must
be treated to reduce its flammability. This is usually done by incorporating
a flame retardant additive, usually an organohalogen compound, into the formulation
as the polymer is being processed. A potentially very efficient way of introducing
flame retardance would be to incorporate a suitable structural unit directly
into the polymer. This can be done by using 2,4,4,5,5-pentaphenyl-1,3,2-dioxaphospholane
as an initiator for styrene polymerization. The strained carbon–carbon
bond of the phospholane undergoes homolysis at moderate temperatures to generate
a diradical which initiates polymerization. The resulting polymer contains
an O–P–O unit in the mainchain. Thermogravimetry indicates that
the thermal stability of the polymer is quite comparable to that of poly(styrene)
generated by conventional methods. 相似文献
993.
Despite the popularity of boron and silicon allylation reagents in stereocontrolled synthesis, they suffer from a number of inherent limitations that have slowed down their development as synthetic tools for nucleophilic additions to carbonyl compounds and imine derivatives. These limitations are the low reactivity and diastereoselectivity of allyl trialkylsilane reagents, and the lack of catalytic systems for the activation and substoichiometric control of enantioselectivity in the additions of allyl boron reagents. To develop more efficient and general methods for the control of absolute stereochemistry in the resulting homoallylic alcohols, new approaches aimed at solving the problem of activation of allylic boron and silicon reagents are needed. This Minireview describes a number of recent approaches that have been devised to address this problem. 相似文献
994.
Kehayias JJ 《Analytical and bioanalytical chemistry》2004,379(2):188-191
Body composition has become the main outcome of many nutritional intervention studies including osteoporosis, malnutrition, obesity, AIDS, and aging. Traditional indirect body composition methods developed with healthy young adults do not apply to the elderly or diseased. Fast neutron activation (for N and P) and neutron inelastic scattering (for C and O) are used to assess in vivo elements characteristic of specific body compartments. Non-bone phosphorus for muscle is measured by the 31P(n,)28Al reaction, and nitrogen for protein via the 14N(n,2n)13N fast neutron reaction. Inelastic neutron scattering is used to measure total body carbon and oxygen. Body fat is derived from carbon after correcting for contributions from protein, bone, and glycogen. Carbon-to-oxygen ratio (C/O) is used to measure the distribution of fat and lean tissue in the body and to monitor small changes of lean mass. A sealed, D–T neutron generator is used for the production of fast neutrons. Carbon and oxygen mass and their ratio are measured in vivo at a radiation exposure of less than 0.06 mSv. Gamma-ray spectra are collected using large BGO detectors and analyzed for the 4.43 MeV state of carbon and 6.13 MeV state of oxygen, simultaneously with the irradiation. P and N analysis by delayed fast neutron activation is performed by transferring the patient to a shielded room equipped with an array of NaI(Tl) detectors. A combination of measurements makes possible the assessment of the quality of fat-free mass. The neutron generator system is used to evaluate the efficacy of new treatments, to study mechanisms of lean tissue depletion with aging, and to investigate methods for preserving function and quality of life in the elderly. It is also used as a reference method for the validation of portable instruments of nutritional assessment. 相似文献
995.
水煤气变换反应的微观动力学分析──Cu基催化剂上H_2S中毒失活原因的 Monte Carlo 模拟研究 总被引:1,自引:0,他引:1
用BOCMP方法及MonteCarlo模拟技术,对H2S导致Cu基催化剂失活的原因进行了计算分析。研究结果表明,当原料气中存在H2S时,WGS反应的活化能明显高于无H2S时的活化能,随着表面H2S浓度的增大(θ=0,0.10,0.25),反应的活化能也逐渐变大(其大小比为1∶1.34∶3.3),究其原因可归结为H2S的存在使得反应物分子的吸附热减小,从而使H2O的解离吸附(WGS反应的速控步骤)活化能增大。 相似文献
996.
Substituted 5-aryl-3-ethylidene-3H-pyrrol-2-ones were synthesized by the reaction of the corresponding 4-aryl-4-oxobutanoic acids with ketones in the presence
of aminating agents. The conditions of this reaction were developed with the use of both the conventional condensation technique
and microwave activation. The structures of the reaction products were con-firmed by elemental analysis, IR spectroscopy,
and 1H NMR spectroscopy.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 693–696, April, 2006. 相似文献
997.
A. K. Galwey 《Journal of Thermal Analysis and Calorimetry》2006,86(1):267-286
This critical
survey argues that the theory, conventionally used to interpret kinetic data
measured for thermal reactions of initially solid reactants, is not always
suitable for elucidating reaction chemistry and mechanisms or for identifying
reactivity controls. Studies of solid-state decompositions published before
the 1960s usually portrayed the reaction rate as determined by Arrhenius type
models closely related to those formulated for homogeneous rate processes,
though scientific justifications for these parallels remained incompletely
established. Since the 1960s, when thermal analysis techniques were developed,
studies of solid-state decompositions contributed to establishment of the
new experimental techniques, but research interest became redirected towards
increasing the capabilities of automated equipment to collect, to store and
later to analyze rate changes for selected reactions. Subsequently, much less
attention has been directed towards chemical features of the rate processes
studied, which have included a range of reactants that is much more diverse
than the simple solid-state reactions with which early thermokinetic studies
were principally concerned. Moreover, the theory applied to these various
reactants does not recognize the possible complexities of behaviour that may
include mechanisms involving melting and/or concurrent/consecutive reactions,
etc. The situation that has arisen following, and attributable to, the eclipse
of solid-state decomposition studies by thermal analysis, is presented here
and the consequences critically discussed in a historical context. It is concluded
that methods currently used for kinetic and mechanistic investigations of
all types of thermal reactions indiscriminately considered by the same, but
inadequate theory, are unsatisfactory. Urgent and fundamental reappraisal
of the theoretical foundations of thermokinetic chemical studies is now necessary
and overdue.
While there are important, but hitherto unrecognized,
delusions in thermokinetic methods and theories, an alternative theoretical
explanation that accounts for many physical and chemical features of crystolysis
reactions has been proposed. However, this novel but general model for the
thermal behaviour and properties of solids has similarly remained ignored
by the thermoanalytical community. The objective of this article is to emphasize
the now pressing necessity for an open debate between these unreconciled opinions
of different groups of researchers. The ethos of science is that disagreement
between rival theories can be resolved by experiment and/or discussion, which
may also strengthen the foundations of the subject in the process. As pointed
out below, during recent years there has been no movement towards attempting
to resolve some fundamental differences of opinion in a field that lacks an
adequate theory. This should be unacceptable to all concerned. Here some criticisms
are made of specific features of the alternative reaction models available
with the stated intention of provoking a debate that might lead to identification
of the significant differences between the currently irreconciled views. This
could, of course, attract the displeasure of both sides, who will probably
criticise me severely. Because I intend to retire completely from this field
soon, it does not matter to me if I am considered to be ‘wrong’,
if it contributes to us all eventually agreeing to get the science ‘right’. 相似文献
998.
Rosario De Lisi Mario Goffredi Vincenzo Turco Liveri 《Journal of solution chemistry》1981,10(5):351-356
The conductances of dilute aqueous solutions of KCl, KBr, and KI have been measured over the temperature range 2 to 8°C and have been analyzed by the Fuoss-Hsia equation. The ionic Walden products at infinite dilution have been discussed in terms of local viscosity. The temperature dependence of these products suggest that near the temperature of maximum density of water, the structure-breaking ability of these ions changes in a regular way. 相似文献
999.
Conformational preference and chemical stability of meso-aryl-substituted [26]hexaphyrins(1.1.1.1.1.1) ([26]ArH) depend upon meso-aryl substituents. Although only a planar and rectangular conformation (type-II conformation) has been identified for [26]ArH so far, we have demonstrated here that a different conformation with all the pyrroles pointing inward (type-I conformation) is preferred for [26]ArH (7 and 11-I) bearing small 2-thienyl or 3-thienyl substituents at 15- and 30-positions. Both type-I and type-II [26]ArH exhibit diatropic ring currents, reflecting aromatic character. Type-I [26]ArH, such as 7 and 11-I, have been shown to serve as an effective ligand for Pd(II) ions to provide bis-Pd(II) complexes 12 and 13 with N(3)C(1) coordination through facile C--H bond activation. 相似文献
1000.
Poly(N-isopropylacrylamide) (PNIPAM) has a low critical solution temperature (LCST) at 32°C in water and the hydrophilicity changes through the LCST. The microspheres whose surface was composed of PNIPAM exhibited phase transition behavior around 32°C. Therefore, the interactions between PNIPAM micropheres and granulocytes depended on the temperature. That is, the oxygen consumption and active oxygen production by cells in contact with PNIPAM-containing microspheres and adhesion of the microspheres to the cell surface were more enhanced above the LCST of PNIPAM than below it, whereas no significant temperature dependence of cell–microspheres interaction was observed in nonthermosensitive microsphere systems. It was suggested that the function of cells could be controlled with temperature using the temperature-sensitive microspheres. 相似文献