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排序方式: 共有6759条查询结果,搜索用时 46 毫秒
121.
Ch. Krüger H. Schwer J. Karpinski K. Conder E. Kaldis C. Rossel M. Maciejewski 《无机化学与普通化学杂志》1994,620(11):1932-1936
Structural investigations on powder samples of Y2Ba4Cu7O15–x with different carbonate content have been performed. Powder x-ray Rietveld refinements showed the remarkable influence of carbonate incorporation on the lattice parameters. Most important is the decrease of Tc with increasing carbonate content. We assign these effects to an incorporation of the carbonate ion into the crystal lattice, copper vacancies at the Cu(1) position and a possible misorientation of the copper oxygen single chains. No change of the structure (e. g. superstructure) could be found. 相似文献
122.
Two important considerations in the design of an aerobic particulate immobilized cell bioreactor are the provision of sufficient
oxygen to maintain the desired metabolism of the immobilized organism, and the biomass holdup (which is proportional to the
number of immobilized cell particles in the reactor).
The Circulating Bed Reactor, a reactor developed for use with those forms of immobilization that result in particles of essentially
neutral buoyancy, operates with an expanded bed of circulating particles. The particle number density attainable in such a
reactor has been found to be dependent upon the circulation cell aspect ratio, the individual particle properties, the static
bed voidage of the particles, and the superficial gas velocity. The oxygen mass transfer characteristics have been found to
be dependent upon the circulatory nature of the system, the particle (solids) holdup, the particle porosity, and the superficial
gas velocity. 相似文献
123.
124.
Brightness reversion of softwood (SW) and hardwood (HW) bleached chemithermomechanical pulps (BCTMP) with a 300–400nm light source under argon, oxygen, and air were studied in the absence and presence of UV-screens using UV–Vis reflectance difference spectroscopy. The UV-Vis difference absorption spectra of control SW and HW BCTMP testsheets indicate that as the concentration of atmospheric oxygen is increased, the absorption at max 360nm increases and a blue shift occurs. In all of the cases studied, brightness reversion was observed to occur under an argon atmosphere. The addition of benzophenone and benzotriazole additives to BCTMP testsheets resulted in a significant decrease in formation of chromophores absorbed at 400nm and 360nm. The possible mechanisms contributing to these effects are discussed in terms of the photoformation of lignin chromophoric structures. 相似文献
125.
通过高温固相合成法首次合成了La2Mo1.8Ga0.2O9陶瓷样品. 粉末XRD结果表明, 该样品为单一立方相La2Mo2O9结构. 以陶瓷样品为固体电解质、多孔性铂为电极, 采用交流阻抗谱、气体浓差电池、氧泵等方法研究了样品在600~1000 ℃下各种气氛中的离子导电特性. 结果表明, 氧浓差电池电动势的实测值与理论值吻合得很好, 氧离子迁移数为1, 表明该陶瓷样品在该温度下氧气气氛中为一纯氧离子导体; 氧泵(氧的电化学透过)实验结果进一步证实了该样品在氧气气氛中为一纯氧离子导体; 在氧分压p(O2)=10-5~105 Pa的高氧分压气氛中, 电导率与氧分压变化基本无关, 表明在该氧分压范围内样品为纯离子导体, 这与氧浓差电池电动势测定结果相吻合; 在低氧分压为10-5~10-15 Pa范围内, 总电导率随氧分压降低而稍有升高, 表明在该氧分压范围样品为氧离子与电子的混合导体; 在600~1000 ℃下氧离子电导率>10-2 S•cm-1, 显著高于母体La2Mo2O9的氧离子电导率, 1000 ℃时的氧离子电导率为0.07 S•cm-1. 相似文献
126.
The paper presents the results of testing
the thermal stability and flammability of butadiene-acrylonitrile rubber vulcanizates
with different contents of combined acrylonitrile: Perbunan NT 1845 and Perbunan
NT 3945 from Bayer, containing unmodified and bromine- or iodine-modified
silica. The test results were obtained with the use of a derivatograph, measurements
of flammability by the method of oxygen index, in air and also with the use
of a cone calorimeter. The effect of the modification on the zeta potential
was also examined.
A considerable reduction in the flammability
of nitrile rubber vulcanizates filled with silica can be obtained by the modification
of filler with bromine or iodine. All the vulcanizates containing modified
silica are self-extinguishing. An appropriate filling of NBR 39 vulcanizates
with bromine-modified silica makes it possible to obtain non-flammable polymeric
materials. They neither ignite nor glow under the action of a flame source
for 30 s.
The findings can be a rational basis for the synthesis
of modified silica that can act as active filler and effective flame-retardant
agent at the same time. 相似文献
127.
Copper is a bioessential element in biology with truly unique chemical characteristics in its two relevant oxidation states +I and +II. Significant progress has been made in recent years in the elucidation of the frequently surprising biochemistry of this trace element. Those advances were especially furthered through mutual stimulation involving results from biochemistry, molecular biology, and medicine on one hand and the synthesis as well as the structural and spectroscopic characterization of low molecular weight model complexes on the other. The most notable features of protein-bound active copper are its almost exclusive function in the metabolism of O2 or N/O compounds (NO, N2O) and its frequent association with oxidizing organic and inorganic radicals such as tyrosyl, semiquinones, superoxide, or nitrosyl. This unique biological role of copper can be rationalized given its chemical and assumed evolutionary background. 相似文献
128.
The chemiluminescence (CL) of peracetic acid (PAA) in alkaline medium is very weak but is strongly enhanced after the addition
of dihydralazine sulfate (DHZS). Based on this phenomenon, a simple, rapid and highly sensitive flow-injection CL method for
the determination of DHZS was developed. The CL emission was linearly related to the DHZS concentration in the range of 20–4000 ng mL−1 with a detection limit (3σ) of 1.2 ng mL−1. As a preliminary application, the proposed method was successfully applied to the determination of DHZS in pharmaceutical
preparations; the recovery of DHZS in human urine was between 96.5% and 102.2%. A detailed CL mechanism was proposed and singlet
molecular oxygen (1O2) was suggested to be produced in the CL reaction process. 相似文献
129.
Millar AJ Doonan CJ Smith PD Nemykin VN Basu P Young CG 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(11):3255-3267
Intermediates in the oxygen atom transfer from Mo(VI) to P(III), [Tp(iPr)MoOX(OPR3)] (Tp(iPr) = hydrotris(3-isopropylpyrazol-1-yl)borate; X = Cl-, phenolates, thiolates), have been isolated from the reactions of [Tp(iPr)MoO2X] with phosphines (PEt3, PMePh2, PPh3). The green, diamagnetic oxomolybdenum(IV) complexes possess local C(1) symmetry (by NMR spectroscopy) and exhibit IR bands assigned to nu(Mo==O) (approximately 950 cm(-1)) and nu(P==O) (1140-1083 cm(-1)) vibrations. The X-ray crystal structures of [Tp(iPr)MoOX(OPEt3)] (X = OC6H4-2-sBu, SnBu), [Tp(iPr)MoO(OPh)(OPMePh2)], and [Tp(iPr)MoOCl(OPPh3)] have been determined. The monomeric complexes exhibit distorted octahedral geometries, with coordination spheres composed of tridentate fac-Tp(iPr) and mutually cis monodentate terminal oxo, phosphoryl (phosphine oxide), and monoanionic X ligands. The electronic structures and stabilities of the complexes have been probed by computational methods, with the three-dimensional energy surfaces confirming the existence of a low-energy steric pocket that restricts the conformational freedom of the phosphoryl ligand and inhibits complete oxygen atom transfer. The reactivity of the complexes is also briefly described. 相似文献
130.
Danilov A. I. Molodkina E. B. Polukarov Yu. M. 《Russian Journal of Electrochemistry》2004,40(6):585-596
The oxidation of polycrystalline platinum in 0.5 M H2SO4 is studied by cyclic voltammetry at potential scan rates of 5–500 mV s–1 while varying the potential cycling range. The scheme, which is proposed for explaining the observed acceleration and deceleration of oxygen sorption at 0.75–1.0 V, accounts for the presence of oxygen in the subsurface layers of platinum (Oss) and the formation of a barrier layer comprising complexes Oss–Pt
n
–SO4. Cycling platinum secures certain steady-state contents of Oss at 0.01–1.35 V. In an anodic scan, Oss accumulates at E > 0.85 V (slow post-electrochemical stage) due to exchange of platinum and oxygen atom sites. In a cathodic scan, the desorption of most oxygen gives way to the adsorption of anions, which prevent residual Oss from appearing on the surface. The residual Oss disappears at E < 0.1 V after a sufficiently complete desorption of anions and the destruction of stable complexes Oss–Pt
n
–SO4. Varying the potential cyclic limit leads, after a delay, to other steady-state Oss contents. 相似文献