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91.
羰基铑催化剂由于其加氢性能较弱,在羰基化反应的研究中,通常仅作为烯烃氢甲酰化制醛的催化剂。产物中得不到醇。本文则报道了以Rh_2(AcO)_4和Rh_6(CO)_16为催化剂,在一个反应器内进行烯烃氢甲酰化,加氢制醇的研究。系统考察了Rh/Pbu_3/EtOH催化体系受各种反应条件的影响。在最佳反应条件下,烯烃转化率达100%。对醇选择性亦在99.5%以上,正异构比在2以上.为烯烃一步制醇建立了铑系催化新体系。文中并利用红外光谱测定了反应过程的催化剂物种.实验证明,由烯烃一步制醇是由烯烃首先进行氢甲酰化反应,然后由生成的醛进一步加氢成醇的一个串联反应过程。前一步骤反应速度较快,2h内可使95%以上的烯烃转化为醛,后面由醛加氢成醇则进行缓慢,在100—120℃下,至少22h,才能使醛全部转化为醇。 相似文献
92.
The deformation processes in impact-modified PMMA, which deforms homogeneously, were determined by means of the stress/strain experiment (, ) with simultaneous lateral strain measurement (lat) in a wide range of strain rates () up to 105%/min (impact stress). The elastic, plastic cavitation and plastic shear processes were determined as a function of strain. Therefore we calculated the elastic strain (
el), the elastic volume expansion (
vol el), the cavitation strain (
cav), which is identical with the plastic volume expansion (
vol pl), the shear strain (
sh) and the energy densities (Wel, Wcav, Wsh) related to these three processes.For strains of 3 % onward it was found that plastic shear processes and plastic cavitation processes are responsible for a partial loss of elastically stored energy. Both plastic processes turn out to be mostly anelastic deformations, their amount depending strongly on the strain rate. The contributions of the processes to the total deformation of the unmodified PMMA in its strain range are similar to those of the impact-modified PMMA, and the high impact strength is caused by a shift of the catastrophic rupture to very high strains. 相似文献
93.
Zhen-hua Yuan De-yan Shen Ren-yuan Qian Polymer Physics Laboratory Center for Molecular Science Institute of Chemistry Chinese Academy of Sciences Beijing China 《高分子科学》2001,(4):399-405
Viscoelastic behavior of the non-Hooke deformation of amorphous PET film before yield was investigated in thetemperature region 74--80.5℃ around the glass transition temperature. The film specimen was drawn to yield point followedby unloading to zero stress, then the residual deformation was held constant, while the subsequent evolution of the stress wasrecorded. An induction period was found in the course of stress evolution fol1owed by a stress step-increase. The inductionperiod decreases with increasing drawing temperature with an activation energy of 1.10 MJ/mol·K, which is attributed tothe time needed for the relaxation of rubbery deformation through cooperative internal rotations. At temperatures lower than74℃, there is no stress increase or the induction period becomes too long to be observed. Thus the nature of anelasticity inthe non-Hooke region before yielding is attributed to stress induced rubbery deformation. The experimental results areinterpreted in terms of Perez' rheological model of a series connected Hooke spring and a Voigt element consisting of aparallel connected elastic spring and a dashpot. 相似文献
94.
Vladimir A Escobar Barrios Alain Petit Rafael Herrera Nájera 《European Polymer Journal》2003,39(6):1151-1167
Three types of butadiene-styrene copolymers, diblock, triblock and random, were partially hydrogenated in their elastomeric units in order to determine the influence of hydrogenation extent on their thermal properties. The hydrogenation reactions were carried out using a Ziegler-Natta type catalyst and the extent of hydrogenation was evaluated by FTIR spectroscopic technique. The percentage of crystallinity was determined by differential scanning calorimetry (DSC), considering the low density polyethylene (LDPE) as reference since the saturation of elastomeric units with low content of 1,2-vinyl bonds gives a structure which resembles to LDPE, thus semi-crystalline polymers were obtained. On the other hand, the glass transition temperature (Tg) for the hydrogenated and non-hydrogenated copolymers as well as their heat of fusion, were also determined by DSC. An equation to evaluate the Tg of partially hydrogenated random copolymers is proposed considering both the saturated and unsaturated fractions. The thermo-oxidative behaviour of certain hydrogenated and non-hydrogenated copolymers was evaluated by thermogravimetric analyses (TGA). The results obtained by TGA suggest that a minimum saturation level is necessary in order to improve the thermo-oxidative resistance of the polymers. 相似文献
95.
The historical background of and the incentive for using ruthenium carbonyl clusters as homogeneous catalysts are outlined.
Keeping in view the possible solutions the uncertainties arising from declusterification and metal colloid formation are discussed.
All ruthenium cluster-catalysed reactions are broadly classified as reactions with or without carbon monoxide as one of the
reactants and the basic differences between such reactions are highlighted. Some of the factors of special relevance to cluster-catalysed
reaction systems are mentioned. The reactions involving carbon monoxide are then discussed. These include water-gas-shift
reaction, carbon monoxide hydrogenation, hydroformylation, reductive carbonylation of nitrobenzene and other carbonylation
reactions. Hydrogenation, transfer hydrogenation, isomerisation and a few other reactions are then discussed. For all these
reactions, special emphasis is laid on well-characterised cluster complexes that have been proposed as catalytic intermediates.
Finally an attempt has been made to identify the path that future research in cluster catalysis is likely to follow. 相似文献
96.
In this paper, the stereoselective homogeneous catalysis polymerization of phenylacetylene by using two kinds of catalysts W(CO)_5CH_3I and W(CO)_4I_2 produced from UV laser photolysis of W (CO)_6 in CH_3I, I_2—C_6H_6 and CHI_3—C_6H_6 respectively was studied. The effects of laser energy, laser irradiation time and lifetime of catalyst on the polymerization of phenylacetylene were discussed. The photoproducts of W (CO)_6 in CH_3I, I2—C_6H_6 and CHI_3—C_6I_6 were determined by IR spectra. The structures of polyphenylacetylene obtained by W (CO)_5CH_3I and W (CO)_4I_2 catalysts were characterized by IR spectra and ~1H NMR spectra. 相似文献
97.
A new simple and efficient homogeneous liquid-liquid extraction method for the selective separation and preconcentration of molybdenyl ions was developed. α-Benzoin oxime (ABO) was investigated as a complexing ligand, and perfluorooctanoate ion (PFOA−) was applied as a phase-separator agent under strongly acidic conditions. Under the optimal conditions ([ABO] = 2.1 × 10−3 M, [PFOA−] = 1.8 × 10−2 M, [HNO3] = 1.7 M, [acetone] = 11.8% (v/v)), 10 μg of molybdenum in 5 ml aqueous phase could be extracted quantitatively into 40 μl of the sedimented phase. The maximum concentration factor was 125-fold. Thiocyanate was applied as a chromogenic reagent for the direct spectrophotometric determination of molybdenum in the sedimented phase. The reproducibility of the proposed method is at the most 2.4%.The influence of the type and concentration of acid solution, the concentration of ABO, the type and volume of the water-miscible organic solvent, the concentration of PFOA−, and the effect of different diverse ions on the extraction and determination of molybdenum(VI) were investigated. The proposed method was applied to the extraction and determination of molybdenum(VI) in natural water, Spinach, and Lucerne samples. A satisfactory agreement exists between the results obtained by the proposed method and those reported by GF-AAS. 相似文献
98.
This study concerns the thermal and mechanical response of several commercial grades of ethylene – tetrafluoroethylene copolymer films. Differential scanning calorimetry was used to show that, although films have similar degrees of crystallinity and melting temperature, the melting endotherms and crystallisation exotherms differ between materials, suggesting small changes in composition between manufacturers. Films were deformed in tension at a range of temperatures and rates. Selected films were unloaded immediately after stretching, and measurement of the elastic recovery highlighted further differences between materials. Batches of films were pre-drawn uniaxially above the glass transition and immediately quenched. When these materials were subsequently re-drawn below the glass transition temperature, most of them exhibited much improved yield stress, modulus and tensile strength (improving by factors of 5, 5 and 4, respectively at a draw ratio of 3), but a reduced strain to failure. In most of the films, the pre-drawing, as well as the initial orientation of the films, is accounted for by a simple shift in the true strain axis. This is indicative of a material response dominated by entropic network stretch. It also suggests that, in the cases where strain superposition does not work, a different arrangement of crystalline lamellae may be present, limiting the extent to which improved properties can be achieved in some materials. 相似文献
99.
A polymer crystal with a noncrystalline surface layer formed by chain loops of different lengths is considered. It is assumed that the length of each loop can be changed by longitudinal diffusion of the molecule through the crystal lattice. From the condition that the free energy of the system is minimum, the loop length distribution and the average loop length as function of temperature are calculated. In contrast to the results for loops of equal length, for the present model, a substantial thickness of the noncrystalline surface layer and a broad melting range is obtained also for the case of adjacent reentry. In order to get this result one has to take into account that even an “ideal fold” consists of at least four rigidly arranged CH2 groups in energetically unfavored conformation. 相似文献
100.
The orientational order parameters fot two liquid crystal materials, 4-cyanophenyl 4-butylbenzoate and 4-cyanophenyl 4-pentylbenzoate, have been derived by measuring the change in the refractive index as function of temperature. The order parameters are compared with MaierSaupe theory, and the sharpness of the transitions has been shown using the Haller's plot. 相似文献