全文获取类型
收费全文 | 289079篇 |
免费 | 2452篇 |
国内免费 | 720篇 |
专业分类
化学 | 153907篇 |
晶体学 | 4290篇 |
力学 | 12585篇 |
综合类 | 18篇 |
数学 | 32813篇 |
物理学 | 88638篇 |
出版年
2020年 | 2402篇 |
2019年 | 2593篇 |
2018年 | 3497篇 |
2017年 | 3437篇 |
2016年 | 5064篇 |
2015年 | 3109篇 |
2014年 | 4821篇 |
2013年 | 11557篇 |
2012年 | 9176篇 |
2011年 | 11098篇 |
2010年 | 7781篇 |
2009年 | 7543篇 |
2008年 | 10337篇 |
2007年 | 10505篇 |
2006年 | 9789篇 |
2005年 | 9335篇 |
2004年 | 8700篇 |
2003年 | 7649篇 |
2002年 | 7250篇 |
2001年 | 7781篇 |
2000年 | 6117篇 |
1999年 | 4653篇 |
1998年 | 4088篇 |
1997年 | 4083篇 |
1996年 | 3901篇 |
1995年 | 3612篇 |
1994年 | 3765篇 |
1993年 | 3478篇 |
1992年 | 3947篇 |
1991年 | 3896篇 |
1990年 | 3776篇 |
1989年 | 3620篇 |
1988年 | 3711篇 |
1987年 | 3605篇 |
1986年 | 3427篇 |
1985年 | 4536篇 |
1984年 | 4790篇 |
1983年 | 4007篇 |
1982年 | 4160篇 |
1981年 | 4083篇 |
1980年 | 4043篇 |
1979年 | 3982篇 |
1978年 | 4336篇 |
1977年 | 4205篇 |
1976年 | 4281篇 |
1975年 | 3939篇 |
1974年 | 4002篇 |
1973年 | 4145篇 |
1972年 | 2885篇 |
1971年 | 2429篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
G. A. Kohring 《Journal of statistical physics》1992,66(3-4):1177-1184
A hydrodynamic cellular automata (HDCA) for simulating two-dimensional fluids with large viscosities is proposed. The model is characterized by a mean free path which is of the same size as in the FHP-II model, but with a viscosity more than 10 times larger. This new model should make simulations of flows at low Reynolds number more efficient. 相似文献
962.
Activities of phenylalanine ammonia-lyase (PAL) and tyrosine ammonia-lyase (TAL) were assessed at each stage of a three-step purification of PAL. Assays were performed by high-performance liquid chromatographic (HPLC) separation and ultraviolet detection of reaction products. Use of HPLC permitted assay of low activities of PAL and TAL for periods up to approximately four and two days, respectively. HPLC also facilitated the accurate quantitation of the product of the TAL reaction, trans-p-coumaric acid, which was observed to isomerize readily under experimental conditions. PAL and TAL were associated throughout the purification procedure, with TAL activity at 0.6-1.3% of PAL activity. It was concluded that, contrary to previous reports, TAL and PAL activities are mediated by the same enzyme, or else by chromatographically very similar enzymes. 相似文献
963.
M. D. Zipper G. P. Simon P. Cherry A. J. Hill 《Journal of Polymer Science.Polymer Physics》1994,32(7):1237-1247
Homopolymers and blends of polycarbonate/ThermX have been investigated by differential scanning calorimetry, dynamic mechanical analysis, density measurements, and positron annihilation lifetime spectroscopy. The study focuses on the chain mobility and free volume in the amorphous miscible regions of the blends and how this mobility and free volume are affected by increasing crystallinity. It is proposed that judicious annealing, which results in increasing crystallinity (while avoiding ageing or transesterification), induces a constraint on the amorphous region leading to an increase in Tg and coalescence of free volume sites. © 1994 John Wiley & Sons, Inc. 相似文献
964.
965.
966.
Previous work carried out in our laboratories has focused on the formation and investigation of a dextran and concanavalin A (con A) based gel, which has the ability to alter its conformational structure in the presence and absence of free and terminal glucoses such that a gel–sol phase transition occurs. Here we report the diffusion and rheological investigations in to the effects of the addition of insulin and varyingconcentrations of magnesium chloride hexahydrate (Mg2Cl26H2O) at 20 and 37 °C. Rheological examination of glucose-sensitive (dextran-con A) gels were conducted using a cone and plate viscometer used in continual rotation and oscillatory modes. The results are interpreted in terms of the structure of the gel network and suggest rheological assessment provides an effective method of assessing the properties of gel systems. The subsequent testing of such formulations in in-vitro diffusion experiments revealed a reduction in the rate of diffusivity in the insulin marker, poly R-478 dye. The performance of this self-regulating drug delivery system has been examined and the addition of insulin and magnesium chloride may alter the way in which the gel operates as a drug delivery device and in the delivery of insulin. This may have implications for other ligands. 相似文献
967.
968.
969.
A. Veider G. Badurek R. Grssinger H. Kronmüller 《Journal of magnetism and magnetic materials》1986,60(2-3):182-194
The domain configuration of amorphous ribbons with positive, vanishing and negative magnetostriction constant λs has been investigated by means of the longitudinal magneto-optical Kerr-effect and a three-dimensional neutron depolarization analysis. The influence of an external tensile stress on the domain arrangement depends on the sign and the magnitude of the magnetostriction constant and could be measured quantitatively in the depolarization experiment. With the aid of the optical observations domain models have been established; these models were tested and completed by means of an analytic calculation of the corresponding depolarization matrix and a comparison with experimental data. Domain reorientation processes within the ribbons under an imposed tensile stress were found to agree with theoretical predictions. The nearly nonmagnetostrictive alloys shows neither stripe domains nor simple wide domains but a more complicated structure with several layers of domains. 相似文献
970.
V. F. Tret’yakov A. G. Zakirova V. A. Matyshak T. N. Burdeinaya V. N. Korchak L. S. Glebov V. V. Lunin 《Kinetics and Catalysis》2006,47(6):873-880
According to X-ray diffraction analysis data, the test catalyst was a Ni-Cr spinel with an impurity of NiO. With the use of in situ IR spectroscopy, it was found that nitrite, nitrate, and acetate surface complexes occurred under the reaction conditions of the selective catalytic reduction of nitrogen oxides by propane in the presence of oxygen on the nickel-chromium catalyst. As the temperature was increased, the nitrite complexes were converted into nitrate species. The molar absorption coefficient of surface nitrate complexes was determined. According to IR-spectroscopic and TPD data, the nitrate complexes were bound relatively weakly to the surface. The temperature region of their existence was 50–200°C. The temperature region of existence of the surface acetate complexes was 200–400°C. The individual adsorption of oxygen was not observed; however, oxygen-containing surface sites (Cr5+=O) participated in the formation of the surface complexes of reactants. 相似文献