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991.
L. Sieminska M. Ferguson T.W. Zerda E. Couch 《Journal of Sol-Gel Science and Technology》1997,8(1-3):1105-1109
Samples of porous sol-gel glass, after being stabilized at 750°C, were impregnated with progesterone, estradiol, estrone,
and hydrocortisone. Diffusion coefficients for those steroids inside the pores filled with pure ethanol, ethanol-water mixture
or physiological solution were determined. It is shown that permeability is favored for steroids having fewer hydroxyl and
carbonyl groups. Solvents that readily dissolve steroids increase the diffusion rate and thus the amount of delivered material.
The flow of steroids in small pores is less restricted than in larger pores. 相似文献
992.
The mechanisms of heat transfer from an argon RF plasma, generated in a water-cooled quartz tube, to a sintering sample immersed
into the plasma and to the walls of the plasma torch have been studied both analytically and experimentally for pressures
from 1 to 50 torr. The model, based on the assumption of chemical equilibrium in a two-temperature plasma with rotational
symmetry, includes the influence of the magnetic field and of the Knudsen number on the thermal conductivity of the plasma.
At pressures below 20 torr heat transfer to the sintering sample is enhanced compared to heat transfer to the wall of the
plasma torch. This nonsymmetry is attributed to the Hall parameter and Knudsen number effect. The relative importance of the
two effects is a function of the pressure. A comparison with experiments, based on calorimetric and indirect heat transfer
measurements for a range of pressures and power levels, indicates satisfactory agreement with analytical predictions, with
the exception of larger discrepancies at higher power levels and relatively low pressures. For pressures below 5 torr, the
chemical equilibrium assumption becomes questionable, i.e., the sintering model underestimates the heat transfer to the sintering
sample. 相似文献
993.
介绍一种掺铒玻璃样品的制作方法,实验测量了单片及两片掺铒玻璃样品的荧光特性.结果表明:两片掺铒玻璃样品级联的荧光强度比单片掺铒玻璃样品的荧光强度高,半值宽度与高浓度单片样品的半值宽度近似相等;在两片掺铒玻璃样品级联的形式中,浓度高的样品靠近抽运光源时的荧光强度比浓度低的样品靠近抽运光源时的荧光强度高;两种低浓度样品组合的荧光强度相对于其单片样品荧光强度的增幅比两种高浓度样品组合的荧光强度相对于其单片样品荧光强度的增幅要高.
关键词:
掺铒玻璃样品
级联
荧光光谱强度
半值宽度 相似文献
994.
A metastable supercooled homogeneous vortex liquid state exists down to zero fluctuation temperature in systems of mutually
repelling objects. The zero temperature liquid state therefore serves as a (pseudo) ‘fixed point’ controlling the properties
of vortex liquid below and even around the melting point. Based on this picture, a quantitative theory of vortex melting and
glass transition in Type II superconductors in the framework of Ginzburg-Landau approach is presented. The melting line location
is determined and magnetization and specific heat jumps are calculated. The point-like disorder shifts the line downwards
and joins the order-disorder transition line. On the other hand, the disorder induces irreversible effects via replica symmetry
breaking. The irreversibility line can be calculated within the Gaussian variational method. Therefore, the generic phase
diagram contains four phases divided by the irreversibility line and melting line: liquid, solid, vortex glass and Bragg glass.
We compare various experimental results with the theoretical formula. 相似文献
995.
M. Okamoto K. Nobuhara K. Fukushima A. Nakano M. Hayada S. Yoshimura 《Chromatographia》1987,23(5):325-327
Summary The liquid chromatographic determination of trimethadione (TMO) and its methabolite, dimethadione (DMO) were studied by high-performance
liquid chromatography (HPLC) on octadecyl-modified microporous glasses, prepared with toluene solution containing octadecyl-dimethylchlorosilane,
using two types of microporous glass with various mean pore diameters and/or specific surface areas. Using acetonitrile-water
mixtures as eluents, TMO and DMO in human serum were separated on the glasses studied, but with different degrees of resolution.
In this present study, we report the development of a rapid and selective HPLC method for the simultaneous analysis of TMO
and DMO in human serum. 相似文献
996.
《Surface and interface analysis : SIA》2004,36(9):1323-1329
Gas adsorption and atomic force microscopy have been used to quantify and compare the porosity, surface area and surface characteristics of five samples from Raqqa in northern Syria dating to ca. 8th century AD . High‐quality high‐pressure liquid chromatography (HPLC) glass was also analysed to compare the results with these characteristics of modern glass. All five ancient samples were found to have some porosity across the microporous (up to 2 nm) and the mesoporous (2–50 nm) range. The reasons for this porosity are not entirely clear at present but are likely to be due to the manufacturing methods used, including the raw materials. A correlation was found between glass chemical composition (especially the total alkali) and pore size, inferring that the melting temperature is one of the parameters that affects the development of pores. The work in this paper presents the preliminary findings from the study of porosity in ancient glass. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
997.
998.
Er3+-Yb3+共掺磷酸盐玻璃放大器的大信号增益与量子效率理论分析 总被引:2,自引:0,他引:2
研究大信号工作状态下的Er^3 -Yb^3 共掺磷酸盐玻璃波导放大器的增益与量子转换效率。从量子转换效率的定义出发,得出了增益、抽运光功率以及量子转换效率三者之间关系的解析表达式。通过数值求解大信号工作状态下的Er^3 -Yb^3 共掺系统的速率方程与光功率传输方程,讨论了Er^3 浓度、Yb^3 浓度、Yb^3 与Er^3 浓度比率、抽运光功率以及放大器长度等因素对量子转换效率的影响。结果表明提高Er^3 浓度与增加放大器长度均有助于提高量子转换效率,高Er^3 浓度掺杂需要相应的高Yb^3 浓度与之相匹配以减小由于高浓度Er^3 掺杂引起的上转换效应,Yb^3 浓度的提高将降低器件的量子转换效率,Yb^3 -Er^3 浓度之比取1~2较好。 相似文献
999.
R. Sridarane G. Raje D. Shanmukaraj B. J. Kalaiselvi M. Santhi S. Subramanian S. Mohan B. Palanivel R. Murugan 《Journal of Thermal Analysis and Calorimetry》2004,75(1):169-178
The understanding of molecular level structural information of phosphate glasses is very much essential. The unique microwave-absorbing ability of NaH2PO4·2H2O was found to be very useful for preparing crystal and glassy sodium super ionic conductors (Nasicon's) as a component of batch mixtures. In this work NaPO3 glass was prepared by both conventional melt quench and microwave heating from NaH2PO4·2H2O as a starting material. The structure of NaPO3 glass and their structural evolution upon heating through glass transition were probed by combination of complementary techniques like differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR) and thermo-Raman spectroscopy.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
1000.
V. Arrighi P. F. Holmes I. J. McEwen H. Qian N. J. Terrill 《Journal of Polymer Science.Polymer Physics》2004,42(21):4000-4016
The presence of a main‐chain correlation distance (dII) in the poly(di‐n‐alkyl itaconate)s was confirmed with small‐angle X‐ray scattering/wide‐angle X‐ray scattering measurements taken over the temperature range of 293–478 K. Data for a series of alkyl acrylate polymers were also obtained for comparison. The intensity of the itaconate dII peak was significant and indicated a greater level of nanophase formation than in analogous systems. In the lower members of the series, nanophase formation appeared to be further enhanced in the temperature range above the glass‐transition temperature (Tg). This was ascribed to the rapidly increasing main‐chain mobility in this region. Macroscopically phase‐separated itaconate blends displayed the individual dII nanospacings of each homopolymer component. Copolymers, on the other hand, showed more interesting behavior. Poly(methyl‐co‐di‐n‐butyl itaconate) followed an average behavior in which the dII spacing and Tg changed progressively with the comonomer content. In contrast, the side‐chain pairing in poly(methyl‐co‐di‐n‐octyl itaconate) generated dII spacings characteristic of separate methyl and octyl nanodomains. The observation of the dioctyl nanodomains, along with the dioctyl side‐chain lower Tg relaxation event, confirmed the concept of independent side‐chain‐domain relaxation in these polymers. The temperature behavior of the poly(methyl‐co‐di‐n‐octyl itaconate) small‐angle X‐ray scattering profiles and scattering correlation lengths indicated that the two nanodomains were not completely structurally independent. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4000–4016, 2004 相似文献