全文获取类型
收费全文 | 22845篇 |
免费 | 3027篇 |
国内免费 | 1280篇 |
专业分类
化学 | 5069篇 |
晶体学 | 282篇 |
力学 | 4089篇 |
综合类 | 238篇 |
数学 | 8144篇 |
物理学 | 9330篇 |
出版年
2024年 | 36篇 |
2023年 | 191篇 |
2022年 | 405篇 |
2021年 | 476篇 |
2020年 | 623篇 |
2019年 | 545篇 |
2018年 | 509篇 |
2017年 | 649篇 |
2016年 | 667篇 |
2015年 | 557篇 |
2014年 | 859篇 |
2013年 | 1872篇 |
2012年 | 1080篇 |
2011年 | 1207篇 |
2010年 | 992篇 |
2009年 | 1184篇 |
2008年 | 1252篇 |
2007年 | 1416篇 |
2006年 | 1287篇 |
2005年 | 1253篇 |
2004年 | 1163篇 |
2003年 | 1145篇 |
2002年 | 980篇 |
2001年 | 855篇 |
2000年 | 824篇 |
1999年 | 704篇 |
1998年 | 627篇 |
1997年 | 596篇 |
1996年 | 408篇 |
1995年 | 364篇 |
1994年 | 313篇 |
1993年 | 286篇 |
1992年 | 258篇 |
1991年 | 201篇 |
1990年 | 165篇 |
1989年 | 102篇 |
1988年 | 120篇 |
1987年 | 105篇 |
1986年 | 101篇 |
1985年 | 137篇 |
1984年 | 102篇 |
1983年 | 53篇 |
1982年 | 89篇 |
1981年 | 72篇 |
1980年 | 51篇 |
1979年 | 57篇 |
1978年 | 63篇 |
1977年 | 46篇 |
1976年 | 33篇 |
1973年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Atopic dermatitis is characterized by leukocyte migration into the skin dermis and typically driven by excessive chemokine production at the site of inflammation. Conventional topical formulations such as gels, creams, and ointments are insufficient for this treatment because of low penetration of drug molecules into the targeted skin tissues. Herein, using a simple, green, sustainable strategy, we have developed novel primary zein nanoparticles embedded in curcumin (Cur) and coated with silk sericin (ZHSCs) for the topical delivery of Cur to penetrate into the dermis and exercise anti-dermatitis effects on the lesion with minimal side-effects. Transdermal delivery experiments and porcine skin fluorescence imaging indicated that ZHSCs facilitate the penetration of Cur across the epidermis layer of skin to reach deep-seated sites. Notably, ZHSCs = 1:0.25 (zein-to-silk sericin mass ratios of 1:0.25) markedly elevated the skin permeability and cumulative turnover of Cur transferred, which were provided a greater than a 3.8-fold increase relative to free Cur. The special nanoparticles of ZHS = 1:0.25 possessed the deepest localization depth and experience a transition of the particle structure and core-shell separation after penetrating into the dermis of skin. In a cell model of dermatitis induced by tumor necrosis factor α/interferon γ co-stimulation, compared with free Cur, Cur-loaded ZHS nanoparticles down-regulated the generation of inflammatory cytokines and chemokines in keratinocytes through suppression of the nuclear translocation of NF-κBp65 and hence exerted an anti-dermatitis effect. This strategy may provide new avenues and direction for the demanding issues of valid topical delivery systems. 相似文献
993.
This paper uses heat transfer experiments and computational fluid dynamics (CFD) simulations to investigate the conjugate heat transfer (CHT) in a high-pressure pneumatic control valve assembly. A heat transfer test rig was constructed, and time–temperature histories of five test points placed on the valve assembly’s outer surface were recorded for study validation. The Unsteady Reynolds-Averaged Navier–Stokes (URANS) CFD methods with the standard k-ε turbulence closure equations were adopted in the numerical computations. Polyhedral grids were used; time step and mesh convergence studies were conducted. Simulated and measured temperatures profile comparisons revealed a good agreement. The CHT results obtained from CFD showed huge velocity fields downstream of the valve throat and the vent hole. The airflow through the valve was icy, mainly in the supersonic flow areas. Low temperatures below 273.15 K were recorded on the internal and external walls of the valve assembly. The consistency of the measured data with the numerical results demonstrates the effectiveness of polyhedral grids in exploring the CHT using CFD methods. The local entropy production rate analysis revealed that irreversibility is mainly due to viscous dissipation. The current CHT investigation provides a potential basis for thermostress analysis and optimization. 相似文献
994.
995.
The reaction of W(CO)6 with pyOSNa (C5-H4NOSNa) and Et4NCl in MeCN affords a new tungsten(0) complex [Et4N][W(pyS)(CO)4] 1 (Mr.= 536.29).The crystal and molecular structures have been determined by X-ray single-crystal diffraction.Complex 1 crystallizes in the orthorhombic system,space group P212121 with a = 8.2429(5),b = 9.1045(4),c =26.8851(14) (A),β = 90.00°,V= 2017.66(18) (A)3,Z = 4,Dc.= 1.765 g/cm3,μ = 58.51 cm-1,F(000) =1048,the final R = 0.0204 and wR = 0.0400 for 4432 observed reflections with I > 2σ(I).X-ray structure analysis revealed that the molecule is acentric and has large first-order hyperpolarizability (7.2 × 10-30 esu),so it could be an IR second-order nonlinear optical candidate material. 相似文献
996.
WU Xiu-Lan WANG Fen REN Qiang 《结构化学》2007,26(6):732-736
Homogeneous cordierite has been synthesized at low cost by talc-magnesite and coal gangue as the main raw materials. The mechanism of synthesizing cordierite under such a com- posing system of raw materials, and the effect of temperature on the crystal cell parameters and microstructure and thermal expansion coefficient of cordierite crystal have been studied via testing methods of XRD, SEM, etc. The result shows that the homogeneous cordierite can be synthesized by the systematic composing materials of “talc-magnesite—coal gangue—talc” with heat pre- servation at 1350 ℃ for 1 h; as the keeping time is prolonged, Al3+ and Mg2+ in cordierite crystal are replaced by a few impurity ions such as Fe3+, Fe2+, etc., and the crystal cell parameters of cordierite present an increase trend; as the high-temperature heat preservation is prolonged, the content of glassy phase in the sample is increased, its density is improved, and its thermal expansion coeffi- cient presents an increase trend. 相似文献
997.
998.
999.
Xi-yan Liu Dong Qiu Mei-li Guo Zhen-zhong Yang 《高分子科学》2005,(5):561-566
Sub-micron sized phenolic epoxy resin waterborne particles were prepared by phase inversion emulsification. Micro-phase separation occurred during the curing process at high temperature. The as-prepared samples possessed one glass transition temperature (Tg) and two exothermal processes during DSC heating scannings. After being thermally treated above the exothermal peak temperature, they possessed two glass transition temperatures with the disappearance of exothermal peaks, whilst a core/shell structure was formed. This was likely related with the outward diffusion of reactive oligomers to the outer layer of particles. 相似文献
1000.
《Surface and interface analysis : SIA》2005,37(1):33-41
A new application of infrared ellipsometry is reported. Specifically, the interdiffusion between thin films of miscible polymers—poly(methyl methacrylate) and poly(vinylidene fluoride)—is detected in a non‐invasive measurement. A novel technique of data analysis for interdiffusion was developed and is described. The validity of the approach is supported by simulations of diffusion in a bilayer. The onset of extensive interdiffusion over a time period of 15 min occurs at a temperature of 160 °C. At a temperature of 190 °C, the data show that complete mixing of a bilayer (850 nm thick) occurs within 30 s, which is consistent with previously reported values of the mutual diffusion coefficient. Infrared ellipsometry is non‐invasive, applicable at elevated temperatures and relatively fast and sensitive. Although, in these measurements, it was unable to determine a concentration profile at the interface, infrared ellipsometry was used successfully to detect when interdiffusion had occurred. Hence, it is a useful means for screening polymer pairs for miscibility. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献