全文获取类型
收费全文 | 27948篇 |
免费 | 3137篇 |
国内免费 | 2188篇 |
专业分类
电工技术 | 1228篇 |
技术理论 | 3篇 |
综合类 | 4011篇 |
化学工业 | 4724篇 |
金属工艺 | 2421篇 |
机械仪表 | 1265篇 |
建筑科学 | 1791篇 |
矿业工程 | 983篇 |
能源动力 | 808篇 |
轻工业 | 1139篇 |
水利工程 | 622篇 |
石油天然气 | 1324篇 |
武器工业 | 222篇 |
无线电 | 1750篇 |
一般工业技术 | 3344篇 |
冶金工业 | 1581篇 |
原子能技术 | 346篇 |
自动化技术 | 5711篇 |
出版年
2024年 | 35篇 |
2023年 | 281篇 |
2022年 | 492篇 |
2021年 | 685篇 |
2020年 | 785篇 |
2019年 | 749篇 |
2018年 | 684篇 |
2017年 | 852篇 |
2016年 | 901篇 |
2015年 | 994篇 |
2014年 | 1511篇 |
2013年 | 1744篇 |
2012年 | 2037篇 |
2011年 | 2173篇 |
2010年 | 1636篇 |
2009年 | 1752篇 |
2008年 | 1713篇 |
2007年 | 2031篇 |
2006年 | 1916篇 |
2005年 | 1646篇 |
2004年 | 1381篇 |
2003年 | 1251篇 |
2002年 | 1019篇 |
2001年 | 805篇 |
2000年 | 691篇 |
1999年 | 553篇 |
1998年 | 408篇 |
1997年 | 382篇 |
1996年 | 354篇 |
1995年 | 328篇 |
1994年 | 320篇 |
1993年 | 223篇 |
1992年 | 196篇 |
1991年 | 166篇 |
1990年 | 136篇 |
1989年 | 109篇 |
1988年 | 86篇 |
1987年 | 45篇 |
1986年 | 26篇 |
1985年 | 26篇 |
1984年 | 24篇 |
1983年 | 18篇 |
1982年 | 29篇 |
1981年 | 17篇 |
1980年 | 17篇 |
1979年 | 17篇 |
1978年 | 4篇 |
1975年 | 3篇 |
1959年 | 5篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
《Geotextiles and Geomembranes》2022,50(5):1020-1035
This paper presents a numerical study on the load-bearing performance of reinforced slopes under footing load using a finite element limit analysis (FELA) method where a non-associated flow rule is assumed in the analysis. The method was validated against results from full-scale model tests and a limit equilibrium (LE) analytical method. A series of parametric analyses was subsequently carried out to examine the influences that the soil dilation angle, footing location, and reinforcement design (i.e. length, tensile strength, and vertical spacing) could have on the load-bearing performance of reinforced slopes. Results indicate that dilation angle has a significant influence on the predicted magnitudes of bearing capacity, slope deformation, and mobilized reinforcement load. The predicted values of bearing capacity using the FELA are smaller than those from the Meyerhof's analytical method for unreinforced semi-infinite foundation, especially for larger friction angle values. Additionally, the ultimate bearing capacity of the slope and its corresponding horizontal deformation increase with the reinforcement tensile strength. Finally, the slip planes under the applied footing load are found to be y-shaped and primarily occur in the upper half of the slope. 相似文献
104.
We propose a general n-fractal aperiodic zone plate generating a beam with the first-order foci with more chosen positions. The construction method of the general n-fractal aperiodic zone plate can apply to many aperiodic zone plates, e.g. fractal, Thue-Morse and Fibonacci zone plates, and the general n-fractal aperiodic zone plates can generate more adjustable first-order foci. Parameters of the n-fractal aperiodic zone plate such as the substitution rule and the fractal order are examined and found not to affect the fractal distribution of the first-order foci. The more adjustable first-order foci generated by the general n-fractal aperiodic zone plate have been verified with both simulations and experiments. 相似文献
105.
106.
The synergistic effects of using several supplementary cementitious materials (SCMs), such as Blast Furnace Slags plus Limestone Filler or Fly Ashes, depend on the OPC composition. When using an OPC which is poor in C3A and alkalis in ternary formulations, a similar initial strength gain to that of a plain OPC is detected and at longer hydration ages, the formation of monocarboaluminate, hemicarbonate and hydrotalcite instead of monosulphate can be seen. If an OPC with a higher C3A content and alkalis is used with SCMs, the higher availability of Al causes the early formation of monocarboaluminate and a lower initial strength gain. At longer hydration times, in ternary blends with both OPCs, the mechanical strengths are higher and the C-S-H gels formed are richer in Al and poorer in C/S ratio with a subsequent lowering of the alkali content in the pore solution when compared to that in plain OPC. 相似文献
107.
108.
S. Tosti A. Santucci A. Pietropaolo S. Brutti O. Palumbo F. Trequattrini A. Paolone 《International Journal of Hydrogen Energy》2018,43(5):2817-2822
An alloy with nominal composition V85Ni15 was prepared in a vacuum induction melting apparatus. The chemical analysis of the sample showed a V (Ni) content of 82.63 (15.68) at% and small contaminations by carbon and aluminum. XRD measurements confirmed that the bcc Ni-V solid solution phase is the main constituent of the sample. However, a minor impurity (approximately 6.5 wt%) due to the precipitation of the sigma NiV3-x phase is present in the sample.Hydrogen sorption measurements extending from 150 °C up to 400 °C in a wide pressure range (up to 90 bar) were performed. Upon hydrogenation below 250 °C, one observes the subsequent presence of an α phase and of two hydride phases with different values of dehydrogenation enthalpy: ΔHdehydr = 21 ± 1 kJ/mol for 0.15 ≤ H/M ≤ 0.30 and ΔHdehydr = 26 ± 2 kJ/mol for 0.53 ≤ H/M ≤ 0.59. Above 300 °C, there is no evidence of the formation of hydrides and only an α phase is present up to the maximum measured composition, with a hydrogenation enthalpy ΔHhydr = 10.0 ± 0.5 kJ/mol. 相似文献
109.
Pradum Pundlikrao Ige Rohit Ravindra Badgujar Pankaj Padmakar Nerkar Hitendra Shaligram Mahajan Raju Onkar Sonawane Sanjay Javarilal Surana 《Particulate Science and Technology》2018,36(5):583-591
Drug which shows extensive first pass effect is difficult task that, needs to be solved by formulators in the pharmaceutical science. The low oral bioavailability (49%) of flutamide may be due to poor wettability, low aqueous solubility and extensive first pass effect. The aim of present investigation was to prepare flutamide loaded microspheres and incorporate it into suppositories for rectal delivery to avoid first pass effect and enhance residence time. Flutamide loaded mucoadhesive microspheres of Ocimum Basilicum mucilage (OBM) were prepared using spray drying and characterized by percent production yield, encapsulation efficiency, particle size, zeta potential, polydispersity index, DSC, SEM, XRPD, in vitro drug release and stability studies. Moreover, ex vivo mucoadhesion was investigated using falling liquid film technique to determine the adhesion of microspheres to sheep rectal mucosa. The microspheres had nearly spherical shape and size about 2.53?μm. The encapsulation efficiency and mucoadhesion of optimized formulation MBF10 were found to be 69.6?±?2.3% and 89.01?±?2.18%, respectively. Percent CDR of optimized flutamide loaded mucoadhesive microspheres was found to be 88.7?±?1.3 at 7?h. In conclusion, OBM microparticles based suppository could be used to deliver drug through rectal delivery. 相似文献
110.
采用伪布尔模型和启发式算法来求解无容量设施选址问题。首先给出了问题的伪布尔(pseudo-Boolean)表示,然后基于Khumawala规则对问题进行预处理,最后提出两种启发式分支准则来求解问题。实验结果表明所提算法简单有效。 相似文献