全文获取类型
收费全文 | 8671篇 |
免费 | 923篇 |
国内免费 | 569篇 |
专业分类
电工技术 | 208篇 |
综合类 | 661篇 |
化学工业 | 396篇 |
金属工艺 | 1062篇 |
机械仪表 | 1475篇 |
建筑科学 | 932篇 |
矿业工程 | 607篇 |
能源动力 | 203篇 |
轻工业 | 169篇 |
水利工程 | 660篇 |
石油天然气 | 790篇 |
武器工业 | 122篇 |
无线电 | 687篇 |
一般工业技术 | 675篇 |
冶金工业 | 286篇 |
原子能技术 | 85篇 |
自动化技术 | 1145篇 |
出版年
2024年 | 25篇 |
2023年 | 129篇 |
2022年 | 291篇 |
2021年 | 300篇 |
2020年 | 321篇 |
2019年 | 301篇 |
2018年 | 262篇 |
2017年 | 342篇 |
2016年 | 357篇 |
2015年 | 388篇 |
2014年 | 530篇 |
2013年 | 526篇 |
2012年 | 603篇 |
2011年 | 649篇 |
2010年 | 410篇 |
2009年 | 417篇 |
2008年 | 403篇 |
2007年 | 541篇 |
2006年 | 496篇 |
2005年 | 429篇 |
2004年 | 380篇 |
2003年 | 343篇 |
2002年 | 299篇 |
2001年 | 262篇 |
2000年 | 204篇 |
1999年 | 182篇 |
1998年 | 152篇 |
1997年 | 112篇 |
1996年 | 97篇 |
1995年 | 102篇 |
1994年 | 74篇 |
1993年 | 55篇 |
1992年 | 34篇 |
1991年 | 32篇 |
1990年 | 23篇 |
1989年 | 23篇 |
1988年 | 16篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1964年 | 3篇 |
1963年 | 2篇 |
1962年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
K. Natesan 《Oxidation of Metals》1988,30(1-2):53-83
Oxidation-sulfidation studies were conducted on sheet samples of nickel aluminide, containing 23.5 at. % Al, 0.5 at. % Hf, and 0.2 at. % B in an annealed condition and after preoxidation treatments. Continuous weight-change measurements were made by a thermogravimetric technique in exposure atmospheres of air, a low-
gas mixture, and low-
gas mixtures with several levels of sulfur. Detailed scanning electron microscopy (SEM), X-ray, and electron microprobe analyses of the corrosion product scale layers were performed. The air-exposed specimens developed predominantly nickel oxide; the specimen exposed to a low-
. 相似文献
122.
The oxidation behavior of a normalized 2.25Cr-1Mo steel tempered previously for 10 hr at different temperatures between 873 and 1023 K has been studied up to a maximum duration of 1000 hr in air at 773–973 K. The oxidation resistance of the steel was found to decrease significantly with the temperature of tempering. Tempering of this steel is reported to cause microstructural changes involving precipitation of Cr as carbides and a decrease in the effective (free) Cr contents, that could influence the oxidation resistance of the Cr-containing alloys. Relative compositions across the thickness of the oxide scales, as analyzed by SEM/EDX and SIMS, suggest that a less Cr-rich (and less protective) and thicker scale on the steel formed because previous tempering caused extensive depletion of free Cr. 相似文献
123.
124.
Thin-skin analysis technique for interaction of arbitrary-shape inducer field with long cracks in ferromagnetic metals 总被引:7,自引:2,他引:7
In using the AC field measurement (ACFM) technique for non-destructive evaluation (NDE) of metals, a current-carrying wire structure is used to induce eddy current within a thin layer of the metal and a magnetic field sensor to measure the field perturbations in the vicinity of the metal. The sensitivity of ACFM crack detection and sizing relies on an appropriate design of the wire structure geometry together with a dully placement of the sensor. This paper presents an analytical modeling technique for evaluating the electromagnetic field interaction of an ACFM probe with a long uniform crack in a ferromagnetic metallic slab. The probe in the proposed model can have an arbitrary-shape wire inducer with no restrictions on its relative sensor position. The technique is accurate and very efficient computationally. It first uses the two-dimensional Fourier transform to obtain the field distribution at the metal surface. The Laplacian field distribution above the metal is then determined by satisfying the so-obtained boundary condition at air–metal interface. To demonstrate the accuracy of the model, we consider the special case of a rhombic wire inducer. The comparison of our results with those obtained using the conventional algorithm in the literature validates the accuracy of the model introduced in this paper. To show the generality of the model, we also present theoretical and experimental results associated with a solenoid inducer with a three-dimensional geometry for which no analytical solution is available in the literature. The theoretical prediction of crack signal supported by experimental results is used to develop a model-based method for inverting crack signal into crack depth. 相似文献
125.
不对称拉延零件的加工,从工艺上考虑,应将其设计成能成对地进行拉延加工的对称结构,经过剖切保证产品最终尺寸要求。本文通过实例说明了确定不对称拉延零件合理工艺方案的重要性,同时介绍了模具结构特点及工作过程。 相似文献
126.
Significant progress has already been achieved in green manufacturing including dry and hard, often high-speed, machining technologies. For instance, the demand for higher productivity has resulted in the wider application of ceramic and PCBN tools with special multi-radii (wiper) geometry. This paper reports some important characteristics of the surface roughness produced in the turning of a hardened low-chromium alloy steel using mixed alumina–titanium carbon (TiC) ceramic cutting tools equipped with both conventional and wiper inserts. The characteristic geometrical features of surfaces obtained in both these turning operations have been assessed by means of representative two-dimensional (2D) surface roughness parameters, and some 3D visualizations, which allowed more complete characterization of the surface topography and prediction of its service properties. Results show that keeping equivalent feed rates, i.e. 0.1 mm/rev for conventional and 0.2 mm/rev for wiper tools, the surfaces obtained have similar 3D height roughness parameters, and comparable values of skew and kurtosis. At defined cutting parameters, surfaces produced by wiper tools contain blunt peaks with distinctly smaller slopes resulting in better bearing properties. Only marginal changes of Ra parameter were recorded during 15 min machining trials. 相似文献
127.
128.
采用正交试验研究了高速铣削钛合金TC4粗加工阶段时切削参数对切削力的影响规律,并以Y向切削力最小和材料去除率最大为优化目标,利用MATLAB基于Pareto遗传算法优化高速铣削TC4的切削参数,结合Pareto最前沿给出了优化后的切削参数最优解集。 相似文献
129.
硬质合金磨削温度的实验研究 总被引:3,自引:0,他引:3
采用半人工和人工热电偶法,对硬质合金YG6和YT30平面磨削的磨削温度进行了实验研究。并对磨削参数与磨削温度的关系,进行了理论分析及实验验证。结果表明:磨削深度和工作台速度增加,磨削温度升高,但工作台速度的改变,对磨削温度的影响较小. 相似文献
130.
Simplified and efficient calibration of a mechanistic cutting force model for ball-end milling 总被引:3,自引:3,他引:3
Abdullahil Azeem Hsi-Yung Feng Lihui Wang 《International Journal of Machine Tools and Manufacture》2004,44(2-3):291-298
Accurate evaluation of the empirical coefficients of a mechanistic cutting force model is critical to the reliability of the predicted cutting forces. This paper presents a simplified and efficient method to determine the cutting force coefficients of a ball-end milling model. The unique feature of this new method is that only a single half-slot cut is to be performed to calibrate the empirical force coefficients that are valid over a wide range of cutting conditions. The instantaneous cutting forces are used with the established helical cutting edge profile on the ball-end mill. The half-slot calibration cut enables successive determination of the lumped discrete values of the varying cutting mechanics parameters along the cutter axis whereas the size effect parameters are determined from the known variation of undeformed chip thickness with cutter rotation. The effectiveness of the present method in determining the cutting force coefficients has been demonstrated experimentally with a series of verification test cuts. 相似文献