全文获取类型
收费全文 | 24894篇 |
免费 | 2878篇 |
国内免费 | 1339篇 |
专业分类
电工技术 | 8145篇 |
综合类 | 2354篇 |
化学工业 | 1151篇 |
金属工艺 | 1203篇 |
机械仪表 | 2104篇 |
建筑科学 | 1867篇 |
矿业工程 | 767篇 |
能源动力 | 644篇 |
轻工业 | 663篇 |
水利工程 | 746篇 |
石油天然气 | 795篇 |
武器工业 | 254篇 |
无线电 | 2710篇 |
一般工业技术 | 1507篇 |
冶金工业 | 947篇 |
原子能技术 | 231篇 |
自动化技术 | 3023篇 |
出版年
2024年 | 93篇 |
2023年 | 243篇 |
2022年 | 501篇 |
2021年 | 623篇 |
2020年 | 712篇 |
2019年 | 515篇 |
2018年 | 536篇 |
2017年 | 670篇 |
2016年 | 703篇 |
2015年 | 939篇 |
2014年 | 1684篇 |
2013年 | 1441篇 |
2012年 | 1988篇 |
2011年 | 2044篇 |
2010年 | 1597篇 |
2009年 | 1629篇 |
2008年 | 1559篇 |
2007年 | 1798篇 |
2006年 | 1547篇 |
2005年 | 1353篇 |
2004年 | 1100篇 |
2003年 | 1039篇 |
2002年 | 849篇 |
2001年 | 809篇 |
2000年 | 614篇 |
1999年 | 573篇 |
1998年 | 394篇 |
1997年 | 326篇 |
1996年 | 286篇 |
1995年 | 215篇 |
1994年 | 153篇 |
1993年 | 124篇 |
1992年 | 105篇 |
1991年 | 79篇 |
1990年 | 62篇 |
1989年 | 58篇 |
1988年 | 44篇 |
1987年 | 19篇 |
1986年 | 24篇 |
1985年 | 20篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1975年 | 2篇 |
1963年 | 2篇 |
1959年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
21.
R. T. DeHoff 《Journal of microscopy》1985,138(2):143-151
Elements of surfaces that bound a phase (β) in a two phase mixture (α+β) may be classified as: (a) convex (++) if both principal curvatures are positive; (b) concave (? ?) if both are negative; and (c) saddle (+ ?) if one is positive and the other negative. This classification excludes the limiting cases for which one or both of the principal curvatures is zero. The traces of these surfaces that form the boundaries of the β areas on a representative two dimensional section may also be: (a) convex (+) if the local curvature is positive; or (b) concave (?) if it is negative. Line intercepts may be tabulated separately for intersections with convex (+) and concave (?) segments of boundary. This paper presents a derivation of fundamental stereological formulae that relate these counting measurements to three-dimensional geometric properties of the structure they sample. 相似文献
22.
介绍了隔河岩电厂220kV线路保护的原理设计及运行情况,以及采用了双重微机化继电保护装置后带来的优越性,简要描述了CSL-101A高频保护和RCS-931A光纤保护的应用特点。 相似文献
23.
本文针对安钢高炉冷却壁破损的形式、原因进行研究分析,探讨了冷却壁的结构、材质、加工与安装工艺对其寿命的影响。介绍了安钢高炉炉役后期冷却壁的维护生产实践。 相似文献
24.
Herbert S. Bennett 《Journal of research of the National Institute of Standards and Technology》2007,112(4):209-221
In this paper, we present the theory for calculating Raman line shapes as functions of the Fermi energy and finite temperatures in zinc blende, n-type GaAs for donor densities between 1016 cm−3 and 1019 cm−3. Compared to other theories, this theory is unique in two respects: 1) the many-body effects are treated self-consistently and 2) the theory is valid at room temperature for arbitrary values of the ratio R = (Q2/α), where Q is the magnitude of the normalized wave vector and α is the normalized frequency used in the Raman measurements. These calculations solve the charge neutrality equation self-consistently for a two-band model of GaAs at 300 K that includes the effects of high carrier concentrations and dopant densities on the perturbed densities of states used to calculate the Fermi energy as a function of temperature. The results are then applied to obtain the carrier concentrations from Fermi energies in the context of line shapes in Raman spectra due to the coupling between longitudinal optical phonons and plasmons. Raman measurements have been proposed as a non-destructive method for wafer acceptance tests of carrier density in semiconductor epilayers. The interpretation of Raman spectra to determine the majority electron density in n-type semiconductors requires an interdisciplinary effort involving experiments, theory, and computer-based simulations and visualizations of the theoretical calculations. 相似文献
25.
The introduction of multiple, independent production lines has helped many firms to increase their production flexibility, provide for redundancy when equipment breaks down, reduce idle time and labor costs, and achieve many other benefits. This paper introduces and formalizes the multiple U-line balancing problem. Optimal solution methodologies are provided for Type I (minimize the number of stations for a given cycle time), Type II (minimize the cycle time for a given number of stations), and cost-minimization line-balancing problems. A branch-and-bound algorithm is also developed for the situation in which equipment requirements are dependent on the line configuration and the task assignment to stations. Computational results indicate that the greatest benefit of exploiting multiple lines occurs for smaller cycle-time problems that require higher output. 相似文献
26.
27.
To find the exact probability distribution of the global maximum or minimum of a random field within a bounded domain is a pending problem even for Gaussian fields. Except for very special examples of fields, recourse must be taken to approximate reasoning or asymptotic considerations to be judged with respect to accuracy by simulations. In this paper, the problem is addressed through a functional equation that leads to the definition of a class of distribution functions that depend solely on process or field characteristics and domain quantities that can be calculated explicitly. This distribution function class is studied for Gaussian processes in earlier works by the author and it has been obtained explicitly for Gaussian fields on rectangular domains in the plane. Simulation studies show that rather good predictions are obtained for sufficiently smooth wide band Gaussian processes and fields. In this paper, the distribution function is obtained in general for Gaussian fields over arbitrary bounded domains with piecewise continuous and differentiable boundaries, and as in earlier works the distribution function is tested against empirical distribution functions obtained by simulation of sample functions of a smooth approximately Gaussian field, herein called a broken line Hino field. For completeness this particular field type is defined in appendix a and appendix b. The paper concludes with a statistical application on data for plain concrete tensile strength. 相似文献
28.
本文介绍核孔膜生产线,重点描述了膜微孔制备工艺的实验研究。对于PC和PES膜,已得到32种工况下的扩孔公式,其形式为D=A+Bt,其中D——孔径,t——扩孔时间,A,B为特定工艺参数下的常数值.通过实验。得到了膜孔密度N与300~#核反应堆功率P、热柱辐照位置L的经验公式,即N=6.97×10~5×10~3×101~(1.18L).在本生产线上可生产最大幅面为3 140mm×240mm,孔径为0.04~10 μm的多系列多规格的核孔膜产品。 相似文献
29.
在宝钢2030mm冷轧厂酸洗机组中,为了满足厚规格IF钢的生产,拟将原有的气动式剪切机改成液压式剪切机。为此,设计了一套中高压大流量的液压系统以满足3号横剪大剪切力(最高达700kN)和快速剪切(3秒/次)的需要。由于采用了蓄能器增速回路和二通插装阀控制技术,使该液压系统较传统的剪切机液压系统具有响应速度快、体积小、重量轻、发热少和降低电机能耗等优点。 相似文献
30.
通过校核Φ76mm自动轧管机组穿孔机顶杆小车的轴承寿命,提出了顶杆小车的改进措施,如重新选配合适的轴承型号,修改有关装配尺寸等。改进后,顶杆小车的使用效果良好。 相似文献