全文获取类型
收费全文 | 32169篇 |
免费 | 4162篇 |
国内免费 | 2277篇 |
专业分类
电工技术 | 563篇 |
综合类 | 1777篇 |
化学工业 | 2907篇 |
金属工艺 | 4661篇 |
机械仪表 | 2973篇 |
建筑科学 | 294篇 |
矿业工程 | 343篇 |
能源动力 | 412篇 |
轻工业 | 768篇 |
水利工程 | 124篇 |
石油天然气 | 206篇 |
武器工业 | 469篇 |
无线电 | 15686篇 |
一般工业技术 | 5293篇 |
冶金工业 | 624篇 |
原子能技术 | 454篇 |
自动化技术 | 1054篇 |
出版年
2024年 | 225篇 |
2023年 | 722篇 |
2022年 | 867篇 |
2021年 | 1086篇 |
2020年 | 1070篇 |
2019年 | 940篇 |
2018年 | 892篇 |
2017年 | 1181篇 |
2016年 | 1158篇 |
2015年 | 1207篇 |
2014年 | 1637篇 |
2013年 | 1733篇 |
2012年 | 2080篇 |
2011年 | 2108篇 |
2010年 | 1548篇 |
2009年 | 1595篇 |
2008年 | 1800篇 |
2007年 | 2127篇 |
2006年 | 1982篇 |
2005年 | 1709篇 |
2004年 | 1600篇 |
2003年 | 1352篇 |
2002年 | 1178篇 |
2001年 | 1095篇 |
2000年 | 880篇 |
1999年 | 752篇 |
1998年 | 619篇 |
1997年 | 578篇 |
1996年 | 538篇 |
1995年 | 463篇 |
1994年 | 461篇 |
1993年 | 396篇 |
1992年 | 316篇 |
1991年 | 268篇 |
1990年 | 191篇 |
1989年 | 89篇 |
1988年 | 62篇 |
1987年 | 16篇 |
1986年 | 13篇 |
1985年 | 12篇 |
1984年 | 19篇 |
1983年 | 3篇 |
1982年 | 11篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1959年 | 3篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
It is essential to automate the scanning path generation process to effectively implement the micro-stereolithography. However, a scanning path that is generated based only on a 3D CAD model introduces dimensional inaccuracies. In micro-stereolithography, the photopolymer solidification is affected by fabrication conditions, such as the optical properties (laser power, laser scanning speed, laser scanning pitch focusing condition, etc.) and material properties of the photopolymer. Thus, the photopolymer solidification phenomena must be considered when generating a laser scanning path. In this paper, a scanning path generation algorithm that uses 3D CAD data and considers the photopolymer solidification phenomena is proposed to improve the dimensional accuracy in micro-stereolithography. Multi-line photopolymer solidification experiments were performed for various laser scanning conditions to examine the photopolymer solidification phenomena. From these experiments, linear relations between the solidification length (width) and scanning length (width) were acquired and stored in a database. Subsequently, these data were utilized to compensate the scanning path of the laser beam. In addition, experiments for determining the layer thickness in the z-direction were performed and these results were also used in the scanning path generation algorithm.This research was supported by the Highly Advanced National Project (http://www.most.go.kr), which performs some of the National R&D Program, and sponsored by the Korean Ministry of Science and Technology under the contract project code M10214000116-02B1500-02010. 相似文献
122.
123.
1 Introduction For increasing the output energy of laser, the pumping power must be enhanced. But the cooperative effect will arise and cause spontaneous radiation light in laser medium sample when the pumping power is high e- nough without the resonator. The spontaneous radiation light is coherent light between laser and fluorescent. It will compete the upper energy level population with ex- cited radiation, and the loss increase. In solid laser medium, such as Nd∶YAG, the Nd ion densityi… 相似文献
124.
研究了铸造WCP/Ni基合金梯度复合涂层组织与摩擦磨损特性。结果表明,梯度复合涂层与基材实现了良好的冶金结合,涂层内有γ-Ni枝晶组织,γ-Ni+M23C 6共晶组织以及凝固结晶析出的M6C、M23C6、M7C3等块状或条状组织;随着铸造WCP体积分数的增加,复合涂层摩擦系数减小,耐磨性增加。19-4试样的耐磨性最高值为4.61,是基材的3倍以上。梯度涂层的磨损机理为磨粒磨损与粘着磨损的复合作用。 相似文献
125.
A. Simon Z. Kntor 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2002,190(1-4):351-356
The formation and deposition of particulates by pulsed laser deposition of Si1−xGex semiconductor alloy thin films are discussed. Using Rutherford backscattering spectrometry with micrometer lateral resolution (micro-RBS) the film composition was measured with high accuracy, even in the presence of particulates with a high areal density of 20,000–30,000 particulates per mm2. We show that on impact of a particulate, the part of the thin film which is already deposited probably melts and its Ge content segregates to the surface. 相似文献
126.
以Bi(NO3)3·5H2O和Ti(OC4H9)4为原料,NaOH为矿化剂,采用水热法制备了形貌规则的单晶Bi4Ti3O12纳米片。X射线衍射(XRD)结果表明,所合成的产物为正交相层状钙钛矿结构的Bi4Ti3O12。场发射扫描电子显微镜(FESEM)研究显示:样品是由大量边缘尺寸接近200nm,厚度约为15nm的片状结构组成。利用X射线光电子能谱(XPS)研究产物的化学组分和价态分布。室温拉曼光谱研究表明,Bi4Ti3O12纳米片的声子寿命和热稳定性低于相应的块体材料。 相似文献
127.
128.
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
129.
NiTi形状记忆合金激光气体氮化层表面特征 总被引:2,自引:0,他引:2
为改善NiTi合金的表面性能,利用2kW连续波Nd:YAG对NiTi合金进行激光气体氮化处理。采用SEM、TEM、XRD、XPS和纳米压痕研究了氮化层的显微组织及表面特征.结果表明:激光气体氮化可以在NiTi合金表面制备连续、无裂纹、厚度为2μm的TiN表面层,该表面层中基本不合有Ni元素且具有很高的硬度,其纳米压痕硬度为29.28GPa. 相似文献
130.
Heat transfer characteristics of a swirling impinging jet have been experimentally examined using a combined particle image velocimetry (PIV) and laser‐induced fluorescence (LIF) technique for simultaneous measurement of velocity and temperature fields. The present study shows that the radial width of the jet stretches with increasing swirl intensity, and that the stretching phenomenon contributes to the maximum local heat transfer coefficient. At the stagnation region, the flow near the heated surface is mixed intermittently by reverse flows toward upstream, and spatial distributions of temperature are correlated with instantaneous velocity vector maps. The dynamic behavior of recirculation zones, attributed to swirl number Sw and impinging distance, mainly determines the turbulent heat transfer at the stagnation region. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(8): 663–673, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10120 相似文献