全文获取类型
收费全文 | 30322篇 |
免费 | 3526篇 |
国内免费 | 2340篇 |
专业分类
电工技术 | 1547篇 |
综合类 | 2135篇 |
化学工业 | 5612篇 |
金属工艺 | 744篇 |
机械仪表 | 2363篇 |
建筑科学 | 346篇 |
矿业工程 | 220篇 |
能源动力 | 400篇 |
轻工业 | 1369篇 |
水利工程 | 130篇 |
石油天然气 | 698篇 |
武器工业 | 262篇 |
无线电 | 12815篇 |
一般工业技术 | 4607篇 |
冶金工业 | 446篇 |
原子能技术 | 283篇 |
自动化技术 | 2211篇 |
出版年
2024年 | 143篇 |
2023年 | 466篇 |
2022年 | 650篇 |
2021年 | 808篇 |
2020年 | 960篇 |
2019年 | 794篇 |
2018年 | 813篇 |
2017年 | 1126篇 |
2016年 | 1249篇 |
2015年 | 1489篇 |
2014年 | 1883篇 |
2013年 | 2114篇 |
2012年 | 2212篇 |
2011年 | 2162篇 |
2010年 | 1532篇 |
2009年 | 1621篇 |
2008年 | 1562篇 |
2007年 | 1985篇 |
2006年 | 1844篇 |
2005年 | 1675篇 |
2004年 | 1327篇 |
2003年 | 1322篇 |
2002年 | 994篇 |
2001年 | 1050篇 |
2000年 | 860篇 |
1999年 | 605篇 |
1998年 | 487篇 |
1997年 | 419篇 |
1996年 | 378篇 |
1995年 | 276篇 |
1994年 | 261篇 |
1993年 | 240篇 |
1992年 | 204篇 |
1991年 | 169篇 |
1990年 | 141篇 |
1989年 | 107篇 |
1988年 | 46篇 |
1987年 | 28篇 |
1986年 | 23篇 |
1985年 | 41篇 |
1984年 | 29篇 |
1983年 | 20篇 |
1982年 | 17篇 |
1981年 | 13篇 |
1980年 | 13篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Thermal Characterization of 1.3 μm InAsP/InGaAsP Ridge Waveguide MQW Lasers Based on Spectroscopy Method 总被引:1,自引:1,他引:0
An experimental way to analyze the thermal characterization of semiconductor lasers based on spectroscopy method under pulse driving conditions has been developed. By using this way the thermal characteristics of strain compensated 1.3 μm InAsP/InGaAsP ridge waveguide MQW laser diodes have been investigated. Results show that by measuring and analyzing the lasing spectra under appropriate driving parameters and temperature ranges, the thermal resistance of the laser diodes could be deduced easily. A higher thermal resistance of 640 K/W has been measured on a narrow ridge laser chip without soldering. Other thermal and spectral properties of the lasers have also been measured and discussed. 相似文献
52.
本文研究了采用锁定放大相干检测技术的等离子体光发射谱检测系统。用该系统检测了仅用CF4作为刻蚀气体刻蚀非晶硅基薄膜的等离子体光发射谱。分析了检测结果和刻蚀机理。 相似文献
53.
Keizo Uematsu Masayori Miyashita Jin-Young Kim Zenji Kato Nozomu Uchida 《Journal of the American Ceramic Society》1991,74(9):2170-2174
Green bodies prepared by compaction of alumina granules were made transparent by an immersion liquid technique, and the internal structure was characterized with an optical microscope to study the effect of forming pressure on the internal structure. Clear images obtained by the technique provide more detailed information than other existing methods for structures ranging from one to tens of micrometers. Intergranular pores were present between unfractured granules. Their sizes and concentration tended to decrease with increasing forming pressure. However, pores were clearly present even in the green body prepared at 600 MPa. A rod- and needlelike feature was also found and was concluded to correspond to a high-density region. The significance of large pores and high-density regions on processing as well as the details of the technique is discussed. 相似文献
54.
A new principle and arrangement for directly determining the angle of incidence of an optical beam on an object are proposed and demonstrated. The novelty of the approach lies in the realization of a ‘smart object’, which extracts a portion of the incident beam's power into an optical waveguide attached to the object's surface or embedded in its body for converting the angle of incidence into the position of a guided beam with finite lateral extent. This ‘integrated optical light pointer’ beam is accomplished by means of creating additional degrees of freedom on the target in two different ways. While a first type is based on introducing spatial variations of the waveguide thickness, a second type makes use of a chirp of the grating periodicity. The feasibility for practical applications has been experimentally demonstrated by a direct comparison with a commercial high-resolution encoder, resulting in an r.m.s. error of <30′'. Measurements have been performed for chips fabricated based on replicated polycarbonate substrates and with no external optics, showing the great potential of this approach for realizing low-cost yet high-performance miniature goniometers. 相似文献
55.
周海光 《红外与毫米波学报》2002,21(Z1):112-114
对布满液晶微粒的聚合物(PDLC)进行了简并四波混频及光学双稳态的研究,并在文中对相关的PDLC中的分子重取向和热效应的非线性光学效应进行了讨论. 相似文献
56.
聚苯硫醚酰胺的合成与表征 总被引:7,自引:1,他引:6
用4-氯苯甲酰4′-氯苯胺和硫化钠为原料在常压下合成了聚苯硫醚酰胺,并对其进行了表征。结果表明所合成的产物为结晶性聚合物,并且有较高的热稳定性。 相似文献
57.
Optical measurements of thermal diffusivity of a material 总被引:2,自引:0,他引:2
The measurement of thermal diffusivity of a material (in particular, a thin film) is important for various reasons, e.g., to predict the heat transfer in the solid subjected to a thermal process, to monitor surface composition or morphology, or to detect invisible subsurface defects like delaminations. This measurement can be done in a noncontact manner using various photothermal methods. Such methods typically involve pulsed heating of the surface by small amounts using a laser source; the decay of the surface temperature after this pulsed photothermal heating is then probed to provide the thermal diffusivity. Various probing methods have been developed in the literature, including the probing of reflection, refraction, and diffraction from the pulsed heated area, infrared thermal radiometry, and surface deformation. This paper provides an overview of such techniques and some examples of their applications. 相似文献
58.
59.
模糊聚类在三维地震参数处理中的应用 总被引:1,自引:1,他引:0
三维地震参数是一个庞大的三维数据体,能从不同侧面反映储集层的特征。通过对三维地震参数的分析,可以评估油藏表征的参数(沉积相、构造、生长历史、流体饱和度等)。针对传统的聚类方法不能很好地综合考虑各个参数之间的相似程度,提出了用模糊C-均值聚类(fuzzy c-means clustering,简称FCM)对三维地震参数进行处理。从三维地震参数和油藏表征参数之间的关系出发,采用模糊C-均值聚类方法对三维地震参数进行处理,依此评估油藏表征的参数。测试结果表明,模糊C-均值聚类方法能够对三维地震参数进行较为准确的分类,并为储集层的研究提供了很好的依据。 相似文献
60.
钱塘江光缆管穿越长度2454.15m,穿越深度为32m,穿越中采用了多项新技术、新工艺、新方法。文章介绍了导向孔对穿技术、套管技术、水下磁场电缆铺设技术、长距离泥浆回流技术、长距离穿越钻杆组合技术在钱塘江光缆管穿越施工中的应用。 相似文献