全文获取类型
收费全文 | 45474篇 |
免费 | 4449篇 |
国内免费 | 2396篇 |
专业分类
电工技术 | 2783篇 |
技术理论 | 7篇 |
综合类 | 3073篇 |
化学工业 | 7656篇 |
金属工艺 | 2816篇 |
机械仪表 | 3024篇 |
建筑科学 | 3563篇 |
矿业工程 | 1422篇 |
能源动力 | 1207篇 |
轻工业 | 3244篇 |
水利工程 | 923篇 |
石油天然气 | 2639篇 |
武器工业 | 371篇 |
无线电 | 5282篇 |
一般工业技术 | 5504篇 |
冶金工业 | 2370篇 |
原子能技术 | 617篇 |
自动化技术 | 5818篇 |
出版年
2024年 | 262篇 |
2023年 | 860篇 |
2022年 | 1491篇 |
2021年 | 1996篇 |
2020年 | 1632篇 |
2019年 | 1361篇 |
2018年 | 1458篇 |
2017年 | 1667篇 |
2016年 | 1500篇 |
2015年 | 2121篇 |
2014年 | 2648篇 |
2013年 | 3022篇 |
2012年 | 3325篇 |
2011年 | 3387篇 |
2010年 | 2751篇 |
2009年 | 2566篇 |
2008年 | 2520篇 |
2007年 | 2484篇 |
2006年 | 2388篇 |
2005年 | 1941篇 |
2004年 | 1294篇 |
2003年 | 1168篇 |
2002年 | 1220篇 |
2001年 | 999篇 |
2000年 | 919篇 |
1999年 | 929篇 |
1998年 | 744篇 |
1997年 | 601篇 |
1996年 | 595篇 |
1995年 | 479篇 |
1994年 | 440篇 |
1993年 | 287篇 |
1992年 | 244篇 |
1991年 | 182篇 |
1990年 | 143篇 |
1989年 | 107篇 |
1988年 | 93篇 |
1987年 | 61篇 |
1986年 | 63篇 |
1985年 | 32篇 |
1984年 | 35篇 |
1983年 | 24篇 |
1982年 | 30篇 |
1981年 | 25篇 |
1980年 | 19篇 |
1979年 | 12篇 |
1978年 | 12篇 |
1977年 | 13篇 |
1976年 | 27篇 |
1975年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
43.
通过研究二连盆地赛汉塔拉凹陷中洼槽陡坡带的含鲕粒块状细砂岩从岩性特征、沉积结构及构造特征、粒度特征、测井曲线特征、地震反射特征以及对其形成机理的分析,认为赛83x含油砂岩体为在半深湖一深湖环境形成的滑塌浊积扇沉积.这种类型的滑塌浊积扇具备分选、磨圆度、物性较好等条件,尤其是此类砂岩体往往被形成于深湖一半深湖相还原环境的深灰色、灰黑色泥岩--成熟烃源岩所包围,易形成岩性圈闭,有利于油气的运移和聚集成藏,是断陷湖盆陡坡带油气勘探的重要目标. 相似文献
44.
La doping effects on intergrowth Bi2WO6–Bi3TiNbO9 ferroelectric ceramics were studied by X-ray diffraction, electron probe microanalysis and dielectric spectroscopy. It was found that the La3+ distribution, ferroelectric phase transition and dielectric relaxation behavior are apparently affected by La doping. With increasing La3+ content, the site of dopant ion varies, the grain growth of Bi5TiNbWO15 is restrained, the Curie temperature is reduced and broadened. Furthermore, two dielectric relaxation loss peaks were observed both in temperature and frequency spectra. The calculated relaxation parameters revealed the oxygen vacancy related to the relaxation process. 相似文献
45.
Huiping Hu Qiyuan Chen Zhoulan Yin Pingmin Zhang Lusheng Ye 《Metallurgical and Materials Transactions A》2003,34(13):793-797
The thermal decompositions of mechanically activated and nonactivated galenas were studied by thermogravimetry analysis (TGA)
at the heating rate of 10 K min−1 in argon. Results indicate that the initial temperature of thermal decomposition (abbreviated as T
di) in the TGA curves for different galenas decreases gradually with increased grinding time. The specific granulometric surface
area (S
G), the structural disorder, and the content of elemental sulfur of mechanically activated galenas were analyzed by an X-ray
diffraction (XRD) laser particle-size analyzer, XRD analysis, and the gravimetric method, respectively, which shows that the
specific granulometric surface area of mechanically activated galenas remains almost constant after a certain grinding time,
but the lattice distortions (ε) rise, the crystallite sizes (D) decrease, and the elemental sulfur contents of mechanically activated galenas increase with increased grinding time. The
results imply that the decrease of the initial temperature of thermal decomposition in the TGA curves for mechanically activated
galenas is mainly caused by the increase of lattice distortions, and the formation of new dangling bonds resulted from the
production of elemental sulfur of mechanically activated galenas with increased grinding time. Finally, the differences in
the thermal-decomposition reactivity between nonactivated and mechanically activated galenas were also discussed. 相似文献
46.
47.
48.
Weitang Li Zhenghui Li Shifu Zhu Shujun Yin Beijun Zhao Guanxiong Chen 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1996,370(2-3):435-437
Instead of the temperature oscillation method (TOM), a modified vapor growth method was applied in this paper to grow large HgI2 crystals with fewer lattice defects by providing a relatively stable temperature field during growth. And a new processing technique of HgI2 crystals was developed for detector fabrication by merging solution string-sawing and hand-cleaving. The lattice deformations caused during cleaving were reduced greatly by eliminating passivated layers on the sawed crystal platelets before cleaving. 相似文献
49.
50.
Collected ratings of communication ease and of engagement for 95 deaf junior and senior high school students (aged 12–21 yrs) in a large, urban, multiethnic school for the deaf. Ratings were made by the students' English teachers and by the students themselves. High teacher ratings for communication ease and engagement were associated with high academic achievement as measured by the Stanford Achievement Test. High student ratings for communication ease were also associated with academic achievement. The 2 best predictors of academic achievement were student-rated communication ease and teacher-rated engagement. Findings suggest that it is important for teachers to be sensitive to the level of communication comfort of their students because students who enjoy easier communication may be more likely to be engaged, or more actively involved, in classroom learning and to demonstrate higher academic achievement. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献