全文获取类型
收费全文 | 21401篇 |
免费 | 1665篇 |
国内免费 | 188篇 |
专业分类
电工技术 | 362篇 |
综合类 | 96篇 |
化学工业 | 5612篇 |
金属工艺 | 527篇 |
机械仪表 | 826篇 |
建筑科学 | 811篇 |
矿业工程 | 37篇 |
能源动力 | 1473篇 |
轻工业 | 2028篇 |
水利工程 | 345篇 |
石油天然气 | 332篇 |
武器工业 | 9篇 |
无线电 | 2233篇 |
一般工业技术 | 3884篇 |
冶金工业 | 675篇 |
原子能技术 | 156篇 |
自动化技术 | 3848篇 |
出版年
2024年 | 92篇 |
2023年 | 423篇 |
2022年 | 815篇 |
2021年 | 1392篇 |
2020年 | 1197篇 |
2019年 | 1392篇 |
2018年 | 1580篇 |
2017年 | 1442篇 |
2016年 | 1397篇 |
2015年 | 841篇 |
2014年 | 1347篇 |
2013年 | 2221篇 |
2012年 | 1438篇 |
2011年 | 1574篇 |
2010年 | 1062篇 |
2009年 | 941篇 |
2008年 | 637篇 |
2007年 | 516篇 |
2006年 | 438篇 |
2005年 | 289篇 |
2004年 | 264篇 |
2003年 | 208篇 |
2002年 | 171篇 |
2001年 | 117篇 |
2000年 | 111篇 |
1999年 | 101篇 |
1998年 | 158篇 |
1997年 | 131篇 |
1996年 | 118篇 |
1995年 | 86篇 |
1994年 | 61篇 |
1993年 | 73篇 |
1992年 | 56篇 |
1991年 | 54篇 |
1990年 | 55篇 |
1989年 | 44篇 |
1988年 | 30篇 |
1987年 | 30篇 |
1986年 | 41篇 |
1985年 | 33篇 |
1984年 | 41篇 |
1983年 | 35篇 |
1982年 | 25篇 |
1981年 | 21篇 |
1980年 | 21篇 |
1979年 | 22篇 |
1978年 | 21篇 |
1977年 | 20篇 |
1976年 | 25篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 77 毫秒
111.
Ali Bayram Agah Uguz Ali Durmus 《Journal of Materials Engineering and Performance》2002,11(5):571-576
Three types of material whose fracture toughness tests were previously performed by using circumferentially notched bars,
namely (1) a dual-phase steel with three different morphologies; (2) an Al-Zn-Mg-Cu-wrought alloy; and (3) Al-Si-cast alloys
with three different Si contents, were investigated in terms of accuracy and reliability of the testing method. Also, the
advantages of using circumferentially notched bars for fracture toughness determination of metallic materials were discussed.
With the help of stress concentration factors, which are associated with the bluntness of the notch, correction factors for
the fracture toughness calculations are derived. The corrected fracture toughness values are found to be close to the uncorrected
ones, implying that the testing procedure is reliable. 相似文献
112.
A Novel UWB Pulse Shape Modulation System 总被引:5,自引:1,他引:4
Ghavami Mohammad Michael Lachlan B. Haruyama Shinichiro Kohno Ryuji 《Wireless Personal Communications》2002,23(1):105-120
In this paper novel modified Hermite polynomial functions for use in impulse radio (ultra-wideband) communications are proposed. With these functions pulse shapes which are orthogonal and have nearly constant pulse width regardless of the pulse order are generated. These properties hold under the effects of differentiation. An M-ary communication system is constructed using these pulse shapes. A Matlab model for generating the pulses is designed and the effect of timing jitter on the performance of the system is investigated by computer simulation. 相似文献
113.
Mohammad Taghi Hajiaghayi Yashar Ganjali 《Information Processing Letters》2002,83(3):163-166
A binary matrix has the Consecutive Ones Property (C1P) for columns if there exists a permutation of its rows that leaves the 1's consecutive in every column. The problem of Consecutive Ones Property for a matrix is a special variant of Consecutive Ones Submatrix problem in which a positive integer K is given and we want to know if there exists a submatrix B of A consisting of K columns of A with C1P property. This paper presents an error in the proof of NP-completeness for this problem in the reference cited in text by Garey and Johnson [Computers and Intractability, A Guide to the Theory of NP-Completeness, 1979]. 相似文献
114.
In this note we present a proof to the conjecture given in the above paper, and therefore establish the equivalence of characterizations of fixed modes for the general case. 相似文献
115.
116.
Compact WLAN disc antennas 总被引:1,自引:0,他引:1
McEwan N.J. Abd-Alhameed R.A. Ibrahim E.M. Excell P.S. Ali N.T. 《Antennas and Propagation, IEEE Transactions on》2002,50(12):1862-1864
A novel conical beam patch antenna design, suitable for local area network applications, uses a central cylindrical connection from the disc to ground to achieve a large reduction in resonant size. Results on efficiency, bandwidth, and pattern are reported for several prototypes. 相似文献
117.
It has been previously reported that Bryostatin 1 (Bryo1) induces differentiation of the human acute lymphoblastic leukemia (ALL) cell line, Reh, to a monocytoid B-cell stage. In this study we demonstrate that a novel protein, ubiquitin COOH-terminal hydrolase (UCH-L1), is associated with this differentiation. Reh cells were treated with 200 nmol/l of Bryo1 for 72 h and analyzed for changes in morphology, surface immunophenotype, acid phosphatase and terminal deoxynucleotidyl transferase. Protein patterns of the parent and differentiated cells, by two-dimensional polyacrylamide gel electrophoresis (2D PAGE), were studied. Bryo1-treated cells expressed morphologic, phenotypic and enzymatic features of the monocytoid B-cell stage. The UCH-L1 enzyme (MW-pl 34-5.3) was detected by 2 D PAGE in the differentiated, but not in parent cells. The presence of UCH-L1 in the Bryo1-treated cells was further confirmed by immunoblotting of 2 D PAGE using UCH-L1 polyclonal antibody. Ubiquitin expression was studied in parent and Bryo1-treated cells and was compared with 12-O-tetradecanoylphorbol-13-acetate (TPA)-treated cells. Both agents, TPA and Bryo1, increased the level of ubiquitin expression as detected by flow cytometry. Sodium borohydride, an inhibitor of UCH-L1, inhibited the Bryo1-induced differentiating effect on Reh cells. To date, the mechanism by which Bryo1, exerts its B-cell differentiating effect is not fully understood. This study shows that UCH-L1 expression may play a major role in Bryo1-induced differentiation in pre-B-ALL. 相似文献
118.
Progress and prospects of group-III nitride semiconductors 总被引:1,自引:0,他引:1
We review recent progress in the group-III nitride and related materials, and electronic and optical devices based on them. Blue and UV (e.g. ultra violet) emitters and detectors, and high temperature/high power electronics which has long been coveted are beginning to be realized either in the laboratory or in the commercial arena, due in part to the breathtaking progress made in the last few years in the art and science of GaN, InN, AlN and their salloys. With brief references to the historical aspect of the relevant developments, this review concerns itself primarily with the current status of wide bandgap gallium nitride and related semiconductors from both the materials and devices points of view. Following a discussion of the structural properties of these materials, their electrical and optical properties are described in detail. The available data on metal contacts, the properties of which are indeed very conducive for the devices mentioned, from the points of view of ohmic contacts and Schottky barriers, are elaborated on. Recent progress on processing issues such as etching are reviewed. The review then embarks on an indash;depth discussion and analysis of field effect transistors, bipolar transistors, light emitting diodes, laser and photo detectors. 相似文献
119.
120.