全文获取类型
收费全文 | 254160篇 |
免费 | 2834篇 |
国内免费 | 871篇 |
专业分类
电工技术 | 4836篇 |
综合类 | 197篇 |
化学工业 | 36502篇 |
金属工艺 | 9537篇 |
机械仪表 | 7570篇 |
建筑科学 | 6135篇 |
矿业工程 | 885篇 |
能源动力 | 7249篇 |
轻工业 | 21296篇 |
水利工程 | 2204篇 |
石油天然气 | 3231篇 |
武器工业 | 15篇 |
无线电 | 34363篇 |
一般工业技术 | 50173篇 |
冶金工业 | 48721篇 |
原子能技术 | 5081篇 |
自动化技术 | 19870篇 |
出版年
2021年 | 2194篇 |
2020年 | 1571篇 |
2019年 | 1927篇 |
2018年 | 3295篇 |
2017年 | 3327篇 |
2016年 | 3425篇 |
2015年 | 2243篇 |
2014年 | 3993篇 |
2013年 | 11546篇 |
2012年 | 6280篇 |
2011年 | 8632篇 |
2010年 | 6933篇 |
2009年 | 7925篇 |
2008年 | 8442篇 |
2007年 | 8344篇 |
2006年 | 7417篇 |
2005年 | 6522篇 |
2004年 | 6306篇 |
2003年 | 6578篇 |
2002年 | 6068篇 |
2001年 | 6535篇 |
2000年 | 5989篇 |
1999年 | 6409篇 |
1998年 | 16528篇 |
1997年 | 11429篇 |
1996年 | 8810篇 |
1995年 | 6629篇 |
1994年 | 5919篇 |
1993年 | 5866篇 |
1992年 | 4150篇 |
1991年 | 4033篇 |
1990年 | 3871篇 |
1989年 | 3660篇 |
1988年 | 3577篇 |
1987年 | 3036篇 |
1986年 | 2955篇 |
1985年 | 3220篇 |
1984年 | 2938篇 |
1983年 | 2844篇 |
1982年 | 2646篇 |
1981年 | 2551篇 |
1980年 | 2483篇 |
1979年 | 2317篇 |
1978年 | 2118篇 |
1977年 | 2614篇 |
1976年 | 3583篇 |
1975年 | 1780篇 |
1974年 | 1742篇 |
1973年 | 1672篇 |
1972年 | 1478篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
Seyeong Choi Alouini M.-S. Qaraqe K.A. Hong-Chuan Yang 《Wireless Communications, IEEE Transactions on》2008,7(2):495-499
We propose and analyze new finger assignment techniques that are applicable for RAKE receivers in the soft handover (SHO) region. Specifically, extending the results for the case of two-base station (BS), we consider the multi-BS situation, attack the statistics of several correlated generalized selection combining (GSC) stages, and provide closed-form expressions for the statistics of the output signal-to-noise ratio (SNR). By investigating the tradeoff among the error performance, the average number of required path estimations/comparisons, and the SHO overhead, we show through numerical examples that the new schemes offer commensurate performance in comparison with more complicated GSC-based diversity systems while requiring a smaller estimation load and SHO overhead. 相似文献
192.
S. K. Chen A. Serquis G. Serrano K. A. Yates M. G. Blamire D. Guthrie J. Cooper H. Wang S. Margadonna J. L. MacManus‐Driscoll 《Advanced functional materials》2008,18(1):113-120
By applying a combination of characterisation tools, changes in structural and superconducting properties with nominal Mg non‐stoichiometry in MgxB2 are found. The non‐stoichiometry produces enhanced in‐field critical current densities (Jc's) and upper critical field / irreversibility field (Hc2/Hirr(T)) values. Upper critical fields of ~ 21 T (4.2 K) were obtained in nominal Mg‐deficient samples compared to ~ 17 T (4.2 K) for near‐stoichiometric samples. 相似文献
193.
Die Regelung über die Erlangung der Parteistellung übergangener Nachbarn durch Geltendmachung von Einwendungen bis l?ngstens
drei Monate nach dem angezeigten Baubeginn ist wegen der Anknüpfung an einen untauglichen Zeitpunkt verfassungswidrig. 相似文献
194.
Hiding biometric data 总被引:5,自引:0,他引:5
Jain A.K. Uludag U. 《IEEE transactions on pattern analysis and machine intelligence》2003,25(11):1494-1498
With the wide spread utilization of biometric identification systems, establishing the authenticity of biometric data itself has emerged as an important research issue. The fact that biometric data is not replaceable and is not secret, combined with the existence of several types of attacks that are possible in a biometric system, make the issue of security/integrity of biometric data extremely critical. We introduce two applications of an amplitude modulation-based watermarking method, in which we hide a user's biometric data in a variety of images. This method has the ability to increase the security of both the hidden biometric data (e.g., eigen-face coefficients) and host images (e.g., fingerprints). Image adaptive data embedding methods used in our scheme lead to low visibility of the embedded signal. Feature analysis of host images guarantees high verification accuracy on watermarked (e.g., fingerprint) images. 相似文献
195.
M E Rentschler S R Platt K Berg J Dumpert D Oleynikov S M Farritor 《IEEE transactions on information technology in biomedicine》2008,12(1):66-75
Long-term human space exploration will require contingencies for emergency medical procedures including some capability to perform surgery. The ability to perform minimally invasive surgery (MIS) would be an important capability. The use of small incisions reduces surgical risk, but also eliminates the ability of the surgeon to view and touch the surgical environment directly. Robotic surgery, or telerobotic surgery, may provide emergency surgical care in remote or harsh environments such as space flight, or extremely forward environments such as battlefields. However, because current surgical robots are large and require extensive support personnel, their implementation has remained limited in forward environments, and they would be difficult, or impossible, to use in space flight or on battlefields. This paper presents experimental analysis of miniature fixed-base and mobile in vivo robots to support MIS surgery in remote and harsh environments. The objective is to develop wireless imaging and task-assisting robots that can be placed inside the abdominal cavity during surgery. Such robots will provide surgical task assistance and enable an on-site or remote surgeon to view the surgical environment from multiple angles. This approach is applicable to long-duration space flight, battlefield situations, and for traditional medical centers and other remote surgical locations. 相似文献
196.
E. M. Zobov M. E. Zobov F. S. Gabibov I. K. Kamilov F. I. Manyakhin E. K. Naimi 《Semiconductors》2008,42(3):277-280
The results of the effect of ultrasonic treatment of ZnSe crystals on the structure of the energy spectrum of electronic states of centers with deep levels forming photoelectric and luminescent properties of this compound are presented. It is for the first time proved experimentally that the climb of edge dislocations under the effect of ultrasound leads to regrouping and generation of defects forming deep levels, which manifest themselves in phenomena of photosensitivity and radiative recombination. 相似文献
197.
V. F. Ivanov A. A. Nekrasov K. V. Tcheberiako A. V. Vannikov A. S. Posed'ko S. I. Lishik Yu. V. Trofimov 《Journal of the Society for Information Display》2003,11(1):11-14
Abstract— An all solid‐state photoelectrochromic element (PECE) was developed on the basis of electrochromic layers of WO3 and polyaniline with a layer of polymer electrolyte placed on a base of polyamidosulfoacid, in which a thin‐film CdSxSe1?x photoresistor was used as an electronic key. The dependence of the sensitometric characteristics of the PECE on the applied voltage was studied. 相似文献
198.
Y. L. Hao R. Yang M. Niinomi D. Kuroda Y. L. Zhou K. Fukunaga A. Suzuki 《Metallurgical and Materials Transactions A》2003,34(4):1007-1012
Alloys for implant devices require improved strength but a reduced Young’s modulus, in order to become mechanically more compatible
with adjacent bone tissues. In this study, a new metastable β-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (wt pct), was subjected to aging treatment to produce different microstructures,
and the resulting mechanical properties, including the Young’s modulus, were measured. The Young’s modulus of this alloy is
found to be sensitive to microstructures generated by various heat treatments. For microstructures varying from (α + β) to (α + β + ω) and (β + ω), the Young’s modulus increases with an accompanying increase in tensile strength and hardness, but decreases in ductility.
The (β + ω) microstructure has a low strength, high modulus, and poor ductility and cannot be used for biomedical applications. For
an (α + β) microstructure, the volume fraction of the phases is shown to be the main factor that determines the mechanical properties. 相似文献
199.
Rajoo R. Lim S.S. Wong E.H. Hnin W.Y. Seah S.K.W. Tay A.A.O. Iyer M. Tummala R.R. 《Advanced Packaging, IEEE Transactions on》2008,31(2):377-385
A wafer level packaging technique has been developed with an inherent advantage of good solder joint co-planarity suitable for wafer level testing. A suitable weak metallization scheme has also been established for the detachment process. During the fabrication process, the compliancy of the solder joint is enhanced through stretching to achieve a small shape factor. Thermal cycling reliability of these hourglass-shaped, stretch solder interconnections has been found to be considerably better than that of the conventional spherical-shaped solder bumps. 相似文献
200.
Zhiping Lin Xu L. Bose N.K. 《IEEE transactions on circuits and systems. I, Regular papers》2008,55(1):445-461