全文获取类型
收费全文 | 636429篇 |
免费 | 8502篇 |
国内免费 | 1910篇 |
专业分类
电工技术 | 12043篇 |
综合类 | 878篇 |
化学工业 | 95764篇 |
金属工艺 | 21911篇 |
机械仪表 | 18046篇 |
建筑科学 | 17283篇 |
矿业工程 | 1577篇 |
能源动力 | 17309篇 |
轻工业 | 63667篇 |
水利工程 | 5151篇 |
石油天然气 | 5162篇 |
武器工业 | 21篇 |
无线电 | 81487篇 |
一般工业技术 | 117867篇 |
冶金工业 | 120381篇 |
原子能技术 | 9432篇 |
自动化技术 | 58862篇 |
出版年
2021年 | 4438篇 |
2019年 | 4100篇 |
2018年 | 6693篇 |
2017年 | 6596篇 |
2016年 | 6931篇 |
2015年 | 5402篇 |
2014年 | 8996篇 |
2013年 | 29875篇 |
2012年 | 15495篇 |
2011年 | 22012篇 |
2010年 | 17074篇 |
2009年 | 19443篇 |
2008年 | 20711篇 |
2007年 | 20851篇 |
2006年 | 18667篇 |
2005年 | 17286篇 |
2004年 | 16831篇 |
2003年 | 16400篇 |
2002年 | 15891篇 |
2001年 | 16045篇 |
2000年 | 15109篇 |
1999年 | 16017篇 |
1998年 | 37283篇 |
1997年 | 27052篇 |
1996年 | 21321篇 |
1995年 | 16585篇 |
1994年 | 14939篇 |
1993年 | 14324篇 |
1992年 | 10709篇 |
1991年 | 10291篇 |
1990年 | 9831篇 |
1989年 | 9478篇 |
1988年 | 9125篇 |
1987年 | 7666篇 |
1986年 | 7761篇 |
1985年 | 9270篇 |
1984年 | 8556篇 |
1983年 | 7719篇 |
1982年 | 7126篇 |
1981年 | 7193篇 |
1980年 | 6754篇 |
1979年 | 6519篇 |
1978年 | 6093篇 |
1977年 | 7410篇 |
1976年 | 9887篇 |
1975年 | 5224篇 |
1974年 | 5003篇 |
1973年 | 4922篇 |
1972年 | 3972篇 |
1971年 | 3489篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
C. Janke R. Jones S. Öberg P. R. Briddon 《Journal of Materials Science: Materials in Electronics》2007,18(7):775-780
Boron is observed to diffuse very slowly in germanium, as opposed to its behaviour in silicon where it exhibits Transient
Enhanced Diffusion effects in implanted samples. As a result of this slow diffusion, boron is a very stable dopant, allowing
devices to be created with very well-defined doping regions. To understand this superior performance, calculations were performed
on a variety of boron diffusion paths, within vacancy and interstitial mediated methods. It was found that the vacancy mediated
diffusion which is associated with the fast diffusion of many other species in germanium exhibits a total barrier of 5.8 eV.
Interstitial-mediated diffusion had a total barrier for migration of 3.4 eV in the neutral and singly negative charge states,
3.2 eV for the positive charge state, but a formation barrier of 4.1 eV. Thus the barrier for interstitial-mediated diffusion
is dominated by the formation energy of the self-interstitial. 相似文献
992.
Bonto-Kane Maria Vicente A. Chin Alvin Mc Carthy Sheila Srikulwong Mayuree Timmins Paul J. 《Pervasive Computing, IEEE》2007,6(4)
Pervasive computing is as much about the user as it is about the technology. So, the Fifth International Conference on Pervasive Computing emphasized desirability rather than just feasibility. Featured themes included user benefits, human-computer interaction, group and social interactions, context awareness, finding and positioning people and objects, and personal privacy. 相似文献
993.
Unicode is rapidly becoming the preferred means for representing symbols used in creating multimedia content, especially for information that's presented in multiple languages. This article discusses a unicode vulnerability that makes such content susceptible to being used for creation of covert channel communications. We also developed a solution architecture, the unified secure message augmentation (USMA) service. The USMA service incorporates rules (in an XML vocabulary) that we can apply to unicode transmissions that will detect an attempt to transmit a potential exploit, alert network managers to the presence of the unicode anomaly, and take action to mitigate the exploit. 相似文献
994.
The US Centers for Disease Control and Prevention (CDC) created the Public Health Information Network to advance fully capable, interoperable information systems in public health organizations. PHIN prioritizes public health information systems' functional requirements, capabilities, performance measures, and operational characteristics while letting the architects of those systems choose enabling approaches, methods, and concepts to meet the requirements. PHIN also provides a certification process for public health administrators to evaluate their information infrastructure's quality. The certification process is important because affected organizations often depend on certification for continued funding. 相似文献
995.
996.
A study of the trace elements emission (As, Se, Cd, Co, Cr, Cu, Zn, Hg, Tl, Pb, Ni, Sn, Sb, V, Mn and Fe) from pulverized coal combustion has been made at six heating and power stations situated in the Czech Republic. The amount of chlorine in coal has considerable influence on volatilization of some elements such as Zn, Cu, Pb, Hg and Tl, which is explained by the formation of thermodynamically stable compounds of these elements with chlorine. Generally, the affinities for Cl follows the order Tl > Cu > Zn > Pb > Co > Mn > Sn > Hg. The experimental data indicates enrichment of some of the trace toxic elements in the emissions (Cu, Zn, As, Se, Cd, Sn, Sb, Hg and Pb) and good agreement was obtained by thermodynamic equilibrium calculations with a few exceptions. In the case of Fe, Mn, Co, Cr and Sn calculated values are overestimated in the bottom ash and there are zero predicted amounts of these elements in the fly ash. In comparison, the results from experiments show up to 80% of these elements retained in fly ash. This implies that there exist additional steps leading to the enrichment by Fe, Mn, Co, Cr and Sn of small particles. Such mechanisms could include the ejection during devolatilization of small inorganic particles from the coal of bottom ash particles, or disintegration of the char containing these metals to small particles of fly ash. On the other hand, there are slightly overestimated or similar values of relative enrichment factors for As, V, Cu, Cd, Sb, Tl and Pb in the fly ashes and zero predicted values for bottom ashes. Our experimental results show about 5% or less of these elements are retained in bottom ashes, so they probably remain in the bottom ash inside unburned parts of coal. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
997.
998.
This study investigated the ability of the Millon Clinical Multiaxial Inventory--Third Edition (MCMI-III) to discriminate students malingering psychopathology (n=106) from bona fide psychiatric inpatients (n=202). Students were randomly assigned to a fake-bad or an honest-responding condition. Analyses investigated the ability of the modifier indices to discriminate fake-bad group participants from the psychiatric inpatients. Scale X raw cutoff score >178 yielded a positive predictive power (PPP) of 0.0, a negative predictive power (NPP) of 63.1, and a hit rate of 63.1%. Optimal cutoff scores were developed. Scale X Base Rate (BR) >84 provided a PPP of 55.6, an NPP of 72.1, and a hit rate of 65.2%. Scale Y BR 相似文献
999.
Ronald R. Delyser Sheila S. Thompson Jerry Edelstein Corinne Lengsfeld Albert J. Rosa Paul J. Rullkoetter Robert Whitman Margaret Whitt 《工程教育杂志》2003,92(3):269-273
A team of faculty members at the University of Denver changed the learning environment in key courses in the Department of Engineering from predominately teacher centered to student centered. Through this funded project new grading methods were implemented, classrooms were renovated and wired with studio layouts to facilitate learning, the Engineering Circuits Laboratory was rewired and instrumented for automated data acquisition and reporting, and two new pedagogical approaches were developed. At the onset of the project, six goals were established related to student learning. The introduction of industry standard hardware and software provided students with unprecedented hands‐on experience and project related activities stimulated faculty innovations in other current and future courses. Assessment results indicate that the new grading system improved the clarity of expectations for students before assignments were given resulting in increased reported motivation for learning in many courses. Even though course GPAs did not always reflect higher achievement on graded work, faculty members firmly believe that deeper understanding was achieved because more complex material was assimilated. 相似文献
1000.