全文获取类型
收费全文 | 21205篇 |
免费 | 1980篇 |
国内免费 | 524篇 |
专业分类
电工技术 | 681篇 |
综合类 | 438篇 |
化学工业 | 5287篇 |
金属工艺 | 631篇 |
机械仪表 | 1204篇 |
建筑科学 | 453篇 |
矿业工程 | 162篇 |
能源动力 | 3635篇 |
轻工业 | 1555篇 |
水利工程 | 67篇 |
石油天然气 | 177篇 |
武器工业 | 113篇 |
无线电 | 3507篇 |
一般工业技术 | 3532篇 |
冶金工业 | 446篇 |
原子能技术 | 369篇 |
自动化技术 | 1452篇 |
出版年
2024年 | 61篇 |
2023年 | 628篇 |
2022年 | 1377篇 |
2021年 | 1670篇 |
2020年 | 905篇 |
2019年 | 735篇 |
2018年 | 705篇 |
2017年 | 853篇 |
2016年 | 852篇 |
2015年 | 891篇 |
2014年 | 1243篇 |
2013年 | 1234篇 |
2012年 | 1264篇 |
2011年 | 1741篇 |
2010年 | 1168篇 |
2009年 | 1073篇 |
2008年 | 938篇 |
2007年 | 979篇 |
2006年 | 837篇 |
2005年 | 701篇 |
2004年 | 546篇 |
2003年 | 533篇 |
2002年 | 444篇 |
2001年 | 363篇 |
2000年 | 329篇 |
1999年 | 246篇 |
1998年 | 283篇 |
1997年 | 216篇 |
1996年 | 134篇 |
1995年 | 93篇 |
1994年 | 106篇 |
1993年 | 70篇 |
1992年 | 67篇 |
1991年 | 70篇 |
1990年 | 63篇 |
1989年 | 39篇 |
1988年 | 23篇 |
1987年 | 22篇 |
1986年 | 19篇 |
1985年 | 26篇 |
1984年 | 16篇 |
1983年 | 13篇 |
1982年 | 8篇 |
1980年 | 13篇 |
1965年 | 9篇 |
1959年 | 7篇 |
1958年 | 10篇 |
1956年 | 8篇 |
1955年 | 13篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
33.
By exploiting the unattended nature of the wireless sensor networks, an attacker can physically capture and compromise sensor nodes and then launch a variety of attacks. He can additionally create many replicas of a few compromised nodes and spread these replicas over the network, thus launching further attacks with their help. In order to minimize the damage incurred by compromised and replicated nodes, it is very important to detect such malicious nodes as quickly as possible. In this review article, we synthesize our previous works on node compromise detection in sensor networks while providing the extended analysis in terms of performance comparison to the related work. More specifically, we use the methodology of the sequential analysis to detect static and mobile compromised nodes, as well as mobile replicated nodes in sensor networks. With the help of analytical and simulation results, we also demonstrate that our schemes provide robust and efficient node compromise detection capability. 相似文献
34.
Vidroha Debroy Author VitaeW. Eric WongAuthor Vitae 《Journal of Systems and Software》2011,84(4):587-602
Test set size in terms of the number of test cases is an important consideration when testing software systems. Using too few test cases might result in poor fault detection and using too many might be very expensive and suffer from redundancy. We define the failure rate of a program as the fraction of test cases in an available test pool that result in execution failure on that program. This paper investigates the relationship between failure rates and the number of test cases required to detect the faults. Our experiments based on 11 sets of C programs suggest that an accurate estimation of failure rates of potential fault(s) in a program can provide a reliable estimate of adequate test set size with respect to fault detection and should therefore be one of the factors kept in mind during test set construction. Furthermore, the model proposed herein is fairly robust to incorrect estimations in failure rates and can still provide good predictive quality. Experiments are also performed to observe the relationship between multiple faults present in the same program using the concept of a failure rate. When predicting the effectiveness against a program with multiple faults, results indicate that not knowing the number of faults in the program is not a significant concern, as the predictive quality is typically not affected adversely. 相似文献
35.
Rachel Cardell-Oliver 《Formal Aspects of Computing》2000,12(5):350-371
A method is introduced for testing the conformance of implemented real-time systems to timed automata specifications. Uppaal
timed automata are transformed into testable timed transition systems (TTTSs) using a test view. Fault hypotheses and a test
generation algorithm for TTTSs are defined. Results of applying the method are presented.
Received October 1999 / Accepted in revised form November 2000 相似文献
36.
Jovanović I Ugrenović S Antić S Stefanović N Mihailović D 《Microscopy research and technique》2007,70(7):617-627
Psammoma bodies (PBs) are one of many choroids plexus aging changes. The aim of our research was to perform the quantification of PBs' presence in human choroids plexus stroma, as well as to evaluate the characteristics of choroids plexus stroma in cases in which PBs were present. Afterwards, the observations of the histochemical analysis would be confirmed by immunohistochemical analysis. Choroid plexuses of 30 cadavers were used for the histochemical and, choroids plexuses of 15 cadavers in which PBs' presence was confirmed during the histochemical analysis, were used as material for the immunohistochemical analysis. Light microscopy, histochemical, immunohistochemical, and morphometric method were applied during the study. Classification of the cases was performed by cluster analysis. We observed increase of choroids plexus PBs' presence during the aging process. But this increase is not linear. Their presence is the largest in the second cluster that is younger than the third and older than the first. Nuclear morphometric parameters of the stroma in these cases showed that the cellular composition in this cluster is different than in other two and, that contain larger number of lymphoid cells. Immunohistochemical analysis showed PBs' positive reaction on vimentin, CD45R0, and LCA markers, while in their vicinity, as well as inside them, numerous T-cells were observed. So, the presence of CD45R0 and LCA-positive T cells, PBs' positive reaction on the same markers, indirectly connect these cells with PBs' formation process. 相似文献
37.
38.
Uri Cohen 《Journal of Electronic Materials》1977,6(6):607-643
Electrodeposition of both epitaxial and polycrystalline continuous films of dense, coherent, and well-adherent silicon coatings
was achieved from molten fluorides. A dissolving Si anode and an operating temperature of about 750 C were utilized. Silicon
electrocrystallization epitaxy (ECE) produced films with the (111) orientation on Si substrates of the same orientation. The
unintentionally doped films were of p-type character with a resistivity in the range 0.05 - 0.10 Ω-cm. Polycrystalline Si
films were similarly electroplated onto various polycrystalline metal substrates. Uniform coherent, and well-adherent coatings
with grain diameters as large as 40 – 50 μm were obtained. The useful rate of electrodeposition of Si could be significantly
increased by the application of an alternating square wave pulse (ASWP)2technique. Cathodic current pulses as high as 300 mA/cm2 (growth rate of about 5 μm/min) were demonstrated. The cathodic current efficiencies, for all modes of growth, were about
70 – 100%. The effects of the various operating parameters, and some prospective applications to the fabrication of solar
cells, are discussed.
This was paper A-6 in the 18th Annual Electronic Materials Conference, Salt Lake City, June 23–25, 1976. 相似文献
39.
Hortolà P 《Microscopy research and technique》2012,75(8):1007-1011
The aboriginal use of reed and bone as raw materials for knives and daggers, respectively, has been well-documented ethnographically in some geographical areas of Melanesia. Because of the significant role that these weapons played in inter- and intra-ethnic aggression, they can potentially have retained smears from the contact with human blood. To carry out a guiding low-vacuum scanning electron microscopy (SEM) study of specific interest to ethnography, the outsides of a fragment of stalk of giant cane (Arundo donax) and tibial diaphysis of domestic sheep (Ovis aries) were smeared with peripheral human blood. No biological specimen preparation was applied to the samples. After just over 1 month, bloodstain boundaries and their neighboring inner areas were examined via secondary electrons by a variable-pressure SEM (VP-SEM) working in low-vacuum mode. On both substrates, bloodstains exhibited micro-scales. No janocyte (erythrocyte negative replica) was observed in the examined areas. However, erythrocytes were seen crowded together as grain-shaped corpuscles in the smear on reed, and several hecatocytes (moon-like shaped erythrocytes) were evidenced in the smear on bone. The results of this study suggest that a VP-SEM working in low-vacuum mode can be used fruitfully to detect blood remains in medium-sized reed and bone antique aboriginal artifacts. This procedure can prospectively help to ethnographic museum curators and aboriginal-art surveyors as an easy guiding test in the valuation of antique traditional weapons prior to acquisition, when the real use of a piece has been claimed by the supplier. 相似文献
40.
本文将现有的在线自学与在线考试系统相结合,设计出一个具备教学与测试的完整的学习系统,并实现学习者学习进度记录、进度相互比较及经验交流等功能,使学习者在学习过程中并不孤独。 相似文献