全文获取类型
收费全文 | 3037篇 |
免费 | 294篇 |
国内免费 | 89篇 |
专业分类
电工技术 | 188篇 |
综合类 | 165篇 |
化学工业 | 668篇 |
金属工艺 | 92篇 |
机械仪表 | 124篇 |
建筑科学 | 142篇 |
矿业工程 | 95篇 |
能源动力 | 94篇 |
轻工业 | 161篇 |
水利工程 | 36篇 |
石油天然气 | 63篇 |
武器工业 | 7篇 |
无线电 | 433篇 |
一般工业技术 | 484篇 |
冶金工业 | 229篇 |
原子能技术 | 34篇 |
自动化技术 | 405篇 |
出版年
2024年 | 7篇 |
2023年 | 33篇 |
2022年 | 69篇 |
2021年 | 82篇 |
2020年 | 62篇 |
2019年 | 44篇 |
2018年 | 68篇 |
2017年 | 71篇 |
2016年 | 99篇 |
2015年 | 110篇 |
2014年 | 143篇 |
2013年 | 197篇 |
2012年 | 175篇 |
2011年 | 199篇 |
2010年 | 187篇 |
2009年 | 156篇 |
2008年 | 188篇 |
2007年 | 147篇 |
2006年 | 173篇 |
2005年 | 120篇 |
2004年 | 97篇 |
2003年 | 109篇 |
2002年 | 133篇 |
2001年 | 107篇 |
2000年 | 71篇 |
1999年 | 76篇 |
1998年 | 69篇 |
1997年 | 69篇 |
1996年 | 50篇 |
1995年 | 47篇 |
1994年 | 31篇 |
1993年 | 25篇 |
1992年 | 23篇 |
1991年 | 34篇 |
1990年 | 12篇 |
1989年 | 12篇 |
1988年 | 13篇 |
1987年 | 6篇 |
1986年 | 10篇 |
1984年 | 9篇 |
1983年 | 12篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1976年 | 12篇 |
1975年 | 5篇 |
1970年 | 4篇 |
1965年 | 3篇 |
1964年 | 3篇 |
排序方式: 共有3420条查询结果,搜索用时 15 毫秒
11.
J.-G. Kim W.-P. Tai Y.-J. Kwon K.-J. Lee W.-S. Cho N.-H. Cho C.M. Whang Y.-C. Yoo 《Journal of Materials Science: Materials in Electronics》2004,15(12):807-811
Donor doped BaTiO3 (n-BaTiO3) ceramics were fabricated by adding polyethylene glycol (PEG) at 20 wt %. The effects of reducing and oxidizing atmospheres on the PTCR characteristics of the porous n-BaTiO3 ceramics were investigated. The PTCR characteristics of the porous n-BaTiO3 ceramics is strongly affected by chemisorbed oxygen at the grain boundaries and are recovered as the atmosphere is changed from the reducing gas to oxidizing gas. The low room-temperature resistivity of the porous n-BaTiO3 ceramics in reducing atmospheres may be caused by the decrease in potential barrier height, which originates from an increase in the number of electrons owing to the desorption of chemisorbed oxygen atoms at the grain boundaries. In addition, the high room-temperature resistivity of the porous n-BaTiO3 ceramics in oxidizing atmospheres may be caused by the increase in potential barrier height, which results from the adsorption of chemisorbed oxygen atoms at the grain boundaries. 相似文献
12.
基于防水墙系统的信息安全与保密解决方案 总被引:3,自引:3,他引:0
一、引言防火墙、IDS、内外网隔离以及其它针对外部网络的访问控制系统,可有效防范来自网络外部的进攻,但对于企业内部的信息保密问题,却一直没有好的防范方法:内部人员可以轻松地将计算机中的机密信息通过网络、存储介质和打印等方式泄露出去,一旦这些敏感信息、重要数据、设计图纸等流失到敌对势力、竞争对手手中,将给国家、企、事业单位造成重大损失。特别是军工行业、政府机关、承担国家敏感课题的科研部门,涉及到更多的国家机密,对于涉密信息采取严密的防护措施更是显得尤为必要。目前,国家制定了很多相关规章制度,明确规定,这些企事… 相似文献
13.
Fatigue behavior and morphology of long glass fiber reinforced semicrystalline polyamide (nylon 6,6) and amorphous polycarbonate (PC) composites were investigated. The fiber length distribution in the molded samples was calculated by image analyzer. The tension-tension fatigue loading tests at various levels of stress amplitudes were studied. The two-parameter Weibull distribution function were applied to obtain the statistical probability distribution of experimental data. A good correlation existed between the experimental data and the Weibull distribution curves. Straight line S? N curves of long glass fiber reinforced semicrystalline polyamide and amorphous polycarbonate composites at various probabilities were established. The stiffness of the composite under tension-tension fatigue loading was measured. The thermal stress history was also investigated by thermo-imaging techniques during fatigue life testing. Further, failure morphology was examined by scanning electron microscopy (SEM). The results showed that the fracture behavior of the ductile damage in polyamide is different from the brittle damage in polycarbonate. 相似文献
14.
15.
An extensive Markov process, which considers both the coding redundancy and the intersample redundancy, is presented to measure the entropy value of an ECG signal more accurately. It utilizes the intersample correlations by predicting the incoming n samples based on the previous m samples which constitute an extensive Markov process state. Theories of the extensive Markov process and conventional n repeated applications of m-th order Markov process are studied first. After that, they are realized for ECG exact coding. Results show that a better performance can be achieved by the authors' system. The average code length for the extensive Markov system on the second difference signals was 2.512 b/sample, while the average Huffman code length for the second difference signals was 3.326 b/sample 相似文献
16.
17.
Jang-Ping Sheu Tsu-Huei Tai 《Parallel and Distributed Systems, IEEE Transactions on》1991,2(4):430-439
A method for executing nested loops with constant loop-carried dependencies in parallel on message-passing multiprocessor systems to reduce communication overhead is presented. In the partitioning phase, the nested loop is divided into blocks that reduce the interblock communication, without regard to the machine topology. The execution ordering of the iterations is defined by a given time function based on L. Lamport's (1974) hyperplane method. The iterations are then partitioned into blocks so that the execution ordering is not disturbed, and the amount of interblock communication is minimized. In the mapping phase, the partitioned blocks are mapped onto a fixed-size multiprocessor system in such a manner that the blocks that have to exchange data frequently are allocated to the same processor or neighboring processors. A heuristic mapping algorithm for hypercube machines is proposed 相似文献
18.
耐高温绝缘GFRP管的真空辅助树脂传递成型工艺研究 总被引:3,自引:0,他引:3
阐述了耐高温绝缘GFRP管的成型工艺及原材料选择,并对影响成型工艺的主要因素作了理论分析及试验验证。研究表明,以TDE-85/DDS体系为为基体,以无碱无捻玻璃纤维方格布为增强材料,用VARTM工艺成型的石油勘探高性能平衡管完全满足技术要求。 相似文献
19.
Hyperdynamic circulation of cirrhotic rats: role of substance P and its relationship to nitric oxide
CJ Chu FY Lee SS Wang FY Chang YT Tsai HC Lin MC Hou SL Wu CC Tai SD Lee 《Canadian Metallurgical Quarterly》1997,32(8):841-846
BACKGROUND: It has been suggested that excessive formation of nitric oxide (NO) is responsible for the hyperdynamic circulation observed in portal hypertension. Substance P is a neuropeptide partly cleared by the liver and causes vasodilatation through the activation of the endothelial NO pathway. However, there are no previously published data concerning the plasma level of substance P in cirrhotic rats and its relationship to NO. METHODS: Plasma concentrations of substance P and nitrate/nitrite (an index of NO production) were determined in control rats and cirrhotic rats with or without ascites using an enzyme-linked immununosorbent assay and a colorimetric assay, respectively. In addition, systemic and portal hemodynamics were evaluated by a thermodilution technique and catheterization. RESULTS: Cirrhotic rats with and without ascites had a lower systemic vascular resistance (2.6 +/- 0.2 and 3.9 +/- 0.4 mmHg ml(-1) x min x 100 g body weight, respectively) and higher portal pressure (14.6 +/- 0.6 and 11.3 +/- 1.8 mmHg) than control rats (6.5 +/- 0.3 mmHg x ml(-1) x min x 100 g BW and 6.8 +/- 0.2 mmHg, respectively, P < 0.05), and cirrhotic rats with ascites had the lowest systemic vascular resistance. Plasma levels of nitrate/nitrite progressively increased in relation to the severity of liver dysfunction (control rats, 2.7 +/- 0.5 nmol/ml; cirrhotic rats without ascites, 5.6 +/- 1.3 nmol/ml; cirrhotic rats with ascites, 8.3 +/- 2.2 nmol/ml; P < 0.05). Cirrhotic rats with ascites displayed higher plasma values of substance P (57.7 +/- 5.9 pg/ml) than cirrhotic rats without ascites (37.9 +/- 3.1 pg/ml, P < 0.05) and control rats (30.1 +/- 1.0 pg/ml, P < 0.05). There was no significant difference in plasma substance P values between control rats and cirrhotic rats without ascites (P > 0.05). No correlation was found between plasma levels of substance P and nitrate/nitrite (r = 0.318, P > 0.05). CONCLUSIONS: Excessive formation of NO may be responsible, at least partly, for the hemodynamic derangements in cirrhosis. Although substance P may not participate in the initiation of a hyperdynamic circulation in cirrhosis, it may contribute to the maintenance of the hyperdynamic circulation observed in cirrhotic rats with ascites. 相似文献
20.
Gerosa G. Gary S. Dietz C. Dac Pham Hoover K. Alvarez J. Sanchez H. Ippolito P. Tai Ngo Litch S. Eno J. Golab J. Vanderschaaf N. Kahle J. 《Solid-State Circuits, IEEE Journal of》1994,29(12):1440-1454
A 28 mW/MHz at 80 MHz structured-custom RISC microprocessor design is described. This 32-b implementation of the PowerPC architecture is fabricated in a 3.3 V, 0.5 μm, 4-level metal CMOS technology, resulting in 1.6 million transistors in a 7.4 mm by 11.5 mm chip size. Dual 8-kilobyte instruction and data caches coupled to a high performance 32/64-b system bus and separate execution units (float, integer, loadstore, and system units) result in peak instruction rates of three instructions per clock cycle. Low-power design techniques are used throughout the entire design, including dynamically powered down execution units. Typical power dissipation is kept under 2.2 W at 80 MHz. Three distinct levels of software-programmable, static, low-power operation-for system power management are offered, resulting in standby power dissipation from 2 mW to 350 mW. CPU to bus clock ratios of 1×, 2×, 3×, and 4× are implemented to allow control of system power while maintaining processor performance. As a result, workstation level performance is packed into a low-power, low-cost design ideal for notebooks and desktop computers 相似文献