全文获取类型
收费全文 | 396643篇 |
免费 | 4342篇 |
国内免费 | 1941篇 |
专业分类
电工技术 | 6815篇 |
综合类 | 2547篇 |
化学工业 | 56572篇 |
金属工艺 | 16989篇 |
机械仪表 | 12744篇 |
建筑科学 | 9607篇 |
矿业工程 | 1879篇 |
能源动力 | 9936篇 |
轻工业 | 29891篇 |
水利工程 | 4153篇 |
石油天然气 | 5537篇 |
武器工业 | 56篇 |
无线电 | 48970篇 |
一般工业技术 | 79106篇 |
冶金工业 | 61496篇 |
原子能技术 | 7558篇 |
自动化技术 | 49070篇 |
出版年
2022年 | 1938篇 |
2021年 | 2943篇 |
2020年 | 2165篇 |
2019年 | 2587篇 |
2018年 | 18476篇 |
2017年 | 17419篇 |
2016年 | 14464篇 |
2015年 | 3598篇 |
2014年 | 5486篇 |
2013年 | 14797篇 |
2012年 | 11216篇 |
2011年 | 19961篇 |
2010年 | 16792篇 |
2009年 | 15469篇 |
2008年 | 17069篇 |
2007年 | 17894篇 |
2006年 | 9361篇 |
2005年 | 9222篇 |
2004年 | 8894篇 |
2003年 | 9160篇 |
2002年 | 7986篇 |
2001年 | 8024篇 |
2000年 | 7576篇 |
1999年 | 7782篇 |
1998年 | 19570篇 |
1997年 | 13630篇 |
1996年 | 10474篇 |
1995年 | 7898篇 |
1994年 | 7027篇 |
1993年 | 7005篇 |
1992年 | 4978篇 |
1991年 | 4930篇 |
1990年 | 4780篇 |
1989年 | 4565篇 |
1988年 | 4387篇 |
1987年 | 3760篇 |
1986年 | 3708篇 |
1985年 | 4023篇 |
1984年 | 3608篇 |
1983年 | 3495篇 |
1982年 | 3216篇 |
1981年 | 3146篇 |
1980年 | 3027篇 |
1979年 | 2873篇 |
1978年 | 2655篇 |
1977年 | 3291篇 |
1976年 | 4391篇 |
1975年 | 2275篇 |
1974年 | 2214篇 |
1973年 | 2139篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
The impact of crosstalk in an arrayed-waveguide N×N wavelength multiplexer is investigated precisely in relation to its application to wavelength-routing N×N all optical networks. In such systems multiple crosstalk light which has the same wavelength as the signal results in signal-crosstalk beat noise. We confirm that the noise is Gaussian and obtain the relation between crosstalk and power penalty. It is shown that the crosstalk must be less than -38 dB for a 16×16 system to keep the power penalty below 1 dB at a bit error rate of 10-9 相似文献
32.
D Sternberg A Peled E Shezen O Abramsky W Jiang F Bertolero D Zipori 《Canadian Metallurgical Quarterly》1996,2(1):29-38
The immunological agglutination reactions of physically absorbed F(ab')2 molecules onto anionic and cationic latex particles have been investigated by means of optical absorbance measurements. These measurements have been conducted under different conditions to determine the most influential factors. Surface F(ab')2 and BSA densities, particle concentration in the reaction medium and polyethylene glycol concentration are some of these factors. Sensitized cationic and anionic latexes differ considerably with respect to their colloidal stability and reactivity. As a general rule, the sensitized cationic latex has a relatively higher colloidal stability and hence, it provides reagents with a better optical response. Less than 0.025 microgram/ml of C-reactive protein has been detected using this particle enhanced optical immunoassay. 相似文献
33.
N Usui S Kamata S Ishikawa T Sawai H Okuyama K Imura A Okada 《Canadian Metallurgical Quarterly》1996,31(2):258-262
Bone marrow examination revealed a lipid-laden histiocytosis in seven patients undergoing long-term total parenteral nutrition necessitated by extensive short-bowel surgical resection. Clinical abnormalities occurred during this treatment which required bone marrow examination. These included hepatosplenomegaly and peripheral blood cytopenia; the median time to the detection of these abnormalities was 64 months. The most striking change within the bone marrow was the presence of many pigment-laden histiocytes which had the typical morphology of sea-blue histiocytes seen in the so-called idiopathic sea-blue histiocyte syndrome. The occurrence of sea-blue histiocytosis in the bone marrow in association with long-term parenteral nutrition for short-bowel syndrome has not, to our knowledge, been reported previously and should now be considered in the differential diagnosis of bone marrow sea-blue histiocytosis. 相似文献
34.
One month following the Great Hanshin Earthquake of January 17, 1995, we conducted a survey of 173 hospitals in Aichi Prefecture to pinpoint problems related to their actual disaster-readiness and the medical backup systems in place to deal with such disasters. This study revealed that staff at 50% of the surveyed hospitals could reach the hospital within an hour, but that communication is almost entirely dependent on phone lines, suggesting that cordless/portable/mobile phones, radio systems, Internet, communications satellites and the like should be studied in the days to come for possible use as effective communication alternatives in times of disaster. Whereas 92% of the surveyed hospitals had manuals dealing with fire outbreaks, other areas were less well represented. For example, only 36.9% of surveyed hospitals had manuals for earthquakes, 31.7% had manuals for power outages and 14.2% had manuals to deal with flooding and water disasters. New manuals must be developed incorporating the key points garnered from experience (especially Hanshin) and be ready for use immediately. It is the time for each hospital to seriously rethink the measures it should take to deal with disasters. 相似文献
35.
K Alanko L Kanerva B Mohell-Talolahti R Jolanki T Estlander 《Canadian Metallurgical Quarterly》1996,35(4):647-648
The biotransformation of oxazepam by Bifidobacterium bifidum was studied. The major metabolite was purified by chromatographic methods and found to be desmethyldiazepam using NMR, IR and other physicochemical data. 相似文献
36.
37.
Bouillet E. Mitra D. Ramakrishnan K.G. 《Selected Areas in Communications, IEEE Journal on》2002,20(4):691-699
The paper proposes a structure for quality-of-service (QoS)-centered service level agreements (SLA), and a framework for their real-time management in multiservice packet networks. The SLA is structured to be fair to both parties, the service provider and their customer. The SLA considered here are for QoS assured delivery of aggregate bandwidth from ingress to egress nodes; however, the control and signaling is for the more granular flows or calls. A SLA monitoring scheme is presented in which revenue is generated by the admission of flows into the network, and penalty incurred when flows are lost in periods when the service provider is not SLA compliant. In the SLA management scheme proposed, the results of a prior off-line design are used, in conjunction with measurements taken locally at ingress nodes, to classify the loading status of routes. The routing and resource management are based on virtual partitioning and its supporting mechanism of bandwidth protection. The effectiveness of SLA management is measured by the robustness in performance in the presence of substantial diversity in actual traffic conditions. A simulation testbed called D'ARTAGNAN has been built from which we report numerical results for a case study. The results show that the SLA management scheme is robust, fair and efficient over a broad range of traffic conditions 相似文献
38.
39.
The effect of high oxide field stress is studied using capacitance-time (C-t) measurements of MOS capacitors. The stress results in parallel shifts of the C-t curve along the time axis. The flatband voltage shift ΔVFB obtained from the initial deep depletion capacitance C(t=0+) follows the same trend as that from the high-frequency C-V characteristics. However, the discrepancy between the two flatband voltages becomes larger as the stress increases due to the effect of interface charges on C-t characteristics. The flatband voltage difference is converted to interface trap density, showing a steady increase of interface trap density with stress, similar to that from low-frequency C-V measurements 相似文献
40.
This paper presents the design criteria, procedure, and implementation of a soft-switched power-factor-correction (PFC) circuit based on the extended-period quasi-resonant (EPQR) principles. All power electronic devices including switches and diodes in the circuit are fully soft switched. The design method is demonstrated in a prototype circuit. The operating principles are confirmed with computer simulation and experimental results. A comparison of the EP-QR operation and zero-voltage-transition (ZVT) pulse-width modulation (PWM) method 相似文献