全文获取类型
收费全文 | 302471篇 |
免费 | 77260篇 |
国内免费 | 50193篇 |
专业分类
电工技术 | 34527篇 |
技术理论 | 9篇 |
综合类 | 28465篇 |
化学工业 | 43898篇 |
金属工艺 | 30779篇 |
机械仪表 | 13891篇 |
建筑科学 | 22303篇 |
矿业工程 | 16406篇 |
能源动力 | 11754篇 |
轻工业 | 27976篇 |
水利工程 | 9351篇 |
石油天然气 | 19570篇 |
武器工业 | 4485篇 |
无线电 | 42766篇 |
一般工业技术 | 43791篇 |
冶金工业 | 12270篇 |
原子能技术 | 2590篇 |
自动化技术 | 65093篇 |
出版年
2024年 | 3186篇 |
2023年 | 6353篇 |
2022年 | 8309篇 |
2021年 | 10297篇 |
2020年 | 12271篇 |
2019年 | 20921篇 |
2018年 | 22625篇 |
2017年 | 24293篇 |
2016年 | 23491篇 |
2015年 | 23824篇 |
2014年 | 23669篇 |
2013年 | 23889篇 |
2012年 | 23755篇 |
2011年 | 20742篇 |
2010年 | 18556篇 |
2009年 | 15103篇 |
2008年 | 13133篇 |
2007年 | 12207篇 |
2006年 | 11644篇 |
2005年 | 10554篇 |
2004年 | 11357篇 |
2003年 | 9533篇 |
2002年 | 8976篇 |
2001年 | 8022篇 |
2000年 | 7790篇 |
1999年 | 7810篇 |
1998年 | 6845篇 |
1997年 | 5982篇 |
1996年 | 5660篇 |
1995年 | 5404篇 |
1994年 | 4420篇 |
1993年 | 3717篇 |
1992年 | 3453篇 |
1991年 | 2594篇 |
1990年 | 2008篇 |
1989年 | 1826篇 |
1988年 | 1417篇 |
1987年 | 566篇 |
1986年 | 448篇 |
1985年 | 302篇 |
1984年 | 206篇 |
1983年 | 154篇 |
1982年 | 205篇 |
1981年 | 175篇 |
1980年 | 128篇 |
1976年 | 227篇 |
1975年 | 205篇 |
1972年 | 236篇 |
1971年 | 127篇 |
1960年 | 205篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
W. Lim C. K. Wang 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1996,370(2-3):568-572
The one-dimensional (1D) position-sensitive superheated-liquid-droplet dosimeter (SLDD) has been fabricated and tested in the laboratory. The 1D SLDD is fabricated from a 9.525-mm OD, 6.35-mm ID, 20-cm long, Plexiglas-walled tube filled with a mixture of superheated-liquid Freon droplets and host medium glycerol. Washer-shaped piezoelectric acoustic transducers are positioned at both ends of the tube; they determine the number and positions of the acoustic events when the superheated-liquid droplets evaporate upon neutron irradiation. The SLDD is irradiated with the 137Cs and 60Co γ-sources, as well as 252Cf neutron source to test for its radiation response and spatial resolution. The SLDD based on the Freon-134a superheated-liquid droplets operating at 20°C and 1 atm is found to be ideal for measuring absorbed neutron dose. This study also proves that the positions of the radiation-induced nucleation acoustic events can be linearly determined from the differences in the transmission times received by the acoustic transducers on the 1D SLDD. The spatial resolution of the neutron depth-dose is 1 mm due the finite response time (1 μs) of the piezoelectric acoustic transducers. 相似文献
52.
53.
The kinetics of substrate removal by the liver and the resulting nonlinear changes in unbound fraction along the flow path at varying input drug concentrations were examined by a model simulation study. Specifically, we varied the binding association constant, KA, and the Michaelis-Menten constants (Km and Vmax) to examine the steady state drug removal (expressed as hepatic extraction ratio E) and changes in drug binding for (i) unienzyme systems and (ii) simple, parallel metabolic pathways; zonal metabolic heterogeneity was also added as a variable. At low KA, E declined with increasing input drug concentration, due primarily to saturation of enzymes; only small differences in binding were present across the liver. At high KA, a parabolic profile for E with concentration was observed; changes in unbound fraction between the inlet and the outlet of the liver followed in parallel fashion. Protein binding was the rate-determining step at low input drug concentrations, whereas enzyme saturation was the rate-controlling factor at high input drug concentration. Heterogeneous enzymic distribution modulated changes in unbound fraction within the liver and at the outlet. Despite marked changes in unbound fraction occurring within the liver for different enzymic distributions, the overall transhepatic differences were relatively small. We then investigated the logarithmic average unbound concentration and the length averaged concentration as estimates of substrate concentration in liver in the presence of nonlinear drug binding. Fitting of simulated data, with and without assigned random error (10%), to the Michaelis-Menten equation was performed; fitting was repeated for simulated data obtained with presence of a specific inhibitor of the high-affinity, anteriorly distributed pathway. Results were similar for both concentration terms: accurate estimates were obtained for anterior, high affinity pathways; an overestimation of parameters was observed for the lower affinity posteriorly distributed pathways. Improved estimations were found for posteriorly distributed pathways upon inhibition with specific inhibitors; with added random error, however, the improvement was much decreased. We applied the method for fitting of several sets of metabolic data obtained from rat liver perfusion studies performed with salicylamide (SAM) (i) without and (ii) with the presence of 2,6-dichloro-4-nitrophenol (DCNP), a SAM sulfation inhibitor. The fitted results showed that SAM sulfation was a high-affinity high-capacity pathway; SAM glucuronidation was of lower affinity but comparable capacity as the sulfation pathway, whereas SAM hydroxylation was of lower affinity and lower capacity. 相似文献
54.
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
55.
56.
57.
58.
LDD方法在提高电路工作电压中的应用研究 总被引:1,自引:0,他引:1
研究了利用轻掺杂漏结构来制作高电源电压器件的工艺方法。分析了LDD结构参数对器件击穿特性的影响,并结合实验结果对N^-区的注入剂量,长度及引入的串联电阻进行了优化设计。 相似文献
59.
先说明市内接入网的单位用户和住家用户两大类使用通信和电视、交互型和分配型业务的要求不相同,相应地对光纤传输的应用须作不同的考虑,文中认为;光纤从市内交换局直连办公大楼是合乎现实需要的,而对于居民住家,宜选用光纤连至路边或光纤与同轴结合和适当利用无源光网络等方案,俟将来时机成熟才实行光纤连至每一家,文末有概括总结,说明接入网不同于长途网,接入网的光纤系统可以使用常规单模光纤,工作于波长1.3μm,而光放大器和波分多路系统不是普遍需要,但光电子集成在光端机中是必要的。 相似文献
60.
NMOS器件两次沟道注入杂质分布和阈电压计算 总被引:1,自引:1,他引:0
分别考虑了深浅两次沟道区注入杂质在氧化扩散过程中对表面浓度的贡献。对两次注入杂质的扩散分别提取了扩散系数的氧化增强系数、氧化衰减系数和有效杂地系数,给出了表面浓度与工艺参数之间的模拟关系式,以峰值浓度为强反型条件计算了开启电压,文章还给出了开启电压、氧化条件、不同注入组合之间的关系式。 相似文献