全文获取类型
收费全文 | 45472篇 |
免费 | 4027篇 |
国内免费 | 2011篇 |
专业分类
电工技术 | 2480篇 |
技术理论 | 2篇 |
综合类 | 2503篇 |
化学工业 | 7693篇 |
金属工艺 | 2608篇 |
机械仪表 | 2931篇 |
建筑科学 | 3021篇 |
矿业工程 | 1296篇 |
能源动力 | 1275篇 |
轻工业 | 2861篇 |
水利工程 | 647篇 |
石油天然气 | 2478篇 |
武器工业 | 337篇 |
无线电 | 5399篇 |
一般工业技术 | 5970篇 |
冶金工业 | 3869篇 |
原子能技术 | 492篇 |
自动化技术 | 5648篇 |
出版年
2024年 | 245篇 |
2023年 | 876篇 |
2022年 | 1511篇 |
2021年 | 2166篇 |
2020年 | 1572篇 |
2019年 | 1460篇 |
2018年 | 1514篇 |
2017年 | 1547篇 |
2016年 | 1451篇 |
2015年 | 1897篇 |
2014年 | 2261篇 |
2013年 | 2694篇 |
2012年 | 2777篇 |
2011年 | 3157篇 |
2010年 | 2485篇 |
2009年 | 2442篇 |
2008年 | 2457篇 |
2007年 | 2185篇 |
2006年 | 2290篇 |
2005年 | 1838篇 |
2004年 | 1333篇 |
2003年 | 1199篇 |
2002年 | 1124篇 |
2001年 | 981篇 |
2000年 | 949篇 |
1999年 | 1032篇 |
1998年 | 1280篇 |
1997年 | 966篇 |
1996年 | 773篇 |
1995年 | 607篇 |
1994年 | 487篇 |
1993年 | 357篇 |
1992年 | 241篇 |
1991年 | 226篇 |
1990年 | 189篇 |
1989年 | 172篇 |
1988年 | 120篇 |
1987年 | 98篇 |
1986年 | 74篇 |
1985年 | 63篇 |
1984年 | 37篇 |
1983年 | 38篇 |
1982年 | 34篇 |
1981年 | 30篇 |
1980年 | 37篇 |
1979年 | 17篇 |
1978年 | 16篇 |
1977年 | 38篇 |
1976年 | 111篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 4 毫秒
141.
142.
用常规电阻率测井资料确定水淹层的剩余油饱和度 总被引:7,自引:0,他引:7
油田综合含水越来越高,利用电阻率测井资料确定地层的剩余油饱和度变得非常困难。针对这一问题,提出了确定地层水民阻率和含油饱和度的方法。(1)利用已知的地怪水分析资料,采用井下自然电位刻度,井间对经和双自然电位一方法来示准地层水混合电阻率,然后利用相邻井相同地层的电阻率对比方法求含水饱和度。(2)利用电阻率的横向探测特性,避开阿尔奇公式中m、a选择上的困难,采用横向法计算水淹层目前的含水饱和度。利用以 相似文献
143.
It has been suggested that volatile anesthetic, isoflurane mediates cardioprotective effects via activation of the ATP-sensitive K+ (KATP) channels. However, no direct evidence has been provided to define whether isoflurane activates cardiac KATP channels using patch-clamp technique. We examined the effects of isoflurane on the KATP channels in rabbit ventricular myocytes by use of patch-clamp technique. Contrary to the results of the in vivo experiments, isoflurane inhibited the channel activity without a change in the single-channel conductance. Isoflurane decreased the channel activity by a decrease in burst duration and an increase in the inter-burst duration. On the other hand, isoflurane diminished the ATP sensitivity of KATP channels, indicating an increased probability of KATP channel opening for a given concentration of ATP after isoflurane anesthesia. The result supports, at least in part, the hypothesis that isoflurane mediates cardioprotective effects via KATP channel activation. 相似文献
144.
145.
146.
某厂锆(Zr)生产流程中不同产物的天然放射性核素含量测定 总被引:2,自引:0,他引:2
本文报道了某厂锆(Zr)生产流程中原料(锆英砂,主要成份为 ZrSiO_4)、半成品(ZrC,ZrCl_4)、废渣和成品锆中天然放射性核素~(238)U、~(226)Ra、~(232)Th 和~(40)K 含量测定结果。采用 NaI(Tl)γ能谱法进行测定,结果表明,原料、半成品和废渣中都含有一定的放射性,各生产环节应采取适当的防护措施;成品锆中基本不含放射性,可安全地应用于各个生产和生活领域。 相似文献
147.
There is agreement on the clinical diagnostic criteria for acute inflammatory demyelinating polyneuropathy (AIDP/GBS) however, there is lack of consensus for detection of demyelination. In order to critically evaluate the prevailing criteria, sixty-six patients who fulfilled NINCDS criteria and had typical features of GBS were studied for electrophysiological abnormalities of peripheral nerves by using standard methods (median, common peroneal, sural and ulnar) between 1 to 12 weeks after the onset of symptoms. The commonest abnormality on motor nerve conduction study was prolonged distal latency (75%-83%) followed by reduction in CMAP amplitude (63%-82%), decreased velocity (48%-62%), conduction block (17%-39%) and f-wave abnormalities (37.8%-59%). Sensory conduction abnormalities were detected in over 20% of median, 25% of ulnar and 33% of sural nerves. All the patients had abnormality of at least two motor conduction parameters in one nerve when values beyond 2 SD of the mean were considered abnormal and over 70% of patients had three abnormalities in two nerves or two abnormalities in three nerves. Comparison with the prevailing criteria for demyelination revealed that the number of patients fulfilling them varied widely: Albers et al. (1985): 74.2%, Albers et al. (1989): 40.9% and Cornblath: 30.3%. We believe that the current criteria for detection of demyelination in acute neuropathy are too strict, underestimate the underlying pathology in GBS and need reassessment. 相似文献
148.
149.
M Kockx MP de Maat HC Knipscheer JJ Kastelein C Kluft HM Princen T Kooistra 《Canadian Metallurgical Quarterly》1997,78(4):1167-1172
Evaluation of fibrate treatment in humans has focused primarily on its anti-lipidaemic effects. A potentially favourable haemostasis-modulating activity of fibrates has also been recognized but the data are not consistent. We sought to learn more about this variability by examining the effects of gemfibrozil and ciprofibrate on plasma levels of tissue-type plasminogen activator (t-PA), plasminogen activator inhibitor-1 (PAI-1) and fibrinogen in primary hyperlipidaemic patients after six and twelve weeks of treatment using different assay systems for PAI-1 and fibrinogen. Although both fibrates effectively lowered triglyceride and cholesterol levels, no effect on the elevated baseline antigen levels of t-PA and PAI-1 was observed after fibrate treatment. However, both fibrates influenced plasma fibrinogen levels, albeit in a different way. Fibrinogen antigen levels were elevated by 17.6% (p <0.05) and 24.3% (p <0.001) with gemfibrozil after six and twelve weeks, respectively, whereas with ciprofibrate there was no effect. Using a Clauss functional assay with either a mechanical end point or a turbidity-based end point, no significant change in fibrinogen levels was seen after six weeks of gemfibrozil treatment. However, after twelve weeks, gemfibrozil enhanced functional fibrinogen levels by 7.2% (p <0.05) as assessed by the Clauss mechanical assay, but decreased functional fibrinogen levels by 12.5% (p <0.0001) when a Clauss assay based on turbidity was used. After six or twelve weeks of ciprofibrate treatment, functional fibrinogen levels were decreased by 10.1% (p <0.001) and 10.5% (p <0.0001), respectively on the basis of Clauss mechanical and by 14.2% (p <0.001) and 28.2% (p <0.0001), respectively with the Clauss turbidimetric assay. A remarkable and consistent finding with both fibrates was the decrease in functionality of fibrinogen as assessed by the ratio of functional fibrinogen (determined by either of the two Clauss assays) to fibrinogen antigen. Taken together, our results indicate that at least part of the variability in the effects of fibrates on haemostatic parameters can be explained by intrinsic differences between various fibrates, by differences in treatment period and/or by the different outcomes of various assay systems. Interestingly, the two fibrates tested both reduced the functionality of fibrinogen. 相似文献
150.
The body color in animals results from billions of years of their natural evolution in order to evade natural enemies, catch
quarries or display themselves beauty, investigation on mechanisms of structural light is an important aspect of bionics.
Based on the phenomenon of Papilio maackii ménétriès’ blue scales changing into green ones immediately after dropping some alcohol aqua on the underwing surface and
soon returning back to the original color, the relationship between microstructure, optics characteristic of scales and changing
color effect were studied using the Olympus Stereomicroscope, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy
(TEM) and Ultraviolet (UV)-Visible Spectrophotometer. The color variation mechanisms of blue scales of Papilio maackii ménétriès in Chinese Northeast were revealed in this paper. When visible lights traveled through the concaver structure with
multilayer reflector and the filled medium with different refractive indices, the reflected lights in definite wavelengths
produced interference and color at that wavelength came into being. It has important academic reference value to biomimetics
design of video stealth materials.
Recommended by Prof. SONG YuQuan, Member of Editorial Committee of Science in China, Series E: Technological Sciences
Supported by the National Natural Science Foundation of China (Grant Nos. 50635030, 30570235), the Key Project of Chinese
Ministry of Education (Grant No. 105059), and Fok Ying Tong Education Foundation (Grant No. 101020) 相似文献