全文获取类型
收费全文 | 24933篇 |
免费 | 2165篇 |
国内免费 | 953篇 |
专业分类
电工技术 | 1190篇 |
综合类 | 1609篇 |
化学工业 | 4923篇 |
金属工艺 | 1034篇 |
机械仪表 | 1091篇 |
建筑科学 | 1450篇 |
矿业工程 | 432篇 |
能源动力 | 660篇 |
轻工业 | 3768篇 |
水利工程 | 531篇 |
石油天然气 | 734篇 |
武器工业 | 136篇 |
无线电 | 2135篇 |
一般工业技术 | 2785篇 |
冶金工业 | 960篇 |
原子能技术 | 215篇 |
自动化技术 | 4398篇 |
出版年
2024年 | 104篇 |
2023年 | 361篇 |
2022年 | 950篇 |
2021年 | 1147篇 |
2020年 | 896篇 |
2019年 | 723篇 |
2018年 | 793篇 |
2017年 | 887篇 |
2016年 | 810篇 |
2015年 | 1164篇 |
2014年 | 1490篇 |
2013年 | 1873篇 |
2012年 | 2150篇 |
2011年 | 2279篇 |
2010年 | 1916篇 |
2009年 | 1838篇 |
2008年 | 1694篇 |
2007年 | 1599篇 |
2006年 | 1271篇 |
2005年 | 953篇 |
2004年 | 645篇 |
2003年 | 460篇 |
2002年 | 390篇 |
2001年 | 265篇 |
2000年 | 202篇 |
1999年 | 171篇 |
1998年 | 171篇 |
1997年 | 132篇 |
1996年 | 94篇 |
1995年 | 75篇 |
1994年 | 60篇 |
1993年 | 57篇 |
1992年 | 42篇 |
1991年 | 38篇 |
1990年 | 33篇 |
1989年 | 37篇 |
1988年 | 23篇 |
1987年 | 35篇 |
1986年 | 28篇 |
1985年 | 25篇 |
1984年 | 20篇 |
1983年 | 19篇 |
1982年 | 9篇 |
1981年 | 18篇 |
1980年 | 21篇 |
1979年 | 8篇 |
1977年 | 6篇 |
1976年 | 20篇 |
1974年 | 9篇 |
1972年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
The effect of pressure on transition displacement between trickle and pulsed regimes (TPR: trickle-pulsed transition) in catalytic trickle bed reactors (CTBR) is not properly predicted by existing theoretical models and empirical correlations. Based on high pressure TPR data available to date, a modified Charpentier diagram is proposed to quantify directly the effect of pressure in non-foaming systems. 相似文献
62.
AJ Morguet RE Gabriel AB Buchwald GS Werner R Nyga H Kreuzer 《Canadian Metallurgical Quarterly》1997,20(4):382-393
BACKGROUND AND OBJECTIVE: Spectroscopic guidance of laser angioplasty has been attempted using a diagnostic He-Cd laser in addition to the therapeutic laser system. This study evaluated a single-laser approach for simultaneous ablation and fluorescence excitation. STUDY DESIGN/MATERIALS AND METHODS: A spectroscopy system was coupled to a clinical XeCl excimer laser. Ablation of 162 human aortic samples in saline and blood with 45 mJ/mm2 per pulse yielded 676 fluorescence spectra validated histologically. The same equipment was used in 16 patients for angioplasty of 18 coronary stenoses applying 500 to 1,725 pulses with 45 to 60 mJ/mm2 under saline flushing. A total of 783 spectra were recorded and validated by intracoronary ultrasound (categories: atheroma, fibrous plaque, calcified lesion). RESULTS: In vitro, 5 types of spectra could be differentiated: (1) atheroma, (2) fibrous plaque, (3) calcified lesion in saline, (4) media, and (5) calcified lesion in blood. Discriminant analysis prospectively classified 576 validation spectra with the following sensitivity and specificity for each type: (1) 83.5 and 97.1%, (2) 85.7 and 96.8% (3) 100 and 98.5%, (4) 98.1 and 99.3%, (5) 98.9 and 100%, respectively. In vivo type 1, 2, 3, and 5 spectra were also observed, but not the media spectrum. The predominant sonographic category also prevailed in spectroscopy. Calcified lesions yielded type 3 and 5 as well as mixed spectra. CONCLUSIONS: Using an excimer laser for angioplasty allows combining ablation and fluorescence excitation without a diagnostic laser. Principal types of atherosclerotic lesions and the media can be differentiated spectroscopically with this approach. 相似文献
63.
64.
Precise timing and asynchronous I/O are appealing features for many applications. Unix kernels provide such features on a per‐process basis, using signals to communicate asynchronous events to applications. Per‐process signals and timers are grossly inadequate for complex multithreaded applications that require per‐thread signals and timers that operate at finer granularity. To respond to this need, we present a scheme that integrates asynchronous (Unix) signals with user‐level threads, using the ARIADNE system as a platform. This is done with a view towards support for portable, multithreaded, and multiprotocol distributed applications, namely the CLAM (connectionless, lightweight, and multiway) communications library. In the same context, we propose the use of continuations as an efficient mechanism for reducing thread context‐switching and busy‐wait overheads in multithreaded protocols. Our proposal for integrating timers and signal‐handling mechanisms not only solves problems related to race conditions, but also offers an efficient and flexible interface for timing and signalling threads. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
65.
着重介绍了静态法测试低温下(-100~50℃)液体饱和蒸气压的原理及方法,给出了低温下液体全氟三乙胺饱和蒸气压的测试结果,并进行了讨论。 相似文献
66.
Vicente Ferreira Cristina Peña Ana Escudero Juan Cacho 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1996,202(4):318-323
The ability of fermentative CO2 to blow off the volatile compounds that are synthesized during fermentation has been studied. Model solutions simulating a fermenting must were purged at different CO2 flow rates and temperatures, and the amount of volatile compounds blown off by the stream of CO2 was recorded by high-resolution gas chromatography. Data showed that under normal fermenting conditions, fatty acid ethyl esters and some fusel alcohol acetates are blown off the solution at a high rate. The maximum loss rate was observed for ethyl decanoate. The purging speed is doubled when temperature increases from 17 °C to 27 °C. Losses can be interpreted by a linear model and are a function of the compound and the flow rate of CO2. These models allow us to reconstruct the volatile synthesis vs time functions through graphic calculus and to estimate the proportion of volatile material retained, hydrolysed and purged. Synthesis takes place during the tumultuous period of fermentation together with CO2 production that blows off the volatile material. Hydrolysis takes place in the last stages of fermentation. In a 10-1 open fermenter, up to 80% of volatile material can be blown off while an average of 10% is retained. Residual esterase activity accounts for about 20% of the total amount of ester synthesized. 相似文献
67.
Víctor Osma-Ruiz Juan I. Godino-Llorente Pedro Gómez-Vilda 《Pattern recognition》2007,40(3):1078-1090
The present paper describes a new algorithm to calculate the watershed transform through rain simulation of greyscale digital images by means of pixel arrowing. The efficiency of this method is based on limiting the necessary neighbouring operations to compute the transform to the outmost, and in the total number of scannings performed over the whole image. The experiments demonstrate that the proposed algorithm is able to significantly reduce the running time of the fastest known algorithm without involving any loss of efficiency. 相似文献
68.
P. B. Malafaya A. J. Pedro A. Peterbauer C. Gabriel H. Redl R. L. Reis 《Journal of materials science. Materials in medicine》2006,17(7):675-675
In the XML file of the original article, H. Redl’s affiliation is incorrect. It is listed correctly in both the paper and
PDF versions of the article, and can be found below:
The online version of the original article can be found at 相似文献
69.
PO Freskgard LC Petersen DA Gabriel X Li E Persson 《Canadian Metallurgical Quarterly》1998,37(20):7203-7212
The binding of the multidomain protein factor VIIa (fVIIa) to tissue factor provides the interprotein communication necessary to make fVIIa an efficient catalyst of the initial event in the extrinsic pathway of blood coagulation. We have investigated the stability of individual domains in fVIIa and the influence of Ca2+ and an irreversible active-site inhibitor (FFR-chloromethyl ketone). Equilibrium guanidine hydrochloride (GuHCl)-induced unfolding monitored by tryptophan fluorescence and far-UV circular dichroism (CD) demonstrated that the gamma-carboxyglutamic acid (Gla) domain unfolds at 0.3 M GuHCl and the serine protease (SP) domain at 3 M GuHCl and that Ca2+ is a prerequisite for the formation of an ordered, compact structure in the Gla domain. The loss of amidolytic activity coincides with the first transition, which is stabilized by the active-site inhibitor, and a change in the environment of the active site is demonstrated using a fluorescent inhibitor (DEGR-chloromethyl ketone). Thermal unfolding monitored by differential scanning calorimetry (DSC) reveals that Ca2+ stabilizes the SP domain slightly, increasing the unfolding temperature by 2.7 degrees C. In addition, Ca2+ is required for a large enthalpy change concomitant with unfolding of the Gla domain, and this unfolding enthalpy is only detectable in the presence of the SP domain, indicating some kind of interaction between these domains. Thermal unfolding measured by CD indicates secondary structural changes at the same temperature as the heat absorption in the DSC but only when both the Gla domain and the SP domain are present together with Ca2+ ions. Taken together, these results indicate a Ca2+-dependent interaction between the Gla domain and the SP domain, implying a high degree of flexibility of the domains in free fVIIa. It is also shown that the epidermal growth factor-like domains are stable at elevated temperatures and high GuHCl concentrations. Moreover, already at physiological temperature, subtle structural changes take place which influence the overall shape of fVIIa and are detrimental to its enzymatic activity. 相似文献
70.
This paper studies the input-output finite-time stabilization problem for time-varying linear singular systems. The output and the input refer to the controlled output and the disturbance input,respectively.Two classes of disturbance inputs are considered,which belong to L-two and L-infinity.Sufficient conditions are firstly provided which guarantee the input-output finite-time stability.Based on this,state feedback controllers are designed such that the resultant closed-loop systems are input-output finite-time stable.The conditions are presented in terms of differential linear matrix inequalities.Finally,an example is presented to show the validity of the proposed results. 相似文献