全文获取类型
收费全文 | 18971篇 |
免费 | 740篇 |
国内免费 | 44篇 |
专业分类
电工技术 | 238篇 |
综合类 | 24篇 |
化学工业 | 3743篇 |
金属工艺 | 467篇 |
机械仪表 | 400篇 |
建筑科学 | 948篇 |
矿业工程 | 108篇 |
能源动力 | 605篇 |
轻工业 | 1643篇 |
水利工程 | 173篇 |
石油天然气 | 68篇 |
无线电 | 1470篇 |
一般工业技术 | 3368篇 |
冶金工业 | 3433篇 |
原子能技术 | 116篇 |
自动化技术 | 2951篇 |
出版年
2023年 | 123篇 |
2022年 | 212篇 |
2021年 | 331篇 |
2020年 | 236篇 |
2019年 | 270篇 |
2018年 | 369篇 |
2017年 | 379篇 |
2016年 | 414篇 |
2015年 | 341篇 |
2014年 | 514篇 |
2013年 | 1220篇 |
2012年 | 827篇 |
2011年 | 1176篇 |
2010年 | 800篇 |
2009年 | 833篇 |
2008年 | 930篇 |
2007年 | 875篇 |
2006年 | 761篇 |
2005年 | 745篇 |
2004年 | 594篇 |
2003年 | 542篇 |
2002年 | 528篇 |
2001年 | 333篇 |
2000年 | 304篇 |
1999年 | 328篇 |
1998年 | 357篇 |
1997年 | 300篇 |
1996年 | 327篇 |
1995年 | 304篇 |
1994年 | 291篇 |
1993年 | 262篇 |
1992年 | 260篇 |
1991年 | 161篇 |
1990年 | 230篇 |
1989年 | 203篇 |
1988年 | 167篇 |
1987年 | 166篇 |
1986年 | 157篇 |
1985年 | 187篇 |
1984年 | 197篇 |
1983年 | 163篇 |
1982年 | 170篇 |
1981年 | 169篇 |
1980年 | 143篇 |
1979年 | 165篇 |
1978年 | 123篇 |
1977年 | 121篇 |
1976年 | 162篇 |
1975年 | 125篇 |
1973年 | 108篇 |
排序方式: 共有10000条查询结果,搜索用时 30 毫秒
11.
Environmental concerns continue to pose the challenge to replace petroleum-based products with renewable ones completely or at least partially while maintaining comparable properties. Herein, rigid polyurethane (PU) foams were prepared using soy-based polyol for structural and thermal insulation applications. Cell size, density, thermal resistivity, and compression force deflection (CFD) values were evaluated and compared with that of petroleum-based PU foam Baydur 683. The roles of different additives, that is, catalyst, blowing agent, surfactants, and different functionalities of polyol on the properties of fabricated foam were also investigated. For this study, dibutyltin dilaurate was employed as catalyst and water as environment friendly blowing agent. Their competitive effect on density and cell size of the PU foams were evaluated. Five different silicone-based surfactants were employed to study the effect of surface tension on cell size of foam. It was also found that 5 g of surfactant per 100 g of polyol produced a foam with minimum surface tension and highest thermal resistivity (R value: 26.11 m2·K/W). However, CFD values were compromised for higher surfactant loading. Additionally, blending of 5 g of higher functionality soy-based polyol improved the CFD values to 328.19 kPa, which was comparable to that of petroleum-based foam Baydur 683. 相似文献
12.
Dr. Iain J. W. McKean Prof. Paul A. Hoskisson Prof. Glenn A. Burley 《Chembiochem : a European journal of chemical biology》2020,21(20):2890-2897
This Concept article describes the latest developments in the emerging area of late-stage biocatalytic alkylation. Central to these developments is the ability to efficiently prepare S-adenosyl methionine (SAM) cofactor analogues and couple this with enzymatic alkyl transfer. Recent developments in the enzymatic synthesis of SAM cofactor analogues are summarized first, followed by their application as alkyl transfer agents catalyzed by methyltransferases (MTases). Second, innovative methods to regenerate SAM cofactors by enzymatic cascades is reported. Finally, future opportunities towards establishing a generalized platform for late-stage alkylation are described. 相似文献
13.
Paul Ocheje Ameh Nnabuk Okon Eddy 《Protection of Metals and Physical Chemistry of Surfaces》2018,54(6):1169-1181
Protection of Metals and Physical Chemistry of Surfaces - In this work, phthalic acid is investigated for its corrosion inhibition properties (for aluminum in solutions of HCl and H2SO4) through... 相似文献
14.
Greg A. Breed Paul M. Severns Andrew M. Edwards 《Journal of the Royal Society Interface》2015,12(103)
Lévy flights have gained prominence for analysis of animal movement. In a Lévy flight, step-lengths are drawn from a heavy-tailed distribution such as a power law (PL), and a large number of empirical demonstrations have been published. Others, however, have suggested that animal movement is ill fit by PL distributions or contend a state-switching process better explains apparent Lévy flight movement patterns. We used a mix of direct behavioural observations and GPS tracking to understand step-length patterns in females of two related butterflies. We initially found movement in one species (Euphydryas editha taylori) was best fit by a bounded PL, evidence of a Lévy flight, while the other (Euphydryas phaeton) was best fit by an exponential distribution. Subsequent analyses introduced additional candidate models and used behavioural observations to sort steps based on intraspecific interactions (interactions were rare in E. phaeton but common in E. e. taylori). These analyses showed a mixed-exponential is favoured over the bounded PL for E. e. taylori and that when step-lengths were sorted into states based on the influence of harassing conspecific males, both states were best fit by simple exponential distributions. The direct behavioural observations allowed us to infer the underlying behavioural mechanism is a state-switching process driven by intraspecific interactions rather than a Lévy flight. 相似文献
15.
16.
Christian Veauthier Gunnar Gaede Helena Radbruch Klaus-Dieter Wernecke Friedemann Paul 《International journal of molecular sciences》2015,16(7):16514-16528
Quality of Life (QoL) is decreased in multiple sclerosis (MS), but studies about the impact of sleep disorders (SD) on health-related quality of Life (HRQoL) are lacking. From our original cohort, a cross-sectional polysomnographic (PSG) study in consecutive MS patients, we retrospectively analysed the previously unpublished data of the Nottingham Health Profile (NHP). Those MS patients suffering from sleep disorders (n = 49) showed significantly lower HRQoL compared to MS patients without sleep disorders (n = 17). Subsequently, we classified the patients into four subgroups: insomnia (n = 17), restless-legs syndrome, periodic limb movement disorder and SD due to leg pain (n = 24), obstructive sleep apnea (n = 8) and patients without sleep disorder (n = 17). OSA and insomnia patients showed significantly higher NHP values and decreased HRQoL not only for the sleep subscale but also for the “energy” and “emotional” area of the NHP. In addition, OSA patients also showed increased NHP values in the “physical abilities” area. Interestingly, we did not find a correlation between the objective PSG parameters and the subjective sleep items of the NHP. However, this study demonstrates that sleep disorders can reduce HRQoL in MS patients and should be considered as an important confounder in all studies investigating HRQoL in MS. 相似文献
17.
Andrea Bedon Jean Paul Viricelle Mathilde Rieu Simone Mascotto Antonella Glisenti 《International Journal of Hydrogen Energy》2021,46(27):14735-14747
In this contribution brownmillerite-based nanocomposite cathode for Single-Chamber Solid Oxide Fuel Cells is developed. These cells can be very attractive especially for small and cheap devices because of the absence of seals. The efficiency of SC-SOFCs is strictly connected to the selectivity of anode and cathode, the bottleneck for this technology. The development of a cathode inert in fuel oxidation is particularly challenging. Our strategy is to start from a catalytically un-active support (CFA = Ca2FeAl0.95Mg0.05O5) and induce the formation of iron oxide based nanoparticles, expected to activate oxygen. Symmetric (CFA + FeOx/CGO/CFA + FeOx) and complete cells (CFA + FeOx/CGO/Ni-CGO) are studied in air and methane/oxygen 2:1 mixture. The Area Specific Resistance of CFA + FeOx is less than 1/3 that of CFA. The high selectivity allows to reach an efficiency of 25%; power still needs to be increased but we demonstrated the possibility to develop selective low cost electrodes. The effect of air, methane/oxygen exposure and the heat treatments were carefully investigated. 相似文献
18.
Paul Feautrier 《International journal of parallel programming》2006,34(5):459-487
Scheduling a program (i.e. constructing a timetable for the execution of its operations) is one of the most powerful methods
for automatic parallelization. A schedule gives a blueprint for constructing a synchronous program, suitable for an ASIC or
VLIW processor. However, constructing a schedule entails solving a large linear program. Even if one accepts the (experimental)
fact that the Simplex is almost always polynomial, the scheduling time is of the order of a large power of the program size.
Hence, the method does not scale well. The present paper proposes two methods for improving the situation. First, a large
program can be divided into smaller units (processes), which can be scheduled separately. This is structured scheduling. Second, one can use projection methods for solving linear programs incrementally. This is specially efficient if the dependence
graph is sparse. 相似文献
19.
Pressurized fabric tubes, pressure-stabilized beams (known as air beams) and air-inflated structures are considered to be valuable technologies for lightweight, rapidly deployable structures. Design optimization of an inflated structure depends on a thorough understanding of woven fabric mechanics. In this paper the bending response of woven pressure-stabilized beams have been experimentally tested and analytically investigated. Additionally, the micromechanical effects of interacting tows have been studied through finite element models containing contact surfaces and nonlinear slip/stick conditions. Local unit cell models consisting of pairs of woven tows were created to characterize the effective constitutive relations. The material properties from the unit cell models were then used for the global continuum model subjected to 4-point flexure. An experimental set-up was designed and manufactured for testing of Vectran and PEN air beams. The air beam mid-span deflections were measured as functions of inflation pressure and bending load. Plots of the elastic and shear moduli with respect to the pressure and coefficient of friction have been generated. It was determined that the effective elastic and shear moduli were functions of inflation pressure, the material used and the geometry of the weave. It was shown that pneumatic or pressurized tube structures differ fundamentally from conventional metal structures. 相似文献
20.
An introduction to Web Services 总被引:1,自引:0,他引:1
Paul Muschamp 《BT Technology Journal》2004,22(1):9-18
This paper provides an introduction to Web Services. A brief history of Web Services is given, leading into an overview of
the key Web Services technologies. The paper describes the way in which the IT industry has embraced Web Services and the
uses to which the technologies are currently being applied. It concludes with a view of the role of both the key developers
and standards bodies in the creation of Web Services and discusses the ways in which this process needs to be supported in
order for Web Services to evolve.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献