全文获取类型
收费全文 | 33013篇 |
免费 | 989篇 |
国内免费 | 66篇 |
专业分类
电工技术 | 367篇 |
综合类 | 35篇 |
化学工业 | 6765篇 |
金属工艺 | 860篇 |
机械仪表 | 655篇 |
建筑科学 | 1843篇 |
矿业工程 | 247篇 |
能源动力 | 1017篇 |
轻工业 | 2763篇 |
水利工程 | 335篇 |
石油天然气 | 207篇 |
武器工业 | 2篇 |
无线电 | 2151篇 |
一般工业技术 | 5211篇 |
冶金工业 | 6667篇 |
原子能技术 | 322篇 |
自动化技术 | 4621篇 |
出版年
2022年 | 170篇 |
2021年 | 387篇 |
2020年 | 332篇 |
2019年 | 399篇 |
2018年 | 487篇 |
2017年 | 505篇 |
2016年 | 519篇 |
2015年 | 462篇 |
2014年 | 736篇 |
2013年 | 2133篇 |
2012年 | 1244篇 |
2011年 | 1596篇 |
2010年 | 1175篇 |
2009年 | 1260篇 |
2008年 | 1442篇 |
2007年 | 1471篇 |
2006年 | 1261篇 |
2005年 | 1174篇 |
2004年 | 1055篇 |
2003年 | 1027篇 |
2002年 | 1037篇 |
2001年 | 639篇 |
2000年 | 617篇 |
1999年 | 577篇 |
1998年 | 609篇 |
1997年 | 503篇 |
1996年 | 608篇 |
1995年 | 548篇 |
1994年 | 535篇 |
1993年 | 536篇 |
1992年 | 486篇 |
1991年 | 321篇 |
1990年 | 441篇 |
1989年 | 426篇 |
1988年 | 382篇 |
1987年 | 425篇 |
1986年 | 383篇 |
1985年 | 516篇 |
1984年 | 493篇 |
1983年 | 444篇 |
1982年 | 465篇 |
1981年 | 449篇 |
1980年 | 354篇 |
1979年 | 365篇 |
1978年 | 330篇 |
1977年 | 308篇 |
1976年 | 270篇 |
1975年 | 319篇 |
1974年 | 243篇 |
1973年 | 281篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
James D. Johnston Ashlin E. Cowger Robert J. Graul Ryan Nash Josie A. Tueller Nathan R. Hendrickson Daniel R. Robinson John D. Beard K. Scott Weber 《Indoor air》2019,29(6):1005-1017
Recent work suggests that evaporative coolers increase the level and diversity of bioaerosols, but this association remains understudied in low‐income homes. We conducted a cross‐sectional study of metropolitan, low‐income homes in Utah with evaporative coolers (n = 20) and central air conditioners (n = 28). Dust samples (N = 147) were collected from four locations in each home and analyzed for dust‐mite allergens Der p1 and Der f1, endotoxins, and β‐(1 → 3)‐d ‐glucans. In all sample locations combined, Der p1 or Der f1 was significantly higher in evaporative cooler versus central air conditioning homes (OR = 2.29, 95% CI = 1.05‐4.98). Endotoxin concentration was significantly higher in evaporative cooler versus central air conditioning homes in furniture (geometric mean (GM) = 8.05 vs 2.85 EU/mg, P < .01) and all samples combined (GM = 3.60 vs 1.29 EU/mg, P = .03). β‐(1 → 3)‐d ‐glucan concentration and surface loads were significantly higher in evaporative cooler versus central air conditioning homes in all four sample locations and all samples combined (P < .01). Our study suggests that low‐income, evaporative cooled homes have higher levels of immunologically important bioaerosols than central air‐conditioned homes in dry climates, warranting studies on health implications and other exposed populations. 相似文献
992.
John A. Killion Sharon Kehoe Luke M. Geever Declan M. Devine Eoin Sheehan Daniel Boyd Clement L. Higginbotham 《Materials science & engineering. C, Materials for biological applications》2013,33(7):4203-4212
Due to the deficiencies of current commercially available biological bone grafts, alternative bone graft substitutes have come to the forefront of tissue engineering in recent times. The main challenge for scientists in manufacturing bone graft substitutes is to obtain a scaffold that has sufficient mechanical strength and bioactive properties to promote formation of new tissue. The ability to synthesise hydrogel based composite scaffolds using photopolymerisation has been demonstrated in this study. The prepared hydrogel based composites were characterised using techniques including Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), Energy-dispersive X-ray spectrometry (EDX), rheological studies and compression testing. In addition, gel fraction, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), porosity and swelling studies of the composites were carried out. It was found that these novel hydrogel bioglass composite formulations did not display the inherent brittleness that is typically associated with bioactive glass based bone graft materials and exhibited enhanced biomechanical properties compared to the polyethylene glycol hydrogel scaffolds along. Together, the combination of enhanced mechanical properties and the deposition of apatite on the surface of these hydrogel based composites make them an ideal candidate as bone graft substitutes in cancellous bone defects or low load bearing applications. 相似文献
993.
The ability to reverse-engineer models of software behaviour is valuable for a wide range of software maintenance, validation and verification tasks. Current reverse-engineering techniques focus either on control-specific behaviour (e.g., in the form of Finite State Machines), or data-specific behaviour (e.g., as pre / post-conditions or invariants). However, typical software behaviour is usually a product of the two; models must combine both aspects to fully represent the software’s operation. Extended Finite State Machines (EFSMs) provide such a model. Although attempts have been made to infer EFSMs, these have been problematic. The models inferred by these techniques can be non-deterministic, the inference algorithms can be inflexible, and only applicable to traces with specific characteristics. This paper presents a novel EFSM inference technique that addresses the problems of inflexibility and non-determinism. It also adapts an experimental technique from the field of Machine Learning to evaluate EFSM inference techniques, and applies it to three diverse software systems. 相似文献
994.
995.
Thread-locking adhesives are commonly added to impart extra torque strength as well preventing screws from backing out during use. Many of these adhesives rely on anaerobic (oxygen free) conditions for curing. Often, if not properly cured, the locking compounds which are usually oily liquids, actually behave in a manner completely opposite of design and screws intended to be strengthened are in fact compromised beyond if no locking compound were present at all. Discussed herein is such an example in which, if a solution were not found to allow for curing of the locking compounds on assembled systems, over 2,000 costly sensor assemblies would have been scrapped. Fortunately, an unconventional solution was found. 相似文献
996.
Four % (wt/wt) aqueous solutions were prepared at corn starch:methylcellulose:whey protein isolate (CS:MC:WPI) ratios of 2:2:2, 1:2:3, 2:1:3, 2:2:0, 1:2:0 and 2:1:0. Glycerol (gly) was used as a plasticiser at CS–MC–WPI:gly ratios of 2:1, 2.5:1 and 3:1. CS–MC–WPI blend films were stronger than CS–WPI films and had lower oxygen permeability (OP) than MC–WPI films. The highest tensile strength (TS) of blend films was 8.01 ± 3.41 MPa, at CS:MC:WPI ratio of 2:2:0 and CS–MC–WPI:gly ratio of 3:1. Lowest OP value was 45.05 ± 7.24 cm3 μm m?2 per day kPa?1, at CS:MC:WPI ratio of 2:2:2 and CS–MC–WPI:gly ratio of 3:1. OP values were predictable based on relative amounts of components. However, TS and elastic modulus properties of the CS–MC–WPI blend films did not reflect the relative amounts of the components. All of CS–MC–WPI films were translucent indicating some degree of immiscibility among the CS, MC and WPI. These results indicate the influence of complex molecular interactions among the components. 相似文献
997.
998.
An NMR-based metabolomic assessment of cultured cobia health in response to dietary manipulation 总被引:1,自引:0,他引:1
Commercial aquaculture feeds rely heavily on fishmeal and fish oil, which can be expensive and ecologically unsustainable. To evaluate the efficacy of reduced fishmeal diets for outgrowth, a dietary study was conducted on the finfish cobia, Rachycentron canadum. NMR-based metabolomic techniques were used to assess the effect of decreasing dietary fishmeal on the health of the cobia. Filtered serum 1H NMR spectra analysed by principal components analysis (PCA) showed cobia fed reduced fishmeal diets were metabolically different than cobia on control diets. In particular, tyrosine and betaine increased in cobia fed reduced fishmeal diets while glucose decreased, suggesting that these cobia were not receiving the necessary nutritional components required for energy and growth. The formulated control diet contributed to enriched growth and significantly elevated lactate levels suggesting enhanced gut microflora metabolism in response to dietary components. The results show that NMR-based metabolomic analysis is a useful tool in aquaculture studies. 相似文献
999.
Throughout the developed world, community sports clubs are a high-risk setting for alcohol-impaired driving. The Good Sports program accredits community sports clubs to encourage implementation of alcohol-focussed harm-reduction and safe-transport strategies. This study tested for associations between participation in the Good Sports program and reduced rates of drink-driving amongst club members. Multilevel modelling indicated that for each season a club was in the program there was an 8% reduction in the odds of drink-driving. These findings may arise due to clubs with lower rates of alcohol use maintaining longer involvement in the program. However, the findings are also compatible with the intention of the Good Sports program to reduce the risk that club members will drive whilst alcohol impaired. 相似文献
1000.