全文获取类型
收费全文 | 6534篇 |
免费 | 290篇 |
国内免费 | 17篇 |
专业分类
电工技术 | 73篇 |
综合类 | 7篇 |
化学工业 | 1535篇 |
金属工艺 | 107篇 |
机械仪表 | 148篇 |
建筑科学 | 328篇 |
矿业工程 | 9篇 |
能源动力 | 226篇 |
轻工业 | 540篇 |
水利工程 | 61篇 |
石油天然气 | 26篇 |
武器工业 | 2篇 |
无线电 | 581篇 |
一般工业技术 | 1107篇 |
冶金工业 | 914篇 |
原子能技术 | 34篇 |
自动化技术 | 1143篇 |
出版年
2023年 | 67篇 |
2022年 | 107篇 |
2021年 | 173篇 |
2020年 | 123篇 |
2019年 | 125篇 |
2018年 | 175篇 |
2017年 | 157篇 |
2016年 | 192篇 |
2015年 | 160篇 |
2014年 | 223篇 |
2013年 | 406篇 |
2012年 | 366篇 |
2011年 | 428篇 |
2010年 | 325篇 |
2009年 | 370篇 |
2008年 | 353篇 |
2007年 | 367篇 |
2006年 | 262篇 |
2005年 | 253篇 |
2004年 | 204篇 |
2003年 | 183篇 |
2002年 | 157篇 |
2001年 | 107篇 |
2000年 | 111篇 |
1999年 | 107篇 |
1998年 | 103篇 |
1997年 | 111篇 |
1996年 | 80篇 |
1995年 | 100篇 |
1994年 | 87篇 |
1993年 | 63篇 |
1992年 | 64篇 |
1991年 | 31篇 |
1990年 | 46篇 |
1989年 | 65篇 |
1988年 | 49篇 |
1987年 | 37篇 |
1986年 | 51篇 |
1985年 | 57篇 |
1984年 | 44篇 |
1983年 | 54篇 |
1982年 | 35篇 |
1981年 | 35篇 |
1980年 | 32篇 |
1979年 | 26篇 |
1978年 | 19篇 |
1977年 | 17篇 |
1976年 | 24篇 |
1975年 | 29篇 |
1974年 | 22篇 |
排序方式: 共有6841条查询结果,搜索用时 0 毫秒
51.
Quantification of secondary structure prediction improvement using multiple alignments 总被引:9,自引:0,他引:9
Levin Jonathan M.; Pascarella Stefano; Argos Patrick; Garnier Jean 《Protein engineering, design & selection : PEDS》1993,6(8):849-854
The use of multiple sequence alignments for secondary structurepredictions is analysed. Seven different protein families, containingonly sequences of known structure, were considered to providea range of alignment and prediction conditions. Using alignmentsobtained by spatial superposition of main chain atoms in knowntertiary protein structures allowed a mean of 8% in secondarystructure prediction accuracy, when compared to those obtainedfrom the individual sequences. Substitution of these alignmentsby those determined directly from an automated sequence alignmentalgorithm showed variations in the prediction accuracy whichcorrelated with the quality of the multiple alignments and distanceof the primary sequence. Secondary structure predictions canbe reliably improved using alignments from an automatic alignmentprocedure with a mean increase of 6.87percnt;, giving an overallprediction accuracy of 68.5%, if there is a minimum of 25% sequenceidentity between all sequences in a family. 相似文献
52.
An examination of the influence of pressure and heating rate on the thermoplastic properties of a weakly coking coal and of coal with various pitch-like additives was carried out using a high pressure dilatometer. Pressure up to 4 MPa markedly increased the swelling properties and increased the plastic range by decreasing the softening temperature, but the effects of pressure were strongly influenced by rate of heating with high heating rates enhancing the effects. Additions of tar or pitch also enhanced swelling at low pressure. The solid carbonization residues from the dilatometer were examined by polarized light microscopy to determine the content and composition of optically anisotropic species. The anisotropic content was increased by increases in pressure and heating rate and pitch additives enhanced the anisotropic content, especially at low pressure, without affecting the composition of the anisotropy. No direct correlations exist between the dilatometric parameters and the optical anisotropy but their dependence on the conditions emphasizes that when considering high pressure gasification of coal, it is necessary to obtain data under appropriate conditions. 相似文献
53.
54.
Social networking sites (SNS) have transformed how individuals interact, build and maintain social relationships. We proposed a research model on the determinants of user continuance using Bagozzi's framework of self-regulation as the theoretical foundation. Following the process of appraisal → emotional reactions → coping responses, we developed the model by leveraging findings from social presence and IS continuance research. Based on survey data from Facebook users, we found that appraisal factors (pleasure, awareness, connectedness, and system quality) were strong determinants of emotional reaction (user satisfaction and sense of belonging). User satisfaction and sense of belonging together positively influenced continuance intention. 相似文献
55.
Mary E. Mossey Yubin Xi Shayne K. McConomy Johnell O. Brooks Patrick J. Rosopa Paul J. Venhovens 《Applied ergonomics》2014
While much research exists on occupant packaging both proprietary and in the literature, more detailed research regarding user preferences for subjective ratings of steering wheel designs is sparse in published literature. This study aimed to explore the driver interactions with production steering wheels in four vehicles by using anthropometric data, driver hand placement, and driver grip design preferences for Generation-Y and Baby Boomers. In this study, participants selected their preferred grip diameter, responded to a series of questions about the steering wheel grip as they sat in four vehicles, and rank ordered their preferred grip design. Thirty-two male participants (16 Baby Boomers between ages 47 and 65 and 16 Generation-Y between ages 18 and 29) participated in the study. Drivers demonstrated different gripping behavior between vehicles and between groups. Recommendations for future work in steering wheel grip design and naturalistic driver hand positioning are discussed. 相似文献
56.
The modification of the interface in immiscible polymer blends is critical in order to optimize physical properties. Despite the great commercial importance of polymer blends, many aspects of the emulsification process remain unclear In this paper, it will be shown that an emulsification curve can be used to estimate the influence of the architecture molar mass of styrene/hydrogenated butadiene block copolymer interfacial modifiers on the emulsifion of polystyrene/ethylene-propylene rubber blends under melt processing conditions. An expression for eing the critical amount of copolymer to saturate the interface, as well as aspects concerning the localisation of the modifier in the blend system will also be addressed. 相似文献
57.
Jun-Ting Xu J.Patrick A. FaircloughShao-Min Mai Chiraporn ChaibunditM. Mingvanish C. BoothAnthony J. Ryan 《Polymer》2003,44(22):6843-6850
The crystallization behavior of poly(oxyethylene)-b-poly(oxybutylene) block copolymers with different compositions, morphologies and architectures (EmBn diblock copolymers and EmBnEm, BnEmBn triblock copolymers) were investigated and the effect of volume fraction and architecture on the crystallization temperature (Tc) in non-isothermal crystallization was determined. It is found that the EmBn diblock copolymers having long E blocks exhibit similar crystallization temperatures, irrespective of volume fraction and morphology, but for the block copolymers with shorter E blocks the crystallization temperature increases with both the volume fraction, φE, and the length, m, of the E block. Some block copolymers with extremely low Tc, which fall into the temperature range normally associated with homogenous nucleation, were chosen for time-resolved small-angle X-ray scattering (SAXS) and isothermal crystallization kinetics experiments. The results show that breakout crystallization occurs in all these block copolymers. Therefore, unlike EmBn/Bh blends, there is no obvious relationship between Tc and crystallization behavior in neat block copolymers and homogeneous nucleation does not definitely lead to confined crystallization. The values of χc/χODT for all the block copolymers with hex and bcc morphology were also calculated. It is found that all the block copolymers have χc/χODT<3, in agreement with the previously reported critical value and consistent with their breakout crystallization behavior. 相似文献
58.
Sykes EC Han P Kandel SA Kelly KF McCarty GS Weiss PS 《Accounts of chemical research》2003,36(12):945-953
Adsorbate interactions and reactions on metal surfaces have been investigated using scanning tunneling microscopy. The manners in which adsorbates perturb the surface electronic structure in their vicinity are discussed. The effects these perturbations have on other molecules are shown to be important in overlayer growth. Interactions of molecules with surface steps are addressed, and each molecule's electron affinity is shown to dictate its adsorption sites at step edges. Standing waves emanating from steps are demonstrated to effect transient molecular adsorption up to 40 A away from the step edge. Halobenzene derivatives are used to demonstrate how the surface is important in aligning reactive intermediates. 相似文献
59.
Reactive mixing in a wavy torus reactor (WTR) has been examined experimentally. Its performances are compared to these of two other reactors: a plane torus reactor (PTR) and a baffled stirred tank reactor (BSTR). hydrodynamics of mixing has been studied using a plug flow model with axial dispersion for the WTR and PTR. The effect of axial dispersion on the kinetic of a chemical reaction was then analysed for the WTR, PTR and BSTR. Mixing times were slightly longer for the WTR due to a weaker axial dispersion. We also noticed an improvement of the convertion rate for low dissipated power. 相似文献
60.
Lipase-catalyzed transesterification of phosphatidylcholine at controlled water activity 总被引:2,自引:0,他引:2
Ingemar Svensson Patrick Adlercreutz Bo Mattiasson 《Journal of the American Oil Chemists' Society》1992,69(10):986-991
The incorporation of a free fatty acid into thesn-1 position of phosphatidylcholine by lipase-catalyzed transesterification was investigated. The thermodynamic water activity
of both the enzyme preparation and the substrate solution was adjusted to the same value prior to the reaction. The reaction
rate increased with increasing water activity but the yield of modified phosphatidylcholine decreased due to hydrolysis. By
using a large excess of the free fatty acid (heptadecanoic acid), the hydrolysis reaction was slowed down, so a higher yield
was obtained at a given degree of incorporation. The best results were obtained withRhizopus arrhizus lipase immobilized by adsorption on a polypropylene support. With this preparation, a yield of 60% and nearly 50% incorporation
of heptadecanoic acid (100% incorporation in thesn-1 position) was obtained at a water activity of 0.064. The enzyme preparation had good operational stability and position
specificity. Little incorporation (<1%) was observed in thesn-2 position, when almost all the fatty acid in thesn-1 position was exchanged. 相似文献