全文获取类型
收费全文 | 314895篇 |
免费 | 30123篇 |
国内免费 | 18303篇 |
专业分类
电工技术 | 20074篇 |
技术理论 | 31篇 |
综合类 | 33001篇 |
化学工业 | 33711篇 |
金属工艺 | 11655篇 |
机械仪表 | 14753篇 |
建筑科学 | 54375篇 |
矿业工程 | 19251篇 |
能源动力 | 9797篇 |
轻工业 | 28375篇 |
水利工程 | 17383篇 |
石油天然气 | 17515篇 |
武器工业 | 3813篇 |
无线电 | 22054篇 |
一般工业技术 | 21230篇 |
冶金工业 | 15250篇 |
原子能技术 | 2114篇 |
自动化技术 | 38939篇 |
出版年
2024年 | 1299篇 |
2023年 | 4017篇 |
2022年 | 7749篇 |
2021年 | 10362篇 |
2020年 | 9930篇 |
2019年 | 7983篇 |
2018年 | 7400篇 |
2017年 | 9235篇 |
2016年 | 11044篇 |
2015年 | 11924篇 |
2014年 | 21834篇 |
2013年 | 19134篇 |
2012年 | 23134篇 |
2011年 | 25421篇 |
2010年 | 19030篇 |
2009年 | 19457篇 |
2008年 | 17843篇 |
2007年 | 21544篇 |
2006年 | 19311篇 |
2005年 | 16841篇 |
2004年 | 14147篇 |
2003年 | 12268篇 |
2002年 | 10055篇 |
2001年 | 8099篇 |
2000年 | 6867篇 |
1999年 | 5554篇 |
1998年 | 3970篇 |
1997年 | 3459篇 |
1996年 | 2792篇 |
1995年 | 2425篇 |
1994年 | 2019篇 |
1993年 | 1428篇 |
1992年 | 1183篇 |
1991年 | 830篇 |
1990年 | 703篇 |
1989年 | 624篇 |
1988年 | 389篇 |
1987年 | 318篇 |
1986年 | 258篇 |
1985年 | 267篇 |
1984年 | 224篇 |
1983年 | 159篇 |
1982年 | 129篇 |
1981年 | 130篇 |
1980年 | 133篇 |
1979年 | 96篇 |
1978年 | 39篇 |
1977年 | 42篇 |
1975年 | 21篇 |
1959年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
171.
Differences between oculomotor and perceptual artifacts for temporally limited head mounted displays
Alexander Goettker Kevin J. MacKenzie T. Scott Murdison 《Journal of the Society for Information Display》2020,28(6):509-519
We used perceptual and oculomotor measures to understand the negative impacts of low (phantom array) and high (motion blur) duty cycles with a high‐speed, AR‐likehead‐mounted display prototype. We observed large intersubject variability for the detection of phantom array artifacts but a highly consistent and systematic effect on saccadic eye movement targeting during low duty cycle presentations. This adverse effect on saccade endpoints was also related to an increased error rate in a perceptual discrimination task, showing a direct effect of display duty cycle on the perceptual quality. For high duty cycles, the probability of detecting motion blur increased during head movements, and this effect was elevated at lower refresh rates. We did not find an impact of the temporal display characteristics on compensatory eye movements during head motion (e.g., VOR). Together, our results allow us to quantify the tradeoff of different negative spatiotemporal impacts of user movements and make subsequent recommendations for optimized temporal HMD parameters. 相似文献
172.
为了寻找抗菌候选化合物,采用基于片段的药物发现方法,以氨基膦酸酯和磺酰氯为原料,设计合成了15个含膦酸酯结构单元的磺胺衍生物,经IR、1HNMR和13CNMR确认结构。采用两倍稀释法测定目标化合物的MIC(最小抑菌浓度)。结果表明:部分目标化合物呈潜在的抗菌活性,对所测试标准菌和耐药菌均有抑制活性。其中,化合物Ⅱf〔N-[(二乙氧基膦酰基)-4-氟苯甲基]-4-甲氧基苯磺酰胺〕对金黄色葡萄球菌(S. aureus)、大肠埃希菌(E. coli)、耐甲氧西林金黄色葡萄球菌(MRSA)及耐氟喹诺酮类大肠杆菌(MREC)的MIC分别为32、64、128和128μg/mL,化合物Ⅱl〔N-[(二乙氧基膦酰基)-4-氟苯甲基]-4-氟苯磺酰胺〕对S. aureus、E. coli、MRSA及MREC的MIC分别为32、32、64和64μg/mL,抗菌活性优于对照药磺胺嘧啶。 相似文献
173.
《岩石力学与岩土工程学报(英文版)》2020,12(3):630-641
Structure is an evident determinant for macroscopic behaviors of soils. However, this is not taken into account in most constitutive models, as structure is a rather complex issue in models. For this, it is important to develop and implement simple models that can reflect this important aspect of soil behavior. This paper tried to model structured soils based on well-established concepts, such as critical state and sub-loading. Critical state is the core of the classic Cam Clay model. The sub-loading concept implies adoption of an inner (sub-loading) yield surface, according to specific hardening rules for some internal strain-like state variables. Nakai and co-workers proposed such internal variables for controlling density (ρ) and structure (ω), using a modified stress space, called tij. Herein, similar variables are used in the context of the better-known invariants (p and q) of the Cam Clay model. This change requires explicit adoption of a non-associated flow rule for the sub-loading surface. This is accomplished by modifying the dilatancy ratio of the Cam Clay model, as a function of the new internal variables. These modifications are described and implemented under three-dimensional (3D) conditions. The model is then applied to simulating laboratory tests under different stress paths and the results are compared to experiments reported for different types of structured soils. The good agreements show the capacity and potential of the proposed model. 相似文献
174.
The present study focuses on experimental investigation of through the thickness displacement and strain field in thin adhesive layer in single sided (unsymmetrical) patch repaired CFRP (carbon fiber reinforced polymer) panel under tensile load. Digital image correlation (DIC) technique is employed to acquire the displacement and strain (longitudinal, peel and shear) field. Experimental determination of shear transfer length based on shear strain field obtained from DIC is introduced to estimate the optimum overlap length which is an essential parameter in patch design for the repair of CFRP structures. Further, DIC experiment with magnified optics is performed to get an insight into complex and localized strain field over thin adhesive layer especially at critical zones leading to damage initiation. The failure mechanism, load displacement behavior, damage initiation and propagation are closely monitored using DIC. The influence of patch edge tapering on strain distribution in adhesive layer is also investigated. The DIC successfully captures the global and localized strain field at critical zones over thin adhesive layer and further helps in monitoring the damage based on strain anomalies. Strains are found to have maximum magnitude at the patch overlap edge and the shear strain level in adhesive layer is higher than the peel strain. Normal tapering increases the peel strain and has negligible influence on shear strain level in adhesive layer. The recommended overlap length is found to be consistent with the recommendation in the literature. Whole field strain pattern and the overlap length obtained from experiment are further compared with the finite element analysis results and they appear to be in good coherence. 相似文献
175.
Numerical dissipation acts as artificial viscosity to make smoke viscous. Reducing numerical dissipation is able to recover visual details smeared out by the numerical dissipation. Great efforts have been devoted to suppress the numerical dissipation in smoke simulation in the past few years. In this paper we investigate methods of combating the numerical dissipation. We describe visual consequences of the numerical dissipation and explore sources that introduce the numerical dissipation into course of smoke simulation. Methods are investigated from various aspects including grid variation, high-order advection, sub-grid compensation, invariant conservation, and particle-based improvement, followed by discussion and comparison in terms of visual quality, computational overhead, ease of implementation, adaptivity, and scalability, which leads to their different applicability to various application scenarios. 相似文献
176.
177.
178.
文章中主要采用有机溶剂萃取法(OSE)对高浓度石油污染土壤进行修复,经过精馏操作,有效回收原油,建立脱附等温曲线,研究了石油污染物在土壤-有机溶剂两相间的迁移规律。 相似文献
179.
The titanium carbides are potential candidates to achieve both high hardness and refractory property. We carried out a structural search for titanium carbides at three pressures of 0 GPa, 30 GPa and 50 GPa. A phase diagram of the Ti-C system at 0 K was obtained by elucidating formation enthalpies as a function of compositions, and their mechanical and metallic properties of titanium carbides were investigated systematically. We also discussed the relation of titanium concentration to the both mechanical and metallic properties of titanium carbides. It has been found that the average valence electron density and tractility improved at higher concentrations of titanium, while the degree of covalent bonding directionality decreased. To this effect, the hardness of titanium carbide decreases as the content of titanium increases. Our results indicated that the titanium content significantly affected the metallic properties of the Ti-C system. 相似文献
180.
Galin Ivanov Ertugrul Bilgucu Ivelina Ivanova Milena Dimitrova 《International Journal of Dairy Technology》2020,73(3):563-569
The present study aimed to investigate the effect of somatic cell count (SCC) of raw cow's milk on the volatile organic compound (VOC) profiles of yoghurt. Test yoghurt samples were produced from three batches of cow's milk with low, medium and high SCC, respectively. The VOCs were determined by gas chromatography–mass spectrometry (GC–MS) analysis. A lower diacetyl and acetoin content and a higher content of 2‐heptanone, and butanoic and hexanoic acids were established in the yoghurt samples from batches with high SCC of above 1 000 000 cells/cm3. The increased SCC of cow's milk had a negative effect on the volatile organic compound profiles of yoghurt. 相似文献