全文获取类型
收费全文 | 43464篇 |
免费 | 4842篇 |
国内免费 | 2662篇 |
专业分类
电工技术 | 2437篇 |
综合类 | 4788篇 |
化学工业 | 7183篇 |
金属工艺 | 4632篇 |
机械仪表 | 2219篇 |
建筑科学 | 10019篇 |
矿业工程 | 1994篇 |
能源动力 | 814篇 |
轻工业 | 2238篇 |
水利工程 | 1670篇 |
石油天然气 | 1452篇 |
武器工业 | 380篇 |
无线电 | 1616篇 |
一般工业技术 | 5403篇 |
冶金工业 | 2706篇 |
原子能技术 | 313篇 |
自动化技术 | 1104篇 |
出版年
2024年 | 99篇 |
2023年 | 592篇 |
2022年 | 1153篇 |
2021年 | 1496篇 |
2020年 | 1401篇 |
2019年 | 1261篇 |
2018年 | 1284篇 |
2017年 | 1757篇 |
2016年 | 1830篇 |
2015年 | 1840篇 |
2014年 | 2588篇 |
2013年 | 2881篇 |
2012年 | 3255篇 |
2011年 | 3319篇 |
2010年 | 2456篇 |
2009年 | 2480篇 |
2008年 | 2335篇 |
2007年 | 2756篇 |
2006年 | 2552篇 |
2005年 | 2201篇 |
2004年 | 1864篇 |
2003年 | 1577篇 |
2002年 | 1366篇 |
2001年 | 1141篇 |
2000年 | 962篇 |
1999年 | 871篇 |
1998年 | 665篇 |
1997年 | 542篇 |
1996年 | 482篇 |
1995年 | 408篇 |
1994年 | 350篇 |
1993年 | 278篇 |
1992年 | 224篇 |
1991年 | 142篇 |
1990年 | 141篇 |
1989年 | 126篇 |
1988年 | 69篇 |
1987年 | 62篇 |
1986年 | 19篇 |
1985年 | 25篇 |
1984年 | 18篇 |
1983年 | 16篇 |
1982年 | 20篇 |
1981年 | 6篇 |
1980年 | 17篇 |
1979年 | 22篇 |
1964年 | 4篇 |
1961年 | 2篇 |
1959年 | 2篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
In this paper, a reproduction of a swing‐up and a giant swing motion of underactuated robots based on technique of the horizontal bar gymnast is discussed with focusing on an equivalent center of mass (ECM) of underactuated robots and the gymnast. At first, the behaviors of the ECM of the gymnast (ECMG) are analyzed by using a motion capturing technique and an efficient motion of the ECMG for the swing‐up and for the giant swing motion are identified from analysis results, respectively. Next, a partial linearization method, which can realize that the ECM of the Acrobot (ECMA) replicates this efficient motion, is designed and reproduces the underactuated robots the swing‐up and giant swing motion like the gymnast. Finally, an effectiveness of the proposed controller is shown by numerical simulations. 相似文献
32.
Mohammadmahdi Davoudi 《工程优选》2019,51(5):775-795
Although topology optimization is established for linear static problems, more effort is required for solving nonlinear plastic problems. A new topology optimization approach with equivalent static loads (ESLs) is suggested to find the optimum topologies and locations of plastic hinges of thin-walled crash boxes by considering crash-induced deformation, the main crash energy-absorbing mechanism. Together with finite element method crashworthiness analyses, considering all nonlinearities with rate-dependent plasticity, the method was developed using an appropriate time-incremental scheme of ESLs without removing any high values of loads. Analyses show that the crash boxes with optimum topologies have energy-absorbing capabilities equivalent to the original structure. The proposed method is evaluated for two crashes: a crash box at low speed and a double cell subjected to high-speed collision. The results indicate that this method captures nonlinear crushing behaviours and accurate locations of plastic hinges where, if proper reinforcements are made, energy absorption can be enhanced. 相似文献
33.
图像增强在提高SAR图像舰船目标检测精度方面具有十分重要的意义。由于传统算法不能很好地对SAR图像进行目标增强,提出了基于改进粗糙集理论和引力场强度的目标增强算法。通过借鉴引力场相关理论知识,将粗糙集条件属性集中的梯度属性改进为引力场强度属性,从而实现对原图像的目标增强。与其他算法进行了实验比较,结果表明提出的改进算法相比于其他算法更适用于SAR图像特性,能更好地对舰船目标像素进行针对性增强,具备一定的工程应用价值。 相似文献
34.
Catherine O'Leary Yvonne de Kluizenaar Piet Jacobs Wouter Borsboom Ian Hall Benjamin Jones 《Indoor air》2019,29(3):423-438
There is growing awareness that indoor exposure to particulate matter with diameter ≤ 2.5 μm (PM2.5) is associated with an increased risk of adverse health effects. Cooking is a key indoor source of PM2.5 and an activity conducted daily in most homes. Population scale models can predict occupant exposures to PM2.5, but these predictions are sensitive to the emission rates used. Reported emission rates are highly variable and are typically for the cooking of single ingredients and not full meals. Accordingly, there is a need to assess PM2.5 emissions from the cooking of complete meals. Mean PM2.5 emission rates and source strengths were measured for four complete meals. Temporal PM2.5 concentrations and particle size distributions were recorded using an optical particle counter (OPC), and gravimetric sampling was used to determine calibration factors. Mean emission rates and source strengths varied between 0.54—3.7 mg/min and 15—68 mg, respectively, with 95% confidence. Using a cooker hood (apparent capture efficiency > 90%) and frying in non‐stick pans were found to significantly reduce emissions. OPC calibration factors varied between 1.5 and 5.0 showing that a single value cannot be used for all meals and that gravimetric sampling is necessary when measuring PM2.5 concentrations in kitchens. 相似文献
35.
Riyas Sharafudeen 《Color research and application》2019,44(1):44-49
Titanium dioxide (TiO2) manufacturing industries measure optical properties such as brightness, colour, tint strength, tint tone, gloss, scatter coefficient, and others to ensure the quality of the product. Product characterization and process control generally focus on the optical properties, which determine its quality. In this work, titania rutile pigment with varying tint strength and tint tone is analyzed and a correlation is established between particle size and the optical properties such as tint strength and tint tone. It is observed that optical properties of titania pigment depends on the particle size as well as particle size distribution. A relatively faster evaluation of tint strength and tint tone can be made using the reflectance and particle size measurements. Analytical samples were prepared by ultrasonic dispersion of pigment in water containing calgon as dispersing agent. To verify the accuracy of the method, pigment tint strength and tint tone obtained from this study are compared with those resulting from traditional analysis. The results showed that the new method is viable. 相似文献
36.
In order to effectively apply soybean meal for the preparation of water-resistant soybean-based adhesives for plywood, the effects of three typical soybean meal products, namely, low-temperature soybean meal (LM), high-temperature soybean meal (HM), and physical soybean meal (PM), on the properties of soybean-based adhesive were investigated. The results indicated that the number of reactive groups in the three soybean meals followed the order LM > HM > PM, which in turn led to various crosslinking densities when these soybean meals were crosslinked by epichlorohydrin-modified polyamide (EMPA) during the curing process. The LM soybean adhesive had 6.6% higher soaking bond strength and 16.5% higher boiling-dry-boiling bond strength than the HM soybean adhesive, and 19% higher soaking bond strength and 33% higher boiling-dry-boiling bond strength than the PM soybean adhesive, respectively. These three soybean meals could be used to prepare soybean adhesives for interior-use plywood because all plywood panels bonded with their adhesives passed a water-soaking test at 63 °C for 3 h, but only the LM soybean adhesive achieved the desired water resistance for floor-base plywood. Among the three evaluated soybean meals, LM was the most promising raw material for the preparation of soybean-based adhesive because of a greater number of reactive groups, higher crosslinking density, and superior bond strength. Plywood panel bonded with HM soybean adhesive had a water resistance lower than, but very close to, the standard required value (>0.8 MPa) for floor-base plywood. 相似文献
37.
不锈钢酸洗污泥安全填埋占用土地且难以消除对环境的危害,将酸洗污泥作为烧结配料使用有望回收其中铁、铬、镍等金属,并充分利用其中的熔剂组分,实现酸洗污泥在冶金企业的闭路资源化利用。铁矿粉配加酸洗污泥烧结黏结相强度试验表明,随着酸洗污泥配加比例的增加,黏结相强度先增加后减小,且随着碱度的增加整体减小,当酸洗污泥配加比例为10%时,试样中赤铁矿、磁铁矿质量分数最大,枪晶石质量分数较小,在碱度为1.5时于1 280 ℃焙烧4 min,试样的黏结相强度最大可达15.12 kN。平衡相烧结试验表明,配加酸洗污泥能改善烧结矿质量,铁矿粉配加10%的酸洗污泥,碱度为1.5,1 300 ℃烧结240 min后,烧结矿的矿相组成和微观结构最好,综合性能最佳。 相似文献
38.
39.
Guilherme Pepplow Piuzzi Hugo Carlos Scheuermann Filho Joe Arnaldo Villena Del Carpio Nilo Cesar Consoli 《Geotextiles and Geomembranes》2021,49(3):864-870
Asphalt concrete is the prevailing material used for road surface construction. Its adequate characteristics in providing stability, durability and driving safety are controlled by complex interactions between its components. Thus, it is important to estimate the sensitivity of asphalt concrete mechanical properties as a function of its volumetrics. For this study, different combinations between asphalt content (3.5, 5 and 7.5%) and porosity values (above 4%) were used in order to disassociate these properties. The influence of mixing in fiberglass (0.5%) was also analyzed. It was found that porosity is significantly more relevant than the asphalt content in the prediction of tensile strength and resilient modulus of fiber-free asphalt concretes. In fiber-reinforced mixtures, the mechanical properties are improved by increasing the asphalt content, which suggests a better bonding between fibers and aggregates. For both cases, decreasing porosity is beneficial. By grouping both sets of results, it was possible to create a unique theoretical curve for both the tensile strength (qt) and the resilient modulus (RM). The RM/qt ratio was 5800 for the fiber-free group, and 3900 for the fiber-reinforced group - suggesting a better fatigue life indicator for asphalt concretes when fibers are added. 相似文献
40.
《Ceramics International》2021,47(22):31268-31276
The relationship between the tensile strength of corroded domestic second-generation (2ed-gen) SiC fibers at various temperatures for 500 h in 46.5LiF-11.5NaF-42.0KF (mol. %) eutectic salt and the typical microstructure was studied. Weibull theory was used to analyze the critical defects that caused the tensile fracture, and the microstructure of fibers before and after corrosion was characterized. It is concluded that the decrease of tensile strength after corrosion at 800 °C is caused by the surface injury of fibers, which led to the shift of critical defects from the internal defects of virgin fibers to surface defects. Moreover, corrosion at higher temperature accelerates the corrosion process and dissolve the surface O-contained layer thoroughly. This shifts the critical defects back to the internal defects and will be helpful for the recovery of tensile strength of corroded fibers at the higher temperature. 相似文献