全文获取类型
收费全文 | 28902篇 |
免费 | 3468篇 |
国内免费 | 1748篇 |
专业分类
电工技术 | 1940篇 |
技术理论 | 2篇 |
综合类 | 3039篇 |
化学工业 | 2699篇 |
金属工艺 | 791篇 |
机械仪表 | 955篇 |
建筑科学 | 5311篇 |
矿业工程 | 2722篇 |
能源动力 | 894篇 |
轻工业 | 1110篇 |
水利工程 | 2399篇 |
石油天然气 | 4032篇 |
武器工业 | 369篇 |
无线电 | 1984篇 |
一般工业技术 | 1588篇 |
冶金工业 | 1177篇 |
原子能技术 | 214篇 |
自动化技术 | 2892篇 |
出版年
2024年 | 122篇 |
2023年 | 400篇 |
2022年 | 844篇 |
2021年 | 914篇 |
2020年 | 1092篇 |
2019年 | 906篇 |
2018年 | 853篇 |
2017年 | 1106篇 |
2016年 | 1188篇 |
2015年 | 1266篇 |
2014年 | 1968篇 |
2013年 | 1693篇 |
2012年 | 2185篇 |
2011年 | 2322篇 |
2010年 | 1713篇 |
2009年 | 1710篇 |
2008年 | 1706篇 |
2007年 | 1891篇 |
2006年 | 1787篇 |
2005年 | 1492篇 |
2004年 | 1201篇 |
2003年 | 1084篇 |
2002年 | 892篇 |
2001年 | 735篇 |
2000年 | 602篇 |
1999年 | 464篇 |
1998年 | 342篇 |
1997年 | 289篇 |
1996年 | 218篇 |
1995年 | 236篇 |
1994年 | 189篇 |
1993年 | 130篇 |
1992年 | 116篇 |
1991年 | 76篇 |
1990年 | 74篇 |
1989年 | 54篇 |
1988年 | 39篇 |
1987年 | 28篇 |
1986年 | 35篇 |
1985年 | 31篇 |
1984年 | 22篇 |
1983年 | 20篇 |
1982年 | 11篇 |
1981年 | 26篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1964年 | 5篇 |
1959年 | 4篇 |
1958年 | 2篇 |
1956年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
171.
讨论了超高相对分子质量聚乙烯(UHMWPE)混炼接枝马来酸酐(MAH)过程中,单体MAH用量、引发剂DCP用量、交联抑制剂己内酰胺(CAILA)用量、流动改性剂硬脂酸钙(CaSt2)用量及混炼温度、时间等工艺条件对UHMWPE接枝率和凝胶含量的影响。用红外光谱表征了接枝物的存在。并用滴定分析法和重量分析法测定了接枝物UHMWPE~g~MAH的接枝率和凝胶含量。实验表明,MAH用量为5份、DCP为0.15份、CALA为0.1份、CaSt2为1份时。混炼温度175∽180℃。混炼时间14min时,可得到接枝率0.75%、凝胶含量1.48%的UHMWPE接枝物。 相似文献
172.
173.
以抚仙湖流域为研究区域,通过系统收集分析流域多年水量水质监测数据,诊断流域保护与发展面临的主要矛盾,并基于流域一体化管理思想,提出了流域保护与发展的可能路径:1创新抚仙湖流域生态文明示范区行政管理体制,从发展思路确立抚仙湖流域实施"严格环境保护、创新生态发展"的转型战略,真正树立和实现"大景区"环境保护和"大旅游"产业发展的生态文明建设理念;2在全面实现生态发展战略的前提下,建议将流域实施分区管控,调减农业用地面积,积极发展现代观光农业和旅游业;3通过生态搬迁,优化城乡布局,实施抚仙湖流域全域"大旅游景区"战略,实现生态资源-资产-资本的良性转化。 相似文献
174.
管材超声波分层检测作为控制产品质量的关键步骤,必须引起相关从业人员的重视,特别是要重点分析分层缺陷检测中盲区的构成原因和分布特征。只有这样,才能切实保证检测结果的准确性,更好地控制管材质量。通过对超声波分层缺陷检测的重要性进行阐释,分析了其中盲区的构成和分布等问题。 相似文献
175.
The objective of this research was to evaluate the effectiveness of several different methods for controlling the pore size and pore size distribution in activated carbon fibers. Variables studied included fiber shape, activation time, and the addition of small amounts of silver nitrate. Pure isotropic pitch and the same isotropic pitch containing 1 wt.% silver were melt spun to form fibers with round and trilobal cross sections. These fibers were then stabilized, carbonized, and activated in carbon dioxide. Field emission scanning electron microscopy (FE SEM), electron dispersive spectra (EDS), and wavelength dispersive spectra (WDS) were used to monitor the size and distribution of the silver particles in the fibers before and after activation. Each of these analyses showed that the distribution of silver particles was extremely uniform before and after activation. The fibers were also weighed before and after activation to determine the percent burn-off. The BET specific surface areas of the activated fibers were determined from N2 adsorption isotherms measured at −196 °C. The results showed that round and trilobal fibers with equivalent cross-sectional areas yielded similar burn-off values and specific surface areas after activation. Also, activation rates were found to be independent of CO2 flow rate. The porosity of the activated fibers depended on the total time of activation and the cross-sectional area of fibers. The N2 adsorption measurements showed that the activated fibers had extremely high specific surface areas (greater than 3000 m2/g) and high degrees of meso- and macro-porosity. FE SEM was also used to investigate surface texture and size of pore openings on the surfaces of the activated fibers. The photos showed that silver particles generated surface macro- and mesopores, in agreement with the inferences from N2 adsorption measurements. 相似文献
176.
Organic/inorganic composite membranes with different inorganic heteropolyacid (HPA) additives maintain sufficient proton conductivities for atmospheric pressure elevated temperature (>100 °C) polymer electrolyte fuel cell (PEFC) operation. However, membrane and membrane electrode assembly (MEA) processing is severely curtailed because of the solubility of the HPA additives in aqueous media. Composite membranes with the HPA (phosphotungstic acid; PTA) additive rendered insoluble by ion exchanging protons with larger cations such as Cs+, NH4+, Rb+ and Tl+ were fabricated. The additive loss in aqueous media was lowered from nearly 100% (unmodified HPA) to about 5% (modified HPA). The membranes were robust, and demonstrated low H2 crossover currents of around 2 mA/cm2 for a 28 μm thick membrane. All membranes were evaluated at high temperatures and low relative humidities in an operating fuel cell. The conductivities of the composite membranes at 120 °C and 35% relative humidity were on the order of 1.6 × 10−2 S/cm. 相似文献
177.
Preparation and characterization of antibacterial silver-dispersed activated carbon aerogels 总被引:2,自引:0,他引:2
Silver-dispersed carbon aerogels (CAs) were obtained by direct immersion of organic aerogels prepared by ambient pressure drying technique in AgNO3 aqueous solution and then carbonization. The effect of preparation conditions such as the resorcinol/catalyst ratio, the feed AgNO3 concentration, the ratio of aerogel mass/solution volume, immersion time and carbonization temperature on the bulk density and silver content as well as the BET surface area of the dispersed CAs was studied. The dispersion and structure of silver nanoparticles in obtained materials were investigated by means of scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The Ag-dispersed CAs prepared exhibit strong and long-term antibacterial activity. 相似文献
178.
针对无线传感器网络(Wireless Sensor Networks,WSN)中的节点在真实环境中的不可靠感知现象及其对目标跟踪精度的影响,首先分析计算了成对传感器节点感知存在的不确定区域及其边界,在此基础上,提出了一种基于成对节点探测不确定性的目标容错跟踪方法(Tracking with Pairwise Uncertainty of RSSI,TPU-RSSI),即通过匹配分组感知采样得到的感知向量(sampling vector)和跟踪区域划分面(face)的特征向量(signature vector)来进行移动目标容错跟踪。该方法在保持跟踪方法灵活性的基础上,能够减小由环境因素带来的跟踪误差。为了降低计算复杂度,提出了一种基于邻居面连接的启发式匹配算法。大量的仿真实验结果均表明,所提方法相比同类的其他方法具有更强的灵活性和更高的定位精度。 相似文献
179.
180.