全文获取类型
收费全文 | 47081篇 |
免费 | 4770篇 |
国内免费 | 2659篇 |
专业分类
电工技术 | 950篇 |
综合类 | 3643篇 |
化学工业 | 13598篇 |
金属工艺 | 5883篇 |
机械仪表 | 1633篇 |
建筑科学 | 2874篇 |
矿业工程 | 1071篇 |
能源动力 | 717篇 |
轻工业 | 5345篇 |
水利工程 | 540篇 |
石油天然气 | 2745篇 |
武器工业 | 682篇 |
无线电 | 3069篇 |
一般工业技术 | 6984篇 |
冶金工业 | 2992篇 |
原子能技术 | 317篇 |
自动化技术 | 1467篇 |
出版年
2024年 | 87篇 |
2023年 | 564篇 |
2022年 | 1223篇 |
2021年 | 1431篇 |
2020年 | 1396篇 |
2019年 | 1256篇 |
2018年 | 1292篇 |
2017年 | 1734篇 |
2016年 | 1779篇 |
2015年 | 1981篇 |
2014年 | 2434篇 |
2013年 | 2652篇 |
2012年 | 3193篇 |
2011年 | 3498篇 |
2010年 | 2701篇 |
2009年 | 2785篇 |
2008年 | 2240篇 |
2007年 | 3250篇 |
2006年 | 3007篇 |
2005年 | 2646篇 |
2004年 | 2239篇 |
2003年 | 1940篇 |
2002年 | 1687篇 |
2001年 | 1367篇 |
2000年 | 1134篇 |
1999年 | 1004篇 |
1998年 | 834篇 |
1997年 | 619篇 |
1996年 | 589篇 |
1995年 | 464篇 |
1994年 | 419篇 |
1993年 | 276篇 |
1992年 | 254篇 |
1991年 | 160篇 |
1990年 | 93篇 |
1989年 | 81篇 |
1988年 | 55篇 |
1987年 | 34篇 |
1986年 | 20篇 |
1985年 | 15篇 |
1984年 | 17篇 |
1983年 | 8篇 |
1982年 | 12篇 |
1981年 | 12篇 |
1980年 | 9篇 |
1979年 | 4篇 |
1975年 | 3篇 |
1973年 | 2篇 |
1959年 | 6篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
论文将利用可视化的算法将DNA序列映射到复杂网络中.分别对人类Y染色体,酿酒酵母,大肠杆菌HS和乳酸杆菌噬菌体的原始分组网络做一个具体详细的分析,提出无论是原核生物还是真核生物,DNA序列都具有小世界属性,并且分组方法几乎不会影响相关的统计属性. 相似文献
992.
随着房地产行业的迅速发展,物业行业正像雨后春笋般茁壮成长。虽然我国的物业行业仍处于初级发展阶段,但因其拥有广阔的发展空间,已受到社会各界越来越多的关注。通过阐述物业管理工作中的各项内容,提出了提升服务质量的办法和措施,以期为我国物业行业的进一步发展提供借鉴。 相似文献
993.
Samples were prepared using stem xylem from cottonwood (Populus deltoides) and two cottonwood hybrids (P. deltoides × Populus maximowiczii and P. deltoides × Populus trichocarpa), which grew in Tennessee, United States. The anatomical characteristics, microfibril angle, and mechanical properties of the cell wall in juvenile wood (two-year-old) were investigated by means of microscopy image analysis system, X-ray diffraction, and nanoindentation (NI). The results showed that the double-wall thickness of the fiber cells in the hybrid poplars was thicker than that of the pure poplar, and the ratio of wall to lumen of fiber cell (0.40) of the P. deltoides × P. trichocarpa, which had the slowest growth rate, reached the greatest value among the three poplar clones. Their microfibril angles (MFA) of the cell wall in the investigated samples ranged between 11.5° and 16.7°, and they correlated positively with growth rates of the three poplar clones. The average hardness and reduced elastic modulus were 0.25 GPa and 8.58 GPa for P. deltoides, 0.28 GPa and 8.34 GPa for P. deltoides × P. maximowiczii, and 0.31 GPa and 12.2 GPa for P. deltoides × P. trichocarpa, respectively. P. deltoides × P. trichocarpa with the slowest growth rate had the greatest micromechanical values among the three poplar clones. In combination with growth characteristics of the three poplar clones, the findings of the analyses on their wood properties provided information-rich data that not only could describe juvenile wood properties but also could be used in selective breeding for the three poplar clones in Tennessee, USA. 相似文献
994.
This paper is a note on “minimizing makespan in three machine flow shop with deteriorating jobs” [J.-B. Wang, M.-Z. Wang, minimizing makespan in three machine flow shop with deteriorating jobs, Computers & Operation Research 40 (2013) 547–557]. Wang and Wang presented a branch-and-bound algorithm with several dominance properties and a lower bound; however, we think that the dominance properties may not be true as they are neither necessary nor sufficient. We first show by means of a counter-example that the published dominance properties are incorrect, and then present a necessary and sufficient condition for them to be true. Moreover, a simplifying remark is provided for the above dominance properties. 相似文献
995.
By performing the Z-scan measurements with ultrafast femtosecond laser centered at 800 nm wavelength, we can unambiguously distinguish the real and imaginary part of the third-order optical nonlinearity of the erbium-doped YAG ceramics. The reverse saturable absorption of the erbium-doped YAG ceramics has been observed experimentally, and the nonlinear refractive index of the ceramics is estimated to be about 10−21 m2/W. The experimental results may provide design guidelines for the high power laser design and its applications. 相似文献
996.
1,4-bis(2-cyano styryl)benzene (2-CSB) crystal with cyano substituent groups introduced to the terminal phenyl rings of distyrylbenzene (DSB) has been prepared and its luminescence efficiency could be as high as ∼55%. Based on the analyses of cyclic voltammetry and crystal structure, cyano substituents not only lower the LUMO level but also result in a change of the packing mode from the herringbone arrangement to the face-to-face slipped π stacking motif. Then field-effect transistors (FETs) based on high-quality 2-CSB crystals grown by the physical vapor transport method have been fabricated and the highest hole and electron mobilities were measured as 0.66 and 0.29 cm2/Vs, which enhanced the corresponding values of DSB crystal by up to one and two orders of magnitude, respectively. 2-CSB crystal simultaneously combined the high luminescence and the well-balanced mobility is expected to be of interest for the fundamental research of organic light-emitting devices. 相似文献
997.
998.
《钢铁研究学报(英文版)》2016,(5):459-465
Electrochemical properties of La_(0. 82)Mg_(0. 18)Ni_(3. 50)Co_(0. 15) alloys synthesized by spark plasma sintering( SPS) were investigated based on the electrochemical measurements,physical parameters and microstructure observation. The sintering behavior of La_(0. 82)Mg_(0. 18)Ni_(3. 50)Co_(0. 15) alloys at the temperatures of 900,950 and 1 000 ℃ is characterized by four stages,i. e.,initial slight shrinkage,expansion,abrupt shrinkage and slight expansion. The maximum shrinkage displacement increases with increasing sintering temperature. All of the alloys consist of( La,Mg)_2( Ni,Co)_7 phase; additionally,temperatures of 900 and 950 ℃ are beneficial to the formation of( La,Mg)( Ni,Co)_3 phase,whereas the LaNi_5 phase is easy to form in the alloy synthesized by SPS at 1 000 ℃. The electrochemical measurements indicate an evident change of the electrochemical performance of the alloys associated with increasing the sintering temperature. The discharge capacity of the alloys first increases and then decreases as sintering temperature rises,whereas their cycle stability clearly grows all the time.Furthermore,the charging-discharging potential difference and discharging efficiency both demonstrate that the electrochemical properties of the alloy electrodes first augment and then decline with increasing sintering temperature. 相似文献
999.
Agricultural and wood residues are principal energy sources for domestic and industrial activities. However, they are often hardly utilized. Conventional wood material for briquetting optimizes combustion and efficient power production. The relationship between strength properties, resistance to humidity and calorific values of sawdust-briquettes from three tropical hardwoods of different densities [Cylicodiscus gabunensis (heavy), Antiaris toxicaria (medium) and Ceiba pentandra (light)] and a Mixed/Composite type was determined. Wood density influenced all the briquette properties and positively correlated with their Calorific Values (CVs) as: C. gabunensis > A. toxicaria > Mixed type > C. pentandra. However, light timber briquettes had greater Compressive Strength, Swelling Value (i.e., less resistance to humidity) and Shatter Index than dense wood briquettes: C. pentandra > Mixed type > A. toxicaria > C. gabunensis. C. gabunensis briquette recorded less elongation value (8.85%) than the standard stipulated (i.e., 20–50%/min.) specifying its quality to resist deterioration on exposure to humidity/water in open sheds. Enormous briquette Swelling Values for A. toxicaria (60.04%), Mixed type (66.16%) and C. pentandra (70.88%) indicate they would deteriorate fast and require great care to store, handle and transport. However, the large Shatter Indices for the Mixed type (98.8%) and C. pentandra (99.16%) denote their high durability to gravitational deterioration. Briquette technology, a “waste-to-energy method”, contributes to offset bio-residue management problems and reduce toxic emissions from its incomplete carbonization. Thus, comprehensive understanding of wood-residue briquette characteristics is significant for fuel-energy generation. 相似文献
1000.
Effect of superfine grinding on physicochemical and antioxidant properties of pomegranate peel 下载免费PDF全文
Chen Zhong Yuangang Zu Xiuhua Zhao Yong Li Yunlong Ge Weiwei Wu Yin Zhang Yuanyuan Li Dongjie Guo 《International Journal of Food Science & Technology》2016,51(1):212-221
Pomegranate peel powders were prepared by superfine grinding, whose effects were investigated on the composition, functional and antioxidant properties of the pomegranate peel products. Fluidised bed jet milling technology was used to process superfine pomegranate peel powder. The physical–chemical properties of coarse powder A (D50 = 413.4 μm) and B (D50 = 197.1 μm), fine powder C (D50 = 142.6 μm) and D (D50 = 41.2 μm), superfine powder E (D50 = 7.68 μm) and raw material powder (RMP) (D50 = 352.2 μm) were investigated in this study. SEM images revealed the shape and surface morphology of six pomegranate peel powders. The physical determinations showed that the smaller the powder particle size was, the greater the surface area (from 0.214 to 1.597 m2 g?1) and bulk density (from 0.653 to 0.751 g mL?1) were, the smaller the angles of repose (from 51.69° to 38.74°) and slide (from 48.32° to 34.18°) were. The water holding capacity (WHC), water‐solubility index (WSI), polyphenols and flavonoids release were significantly improved as the size of pomegranate peel particle decreased. The results of FTIR and UV indicated that grinding process would not influence chemical composition of pomegranate peel. Vitamin C (VC) and butylated hydroxytoluene (BHT) were used in DPPH scavenging activity determination, and DPPH scavenging activity was A < RMP < BHT < B < C < D < E < VC. 相似文献