全文获取类型
收费全文 | 854821篇 |
免费 | 130668篇 |
国内免费 | 87153篇 |
专业分类
电工技术 | 78237篇 |
技术理论 | 14篇 |
综合类 | 85584篇 |
化学工业 | 114204篇 |
金属工艺 | 66280篇 |
机械仪表 | 53930篇 |
建筑科学 | 64612篇 |
矿业工程 | 38251篇 |
能源动力 | 25272篇 |
轻工业 | 84404篇 |
水利工程 | 26767篇 |
石油天然气 | 38756篇 |
武器工业 | 12405篇 |
无线电 | 101206篇 |
一般工业技术 | 90156篇 |
冶金工业 | 36993篇 |
原子能技术 | 11606篇 |
自动化技术 | 143965篇 |
出版年
2024年 | 6099篇 |
2023年 | 14780篇 |
2022年 | 29410篇 |
2021年 | 37426篇 |
2020年 | 30732篇 |
2019年 | 30577篇 |
2018年 | 32988篇 |
2017年 | 37636篇 |
2016年 | 35007篇 |
2015年 | 44478篇 |
2014年 | 51814篇 |
2013年 | 58817篇 |
2012年 | 67972篇 |
2011年 | 68618篇 |
2010年 | 63884篇 |
2009年 | 59456篇 |
2008年 | 58800篇 |
2007年 | 57182篇 |
2006年 | 50299篇 |
2005年 | 42199篇 |
2004年 | 33477篇 |
2003年 | 24284篇 |
2002年 | 22604篇 |
2001年 | 20416篇 |
2000年 | 17847篇 |
1999年 | 12532篇 |
1998年 | 9477篇 |
1997年 | 8028篇 |
1996年 | 7400篇 |
1995年 | 6830篇 |
1994年 | 5591篇 |
1993年 | 4877篇 |
1992年 | 4312篇 |
1991年 | 3148篇 |
1990年 | 2555篇 |
1989年 | 2366篇 |
1988年 | 1774篇 |
1987年 | 865篇 |
1986年 | 730篇 |
1985年 | 544篇 |
1984年 | 395篇 |
1983年 | 337篇 |
1982年 | 339篇 |
1981年 | 361篇 |
1980年 | 382篇 |
1979年 | 262篇 |
1976年 | 304篇 |
1975年 | 248篇 |
1972年 | 258篇 |
1960年 | 207篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
22.
Jinfeng Zeng Zhiting Liu Hanbo Zou Wei Yang Haosen Fan Haijun Yu Shengzhou Chen 《金属学报(英文版)》2021,34(8):1153-1162
A appropriate size with three-dimension(3 D) channels for lithium diffusion plays an important role in constructing highperforming LiNi_(0.5)Mn_(1.5)O_4(LNMO) cathode materials, as it can not only reduce the transport path of lithium ions and electrons, but also reduce the side effects and withstand the structural strain in the process of repetitive Li~+ intercalation/deintercalation. In this work, an e fficient method for designing the hollow LNMO microsphere with 3 D channels structure by using polyethylene oxide(PEO) as soft template agent assisted solvothermal method is proposed. Experimental results indicate that PEO can make the reagents mingle evenly and nucleate slowly in the solvothermal process, thus obtaining a homogeneous distribution of carbonate precursors. In the final LNMO products, the hollow 3 D channels structure obtained by the decomposition of PEO and carbonate precursor in the calcination can provide abundant electroactive zones and electron/ion transport paths during the charge/discharge process, which benefits to improve the cycling performance and rate capability. The LNMO prepared by adding 1 g PEO possesses the most outstanding electrochemical performance, which presented an excellent discharge capacity of 143.1 mAh g~(-1) at 0.1 C and with a capacity retention of 92.2% after 100 cycles at 1 C. The superior performance attributed to the 3 D channels structure of hollow microspheres, which provide uninterrupted conductive systems and therefore achieve the stable transfer for electron/ion. 相似文献
23.
24.
Pengfei Chen Honggang Chang Tao Peng Yongfan Tang Youquan Liu Chao Xiang 《应用聚合物科学杂志》2021,138(30):50314
Hydraulic fracturing with slickwater is a field-proven stimulation technology used in tight reservoirs. Because of the high pumping rate associated with slickwater fracturing, drag reduction (DR) is critical in minimizing pressure drop and the success of oilfield operations. In this paper, a new type of drag reducer (SPR) was synthesized with acrylamide and 12-allyloxydodecyl acid sodium, and its drag reduction performance was evaluated. The results showed that the new drag reducer features low molecular weight, fast-dissolving rate and low interfacial tension. The algorithm of estimating the drag reduction rate of non-Newtonian fluid SPR was proposed and validated. Empirical or semianalytical models for estimating the friction ratio (σ) or friction factor (λ or f) were used to simulate the turbulence behavior of the SPR drag reducer under different Reynolds numbers (Re). The modified Virk's correlation could accurately model the turbulent behavior of the SPR drag reducer. A unified calculation formula was established in this study for different pipe diameters. 相似文献
25.
Ping-Chi Hsu Jia-Ying Jhong Li-Ping Huang Kuo-Hsin Lee Hsin-Pao Chen Yue-Leon Guo 《International journal of molecular sciences》2021,22(8)
Di(2-ethylhexyl) phthalate (DEHP) is widely used as a plasticizer in the manufacture of polyvinylchloride plastics and has been associated with concerns regarding male reproductive toxicity. In this study, we hypothesized that maternal exposure to DEHP induces transgenerational inheritance of adult-onset adverse reproductive outcomes through the male germline in the F1, F2, and F3 generations of male offspring. Pregnant rats were treated with 5 or 500 mg of DEHP/kg/day through gavage from gestation day 0 to birth. The offspring body weight, anogenital distance (AGD), anogenital index (AGI), sperm count, motility, and DNA fragmentation index (DFI) were measured for all generations. Methyl-CpG binding domain sequencing was performed to analyze sperm DNA methylation status in the F3. DEHP exposure at 500 mg/kg affected AGD, AGI, sperm count, mean DFI, and %DFI in the F1; AGD, sperm count, and mean DFI in the F2; and AGD, AGI, mean DFI, and %DFI in the F3. DEHP exposure at 5 mg/kg affected AGD, AGI, sperm count, and %DFI in the F1; sperm count in the F2; and AGD and AGI in F3. Compared with the control group, 15 and 45 differentially hypermethylated genes were identified in the groups administered 5 mg/kg and 500 mg/kg DEHP, respectively. Moreover, 130 and 6 differentially hypomethylated genes were observed in the groups administered 5 mg/kg and 500 mg/kg DEHP. Overall, these results demonstrated that prenatal exposure to DEHP caused transgenerational epigenetic effects, which may explain the observed phenotypic changes in the male reproductive system. 相似文献
26.
恶意代码数量已经呈现爆炸式增长,对于恶意代码的检测防护显得尤为重要.近几年,基于深度学习的恶意代码检测方法开始出现,基于此,提出一种新的检测方法,将恶意代码二进制文件转化为十进制数组,并利用一维卷积神经网络(1 Dimention Convolutional Neural Networks,1D CNN)对数组进行分类和识别.针对代码家族之间数量不平衡的现象,该算法选择在分类预测上表现良好的XGBoost,并对Vision Research Lab中的25个不同恶意软件家族的9458个恶意软件样本进行了实验.实验结果表明,所提的方法分类预测精度达到了97%. 相似文献
27.
Yixuan ZHOU Huajie WANG Yi YU Yihang CHEN Rui KE Min XU Chijie XIAO Zhanhui WANG Jiquan LI Xuru DUAN Minyou YE 《等离子体科学和技术》2021,23(7):75105-52
In this article, we present the optical design of a novel diagnostic on the HL-2 A tokamak, i.e. the20-channel edge Lyman-alpha beam emission spectroscopy, which is a promising solution for edge density turbulence research on tokamaks, as it offers the possibility of density fluctuation measurement with a 3.3 mm spatial resolution while maintains a high temporal resolution of1 μs. The optical path, including the reflective collection optics, the high-dispersion spectrometer, and the linear detector array, is carefully optimized to obtain a good image quality and a high throughput. The maximum root mean square radius of the collection optics is 64 μm.The detected photon flux is estimated to be about 10~(11) photons/s/channel. 相似文献
30.
Oxide-based near infrared (IR)-shielding coatings consisting of quarter‐wave stacks of oxygen-deficient tantalum oxide (Ta2O5?x) and silicon oxide (SiO2) multilayers and tin-doped indium oxide (In2O3) (ITO) films with the thicknesses of 200–600 nm can block the passage of IR-A (wavelength: 760–1400 nm) and IR-B (wavelength: 1400–3000 nm) radiation, respectively. In this study, the optical properties and microstructure of these oxide-based IR-shielding coatings were investigated. Transmission electron microscopy images indicated that amorphous Ta2O5?x/amorphous SiO2 multilayers were uniform and dense. ITO films were found to be highly crystalline and show carrier concentrations of up to 7.1 × 1020 cm?3, resulting in the strong IR-B optical absorption due to the plasma excitation of the free carriers. Oxide-based IR-shielding coatings with an ITO thickness of 420 nm were found to have near-IR shielding rates of >90% and an average visible light transmittance of >70%. The effects of IR on human keratinocytes were studied to evaluate the IR-induced photoaging in human skin. It was found that the downregulation of cellular proliferation and the enhancement of senescence-associated β-galactosidase activity induced by IR irradiation were significantly inhibited by oxide-based IR-shielding coatings. Thus, this study provides a facile method for the development of coatings for smart windows with high IR-shielding ability and high visible light transmittance. 相似文献