全文获取类型
收费全文 | 45758篇 |
免费 | 4365篇 |
国内免费 | 2620篇 |
专业分类
电工技术 | 3062篇 |
技术理论 | 1篇 |
综合类 | 3156篇 |
化学工业 | 9718篇 |
金属工艺 | 6772篇 |
机械仪表 | 1886篇 |
建筑科学 | 4300篇 |
矿业工程 | 1251篇 |
能源动力 | 2464篇 |
轻工业 | 2909篇 |
水利工程 | 891篇 |
石油天然气 | 1361篇 |
武器工业 | 411篇 |
无线电 | 4041篇 |
一般工业技术 | 5503篇 |
冶金工业 | 1867篇 |
原子能技术 | 2015篇 |
自动化技术 | 1135篇 |
出版年
2024年 | 111篇 |
2023年 | 840篇 |
2022年 | 1393篇 |
2021年 | 1918篇 |
2020年 | 1663篇 |
2019年 | 1376篇 |
2018年 | 1249篇 |
2017年 | 1787篇 |
2016年 | 1747篇 |
2015年 | 1699篇 |
2014年 | 2386篇 |
2013年 | 2921篇 |
2012年 | 3087篇 |
2011年 | 3464篇 |
2010年 | 2423篇 |
2009年 | 2792篇 |
2008年 | 2241篇 |
2007年 | 2760篇 |
2006年 | 2721篇 |
2005年 | 2259篇 |
2004年 | 1921篇 |
2003年 | 1698篇 |
2002年 | 1376篇 |
2001年 | 1175篇 |
2000年 | 926篇 |
1999年 | 854篇 |
1998年 | 681篇 |
1997年 | 560篇 |
1996年 | 464篇 |
1995年 | 469篇 |
1994年 | 381篇 |
1993年 | 266篇 |
1992年 | 243篇 |
1991年 | 186篇 |
1990年 | 140篇 |
1989年 | 112篇 |
1988年 | 97篇 |
1987年 | 80篇 |
1986年 | 47篇 |
1985年 | 44篇 |
1984年 | 39篇 |
1983年 | 25篇 |
1982年 | 34篇 |
1981年 | 16篇 |
1980年 | 14篇 |
1979年 | 7篇 |
1962年 | 3篇 |
1960年 | 3篇 |
1959年 | 16篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
通过对电阻层析成像数据采集原理和深度学习网络的研究,提出了一种基于阵列电阻值和多层感知器深度学习网络相结合的流型识别方法。利用电阻层析成像系统中的16个电极传感器来获取流型样本数据,并构建出流型识别数据库,然后对多层感知器深度学习网络进行训练,获得可以识别不同流型的网络。实验结果表明,采用阵列电阻值结合多层感知器网络对流型进行学习和识别的方法,流型识别准确率可以达到95%,解决了流型图像生成过程与数据特征预选过程中流型特征损失的问题,流型识别性能得到了提高。 相似文献
92.
Rhyzopertha dominica is a key pest of stored grain. Understanding the movement of this beetle on broad geographic scales is crucial, particularly when developing strategies to prevent the spread of phosphine resistance. We assessed population genetic structuring in this pest across Turkey, using a combination of mitochondrial (cytochrome oxidase I) and microsatellite markers. In addition, we screened samples for Wolbachia, as this endosymbiont has previously been suggested to be associated with low mitochondrial genetic diversity in this beetle. Mitochondrial genetic diversity was low, with only six haplotypes identified. The genetic diversity was, however, substantially higher than that previously found in Australia or India, suggesting that R. dominica may have originated in the Middle East. Wolbachia were detected only at a single site, indicating they are not impacting the mitochondrial genetic diversity of R. dominica across Turkey. Microsatellite markers indicated there is significant geographic genetic structuring across Turkey, even among sites less than 100 km apart, suggesting there is little movement of beetles across regions within the country. This contrasts with the significantly higher levels of gene-flow found in Australia and the United States. We suggest that the limited movement of beetles across Turkey may be due to a combination of the historically localised agricultural practices (which limits anthropogenic movement among regions), and the mountainous landscape (which limits active flight among regions). Our results demonstrate that the movement of stored product pests may differ significantly across studies conducted in different countries. As a consequence, phosphine resistance management strategies must incorporate region specific information on the extent of beetle movement. 相似文献
93.
超高性能混凝土(UHPC)在钢桥面铺装结构中由于铺装材料受到钢板、栓钉等的约束,加上材料本身水胶比小,更易收缩,早期容易承受拉应力导致开裂。通过在拌和过程中添加膨胀剂可以起到减小收缩的作用,但该方法对于约束条件下的UHPC铺装的早期抗裂性能提升是否有促进作用,仍需通过更多试验进行合理评估和深入研究。通过圆环法对3组不同配方的UHPC在均匀约束条件下的早期抗裂性能进行定量测试,并将试验数据进行回归分析和计算,得到了各组的平均应力发展速率,进而评估了各组的开裂风险等级。试验结果表明,通过在UHPC中加入适量膨胀剂,可使其最终收缩应力减小,并可降低其收缩应力发展速率,进一步降低其在约束条件下的开裂风险。 相似文献
94.
Andrea Luca Tasca Eleonora Stefanelli Anna Maria Raspolli Galletti Riccardo Gori Gemma Mannarino Sandra Vitolo Monica Puccini 《化学工程与技术》2020,43(12):2382-2392
Hydrothermal carbonization of sewage sludge was carried out with the aim to evaluate the influence of process severity and initial solid content. Response surface methodology was applied to model yield and C yield responses. Enhanced dewaterability performance was recorded under mild processing conditions. The treatment promoted concentration and immobilization of Pb, Cd, Ni, Zn, and Cu. Variation of the solid content showed a stronger influence than severity on average yield and C yield. Higher heating values (HHVs) and energy retention efficiencies (EREs) of hydrochars obtained at the lowest solid content displayed the lowest values. Hence, the energy requirements of a first dewatering step should be compared with the related improvement in terms of HHV and ERE when sludge is used as feedstock. 相似文献
95.
《Ceramics International》2020,46(12):19835-19842
The present work focused on the effect of Y2O3 co-doping on the phase composition, microstructure, ionic conductivity and thermal shock resistance of 8 mol% MgO stabilized ZrO2 (Mg-PSZ) electrolyte ceramics for high temperature applications. The addition of Y2O3 could promote the process of monoclinic-to-cubic/tetragonal phase transformation and became the metastable phase at room temperature. Meanwhile, the grain size of Mg-PSZ decreased. It was demonstrated that an appreciable increase in the ionic conductivity and compressive strength occurred on substituting MgO with Y2O3 in the Mg-PSZ electrolyte ceramics across the measured temperature range. Moreover, the Y2O3 addition could restrain the adverse effect of the cyclic thermal shock on the ionic conductivity and compressive strength of Mg-PSZ. The main reason was that the increase of the amount of monoclinic phase caused by cubic/tetragonal-to-monoclinic phase transformation by the cyclic thermal shock was restrained after the Y2O3 addition. 相似文献
96.
Maria V. Deligiorgi Charis Liapi Dimitrios T. Trafalis 《International journal of molecular sciences》2020,21(23)
(1) Background: the present review provides a comprehensive and up-to date overview of the potential exploitation of fasting as an anticancer strategy. The rationale for this concept is that fasting elicits a differential stress response in the setting of unfavorable conditions, empowering the survival of normal cells, while killing cancer cells. (2) Methods: the present narrative review presents the basic aspects of the hormonal, molecular, and cellular response to fasting, focusing on the interrelationship of fasting with oxidative stress. It also presents nonclinical and clinical evidence concerning the implementation of fasting as adjuvant to chemotherapy, highlighting current challenges and future perspectives. (3) Results: there is ample nonclinical evidence indicating that fasting can mitigate the toxicity of chemotherapy and/or increase the efficacy of chemotherapy. The relevant clinical research is encouraging, albeit still in its infancy. The path forward for implementing fasting in oncology is a personalized approach, entailing counteraction of current challenges, including: (i) patient selection; (ii) fasting patterns; (iii) timeline of fasting and refeeding; (iv) validation of biomarkers for assessment of fasting; and (v) establishment of protocols for patients’ monitoring. (4) Conclusion: prescribing fasting as anticancer medicine may not be far away if large randomized clinical trials consolidate its safety and efficacy. 相似文献
97.
Tomoko Okuyama Jun Shirakawa Kazuki Tajima Yoko Ino Heidrun Vethe Yu Togashi Mayu Kyohara Ryota Inoue Daisuke Miyashita Jinghe Li Nozomi Goto Taiga Ichikawa Shingo Yamasaki Haruka Ohnuma Rie Takayanagi Yayoi Kimura Hisashi Hirano Yasuo Terauchi 《International journal of molecular sciences》2020,21(21)
98.
Tatiana V. Rozhko Elena V. Nemtseva Maria V. Gardt Alexander V. Raikov Albert E. Lisitsa Gennadii A. Badun Nadezhda S. Kudryasheva 《International journal of molecular sciences》2020,21(22)
The present study considers a possible role of enzymatic reactions in the adaptive response of cells to the beta-emitting radionuclide tritium under conditions of low-dose exposures. Effects of tritiated water (HTO) on the reactions of bacterial luciferase and NAD(P)H:FMN-oxidoreductase, as well as a coupled system of these two reactions, were studied at radioactivity concentrations ≤ 200 MBq/L. Additionally, one of the simplest enzymatic reactions, photobiochemical proton transfer in Coelenteramide-containing Fluorescent Protein (CLM-FP), was also investigated. We found that HTO increased the activity of NAD(P)H:FMN-oxidoreductase at the initial stage of its reaction (by up to 230%); however, a rise of luciferase activity was moderate (<20%). The CLM-FP samples did not show any increase in the rate of the photobiochemical proton transfer under the exposure to HTO. The responses of the enzyme systems were compared to the ‘hormetic’ response of luminous marine bacterial cells studied earlier. We conclude that (1) the oxidoreductase reaction contributes significantly to the activation of the coupled enzyme system and bacterial cells by tritium, and (2) an increase in the organization level of biological systems promotes the hormesis phenomenon. 相似文献
99.
100.
通过盐雾试验模拟潮湿环境,对裸钢试片、电镀锌钢试片、化学镀镍-磷钢试片和化学镀镍-钴-磷钢试片进行了宏观形貌、微观形貌和腐蚀产物成分分析,比较了四个试片的耐盐雾腐蚀性能。结果表明:在盐雾环境中,四个试片均会发生电化学腐蚀,生成不同的腐蚀产物;在盐雾腐蚀周期内,裸钢试片的腐蚀速率最高,化学镀镍-磷钢试片和化学镀镍-钴-磷钢试片的腐蚀速率较低;四个试片在腐蚀过程中的阳极反应和阴极反应不同,腐蚀后的微观形貌存在明显差异。 相似文献