全文获取类型
收费全文 | 137754篇 |
免费 | 13908篇 |
国内免费 | 7718篇 |
专业分类
电工技术 | 9886篇 |
技术理论 | 15篇 |
综合类 | 10285篇 |
化学工业 | 21054篇 |
金属工艺 | 7670篇 |
机械仪表 | 8822篇 |
建筑科学 | 11327篇 |
矿业工程 | 4260篇 |
能源动力 | 4009篇 |
轻工业 | 10312篇 |
水利工程 | 3057篇 |
石油天然气 | 6861篇 |
武器工业 | 1439篇 |
无线电 | 17193篇 |
一般工业技术 | 15360篇 |
冶金工业 | 5828篇 |
原子能技术 | 1722篇 |
自动化技术 | 20280篇 |
出版年
2024年 | 615篇 |
2023年 | 2370篇 |
2022年 | 4697篇 |
2021年 | 6728篇 |
2020年 | 5024篇 |
2019年 | 3863篇 |
2018年 | 4379篇 |
2017年 | 4720篇 |
2016年 | 4326篇 |
2015年 | 6228篇 |
2014年 | 7864篇 |
2013年 | 9073篇 |
2012年 | 10548篇 |
2011年 | 11149篇 |
2010年 | 9638篇 |
2009年 | 9018篇 |
2008年 | 8702篇 |
2007年 | 7903篇 |
2006年 | 7057篇 |
2005年 | 5883篇 |
2004年 | 4105篇 |
2003年 | 3181篇 |
2002年 | 2894篇 |
2001年 | 2438篇 |
2000年 | 2435篇 |
1999年 | 2643篇 |
1998年 | 2108篇 |
1997年 | 1747篇 |
1996年 | 1686篇 |
1995年 | 1408篇 |
1994年 | 1198篇 |
1993年 | 835篇 |
1992年 | 640篇 |
1991年 | 481篇 |
1990年 | 398篇 |
1989年 | 347篇 |
1988年 | 261篇 |
1987年 | 171篇 |
1986年 | 125篇 |
1985年 | 85篇 |
1984年 | 63篇 |
1983年 | 44篇 |
1982年 | 60篇 |
1981年 | 43篇 |
1980年 | 52篇 |
1979年 | 29篇 |
1976年 | 15篇 |
1974年 | 11篇 |
1959年 | 15篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
51.
Li Lin Harry Haoxiang Wang Yuewei Liu Ciyong Lu Weiqing Chen Vivian Yawei Guo 《Indoor air》2021,31(6):2158-2166
A cross-sectional study was conducted to investigate the impact of solid fuel use for heating and cooking on blood pressure (BP) and hypertension, using data from the China Health and Retirement Longitudinal Study (CHARLS). The primary fuels used for indoor heating and cooking were collected by questionnaires, respectively. Hypertension was defined based on self-report of physician's diagnosis, and/or measured BP, and/or anti-hypertensive medication use. Multivariate logistic regression models were constructed to assess the associations. Among 10 450 eligible participants, 68.2% and 57.2% used indoor solid fuel for heating and cooking, respectively. Compared with none/clean fuel users, solid fuel for heating was associated with elevated BP (adjusted β: 2.02, 95% CI: 1.04–3.01 for systolic BP; adjusted β: 1.36, 95% CI: 0.78–1.94 for diastolic BP) and increased risk of hypertension (adjusted odds ratio: 1.15, 95% CI: 1.03–1.29). The impact of indoor solid fuel for heating on BP was more evident in rural and north residents, and hypertensive patients. We did not detect any significant associations between solid fuel use for cooking and BP/hypertension. Indoor solid fuel use is prevalent in China, especially in the rural areas. Its negative impact on BP suggested that modernization of household fuel use may help to reduce the burden of hypertension in China. 相似文献
53.
54.
55.
针对领域自适应问题中源域和目标域的联合分布差异最小化问题,提出两阶段领域自适应学习方法.在第一阶段考虑样本标签和数据结构的判别信息,通过学习一个共享投影变换,使投影后的共享空间中边缘分布的差异最小.第二阶段利用源域标记数据和目标域非标记数据学习一个带结构风险的自适应分类器,不仅能最小化源域和目标域条件分布差异,还能进一步保持源域和目标域边缘分布的流形一致性.在3个基准数据集上的实验表明,文中方法在平均分类准确率和Kappa系数两项评价指标上均表现较优. 相似文献
56.
Yue Gao Miao-miao Zhang Xiao-peng Guo Wen-jian Li Dong Lu 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2020,95(5):1290-1297
Toxicity caused by the accumulation of butanol in fermentation media is an important factor limiting the concentration of butanol. There is currently no systematic research in place investigating the butanol tolerance mechanism of bacteria such as Clostridium acetobutylicum, which adapts to butanol stress and regulates its growth and metabolism. Here, research results related to the butanol tolerance of C. acetobutylicum are reviewed to understand the molecular basis of changes in butanol-tolerant strains. Organic solvent-tolerant bacteria play an important role in the fields of biofuel production, enzyme preparation and bioremediation. An analysis of limitations of the application of organic solvent-tolerant bacteria has revealed that future research should focus on combining the microbial tolerance phenotype with specific utilization to achieve an optimal balance between organic solvent tolerance and production. This review serves as a reference for the improvement and engineering of strains that tolerate organic solvents. © 2019 Society of Chemical Industry 相似文献
57.
为了保证上海光源X射线干涉光刻光束线的稳定性,减小热变形对实验结果的影响,对X射线干涉光刻光束线的3个关键光学元件——偏转镜、聚焦镜和精密四刀狭缝进行热-结构耦合分析。首先,计算偏转镜、聚焦镜和精密四刀狭缝所承载的功率密度;然后,建立其有限元模型;最后,获得光学元件的温度场和热变形的结果。结果表明,偏转镜和聚焦镜采用间接水冷方式可有效抑制热变形,冷却后的最大面形误差分别为7.2μrad和9.2μrad。精密四刀狭缝未冷却时,刀片组件温度介于271.56~273.27℃,刀口热变形为0.19 mm,直线导轨热变形为0.08 mm;经过铜辫子冷却后,刀片组件温度降至22.24~23.94℃,刀口热变形降至0.2μm,直线导轨热变形降至0.1μm;采用影像法和接触探头法测试后,刀口直线度、平行度和重复精度均满足技术要求。偏转镜、聚焦镜和精密四刀狭缝的热变形通过间接水冷和铜辫子的冷却方式可以得到很大程度的抑制,进而保证光斑质量。 相似文献
58.
59.
60.
Huimin Zhao Wensi Wang Yunmei Du Yu Yang Minghui Wang Shaoxiang Li Ruixin Chen Yanru Liu Lei Wang 《International Journal of Hydrogen Energy》2021,46(18):10763-10772
In this work, we synthesized Se doped MoS2@Ni3S2 with nanosheets coated nanorods structure supported on Ni foam (MoNiSeS). Firstly, MoS2@Ni3S2 (MoNiS) nanorods was synthesized by hydrothermal method. After selenization treatment, MoSe2 successfully formed on the edge of MoS2 nanosheets and particle Ni3S2 transformed into NiSe, in which MoSe2 and NiSe acted as new phase in MoNiSeS. The obtained MoNiSeS only needs a low overpotential of 68 mV to reach the current density of 10 mA cm?2, and has a low Tafel plots of 72.77 mV dec?1 and good electrochemical durability, whose electrochemical activity is much better than that of MoNiS and NiSeS, implying the introduction of Mo and Se is beneficial to improve the electrocatalytic performance of NiS for HER. In addition, the proper amount of Mo source, which has an effect on the morphology of product, has also been investigated. For MoNiSeS, the typical nanosheets coated nanarods expose more active sites and the synergic effects is good to the improvement of the catalytic activity. Meanwhile, WNiSeS has also been prepared using the same method and the corresponding results show that the electrochemical activity of WNiSeS is much better than that of NiSeS, proving the universality of this strategy. 相似文献