全文获取类型
收费全文 | 108940篇 |
免费 | 11601篇 |
国内免费 | 6053篇 |
专业分类
电工技术 | 8174篇 |
技术理论 | 3篇 |
综合类 | 7815篇 |
化学工业 | 17099篇 |
金属工艺 | 6360篇 |
机械仪表 | 7103篇 |
建筑科学 | 8404篇 |
矿业工程 | 3714篇 |
能源动力 | 3061篇 |
轻工业 | 7392篇 |
水利工程 | 2328篇 |
石油天然气 | 6074篇 |
武器工业 | 1162篇 |
无线电 | 13467篇 |
一般工业技术 | 12721篇 |
冶金工业 | 4631篇 |
原子能技术 | 1075篇 |
自动化技术 | 16011篇 |
出版年
2024年 | 483篇 |
2023年 | 2268篇 |
2022年 | 3873篇 |
2021年 | 5792篇 |
2020年 | 4186篇 |
2019年 | 3425篇 |
2018年 | 3596篇 |
2017年 | 3963篇 |
2016年 | 3575篇 |
2015年 | 4767篇 |
2014年 | 5776篇 |
2013年 | 6776篇 |
2012年 | 7716篇 |
2011年 | 8173篇 |
2010年 | 6891篇 |
2009年 | 6533篇 |
2008年 | 6320篇 |
2007年 | 5930篇 |
2006年 | 5989篇 |
2005年 | 5100篇 |
2004年 | 3423篇 |
2003年 | 2779篇 |
2002年 | 2485篇 |
2001年 | 2206篇 |
2000年 | 2239篇 |
1999年 | 2280篇 |
1998年 | 1878篇 |
1997年 | 1581篇 |
1996年 | 1433篇 |
1995年 | 1180篇 |
1994年 | 1019篇 |
1993年 | 679篇 |
1992年 | 520篇 |
1991年 | 438篇 |
1990年 | 304篇 |
1989年 | 250篇 |
1988年 | 209篇 |
1987年 | 132篇 |
1986年 | 121篇 |
1985年 | 66篇 |
1984年 | 34篇 |
1983年 | 18篇 |
1982年 | 38篇 |
1981年 | 22篇 |
1980年 | 32篇 |
1979年 | 21篇 |
1976年 | 14篇 |
1975年 | 10篇 |
1959年 | 7篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 29 毫秒
81.
Yan Xiong Xianwu Du Mingyu Xiang Hao Wang Weimin Wang Zhengyi Fu 《Journal of the European Ceramic Society》2018,38(12):4167-4172
The densification behaviors of pure B4C and B4C-ZrO2 mixtures were compared during hot pressing. The results showed that in-situ formed ZrB2 effectively enhanced the densification process of B4C-ZrO2 mixtures, more significantly during the intermediate stage. Within the relative density ranging from 0.75 to 0.90, the B4C-15?wt%ZrO2 mixture (B15Z) achieved the maximum densification rate as twice much as that of pure B4C. The stress exponent n>3 indicated plastic deformation was the dominant densification mechanism of B15Z. The viscosities of plastic flow were evaluated using Murray-Rodger-William equation and the viscosity of B15Z was only a quarter of that in pure B4C. The sintering activation energy was calculated to be 305.9?kJ/mol for pure B4C and 197?kJ/mol for B15Z, respectively. It was proposed that the lower viscosity of plastic flow and activation energy accelerated the sliding and propagating motions of plastic flow, by which underlain the enhanced densification behaviors of B4C-ZrO2 mixtures. 相似文献
82.
Breast cancer is the most frequently diagnosed cancer in women worldwide. The disease and its treatments exert profound effects on an individual’s physical and mental health. There are many factors that impact an individual’s risk of developing breast cancer, their response to treatments, and their risk of recurrence. The community of microorganisms inhabiting the gastrointestinal tract, the gut microbiota, affects human health through metabolic, neural, and endocrine signaling, and immune activity. It is through these mechanisms that the gut microbiota appears to influence breast cancer risk, response to treatment, and recurrence. A disrupted gut microbiota or state of ‘dysbiosis’ can contribute to a biological environment associated with higher risk for cancer development as well as contribute to negative treatment side-effects. Many cancer treatments have been shown to shift the gut microbiota toward dysbiosis; however, the microbiota can also be positively manipulated through diet, prebiotic and probiotic supplementation, and exercise. The objective of this review is to provide an overview of the current understanding of the relationship between the gut microbiota and breast cancer and to highlight potential strategies for modulation of the gut microbiota that could lead to improved clinical outcomes and overall health in this population. 相似文献
83.
We propose an analytical model to evaluate the lightpath blocking performance for a single ROADM node with intra-node add/drop contention,in which the number of lightpaths that can be added/dropped with the same wavelength is limited by the add/drop contention factor.Different models of traffic load per nodal degree are considered to validate the effectiveness of the analytical model.The simulation results show that the proposed analytical model is effective in predicting the performance for different values of add/drop contention factor C and for variable offered loads at the node.The add/drop contention factor shows an important impact on the lightpath blocking performance and properly raising the contention factor can significantly improve the lightpath blocking performance.When the add/drop contention factor C exceeds a certain level,the performance of a ROADM with intra-node contention is close to that of a contentionless ROADM. 相似文献
84.
85.
86.
87.
88.
In this work,the ionospheric variability is analyzed by applying the wavelet decomposition technique to the noontime fo F2,F10.7,interplanetary magnetic field(IMF)Bz,Ap,and lower thermospheric temperature at pressure of 10?4 h Pa in 2002.Results show that the variance of periodic oscillations in the ionosphere is largest in the 2–4-day period and declines with the increase of the period.The maximum variance of the periodic oscillations in solar irradiation is in the 16–32-day period.For geomagnetic activities,most of the variance is about equally distributed on intervals of periods shorter than 32 days.Variance distributions of IMF Bz and lower thermospheric temperature are similar to those of the ionosphere.They show the maximum in the 2–4-day period and decline with the increase of the period.By analyzing the distributions of the variances,the potential connections between the ionosphere and the external sources are discussed. 相似文献
89.
90.