全文获取类型
收费全文 | 148569篇 |
免费 | 14628篇 |
国内免费 | 9276篇 |
专业分类
电工技术 | 12354篇 |
技术理论 | 3篇 |
综合类 | 18460篇 |
化学工业 | 16141篇 |
金属工艺 | 6442篇 |
机械仪表 | 10804篇 |
建筑科学 | 18732篇 |
矿业工程 | 6864篇 |
能源动力 | 5014篇 |
轻工业 | 8028篇 |
水利工程 | 6707篇 |
石油天然气 | 6579篇 |
武器工业 | 2001篇 |
无线电 | 10080篇 |
一般工业技术 | 18610篇 |
冶金工业 | 6551篇 |
原子能技术 | 2338篇 |
自动化技术 | 16765篇 |
出版年
2024年 | 617篇 |
2023年 | 1726篇 |
2022年 | 3350篇 |
2021年 | 3894篇 |
2020年 | 4476篇 |
2019年 | 3828篇 |
2018年 | 3706篇 |
2017年 | 4670篇 |
2016年 | 5204篇 |
2015年 | 5469篇 |
2014年 | 8948篇 |
2013年 | 8479篇 |
2012年 | 11395篇 |
2011年 | 11576篇 |
2010年 | 8987篇 |
2009年 | 9242篇 |
2008年 | 8511篇 |
2007年 | 10593篇 |
2006年 | 9357篇 |
2005年 | 7892篇 |
2004年 | 6501篇 |
2003年 | 5623篇 |
2002年 | 4675篇 |
2001年 | 3918篇 |
2000年 | 3420篇 |
1999年 | 2964篇 |
1998年 | 2330篇 |
1997年 | 2025篇 |
1996年 | 1700篇 |
1995年 | 1522篇 |
1994年 | 1285篇 |
1993年 | 937篇 |
1992年 | 830篇 |
1991年 | 580篇 |
1990年 | 483篇 |
1989年 | 488篇 |
1988年 | 349篇 |
1987年 | 199篇 |
1986年 | 164篇 |
1985年 | 68篇 |
1984年 | 72篇 |
1983年 | 35篇 |
1982年 | 43篇 |
1981年 | 56篇 |
1980年 | 31篇 |
1979年 | 37篇 |
1978年 | 18篇 |
1976年 | 14篇 |
1975年 | 16篇 |
1959年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
One specific class of non-linear evolution equations, known as the Tzitzéica-type equations, has received great attention from a group of researchers involved in non-linear science. In this article, new exact solutions of the Tzitzéica-type equations arising in non-linear optics, including the Tzitzéica, Dodd–Bullough–Mikhailov and Tzitzéica–Dodd–Bullough equations, are obtained using the expa function method. The integration technique actually suggests a useful and reliable method to extract new exact solutions of a wide range of non-linear evolution equations. 相似文献
3.
4.
反应堆屏蔽计算中经常出现厚屏蔽、小探测器问题,常规蒙特卡罗方法难以有效解决。基于自动重要抽样(AIS)方法,本文提出了小探测器自动重要抽样(SDAIS)方法,并针对小探测器问题,优化了AIS方法的虚粒子赌分裂算法。该方法在自主开发的蒙特卡罗屏蔽程序MCShield上进行了实现。使用NUREG/CR-6115 PWR基准题验证该方法的正确性和计算效率。结果表明,SDAIS方法可有效地解决厚屏蔽小探测器问题,相比AIS方法及传统的重要性方法,计算效率提升1~2个量级。 相似文献
5.
不同给液方式对铜电解过程中有重要的影响,不同的循环方式会影响槽内温度分布、电解液成分及阳极泥沉降等,因此,根据铜电解生产不同情况的需要,分析对比了多种给液方式在贵冶电解车间的应用,总结了这几种给液方式的优缺点和适用条件。 相似文献
6.
大型综合室内亲子乐园属于高大空间,设有游乐设施和游戏的特殊性使得对空间的舒适性要求一致,但是送风气流遇阻严重,室内存在较多气流死角,影响室内空气质量和儿童健康。因此其空调设计不仅需要考虑温度、风速的空间均匀度,还要考虑各点的空气龄和PMV-PPD指标。以天津某亲子乐园为研究对象,利用scSTREAM软件对适用于该房间的辐射供冷加新风、置换通风、混合通风三种空调方式的送风效果进行数值模拟分析,从流场的均匀性、人员的热舒适性等方面对模拟结果进行探讨,研究结果表明辐射供冷加新风方式的空间均匀性和PMV指标最佳,混合通风方式的空气龄最小。 相似文献
7.
Kevin J. Hanley 《International journal for numerical methods in engineering》2020,121(21):4865-4877
An algorithm is presented for discrete element method simulations of energy-conserving systems of frictionless, spherical particles in a reversed-time frame. This algorithm is verified, within the limits of round-off error, through implementation in the LAMMPS code. Mechanisms for energy dissipation such as interparticle friction, damping, rotational resistance, particle crushing, or bond breakage cannot be incorporated into this algorithm without causing time irreversibility. This theoretical development is applied to critical-state soil mechanics as an exemplar. It is shown that the convergence of soil samples, which differ only in terms of their initial void ratio, to the same critical state requires the presence of shear forces and frictional dissipation within the soil system. 相似文献
8.
《Journal of the European Ceramic Society》2020,40(13):4562-4571
Discrete Element Method (DEM) has been used for numerical investigation of sintering-induced structural deformations occurring in inverse opal photonic structures. The influence of the initial arrangement of template particles on the stability of highly porous inverse opal α-Al2O3 structures has been analyzed. The material transport, densification, as well as formation of defects and cracks have been compared for various case studies. Three different stages of defects formation have been distinguished starting with local defects ending with intrapore cracks. The results show that the packing of the template particles defined during the template self-assembly process play a crucial role in the later structural deformation upon thermal exposure. The simulation results are in very good agreement with experimental data obtained from SEM images and previous studies by ptychographic X-ray tomography. 相似文献
9.
High amplitude non-linear acoustic methods have shown potential for the identification of micro damage in brittle materials such as concrete. Commonly, these methods evaluate a non-linearity parameter from the relative change in frequency and attenuation with strain amplitude. Here, a novel attenuation model is introduced to describe the free reverberation from a standard impact resonance frequency test, together with an algorithm for estimating the unknown model coefficients. The non-linear variation can hereby by analyzed over a wider dynamic range as compared to conventional methods. The experimental measurement is simple and fully compatible with the standardized free-free linear impact frequency test. 相似文献
10.
We investigate the effect of dopant random fluctuation on threshold voltage and drain current variation in a two-gate nanoscale transistor. We used a quantum-corrected technology computer aided design simulation to run the simulation (10000 randomizations). With this simulation, we could study the effects of varying the dimensions (length and width), and thicknesses of oxide and dopant factors of a transistor on the threshold voltage and drain current in subthreshold region (off) and overthreshold (on). It was found that in the subthreshold region the variability of the drain current and threshold voltage is relatively fixed while in the overthreshold region the variability of the threshold voltage and drain current decreases remarkably, despite the slight reduction of gate voltage diffusion (compared with that of the subthreshold). These results have been interpreted by using previously reported models for threshold current variability, load displacement, and simple analytical calculations. Scaling analysis shows that the variability of the characteristics of this semiconductor increases as the effects of the short channel increases. Therefore, with a slight increase of length and a reduction of width, oxide thickness, and dopant factor, we could correct the effect of the short channel. 相似文献