全文获取类型
收费全文 | 9071篇 |
免费 | 666篇 |
国内免费 | 379篇 |
专业分类
电工技术 | 241篇 |
综合类 | 479篇 |
化学工业 | 1509篇 |
金属工艺 | 334篇 |
机械仪表 | 314篇 |
建筑科学 | 661篇 |
矿业工程 | 110篇 |
能源动力 | 405篇 |
轻工业 | 812篇 |
水利工程 | 214篇 |
石油天然气 | 124篇 |
武器工业 | 37篇 |
无线电 | 1006篇 |
一般工业技术 | 1599篇 |
冶金工业 | 1228篇 |
原子能技术 | 473篇 |
自动化技术 | 570篇 |
出版年
2024年 | 19篇 |
2023年 | 143篇 |
2022年 | 238篇 |
2021年 | 364篇 |
2020年 | 256篇 |
2019年 | 253篇 |
2018年 | 222篇 |
2017年 | 290篇 |
2016年 | 296篇 |
2015年 | 285篇 |
2014年 | 387篇 |
2013年 | 721篇 |
2012年 | 446篇 |
2011年 | 645篇 |
2010年 | 497篇 |
2009年 | 471篇 |
2008年 | 447篇 |
2007年 | 538篇 |
2006年 | 502篇 |
2005年 | 369篇 |
2004年 | 374篇 |
2003年 | 295篇 |
2002年 | 308篇 |
2001年 | 228篇 |
2000年 | 170篇 |
1999年 | 155篇 |
1998年 | 210篇 |
1997年 | 133篇 |
1996年 | 122篇 |
1995年 | 84篇 |
1994年 | 78篇 |
1993年 | 62篇 |
1992年 | 48篇 |
1991年 | 55篇 |
1990年 | 55篇 |
1989年 | 51篇 |
1988年 | 35篇 |
1987年 | 23篇 |
1986年 | 21篇 |
1985年 | 37篇 |
1984年 | 24篇 |
1983年 | 22篇 |
1982年 | 16篇 |
1981年 | 7篇 |
1966年 | 7篇 |
1964年 | 22篇 |
1963年 | 11篇 |
1960年 | 9篇 |
1959年 | 7篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 625 毫秒
991.
Bhagwati Bishnoi P.K. Mehta C.J. Panchal M.S. Desai Ravi Kumar V. Ganesan 《Materials Chemistry and Physics》2011
We present the preliminary results of temperature and frequency dependent dielectric measurements on Ba(Co1/3Nb2/3)O3 (BCN) thin films. These films were prepared on indium tin oxide (ITO) coated glass substrates by the pulse laser deposition (PLD) technique. It exhibits single-phase hexagonal symmetry. These films were irradiated with Ag15+ (200 MeV) and O7+ (100 MeV) beams at the fluence 1 × 1011, 1 × 1012, and 1 × 1013 ions/cm2. On irradiating these films, its dielectric constant (?′) and dielectric loss (tan δ) parameters improve compared to un-irradiated film. Compared to O7+ irradiation induced point/cluster defects Ag15+ induced columnar defects are more effective in reducing/pinning trapped charges within grains. The present paper highlights the role of swift heavy ion irradiation in engineering the dielectric properties of conductive samples to enable them to be useful for microwave device applications. 相似文献
992.
In this study, the strain rate effects on transverse tensile and compressive properties of unidirectional Glass fiber reinforced polymeric composites are investigated. To demonstrate strain rate effects, the tensile and compressive composite specimens with identical configuration are fabricated and tested to failure in the transverse direction at quasi-static strain rate of approximately 0.001 s−1 and intermediate strain rates of 1–100 s−1. The tensile and compressive tests are performed using a servo-hydraulic testing apparatus equipped with strain rate increasing mechanisms. For performing the practical tests, a jig and a fixture and other test supplies are designed and manufactured. The performance of the test jig is evaluated and showed that it is adequate for composites testing under tension and compression loads. The effects of strain rate on mechanical properties (maximum strength, modulus, and strain to failure) are considered. The characteristic results for the transverse properties indicate that damage evolution is strain-rate-dependent for the examined material. Also, a strain-rate-dependent empirical material model associated with different regression constants is proposed based on the experimental results obtained to characterize the rate dependent behavior of Glass/Epoxy composite material. 相似文献
993.
The present paper provides a game theoretic analysis of strategic cooperation on safety and security among chemical companies within a chemical industrial cluster. We suggest a two-stage sequential move game between adjacent chemical plants and the so-called Multi-Plant Council (MPC). The MPC is considered in the game as a leader player who makes the first move, and the individual chemical companies are the followers. The MPC's objective is to achieve full cooperation among players through establishing a subsidy system at minimum expense. The rest of the players rationally react to the subsidies proposed by the MPC and play Nash equilibrium. We show that such a case of conflict between safety and security, and social cooperation, belongs to the 'coordination with assurance' class of games, and we explore the role of cluster governance (fulfilled by the MPC) in achieving a full cooperative outcome in domino effects prevention negotiations. The paper proposes an algorithm that can be used by the MPC to develop the subsidy system. Furthermore, a stepwise plan to improve cross-company safety and security management in a chemical industrial cluster is suggested and an illustrative example is provided. 相似文献
994.
995.
996.
Scope: Curcumin, a component of the spice turmeric, was tested for its potential hormetic anti‐aging effects as an inducer of mild stress. Methods and results: Early passage young human skin fibroblasts treated with low doses of curcumin (below 20 μM) showed a time‐ and concentration‐dependent induction of heme oxygenase‐1 (HO‐1), followed by compensatory increase in glutathione‐S‐transferase activity, GSH levels and GSH/GSSG ratio. These effects were preceded by induction of oxidative stress (increased levels of reactive oxygen species and DNA damage) and impairment of cells' GSH redox state. Curcumin also induced nuclear factor‐erythroid‐2‐related factor 2 accumulation in the nuclei. The use of the antioxidant N‐acetyl cysteine prevented the induction of HO‐1 by curcumin. Pharmacological inhibition of phosphatidylinositol 3‐kinase, but not other kinases, significantly prevented curcumin‐induced HO‐1 levels, which was corroborated by the induction of phospho‐Akt levels by curcumin. Late passage senescent cells already had higher HO‐1 levels, and further induction of HO‐1 by curcumin was considerably impaired. The induction of stress responses by curcumin in human cells led to protective hormetic effects to further oxidant challenge. Conclusion: Curcumin induces cellular stress responses in normal human skin fibroblasts through phosphatidylinositol 3‐kinase/Akt pathway and redox signaling, supporting the view that curcumin‐induced hormetic stimulation of cellular antioxidant defenses can be a useful approach toward anti‐aging intervention. 相似文献
997.
考察了 Mo、Ni、Co 3种自制油溶性催化剂在渣油悬浮床加氢裂化反应中的催化效果,并通过光学显微镜、激光粒度仪、XRD 和 SEM 表征了它们硫化后的性质。结果表明,在渣油悬浮床加氢裂化条件下,油溶性Mo催化剂加氢活性最高,油溶性Mo催化剂比油溶性Ni 催化剂和油溶性Co催化剂更易发生硫化,硫化后的油溶性Mo催化剂颗粒数目较多,发生了团聚现象,形成较大的颗粒,主要以MoS2(六方晶系)晶体存在,且呈微晶状态。 相似文献
998.
999.
Dulal Pal Hiranmoy Mondal 《International Communications in Heat and Mass Transfer》2011,38(4):463-467
A study has been carried out to analyze the effects of variable thermal conductivity, Soret (thermal-diffusion) and Dufour (diffusion-thermo) on MHD non-Darcy mixed convection heat and mass transfer over a non-linear stretching sheet embedded in a saturated porous medium in the presence of thermal radiation, viscous dissipation, non-uniform heat source/sink and first-order chemical reaction. The governing differential equations transform into a set of non-linear coupled ordinary differential equations using similarity analysis. Similarity equations are then solved numerically using shooting algorithm with Runge-Kutta Fehlberg integration scheme over the entire range of physical parameters. A comparison with previously published work has been carried out and the results are found to be in good agreement. Graphical presentation of the local skin-friction coefficient, the local Nusselt number and the local Sherwood number as well as the temperature profiles show interesting features of the physical parameters. 相似文献
1000.
针对经验模态分解(Empirical Mode Decomposition,EMD)的端点效应问题,分析了三次样条插值产生端点效应的机理,指出了现有延拓方法的不足,提出采用Lyapunov指数预测模型进行边界延拓,以此减小端点效应在经验模态分解过程中产生的影响。在采用最大Lyapunov指数法进行边界延拓时,针对Lyapunov指数预测模型所表示的平均发散度仅是轨道演化规律的一个近似模型,提出采用局域发散度代替最大Lyapunov指数进行改进,以改进预测模型的预测精度。基于改进型Lyapunov指数边界延拓方法,由于引入时间序列预测模型使端点处的延拓更加合理,所延拓数据更加趋于真实,在希尔伯特-黄变换(Hilbert-Huang Transform,HHT)实现过程中仅需一次延拓,实现了准确的EMD分解。仿真计算和转子系统故障试验分析结果表明,所用方法可以有效解决EMD的端点效应问题。 相似文献