全文获取类型
收费全文 | 179965篇 |
免费 | 12956篇 |
国内免费 | 5629篇 |
专业分类
电工技术 | 8285篇 |
技术理论 | 4篇 |
综合类 | 8012篇 |
化学工业 | 30179篇 |
金属工艺 | 8976篇 |
机械仪表 | 10417篇 |
建筑科学 | 10740篇 |
矿业工程 | 2745篇 |
能源动力 | 5577篇 |
轻工业 | 13068篇 |
水利工程 | 2547篇 |
石油天然气 | 6495篇 |
武器工业 | 869篇 |
无线电 | 25869篇 |
一般工业技术 | 26782篇 |
冶金工业 | 12100篇 |
原子能技术 | 2039篇 |
自动化技术 | 23846篇 |
出版年
2024年 | 437篇 |
2023年 | 2307篇 |
2022年 | 3793篇 |
2021年 | 6162篇 |
2020年 | 4357篇 |
2019年 | 3848篇 |
2018年 | 4473篇 |
2017年 | 5063篇 |
2016年 | 4962篇 |
2015年 | 5865篇 |
2014年 | 8003篇 |
2013年 | 11057篇 |
2012年 | 11154篇 |
2011年 | 12880篇 |
2010年 | 10815篇 |
2009年 | 10655篇 |
2008年 | 10303篇 |
2007年 | 9647篇 |
2006年 | 9242篇 |
2005年 | 7795篇 |
2004年 | 5801篇 |
2003年 | 5021篇 |
2002年 | 4948篇 |
2001年 | 4117篇 |
2000年 | 3966篇 |
1999年 | 4146篇 |
1998年 | 4843篇 |
1997年 | 3764篇 |
1996年 | 3367篇 |
1995年 | 2719篇 |
1994年 | 2157篇 |
1993年 | 1784篇 |
1992年 | 1402篇 |
1991年 | 1197篇 |
1990年 | 973篇 |
1989年 | 856篇 |
1988年 | 688篇 |
1987年 | 547篇 |
1986年 | 470篇 |
1985年 | 409篇 |
1984年 | 348篇 |
1983年 | 243篇 |
1982年 | 252篇 |
1981年 | 209篇 |
1980年 | 194篇 |
1979年 | 148篇 |
1978年 | 129篇 |
1977年 | 160篇 |
1976年 | 219篇 |
1975年 | 97篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Ji Hye Yang Sae Kwang Ku IL Je Cho Je Hyeon Lee Chang-Su Na Sung Hwan Ki 《International journal of molecular sciences》2021,22(4)
Hepatic fibrosis occurs when liver tissue becomes scarred from repetitive liver injury and inflammatory responses; it can progress to cirrhosis and eventually to hepatocellular carcinoma. Previously, we reported that neoagarooligosaccharides (NAOs), produced by the hydrolysis of agar by β-agarases, have hepatoprotective effects against acetaminophen overdose-induced acute liver injury. However, the effect of NAOs on chronic liver injury, including hepatic fibrosis, has not yet been elucidated. Therefore, we examined whether NAOs protect against fibrogenesis in vitro and in vivo. NAOs ameliorated PAI-1, α-SMA, CTGF and fibronectin protein expression and decreased mRNA levels of fibrogenic genes in TGF-β-treated LX-2 cells. Furthermore, downstream of TGF-β, the Smad signaling pathway was inhibited by NAOs in LX-2 cells. Treatment with NAOs diminished the severity of hepatic injury, as evidenced by reduction in serum alanine aminotransferase and aspartate aminotransferase levels, in carbon tetrachloride (CCl4)-induced liver fibrosis mouse models. Moreover, NAOs markedly blocked histopathological changes and collagen accumulation, as shown by H&E and Sirius red staining, respectively. Finally, NAOs antagonized the CCl4-induced upregulation of the protein and mRNA levels of fibrogenic genes in the liver. In conclusion, our findings suggest that NAOs may be a promising candidate for the prevention and treatment of chronic liver injury via inhibition of the TGF-β/Smad signaling pathway. 相似文献
3.
Wireless Networks - Geolocation is important for many emerging applications such as disaster management and recommendation system. In this paper, we propose a multilayer recognition model (MRM) to... 相似文献
4.
5.
6.
This paper investigates PID control design for a class of planar nonlinear uncertain systems in the presence of actuator saturation. Based on the bounds on the growth rates of the nonlinear uncertain function in the system model, the system is placed in a linear differential inclusion. Each vertex system of the linear differential inclusion is a linear system subject to actuator saturation. By placing the saturated PID control into a convex hull formed by the PID controller and an auxiliary linear feedback law, we establish conditions under which an ellipsoid is contractively invariant and hence is an estimate of the domain of attraction of the equilibrium point of the closed-loop system. The equilibrium point corresponds to the desired set point for the system output. Thus, the location of the equilibrium point and the size of the domain of attraction determine, respectively, the set point that the output can achieve and the range of initial conditions from which this set point can be reached. Based on these conditions, the feasible set points can be determined and the design of the PID control law that stabilizes the nonlinear uncertain system at a feasible set point with a large domain of attraction can then be formulated and solved as a constrained optimization problem with constraints in the form of linear matrix inequalities (LMIs). Application of the proposed design to a magnetic suspension system illustrates the design process and the performance of the resulting PID control law. 相似文献
7.
Applied Composite Materials - In this paper, the low-velocity impact deformation behavior of biaxial warp-knitted flexible composite was investigated. A simplified finite element model (FEM) of the... 相似文献
8.
Shin Hansub Sim Sungyong Kwon Hyukyoon Hwang Sangheum Lee Younho 《International Journal of Information Security》2022,21(1):25-36
International Journal of Information Security - This paper deals with a well-known problem in the area of the smudge attacks: when a user draws a pattern to unlock the pattern lock on a smartphone... 相似文献
10.
Pengfei Chen Honggang Chang Tao Peng Yongfan Tang Youquan Liu Chao Xiang 《应用聚合物科学杂志》2021,138(30):50314
Hydraulic fracturing with slickwater is a field-proven stimulation technology used in tight reservoirs. Because of the high pumping rate associated with slickwater fracturing, drag reduction (DR) is critical in minimizing pressure drop and the success of oilfield operations. In this paper, a new type of drag reducer (SPR) was synthesized with acrylamide and 12-allyloxydodecyl acid sodium, and its drag reduction performance was evaluated. The results showed that the new drag reducer features low molecular weight, fast-dissolving rate and low interfacial tension. The algorithm of estimating the drag reduction rate of non-Newtonian fluid SPR was proposed and validated. Empirical or semianalytical models for estimating the friction ratio (σ) or friction factor (λ or f) were used to simulate the turbulence behavior of the SPR drag reducer under different Reynolds numbers (Re). The modified Virk's correlation could accurately model the turbulent behavior of the SPR drag reducer. A unified calculation formula was established in this study for different pipe diameters. 相似文献