全文获取类型
收费全文 | 44918篇 |
免费 | 5014篇 |
国内免费 | 4149篇 |
专业分类
电工技术 | 3360篇 |
技术理论 | 2篇 |
综合类 | 7033篇 |
化学工业 | 4485篇 |
金属工艺 | 1526篇 |
机械仪表 | 2736篇 |
建筑科学 | 2751篇 |
矿业工程 | 1102篇 |
能源动力 | 1003篇 |
轻工业 | 2764篇 |
水利工程 | 1040篇 |
石油天然气 | 1046篇 |
武器工业 | 531篇 |
无线电 | 5423篇 |
一般工业技术 | 4557篇 |
冶金工业 | 1416篇 |
原子能技术 | 939篇 |
自动化技术 | 12367篇 |
出版年
2024年 | 204篇 |
2023年 | 622篇 |
2022年 | 1177篇 |
2021年 | 1282篇 |
2020年 | 1283篇 |
2019年 | 1153篇 |
2018年 | 1166篇 |
2017年 | 1403篇 |
2016年 | 1564篇 |
2015年 | 1585篇 |
2014年 | 2339篇 |
2013年 | 2716篇 |
2012年 | 3072篇 |
2011年 | 3301篇 |
2010年 | 2603篇 |
2009年 | 2811篇 |
2008年 | 2872篇 |
2007年 | 3362篇 |
2006年 | 2971篇 |
2005年 | 2638篇 |
2004年 | 2211篇 |
2003年 | 1849篇 |
2002年 | 1536篇 |
2001年 | 1301篇 |
2000年 | 1152篇 |
1999年 | 951篇 |
1998年 | 776篇 |
1997年 | 662篇 |
1996年 | 625篇 |
1995年 | 533篇 |
1994年 | 469篇 |
1993年 | 349篇 |
1992年 | 297篇 |
1991年 | 270篇 |
1990年 | 233篇 |
1989年 | 195篇 |
1988年 | 137篇 |
1987年 | 93篇 |
1986年 | 49篇 |
1985年 | 51篇 |
1984年 | 40篇 |
1983年 | 40篇 |
1982年 | 33篇 |
1981年 | 17篇 |
1980年 | 22篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
首先从材料力学角度分析了抚顺石化公司干法腈纶装置原进口切断刀盘圆环失效的原因 ,认为此种切断刀盘圆环系二维增强结构层压板 ,层间没有纤维增强 ,需要解决由二维增强向三维增强的过渡。给出了改进办法 ,寻求到三维增强的替代材料。同时介绍了机械加工测试及在线实验 相似文献
102.
E.J. Vanderperre 《International journal of systems science》2014,45(9):1970-1977
We analyse the survival time of a repairable duplex system characterised by cold standby and by a pre-emptive priority rule. We allow general probability distributions for failure and repair. Moreover, an important realistic feature of the system is the general assumption that the non-priority unit has a memory. This combination of features has not been analysed in the previous literature. Our (new) methodology is based on a concatenation of a Cauchy-type integral representation of the modified Heaviside unit-step function and a two-sided stochastic inequality. Finally, we introduce a security interval related to a security level and a suitable risk-criterion based on the survival function of the system. As a practical application, we analyse some particular cases of the survival function jointly with the security interval corresponding to a security level of 90. 相似文献
103.
Yuzhu Guo L.Z. Guo Daniel Coca Z.Q. Lang 《International journal of systems science》2014,45(10):2133-2144
A new parametric frequency response algorithm is introduced to investigate linear and non-linear dynamic systems with time-varying parameters. In the new algorithm the time-varying parameters are regarded as additional inputs of the systems and the non-linear generalised frequency response functions for multi-input-single-output systems are then employed to obtain Zadeh's system functions from a differential equation representation. The parametric frequency response method reveals how the time-varying parameters affect the behaviour of the systems through a time-varying term. The new method can be applied to both linear and non-linear time-varying systems. 相似文献
104.
Visual tracking techniques based on stereo endoscope are developed to measure tissue motion in robot-assisted minimally invasive surgery. However, accurate 3D tracking of tissue surfaces remains challenging due to complicated deformation, poor imaging conditions, specular reflections and other dynamic effects during surgery. This study employs a robust and efficient 3D tracking scheme with two independent recursive processes, namely kernel-based inter-frame motion estimation and model-based intra-frame 3D matching. In the first process, target region is represented in joint spatial-color space for robust estimation. By defining a probabilistic similarity measure, a mean-shift-based iterative algorithm is derived for location of the target region in a new image. In the second process, the thin-plate spline model is used to fit the 3D shape of tissue surfaces around the target region. An iterative algorithm based on an efficient second-order minimization technique is derived to compute optimal model parameters. The two processes can be computed in parallel. Their outputs are combined to recover 3D information about the target region. The performance of the proposed method is validated using phantom heart videos and in vivo videos acquired by the daVinci® surgical robotic platform and a synthesized data set with known ground truth. 相似文献
105.
Anugrah K. Pamosoaji Pham Thuong Cat 《International journal of systems science》2014,45(12):2515-2528
An obstacle avoidance problem of rear-steered wheeled vehicles in consideration of the presence of uncertainties is addressed. Modelling errors and additional uncertainties are taken into consideration. Controller designs for driving and steering motors are designed. A proportional-derivative-type driving motor controller and a sliding-mode steering controller combined with radial basis function neural network (RBFNN) based estimators are proposed. The convergence properties of the RBFNN-based estimators are proven by the Stone–Weierstrass theorem. The stability of the proposed control law is proven using Lyapunov stability analysis. The obstacle avoidance strategy utilising the sliding surface adjustment to an existing navigation method is presented. It is concluded that the driving velocity and steering-angle performances of the proposed control system are satisfactory. 相似文献
106.
In this paper, we investigate the mixed H2/H∞ robust model predictive control (RMPC) for polytopic uncertain systems, which refers to the infinite horizon optimal guaranteed cost control (OGCC). To fully use the capability of actuators, we adopt a saturating feedback control law as the control strategy of RMPC. As the saturating feedback control law can be effectively represented by the convex hull of a group of auxiliary linear feedback laws, the auxiliary feedback laws allow us to design the actual feedback control law without consideration of the input constraints directly to achieve the improved performance. Moreover, we suggest the relative weights on the actual and auxiliary feedback laws to the RMPC, which in turn improves the closed-loop system performance. Furthermore, an off-line design of the proposed RMPC is also developed to make it more practical. Numerical studies demonstrate the effectiveness of the proposed algorithm. 相似文献
107.
This paper presents a new loss function for neural network classification, inspired by the recently proposed similarity measure called Correntropy. We show that this function essentially behaves like the conventional square loss for samples that are well within the decision boundary and have small errors, and L0 or counting norm for samples that are outliers or are difficult to classify. Depending on the value of the kernel size parameter, the proposed loss function moves smoothly from convex to non-convex and becomes a close approximation to the misclassification loss (ideal 0–1 loss). We show that the discriminant function obtained by optimizing the proposed loss function in the neighborhood of the ideal 0–1 loss function to train a neural network is immune to overfitting, more robust to outliers, and has consistent and better generalization performance as compared to other commonly used loss functions, even after prolonged training. The results also show that it is a close competitor to the SVM. Since the proposed method is compatible with simple gradient based online learning, it is a practical way of improving the performance of neural network classifiers. 相似文献
108.
In this paper, we propose a data-driven feedback controller design method based on Lyapunov approach, which can guarantee the asymptotic stability of the closed-loop and enlarge the estimate of domain of attraction (DOA) for the closed-loop. First, sufficient conditions for a feedback controller asymptotically stabilizing the discrete-time nonlinear plant are proposed. That is, if a feedback controller belongs to an open set consisting of pairs of control input and state, whose elements can make the difference of a control Lyapunov function (CLF) to be negative-definite, then the controller asymptotically stabilizes the plant. Then, for a given CLF candidate, an algorithm, to estimate the open set only using data, is proposed. With the estimate, it is checked whether the candidate is or is not a CLF. If it is, a feedback controller is designed just using data, which satisfies sufficient conditions mentioned above. Finally, the estimate of DOA for closed-loop is enlarged by finding an appropriate CLF from a CLF candidate set based on data. Because the controller is designed directly from data, complexity in building the model and modeling error are avoided. 相似文献
109.
110.
为了定量、客观、全面地评价光学镜头的像质,介绍了光学镜头调制传递函数的测试。先简要叙述了测试的原理,并给出计算公式;然后介绍了测试步骤,其中包括固定、穿轴、测试中心视场和测试轴外视场;最后介绍了测试时的注意事项,包括对测试工装的要求、对测试平面的要求和正、负轴外视场测试值相差较大时的处理办法。 相似文献