全文获取类型
收费全文 | 10170篇 |
免费 | 442篇 |
专业分类
公路运输 | 2849篇 |
综合类 | 2960篇 |
水路运输 | 2531篇 |
铁路运输 | 1924篇 |
综合运输 | 348篇 |
出版年
2024年 | 20篇 |
2023年 | 46篇 |
2022年 | 325篇 |
2021年 | 418篇 |
2020年 | 320篇 |
2019年 | 121篇 |
2018年 | 156篇 |
2017年 | 155篇 |
2016年 | 174篇 |
2015年 | 340篇 |
2014年 | 439篇 |
2013年 | 608篇 |
2012年 | 707篇 |
2011年 | 774篇 |
2010年 | 817篇 |
2009年 | 797篇 |
2008年 | 798篇 |
2007年 | 927篇 |
2006年 | 855篇 |
2005年 | 637篇 |
2004年 | 219篇 |
2003年 | 159篇 |
2002年 | 158篇 |
2001年 | 161篇 |
2000年 | 139篇 |
1999年 | 77篇 |
1998年 | 46篇 |
1997年 | 34篇 |
1996年 | 38篇 |
1995年 | 30篇 |
1994年 | 23篇 |
1993年 | 27篇 |
1992年 | 13篇 |
1991年 | 22篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 7篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
891.
892.
为了解决现有基于GPS数据的路段平均速度估计模型应用条件苛刻、难以满足低成本和高精度信息需求问题,考虑不同类型GPS车辆运行特征,设计了两个基于出租车GPS数据估计路段平均速度的改进模型.基于两个改进模型,设计了路段平均速度的融合估计方法.用某城市局部路网的出租车GPS数据验证两个改进模型,并与传统模型进行了对比分析.... 相似文献
893.
车间设备布局问题,是一个NP难问题.许多学者利用启发式算法来求解并取得了一定的成果,但在模型中存在距离定义不合理的情况,均采用绝对距离的方式,存在不符合实际和计算不准确的情况;本文对距离的定义进行了改进,并利用遗传算法对改进后的模型进行求解,效果良好,达到了预期目标. 相似文献
894.
基于禁忌搜索算法求解车间作业调度问题 总被引:1,自引:0,他引:1
考虑了一个有限经济批量和交货时间计划的车间作业调度问题.在这条供应链上包含两个大的部门(生产加工部门和组装部门);多种工件首先需要经过加工部门多个车间的加工,然后送到组装部门组装成为成品;目标是如何组织安排各种工件在各个车间的各个机器上的加工顺序和加工开始时间使得此供应链上单位时间内的运输费,组装费和存储费用最小.此问题是一个NP难问题,为了找到满意解,本文利用禁忌搜索算法来解决此问题,并用MATLAB软件编写求解此问题的算法程序.从算法的数值试验过程来看,禁忌搜索的效率和效果均令人满意. 相似文献
895.
以浙北旅游公路(公路与堤坝相结合的道路)为例,介绍现有堤坝土、送检石灰、粉煤灰样本的特性,通过控制不同掺灰量对老堤坝土路基进行改善试验,得出最优经济方案,从而达到堤坝抗渗的目的和道路填筑材料CBR值的要求。 相似文献
896.
设计了基于神经网络的自主车导向控制器,建立了异构模糊神经网络控制器的结构,并由实验数据产生训练样本和验证样本集.该控制器通过精确控制2个驱动轮的差动转速实现路径跟踪.实验结果表明,采用异构模糊神经网络集成算法的导向控制器能够稳定地实现跟踪导向路径的控制功能. 相似文献
897.
Interfacial heat transfer is a key issue in many solidification processes. In the paper, a novel experimental apparatus has
been designed and on this basis, the instantaneous interfacial heat transfer between molten steel or solidified shell and
copper substrate during the first 0.2 s has been studied. The investigated parameters include melt superheat, substrate temperature
and surface roughness. The results show that the peak value of the interfacial heat flux in the first stage of liquid/solid
contact increases with melt superheat and changes slightly with substrate temperature and surface roughness. The interfacial
heat flux in the stage of solid/solid contact has a similar trend of slow decrease in most conditions. 相似文献
898.
To explore the significance of sacroiliac joint aerocele in the diagnosis of ankylosing spondylitis, the data of 196 patients
with ankylosing spondylitis (AS) were collected during December of 2008 to May of 2009. And 50 patients with osteoarthritis
(OA), 15 patients with sclerosing osteitis (SO) and 47 patients with sacroiliac joint tumors were investigated as the control
groups. The feature of sacroiliac joint aerocele in computed tomography (CT) images was observed carefully. In AS group there
were 130 patients (66.3%) diagnosed as AS according to CT results, and 32 of them (24.6%) were observed with aerocele within
sacroiliac joint cavity, majority of whom were earlier AS patients with slight bone destruction. Other 66 patients were diagnosed
as early AS according to magnetic resonance imaging (MRI) and ultrasonography. CT examination showed that the 66 patients
did not have apparent bone destruction, of whom, 26 (39.4%) patients had aerocele within sacroiliac joint cavity. Among the
control groups of 15 (15/50, 30.0%) patients with OA, 5 (5/15, 33.3%) patients with SO were observed sacroiliac joint aerocele.
The 47 patients with sacroiliac joint tumors were observed with bone or cartilage destruction, but without signs of sacroiliac
joint aerocele. The sacroiliac joint aerocele in CT images of AS patients usually appeared as spots, streaks, small or larger
round blocks, and it often happened in patients with earlier stage of diseases. Sacroiliac joint aerocele may be useful to
early diagnosis of AS. 相似文献
899.
To tackle the key-exposure problem in signature settings, this paper introduces a new cryptographic primitive named threshold
key-insulated signature (TKIS) and proposes a concrete TKIS scheme. For a TKIS system, at least k out of n helpers are needed to update a user’s temporary private key. On the one hand, even if up to k−1 helpers are compromised in addition to the exposure of any of temporary private keys, security of the non-exposed periods
is still assured. On the other hand, even if all the n helpers are compromised, we can still ensure the security of all periods as long as none of temporary private keys is exposed.
Compared with traditional key-insulated signature (KIS) schemes, the proposed TKIS scheme not only greatly enhances the security
of the system, but also provides flexibility and efficiency. 相似文献
900.
Based on the analysis of heat transfer mechanics, physical and chemical change of pellet drying and preheating process in
grate, the mathematical model is established and solved by three-diagonal matrix algorithm. With Visual Basic 6.0 a simulation
software is developed. The model is verified by measurements at a domestic pellet plant, and the temperature distribution
of pellet bed is gained. Meanwhile, the influence of different operation parameters on the pellet thermal process is studied.
The results can be taken as a basis of practical production control and the grate optimizing design. 相似文献