全文获取类型
收费全文 | 272090篇 |
免费 | 21837篇 |
国内免费 | 13845篇 |
专业分类
电工技术 | 19685篇 |
技术理论 | 53篇 |
综合类 | 37544篇 |
化学工业 | 28646篇 |
金属工艺 | 9850篇 |
机械仪表 | 14839篇 |
建筑科学 | 37485篇 |
矿业工程 | 14919篇 |
能源动力 | 8029篇 |
轻工业 | 14082篇 |
水利工程 | 14009篇 |
石油天然气 | 11050篇 |
武器工业 | 2892篇 |
无线电 | 22298篇 |
一般工业技术 | 18838篇 |
冶金工业 | 15220篇 |
原子能技术 | 2825篇 |
自动化技术 | 35508篇 |
出版年
2024年 | 723篇 |
2023年 | 2496篇 |
2022年 | 4829篇 |
2021年 | 5994篇 |
2020年 | 6241篇 |
2019年 | 5244篇 |
2018年 | 4901篇 |
2017年 | 6012篇 |
2016年 | 7290篇 |
2015年 | 8336篇 |
2014年 | 15158篇 |
2013年 | 13822篇 |
2012年 | 18151篇 |
2011年 | 19404篇 |
2010年 | 15421篇 |
2009年 | 16053篇 |
2008年 | 15093篇 |
2007年 | 19716篇 |
2006年 | 18650篇 |
2005年 | 16274篇 |
2004年 | 13780篇 |
2003年 | 12407篇 |
2002年 | 10226篇 |
2001年 | 8676篇 |
2000年 | 7318篇 |
1999年 | 5953篇 |
1998年 | 4493篇 |
1997年 | 3976篇 |
1996年 | 3655篇 |
1995年 | 3120篇 |
1994年 | 2760篇 |
1993年 | 2072篇 |
1992年 | 1818篇 |
1991年 | 1354篇 |
1990年 | 1189篇 |
1989年 | 1032篇 |
1988年 | 825篇 |
1987年 | 567篇 |
1986年 | 422篇 |
1985年 | 358篇 |
1984年 | 337篇 |
1983年 | 243篇 |
1982年 | 220篇 |
1981年 | 168篇 |
1980年 | 130篇 |
1979年 | 113篇 |
1978年 | 64篇 |
1977年 | 74篇 |
1976年 | 55篇 |
1975年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
121.
122.
Considering autonomous mobile robots with a variety of specific functions as a kind of service, when there are many types and quantities of services and the density of regional services is large, proposing an algorithm of Circular Area Search (CAS) because of the problem of multi-robot service scheduling in various areas. Firstly, Django is used as the web framework to build the Service-Oriented Architecture (SOA) multi-robot service cloud platform, which is the basic platform for multi-service combination. Then, the service type, the latitude and longitude and the scoring parameters of the service are selected as the service search metrics to design the CAS algorithm that based on the existing service information registered in MySQL and the Gaode Map for screening optimal service, and then providing the service applicant with the best service. Finally, the service applicant applies for the self-driving tour service as an example to perform performance simulation test on the proposed CAS algorithm. The results show that the CAS algorithm of the multi-robot service cloud platform proposed in this paper is practical compared to the global search. And compared with the Greedy Algorithm experiment, the service search time is reduced about 58% compared with the Greedy Algorithm, which verifies the efficiency of CAS algorithm. 相似文献
123.
Since researchers began studying the mechanism of flavonoids’ anticancer activity, little attention has been focused on the modulation of redox state in cells as a potential chemotherapeutic strategy. However, recent studies have begun identifying that the anticancer effect of flavonoids occurs both in their antioxidative activity which scavenges ROS and their prooxidative activity which generates ROS. Against this backdrop, this study attempts to achieve a comprehensive analysis of the individual and separate study findings regarding flavonoids’ modulation of redox state in cancer cells. It focuses on the mechanism behind the anticancer effect, and mostly on the modulation of redox potential by flavonoids such as quercetin, hesperetin, apigenin, genistein, epigallocatechin-3-gallate (EGCG), luteolin and kaempferol in both in vitro and animal models. In addition, the clinical applications of and bioavailability of flavonoids were reviewed to help build a treatment strategy based on flavonoids’ prooxidative potential. 相似文献
124.
Risk allocation decisions are of critical importance in project management. The present study proposes an explanation for how risk allocation in a contract motivates a contractor to cooperate with a project owner. Theories of risk allocation and trust were used to motivate the research. Using a survey methodology, we collected data concerning 124 construction projects in China. We found that risk allocation influenced the contractor’s role behavior through the contractor’s feeling of being trusted but not the contractor’s trust in the owner. Feeling of being trusted partially mediated the effect of risk allocation on the contractor’s in-role (i.e., contractual) behavior and fully mediated the effect on extra-role behavior. The study introduces a social and psychological view of the impacts of risk allocation to the project and engineering management literature. We contribute to theory by arguing and demonstrating the mediating effect of trust on the relationship between risk allocation and contractor behavior. From a practical standpoint, we conclude that contractual risk allocation has a significant impact on building a trusting relationship between owners and contractors and that contractors who feel trusted perform both contractually mandated actions and actions external to the contract more diligently, resulting in the likelihood of improved outcomes for both parties. 相似文献
125.
通过百泉泉区天然状态与超采状态下的水环境对比分析,并对岩溶水补给量和开采量进行计算,阐述恢复邢台百泉泉水流量的可行性,随着“引朱济邢”和“南水北调”供水工程的实施,邢台百泉水生态环境的恢复将变为现实。 相似文献
126.
孙新忠 《水利水电科技进展》2006,26(2):26-29
在运城市夹马口灌区和红旗灌区进行了1996,1997两个年度的玉米渗灌试验,研究了不同毛管间距条件下渗灌对其产量及水分生产率等的影响。结果表明,玉米渗灌毛管间距采用0.8~1.0 m较为适宜。毛管间距愈大,产量愈低;渗灌较地面灌平均减产7.23%,较旱地平均增产30.8%;玉米生长期内总耗水量地面灌最大,渗灌次之,旱地最小。渗灌可明显提高玉米水分生产率,渗灌处理水分生产率平均为1.65 kg/m3,是地面灌的1.2倍,是旱地的1.33倍;两年度渗灌较地面灌平均节水44.4%。 相似文献
127.
随钻扩眼工具及技术研究 总被引:1,自引:0,他引:1
基于随钻扩眼技术优势的分析,研究了机械式、液压式和偏心式随钻扩眼工具执行机构和扩眼总成的机构原理,并介绍了国内所开展的相关研究。文章提出应加强现有工具的适应性和匹配性研究,发掘各类工具的优势。优化执行机构、扩眼总成和水力机构、重视底部钻具组合力学特性的分析是今后发展和完善随钻扩眼工具及技术的几个重要内容。实践表明,随钻扩眼技术在处理井下复杂情况、降低钻井综合成本、提高钻井速度、提高建井质量和安全性等方面具有显著的优势,随钻扩眼工具也正逐渐成为一种重要的石油钻井配套工具。 相似文献
128.
129.
基于CVSD编码的无线语音系统方案的设计 总被引:2,自引:0,他引:2
简要介绍了连续可变斜率增量(CVSD)调制的原理。与目前应用较为广泛的其它语音编码方式相比较,CVSD拥有更优的数字特性。着重介绍了由CML公司研制开发的基于CVSD的语音编码芯片———CMX649的特点及相关的应用方式。CMX649能够成功地应用在广泛的语音编码系统中,尤其适合无线语音系统应用。在此基础上,给出了一种实用性很强的低成本、低功耗无线语音系统的设计与应用方案。该方案可提供清晰可靠的语音传输,可广泛应用于农村地区,具有广阔的市场空间。 相似文献
130.
Defects are often present in rolled products, such as wire rod. The market demand for wire rod without any defects has increased. In the final wire rod products, defects originating from steel making, casting, pre‐rolling of billets and during wire rod rolling can appear. In this work, artificial V‐shaped longitudinal surface cracks have been analysed experimentally and by means of FEM. The results indicate that the experiments and FEM calculations show the same tendency except in two cases, where instability due to fairly “round” false round bars disturbed the experiment. FE studies in combination with practical experiments are necessary in order to understand the behaviour of the material flows in the groove and to explain whether the crack will open up as a V‐shape or if it will be closed as an I‐shape. 相似文献