全文获取类型
收费全文 | 56726篇 |
免费 | 740篇 |
国内免费 | 1369篇 |
学科分类
工业技术 | 58835篇 |
出版年
2023年 | 91篇 |
2022年 | 141篇 |
2021年 | 210篇 |
2020年 | 104篇 |
2018年 | 102篇 |
2015年 | 110篇 |
2014年 | 264篇 |
2013年 | 249篇 |
2012年 | 5373篇 |
2011年 | 6915篇 |
2010年 | 1528篇 |
2009年 | 799篇 |
2008年 | 4787篇 |
2007年 | 4610篇 |
2006年 | 3931篇 |
2005年 | 3432篇 |
2004年 | 2821篇 |
2003年 | 2465篇 |
2002年 | 2232篇 |
2001年 | 2110篇 |
2000年 | 2014篇 |
1999年 | 1224篇 |
1998年 | 729篇 |
1997年 | 690篇 |
1996年 | 652篇 |
1995年 | 668篇 |
1994年 | 596篇 |
1993年 | 454篇 |
1992年 | 623篇 |
1991年 | 640篇 |
1990年 | 598篇 |
1989年 | 593篇 |
1988年 | 563篇 |
1987年 | 627篇 |
1986年 | 633篇 |
1985年 | 669篇 |
1984年 | 585篇 |
1983年 | 541篇 |
1982年 | 575篇 |
1981年 | 471篇 |
1980年 | 390篇 |
1979年 | 301篇 |
1978年 | 217篇 |
1976年 | 91篇 |
1975年 | 109篇 |
1974年 | 92篇 |
1965年 | 130篇 |
1964年 | 105篇 |
1958年 | 84篇 |
1956年 | 87篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
提出一种通用的基于视觉传感器的无人系统多模态视觉感知平台的测试与评估的方法,研究了可见光波段和红外光波段下的动态测距实验与复杂光变测距实验. 整个过程采用基于北斗卫星实时授时的时间同步技术和真值采集设备,输出带有时间戳的无人系统多模态感知单元的测量数据和真值数据,并保证了不同设备之间的时间同步误差小于10 ms. 最后,对比测量数据和真值数据,给出测试设备的性能与功能的量化评估. 实验结果表明,该测试评估方法有效地获取了真值,并进行了时间同步,满足实际的需求,具备推广性. 相似文献
2.
3.
Laser aided additive manufacturing(LAAM)was used to fabricate bulk Fe49.5Mn30Co10Cr10C0.5 interstitial multicomponent alloy using pre-alloyed powder.The room temperature yield strength(σy),ultimate tensile strength(σUTS)and elongation(εUST)were 645 MPa,917 MPa and 27.0%respectively.The as-built sample consisted of equiaxed and dendritic cellular structures formed by elemental segregation.These cellular structures together with oxide particle inclusions were deemed to strengthen the material.The other contributing components include dislocation strengthening,friction stress and grain bound-ary strengthening.The high εUTS was attributed to dislocation motion and activation of both twinning and transformation-induced plasticity(TWIP and TRIP).Tensile tests performed at-40℃and-130℃demonstrated superior tensile strength of 1041 MPa and 1267 MPa respectively.However,almost no twinning was observed in the fractured sample tested at-40℃and-130℃.Instead,higher fraction of strain-induced hexagonal close-packed(HCP)ε phase transformation of 21.2%were observed for fractured sample tested at-40℃,compared with 6.3%in fractured room temperature sample. 相似文献
4.
Guan-Qiang Wang Ming-Song Chen Hong-Bin Li Y.C.Lin Wei-Dong Zeng Yan-Yong Ma 《材料科学技术学报》2021,77(18):47-57
The uniform refinement mechanisms and methods of deformed mixed and coarse grains inside a solution-treatment Ni-based superalloy during two-stage annealing treatment have been investigated.The two-stage heat treatment experiments include an aging annealing treatment(AT)and a subsequent recrystallization annealing treatment(RT).The object of AT is to precipitate some δ phases and consume part of storage energy to inhibit the grain growth during RT,while the RT is to refine mixed and coarse grains by recrystallization.It can be found that the recrystallization grains will quickly grow up to a large size when the AT time is too low or the RT temperature is too high,while the deformed coarse grains cannot be eliminated when the AT time is too long or the RT temperature is too low.In addition,the mixed microstructure composed of some abnormal coarse recrystallization grains(ACRGs)and a large number of fine grains can be observed in the annealed specimen when the AT time is 3 h and RT tem-perature is 980℃.The phenomenon attributes to the uneven distribution of δ phase resulted from the heterogeneous deformation energy when the AT time is too short.In the regions with a large number of δ phases,the recrystallization nucleation rate is promoted and the growth of grains is limited,which results in fine grains.However,in the regions with few δ phases,the recrystallization grains around grain boundaries can easily grow up,and the new recrystallization nucleus is difficult to form inside grain,which leads to ACRGs.Thus,in order to obtain uniform and fine annealed microstructure,it is a prereq-uisite to precipitate even-distributed δ phase by choosing a suitable AT time,such as 12 h.Moreover,a relative high RT temperature is also needed to promote the recrystallization nucleation around δ phase.The optimal annealing parameters range for uniformly refining mixed crystal can be summarized as:900℃×12 h+990℃×(40-60 min)and 900℃×12 h+1000℃×(10-15 min). 相似文献
5.
管道泄漏不仅会造成环境污染,还可能引发火灾、人员伤亡等严重后果和巨大的经济损失。传统的管道泄漏在线检测与定位系统均使用单一算法进行信号处理,漏判误判多,应用效果较差。针对目前集输管道泄漏检测准确性和灵敏度较低的现状,研究一种多算法融合的方法,通过采集管道压力、流量等多种特征信号,采用最优加权融合算法,将专家经验分析法、向量机(SVM)模式识别法、序贯概率比检测法等多种信号处理方法进行综合应用,扩展了时间和空间上的检测范围,提高了泄漏检测系统的灵敏度和可靠性。利用正常运行集输管道进行了现场泄漏应用试验,试验结果验证了多算法融合检漏方法比单一检漏方法具有明显的优越性。 相似文献
6.
7.
8.
In the context of the global response to climate change,effective use of new energy and building a clean and diversified energy system is one of the important goals of China′s high-quality development.The rapid development of high-capacity power batteries had made great contributions to China′s efforts to achieve "carbon peaking and carbon neutralization".However,with the retirement of a large number of power batteries,China would bear huge ecological and environmental pressure in the future.This paper discussed the current situation of the recycling of retired power batteries in China.Due to technology,cost and market reasons,the construction of the recycling system of retired power batteries in China was not perfect.We should strive for finance and policy,build a green science and technology public service platform,improve the production,education and research personnel and intellectual property protection system to build a green and environment-friendly system for the cascade utilization,disassembly and recycling of retired power batteries,and efficiently sort and recover lithium,cobalt nickel and other key raw materials could ensure the healthy and sustainable development of China′s new energy power battery and related industries,and contribute to China′s energy system in the new era. 相似文献
9.
寒区隧道受多重因素影响容易发生渗水结冰现象,为研究该冰害形成原因和冰柱生长发育过程,将保健路隧道作为研究对象,利用现场监测和理论分析得出低温环境和水分入渗是导致冰害问题的主要原因。通过试验模拟冰柱生长发育过程,分析隧道、输电线路、桥梁等其他工程中相似的结冰现象,总结冰柱的生长形态和发育规律。结果表明:冰柱垂直生长速度远大于横向生长速度,后续水流沿着冰面呈规律性向下滴落,促成平均直径上大下小的生长形态;通过建立平衡方程,推算冰柱可能发育的最大长度,发现热通量、供水率是影响冰体尺寸的重要参数。依据上述现场调查和模拟试验所得结论,不仅可为隧道冰柱形成原因做出理论分析,也对类似工程实际具有指导意义,为隧道冰害防治提供新的研究思路。 相似文献
10.
福建省既有石结构房屋保有量大,石结构房屋由石墙、石柱、石梁和石楼板这四种石构件堆砌组成,结构抗震性能极差。石结构房屋通常设有外走廊,外走廊相对于其他部位较为独立,在地震中和其他环境振动下极易倒塌。在既有石结构房屋未进行抗震加固前,为确保外走廊安全,提出拆除外走廊石构件,采用钢筋混凝土(RC)结构重建置换的加固方法。设计与分析表明:应当尽可能地增大RC构件的刚度,以减少地震作用下石结构房屋的侧向位移;RC构件与相邻的石构件应可靠连接。外走廊RC构件重建置换的加固方法可为类似石结构民宅加固提供参考。 相似文献