全文获取类型
收费全文 | 27276篇 |
免费 | 2668篇 |
国内免费 | 1120篇 |
专业分类
电工技术 | 2395篇 |
技术理论 | 1篇 |
综合类 | 2470篇 |
化学工业 | 2425篇 |
金属工艺 | 1850篇 |
机械仪表 | 2385篇 |
建筑科学 | 3079篇 |
矿业工程 | 641篇 |
能源动力 | 2738篇 |
轻工业 | 2515篇 |
水利工程 | 572篇 |
石油天然气 | 1036篇 |
武器工业 | 320篇 |
无线电 | 1108篇 |
一般工业技术 | 3466篇 |
冶金工业 | 1866篇 |
原子能技术 | 469篇 |
自动化技术 | 1728篇 |
出版年
2024年 | 163篇 |
2023年 | 429篇 |
2022年 | 916篇 |
2021年 | 1009篇 |
2020年 | 1003篇 |
2019年 | 819篇 |
2018年 | 778篇 |
2017年 | 934篇 |
2016年 | 1047篇 |
2015年 | 1064篇 |
2014年 | 1672篇 |
2013年 | 1661篇 |
2012年 | 1697篇 |
2011年 | 2144篇 |
2010年 | 1517篇 |
2009年 | 1579篇 |
2008年 | 1404篇 |
2007年 | 1598篇 |
2006年 | 1473篇 |
2005年 | 1326篇 |
2004年 | 1111篇 |
2003年 | 961篇 |
2002年 | 859篇 |
2001年 | 728篇 |
2000年 | 531篇 |
1999年 | 510篇 |
1998年 | 372篇 |
1997年 | 323篇 |
1996年 | 301篇 |
1995年 | 220篇 |
1994年 | 197篇 |
1993年 | 133篇 |
1992年 | 107篇 |
1991年 | 83篇 |
1990年 | 76篇 |
1989年 | 55篇 |
1988年 | 45篇 |
1987年 | 42篇 |
1986年 | 27篇 |
1985年 | 21篇 |
1984年 | 24篇 |
1983年 | 17篇 |
1982年 | 17篇 |
1981年 | 8篇 |
1980年 | 15篇 |
1979年 | 10篇 |
1965年 | 4篇 |
1964年 | 5篇 |
1963年 | 4篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
81.
Schnurr Paula P.; Hayes Andrew F.; Lunney Carole A.; McFall Miles; Uddo Madeline 《Canadian Metallurgical Quarterly》2006,74(4):707
This study examined how change in posttraumatic stress disorder (PTSD) symptoms relates to change in quality of life. The sample consisted of 325 male Vietnam veterans with chronic PTSD who participated in a randomized trial of group psychotherapy. Latent growth modeling was used to test for synchronous effects of PTSD symptom change on psychosocial and physical health-related quality of life within the same time period and lagged effects of initial PTSD symptom change on later change in quality of life. PTSD symptoms were associated with reduced quality of life before treatment. There were synchronous effects of symptom change on change in quality of life but no significant lagged effects. Results indicate the importance of measuring quality of life in future investigations of PTSD treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
82.
本文对混合工质R407C与R12的物理和热力性质进行了比较分析,并针对汽车空调制冷系统的特点,对两种工质在变工况下进行了制冷系统的理论循环分析,阐明了在汽车空调制冷系统中使用R407C的可行性。 相似文献
83.
Current understanding of the mechanisms involved in osseointegration following implantation of a biomaterial has led to adhesion quantification being implemented as an assay of cytocompatibility. Such measurement can be hindered by intra-sample variation owing to morphological changes associated with the cell cycle. Here we report on a new scanning electron microscopical method for the simultaneous immunogold labelling of cellular focal adhesions and S-phase nuclei identified by BrdU incorporation. Prior to labelling, cellular membranes are removed by tritonization and antigens of non-interest blocked by serum incubation. Adhesion plaque–associated vinculin and S-phase nuclei were both separately labelled with a 1.4 nm gold colloid and visualized by subsequent colloid enhancement via silver deposition. This study is specifically concerned with the effects microgroove topographies have on adhesion formation in S-phase osteoblasts. By combining backscattered electron (BSE) imaging with secondary electron (SE) imaging it was possible to visualize S-phase nuclei and the immunogold-labelled adhesion sites in one energy 'plane' and the underlying nanotopography in another. Osteoblast adhesion to these nanotopographies was ascertained by quantification of adhesion complex formation. 相似文献
84.
Philip Tipping 《International Journal of Pressure Vessels and Piping》1996,66(1-3):17-25
The susceptibility and tendency for nuclear power plant (NPP) components to undergo changes in their mechanical and physical properties in the course of the NPP lifetime is generally termed as “ageing”. The light water reactor (LWR) nuclear environment is not a begnign one; it is characterized not only by fast neutrons, which can degrade metallic structures, but also relatively high temperatures of coolant water (around 300°C) which may contain impurities (e.g. sulphate, chloride, peroxides) which can cause corrosion. The hydrodynamical conditions of the coolant in steam generators, for example, can cause thermal fatigue, erosion and corrosion; suspended particulate matter can accelerate erosion processes which can lead to wall thinning and lowering of safety margins. Ageing is, therefore, a very complex mixture of factors concerned with materials, temperatures, times of exposure to environments which vary with time and with respect to chemical composition and flow charactertistics.
The paper describes a few ageing phenomena which can be considered important due to their impact on nuclear safety issues; their influence on economic aspects (availability) of NPP is outlined. Mitigation measures for NPP component ageing problems are given together with recommendations for addressing such issues in NPP now and in the future. 相似文献
85.
LOW-CYCLE FATIGUE UNDER NON-PROPORTIONAL LOADING 总被引:4,自引:0,他引:4
X. Chen Q. Gao X.-F. Sun 《Fatigue & Fracture of Engineering Materials & Structures》1996,19(7):839-854
A series of strain-controlled, low-cycle fatigue experiments have been conducted on 42CrMo steel under various loading paths including circular, square, cruciform, and rectangular paths. Present experiments have shown that there is additional hardening under non-proportional cyclic loading. Non-proportional cyclic additional hardening also results in a shorter life for multiaxial low cycle fatigue. A non-proportionality measure of strain path based on both a physical basis and macromechanical phenomena is proposed. The loading path effect on additional hardening is also described well. Low-cycle fatigue damage accumulation and the evolution process under non-proportional loading is analysed via the Continuum Damage Mechanics Model of Chaboche. A non-proportinality measure is introduced in the damage evolution equation and a modified Coffin-Manson type formula is derived. A novel fatigue life prediction approach based on the critical-plane concept of Brown and Miller is proposed. 相似文献
86.
通过在三种不同的强化负荷下进行深沟球轴承疲劳寿命试验,并与常规试验一组结果对比。结果表明,适当地加大滚动轴承疲劳寿命试验负荷,可以大大缩短试验时间,而疲劳寿命依然服从Weibul分布,且与常规试验结果基本一致,同时疲劳破坏的形式仍是表面下萌生裂纹,然后扩展至表面形成剥落。 相似文献
87.
Forest and bioenergy strategies offer the prospect of reduced CO2 emissions to the atmosphere. Such strategies can affect the net flux of carbon to the atmosphere through 4 mechanisms: storage of C in the biosphere; storage of C in forest products; use of biofuels to displace fossil-fuel use; use of wood products which often displaces other products that require more fossil fuel for their production. We use the mathematical model GORCAM (Graz/Oak Ridge Carbon Accounting Model) to examine these mechanisms for 16 land-use scenarios. Over long time intervals the amount of C stored in the biosphere and in forest products reaches a steady state and continuing mitigation of C emissions depends on the extent to which fossil fuel use is displaced by the use of bioenergy and wood products. The relative effectiveness of alternative forest and bioenergy strategies and their impact on net C emissions strongly depend, for example, on the productivity of the site, its current usage, and the efficiency with which the harvest is used. When growth rates are high and harvest is used efficiently, the dominant opportunity for net reduction in C emissions is seen to be fossil-fuel displacement. At the growth rates and efficiencies of harvest utilization adopted in many of our base scenarios, the net C balance at the end of 100 years is very similar whether trees are harvested and used for energy and traditional forest products, or reforestation and forest protection strategies are implemented. The C balance on a plantation system that provides a constant output of biomass products can look different than the balance of a single parcel of land. 相似文献
88.
89.
《International Journal of Pressure Vessels and Piping》1996,66(1-3):187-198
The limit carrying capacity of gas pipelines having corrosion defects were evaluated by means of an improved FEM analysis, together with the ANSI/ASME defect judgement and an experimental verification. When compared with our past presentation at the proceedings of the CAPE'93 Colloquium (dealing with reproduced defects), this paper evaluates the remaining lifetime of a pipeline having natural faults. The new improved analysis includes geometrical nonlinearities leading to a modification of limit state parameters and thus matching better with actuality. This presented work was initiated by the firm of Trans-Gas in Prague after having had a pipeline inspected proving some parts of it as being heavily corroded. The task in hand was to determine the remaining pipeline lifetime with the view to at least a two-year period. 相似文献
90.
许进 《西安电子科技大学学报(自然科学版)》1994,(3)
文中解决了2-重自补图的计数问题,获得了具有p个顶点的2-重自补图的数目是其中Z(A)表示置换群A的圈指标,S ̄(2)_p表示p次对称群的对群. 相似文献