首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   6810篇
  免费   224篇
  国内免费   15篇
电工技术   69篇
综合类   6篇
化学工业   1292篇
金属工艺   82篇
机械仪表   170篇
建筑科学   257篇
矿业工程   48篇
能源动力   158篇
轻工业   532篇
水利工程   95篇
石油天然气   16篇
无线电   375篇
一般工业技术   1115篇
冶金工业   1646篇
原子能技术   47篇
自动化技术   1141篇
  2023年   46篇
  2022年   74篇
  2021年   111篇
  2020年   84篇
  2019年   96篇
  2018年   141篇
  2017年   121篇
  2016年   122篇
  2015年   129篇
  2014年   184篇
  2013年   417篇
  2012年   335篇
  2011年   408篇
  2010年   290篇
  2009年   262篇
  2008年   365篇
  2007年   358篇
  2006年   309篇
  2005年   285篇
  2004年   246篇
  2003年   210篇
  2002年   219篇
  2001年   137篇
  2000年   108篇
  1999年   136篇
  1998年   119篇
  1997年   125篇
  1996年   119篇
  1995年   105篇
  1994年   116篇
  1993年   93篇
  1992年   112篇
  1991年   54篇
  1990年   101篇
  1989年   78篇
  1988年   73篇
  1987年   89篇
  1986年   58篇
  1985年   72篇
  1984年   60篇
  1983年   67篇
  1982年   60篇
  1981年   47篇
  1980年   45篇
  1979年   45篇
  1978年   37篇
  1977年   43篇
  1976年   28篇
  1975年   33篇
  1973年   19篇
排序方式: 共有7049条查询结果,搜索用时 15 毫秒
81.
82.
83.
We report a total‐area power conversion efficiency of 15% for a copper indium gallium disulfoselenide (CIGSSe) solar cell fabricated from a copper indium gallium disulfide (CIGS) nanoparticle ink based process. Careful optimization of the fabrication process has resulted in a significant improvement in efficiency compared to our previously reported efficiency of 12%. This efficiency ranks among the highest reported in the literature for solution processed CIGSSe. Despite having an absorber thickness of approximately 700–800 nm, which is less than half the thickness of high efficiency devices grown by both coevaporation and solution processes in the literature, our devices show good short‐circuit current (32.1 mA/cm2). Surprisingly, the sintered film shows lateral composition fluctuations, which have not been reported for other high efficiency devices and may be responsible for the lower open circuit voltage (636 mV) observed here. This suggests an avenue for further improvement through optimization of the nanoparticle selenization process to better control composition in the sintered film. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
84.
A hydroponic growth procedure which enables the intrinsic 42Ca-labelling of green beans ( Phaseolus vulgaris L) has been developed. Whole-plant Ca influx was measured from planting through the period of pod expansion for a crop of 60 plants grown hydroponically in a 3m2area. Total Ca influx was 10·1mmol per plant; 35% of this influx occurred during the period of pod growth. Plants were labelled with 42Ca via the nutrient solution during the period of pod expansion; isotopic composition of harvested pods was nearly identical to that of the administered solution. Recovery of isotopic tracer at harvest was as follows: pods 8·4%; leaves, 61·1%; stems, 17·1%, roots, 9·0%. Pod yield was 98·8g FW per plant. 42Ca-labelled green beans can be used safely to investigate Ca bioavailability in humans.  相似文献   
85.
86.
This paper analyzes the performance of a discrete-event combat simulation executed on a parallel processor under control of the Time Warp Operating System. Time Warp is in a class of distributed simulation methods called Optimistic methods which have proven to be useful over a wide range of simulations. The combat simulation used for this performance study, called STB88, is a division-corps model incorporating a number of different types of computations. The speed-up for three versions of this model on the Caltech/JPL Mark III Hypercube and the BBN Butterfly parallel processors was measured relative to an efficient sequential execution of the same model on the same hardware. The results indicate that STB88 version 1 achieves a speed-up of 28.6 on 60 Mark III processors, while STB88 version 2 achieves a speed-up of 36.8 on 100 Butterfly processors. Version 3 of STB88 achieved a speed-up of 38.5 on 128 Mark III processors. The versions differed only in their interface to Time Warp. On the Butterfly, the sequential execution completed in 2 hours, while the 100 processor execution completed in 3.2 minutes.  相似文献   
87.
For photovoltaic (PV) technology to play an increasing role in the utility sector at its present price, the technology needs to be developed in a manner that is consistent with, and takes advantage of, the economics of the demand-side management (DSM) market. High-value applications in this direction are for photovoltaics to perform a DSM function either as a direct load control (DLC) device or as a peak-shaving option, which has the effect of raising the end-use efficiency of customers' electrical equipment. This paper describes two PV-DSM applications involving a water heater and an air conditioner studied at a residential PV test facility, Solar One House, located on the campus of the University of Delaware. A single 55-W PV module directly connected to an electric water heater was found to offset standby and mixing losses, resulting in a 2°C increase in water temperature at the end of the afternoon compared to the standard DLC (grid-disconnected) case. A conservatively sized PV array without storage could meet the house air-conditioning load over 97% of the time from noon to 3 p.m., but only 69% from 3 p.m. to 6 p.m. If a PV system is combined with an air-conditioning cycling program, success rates for supply of an air-conditioning load are greatly increased, meeting almost 100% of the load between noon and 3 p.m. and 85% during 3 p.m. to 6 p.m. Furthermore, our results suggest that a modest-size PV array with storage could significantly shave peak air-conditioning loads during 3 p.m. to 6 p.m., thus reducing the peak demand faced by a utility. Preliminary analyses support the economic compatibility of a PV system as a DLC device or a peak-shaving tool.  相似文献   
88.
Stereotactic body radiotherapy (SBRT) is known to induce important immunologic changes within the tumor microenvironment (TME). However, little is known regarding the early immune responses within the TME in the first few weeks following SBRT. Therefore, we used the canine spontaneous tumor model to investigate TME responses to SBRT, and how local injection of immune modulatory antibodies to OX40 and TLR 3/9 agonists might modify those responses. Pet dogs with spontaneous cancers (melanoma, carcinoma, sarcoma, n = 6 per group) were randomized to treatment with either SBRT or SBRT combined with local immunotherapy. Serial tumor biopsies and serum samples were analyzed for immunologic responses. SBRT alone resulted at two weeks after treatment in increased tumor densities of CD3+ T cells, FoxP3+ Tregs, and CD204+ macrophages, and increased expression of genes associated with immunosuppression. The addition of OX40/TLR3/9 immunotherapy to SBRT resulted in local depletion of Tregs and tumor macrophages and reduced Treg-associated gene expression (FoxP3), suppressed macrophage-associated gene expression (IL-8), and suppressed exhausted T cell-associated gene expression (CTLA4). Increased concentrations of IL-7, IL-15, and IL-18 were observed in serum of animals treated with SBRT and immunotherapy, compared to animals treated with SBRT. A paradoxical decrease in the density of effector CD3+ T cells was observed in tumor tissues that received combined SBRT and immunotherapy as compared to animals treated with SBRT only. In summary, these results obtained in a spontaneous large animal cancer model indicate that addition of OX40/TLR immunotherapy to SBRT modifies important immunological effects both locally and systemically.  相似文献   
89.
Soft tissue defects are common following trauma and tumor extirpation. These injuries can result in poor functional recovery and lead to a diminished quality of life. The healing of skin and muscle is a complex process that, at present, leads to incomplete recovery and scarring. Regenerative medicine may offer the opportunity to improve the healing process and functional outcomes. Barriers to regenerative strategies have included cost, regulatory hurdles, and the need for cell-based therapies. In recent years, exosomes, or extracellular vesicles, have gained tremendous attention in the field of soft tissue repair and regeneration. These nanosized extracellular particles (30–140 nm) can break the cellular boundaries, as well as facilitate intracellular signal delivery in various regenerative physiologic and pathologic processes. Existing studies have established the potential of exosomes in regenerating tendons, skeletal muscles, and peripheral nerves through different mechanisms, including promoting myogenesis, increasing tenocyte differentiation and enhancing neurite outgrowth, and the proliferation of Schwann cells. These exosomes can be stored for immediate use in the operating room, and can be produced cost efficiently. In this article, we critically review the current advances of exosomes in soft tissue (tendons, skeletal muscles, and peripheral nerves) healing. Additionally, new directions for clinical applications in the future will be discussed.  相似文献   
90.
Trigeminal neuralgia (TN) is a complex orofacial pain syndrome characterized by the paroxysmal onset of pain attacks in the trigeminal distribution. The underlying mechanism for this debilitating condition is still not clearly understood. Decades of basic and clinical evidence support the demyelination hypothesis, where demyelination along the trigeminal afferent pathway is a major driver for TN pathogenesis and pathophysiology. Such pathological demyelination can be triggered by physical compression of the trigeminal ganglion or another primary demyelinating disease, such as multiple sclerosis. Further examination of TN patients and animal models has revealed significant molecular changes, channelopathies, and electrophysiological abnormalities in the affected trigeminal nerve. Interestingly, recent electrophysiological recordings and advanced functional neuroimaging data have shed new light on the global structural changes and the altered connectivity in the central pain-related circuits in TN patients. The current article aims to review the latest findings on the pathophysiology of TN and cross-examining them with the current surgical and pharmacologic management for TN patients. Understanding the underlying biology of TN could help scientists and clinicians to identify novel targets and improve treatments for this complex, debilitating disease.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号