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   23950篇
  免费   1238篇
  国内免费   579篇
电工技术   556篇
综合类   460篇
化学工业   4129篇
金属工艺   1056篇
机械仪表   735篇
建筑科学   1303篇
矿业工程   247篇
能源动力   680篇
轻工业   1992篇
水利工程   278篇
石油天然气   171篇
武器工业   59篇
无线电   1890篇
一般工业技术   3783篇
冶金工业   4776篇
原子能技术   214篇
自动化技术   3438篇
  2023年   184篇
  2022年   334篇
  2021年   558篇
  2020年   390篇
  2019年   405篇
  2018年   494篇
  2017年   510篇
  2016年   537篇
  2015年   502篇
  2014年   735篇
  2013年   1479篇
  2012年   1146篇
  2011年   1472篇
  2010年   1115篇
  2009年   1157篇
  2008年   1229篇
  2007年   1189篇
  2006年   1040篇
  2005年   952篇
  2004年   736篇
  2003年   663篇
  2002年   630篇
  2001年   420篇
  2000年   384篇
  1999年   395篇
  1998年   784篇
  1997年   546篇
  1996年   464篇
  1995年   384篇
  1994年   360篇
  1993年   351篇
  1992年   282篇
  1991年   189篇
  1990年   260篇
  1989年   221篇
  1988年   181篇
  1987年   180篇
  1986年   167篇
  1985年   195篇
  1984年   199篇
  1983年   166篇
  1982年   175篇
  1981年   174篇
  1980年   155篇
  1979年   165篇
  1978年   124篇
  1977年   144篇
  1976年   237篇
  1975年   128篇
  1973年   109篇
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
1.
2.
In this article, we present the optical design of a novel diagnostic on the HL-2 A tokamak, i.e. the20-channel edge Lyman-alpha beam emission spectroscopy, which is a promising solution for edge density turbulence research on tokamaks, as it offers the possibility of density fluctuation measurement with a 3.3 mm spatial resolution while maintains a high temporal resolution of1 μs. The optical path, including the reflective collection optics, the high-dispersion spectrometer, and the linear detector array, is carefully optimized to obtain a good image quality and a high throughput. The maximum root mean square radius of the collection optics is 64 μm.The detected photon flux is estimated to be about 10~(11) photons/s/channel.  相似文献   
3.
Number entry is a ubiquitous activity and is often performed in safety- and mission-critical procedures, such as healthcare, science, finance, aviation and in many other areas. We show that Monte Carlo methods can quickly and easily compare the reliability of different number entry systems. A surprising finding is that many common, widely used systems are defective, and induce unnecessary human error. We show that Monte Carlo methods enable designers to explore the implications of normal and unexpected operator behaviour, and to design systems to be more resilient to use error. We demonstrate novel designs with improved resilience, implying that the common problems identified and the errors they induce are avoidable.  相似文献   
4.
5.
The diagnosis and treatment of prostate cancer (PCa) is a major health-care concern worldwide. This cancer can manifest itself in many distinct forms and the transition from clinically indolent PCa to the more invasive aggressive form remains poorly understood. It is now universally accepted that glycan expression patterns change with the cellular modifications that accompany the onset of tumorigenesis. The aim of this study was to investigate if differential glycosylation patterns could distinguish between indolent, significant, and aggressive PCa. Whole serum N-glycan profiling was carried out on 117 prostate cancer patients’ serum using our automated, high-throughput analysis platform for glycan-profiling which utilizes ultra-performance liquid chromatography (UPLC) to obtain high resolution separation of N-linked glycans released from the serum glycoproteins. We observed increases in hybrid, oligomannose, and biantennary digalactosylated monosialylated glycans (M5A1G1S1, M8, and A2G2S1), bisecting glycans (A2B, A2(6)BG1) and monoantennary glycans (A1), and decreases in triantennary trigalactosylated trisialylated glycans with and without core fucose (A3G3S3 and FA3G3S3) with PCa progression from indolent through significant and aggressive disease. These changes give us an insight into the disease pathogenesis and identify potential biomarkers for monitoring the PCa progression, however these need further confirmation studies.  相似文献   
6.
7.
Journal of Mechanical Science and Technology - This study delivers equations useful for low-height pleated fibrous filter design: two pressure drop equations and one set of optimum design equations...  相似文献   
8.
Combined photochemical arylation, “nuisance effect” (SNAr) reaction sequences have been employed in the design of small arrays for immediate deployment in medium-throughput X-ray protein–ligand structure determination. Reactions were deliberately allowed to run “out of control” in terms of selectivity; for example the ortho-arylation of 2-phenylpyridine gave five products resulting from mono- and bisarylations combined with SNAr processes. As a result, a number of crystallographic hits against NUDT7, a key peroxisomal CoA ester hydrolase, have been identified.  相似文献   
9.
陕南山地烟田不同植烟年限土壤养分的变化   总被引:1,自引:0,他引:1  
为给陕南山地烟草生产布局及有针对性的施肥措施提供依据,分析了陕南山地烟田不同植烟年限(0~15年)与土壤养分含量的关系。结果表明:随着植烟年限延长,有机质线性下降,全氮和速效钾显著上升,有效磷先上升后下降;氯、有效铁、有效锰、有效硼和有效铜无显著变化或变化很小,有效锌则在第1年急剧下降,之后保持稳定,10年后再次显著下降。认为陕南山地烟区烟叶生产中应适当增加有机肥的施用而合理控制氮肥、磷肥和钾肥的施用,并要注意锌肥的补充。  相似文献   
10.
To quantify the evacuation process, evacuation practitioners use engineering egress data describing the occupant movement characteristics. These data are typically based to young and fit populations. However, the movement abilities of occupants who might be involved in evacuations are becoming more variable—with the building populations of today typically including increasing numbers of individuals: with impairments or who are otherwise elderly or generally less mobile. Thus, there will be an increasing proportion of building occupants with reduced ability to egress. For safe evacuation, there is therefore a need to provide valid engineering egress data considering pedestrians with disabilities. Gwynne and Boyce recently compiled a series of data sets related to the evacuation process to support practitioner activities in the chapter Engineering Data in the SFPE Handbook of Fire Protection Engineering. This paper supplements these data sets by providing information on and presenting data obtained from additional research related to the premovement and horizontal movement of participants with physical‐, cognitive‐, or age‐related disabilities. The aim is to provide an overview of currently available data sets related to, and key factors affecting the egress performance of, mixed ability populations which could be used to guide fire safety engineering decisions in the context of building design.  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