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   426105篇
  免费   5147篇
  国内免费   1324篇
电工技术   7920篇
综合类   467篇
化学工业   61620篇
金属工艺   16831篇
机械仪表   13358篇
建筑科学   10259篇
矿业工程   2260篇
能源动力   10719篇
轻工业   36605篇
水利工程   4501篇
石油天然气   7353篇
武器工业   75篇
无线电   52820篇
一般工业技术   83060篇
冶金工业   78717篇
原子能技术   9389篇
自动化技术   36622篇
  2021年   3366篇
  2019年   3348篇
  2018年   5554篇
  2017年   5709篇
  2016年   5999篇
  2015年   3839篇
  2014年   6559篇
  2013年   18839篇
  2012年   10732篇
  2011年   14696篇
  2010年   11690篇
  2009年   13138篇
  2008年   13909篇
  2007年   13929篇
  2006年   12319篇
  2005年   11391篇
  2004年   10971篇
  2003年   10744篇
  2002年   10081篇
  2001年   10230篇
  2000年   9863篇
  1999年   10098篇
  1998年   23758篇
  1997年   17118篇
  1996年   13478篇
  1995年   10276篇
  1994年   9233篇
  1993年   9008篇
  1992年   7100篇
  1991年   6694篇
  1990年   6387篇
  1989年   6219篇
  1988年   5945篇
  1987年   5210篇
  1986年   5026篇
  1985年   5904篇
  1984年   5490篇
  1983年   5023篇
  1982年   4623篇
  1981年   4832篇
  1980年   4445篇
  1979年   4437篇
  1978年   4262篇
  1977年   4960篇
  1976年   6382篇
  1975年   3864篇
  1974年   3815篇
  1973年   3826篇
  1972年   3056篇
  1971年   2857篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
A new equation is derived for the rotational oscillations of a deep massive foundation flexibly restrained in the ground. An error in the corresponding equation published in the literature is indicated. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 6, pp. 7–8, November–December, 1996.  相似文献   
142.
143.
Modeling ion implantation of HgCdTe   总被引:2,自引:0,他引:2  
Ion implantation of boron is used to create n on p photodiodes in vacancy-doped mercury cadmium telluride (MC.T). The junction is formed by Hg interstitials from the implant damage region diffusing into the MC.T and annihilating Hg vacancies. The resultant doping profile is n+/n-/p, where the n+ region is near the surface and roughly coincides with the implant damage, the n- region is where Hg vacancies have been annihilated revealing a residual grown-in donor, and the p region remains doped by Hg vacancy double acceptors. We have recently developed a new process modeling tool for simulating junction formation in MC.T by ion implantation. The interstitial source in the damage region is represented by stored interstitials whose distribution depends on the implant dose. These interstitials are released into the bulk at a constant, user defined rate. Once released, they diffuse away from the damage region and annihilate any Hg vacancies they encounter. In this paper, we present results of simulations using this tool and show how it can be used to quantitatively analyze the effects of variations in processing conditions, including implant dose, annealing temperature, and doping background.  相似文献   
144.
The immunological agglutination reactions of physically absorbed F(ab')2 molecules onto anionic and cationic latex particles have been investigated by means of optical absorbance measurements. These measurements have been conducted under different conditions to determine the most influential factors. Surface F(ab')2 and BSA densities, particle concentration in the reaction medium and polyethylene glycol concentration are some of these factors. Sensitized cationic and anionic latexes differ considerably with respect to their colloidal stability and reactivity. As a general rule, the sensitized cationic latex has a relatively higher colloidal stability and hence, it provides reagents with a better optical response. Less than 0.025 microgram/ml of C-reactive protein has been detected using this particle enhanced optical immunoassay.  相似文献   
145.
Storage performance-metrics and benchmarks   总被引:2,自引:0,他引:2  
The metrics and benchmarks used in storage performance evaluation are discussed. The technology trends taking place in storage systems, such as disk and tape evolution, disk arrays, and solid-state disks, are highlighted. The current popular I/O benchmarks are then described, reviewed, and run on three systems: a DECstation 5000/200 running the Sprite Operating System, a SPARCstation 1+ running SunOS, and an HP Series 700 (Model 730) running HP-UX. Two approaches to storage benchmarks-LADDIS and a self-scaling benchmark with predicted performance-are also described  相似文献   
146.
Wavelength conversion of optical signals over 20 nm is demonstrated using highly nondegenerate four-wave mixing in a semiconductor traveling-wave optical amplifier. This technique has the potential for extremely-high-speed operation and allows continuous tuning of both input and output wavelengths over the amplifier gain bandwidth. It is demonstrated that, even for such a large wavelength conversion range, it is possible to obtain conversion efficiencies in excess of -10 dB and high extinction ratios. The feasibility of the technique is demonstrated by system measurements at 622 Mb/s, showing a 1.1-dB power penalty at 10-9 bit error rate (BER)  相似文献   
147.
Ion beam assisted deposition (IBAD) of thin films is still a new technology with respect to the number of applications. A broader industrial application depends on the availability and versatility of facilities which are able to process various kinds of workpieces under appropriate conditions. Recently, IBAD facilities of the second generation were described in literature and are partially commercially available. In the present report such IBAD machines with their special features such as number and kind of ion sources and evaporators are described. Particularly, the set-up of the ALLIGATOR, a versatile IBAD device for coating complex workpieces under ion bombardment with a broad range of ion energies, is described. As an application example, recent results on the treatment of medical implants are discussed. In -vivo tests of coated cardiovascular stents showed that the deposited noble metal films were effective in influencing the corrosivity and thromboresistance of the implant  相似文献   
148.
In a prospective study we found good results concerning postoperative complications (21%), perioperative lethality (3.2%) and lethality during hospital stay (6.5%) after implantation of dynamic hip screws (DHS) in patients with per- and subtrochanteric fractures of the femur. The ability to walk, as well as housing and social care postoperatively and follow-up for at least six months after dismissal demonstrates the importance of these fractures for the elderly. One of three patients needs professional care, 21% at home, 13% in nursing homes. Six months after operation the lethality is nearly 20%, i.e. three times higher than in hospital. These are the essential data for all techniques of osteosynthesis used in patients with these fractures, which could only be documented in prospective studies.  相似文献   
149.
Herbert Olivecrona (1891-1980) singlehandedly founded Swedish neurosurgery. At the International Congress in Neurology in Bern in August, 1931, Harvey Cushing invited the cream of the world's medical society to a private banquet. Among the 28 specially invited guests was Herbert Olivecrona. At 40 years old, Olivecrona took his seat with pioneers such as Otfrid Foerster, Percival Bailey, Hugh Cairns, Geoffrey Jefferson, and Sir Charles Sherrington. This suggests that Cushing was impressed by the Swedish aristocrat's didactic deeds when he visited the Serafimer Hospital in Stockholm 2 years earlier. During the mid-1920's, the radiologist Erik Lysholm greatly improved the technique of ventriculography and, challenged by Olivecrona, his diagnostic neuroradiology became of superior quality. In the early 1930's, utilizing technical innovations of his own, Lysholm became a master at demonstrating and localizing posterior fossa tumors, which Olivecrona then operated on. Olivecrona's clinic became the mecca to which many scholars, thirsting for more knowledge, went on a pilgrimage. The international reputation of the clinic was founded, not on epoch-making discoveries, but by the resolute and practical application of methods already launched elsewhere and the exemplary organization that Olivecrona had established in collaboration with Lysholm. In spite of hardships and primitive working conditions, the clinic at the Serafimer Hospital gradually developed into the ideal prototype for a modern neurosurgical department. Olivecrona trained many colorful personalities who later were to lay the foundation for neurosurgery in their home countries; these included Wilhelm T?nnis of Germany, Edvard Busch of Denmark, and Aarno Snellman of Finland. Olivecrona was a true pioneer who made major contributions in practically all fields of conventional neurosurgery.  相似文献   
150.
Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 11, pp. 17–18, 23, November, 1993.  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