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   813255篇
  免费   11898篇
  国内免费   2450篇
电工技术   14822篇
综合类   825篇
化学工业   121990篇
金属工艺   29767篇
机械仪表   23141篇
建筑科学   21132篇
矿业工程   2937篇
能源动力   22226篇
轻工业   75121篇
水利工程   7356篇
石油天然气   10699篇
武器工业   49篇
无线电   97241篇
一般工业技术   153316篇
冶金工业   160278篇
原子能技术   14255篇
自动化技术   72448篇
  2021年   6656篇
  2020年   4821篇
  2019年   6135篇
  2018年   10300篇
  2017年   10122篇
  2016年   10732篇
  2015年   7874篇
  2014年   12918篇
  2013年   37888篇
  2012年   21094篇
  2011年   29573篇
  2010年   23182篇
  2009年   26075篇
  2008年   27131篇
  2007年   27042篇
  2006年   23933篇
  2005年   21999篇
  2004年   21207篇
  2003年   20911篇
  2002年   19969篇
  2001年   19977篇
  2000年   18542篇
  1999年   19783篇
  1998年   49585篇
  1997年   35202篇
  1996年   27189篇
  1995年   20782篇
  1994年   18222篇
  1993年   17794篇
  1992年   12861篇
  1991年   12255篇
  1990年   11802篇
  1989年   11457篇
  1988年   10794篇
  1987年   9400篇
  1986年   9251篇
  1985年   10813篇
  1984年   10103篇
  1983年   8874篇
  1982年   8313篇
  1981年   8389篇
  1980年   7935篇
  1979年   7738篇
  1978年   7347篇
  1977年   8900篇
  1976年   11977篇
  1975年   6295篇
  1974年   5991篇
  1973年   5987篇
  1972年   4872篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Aspects of a prototype binding of GKS to the C++ programming language are presented. The binding makes use of classes and derived classes to define GKS concepts such as segments and workstations. Operator overloading is used for some GKS Functions.  相似文献   
992.
A sequence of Co78Cr22films, 500 nm in thickness, was prepared by deposition on glass in a modified Varian D.C. magnetron S-gun sputtering system. The substrate temperature during deposition, Ts, was fixed at various values with an upper limit of 300°C. Specimens were examined by VSM, TM, FMR and TEM. Msrises significantly with increasing Ts, peaking at 200°C at 370 emu/cm3. The effective volume-averaged anisotropy drops for Ts>110°C from +1.6 KOe to progressively negative values (-4.3 KOe at 300°C). From FMR we find indications of the presence, in addition to the transition and bulk layers, of a highly negative anisotropy constituent (sim-11.5KOe anisotropy field). This resonance appears at Tsvalues of 150°C and above. TEM plane and cross-section views taken on a Ts= 150°C specimen show islands composed of tilted columns within the bulk. For vertical recording, specimens prepared at Tsvalues between 50 and 100°C are recommended. On the other hand, for longitudinal recording applications, films prepared at Tsvalues above 250°C would seem to be appropriate.  相似文献   
993.
Summary The problem of fairly densily packed particles with rate independent though otherwise arbitrary interaction is investigated in two dimensions. It is shown that slow changes in a statistically uniform medium in the pre-failure deformation state can be described by a stiffness tensor. An approximate expression for this tensor is obtained from first principles. The connection with the perfectly random heterogeneous medium is established. A simple example for round rough particles in an isotropic packing of four contacts is given.With 8 Figure  相似文献   
994.
995.
A new technique for exciting nonlinear waves on a charged surface of liquid hydrogen is described. Methods of optical detection of surface oscillations in experiments on capillary turbulence at frequencies of up to 10 kHz are discussed. The results of a study of capillary waves on the surface of liquid hydrogen are presented.  相似文献   
996.
The usefulness of selected PCR-protocols for the detection of Salmonella in 117 samples of animal origin (17 raw minced meat, 27 raw chicken meat, 8 raw sausages, and 25 egg samples, as well as 18 poultry faecal, and caecal swabs samples) and DNA-fingerprinting typing is shown. To establish an accurate PCR-procedure for Salmonella detection the following parameters were evaluated: two pre-PCR concentration procedures, centrifugation and immunomagnetic separation (IMS) using Dynabeads anti- Salmonella; the specificity and sensitivity of 10 sets of primers; and different conditions of the amplification reaction. In light of the results obtained from the use of PCR-based procedures alone or in combination with conventional methods, the following findings can be underlined: First, IMS is more efficient than centrifugation in the recovery of Salmonella. Second, the selected IMS/PCR-detection protocol is less time-consuming (45 h) than the IMS/culture procedure (90 h), and a good concordance between them was found when the Kappa coefficient was calculated (0·87). Third, PCR-ribotyping technique showed a very low discrimination power, being able to differentiate only three profiles. Fourth, RAPD technique using specific primers supports previous works in which it was proposed as a simple and useful tool for discriminating isolates between and within serotypes. Fifth, The efficiency, rapidity, and flexibility of the PCR-protocols applied were high, and they can be performed using two PCR-programs and the same basic equipment.  相似文献   
997.
998.
Results of a numerical investigation of heat and mass transfer at the initial stage of fire within a building in combustion of kerosene, carried out with the use of a three-dimensional mathematical field model, are presented. A comparison of the distribution of the averaged temperatures and velocities along the vertical axis of the convective column and of the mass rates of gas flows through an open opening with the experimental data has been made. Substantial three-dimensional inhomogeneities of the velocities and the temperatures in the near-ceiling layer have been revealed. It has been established that near the opening there is a critical separation zone which influences significantly the parameters of natural gas transfer.  相似文献   
999.
The behavior of two series of concrete slabs exposed to sulfate-bearing soils was investigated by a numerical model called STADIUM. In addition to the diffusion of ions and moisture, the model also accounts for the effects of dissolution/precipitation reactions on the transport mechanisms. The simulations yielded by the model were compared to the actual degradation of the slabs after 8 years of exposure. The microstructural alterations of concrete resulting from the penetration of magnesium, chloride and sulfate ions were studied by backscatter mode scanning electron microscope observations and energy-dispersive X-ray analyses. The comparison of both series of data indicates that the model can reliably predict the various features of the microstructural alterations of concrete.
Résumé Le comportement de deux séries de dalles sur sol en béton exposées à des sols chimiquement agressifs a été étudié à l'aide d'un code de calcul numérique appelé STADIUM. Ce modèle permet de décrire le transport couplé de l'eau et des ions dans des matériaux poreux non-saturés en prenant en considération l'influence des réactions chimiques. Les résultats des simultations de la dégradation du béton après huit ans d'exposition à des ions chlore, sulfate et magnésium. Les observations ont été réalisées par microscopie électronique à balayage. Des analyses par dispersion des rayons X ont également été effectuées. Les données démontrent clairement que le modèle perment de prédire avec précision le comportement du béton soumis à différents types d'agression chimique.


Editorial Note Laval University (Canada) is a RILEM Titular Member. Prof. J. Marchand was awarded the 2000 Robert L'Hermite Medal. He is Editor in Chief for Concrete Science and Engineering and Associate Editor for Materials and Structures. He participates in RILEM TC 186-ISA ‘Internal Sulfate attack’.  相似文献   
1000.
Consideration is given to the possibility of controlling the efficiency of the process of superdeep penetration of a high-velocity microstriker flux into metal obstacles due to the employment of ballast elements in the jet and to additional supply of energy in compression by an explosive charge along the external perimeter.  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