全文获取类型
收费全文 | 4971篇 |
免费 | 94篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 46篇 |
综合类 | 1篇 |
化学工业 | 782篇 |
金属工艺 | 129篇 |
机械仪表 | 115篇 |
建筑科学 | 179篇 |
矿业工程 | 21篇 |
能源动力 | 96篇 |
轻工业 | 352篇 |
水利工程 | 26篇 |
石油天然气 | 11篇 |
无线电 | 584篇 |
一般工业技术 | 811篇 |
冶金工业 | 1501篇 |
原子能技术 | 35篇 |
自动化技术 | 384篇 |
出版年
2021年 | 43篇 |
2020年 | 30篇 |
2019年 | 35篇 |
2018年 | 48篇 |
2017年 | 36篇 |
2016年 | 44篇 |
2015年 | 39篇 |
2014年 | 64篇 |
2013年 | 197篇 |
2012年 | 121篇 |
2011年 | 118篇 |
2010年 | 140篇 |
2009年 | 153篇 |
2008年 | 152篇 |
2007年 | 156篇 |
2006年 | 144篇 |
2005年 | 129篇 |
2004年 | 107篇 |
2003年 | 115篇 |
2002年 | 92篇 |
2001年 | 116篇 |
2000年 | 127篇 |
1999年 | 128篇 |
1998年 | 388篇 |
1997年 | 271篇 |
1996年 | 184篇 |
1995年 | 142篇 |
1994年 | 113篇 |
1993年 | 117篇 |
1992年 | 66篇 |
1991年 | 71篇 |
1990年 | 93篇 |
1989年 | 96篇 |
1988年 | 59篇 |
1987年 | 69篇 |
1986年 | 56篇 |
1985年 | 68篇 |
1984年 | 74篇 |
1983年 | 68篇 |
1982年 | 55篇 |
1981年 | 72篇 |
1980年 | 54篇 |
1979年 | 59篇 |
1978年 | 34篇 |
1977年 | 77篇 |
1976年 | 80篇 |
1975年 | 42篇 |
1974年 | 43篇 |
1973年 | 55篇 |
1972年 | 29篇 |
排序方式: 共有5073条查询结果,搜索用时 15 毫秒
91.
Hemicyanine dyes are an extensively investigated group of materials which show promise for second-order non-linear optical properties; they have also proved to be good materials for deposition by the Langmuir-Blodgett technique. This work concerns a closely related group of materials which contain a thiophene moiety in place of the nitrogen heterocycle of the hemicyanine material. The synthesis of several groups of novel amphiphiles containing the thiophene moiety, and their subsequent screening as materials for deposition by the Langmuir Blodgett technique is described. General trends in the behaviour of the simplest materials are noted, whilst the report of the characterization of the more complex D--A thiophenes is extended to include data relating to the production of heterogeneous monolayer and alternate layer structures. 相似文献
92.
Model-based 3-D segmentation of multiple sclerosis lesions in magnetic resonance brain images 总被引:2,自引:0,他引:2
Kamber M Shinghal R Collins DL Francis GS Evans AC 《IEEE transactions on medical imaging》1995,14(3):442-453
Human investigators instinctively segment medical images into their anatomical components, drawing upon prior knowledge of anatomy to overcome image artifacts, noise, and lack of tissue contrast. The authors describe: 1) the development and use of a brain tissue probability model for the segmentation of multiple sclerosis (MS) lesions in magnetic resonance (MR) brain images, and 2) an empirical comparison of the performance of statistical and decision tree classifiers, applied to MS lesion segmentation. Based on MR image data obtained from healthy volunteers, the model provides prior probabilities of brain tissue distribution per unit voxel in a standardized 3-D "brain space". In comparison to purely data-driven segmentation, the use of the model to guide the segmentation of MS lesions reduced the volume of false positive lesions by 50-80% 相似文献
93.
S. A. Matar M. J. Edirisinghe J. R. G. Evans E. H. Twizell J. H. Song 《Journal of Materials Science》1995,30(15):3805-3810
A shrinking undegraded core and a porous outer layer result, if the organic vehicle used for shaping ceramic or metal powder mouldings recedes in the interparticle space of the moulded body during pyrolysis. In the present work, a numerical model has been used which simulates the undegraded shrinking core situation and quantifies degradation of the organic vehicle and the diffusion of the resulting products in solution in the organic phase during pyrolysis of a ceramic moulding. This model is extended to include gaseous mass transport in the porous outer layer for a moulding in the shape of an infinite cylinder. The effect of resistance to gaseous mass transport in the porous outer region on defects originating in inner regions was estimated. It is shown that the greatest obstruction to mass transport is diffusion of degradation products in solution in the organic phase. However, the permeability coefficient for gas transport in the outer region begins to affect the critical heating rate required for avoidance of defects only when it is less than 10–15m2.Nomenclature
C
Concentration,C=C (r, t), based on the total volume of ceramic suspension
-
d
Effective molecular diameter of alphamethylstyrene
-
D
Diffusion coefficient,D=D (C, T)
-
e
Porosity of powder
-
E
Activation energy for thermal degradation
-
h
Remaining weight fraction of polymer
- Hvap
Enthalphy of vaporization
-
i
Node number
-
I
Pre-exponential constant in Equation 13
-
j
Time step
-
K
p
Permeability coefficient
-
K
0
Specific rate constant
-
m
Mass of monomer displaced
-
M
Mass of one alphamethylstyrene molecule
-
P
Monomer vapour pressure
-
P
s
Monomer vapour pressure at outer surface of the cylinder
-
P
1
0
Vapour pressure of monomer over its pure liquid
-
Q
Rate of production of monomer, based on the total volume of ceramic suspension
-
r
Radius of the cylinder
-
r
j
Distance from central axis to the inner surface of the porous layer at time stepj
-
r
0
Initial radius of the cylinder
-
R
Universal gas constant
-
S
0
Specific surface area of powder per unit solid volume
-
t
Time
-
T
Absolute temperature
-
T
c
Temperature at maximum vapour pressure of monomer and atZ
c
-
V
Volume of monomer
-
V
c
Ceramic volume fraction
-
V
p
Polymer volume fraction
-
w
Mass of monomer stored in the porous annulus
-
Z
Heating rate
-
Z
c
Critical heating rate
- 1
Volume fraction of monomer in the polymer-monomer solution
-
Viscosity of the monomer vapour
- p
Density of the polymer
-
Polymer-monomer interaction constant 相似文献
94.
Energy Storage: Confined Assembly of Hollow Carbon Spheres in Carbonaceous Nanotube: A Spheres‐in‐Tube Carbon Nanostructure with Hierarchical Porosity for High‐Performance Supercapacitor (Small 19/2018)
下载免费PDF全文
![点击此处可从《Small (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
95.
Professor F. T. Evans 《AI & Society》1998,12(3):185-213
Instead of seeing technology as outside ourselves, it is argued that it is an innate human function and the main driving force in human evolution. Opportunistic thing using, long before stone tools appeared, was the likeliest cause of bipedalism. It also forced brain development and the emergence of creativity. The neural basis for this creative technical activity later provided the brain functions on which language could develop. This simple unifying hypothesis has interesting implications for the way that we see technology in history, and for determinist theories of the future. It also bears on the way engineers are trained, and more important, the human faculties which need to be fostered in children. 相似文献
96.
A method for rapid limited-angle tomography is suggested thatallows the reconstruction of density distribution in hardwood sampleswith high accuracy and spatial resolution from only a few x-rayprojections. The sparsity of the experimental x-ray data iscompensated by incorporation of a priori knowledge aboutgeneric wood macrostructure, as well as some morphological informationobtainable from optical images of the sample surface, in themathematical framework of the tomographic analysis. Numerical testsof the proposed method confirm its potential as a practical techniquefor nondestructive testing of trees for scientific and industrialpurposes. It can also be useful for the analysis of other types ofobject with an underlying layered structure. 相似文献
97.
DY Graham R Genta DG Evans R Reddy JE Clarridge CA Olson AL Edmonds N Siepman 《Canadian Metallurgical Quarterly》1996,91(10):2120-2124
BACKGROUND: Omeprazole is known to have an effect on Helicobacter pylori in vivo. One opinion is that H. pylori "migrates" from the antrum to the corpus in response to omeprazole therapy. METHODS: To determine whether H. pylori migrates in response to omeprazole, we assessed the presence of H. pylori in the antrum and corpus in duodenal ulcer patients receiving omeprazole for 4 wk. Culture and histological examination of antral biopsies (Genta stain) were performed before patients received omeprazole, at the end of therapy, and 4-6 wk later. The end points were presence or absence of H. pylori and the number of H. pylori colonies per biopsy. RESULTS: Seventy-two patients had H. pylori in both the antrum and corpus at entry and 4-6 wk after ending therapy. Three general patterns were prevalent at the end of omeprazole therapy: antrum- and corpus-positive (54%), antrum-negative and corpus-positive (24%), both antrum- and corpus-negative (21%), and one patient had antrum-positive with corpus-negative (1%). Evaluation of the number of colonies per biopsy in those who remained H. pylori-positive in both the antrum and corpus throughout showed that the number of H. pylori decreased in both the antrum and corpus during therapy (507 +/- 60 vs. 225 +/- 51, p < 0.01 and 415 +/- 58 vs. 290 +/- 46 0.1) for antrum and corpus, respectively, and tended to return to pre-therapy levels 4-6 wk later. The number of H. pylori in the corpus also decreased in the antrum-negative and corpus-positive group during therapy with omeprazole (433 +/- 87 vs. 185 +/- 61, p < 0.05). In most of the patients studied, the number of H. pylori in the corpus was less posttreatment than it was pretreatment. The decrease in H. pylori load was also reflected in the development of false-negative urea breath tests. CONCLUSIONS: Omeprazole is detrimental to H. pylori in both the antrum and the corpus; migration from the antrum to the corpus in response to omeprazole is a myth. 相似文献
98.
Ian Scott Evans Jessica Miki Jessee Ho Derek T. Robinson 《International journal of remote sensing》2016,37(6):1411-1430
Topographic and elevation data are essential in the development of supporting infrastructure around mining sites. The de facto standard for acquiring elevation data is through light detection and ranging (lidar). The high labour and monetary cost of acquiring lidar has fostered more cost-effective approaches for creating elevation models that use stereo photogrammetry. To assess the accuracy of stereo-photogrammetry-derived elevation models and their potential application, we benchmark satellite (Worldview-2) and aircraft (South Central Ontario Orthoimagery Project; SCOOP) stereo-derived digital surface models (DSMs) against a lidar-derived DSM. Our results show that both stereo-derived DSMs have strong monotonic correlations with lidar across a range of land-cover types and slopes. The overall vertical accuracy of Worldview-2 and SCOOP DSMs are similar and do not meet the United States National Digital Elevation Program (NDEP) standards. However, accuracy assessment across land-cover types and slope categories show that specific land cover types (i.e. grass, row crops/pasture, sparse vegetation and marsh) on gently sloping terrain compare well to lidar data and meet NDEP accuracy standards. We situate the presented research in the context of northern resource development and discuss opportunities to improve the vertical accuracy of stereo-derived DSMs, for example, through unmanned aerial systems. 相似文献
99.
Quantum games with incomplete information can be studied within a Bayesian framework. We consider a version of prisoner’s dilemma (PD) in this framework with three players and characterize the Nash equilibria. A variation of the standard PD game is set up with two types of the second prisoner and the first prisoner plays with them with probability p and \(1-p\), respectively. The Bayesian nature of the game manifests in the uncertainty that the first prisoner faces about his opponent’s type which is encoded either in a classical probability or in the amplitudes of a wave function. Here, we consider scenarios with asymmetric payoffs between the first and second prisoner for different values of the probability, p, and the entanglement. Our results indicate a class of Nash equilibria (NE) with rich structures, characterized by a phase relationship on the strategies of the players. The rich structure can be exploited by the referee to set up rules of the game to push the players toward a specific class of NE. These results provide a deeper insight into the quantum advantages of Bayesian games over their classical counterpart. 相似文献
100.
Mei Kum Khaw Chin Hong Ooi Faisal Mohd-Yasin Anh V. Nguyen Geoffrey M. Evans Nam-Trung Nguyen 《Microfluidics and nanofluidics》2017,21(6):110
This paper reports the dynamic behaviour of a magnetically actuated floating liquid marble by analysing the oscillation of the marble. A liquid marble is a liquid droplet coated with hydrophobic powder. Magnetite particles inside the marble make it magnetic. The marble floats on a carrier liquid that contains aqueous glycerol of various concentrations. A permanent magnet located under the carrier liquid drives the floating marble with the initial velocity. Stopping the magnet abruptly causes the marble to oscillate around its final position for a few seconds. The oscillation was recorded and analysed using customised image processing and evaluation software. The damped harmonic motion model was then applied to the data and tested. Subsequently, critical parameters of the system such as the initial displacement, friction correction factor, the apparent frequency and the spring constant were determined and discussed. The simple experimental set-up and convenient theoretical approach allow us to characterise the marble motion under the influence of a magnet with good accuracy. 相似文献