全文获取类型
收费全文 | 85816篇 |
免费 | 1032篇 |
国内免费 | 462篇 |
专业分类
电工技术 | 850篇 |
综合类 | 2404篇 |
化学工业 | 11694篇 |
金属工艺 | 4860篇 |
机械仪表 | 3079篇 |
建筑科学 | 2284篇 |
矿业工程 | 593篇 |
能源动力 | 1187篇 |
轻工业 | 3726篇 |
水利工程 | 1294篇 |
石油天然气 | 357篇 |
武器工业 | 2篇 |
无线电 | 9459篇 |
一般工业技术 | 16575篇 |
冶金工业 | 3098篇 |
原子能技术 | 276篇 |
自动化技术 | 25572篇 |
出版年
2022年 | 23篇 |
2021年 | 28篇 |
2019年 | 26篇 |
2018年 | 14465篇 |
2017年 | 13407篇 |
2016年 | 9997篇 |
2015年 | 649篇 |
2014年 | 285篇 |
2013年 | 312篇 |
2012年 | 3190篇 |
2011年 | 9452篇 |
2010年 | 8323篇 |
2009年 | 5619篇 |
2008年 | 6834篇 |
2007年 | 7849篇 |
2006年 | 192篇 |
2005年 | 1266篇 |
2004年 | 1212篇 |
2003年 | 1275篇 |
2002年 | 704篇 |
2001年 | 217篇 |
2000年 | 246篇 |
1999年 | 113篇 |
1998年 | 199篇 |
1997年 | 120篇 |
1996年 | 124篇 |
1995年 | 60篇 |
1994年 | 46篇 |
1993年 | 59篇 |
1992年 | 43篇 |
1991年 | 46篇 |
1990年 | 22篇 |
1989年 | 25篇 |
1988年 | 23篇 |
1977年 | 25篇 |
1976年 | 22篇 |
1969年 | 25篇 |
1968年 | 44篇 |
1967年 | 38篇 |
1966年 | 46篇 |
1965年 | 44篇 |
1963年 | 28篇 |
1962年 | 22篇 |
1960年 | 30篇 |
1959年 | 36篇 |
1958年 | 38篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 64篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Melissa Kurtz 《Journal of Failure Analysis and Prevention》2007,7(3):175-178
Fuel system assemblies used on recreational watercraft failed after a short time in service in a seawater environment. Examination
of the assemblies revealed significant degradation of the polyacetal connectors of the wire subassemblies. Optical and microscopic
evaluations indicated the complete loss of connector material implying decomposition of the resin, along with mud-cracking
and a rough surface morphology signifying chemical attack. An elemental analysis performed on both an intact connector and
degraded connector suggested a potential chemical agent in the form of zinc chloride. At elevated temperatures, concentrated
zinc chloride solutions are known to decompose polyacetal resins. The source of the zinc chloride was established as corrosion
products that resulted during the dezincification of the internal brass connector through exposure to saltwater in the application. 相似文献
102.
Véronique Baroghel-Bouny Patrick Belin Matthias Maultzsch Dominique Henry 《Materials and Structures》2007,40(8):759-781
Within the framework of the evaluation and the prediction of chloride-induced corrosion risks, simple and rapid AgNO3 spray tests can be proposed for various issues. This paper forms the first part of a series. In this first part, the Maultzsch
procedure (spraying of 0.1-N AgNO3 solution + K2CrO4) as well as the procedure based on the use of a sole AgNO3 solution have been investigated on a broad range of concretes. These procedures have also been compared to the Collepardi
procedure (spraying of 0.1-N AgNO3 + fluoresceine). The feasibility of these colorimetric techniques on saturated specimens cast in laboratory, after non-steady-state
diffusion tests carried out in various conditions, is discussed. In addition, the results obtained from applying such spray
tests in field conditions on cores drilled out from various RC test specimens exposed to a marine environment (tidal zone)
and to a road and cold environment (freezing-thawing cycles and spraying of deicing salts) are presented. Colorimetric methods
have in particular been applied here to the assessment of the average chloride penetration depth and of its evolution versus
time (kinetics). Moreover, the detection threshold of these techniques has been investigated in various environments. The
possible sources of discrepancy on the results have been analysed. 相似文献
103.
Xiao-Ying Wang Jonathan M. Garibaldi Benjamin Bird Michael W. George 《Applied Intelligence》2007,27(3):237-248
Recently Fourier Transform Infrared (FTIR) spectroscopic imaging has been used as a tool to detect the changes in cellular
composition that may reflect the onset of a disease. This approach has been investigated as a mean of monitoring the change
of the biochemical composition of cells and providing a diagnostic tool for various human cancers and other diseases. The
discrimination between different types of tissue based upon spectroscopic data is often achieved using various multivariate
clustering techniques. However, the number of clusters is a common unknown feature for the clustering methods, such as hierarchical
cluster analysis, k-means and fuzzy c-means. In this study, we apply a FCM based clustering algorithm to obtain the best number
of clusters as given by the minimum validity index value. This often results in an excessive number of clusters being created
due to the complexity of this biochemical system. A novel method to automatically merge clusters was developed to try to address
this problem. Three lymph node tissue sections were examined to evaluate our new method. These results showed that this approach
can merge the clusters which have similar biochemistry. Consequently, the overall algorithm automatically identifies clusters
that accurately match the main tissue types that are independently determined by the clinician. 相似文献
104.
Squeeze-film effects of perforated plates for small amplitude vibration are analyzed through modified Reynolds equation (MRE).
The analytical analysis reckons in most important influential factors: compressibility of the air, border effects, and the
resistance caused by vertical air flow passing through perforated holes. It is found that consideration of air compressibility
is necessary for high operating frequency and small ratio of the plate width to the attenuation length. The analytical results
presented in this paper agree with ANSYS simulation results better than that under the air incompressibility assumption. The
analytical analysis can be used to estimate the squeeze-film effects causing damping and stiffness added to the system. Since
the value of Reynolds number involved in this paper is low (< 1), inertial effects are neglected. 相似文献
105.
In this paper we consider A(θ)-stable finite difference methods for numerical solutions of dissipative partial differential equations of parabolic type.
Combining two rational approximation methods with different orders of accuracy, where the lower order method is applied n
0 times (n
0 fixed) at each time step, we prove the existence of a second order method which is contractive for all time steps. Moreover,
we shed light on the conditions on the lower order method which are sufficient (and sometimes necessary) to obtain the optimal
order of accuracy. For the one-dimensional heat equation we construct a family of numerical methods which are contractive
in the maximum norm for all values of the discretization parameters. We also present numerical examples to illustrate our
results.
Received: May 2002 / Accepted: January 2003 相似文献
106.
Huiping Hu Qiyuan Chen Zhoulan Yin Pingmin Zhang Lusheng Ye 《Metallurgical and Materials Transactions A》2003,34(13):793-797
The thermal decompositions of mechanically activated and nonactivated galenas were studied by thermogravimetry analysis (TGA)
at the heating rate of 10 K min−1 in argon. Results indicate that the initial temperature of thermal decomposition (abbreviated as T
di) in the TGA curves for different galenas decreases gradually with increased grinding time. The specific granulometric surface
area (S
G), the structural disorder, and the content of elemental sulfur of mechanically activated galenas were analyzed by an X-ray
diffraction (XRD) laser particle-size analyzer, XRD analysis, and the gravimetric method, respectively, which shows that the
specific granulometric surface area of mechanically activated galenas remains almost constant after a certain grinding time,
but the lattice distortions (ε) rise, the crystallite sizes (D) decrease, and the elemental sulfur contents of mechanically activated galenas increase with increased grinding time. The
results imply that the decrease of the initial temperature of thermal decomposition in the TGA curves for mechanically activated
galenas is mainly caused by the increase of lattice distortions, and the formation of new dangling bonds resulted from the
production of elemental sulfur of mechanically activated galenas with increased grinding time. Finally, the differences in
the thermal-decomposition reactivity between nonactivated and mechanically activated galenas were also discussed. 相似文献
107.
108.
Michael Fox Richard Hastings Scott Lovald Juan Heinrich 《Journal of Failure Analysis and Prevention》2007,7(3):165-174
A failure analysis case study is presented for a two-piece aerosol containing tetrafluoroethane, commonly referred to as Refrigerant
134a. A gentleman was preparing to recharge the air conditioning system of an automobile when the bottom exploded off the
aerosol container, propelling the body of the aerosol container like a rocket, which hit the man in the eye and blinded him
in that eye. The aerosol was never connected to the air conditioner, therefore backpressure from the air conditioner (AC)
compressor was ruled out as a cause for the explosion. The objective of the study was to determine why the aerosol exploded.
Several recently developed test methods were used, including two types of heat-to-burst tests and a puncture chamber to measure
the pressure-versus-temperature behavior of aerosols. More common test methods were also used, such as water bath pressure
tests, hydro pressure burst tests, pneumatic pressure burst tests, hardness measurements, weight measurements, metallography,
scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and an accident scenario recreation. A semi-empirical
correlation between the hardness and weights of the container bottoms was used to determine the explosion temperature and/or
pressure. This semi-empirical correlation agrees in principle with an analysis of the explosion pressures using finite-element
analysis (FEA). The root cause for the explosion was determined to be a lack of strength of the bottom of the two-piece aerosol
coupled with heating the aerosol to temperatures significantly above room temperature. 相似文献
109.
M. Del C. Ruiz J. A. González J. B. Rivarola 《Metallurgical and Materials Transactions B》2004,35(3):439-448
The mechanism and kinetics of β-Ta2O5 chlorination, mixed with sucrose carbon, have been studied by a thermogravimetric technique. The investigated temperature
range was 500 °C to 850 °C. The reactants and reaction residues were analyzed by scanning electronic microscopy (SEM), X-ray
diffraction (XRD), and Brunauer-Emmett-Teller method for surface area (BET). The effect of various experimental parameters
was studied, such as carbon percentage, temperature, chlorine partial pressure, and flow, use of the multiple sample method,
and carbon previous oxidation. The carbon percentage and previous treatment have an effect on the system reactivity. The temperature
has a marked effect on the reaction rate. In the 500 °C to 600 °C temperature interval, the apparent activation energy is
144 kJ/mol of oxide, while at higher temperatures, the activation energy decreases. With high chorine partial pressures, the
order of reaction is near zero. The kinetic contractile plate model, X=kt, considering carbon oxidation as the controlling stage, is the one with the best fit to the experimental data. A probable
mechanism for the carbochlorination of β-Ta2O5 is proposed: (1) activation of chlorine on the carbon surface, (2) chlorination of Ta2O5, (3) oxidation of carbon, and (4) recrystallization of β-Ta2O5. 相似文献
110.