全文获取类型
收费全文 | 1142篇 |
免费 | 51篇 |
专业分类
电工技术 | 7篇 |
综合类 | 6篇 |
化学工业 | 221篇 |
金属工艺 | 11篇 |
机械仪表 | 7篇 |
建筑科学 | 90篇 |
矿业工程 | 1篇 |
能源动力 | 11篇 |
轻工业 | 162篇 |
水利工程 | 20篇 |
石油天然气 | 4篇 |
无线电 | 56篇 |
一般工业技术 | 168篇 |
冶金工业 | 327篇 |
原子能技术 | 2篇 |
自动化技术 | 100篇 |
出版年
2024年 | 5篇 |
2023年 | 10篇 |
2022年 | 15篇 |
2021年 | 37篇 |
2020年 | 18篇 |
2019年 | 23篇 |
2018年 | 32篇 |
2017年 | 27篇 |
2016年 | 31篇 |
2015年 | 16篇 |
2014年 | 19篇 |
2013年 | 57篇 |
2012年 | 45篇 |
2011年 | 94篇 |
2010年 | 64篇 |
2009年 | 62篇 |
2008年 | 76篇 |
2007年 | 74篇 |
2006年 | 61篇 |
2005年 | 59篇 |
2004年 | 54篇 |
2003年 | 49篇 |
2002年 | 49篇 |
2001年 | 22篇 |
2000年 | 16篇 |
1999年 | 11篇 |
1998年 | 23篇 |
1997年 | 26篇 |
1996年 | 16篇 |
1995年 | 8篇 |
1994年 | 12篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1957年 | 1篇 |
1945年 | 1篇 |
排序方式: 共有1193条查询结果,搜索用时 31 毫秒
161.
Adam M Leventhal Susan E Ramsey Richard A Brown Heather R LaChance Christopher W Kahler 《Nicotine & tobacco research》2008,10(3):507-517
Because different psychopathologic components of depressive symptoms may have distinct etiologies, examining their differential effects on smoking cessation may elucidate mechanisms underlying the smoking-depression relationship. Negative affect (NA), somatic features (SF), low positive affect/anhedonia (PA), and interpersonal disturbance (IP) have been identified as unique dimensions of depression that can be measured using the Center for Epidemiologic Studies Depression Scale (CESD). This study examined common and unique associations between CESD subscales and baseline smoking characteristics, nicotine withdrawal, and relapse in 157 participants enrolled in a smoking cessation trial for heavy social drinkers. Each dimension was univariately associated with negative and positive reinforcement smoking motives. Only SF had unique relations with tolerance smoking motives and univariate associations with nicotine dependence severity. Only PA predicted cessation-related changes in withdrawal symptoms on quit day. Analyses predicting abstinence at 8, 16, and 26 weeks post quit date showed that NA, SF, and PA each univariately predicted relapse, ps< or =.0083. Only low PA predicted poorer outcomes incrementally to the other dimensions, even when controlling for level of nicotine dependence, smoking frequency, and history of major depression, p = .0018. Interventions targeting anhedonia and low positive affect may be useful for smokers trying to quit. 相似文献
162.
Stapleton HM Allen JG Kelly SM Konstantinov A Klosterhaus S Watkins D McClean MD Webster TF 《Environmental science & technology》2008,42(18):6910-6916
Due to the voluntary withdrawals and/or bans on the use of two polybrominated diphenyl ether (PBDE) commercial mixtures, an increasing number of alternate flame retardant chemicals are being introduced in commercial applications. To determine if these alternate BFRs are present in indoor environments, we analyzed dust samples collected from 19 homes in the greater Boston, MA area during 2006. Using pure and commercial standards we quantified the following brominated flame retardant chemicals using GC/ECNI-MS methods: hexabromocyclododecane (sigma HBCD), bis(2,4,6,-tribromphenoxy)ethane (BTBPE), decabromodiphenyl ethane (DBDPE), and the brominated components found in Firemaster 550 (FM 550): 2-ethylhexyl 2,3,4,5-tetrabromobenzoate (TBB) and (2-ethylhexyl)tetrabromophthalate (TBPH), the latter compound being a brominated analogue of di(2-ethylhexyl)phthalate (DEHP). The concentrations of all compounds were log-normally distributed and the largest range in concentrations was observed for HBCD (sum of all isomers), with concentrations ranging from <4.5 ng/g to a maximum of 130,200 ng/g with a median value of 230 ng/g. BTBPE ranged from 1.6 to 789 ng/g with a median value of 30 ng/g and DBDPE ranged from <10.0 to 11,070 ng/g with a median value of 201 ng/g. Of the FM 550 components, TBB ranged from <6.6 to 15,030 ng/g with a median value of 133 ng/g; whereas TBPH ranged from 1.5 to 10,630 ng/g with a median value of 142 ng/g. Furthermore, the ratio of TBB/TBPH present in the dust samples ranged from 0.05 to 50 (average 4.4), varying considerably from the ratio observed in the FM 550 commercial mixture (4:1 by mass), suggesting different sources with different chemical compositions, and/or differential fate and transport within the home. Analysis of paired dust samples collected from different rooms in the same home suggests HBCD, TBB, and TBPH are higher in dust from the main living area compared to dust collected in bedrooms; however, BTBPE and DBDPE levels were comparable between rooms. This study highlights the fact that numerous types of brominated flame retardants are present in indoor environments, raising questions about exposure to mixtures of these contaminants. 相似文献
163.
Long Zhang Yichao Huang Fengjiang Sun Da Chen Michael Netzel Heather E. Smyth Yasmina Sultanbawa Yongfeng Deng Mingliang Fang Daniel Cozzolino 《International Journal of Food Science & Technology》2021,56(6):2621-2627
The objective of this study was to evaluate the effect of sample presentation (tissue type) and maturity (ripe and unripe) on the classification of banana (Musa Cavendish) samples sourced from two different geographical regions and analysed using mid infrared (MIR) spectroscopy. The coefficient of determination (R2) and the standard error of cross-validation (SECV) obtained using partial least squares discriminant analysis were 0.83 (0.33), 0.75 (0.25) and 0.94 (0.19) for the prediction of maturity, geographical origin and tissue type, respectively. No effect of either of type of tissue (e.g. pulp or peel) or maturity was observed. The results of this study demonstrated that MIR spectroscopy might be used to classify the origin of the banana samples at different degrees of ripeness. However, one of the limitations of this study is on the number of samples analysed and further validation must be recommended using samples from other sources, regions and harvest seasons. 相似文献
164.
Lubold Nichola Walker Erin Pon-Barry Heather 《User Modeling and User-Adapted Interaction》2021,31(1):35-73
User Modeling and User-Adapted Interaction - Social robots such as learning companions, therapeutic assistants, and tour guides are dependent on the challenging task of establishing a rapport with... 相似文献
165.
Stuart C. Burgess David F. Moore David E. Newland Heather L. Klaubert 《Research in Engineering Design》1997,9(1):46-60
This paper shows that there are three main categories of factors that make the optimum mechanical design of micro-systems different from macro-systems: scale effects, a limited range of materials, and a limited range of production processes. The combined effect of these factors can make the optimum configuration of a micro-system potentially very different from that of the same system on a macro-scale. In particular, the use of flexible elements for hinges is much more feasible and desirable on a micro-scale.Notation
a
acceleration (m/s2)
-
A
cross-sectional area (m2)
-
B
magnetic flux [wb/m2]
-
b
width [m]
-
C
constant
-
d
depth [m]
-
D
drag [N]
-
E
Young's modulus [N/m2]
-
E*=
-
f
resonant frequency [Hz]
-
F
D
drive force [N]
-
F
E
electrostatic pulling force [N]
-
F
emmisivity function
-
F
G
geometric view factor
-
g
gravitational constant [m/s2]
-
h
c
convention heat transfer coefficient [W/m2K]
-
h
height [m]
-
i
current [A]
-
I
A
second moment of area [m4]
-
I
I
moment of inertia [kg m2]
-
J
polar second moment of area [m4]
-
k
stiffness [N/m]
-
K
thermal conductivity [W/m K]
-
l
length [m]
-
m
mass [kg]
-
M
moment [N m]
-
P
load [N]
-
P
H
Hertz contact pressure [N/m2]
-
P
C
cylinder pressure [N/m2]
-
q
heat transfer rate [W]
-
R, r
radius [m]
-
Re
Reynolds number
-
T, t
temperature [K]
-
T
A
atomic friction torque [N m]
-
T
D
drive torque [N m]
-
T
F
Coulomb friction torque [N m]
-
T
I
inertial resistive torque [N m]
-
u
velocity [m/s]
-
mean velocity [m/s]
-
V
volume [m3]
-
V
e
voltage [V]
-
x
distance between electrodes [m]
-
y
maximum distance to neutral axis [m]
-
angular acceleration [rad/s2]
-
d
thermal diffusivity [1/K]
-
rolling friction factor
- P
pressure difference [N/m2]
-
0
dialectric constant [F/m]
-
strain
-
dynamic viscosity [Pa s]
-
scale factor
-
S
coefficient of sliding friction
-
R
coefficient of rolling friction
-
1, 2
Poisson's ratio
-
density (kg/m3)
-
temperature rise [°C]
-
B
bending stress [N/m2]
-
y
yield strength [N/m2]
-
shear stress [N/m2]
-
reliability constant 相似文献
166.
Zhen Xu Fei Xie Jing Wang Heather Au Mike Tebyetekerwa Zhenyu Guo Shengyuan Yang Yong‐Sheng Hu Maria‐Magdalena Titirici 《Advanced functional materials》2019,29(39)
Na‐ion hybrid capacitors consisting of battery‐type anodes and capacitor‐style cathodes are attracting increasing attention on account of the abundance of sodium‐based resources as well as the potential to bridge the gap between batteries (high energy) and supercapacitors (high power). Herein, hierarchically structured carbon materials inspired by multiscale building units of cellulose from nature are assembled with cellulose‐based gel electrolytes into Na‐ion capacitors. Nonporous hard carbon anodes are obtained through the direct thermal pyrolysis of cellulose nanocrystals. Nitrogen‐doped carbon cathodes with a coral‐like hierarchically porous architecture are prepared via hydrothermal carbonization and activation of cellulose microfibrils. The reversible charge capacity of the anode is 256.9 mAh g?1 when operating at 0.1 A g?1 from 0 to 1.5 V versus Na+/Na, and the discharge capacitance of cathodes tested within 1.5 to 4.2 V versus Na+/Na is 212.4 F g?1 at 0.1 A g?1. Utilizing Na+ and ClO4? as charge carriers, the energy density of the full Na‐ion capacitor with two asymmetric carbon electrodes can reach 181 Wh kg?1 at 250 W kg?1, which is one of the highest energy devices reported until now. Combined with macrocellulose‐based gel electrolytes, all‐cellulose‐based quasi‐solid‐state devices are demonstrated possessing additional advantages in terms of overall sustainability. 相似文献
167.
Jiayi Yang David Tang Jinping Ao Tushar Ghosh Taylor V. Neumann Dongguang Zhang Egor Piskarev Tingting Yu Vi Khanh Truong Kai Xie Ying‐Chih Lai Yang Li Michael D. Dickey 《Advanced functional materials》2020,30(36)
Soft, capacitive tactile (pressure) sensors are important for applications including human–machine interfaces, soft robots, and electronic skins. Such capacitors consist of two electrodes separated by a soft dielectric. Pressing the capacitor brings the electrodes closer together and thereby increases capacitance. Thus, sensitivity to a given force is maximized by using dielectric materials that are soft and have a high dielectric constant, yet such properties are often in conflict with each other. Here, a liquid metal elastomer foam (LMEF) is introduced that is extremely soft (elastic modulus 7.8 kPa), highly compressible (70% strain), and has a high permittivity. Compressing the LMEF displaces the air in the foam structure, increasing the permittivity over a large range (5.6–11.7). This is called “positive piezopermittivity.” Interestingly, it is discovered that the permittivity of such materials decreases (“negative piezopermittivity”) when compressed to large strain due to the geometric deformation of the liquid metal droplets. This mechanism is theoretically confirmed via electromagnetic theory, and finite element simulation. Using these materials, a soft tactile sensor with high sensitivity, high initial capacitance, and large capacitance change is demonstrated. In addition, a tactile sensor powered wirelessly (from 3 m away) with high power conversion efficiency (84%) is demonstrated. 相似文献
168.
169.
Heather A. Nyman Adhish Agarwal Harry O. Senekjian John K. Leypoldt Alfred K. Cheung 《Hemodialysis international. International Symposium on Home Hemodialysis》2018,22(3):383-387
Introduction: Hemodialysis patients frequently receive vancomycin for treatment of gram‐positive bacterial infections. This drug is most conveniently administered in outpatient dialysis units during the hemodialysis treatment. However, there is a paucity of data on the removal of vancomycin by high‐flux polyamide dialyzers. Methods: This is a prospective crossover study in which seven uninfected chronic hemodialysis patients at three dialysis units received vancomycin 1 gram intravenously over one hour immediately after the dialysis treatment (Phase 1), and vancomycin 1.5 grams during the last hour of dialysis treatment using a polyarylethersulfone, polyvinylpyrrolidone, polyamide high‐flux (Polyflux 24R) dialyzer (Phase 2). There was a three‐week washout period between phases. Serial serum vancomycin concentrations were used to determine the removal of vancomycin when administered during dialysis. Findings: Dialysis removed 35 ± 15% (range 18‐56%) of the vancomycin dose when administered during the last hour of dialysis. The calculated area under the curve (AUC) of vancomycin levels for 0‐44.5 hours from the start of infusion were similar between the two phases (AUCPhase 1 884 ± 124 mg‐hr/L, mean ± SD; AUCPhase 2 856 ± 208 mg‐hr/L; P=0.72). Serum vancomycin concentrations immediately prior to the next dialysis treatment following vancomycin administration were also similar between the two phases (13.1 ± 2.7 mg/L in Phase 1 and 12.3 ± 3.3 mg/L in Phase 2; P=0.55). Discussion: When using a polyarylethersulfone, polyvinylpyrrolidone, and polyamide high‐flux HD membrane with a 24R Polyflux dialyzer, vancomycin can be administered during the last hour of dialysis if the dose that is prescribed for intra‐dialysis dosing is empirically increased to account for intra‐dialytic drug removal. 相似文献
170.