全文获取类型
收费全文 | 1398篇 |
免费 | 71篇 |
专业分类
电工技术 | 20篇 |
化学工业 | 384篇 |
金属工艺 | 25篇 |
机械仪表 | 32篇 |
建筑科学 | 53篇 |
矿业工程 | 3篇 |
能源动力 | 20篇 |
轻工业 | 75篇 |
水利工程 | 20篇 |
石油天然气 | 6篇 |
无线电 | 98篇 |
一般工业技术 | 177篇 |
冶金工业 | 398篇 |
原子能技术 | 6篇 |
自动化技术 | 152篇 |
出版年
2023年 | 9篇 |
2021年 | 23篇 |
2020年 | 11篇 |
2019年 | 18篇 |
2018年 | 24篇 |
2017年 | 24篇 |
2016年 | 35篇 |
2015年 | 13篇 |
2014年 | 32篇 |
2013年 | 51篇 |
2012年 | 43篇 |
2011年 | 67篇 |
2010年 | 51篇 |
2009年 | 61篇 |
2008年 | 80篇 |
2007年 | 50篇 |
2006年 | 63篇 |
2005年 | 54篇 |
2004年 | 50篇 |
2003年 | 31篇 |
2002年 | 37篇 |
2001年 | 45篇 |
2000年 | 33篇 |
1999年 | 30篇 |
1998年 | 62篇 |
1997年 | 45篇 |
1996年 | 43篇 |
1995年 | 29篇 |
1994年 | 32篇 |
1993年 | 32篇 |
1992年 | 13篇 |
1991年 | 18篇 |
1990年 | 16篇 |
1989年 | 19篇 |
1988年 | 11篇 |
1987年 | 11篇 |
1986年 | 14篇 |
1985年 | 12篇 |
1984年 | 13篇 |
1983年 | 14篇 |
1982年 | 9篇 |
1981年 | 13篇 |
1980年 | 16篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1977年 | 12篇 |
1976年 | 14篇 |
1975年 | 17篇 |
1974年 | 11篇 |
1972年 | 6篇 |
排序方式: 共有1469条查询结果,搜索用时 171 毫秒
91.
The report of work-related musculoskeletal pain may be related to worker evaluations of the design and management of work through two mechanisms: one biomechanical and the other stress-related. This study of engineering workers (n = 204) explored the validity of these mechanisms using sequential logistic regression. Analyses suggested that workers' ratings of the adequacy of the design and management of their work were related to their report of work-related musculoskeletal pain. However, the mechanisms appeared to be activated in certain conditions. The reporting of pain in the upper body was both biomechanically- and stress-related, whereas that in the lower body was only biomechanically-related. It is argued that the mechanism activated appeared to be determined by the anatomical location of the pain, and probably the variance shared between the different aspects of work design and management, on the one hand, and the mechanical load of the job, on the other. 相似文献
92.
Deborah C. Blaine Seong Jin Park Randall M. German Pavan Suri 《Metallurgical and Materials Transactions A》2006,37(9):2827-2835
One of the current challenges facing the particulate materials industry is developing simple, accurate models to predict sintered
properties. Work-of-sintering concepts, where time-temperature integrals are used in such models, offer a solution to this
problem. In this study, the master sintering curve concept is applied to several powder metal systems: 17 to 4PH stainless
steel, 316L stainless steel, nickel, niobium, tungsten heavy alloys with two different compositions, and molybdenum. A detailed
explanation of the construction of these curves is given, including methods used to calculate the apparent activation energy
for sintering and to curve-fit experimental data to a sigmoid function describing the master sintering curve. Discussion of
the results shows that the master sintering curve can be applied to powder metal systems, even those that use liquid phase
during sintering. 相似文献
93.
94.
Emine Ubay Cokgor Gulsum Emel Zengin Didem Okutman Tas Seda Oktay Clifford Randall Derin Orhon 《Canadian Metallurgical Quarterly》2006,132(1):68-74
This study investigates the potential of primary sludge fermentation for the generation of readily biodegradable substrate. Experimental evaluation indicates that uncontrolled fermentation converted 22% of the initial volatile suspended solids in the sludge into soluble biodegradable chemical oxygen demand (COD). More than 85% of the soluble COD generated was associated with the formation of short chain volatile fatty acids (VFAs). The recoverable fraction of the fermented sludge supernatant may potentially increase the biodegradable COD content of the primary effluent by 5%. The VFA composition predominantly involved acetic and propionic acids as reported in the literature. Due to the high VFA content, activated sludge Model No. 1 could not predict the COD fractionation in the primary sludge; activated sludge Model No. 3 provided a better interpretation of the oxygen uptake profile through initial storage of the VFAs in the sludge. 相似文献
95.
Randall J. Charbeneau Andrew D. Henderson Lee C. Sherman 《Canadian Metallurgical Quarterly》2006,132(5):474-481
This paper presents a versatile two-parameter model describing the hydraulic performance of highway culverts operating under inlet control for both unsubmerged and submerged conditions. Applications show that the model can accurately represent the Federal Highway Administration (FHwA) performance curves (which use four parameters) for a range of culvert types and materials. Laboratory data from an investigation of the hydraulic performance of single- and multiple-barrel low-headwater box culverts are also used, and the resulting model predicts a smaller culvert size as compared with the FHwA equations for a given design discharge. Design recommendations are presented for low-headwater box culverts. 相似文献
96.
Densification behavior of tungsten heavy alloy based on master sintering curve concept 总被引:1,自引:0,他引:1
S. J. Park Randall M. German J. M. Martin J. F. Guo J. L. Johnson 《Metallurgical and Materials Transactions A》2006,37(9):2837-2848
The master sintering curve (MSC) theory is modified by substituting the densification ratio (φ) for the densification parameter
(ψ) to identify regions where shrinkage occurs by a similar combination of sintering mechanisms. The modified MSC theory is
used to analyze the results of dilatometry experiments conducted with W-Ni-Fe heavy alloys, in which a phase change occurs
during sintering. Apparent activation energies for sintering in three regions (solid state, transition, and liquid phase)
are calculated. These activation energies are compared with experimental values for diffusion and other mass-transport phenomena
to identify the dominant mechanisms in each region. A series of master sinter curves for varying W contents are developed
into a master sintering surface that includes tungsten content and integral work. 相似文献
97.
Ramnath Ganesan Anthony Griffo Randall M. German 《Metallurgical and Materials Transactions A》1998,29(2):659-664
Liquid phase sintering (LPS) is a common technique to consolidate materials that are difficult to process by fusion techniques,
such as tungsten heavy alloys. One of the major processing difficulties associated with liquid phase sintered alloys is component
distortion and loss of component shape. In LPS, this distortion is the result of viscous flow driven by curvature effects
and gravity. A finite element model is developed for viscous flow of the semisolid sintering structure using Stokes equations.
This model considers solid volume fraction and effective viscosity of the solid-liquid mixture. The simulation predictions
are compared to distortion results for microgravity and ground-based sintering experiments, and they show good agreement.
The model results indicate that the effective semisolid viscosity is significantly greater than the liquid metal viscosity.
Hence, future work needs to quantitatively examine the factors controlling viscosity and the benefits from such high viscosities
in liquid phase sintered systems. 相似文献
98.
Whole-cell patch-clamp recordings were used to characterize the membrane properties and ion channel complement of floor plate neuroepithelia in embryonic and neonatal rats. The average resting potential was close to -60 mV, the capacitance was approximately 7 pS and the membrane time constant averaged 31 ms, in both neonates and embryos. Two types of K+ current were identified (i) a slowly activating, slowly inactivating current that was present in all cells, and (ii) a rapidly inactivating current that was present in 39% of cells from neonates and 64% of cells from embryos. K+ currents were significantly larger in neonates than embryos. Na+ currents were absent from all neuroepithelial cells examined. In contrast, the majority of floor plate cells exhibited a significant Ca2+ current. Biophysically this current activated at potentials positive to 60 mV and exhibited fast, voltage-dependent, inactivation. The Ca2+ current was equipermeant to Ca2+ and Ba2+, sensitive to 40-120 microM Ni2+ and only slightly inhibited by 100 microM Cd2+. These and other observations indicated this current is mediated by low-voltage-activated (i.e. T-type) Ca2+ channels. The majority of floor plate cells tested also exhibited responses to the neurotransmitter GABA which produced robust inward currents at negative membrane potentials, in chloride-loaded cells. Both the pharmacology and voltage-dependence of the GABA-activated currents indicated they arose from activation of GABA(A) receptors. 相似文献
99.
RC Becker CP Cannon EG Bovill RP Tracy B Thompson GL Knatterud A Randall B Braunwald 《Canadian Metallurgical Quarterly》1996,78(2):142-147
The records of 60 patients with gallbladder carcinoma (GBC) operatively treated between 1966 and 1993 at Belen Hospital, Trujillo, Perú, were retrospectively reviewed. The ratio of men to women was 1:7.5 and the average of age was 61 years. The accuracy of ultrasonography and oral cholecystograms for the specific diagnosis was 21% and 0% respectively. The surgical procedures employed were simple cholecystectomy (n = 56), right hepatectomy (n = 2). Whipple operation (n = 1) and extended cholecystectomy (n = 1), and our resectability rate for GBC is currently 50%. Simple cholecystectomy was a potentially curative surgical procedure in patients with in situ cancer (stage O) and early GBC (stage 1). In hospital mortality was 11.6% and 5-year survival rate for the total series was 15%. Gallstones were present in 95% of patients and most tumors (58%) had grown by diffuse infiltration or were associated with empyema (38%). Tumor stage, depth of invasion, tumor grade histologic type were all predictive of patient outcome. This report reinforces the difficulty in diagnosis and the poor prognosis for patients with GBC. We hold the view that more radical approaches for invasive cancers will enhance the operative results. 相似文献
100.
Plasma proteins are only somewhat larger than the intercellular spaces of the cerebral microvessels that constitute the blood-brain barrier or of the choroid plexus villi that elaborate cerebrospinal fluid (CSF). We hypothesized that the integrity of these barriers in anesthetized rabbits might be compromised during head-down tilt (HDT). Plasma protein and osmolality, hematocrit, and CSF protein concentration were compared in rabbits exposed to 1 h of HDT (n = 20) and prone rabbits (n = 10). In addition, the concentration of trypan blue dye, injected intravenously at the end of HDT or the prone position, was measured in brain homogenate. Finally, arterial blood pressure was measured via a catheterized carotid artery. HDT disrupted the barrier between blood and CSF, as indicated by a significantly (P < 0.01) greater brain trypan blue concentration in the HDT rabbits [172.2 +/- 14.4 (SD) micrograms/g dry wt] than in the prone rabbits (29.8 +/- 4.4 micrograms/g dry wt). Moreover CSF protein 5 min after HDT onset was significantly increased compared with control in HDT rabbits (54.6 +/- 1.9 vs. 81.4 +/- 5.2 mg/dl; n = 8) but not in prone rabbits (55.6 +/- 2.7 vs. 57.2 +/- 5.0 mg/dl; n = 6). Changes in the plasma protein-to-hematocrit ratio in the HDT animals, but not in the prone animals, were also compatible with a loss of fluid from the vascular compartment.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献