全文获取类型
收费全文 | 1953篇 |
免费 | 30篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 17篇 |
化学工业 | 295篇 |
金属工艺 | 49篇 |
机械仪表 | 62篇 |
建筑科学 | 63篇 |
矿业工程 | 5篇 |
能源动力 | 55篇 |
轻工业 | 127篇 |
水利工程 | 6篇 |
石油天然气 | 15篇 |
无线电 | 205篇 |
一般工业技术 | 312篇 |
冶金工业 | 550篇 |
原子能技术 | 13篇 |
自动化技术 | 212篇 |
出版年
2022年 | 16篇 |
2021年 | 14篇 |
2020年 | 12篇 |
2019年 | 18篇 |
2017年 | 20篇 |
2016年 | 21篇 |
2015年 | 18篇 |
2014年 | 24篇 |
2013年 | 103篇 |
2012年 | 32篇 |
2011年 | 71篇 |
2010年 | 49篇 |
2009年 | 45篇 |
2008年 | 54篇 |
2007年 | 53篇 |
2006年 | 58篇 |
2005年 | 58篇 |
2004年 | 48篇 |
2003年 | 44篇 |
2002年 | 38篇 |
2001年 | 45篇 |
2000年 | 45篇 |
1999年 | 44篇 |
1998年 | 162篇 |
1997年 | 109篇 |
1996年 | 74篇 |
1995年 | 57篇 |
1994年 | 61篇 |
1993年 | 68篇 |
1992年 | 29篇 |
1991年 | 23篇 |
1990年 | 28篇 |
1989年 | 36篇 |
1988年 | 24篇 |
1987年 | 31篇 |
1986年 | 19篇 |
1985年 | 25篇 |
1984年 | 15篇 |
1983年 | 31篇 |
1982年 | 30篇 |
1981年 | 21篇 |
1980年 | 15篇 |
1979年 | 15篇 |
1978年 | 14篇 |
1977年 | 28篇 |
1976年 | 27篇 |
1975年 | 11篇 |
1974年 | 13篇 |
1973年 | 14篇 |
1972年 | 12篇 |
排序方式: 共有1986条查询结果,搜索用时 15 毫秒
21.
22.
AU Teuscher M Lerch S Shaw G Pacini P Ferrari P Weidmann 《Canadian Metallurgical Quarterly》1998,16(9):1279-1284
OBJECTIVES: Elevated plasma endothelin (ET)-1 levels have been described in insulin-resistant states such as syndrome X, obesity, non-insulin-dependent diabetes mellitus, and in some studies in essential hypertension. To investigate whether increases in circulating ET-1 to levels observed in insulin-resistant states can modulate insulin levels and/or insulin sensitivity in humans, we assessed these variables during low, non-pressor-dose ET-1 compared with placebo infusion. DESIGN: In a randomized, single blind, crossover design, 10 lean normotensive male subjects received either an intravenous infusion of subpressor doses of ET-1 dissolved in polygeline or a control infusion of polygeline only (placebo). Using dynamic assessment by the minimal model approach with the modified frequent sampling intravenous glucose tolerance test (FSIGT) the following and other parameters were measured: insulin sensitivity; acute insulin response to glucose (AIR(G)) calculated as the average of the three peak values between 2 and 5 min after injection of glucose from which the basal insulin levels were subtracted; the initial area under the curve (AUC(1-19)) from insulin values between time 0 and 19 min and the first-phase insulin secretion (phi1) from insulin kinetics parameters. RESULTS: ET-1 infusion reduced AIR(G) (to 34.85 +/- 4.27 compared with 49.3 +/- 6.9 microU/ml during placebo, P=0.017) and the acute C-peptide response to glucose (to 2.33 +/- 0.41 compared with 3.1 +/- 0.44 ng/ml, P=0.018), decreased plasma insulin levels during the FSIGT compared with placebo (analysis of variance P<0.0001) and decreased the AUC(1-19) (to 2.1 +/- 0.2 compared with 2.9 +/- 0.3 U/l per 20 min, P<0.01) while phi1 tended to be lower. S1 measured during ET-1 infusion was unaltered (11.11 +/- 1.91 x 10(-4) versus 10.88 +/- 2.11 10(-4)/min per mU per l, NS). CONCLUSIONS: These findings demonstrate that an increase in circulating ET-1 to levels observed in insulin-resistant states acutely diminishes the insulin secretory response but does not significantly modify insulin sensitivity. 相似文献
23.
Polyimide/silica ceramers, based on the products of the hydrolysis of tetraethoxysilane (TEOS) and a commercial poly(amic acid) solution, were used to fabricate unidirectional carbon fibre composites, which were subsequently evaluated with respect to thermal and mechanical properties. There is evidence to suggest that the silica component of these ceramers is present as dispersed discrete particles at low silica concentration (i.e. 7 wt%) and as fine interconnected domains trapped within the polyimide matrix at higher silica content (i.e. 14 wt%). The dimensions of the silica domains were in the region of 7–20 nm. Carbon fibre composites produced from ceramer solutions (CF/ceramers) were found to exhibit lower thermal expansion and a greater retention of flexural and interlaminar shear properties at elevated temperature than the corresponding polyimide-matrix composites (CF/polyimide). The properties of CF/ceramers were generally better for systems containing the higher amount of silica and were improved further by lowering the pH value of the precursor ceramer solution. This is believed to have resulted from the enhanced fluidity of the ceramer gel within the pre-impregnated fibres, giving rise to a higher packing density of the fibres and a more homogeneous distribution of fibres. CF/ceramers were also found to exhibit a better thermal oxidative stability at 350°C than the corresponding CF/polyimide, although a substantial amount of porosity developed in the case of ceramers with the higher silica content. 相似文献
24.
Parallel electrocorticograms (ECoG) and electroencephalograms (EEG) were recorded during stun-recovery and stun-slaughter of eight calves 4-6 weeks old. Epochs of 8·2 s duration, derived from the ECoG and EEG signals pre-stun, during recovery and during exsanguination, were compared for differences in power content and frequency distribution using Fast Fourier Transform analysis. ECoG signals recorded during the quiescent phase post-stun had a markedly lower power content compared with pre-stun, whereas the EEG signal showed no such reduction in power content. During exsanguination, the mean rate of decline in the ECoG power content was 0·025 log units/s, three times faster than the mean rate of decline of the EEG at 0·008 log units/s. The duration of the electroplectic fit post-stun was detected equally well by the two techniques. The differences between EEG and ECoG traces in this study are thought to arise from differences in the signal-noise ratio of the two techniques and by artefacts in the EEG signal, caused by microscopic movement between EEG electrodes and the surrounding tissue. The slower rate of decline in the power content of the EEG during slaughter means that the time to onset of isoelectric cortical electrical activity will be longer if determined by EEG measurements than by ECoG recording. 相似文献
25.
Sinha Swati Shaw Siddharth Biswas Kunal De Debashis Das Samir Chandra Sarkar Angsuman Bandyopadhyay Jaya 《Microsystem Technologies》2021,27(11):4087-4100
Microsystem Technologies - Single-Walled Carbon Nanotubes (SWCNTs) are widely used as potential carriers in drug delivery systems. The objective of this work was to observe the effects of pristine,... 相似文献
26.
Summary A thin viscoelastic plate on a Winkler foundation is subjected to vertical loads. Its response is strongly affected by the presence of a vertical temperature gradient which causes a very pronounced change in the viscosity coefficient through the plate thickness. While eventually the entire load will be transferred to the underlying foundation, during the time dependent deformation process it is possible that some bending stresses will actually increase rather than decrease as would normally be expected with this relaxation process. The rationale for this behavior lies in the competition between the two physical processes of a) the load transfer to the foundation causing an overall relief of the bending moment and thus the bending stress and b) the rapid relaxation of bending stress in the hot lower portion of the plate causing the colder upper portion to carry a larger share of that portion of the bending moment still carried by the plate. The simple case of a clamped circular plate of a metallic material and subjected to a uniform load is used to illustrate this behavior. Certain simplifications are made to allow an analytic solution; these simplifications do not alter the basic behavior. In the present case, these simplifications are the neglect of Poisson's ratio effects and the assumption of a linear equivalent viscoelastic material behavior. This latter point is discussed in an appendix. Numerical solutions containing more general behavior indicate that the basic behavior is still well modeled even with these assumptions.With 4 Figures 相似文献
27.
Conventional random access memories are capable only of writing data into and reading data from the storage location corresponding to a given address. The availability of VLSI circuits containing hundreds of thousands of switching devices, however, has recently made practical the implementation of active memory chips capable of performing a range of complex operations on their stored data. Such designs are characterized by the extensive intermingling of processing and memory resources within a single chip to achieve the rapid and cost-effective parallel execution of operations relevant to such tasks as image processing, computer graphics, artificial intelligence, and database management.This paper presents a brief survey of a number of active memory chips that have been implemented or proposed, along with a more detailed examination of a particular active memory circuit, the NON-VON 3 primary processing subsystem chip.This research was supported in part by the Defense Advanced Research Projects Agency, under contract N00039-84-C-0165, in part by the New York Center for Advanced Technology in Computers and Information Systems at Columbia University, and in part by an IBM Faculty Development Award. 相似文献
28.
The effect of tempering on the magnetic Barkhausen noise (MBN) signal profile was studied in case-carburised EN36 steel using a range of magnetic excitation frequencies and a number of frequency ranges for analysis of the MBN signal. The MBN level generally increases with tempering due to coarsening of the microstructure. With higher values of excitation frequency, fEX, the MBN profile exhibits a single peak, but with low values of fEX, double peaks are observed. The MBN peak obtained with higher fEX was found to correlate well with hardness changes in a region, down to 100 μm below the surface. The analysis of the MBN signal produced with low fEX, in narrow frequency ranges selected by software frequency filtering, showed variations in the extent of changes in the relative height of the two MBN peaks in the profile. After taking into account the skin depth-frequency relation for the MBN signal, variations in the values of the two MBN peaks in different analysing frequency ranges were found to correlate well with hardness variations at different depths down to 425 μm below the surface. An empirical relationship has been established between the hardness-depth profile and the MBN measurements. 相似文献
29.
James E. Shaw 《Journal of the American Oil Chemists' Society》1984,61(8):1389-1394
Oil displacement tests in water wet Berea sandstone cores containing residual crude oil flooded with water have shown that
high tertiary oil recoveries can be obtained using the sodium salts of readily available carboxylic acids. Using a 10% pore
volume surfactant slug containing 3.0% sodium isostearate and 3.0% isopentyl alcohol followed by a polyacrylamide mobility
buffer resulted in a 92% tertiary oil recovery, which compares well with recoveries using petroleum solfonates. Oil recoveries
were highly dependent on pH and added base. Aliphatic C18 carboxylates gave higher recoveries at lower pH using sodium bicarbonate
as the added base (pH 8.5) rather than sodium hydroxide, sodium carbonate or sodium orthosilicate (pH 11–13). In contrast,
aromatic carboxylates e.g., sodium p-(1-pentylnonyl)benzoate, gave higher recoveries at higher pH using sodium carbonate rather
than sodium bicarbonate. Carboxylates with branched alkyl groups, e.g., isostearate, gave higher tertiary oil recoveries than
unbranched carboxylates, e.g., oleate or stearate. Low cost tall oils and tall-oil fatty acids, when neutralized with base,
gave oil recoveries of 60–80%. Carboxylates were found to give good oil recoveries even when significant amounts of calcium
ion were present. 相似文献
30.
Fatty acid monoesters of propylene glycol (1,2-propanediol) are good water-in-oil emulsifiers. These esters were synthesized
enzymatically to overcome the problems associated with chemical processes. APseudomonas lipase was added to reaction mixtures containing propylene glycol and various acyl donors (fatty acids, fatty acid ethyl
esters, fatty acid anhydrides and triglycerides) in organic solvents, and the mixtures were shaken at 30°C. The products were
analyzed by gas chromatography. The yield of monoesters was affected by the acyl donors, organic solvents, temperature, water
content, pH memory and reaction time. The anhydrous (lyophilized) enzyme and fatty acid anhydrides were best for monoester
production. The optimum pH ranges were 4–5 and 8–10. The yields of propylene glycol monolaurate, monomyristate, monopalmitate,
monostearate and monooleate with 50 mM fatty acid anhydrides as acyl donors were 97.2, 79.6, 83.7, 89.7 and 93.4 mM, respectively;
those with 50 mM fatty acids as acyl donors were 37.3, 28.7, 28.7, 35.3 and 36.2 mM, respectively. The yields of propylene
glycol monopalmitate, monostearate and monooleate with 50 mM triglycerides as acyl donors were 87.4, 65.1 and 83.2 mM, respectively. 相似文献