全文获取类型
收费全文 | 2689篇 |
免费 | 203篇 |
国内免费 | 11篇 |
专业分类
电工技术 | 40篇 |
综合类 | 18篇 |
化学工业 | 540篇 |
金属工艺 | 56篇 |
机械仪表 | 59篇 |
建筑科学 | 154篇 |
矿业工程 | 8篇 |
能源动力 | 81篇 |
轻工业 | 187篇 |
水利工程 | 28篇 |
石油天然气 | 28篇 |
无线电 | 322篇 |
一般工业技术 | 547篇 |
冶金工业 | 241篇 |
原子能技术 | 8篇 |
自动化技术 | 586篇 |
出版年
2023年 | 42篇 |
2022年 | 68篇 |
2021年 | 109篇 |
2020年 | 79篇 |
2019年 | 88篇 |
2018年 | 98篇 |
2017年 | 86篇 |
2016年 | 107篇 |
2015年 | 96篇 |
2014年 | 115篇 |
2013年 | 207篇 |
2012年 | 136篇 |
2011年 | 232篇 |
2010年 | 144篇 |
2009年 | 159篇 |
2008年 | 161篇 |
2007年 | 164篇 |
2006年 | 123篇 |
2005年 | 89篇 |
2004年 | 53篇 |
2003年 | 53篇 |
2002年 | 43篇 |
2001年 | 40篇 |
2000年 | 36篇 |
1999年 | 25篇 |
1998年 | 31篇 |
1997年 | 27篇 |
1996年 | 22篇 |
1995年 | 22篇 |
1994年 | 26篇 |
1993年 | 9篇 |
1992年 | 18篇 |
1991年 | 7篇 |
1990年 | 12篇 |
1989年 | 13篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1986年 | 6篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1982年 | 13篇 |
1981年 | 7篇 |
1979年 | 9篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1975年 | 8篇 |
1974年 | 13篇 |
1973年 | 5篇 |
1969年 | 5篇 |
排序方式: 共有2903条查询结果,搜索用时 15 毫秒
91.
Renata Silvrio Robson Barth Andrea S. Heimann Patrícia Reckziegel Gustavo J. dos Santos Silvana Y. Romero-Zerbo Francisco J. Bermúdez-Silva Alex Rafacho Emer S. Ferro 《International journal of molecular sciences》2022,23(8)
Peptide DIIADDEPLT (Pep19) has been previously suggested to improve metabolic parameters, without adverse central nervous system effects, in a murine model of diet-induced obesity. Here, we aimed to further evaluate whether Pep19 oral administration has anti-obesogenic effects, in a well-established high-fat diet-induced obesity model. Male Swiss mice, fed either a standard diet (SD) or high-fat diet (HFD), were orally administrated for 30 consecutive days, once a day, with saline vehicle or Pep19 (1 mg/kg). Next, several metabolic, morphological, and behavioral parameters were evaluated. Oral administration of Pep19 attenuated HFD body-weight gain, reduced in approximately 40% the absolute mass of the endocrine pancreas, and improved the relationship between circulating insulin and peripheral insulin sensitivity. Pep19 treatment of HFD-fed mice attenuated liver inflammation, hepatic fat distribution and accumulation, and lowered plasma alanine aminotransferase activity. The inguinal fat depot from the SD group treated with Pep19 showed multilocular brown-fat-like cells and increased mRNA expression of uncoupling protein 1 (UCP1), suggesting browning on inguinal white adipose cells. Morphological analysis of brown adipose tissue (BAT) from HFD mice showed the presence of larger white-like unilocular cells, compared to BAT from SD, Pep19-treated SD or HFD mice. Pep19 treatment produced no alterations in mice behavior. Oral administration of Pep19 ameliorates some metabolic traits altered by diet-induced obesity in a Swiss mice model. 相似文献
92.
Alex Bach Isabel Guasch Guillermo Elcoso Julie Duclos Hajer Khelil-Arfa 《Journal of dairy science》2018,101(11):9777-9788
With the objective of evaluating the potential effects of sodium bicarbonate or a magnesium-based product on rumen pH and milk performance of dairy cattle exposed to a dietary challenge, 30 lactating Holstein cows (648 ± 67 kg of body weight; 44.4 ± 9.9 kg/d of milk yield; 155 ± 75 d in milk) were blocked by parity (9 primiparous and 21 multiparous) and randomly distributed to 3 treatment groups. One group received a total mixed ration (TMR) that acted as a control (CTR), a second group (SB) received the same TMR but with an additional supplementation of 0.8% of sodium bicarbonate, and a third group (MG) received the same TMR as CTR but an additional supplementation of 0.4% of a magnesium-based product (pHix-Up, Timab, Dinard, France). After 1 wk of exposure to this TMR, all 3 rations were supplemented with 1 kg/d of barley, which was then increased 1 kg/wk until reaching 3 kg/d of barley during wk 4 of the study. Every kilogram of barley replaced 1 kg of forage in the diet. Individual feed intake and behavior were monitored using electronic feed bins. Seven cows per treatment were equipped with an intraruminal bolus that recorded pH every 15 min. As the severity of the barley challenge increased, dry matter intake decreased, but this decrease was more pronounced in SB cows than in MG cows, with an intermediate response for CTR cows. The MG cows produced more milk when challenged with 2 or 3 kg/d of additional barley than when challenged with 1 kg/d, whereas CTR cows produced less milk with the 3 kg/d challenge compared with 1 or 2 kg/d, and the SB cows maintained milk production. Milk fat content decreased with barley challenges, with CTR cows experiencing a more severe decrease than SB cows, which maintained stable butterfat values throughout the study, and MG cows showed a decline in milk fat content only with the 3 kg/d of additional barley. Meal size was also reduced as the severity of barley challenge increased, and this reduction was more modest in MG cows than in SB cows. The number of daily meals consumed by SB and MG cows was more constant than that recorded in CTR cows. Cows on the CTR and SB treatments showed a marked decrease in rumen pH with the 3 kg/d of additional barley, whereas MG cows maintained stable rumen pH during the barley challenges and had greater average rumen pH (5.93 ± 0.04) than CTR cows (5.83 ± 0.04) with the 3 kg/d of additional barley; SB cows showed intermediate values (5.85 ± 0.04). Last, MG cows spent less time (32.3 ± 6.1%) with rumen pH ≤5.8 when exposed to the 3 kg/d of barley challenge than CTR and SB cows (50.7 ± 5.02%). In conclusion, supplementation with MG prevents the decline in dry matter intake and milk production induced by a rumen challenge, whereas supplementation with SB prevents the decay in milk production but does not prevent the decrease in feed intake. These changes were probably due to the ability of the MG treatment to prevent a reduction in rumen pH when challenging cows with 3 kg/d of additional barley in the ration. 相似文献
93.
Lipid peroxidation in unilamellar liposomes of known cholesterol-phospholipid composition was monitored under conditions of
autoxidation or as induced by a superoxide radical generating system, γ-irradiation or cumene hydroperoxide. Formation of
cholesterol oxidation products was indexed to the level of lipid peroxidation. The major cholesterol oxidation products identified
were 7-keto-cholesterol, isomeric cholesterol 5,6-epoxides, isomeric 7-hydroperoxides and isomeric 3,7-cholestane diols. Other
commonly encountered products included 3,5-cholestadiene-7-one and cholestane-3β,5α,6β-triol. Superoxide-dependent peroxidation
required iron and produced a gradual increase in 7-keto-cholesterol and cholesterol epoxides. Cholesterol oxidation was greatest
in liposomes containing high proportions of unsaturated phospholipid to cholesterol (4∶1 molar ratio), intermediate with low
phospholipid to cholesterol ratios (2∶1) and least in liposomes prepared with dipalmitoylphosphatidylcholine and cholesterol.
This relationship held regardless of the oxidizing conditions used. Cumene hydroperoxide-dependent lipid peroxidation and/or
more prolonge oxidations with other oxidizing systems yielded a variety of products where cholesterol-5β,6β-epoxide, 7-ketocholesterol
and the 7-hydroperoxides were most consistently elevated. Oxyradical initiation of lipid peroxidation produced a pattern of
cholesterol oxidation products distinguishable from the pattern derived by cumene hydroperoxide-dependent peroxidation. Our
findings indicate that cholesterol autoxidation in biological membranes is modeled by the peroxide-induced oxidation of liposomes
bearing unsaturated fatty acids and suggest that a number of cholesterol oxidation products are derived from peroxide-dependent
propagation reactions occurring in biomembranes. 相似文献
94.
Kay A. Buist Alex C. van der Gaag Niels G. Deen Johannes A. M. Kuipers 《American Institute of Chemical Engineers》2014,60(9):3133-3142
Noninvasive monitoring of multiphase flow is rapidly gaining increased interest. More specifically noninvasive particle tracking techniques have received a lot of attention in recent years to study dense granular flow. However, these techniques are usually quite expensive and require strict safety measures. An improved magnetic particle tracking (MPT) technique for dense granular flow will be presented in this article. The improvements of the analysis technique for MPT will be demonstrated and rigorously tested with a three‐dimensional system and two‐dimensional sensor system. The strengths and limitations of the MPT technique will also be reported. Finally, the results of the MPT are compared with data obtained from a combined particle image velocimetry and digital image analysis technique. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3133–3142, 2014 相似文献
95.
Plant sources of omega-3 fatty acids (FA) are needed that can materially raise tissue levels of long-chain omega-3 FA [i.e.,
eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 20:6n-3)]. Stearidonic acid (SDA; 18:4n-3) is the delta-6
desaturase product of alpha-linolenic acid (ALA; 18:3n-3), and when fed to humans, increases red blood cell (RBC) content
of EPA to a greater extent than does ALA. This study was undertaken to determine the dose-dependence and time course of the
increase in the EPA and DHA content of the heart and RBC in dogs. Adult male Beagles were fed 21, 64, or 193 mg/kg of SDA
in in their food daily for up to 12 weeks. Positive and negative controls were given EPA (43 mg/kg) or high oleic acid sunflower
oil, respectively. The baseline EPA content of RBC was 0.38 ± 0.03% which increased (P < 0.01) in a dose-dependent manner, with the high dose of SDA and EPA achieving levels of 1.33 ± 0.26 and 1.55. ± 0.28%,
respectively. In the heart, the content of EPA rose from 0.06 ± 0.01 to 1.24 ± 0.22% in the EPA group and to 0.81 ± 0.32%
in the high SDA group (both P < 0.01). In both tissues, DHA did not change. Compared to dietary EPA, SDA was 20–23% as efficient in raising tissue EPA
levels. In conclusion, SDA supplementation increased the EPA content of RBC and heart and may have utility as a plant-based
source of omega-3 FA. 相似文献
96.
Qianhong Li Yiru Guo Yibing Nong Alex Tomlin Anna Gumpert Xiaoping Zhu Syed Adeel Hassan Roberto Bolli 《International journal of molecular sciences》2021,22(6)
Using a murine model of chronic ischemic cardiomyopathy caused by an old myocardial infarction (MI), we have previously found that three doses of 1 × 106 c-kit positive cardiac cells (CPCs) are more effective than a single dose of 1 × 106 cells. The goal of this study was to determine whether the beneficial effects of three doses of CPCs (1 × 106 cells each) can be fully replicated by a single combined dose of 3 × 106 CPCs. Mice underwent a 60-min coronary occlusion; after 90 days of reperfusion, they received three echo-guided intraventricular infusions at 5-week intervals: (1) vehicle × 3; (2) one combined dose of CPCs (3 × 106) and vehicle × 2; or (3) three doses of CPCs (1 × 106 each). In the combined-dose group, left ventricular ejection fraction (LVEF) improved after the 1st CPC infusion, but not after the 2nd and 3rd (vehicle) infusions. In contrast, in the multiple-dose group, LVEF increased after each CPC infusion; at the final echo, LVEF averaged 35.2 ± 0.6% (p < 0.001 vs. the vehicle group, 27.3 ± 0.2%). At the end of the study, the total cumulative change in EF from pretreatment values was numerically greater in the multiple-dose group (6.6 ± 0.6%) than in the combined-dose group (4.8 ± 0.8%), although the difference was not statistically significant (p = 0.08). Hemodynamic studies showed that several parameters of LV function in the multiple-dose group were numerically greater than in the combined-dose group (p = 0.08 for the difference in LVEF). Compared with vehicle, cardiomyocyte cross-sectional area was reduced only in the multiple-dose group (−32.7%, 182.6 ± 15.1 µm2 vs. 271.5 ± 27.2 µm2, p < 0.05, in the risk region and −28.5%, 148.5 ± 12.1 µm2 vs. 207.6 ± 20.5 µm2, p < 0.05, in the noninfarcted region). LV weight/body weight ratio and LV weight/tibia length ratios were significantly reduced in both cell treated groups vs. the vehicle group, indicating the attenuation of LV hypertrophy; however, the lung weight/body weight ratio was significantly reduced only in the multiple-dose group, suggesting decreased pulmonary congestion. Taken together, these results indicate that in mice with chronic ischemic cardiomyopathy, the beneficial effects of three doses of CPCs on LV function and hypertrophy cannot be fully replicated with a single dose, notwithstanding the fact that the total number of cells delivered with one or three doses is the same. Thus, it is the multiplicity of doses, and not the total number of cells, that accounts for the superiority of the repeated-dose paradigm. This study supports the idea that the efficacy of cell therapy in heart failure can be augmented by repeated administrations. 相似文献
97.
Bin Li Shen-Gen Zhang Kun Zhang De-An Pan Jian-Jun Tian Hu Liu Alex A. Volinsky 《稀有金属(英文版)》2014,33(5):598-603
In this study, Pb was separated and used to prepare BaPbO3 conductive ceramics from leaded waste.The experimental results show that BaPbO3 powder synthesized at 700 °C has particle size of 2–5 lm. The powders were densified by sintering at 1,000 °C for 2 h in the air.Synthesized BaPbO3 ceramics have high Curie temperature and high-temperature positive temperature coefficient(PTC) resistivity characteristics. Electrical resistivity of BaPbO3 compact increases from 5 × 10^-6Ω·m at room temperature to 4 × 10^-4Ω·m at 750 °C. Compared with the one prepared by pure chemical reagents, the BaPbO3 prepared from leaded waste has the similar characteristics of high Curie temperature and PTC resistivity. 相似文献
98.
There are many multi-stage optimization problems that are not easily solved through any known direct method when the stages are coupled. For instance, the problem of planning a vehicle's control sequence to negotiate obstacles and reach a goal in minimum time is investigated. The vehicle has a known mass, and the controlling forces have finite limits. A genetic programming technique is developed that finds admissible control trajectories that tend to minimize the vehicle's transit time through the obstacle field. The immediate application is that of a space robot that must rapidly traverse around two or three dimensional structures via application of a rotating thruster or non-rotating on-off thrusters. (An air-bearing floor test-bed for such vehicles is located at the Marshal Space Flight Center in Huntsville, Alabama.) It appears that the developed method is applicable to a general set of optimization problems in which the cost function and the multi-dimensional multi-state system can be any non-linear functions that are continuous in the operating regions. Other applications include: the planning of optimal navigation pathways through a traversability graph, the planning of control input for underwater maneuvering vehicles which have complex control state-space relationships, the planning of control sequences for milling and manufacturing robots, the planning of control and trajectories for automated delivery vehicles, and the optimization of control for racing vehicles and athletic training in slalom sports. 相似文献
99.
Masaru Tsuchiya Bo-Kuai Lai Alex C. Johnson Shriram Ramanathan 《Journal of power sources》2010,195(4):541-1000
We report on the synthesis and functional properties of nanoscale (50 nm) dense Y-doped zirconia (YDZ) electrolyte thin films by photon-assisted oxidation of Zr–Y precursor alloy thin films. Crystalline zirconia films with grain size of 5 nm were successfully grown at room temperature by oxidation under ultra-violet (UV) photon irradiation. Microstructure of the films was characterized by transmission electron microscopy. The electrochemical conductivity of UV grown YDZ electrolytes was investigated over a broad range of temperatures using Pt electrodes as a function of yttria doping concentration. The slightly lower electrical conductivity in UV grown films at intermediate temperature range (400–550 °C) is consistent with previous reports on oxygen defect annihilation under photo-excitation. Micro-fuel cells utilizing such ultra-thin YDZ membranes yielded 12 mW cm−2 power density at 550 °C. The results are of potential relevance in advancing low temperature ultra-thin oxide membrane synthesis for energy applications. 相似文献
100.
Kuo-Hsin Lin Wen-Hsiung Lin Chia-Hsing Hsiao Hsin-Fu Chang Alex C.-C. Chang 《International Journal of Hydrogen Energy》2012
The aim of this study is to produce hydrogen through the glycerol steam reforming process. The reaction is carried out in a traditional reactor and an electrolessly plated Pd/Ag alloy membrane reactor, with varying reaction temperature, weight hourly specific velocity (WHSV) and water glycerol molar ratio (WGMR). The non-catalytic test was also employed for comparative purposes. The results show that the reaction is highly depending on temperature, and the maximum glycerol conversion achieved to 96.24% at 800 °C with a hydrogen yield of 5.82 mol-H2/mol-C3H8O3. It also found that the Pd/Ag membrane can effectively separate hydrogen from the reaction side and subsequently enhance the reaction rate in the membrane reactor. TGA measurements were employed to quantify the amounts of deposited carbon and the results also confirmed that the CeO2 modified catalyst can improve the carbon resistance as well as activity and stability. 相似文献