全文获取类型
收费全文 | 2131篇 |
免费 | 77篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 51篇 |
综合类 | 2篇 |
化学工业 | 804篇 |
金属工艺 | 34篇 |
机械仪表 | 37篇 |
建筑科学 | 162篇 |
矿业工程 | 6篇 |
能源动力 | 70篇 |
轻工业 | 151篇 |
水利工程 | 3篇 |
石油天然气 | 2篇 |
无线电 | 112篇 |
一般工业技术 | 239篇 |
冶金工业 | 214篇 |
原子能技术 | 11篇 |
自动化技术 | 312篇 |
出版年
2022年 | 13篇 |
2021年 | 22篇 |
2020年 | 19篇 |
2019年 | 25篇 |
2018年 | 26篇 |
2017年 | 22篇 |
2016年 | 50篇 |
2015年 | 55篇 |
2014年 | 79篇 |
2013年 | 77篇 |
2012年 | 95篇 |
2011年 | 104篇 |
2010年 | 73篇 |
2009年 | 91篇 |
2008年 | 100篇 |
2007年 | 83篇 |
2006年 | 91篇 |
2005年 | 80篇 |
2004年 | 82篇 |
2003年 | 57篇 |
2002年 | 51篇 |
2001年 | 42篇 |
2000年 | 52篇 |
1999年 | 50篇 |
1998年 | 55篇 |
1997年 | 46篇 |
1996年 | 44篇 |
1995年 | 34篇 |
1994年 | 47篇 |
1993年 | 41篇 |
1992年 | 37篇 |
1991年 | 32篇 |
1990年 | 24篇 |
1989年 | 29篇 |
1988年 | 24篇 |
1987年 | 20篇 |
1986年 | 23篇 |
1985年 | 31篇 |
1984年 | 31篇 |
1983年 | 24篇 |
1982年 | 27篇 |
1981年 | 24篇 |
1980年 | 21篇 |
1979年 | 10篇 |
1978年 | 17篇 |
1977年 | 14篇 |
1976年 | 9篇 |
1975年 | 21篇 |
1973年 | 14篇 |
1972年 | 13篇 |
排序方式: 共有2210条查询结果,搜索用时 15 毫秒
101.
The aim of this study was to explore the long-term effects of affect-focused body psychotherapy (ABP) for patients with generalized anxiety disorder (GAD). A group of 61 consecutive patients, 21–55 years old, were randomized to ABP and psychiatric treatment as usual (TAU). The patients were assessed before treatment and followed up 1 and 2 years after inclusion. The ABP patients received one session of treatment per week during 1 year. Three self-report questionnaires were administered; Symptom Checklist—90, Beck Anxiety Inventory, and the WHO (Ten) Well-Being Index. In both groups, there was a significant improvement. On termination, the ABP group had improved significantly more on the SCL-90 Global Symptom Index than the TAU group, whereas the differences were short of significance on the other two scales. The integration of bodily techniques with a focus on affects in a psychodynamically informed treatment seems to be a viable treatment alternative for patients with GAD. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
102.
Thirty strains of Listeria monocytogenes were screened for their pressure tolerance phenotype at 400 MPa for 2 min at 21 °C. The strains exhibited reductions ranging from 1.9 to 7.1log10 CFU/ml in tryptic soy broth with 6% yeast extract (TSBYE). The 3 most and the 3 least pressure-tolerant strains were further tested for their thermal resistance (based on their ability to survive at 55 °C), acid tolerance (based on their ability to survive in acidified TSBYE; pH 2.0) and for their nisin sensitivity. No correlation between pressure tolerance and heat, acid or nisin resistances was found. Nucleotide sequence analysis of the ctsR region in these 6 strains demonstrated that this gene codes for a CtsR protein with identical predicted amino acid sequences. The sequences of the 200-bp region located immediately upstream of the ctsR start codon of the different strains were virtually identical and it is therefore likely that differences in pressure tolerance are based on factors other than the stress gene regulator CtsR. The pressure sensitivity of a cocktail of the 2 most pressure-resistant strains and a cocktail of the 2 most-sensitive strains was investigated when the cocktails were inoculated into a real food system consisting of ground chicken meat. We demonstrated that the nature of the suspending substrate or the temperature did not change the expected pressure tolerance of the cocktails. 相似文献
103.
104.
105.
Multiple inhibitory effects of garlic extracts on cholesterol biosynthesis in hepatocytes 总被引:2,自引:0,他引:2
Rolf Gebhardt 《Lipids》1993,28(7):613-619
Exposure of primary rat hepatocytes and human HepG2 cells to water-soluble garlic extracts resulted in the concentration-dependent
inhibition of cholesterol biosynthesis at several different enzymatic steps. At low concentrations, sterol biosynthesis from
[14C]acetate was decreased in rat hepatocytes by 23% with an IC50 (half-maximal inhibition) value of 90μg/mL and in HepG2 cells by 28% with an IC50 value of 35 μg/mL. This inhibition was exerted at the level of hydroxymethylglutaryl-COA reductase (MHG-CoA reductase) as
indicated by direct enzymatic measurements and the absence of inhibition if [14C]mevalonate was used as a precursor. At high concentrations (above 0.5 mg/mL), inhibition of cholesterol biosynthesis was
not only seen at an early step where it increased considerably with dose, but also at later steps resulting in the accumulation
of the precursors lanosterol and 7-dehydrocholesterol. No desmosterol was formed which, however, was a major precursor accumulating
in the presence of triparanol. Thus, the accumulation of sterol precursors seem to be of less therapeutic significance during
consumption of garlic, because it requires concentrations one or two orders of magnitude above those affecting HMG-CoA reductase.
Alliin, the main sulfur-containing compound of garlic, was without effect itself. If converted to allicin, it resulted in
similar changes of the sterol pattern. This suggested that the latter compound might contribute to the inhibition at the late
steps. In contrast, nicotinic acid and particularly adenosine caused moderate inhibition of HMG-CoA reductase activity and
of cholesterol biosynthesis suggesting that these compounds participate, at least in part, in the early inhibition of sterol
synthesis by garlic extracts.
Dedication: This article is dedicated to Prof. Dr. D. Mecke on the occasion of his 60th birthday. 相似文献
106.
The modulation of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) biosynthesis by sulfur-substituted fatty acid
analogues has been investigated in rats. We have compared the effects of two non-β-oxidizable fatty acid analogues, 3-thiadicarboxylic
acid and tetradecylthioacetic acid, which induce proliferation of peroxisomes, with those of the analogue tetradecylthiopropionic
acid, which is a weak peroxisome proliferator. Repeated administration of 3-thiadicarboxylic acid for seven days resulted
in increased hepatic concentrations of both PC and PE, but the PC/PE ratio was decreased. PC synthesis was increased, as evidenced
by increased incorporation of [3H]choline into PC and an increased activity of cytidinetriphosphate (CTP): phosphocholine cytidylyltransferase. This was accompanied
by a reduction in the pool sizes of choline and phosphocholine. TheS-adenosylmethione/S-adenosylhomocysteine ratio (AdoMet/AdoHcy) was marginally affected, indicating no increase in the rate of methylation of
PE to PC. Administration of tetradecylthioacetic acid also resulted in increased hepatic phospholipid levels, increased AdoMet/AdoHcy
ratios and in slightly elevated activity of CTP:phosphocholine cytidylyltransferase. The most striking effect observed after
tetradecylthiopropionic acid treatment was the development of fatty liver. The activity of CTP:phosphocholine cytidylyltransferase
and the incorporation of [3H]choline into PC was reduced compared to 3-thiadicarboxylic acid treatment. Although the rate of methylation of PE seemed
to be increased at an elevated AdoMet/AdoHcy ratio, this resulted in only minor changes in the hepatic PC and PE levels, and
the PC/PE ratio remained unchanged. Furthermore, the hepatic levels of choline and phosphocholine were reduced in these rats.
The activities of the two enzymes competing for choline in the liver, choline kinase and choline dehydrogenase were changed
in opposite directions, with the activity of choline kinase increasing approximately 1.5-fold. In addition, it was found that
the level of homocysteine was elevated in the liver of tetradecylthiopropionic acid-treated rats. The possibility is discussed
that this reflects a reduced flux of choline through the oxidative pathway in the liver. In tetradecylthiopropionic acid-treated
rats, there seemed to be a coordinated regulation of the two pathways for PC biosynthesis, with an increase in the methylation
of PE to PC and a reduced synthesisvia the CDPcholine pathway. The increase in PC observed in rats treated with 3-thiadicarboxylic acid and tetradecylthioacetic
acid suggests that increased PC synthesis is linked to peroxisome proliferation. 相似文献
107.
Robert Schafranek Andre Giere Adam G. Balogh Thorsten Enz Yuliang Zheng Patrick Scheele Rolf Jakoby Andreas Klein 《Journal of the European Ceramic Society》2009,29(8):1433-1442
Barium strontium titanate (BST) thin films are studied with respect to their application as tunable dielectric at microwave frequencies. BST thin films are deposited by means of radio-frequency magnetron sputtering on platinized Si substrates. The substrate to target distance during sputter deposition is varied and the effect on structure, topology, composition and electronic properties is monitored using X-ray diffraction, atomic force microscopy, Rutherford backscattering spectrometry and X-ray photoelectron spectroscopy. These findings are related to the dielectric measurements, which are carried out at 1 MHz and in the microwave range up to 8 GHz using metal-insulator-metal structures with Pt electrodes. For further device evaluation, leakage current measurements are carried out. Changing the process parameter strongly affects the composition of the films. The results emphasize the possibility for enhancing the microwave properties by fine-tuning of the chosen process parameter. 相似文献
108.
Rolf C. A. Rottlnder 《European Journal of Lipid Science and Technology》1985,87(8):314-317
Indication and Identification of Archaeologic Fats In comparison to the food chemistry, the special tasks of fat indication in archaeologic discoveries consist in regarding possible changes of the fatty acid chains by soil storage. But changes of the composition expressed as percentages need not inevitably occur. There are many examples especially from zoologically determined subrecent bones that the total fat amount is indeed highly reduced, but the remaining residue seems unsignificantly altered. In case of alteration on an empiric basis a solution possibility can be achieved from two sides: pure fatty acid methylates are left to the effects of the natural environment. After some time the occurred changes are analysed. Since because of the relatively short period only introducing changes can be determined, you start from the other end: For archaeological findings enough time for changes has been available. Fats are extracted from objects which were identified by an archaeobotanist as seeds of certain plants or by an archaeozoologist as bones of certain animals and compared with recent fats. Ways of conversion get visible especially by a graduation of the findings according to the age. 相似文献
109.
The aim of the present study was to investigate the influence of partially hydrogenated vegetable and marine oils on membrane
composition and function of liver microsomes and platelets with particular reference to the metabolism of linoleic acid and
the production of arachidonic acid metabolites. Four groups of male weanling rats were fed linoleic acid supplemented diets
containing 20% (w/w) of partially hydrogenated low erucic acid rapeseed oil (HLRSO), partially hydrogenated herring oil (HHO),
olive oil (OO) and trierucin + triolein (TE) for 10 weeks. An additional two groups were fed partially hydrogenated low erucic
acid rapeseed oil and partially hydrogenated herring oil without linoleic acid supplementation (HLRSO- and HHO-, respectively).
Substantial amounts oftrans fatty acids were incorporated into liver microsomes (12.6% in group HLRSO) and platelets (7.0% in group HLRSO-). This incorporation
was not dependent on the dietary linoleic acid level. Hepatic microsomal Δ5-desaturase activity was significantly increased after HLRSO feeding compared to OO feeding. Δ6-Desaturase activity did not vary in the linoleic acid supplemented groups. Both Δ5- and Δ6-desaturase activities were significantly increased in groups without linoleic acid supplementation.
Docosenoic acid was incorporated into platelet phospholipids in contrast to liver microsomes. In the platelet, docosenoic
acid seemed to have a special preference for phosphatidylserine. Very small amounts were incorporated into platelet phosphatidylinositol.
Feeding diets HLRSO, HHO and OO did not influence rat platelet cyclooxygenase or 12-lipoxygenase activity. Platelets from
rats fed TE, however, produced significantly less 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE) than platelets from
rats fed OO. Feeding of HLRSO- and HHO- resulted in a significantly diminished production of the arachidonic acid metabolites
12-HETE, 12-hydroxy-5,8,10-heptadecatrienoic acid (HHT) and 6-keto-prostaglandin F1α in stimulated platelets and aorta. Thus, high dietary levels oftrans isomers of monoenoic acids do not interfere with platelet cyclooxygenase or lipoxygenase activity provided sufficient amounts
of linoleic acid are available. 相似文献
110.
Removal of oxide nanoparticles in a model wastewater treatment plant: influence of agglomeration and surfactants on clearing efficiency 总被引:2,自引:0,他引:2
Limbach LK Bereiter R Müller E Krebs R Galli R Stark WJ 《Environmental science & technology》2008,42(15):5828-5833
The rapidly increasing production of engineered nanoparticles has created a demand for particle removal from industrial and communal wastewater streams. Efficient removal is particularly important in view of increasing long-term persistence and evidence for considerable ecotoxicity of specific nanoparticles. The present work investigates the use of a model wastewater treatment plant for removal of oxide nanoparticles. While a majority of the nanoparticles could be captured through adhesion to clearing sludge, a significant fraction of the engineered nanoparticles escaped the wastewater plant's clearing system, and up to 6 wt % of the model compound cerium oxide was found in the exit stream of the model plant. Our study demonstrates a significant influence of surface charge and the addition of dispersion stabilizing surfactants as routinely used in the preparation of nanoparticle derived products. A detailed investigation on the agglomeration of oxide nanoparticles in wastewater streams revealed a high stabilization of the particles against clearance (adsorption on the bacteria from the sludge). This unexpected finding suggests a need to investigate nanoparticle clearance in more detail and demonstrates the complex interactions between dissolved species and the nanoparticles within the continuously changing environment of the clearing sludge. 相似文献