首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1722篇
  免费   55篇
  国内免费   1篇
电工技术   30篇
综合类   2篇
化学工业   230篇
金属工艺   34篇
机械仪表   22篇
建筑科学   81篇
能源动力   82篇
轻工业   226篇
水利工程   22篇
石油天然气   2篇
武器工业   1篇
无线电   138篇
一般工业技术   202篇
冶金工业   432篇
原子能技术   33篇
自动化技术   241篇
  2023年   5篇
  2022年   16篇
  2021年   18篇
  2020年   13篇
  2019年   23篇
  2018年   33篇
  2017年   38篇
  2016年   46篇
  2015年   38篇
  2014年   53篇
  2013年   80篇
  2012年   70篇
  2011年   104篇
  2010年   64篇
  2009年   77篇
  2008年   86篇
  2007年   67篇
  2006年   63篇
  2005年   57篇
  2004年   48篇
  2003年   43篇
  2002年   42篇
  2001年   26篇
  2000年   28篇
  1999年   30篇
  1998年   124篇
  1997年   89篇
  1996年   49篇
  1995年   47篇
  1994年   34篇
  1993年   37篇
  1992年   25篇
  1991年   17篇
  1990年   12篇
  1989年   13篇
  1988年   5篇
  1987年   11篇
  1986年   11篇
  1985年   15篇
  1984年   15篇
  1983年   12篇
  1982年   9篇
  1981年   13篇
  1980年   8篇
  1979年   8篇
  1978年   7篇
  1977年   6篇
  1976年   20篇
  1971年   4篇
  1968年   5篇
排序方式: 共有1778条查询结果,搜索用时 265 毫秒
61.
This paper presents a novel and useful spatial modelling technique to create a topographic surface that estimates a floodplain's elevation relative to the average low-flow water surface elevation of a river channel. This model was applied to a 121 km study area of the middle Sacramento River, California, USA, where it was tested as a surrogate for observed water table depth and an observed 3.3 year recurrence interval flood inundation surface using independent data sets. The modelled relative elevation topographic surface correlated significantly (p < 0.005) to observed well water depths suggesting that the modelled surface reflected a reasonable approximation of vertical distance to the water table. Results from a flood inundation pattern analysis indicated an overall accuracy of 79% for correctly predicting inundated and non-inundated zones. The model was then used to measure relative channel bank height and the distribution of riparian plant communities to examine landscape ecological relationships.  相似文献   
62.
Oil from the marine copepod, Calanus finmarchicus, which contains >86 % of fatty acids present as wax esters, is a novel source of n‐3 fatty acids for human consumption. In a randomized, two‐period crossover study, 18 healthy adults consumed 8 capsules providing 4 g of Calanus® Oil supplying a total of 260 mg EPA and 156 mg DHA primarily as wax esters, or 1 capsule of Lovaza® providing 465 mg EPA and 375 mg DHA as ethyl esters, each with an EPA‐ and DHA‐free breakfast. Plasma EPA and DHA were measured over a 72 h period (t = 1, 2, 4, 6, 8, 10, 12, 24, 48, and 72 h). The positive incremental area under the curve over the 72 h test period (iAUC0‐72 h) for both EPA and DHA was significantly different from zero (p < 0.0001) in both test conditions, with similar findings for the iAUC0–24 h and iAUC0–48 h, indicating the fatty acids were absorbed. There was no difference in the plasma iAUC0–72 h for EPA + DHA, or DHA individually, in response to Calanus Oil vs the ethyl ester condition; however, the iAUC0–48 h and iAUC0–72 h for plasma EPA in response to Calanus Oil were both significantly increased relative to the ethyl ester condition (iAUC0–48 h: 381 ± 31 vs 259 ± 39 μg*h/mL, p = 0.026; iAUC0‐72 h: 514 ± 47 vs 313 ± 49 μg*h/mL, p = 0.009). These data demonstrate a novel wax ester rich marine oil is a suitable alternative source of EPA and DHA for human consumption.  相似文献   
63.
Graphite oxide (GO) produced by Hummers method was added to epoxy for strengthening purpose. Generally the E‐modulus was increased due to the GO addition; however, depending on the treatment of the GO an increase or decrease was observed for the glass transition temperature. The change in glass transition was a result of changes in the curing behavior. Addition of GO initially increased the curing speed; however, the final curing degree was lower and was dependent on the type of GO added. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43591.  相似文献   
64.
Although the selective excitatory amino acid transporter subtype 1 (EAAT1) inhibitor UCPH‐101 has become a standard pharmacological tool compound for in vitro and ex vivo studies in the EAAT research field, its inability to penetrate the blood–brain barrier makes it unsuitable for in vivo studies. In the present study, per os (p.o.) administration (40 mg kg?1) of the closely related analogue UCPH‐102 in rats yielded respective plasma and brain concentrations of 10.5 and 6.67 μm after 1 h. Three analogue series were designed and synthesized to improve the bioavailability profile of UCPH‐102, but none displayed substantially improved properties in this respect. In vitro profiling of UCPH‐102 (10 μm ) at 51 central nervous system targets in radioligand binding assays strongly suggests that the compound is completely selective for EAAT1. Finally, in a rodent locomotor model, p.o. administration of UCPH‐102 (20 mg kg?1) did not induce acute effects or any visible changes in behavior.  相似文献   
65.
We analyzed the effect of modified nucleotides within gapmer antisense oligonucleotides on RNase H mediated gene silencing. Additionally, short hairpins were introduced into antisense oligonucleotides as structural motifs, and their influence on biological and physicochemical properties of pre-structured gapmers was investigated for the first time. The results indicate that two LNA residues in specified positions of the gap flanking regions are sufficient and favorable for efficient knock-down of the β-actin gene. Furthermore, the introduction of other modified nucleotides, i. e. glycyl-amino-LNA−T, 2′-O-propagyluridine, polyamine functionalized uridine, and UNA, in specified positions, also increases the inhibition of β-actin expression. Importantly, the presence of hairpins within the gapmers improves their silencing properties.  相似文献   
66.
Lipoprotein lipase (LPL) activity and free fatty acid levels were studied in freshly milked, uncooled milk from individual Danish Holstein or Jersey cows, or after storage for up to 24 h at either a cooling temperature (4°C) or at the milking temperature (31°C). Upon cooling for up to 24 h, LPL activity increased in the cream phase, whereas the activity in the skim milk was steady, as observed for Jersey cows, or increased, as seen for the Holsteins. Storage at 31°C decreased the LPL activity in both the cream phase and the skim milk phase. The increase in free fatty acid levels was found to depend on LPL activity, incubation temperature, substrate availability, and incubation time. Furthermore, the migration of milk proteins between the skim milk phase and the cream phase upon cooling of milk from Jersey cows or from Danish Holstein cows was studied using proteomic methods involving 2-dimensional gel electrophoresis and mass spectrometry. Proteins associated with the milk fat globules were isolated from all milk fractions and analyzed. Major changes in the distributions of proteins between the skim milk phase and the cream phase were observed after cooling at 4°C for 4 h, where a total of 29 proteins between the 2 breeds was found to change their association with the milk fat globule membrane (MFGM) significantly. Among these, the MFGM proteins adipophilin, fatty acid-binding protein, and lactadherin, as well as the non-MFGM proteins β-casein, lactoferrin, and heat shock protein-71, were identified. Adipophilin, lactadherin, and lactoferrin were quantitatively more associated with the MFGM upon cold storage at 4°C, whereas β-casein, fatty acid-binding protein, and heat shock protein-71 were found to be less associated with the MFGM upon cold storage.  相似文献   
67.
One potential way of preventing parturient hypocalcemia in the dairy cow is to feed dry cow rations very low in calcium (<20 g/d); but, because it is difficult to formulate rations sufficiently low in calcium, this principle has been almost abandoned. Recent studies have shown, however, that it is possible to prevent milk fever, as well as subclinical hypocalcemia, by supplementing the dry cow ration with sodium aluminium silicate (zeolite A), which has the capacity to bind calcium. The aim of this study was to further evaluate the effect, if any, of such supplementation on other blood constituents, feed intake, and milk production in the subsequent lactation. A total of 31 pregnant dry cows about to enter their third or later lactation were assigned as experimental or control cows according to parity and expected date of calving. The experimental cows received 1.4 kg of zeolite pellets per d (0.7 kg of pure zeolite A) for the last 2 wk of pregnancy. Blood samples were drawn from all cows 1 wk before the expected date of calving, at calving, at d 1 and 2 after calving, and 1 wk after calving. Additionally, a urine sample was drawn 1 wk before the expected date of calving. Zeolite supplementation significantly increased the plasma calcium level on the day of calving, whereas plasma magnesium as well as inorganic phosphate was suppressed. Serum 1,25(OH)2D was significantly increased 1 wk before the expected date of calving among the experimental cows, whereas there was no difference in the urinary excretion of the bone metabolite deoxypyridinoline between the two groups. Feed intake was decreased among the zeolite-treated cows during the last 2 wk of pregnancy. No effect was observed on milk yield, milk fat, and milk protein in the subsequent lactation. The mechanisms and interactions involved in zeolite supplementation are discussed in relation to the observed improvement in parturient calcium homeostasis and to the observed depression in blood magnesium and inorganic phosphate.  相似文献   
68.
In an effort to purify potato proteins of superior food grade quality, a new procedure involving anion exchange (ion exchange (IEX)) and hydrophobic interaction chromatography (HIC) was established. Liquid potato fruit juice (PFJ) or re-suspended spray-dried protein was separated by IEX yielding two fractions: a protease inhibitor (PI)-rich fraction and a patatin-rich fraction. Each of these fractions was re-chromatographed on HIC, resulting in two new sub-fractions which were characterised by electrophoresis and mass spectrometry. A high-quality powder should have high lightness, low polyphenol oxidase (PPO) activity and glycoalkaloid content below 150 μg/g. The PI fraction from spray-dried powder had high lightness (L* = 83) compared to patatin (L* = 50), whereas IEX purification from PFJ resulted in a PI fraction with decreased lightness (L* = 66) and a patatin fraction with increased lightness (L* = 68). HIC fractionation led to increased lightness for patatin fraction, but decreased lightness for the PFJ PI fractions. HIC purification significantly lowered PPO activity in the fractions due to its selective affinity. The lowest total glycoalkaloid content was generally found in HIC fractions from spray-dried powder (150 μg/g), while high levels (>1000 μg/g) were found in PI fractions from PFJ. In conclusion, it was possible to obtain a PI-rich protein isolate from powder with good-quality attributes after both IEX and HIC, while for patatin, the best quality was obtained after the HIC only, and there, the colour or PPO activity may still be a problem depending on source material.  相似文献   
69.
Farmed New Zealand King Salmon (Oncorhynchus tshawytscha) was prepared according to common consumer techniques; raw, poached, steamed, microwaved, pan fried (no added oil), oven baked (no added oil) and deep fried (in sunflower oil). The fatty acid profile was investigated to determine the optimal preparation techniques to achieve both optimal sensory and nutritional qualities, in particular the levels of long chain polyunsaturated omega-3 fatty acids. The modified Bligh and Dyer method was used for lipid extraction and the Hartman and Lago method for FAMES preparation. Fatty acid composition was determined by gas chromatography. There were moisture and lipid losses during cooking amongst the different methods. The fatty acid profile showed only minor differences between the methods apart from an increase in PUFA in the deep fried salmon due to linoleic acid uptake from the frying oil. In all the cooking methods the omega-3 fatty acids were well preserved. However, deep fried showed the lowest amounts of omega-3 fatty acids. As the results showed good preservation of omega-3 fatty acids regardless of cooking method, there may be possible “internal protection” of omega-3 fatty acids in King Salmon that warrants future research.  相似文献   
70.
We have studied the rate of methanol formation over Cu(100) and Ni/Cu(100) from various mixtures of CO, CO2 and H2. It is found that the presence of submonolayer quantities of Ni leads to a strong increase in the rate of methanol formation from mixtures containing all three components whereas Ni does not influence the rate from mixtures of CO2/H2 and CO/H2, respectively. The influence of the partial pressures of CO and CO2 on the rate indicates that the role of CO is strictly promoting. From temperature-programmed desorption spectra it follows that the surface concentration of Ni depends strongly on the partial pressure of CO. In this way the increase in reactivity is interpreted as a CO-induced structural promotion introduced by the stronger bonding of CO to Ni as compared to Cu. It is suggested that this type of promotional behavior will be of general importance in existent catalysts and perhaps even more relevant in the development of new or improved bimetallic catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号