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   540篇
  免费   14篇
综合类   1篇
化学工业   211篇
金属工艺   8篇
机械仪表   10篇
建筑科学   18篇
能源动力   15篇
轻工业   116篇
水利工程   3篇
石油天然气   1篇
无线电   14篇
一般工业技术   79篇
冶金工业   39篇
原子能技术   10篇
自动化技术   29篇
  2023年   3篇
  2022年   10篇
  2021年   23篇
  2020年   9篇
  2019年   8篇
  2018年   7篇
  2017年   11篇
  2016年   9篇
  2015年   6篇
  2014年   13篇
  2013年   34篇
  2012年   31篇
  2011年   30篇
  2010年   16篇
  2009年   25篇
  2008年   35篇
  2007年   30篇
  2006年   30篇
  2005年   27篇
  2004年   33篇
  2003年   24篇
  2002年   21篇
  2001年   10篇
  2000年   7篇
  1999年   9篇
  1998年   18篇
  1997年   11篇
  1996年   6篇
  1995年   5篇
  1994年   4篇
  1993年   6篇
  1992年   3篇
  1991年   7篇
  1990年   2篇
  1989年   5篇
  1988年   1篇
  1987年   2篇
  1986年   7篇
  1984年   4篇
  1983年   1篇
  1982年   1篇
  1980年   2篇
  1979年   2篇
  1976年   1篇
  1975年   1篇
  1973年   1篇
  1972年   1篇
  1969年   2篇
排序方式: 共有554条查询结果,搜索用时 15 毫秒
411.
Using an experimentally induced cooperation task, the authors investigated whether tufted capuchin monkeys (Cebus apella) share the following 3 characteristics of cooperation with humans: division of labor, communication, and reciprocal altruism. In Experiment 1, the authors trained individual monkeys to perform the necessary sequence of actions for rewards and tested them in pairs to assess whether they could solve the task by spontaneously dividing the sequence of actions. All pairs solved this task. In Experiment 2, monkeys worked in the cooperation task and a task requiring no partner help. They looked at the partner significantly longer in the former task than in the latter, but communicative intent could not be determined. In Experiment 3, only 1 of 2 participants obtained a reward on each trial. Monkeys maintained cooperation when their roles were reversed on alternate trials. Their cooperative performances demonstrated division of labor; results suggest task-related communication and reciprocal altruism. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
412.
The aim of this study was to investigate the effect of a high volume of roof-tile waste coarse aggregate (5–13 mm) as an internal curing agent on the compressive strength, modulus of elasticity, pore structure, and hydration and pozzolanic reactions in paste of fly-ash concrete with a low water-to-binder ratio of 0.30. The fly-ash concrete specimens in which the replacement ratio of cement by Class-F fly ash was 40% by mass and that of normal coarse aggregate by roof-tile waste aggregate was 40% by volume, were cured up to 728 days. Internal curing with roof-tile waste aggregate increased the compressive strength of the fly-ash concrete by 8.4–16.5% and decreased the modulus of elasticity by 4.9–12.8%. The use of a high volume of waste aggregate decreased the volume of the capillary pores in the 0.01–10 µm range and the volume proportion of the 0.02–0.33-µm pores after 28 days, but increased the volume proportion of 0.003–0.02-µm pores slightly at 7 days and significantly up to 728 days, and the consumption of Ca(OH)2 in the fly-ash concrete. This roof-tile waste aggregate can be used as an internal water reservoir to increase the compressive strength and to improve the pore structure of concrete with a high-volume (40%) replacement of Class-F fly ash.  相似文献   
413.
1,1,3,3-tetramethylguanidium (TMG) salt of alpha-cyano-4-hydroxycinnamic acid (CHCA) (G(2)CHCA) was reported by Tatiana et al. as a useful ionic liquid matrix (ILM) for sulfated oligosaccharides to suppress the loss of sulfate groups. However, the report mainly referred to positive ion spectra only and amounts of 10 pmol or more of the analyte were used. Herein, we demonstrated highly sensitive detection of sulfated/sialylated/neutral oligosaccharides and preferential ionization of glycopeptides by optimizing a newly synthesized ILM: TMG salt of p-coumaric acid (G(3)CA) and the existing G(2)CHCA in both positive and negative ion extraction modes. Sulfated oligosaccharides were detected with high sensitivity (e.g., 1 fmol) in both ion extraction modes, and the dissociation of sulfate groups was suppressed especially using G(3)CA. Sialylated and neutral oligosaccharides were also detected with high sensitivity (e.g., 1 fmol) with positive ion extraction while the dissociation of sialic acids was suppressed especially using G(3)CA. Additionally, glycopeptide ions were detected preferentially using the ILMs among the digest of a glycoprotein, ribonuclease B, in both ion extraction modes but particularly in the negative ion mode. As a result, the use of optimized ILMs provides an effective method for carbohydrate analysis due to the highly sensitive soft-ionization achieved in both ion extraction modes as well as the homogeneity of analyte-matrix mixtures.  相似文献   
414.
Today, two-dimensional mass spectrometry analysis of biological tissues by means of a technique called mass imaging, mass spectrometry imaging (MSI), or imaging mass spectrometry (IMS) has found application in investigating the distribution of moleculesMSI with matrix-assisted laser desorption/ionization (MALDI) and secondary ion MS (SIMS). However, the size of the matrix crystal and the migration of analytes can decrease the spatial resolution in MALDI, and SIMS can only ionize compounds with relatively low molecular weights. To overcome these problems, we developed a nanoparticle-assisted laser desorption/ionization (nano-PALDI)-based MSI. We used nano-PALDI MSI to visualize lipids and peptides at a resolution of 15 microm in mammalian tissues.  相似文献   
415.
The extraction of Eu(III) with β-diketone, HA, and monodentate or bidentate Lewis bases, B, into chloroform and the luminescence properties of the extracted species were studied. Pivaloyltrifluoroacetone, Hpta, and 2-thenoyltrifluoroacetone, Htta, were used as the β-diketones. The Lewis bases, B, were tetraethyl methylene diphosphonate, POPO, which was bidentate, and diethyl benzylphosphonate, PhPO which was monodentate. Based on the extraction data, the stability constants, log β of the first complexes between tris(β-diketonato)Eu(III) and the phosphonate, EuA3B, were determined to be 6.0 for the POPO complex and 3.40 for the PhPO complex. The Eu(III) luminescence intensity in the EuA3POPO was larger than EuA3 where A was either pta or tta at similar concentrations of Eu(III), while that in Eu(pta)3PhPO was stronger than EuA3; however, in Eu(tta)3PhPO, it was weaker than Eu(tta)3. The POPO functions as a sensitizer, and the PhPO functions as a quencher for the tta chelate and as a sensitizer for the pta chelate. From the lifetime and quantum yield, φ, of the Eu(III) luminescence in the complexes as well as the observation of the extractability of Eu(III) with the Hpta and the phosphonates and of the luminescence spectra of the complexes, it was confirmed that the extraction of Eu(III) was remarkably enhanced with a β-diketonate and a strong Lewis base, and also the ternary complex that was formed as the extracted species, showed luminescence enhancement. This phenomenon may be due the formation of a strong bond between the Eu(III) and the strong Lewis base leading to more hydrophobicity in the extracted species and also to more effective energy transfer from the Lewis base to the Eu(III). It was not significant whether the donor atoms were N or O.  相似文献   
416.
Nanotechnologies to allow the nondisruptive introduction of carriers in vivo have wide potential for therapeutic delivery system. We have prepared functional nano-magnetic particles (d = 3 nm) by silanization with (3-aminopropyl) triethoxysilane. For the purpose of functionalizing the surface of the nanoparticles with amino groups for subsequent cross-linking with pharmaceuticals and biomolecules. The extremely small particles were successfully introduced into living cells without any further modification to enhance endocytic internalization, such as the use of a cationic help. The cells containing the internalized particles continued to thrive, indicating that the particles have no inhibition effect for mitosis. In addition, the particles could be incorporated into the subcutaneous tissue of mouse's ear from ear skin and were able to be localized upon application of an external magnetic field. The functionalized nano-magnetic particles are expected to be useful as a new delivery tool.  相似文献   
417.
An efficient stereocontrolled synthesis afforded alkoxymethylenephosphonate (MP) analogues of lysophosphatidic acid (LPA) and phosphatidic acid (PA). The pharmacological properties of MP-LPA and MP-PA analogues were characterized for LPA receptor subtype-specific agonist and antagonist activity using Ca(2+)-mobilization assays in RH7777 cells expressing the individual LPA(1)-LPA(3) receptors and CHO cells expressing LPA(4). In addition, activation of a PPARgamma reporter gene construct expressed in CV-1 cells was assessed. These metabolically stabilized LPA analogues exhibited an unexpected pattern of partial agonist/antagonist activity for the LPA G-protein-coupled receptor family and the intracellular LPA receptor PPARgamma. Analogues were compared with 18:1 LPA for activation of downstream signaling in HT-29 colon cancer cells, which exclusively express LPA(2), and both SKOV3 and OVCAR3 ovarian cancer cells, which express LPA(1), LPA(2), and LPA(3). Unexpectedly, reverse phase protein arrays showed that four MP-LPA and MP-PA analogues selectively activated downstream signaling in HT-29 cells with greater potency than LPA. In particular, the oleoyl MP-LPA analogue strongly promoted phosphorylation and activation of AKT, MEK, and pS6 in HT-29 cells in a concentration-dependent manner. In contrast, the four MP-LPA and MP-PA analogues were equipotent with LPA for pathway activation in the SKOV3 and OVCAR3 cells. Taken together, these results suggest that the MP analogues may selectively activate signaling via the LPA(2) receptor subtype, while simultaneously suppressing signaling through the LPA(1) and LPA(3) subtypes.  相似文献   
418.
Complex hydrides for hydrogen storage   总被引:5,自引:0,他引:5  
  相似文献   
419.
Minami Y  Yokoi S  Setoyama M  Bando N  Takeda S  Kawai Y  Terao J 《Lipids》2007,42(11):1055-1063
We have established a sensitive and convenient method for analysis of cholesterol hydroperoxides (Chol-OOHs) as trimethylsilyloxyl derivatives using diphenylpyrenylphosphine (DPPP)-thin-layer chromatography (TLC) blotting and gas chromatography–electron ionization–mass spectrometry/selected-ion monitoring (GC–EI–MS/SIM). Chol-OOH standards were prepared by photosensitized oxidation and azo radical-induced peroxidation of cholesterol. Trimethylsilyloxyl derivatives of cholesterol 5α-hydroperoxide (Chol 5α-OOH), cholesterol 7α-hydroperoxide (Chol 7α-OOH), and cholesterol 7β-hydroperoxide (Chol 7β-OOH) could be separated from one another in the SIM chromatogram using a fragment ion with elimination of trimethylsilanol from the molecular ion. This method was used to characterize peroxidized cholesterol from azo radical-exposed human low-density lipoprotein and UVA-irradiated human keratinocytes in the presence of hematoporphyrin. Finally, we succeeded in the quantification of each Chol-OOH isomer present in hairless mouse skin with and without UVA irradiation by use of β-sitosterol hydroperoxide as internal standard. The accumulation of Chol 5α-OOH with Chol 7α/βOOH in the skin indicates that singlet molecular oxygen (1O2) participated in the peroxidation of skin cholesterol, because Chol 5α-OOH is known to be a 1O2 specific cholesterol peroxidation product. We concluded that the combination of DPPP-TLC blotting and GC–EI–MS/SIM is useful for quantifying peroxidized cholesterol in biological samples and confirming the participation of 1O2 in oxidative stress.  相似文献   
420.
Male Wistar rats were fed ad libitum for 12 weeks a powdered diet (AIN93G; no fat) containing 7 wt% of fresh oil (control), and frying oils heated for 20 h at 180 degrees C with amino acids, gluten, sugar, and wheat starch, respectively. The rats were subjected to anthropometric measurements, hematological analyses, and observations of the liver and kidneys. All of the rats grew well, and no gross symptoms attributable to the experimental oils were observed. The serum of all the experimental groups showed a tendency toward lower levels of triacylglycerol and free fatty acids and higher levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) than that of the control group. Among experimental groups, the rats fed a diet containing oil heated with gluten were least influenced by thermally deteriorated oil in terms of serum levels of glucose, triacylglycerol, phospholipids, cholesterol, and insulin; histological evaluations; and number of dark-red patches found on the surface of the liver.  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