全文获取类型
收费全文 | 9629篇 |
免费 | 933篇 |
国内免费 | 452篇 |
学科分类
工业技术 | 11014篇 |
出版年
2024年 | 41篇 |
2023年 | 146篇 |
2022年 | 266篇 |
2021年 | 375篇 |
2020年 | 294篇 |
2019年 | 267篇 |
2018年 | 287篇 |
2017年 | 316篇 |
2016年 | 336篇 |
2015年 | 372篇 |
2014年 | 451篇 |
2013年 | 653篇 |
2012年 | 564篇 |
2011年 | 605篇 |
2010年 | 516篇 |
2009年 | 513篇 |
2008年 | 472篇 |
2007年 | 429篇 |
2006年 | 440篇 |
2005年 | 397篇 |
2004年 | 262篇 |
2003年 | 248篇 |
2002年 | 218篇 |
2001年 | 178篇 |
2000年 | 175篇 |
1999年 | 195篇 |
1998年 | 519篇 |
1997年 | 316篇 |
1996年 | 209篇 |
1995年 | 161篇 |
1994年 | 126篇 |
1993年 | 143篇 |
1992年 | 42篇 |
1991年 | 60篇 |
1990年 | 40篇 |
1989年 | 45篇 |
1988年 | 39篇 |
1987年 | 27篇 |
1986年 | 23篇 |
1985年 | 21篇 |
1984年 | 16篇 |
1983年 | 10篇 |
1982年 | 17篇 |
1981年 | 17篇 |
1980年 | 24篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 41篇 |
1976年 | 56篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
OBJECTIVE: Microvascular pericytes may contract in two different ways: In the first, a circumferential or radial mechanical force applied at right angles to the long axis of the vessel may constrict the underlying vessel affecting blood flow and transmural pressure. Retraction and elongation of pericyte processes may also occur tangentially and at right angles to the vessel axis and alter microvessel permeability by changing the amount of ablumenal surface covered or the openness of interendothelial junctions. In this study, cultured pericytes were utilized as a model experimental system to determine if vasoactive stimulation changes their shape in a manner consistent with this hypothesis. METHODS: Pericytes cultured from isolated rate capillaries were subjected to angiotensin II and histamine. Their response was monitored by measuring the area of non-yielding substrate covered by the pericytes and the manner in which their shape changed. Shape changes were quantified by calculating the surface area: perimeter perimeter ratios. RESULTS: Histamine significantly reduced surface area covered and the surface area:perimeter ratio. The pericyte processes retracted, resulting in elongated, spindle-shaped cells. These effects were nullified by the H1 blocker diphenhydramine suggesting a receptor-specific response. Angiotensin II also elicited contraction and reduced surface area, but the cells contracted laterally and longitudinally. The surface area: perimeter ratios also decreased. CONCLUSIONS: These results indicate that pericytes are capable of two types of contractile responses in culture, depending on the specific vasoactive stimulus. 相似文献
23.
24.
Han-Jun Oh Jong-Ho Lee Hong-Joo Ahn Yongsoo Jeong Chang-Hoe Heo Choong-Soo Chi 《Journal of Electroceramics》2006,17(2-4):369-373
The characteristics and growth behaviors of alumina dielectric layer formed by anodic oxidation were investigated. The aluminum oxide layer anodized at 400 V was predominantly amorphous alumina, but at the applied potentials more than 500 V, amorphous and crystalline γ-alumina were existed in anodic oxide layer and the ratio of γ-alumina increased with the increasing applied potential. During the heat treatment at 600°C or higher temperature, amorphous alumina layer was transformed into the crystalline γ-alumina. The phase transition of anodic amorphous alumina into crystalline depends on anodic applied potentials and heat-treatment temperatures. 相似文献
25.
Ching‐Nan Chuang Liang Chao Ying‐Jie Huang Tar‐Hwa Hsieh Hung‐Yi Chuang Shu‐Chi Lin Ko‐Shan Ho 《应用聚合物科学杂志》2008,107(6):3917-3924
The synthesis of a p‐toluidine/formaldehyde (PTF) resin was performed, and the effects of the molar ratio of the individual monomers and the polymerization conditions on the structure of the PTF resin were studied. Fourier transform infrared and 13C‐NMR spectra were used to characterize the PTF. Wide‐angle X‐ray diffraction patterns revealed the crystalline structures of various PTFs. Polarized optical microscopy revealed that the molar ratio of the monomers had a strong effect on the crystalline morphologies. A longer polymerization time turned out a polymer with a higher intrinsic viscosity and molecular weight, which led to differences in the proton conductivity. All of the PTFs showed a higher proton conductivity than a commercial Nafion membrane at 90–100°C and 0% relative humidity. The proton conductivity of the PTF series could be improved by sulfonation with sulfuric acid and could be maintained after blending with polyurethane. Pure methanol could be used as a fuel source because of the insolubility and nonwetting properties of PTF in methanol to increase the output current density for a PTF membrane electrode assembly. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008 相似文献
26.
Using chloroform/dimethylformamide (CF/DMF) co-solvent, electrospinning of poly[(R)-3-hydroxybutyrate] (PHB) solutions was carried out at ambient temperature. The effects of the applied voltage (V), flow-rate (Q), and solution viscoelastic properties on the Taylor cone, electrified jet, and fiber morphology were investigated. In addition, the electric field developed by the needle-plate electrode configuration was calculated using a finite element analysis to reveal the tip-to-collector (H) effect. Among the processing parameters (V, Q and H), it was found that Q played a key role in determining the jet diameter (dj) and electrospun fiber diameter (df), and scaling laws existed between them, i.e., dj-Q0.61 and df-Q0.33. The diameter reduction ratios of Do/dj (Do is the needle diameter) and dj/df were measured as 50-120 and 5-10, respectively; it suggested that major jet stretching took place in the straight electrified jet region, and further chain orientation could be gained by the subsequent process of jet whipping. By changing PHB concentrations from 5 to 15 wt%, the solution viscosity (ηo) was increased from 100 to 4900 cP, whereas the surface tension and solution conductivity remained unchanged; it provided a good model solution to exclusively reveal the ηo effect on the electrospinning process. Our results showed that the ηo-dependence of dj and df also followed simple scaling laws: dj-ηo0.06, and df-ηo0.39, with a prefactor depending on the processing variables, mainly the flow-rate. Regardless of the PHB concentrations used, the obtained PHB fibers showed a similar crystallinity fraction of ca. 0.63 and possession of major α-crystals together with a small amount of β-crystals with zigzag chain conformation. 相似文献
27.
The effect of end groups (2NH2) of poly(ethylene glycol) (PEG) on the miscibility and crystallization behaviors of binary crystalline blends of PEG/poly(L ‐lactic acid) (PLLA) were investigated. The results of conductivity meter and dielectric analyzer (DEA) implied the existence of ions, which could be explained by the amine groups of PEG gaining the protons from the carboxylic acid groups of PLLA. The miscibility of PEG(2NH2)/PLLA blends was the best because of the ionic interaction as compared with PEG(2OH, 1OH‐1CH3, and 2CH3)/PLLA blends. Since the ionic interaction formed only at the chain ends of PEG(2NH2) and PLLA, unlike hydrogen bonds forming at various sites along the chains in the other PEG/PLLA blend systems, the folding of PLLA blended with PEG(2NH2) was affected in a different manner. Thus the fold surface free energy played an important role on the crystallization rate of PLLA for the PEG(2NH2)/PLLA blend system. PLLA had the least fold surface free energy and the fast crystallization rate in the PEG(2NH2)/PLLA blend system, among all the PEG/PLLA systems studied. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
28.
Han‐Lang Wu Chen‐Chi M. Ma Chun‐Chieh Lin Yie‐Chan Chiu Chih‐Yuan Chen Chin‐Lung Chiang 《应用聚合物科学杂志》2008,107(5):3236-3243
Poly(arylene ether benzonitrile) (PAEBN) was synthesized with 2,6‐dichlorobenzonitrile and biphenol. PAEBNs with various molecular weights (MWs), 1,640,000 and 185,000 g/mol, were synthesized by control of the stoichiometry of the monomers and were blended with sulfonated poly(ether ether ketone) (SPEEK). The effects of MW on the water uptake, swelling, methanol permeability, and proton conductivity of the SPEEK/PAEBN blend membranes were investigated. The molecular mobility of the SPEEK/PAEBN blends was also examined in this study. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
29.
30.
An initial Bentall operation was performed on a patient aged 38 years with annuloaortic ectasia and aortic regurgitation. An echocardiogram and RI angiogram revealed a perigraft aortic aneurysm on the same patient aged 45 years. The aneurysm gradually developed and the maximum diameter reached 90 mm in size. The Redo-Bentall operation (Piehler modification) was successfully done once again on the same patient aged 56 years. The anastmosis between the right coronary orifice and the graft was detached on all sides. The anastmosis between the left coronary orifice and the graft was detached two thirds of all sides. 相似文献