全文获取类型
收费全文 | 37104篇 |
免费 | 3870篇 |
国内免费 | 1631篇 |
专业分类
电工技术 | 1916篇 |
综合类 | 1572篇 |
化学工业 | 10149篇 |
金属工艺 | 2335篇 |
机械仪表 | 1754篇 |
建筑科学 | 727篇 |
矿业工程 | 348篇 |
能源动力 | 8115篇 |
轻工业 | 3103篇 |
水利工程 | 182篇 |
石油天然气 | 274篇 |
武器工业 | 157篇 |
无线电 | 3661篇 |
一般工业技术 | 4638篇 |
冶金工业 | 1096篇 |
原子能技术 | 371篇 |
自动化技术 | 2207篇 |
出版年
2024年 | 56篇 |
2023年 | 753篇 |
2022年 | 981篇 |
2021年 | 2179篇 |
2020年 | 1540篇 |
2019年 | 1481篇 |
2018年 | 1273篇 |
2017年 | 1540篇 |
2016年 | 1455篇 |
2015年 | 1403篇 |
2014年 | 2220篇 |
2013年 | 2481篇 |
2012年 | 2474篇 |
2011年 | 3309篇 |
2010年 | 2477篇 |
2009年 | 2228篇 |
2008年 | 2217篇 |
2007年 | 2174篇 |
2006年 | 1891篇 |
2005年 | 1468篇 |
2004年 | 1251篇 |
2003年 | 989篇 |
2002年 | 885篇 |
2001年 | 665篇 |
2000年 | 484篇 |
1999年 | 398篇 |
1998年 | 356篇 |
1997年 | 282篇 |
1996年 | 230篇 |
1995年 | 255篇 |
1994年 | 208篇 |
1993年 | 173篇 |
1992年 | 161篇 |
1991年 | 127篇 |
1990年 | 95篇 |
1989年 | 86篇 |
1988年 | 56篇 |
1987年 | 43篇 |
1986年 | 37篇 |
1985年 | 52篇 |
1984年 | 36篇 |
1983年 | 24篇 |
1982年 | 45篇 |
1981年 | 16篇 |
1980年 | 15篇 |
1979年 | 13篇 |
1978年 | 5篇 |
1975年 | 6篇 |
1973年 | 2篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
71.
Material encapsulation is a relatively new technique for coating a micro/nanosize particle or droplet with polymeric or inorganic shell. Encapsulation technology has many applications in various fields including drug delivery, cosmetic, agriculture, thermal energy storage, textile, and self-healing polymers. Poly(methyl methacrylate) (PMMA) is widely used as shell material in encapsulation due to its high chemical stability, biocompatibility, nontoxicity, and good mechanical properties. The main approach for micro/nanoencapsulation of materials using PMMA as shell comprises emulsion-based techniques such as emulsion polymerization and solvent evaporation from oil-in-water emulsion. In the present review, we first focus on the encapsulation techniques of liquid materials with PMMA shell by analyzing the effective processing parameters influencing the preparation of PMMA micro/nanocapsules. We then describe the morphology of PMMA capsules in emulsion systems according to thermodynamic relations. The techniques to investigation of mechanical properties of capsule shell and the release mechanisms of core material from PMMA capsules were also investigated. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48039. 相似文献
72.
《中国稀土学报(英文版)》2019,37(11):1183-1187
Upconversion nanophosphors are new promising nanomaterials to be used as biolabels for detection and imaging of cancer cells.These nanophosphors absorb long-wavelength excitation radiation in the infrared or near infrared region and emit shorter wavelength,higher energy radiation from ultraviolet to infrared.In this paper,we studied the hydrothermal method and optical properties of the functionalized NaYF_4:Yb~(3+),Er~(3+)for biomedical application.After synthesis,these NaYF_4:Yb~(3+),Er~(3+)nanophosphors were functionalized with aminosilanes and folic acid.Folic acid binds to the folate receptor on the surface of MCF-7 breast cancer cells and this binding promotes internalization of the nanophosphors via endocytosis.The sizes of the functionalized NaYF_4:Yb~(3+),Er~(3+)@silica-N=FA(folic acid) nanophosphors can be controlled with length of the rod about 300-800 nm and diameter of the rod about 100-200 nm.Phase structure of NaYF_4:Yb~(3+),Er~(3+)is in hexagonal crystal system.The photo luminescence(PL) spectra of the functionalized NaYF_4:Yb~(3+),Er~(3+)@silica-N=FA nanophosphors were measured.These nanophosphors emit in red color with the strongest band at 650 nm under 980 nm excitation.This result can provide NaYF_4:Er~(3+),Yb~(3+)@silica-N=FA complex for developing fluorescence label and image tool in cancer biology and medicine. 相似文献
73.
Kaoru Uesugi Yui Sakuma Yoshitake Akiyama Yoshikatsu Akiyama Kikuo Iwabuchi Teruo Okano 《Advanced Robotics》2019,33(5):219-231
ABSTRACTFor the first time, we have fabricated insect-derived cell sheets by using temperature-responsive culture surfaces having a phase-transition temperature below 25°C. We prepared the temperature-responsive cell culture surfaces (tissue culture polystyrene, TCPS) by grafting a copolymeric gel consisting of hydrophobic N-tert-butylacrylamide (tBAAm) and N-isopropylacrylamide (IPAAm) units. First, to characterize the hydrophilic and hydrophobic properties of the copolymeric gel-grafted surfaces, static water contact angles of each surface were measured at various temperatures. By increasing the amount of tBAAm in the grafted copolymeric gel, the transition temperature of the gel was shifted to lower temperatures. At 25°C, the grafted copolymeric gel was dehydrated, and the insect-derived cells (AeAl2 cells) adhered on all the copolymeric gel-grafted surfaces. At 20°C, AeAl2 cells cannot adhere on the P(IPAAm-1.62tBAAm)-TCPS surface (the initial molar ratio of IPAAm and tBAAm (tBAAm?=?1.62 mol%)) better than on other surfaces (TCPS and tBAAm?=?4.88, 8.17 mol%). These two findings implied that the lower critical solution temperature of the copolymeric gel-grafted-TCPS existed from 20°C to 25°C. The laminin-coated P(IPAAm-1.62tBAAm)-TCPS surface showed temperature-dependent cell attachment and detachment properties, while AeAl2 cells were not detached from the extracellular matrix uncoated P(IPAAm-1.62tBAAm)-TCPS surface. AeAl2 cells and insect muscle cells were harvested as the respective sheets. 相似文献
74.
Multiple degrees‐of‐freedom (multi‐DOF) cell orientation control is a vital important technique involved in single cell surgery applications. Currently, few studies have been performed toward automation of multi‐DOF cell orientation control using robotically controlled optical tweezers. In this paper, a robust control framework is developed to perform multi‐DOF cell rotational control with consideration of model uncertainties and external disturbances. Both simulation and experimental studies are presented to illustrate the performance of the proposed control strategy. The main contributions of this work lie in that this is the first time to develop a unified framework to achieve multi‐DOF cell orientation control without the need for accurate dynamic model parameters and/or any knowledge about uncertainty characteristic, which greatly enhances the robustness of the overall system. 相似文献
75.
In a sample quenched during equiaxed solidification of an Al-5 wt.% Cu alloy, the multi-scales 3-dimensional morphology of equiaxed dendrite was observed. The slim primary stem and secondary branches constitute the frame of dendrite, and rows of dense tertiary branches further divide the 3-dimensional space. In the divided space, the quartic branches grow further. The dendritic branches,which are perpendicular to each other, can change their growth directions and coalesce into a whole. In the tertiary branches and quartic branches, the formation of double branch structures is induced by competitive growth. The branch that wins in the competitive growth will produce a cabbage-like structure by wrapping the failed branches. In addition, the side branch can also wrap the original parent branch to produce cabbage-like structures. Depending on the historical growth direction, the dendritic arms can form vein-like and spicate structures, and the shapes of single dendritic arm may be the cylinder, plate and trapezoid platform. According to the compositions and etching morphology, the single dendritic arm in the final solidification structures should coalesce from a fine porous structure. The porous structures at different length-scales are principally induced by the preferential growth. Based on 3-dimensional morphology of equiaxed dendrite, a new research object for the investigation of microsegregation was suggested. 相似文献
76.
Sabyasachi Swain 《国际聚合物材料杂志》2019,68(13):796-804
In this study, a novel micro porous honeycomb structured Crg-GG-IPN material was incepted to be applicable as scaffold and accomplished. The hydrophilicity was confirmed by FT-IR and OCA. Amorphous nature and micro-rough surface were confirmed by XRD and AFM. Void fraction was 0.61?±?0.04. Void space, hemocompatibility and platelet adhesion were captured by SEM. Degradability of the material was confirmed by in-vitro degradation study. Incision method using mice model was a clear evidence for cell attachment and non-toxicity and was confirmed from hematology and histopathology. Thus, it appears that Crg-GG scaffolds can be useful as wound healing material for clinical applications. 相似文献
77.
《Ceramics International》2019,45(15):18876-18886
Red-emitting Sr0.8Ca0.19AlSiN3:0.01Eu2+ phosphor with halide fluxes for use in the production of white light-emitting diodes (white LEDs) with high-colour rendering indices (CRIs) was prepared through the high-temperature solid-state method. Fluoride (NaF, SrF2, BaF2, CaF2, AlF3·3H2O and CeF3), chloride (NH4Cl, BaCl2, MgCl2, NaCl and LiCl) and composite fluxes (NaF + SrF2, SrF2+NH4Cl and NaF + NH4Cl) were applied in the phosphors. NaF, SrF2, NH4Cl and NaF + SrF2 fluxes had prominent effects on the characteristics of Sr0.8Ca0.19AlSiN3:0.01Eu2+ phosphors. Sr0.8Ca0.19AlSiN3:0.01Eu2+ phosphors with various powder morphologies can be obtained through the addition of fluxes, which are conducive for phosphor formation. The powder morphologies of phosphors incorporated with NaF + SrF2 were preferable to those of powders incorporated with other fluxes. This result indicated that the incorporation of NaF + SrF2 into Sr0.8Ca0.19AlSiN3:0.01Eu2+ yielded phosphors with high luminescent intensity and quantum efficiency, excellent thermal stability, narrow full widths at half-maximum (FWHM, 75.2 nm), uniform rod-like morphologies with large particle sizes (D50 = 16.99 μm) and good particle dispersion. White LEDs with high CRIs were obtained by combining prepared phosphors (NaF + SrF2 additive) with the commercial green-emitting phosphors Y3(Al,Ga)5O12:Ce3+ and (Sr,Ba)2SiO4:Eu2+. White LEDs with Y3(Al,Ga)5O12:Ce3+ and (Sr,Ba)2SiO4:Eu2+ phosphors had correlated colour temperatures (CCTs) of 3064 and 3023 K, respectively, and CRIs of 81.8 and 92.4, respectively. Therefore, NaF + SrF2 can be used as a favourable flux for the production of Sr0.8Ca0.19AlSiN3:0.01Eu2+. 相似文献
78.
Jing Wang Hangyan Chen Su‐Huai Wei Wan‐Jian Yin 《Advanced materials (Deerfield Beach, Fla.)》2019,31(17)
Tetrahedral coordination structures, e.g. crystalline Si, GaAs, CdTe, and octahedral coordination structures, e.g. perovskites, represent two classes of successful crystal structures hitherto for solar cell absorbers. Here, via first‐principles calculations and crystal symmetry analysis, the two classes of semiconductors are shown exhibiting complementary properties in terms of bond covalency/ionicity, optical property, defect tolerance, and stability, which are correlated with their respective coordination number. Therefore, a spinel structure is proposed, which combines tetrahedral and octahedral coordination into a single crystal structure, as an alternative to perovskite and conventional semiconductors for potential photovoltaic applications. The case studies of a class of 105 spinel AB2X4 systems identify five spinel compounds HgAl2Se4, HgIn2S4, CdIn2Se4, HgSc2S4, and HgY2S4 as promising solar cell absorbers. In particular, HgAl2Se4 has suitable bandgap (1.36 eV by GW0 calculation), small direct–indirect bandgap difference (24 meV), appropriate carrier effective mass (me = 0.08 m0, and mh = 0.69 m0), strong optical absorption, and high dynamic stability. This study suggests that crystal systems with mixed tetrahedral and octahedral coordination may open a viable route for emerging solar cell absorbers. 相似文献
79.
80.
Luana Machado Barros Ana Lúcia Nunes Gutjahr Ruth Leila Ferreira‐ Keppler Renato Tavares Martins 《Microscopy research and technique》2019,82(3):178-189
In the dipteran genus Hermetia, only 6 of the 78 valid species have documented immature stages: H. albitarsis Fabricius, 1805, H. aurata Bellardi, 1859, H. concinna Williston, 1900, H. illucens (Linnaeus, 1758), H. panamensis Greene, 1940 and H. pulchra Weidemann, 1830. In particular, H. illucens stands out due to its reported applicability for forensic, medical and economic purposes. Here, we described the morphology of eggs and immature stages of this species, with a view to detecting differences between instars and in the pupal stage, which should eventually help properly identifying larval age. We utilized both optical and scanning electron microscopy tools. The eggs are elliptical and elongated, and color varies from cream white to yellowish. The larvae are apodal, hemichephalic and holopneustic, flattened dorso‐ventrally and may be recognized by the head elongated, dorsal and ventral chaetotaxy of the cephalic capsule, thoracic and abdominal segments, and the morphology of the anterior and posterior spiracles. The pupae are adecticous and coarctate, tegument dark brown and pruinescence varying from brown to golden. The overall morphology across instars is similar, but marked variations were observed in the shape of the antennal articuli and the shape of the setae (first instar compared to the others). Our results supplement the biological information on Hermetia illucens and should aid the proper identification and aging of juveniles in the field, as a way to minimize errors in the calculation of the post‐mortem interval. 相似文献