首页 | 官方网站   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   6299篇
  免费   451篇
  国内免费   259篇
工业技术   7009篇
  2023年   87篇
  2022年   120篇
  2021年   238篇
  2020年   196篇
  2019年   173篇
  2018年   150篇
  2017年   185篇
  2016年   165篇
  2015年   173篇
  2014年   259篇
  2013年   366篇
  2012年   322篇
  2011年   417篇
  2010年   336篇
  2009年   313篇
  2008年   349篇
  2007年   325篇
  2006年   350篇
  2005年   315篇
  2004年   213篇
  2003年   217篇
  2002年   174篇
  2001年   174篇
  2000年   138篇
  1999年   190篇
  1998年   184篇
  1997年   132篇
  1996年   144篇
  1995年   114篇
  1994年   94篇
  1993年   80篇
  1992年   51篇
  1991年   50篇
  1990年   35篇
  1989年   35篇
  1988年   28篇
  1987年   19篇
  1986年   19篇
  1985年   9篇
  1984年   7篇
  1983年   7篇
  1982年   6篇
  1981年   8篇
  1979年   5篇
  1978年   4篇
  1976年   7篇
  1975年   7篇
  1971年   2篇
  1969年   2篇
  1963年   2篇
排序方式: 共有7009条查询结果,搜索用时 15 毫秒
1.
Thermal action in extraction process had effects on characteristic tryptic peptides identification and gelling properties of porcine gelatin. SDS-PAGE, HPLC-LTQ/Orbitrap high-resolution mass spectrometry, texture analyser and rheometer were used to evaluate collagen depolymerisation degree, characteristic tryptic peptides and gelling properties of gelatins prepared in various thermal actions. Results showed that with increasing temperature and time, depolymerisation degree enlarged, while gel strength, gelling and melting temperature decreased. Mass spectra showed that 47 and 49 common characteristic tryptic peptides were identified in gelatins extracted at 50 °C and 100 °C with various times, respectively. Moreover, 34 common characteristic tryptic peptides were identified in all gelatin samples. Further comparison between this work and our previous investigations yielded 20 common characteristic tryptic peptides, which stably exist in various thermal actions. These common characteristic tryptic peptides may be very helpful for the accurate authentication of porcine gelatin.  相似文献   
2.
Konjac glucomannan/sodium alginate composite edible boba (KGM/SA-boba) with good taste is very popular in China, and it is an outstanding carrier for health potential ingredients. In this work, KGM/SA-boba were fortified with 0.25, 0.50, 0.75 and 1.00% purple sweet potato anthocyanin (PSPA), then characterised by the water distribution, texture, microstructure, in vitro release property of PSPA and antioxidant capacity. LF-NMR analysis demonstrated that the free water of KGM/SA-boba could transfer to tightly bound water with the addition of PSPA that made it with better water-binding ability, higher springiness and lower hardness. And the results of SEM and rheology showed that PSPA could stabilise the microstructure of KGM/SA-boba by forming more amorphous regions and hydrogen bonds proved by the results of DSC and FT-IR. Furthermore, 50% of PSPA in PSPA-fortified KGM/SA-boba can be released at the first hour in a simulated gastrointestinal environment. And the scavenging capacity of DPPH and ABTS of the PSPA-fortified KGM/SA-boba after digestion was higher than that of PSPA alone. Generally, PSPA could improve the texture while KGM/SA-boba in turn would make PSPA more stable in the gastrointestinal digestive system.  相似文献   
3.
To prevent the adulteration of agricultural resources and provide a solution to enhance the green coffee bean supply chain, authentication using the near-infrared spectroscopy (NIRS) technique was investigated. Partial least square with discrimination analysis (PLS-DA) models combined with various preprocessing methods were built from NIR spectra of 153 Vietnamese green coffee samples. The model combined with the standard normal variate and the first order of derivative yielded excellent performance in predicting coffee species with the error cross-validation of 0.0261. PLS-DA model of mean centre and first-order derivative spectra also yielded good performance in verifying geographical indication of green coffee with the error of 0.0656. By contrast, the predicting abilities of post-harvest methods were poor. The overall results showed a high potential of the NIRS in online authentication practices.  相似文献   
4.
Here we report a transparent dual-phase ZnO·2.7Al2O3 ceramic. The composite is pore-free and consists of thin nanosheets with a spinel phase and a hexagonal phase, while the two phases match closely in both lattice and refractive index. Such features result in excellent optical transmittance (maximum value >80% in the visible spectrum) at comparable phase volume. This work may provide a new thought for the rational structural design of optical nanocomposites.  相似文献   
5.
Knowledge on the mechanical and thermophysical properties of ZnO·nAl2O3 is essential for practical applications. Based on the first-principles calculations and the bond valence method, the disordered spinel-type structure of ZnO·nAl2O3 (n = 1–4) was constructed to investigate the composition-dependent mechanical and thermophysical properties. The effects of cation substitution on the hardness, elastic modulus, thermal expansion, and thermal conductivity were revealed from the insights into the chemical bonds. At a higher n, the tetrahedral bond is stronger, manifested as its higher hardness and bulk modulus as well as smaller thermal expansion coefficient. Meanwhile, the octahedral bond is weaker, leading to the lower hardness and bulk modulus, along with the larger expansion coefficient. In consequence, the hardness and elastic moduli of ZnO·nAl2O3 are improved moderately while the expansion coefficient is decreased with the rise of n. Due to the different vibration characteristics of ZnIV and AlIV, the cation disorder in the 8a site provides the primary source of phonon scattering, resulting in the dramatic reduction of thermal conductivity as n increases. The understanding offers guidance on the application-oriented design of new oxide spinels.  相似文献   
6.
Glycine N-methyltransferase (GNMT) regulates S-adenosylmethionine (SAMe), a methyl donor in methylation. Over-expressed SAMe may cause neurogenic capacity reduction and memory impairment. GNMT knockout mice (GNMT-KO) was applied as an experimental model to evaluate its effect on neurons. In this study, proteins from brain tissues were studied using proteomic approaches, Haemotoxylin and Eosin staining, immunohistochemistry, Western blotting, and ingenuity pathway analysis. The expression of Receptor-interacting protein 1(RIPK1) and Caspase 3 were up-regulated and activity-dependent neuroprotective protein (ADNP) was down-regulated in GNMT-KO mice regardless of the age. Besides, proteins related to neuropathology, such as excitatory amino acid transporter 2, calcium/calmodulin-dependent protein kinase type II subunit alpha, and Cu-Zn superoxide dismutase were found only in the group of aged wild-type mice; 4-aminobutyrate amino transferase, limbic system-associated membrane protein, sodium- and chloride-dependent GABA transporter 3 and ProSAAS were found only in the group of young GNMT-KO mice and are related to function of neurons; serum albumin and Rho GDP dissociation inhibitor 1 were found only in the group of aged GNMT-KO mice and are connected to neurodegenerative disorders. With proteomic analyses, a pathway involving Gonadotropin-releasing hormone (GnRH) signal was found to be associated with aging. The GnRH pathway could provide additional information on the mechanism of aging and non-aging related neurodegeneration, and these protein markers may be served in developing future therapeutic treatments to ameliorate aging and prevent diseases.  相似文献   
7.
Cr2AlC MAX phase thin films prepared by radio-frequency magnetron sputtering were irradiated at room temperature by 100 keV helium ions to a fluence of 1 × 1017 ions cm−2. The effects of thermal annealing on the structural and mechanical properties of the helium-irradiated Cr2AlC films as well as the helium release were investigated by grazing-incidence X-ray diffraction (GIXRD), Raman spectroscopy, and scanning electron microscope (SEM) in combination with nano-indentation and elastic recoil detection (ERD) analysis. The irradiation-induced structural damage in the Cr2AlC is significantly recovered by thermal annealing at temperatures around 600℃, attributed to high defect diffusivity. After annealing to 750℃, the hardness of irradiated films recovered almost completely, which is ascribes to both defect recombination and reformation of damaged chemical bonds. Substantial helium release occurring at this annealing temperature is closely related to the damage recovery due to helium irradiation.  相似文献   
8.
In the development of fuel cells, it is the key to large-scale commercialization of fuel cells to rationally design and synthesize efficient and non-noble metals-based bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In this paper, spinel CoFe2O4/carbon nanotube composites (CoFe2O4/CNTs/FA) were synthesized by solvothermal and calcination method. XRD, TEM, XPS and BET characterizations indicate that the addition of complexing agent fumaric acid can improve the crystal growth kinetics and morphology of CoFe2O4/CNTs nanohybirds. The as-synthesized CoFe2O4/CNTs/FA pyrolyzed at 500 °C have an outstanding bifunctional catalytic activity for ORR and OER with the potential of 1.62V (vs. RHE) at a current density of 10 mA/cm2 and half-wave potential E1/2 = 0.808V (vs. RHE) in alkaline electrolyte, respectively. It is obviously better than unloaded CoFe2O4 nanoparticles and commercial CNTs. CoFe2O4/CNTs/FA also exhibit better methanol tolerance ability and durability than commercial Pt/C and RuO2 catalyst. This investigation broadens an idea of simple compounding of spinel with carbon-based materials to improve electrochemical properties.  相似文献   
9.
为了提高聚乳酸(PLA)复合材料3D打印制件的性能,采用三因素三水平正交试验设计,研究了用熔融沉积成型(FDM)工艺3D打印PLA/石墨烯复合材料制件过程中,打印层高、填充密度以及构建取向对制件弯曲性能的影响。结果表明,石墨烯对PLA/石墨烯复合材料制件有较好增强效果,各试验参数对3D打印PLA/石墨烯复合材料制件弯曲强度的影响大小顺序为:构建取向>填充密度>层高,且当构建取向为侧立方式,填充密度为80%,层高为0.2 mm时,制件具有最佳的弯曲强度;对复合材料制件弯曲弹性模量的影响大小依次为:填充密度>层高>构建取向,且当构建取向为侧立,填充密度为80%,层高为0.1 mm时,制件具有最佳的弯曲弹性模量。  相似文献   
10.
文章在回顾过程装备与控制工程专业发展历程的基础上,辨析了新经济形势下该专业存在的问题,并提出“四位一体”的专业升级模式及具体举措。该模式的实施,有助于提高学生的工程实践能力、创新能力及跨界整合能力,同时有助于提升本专业的影响力。  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-23

京公网安备 11010802026262号