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   2415篇
  免费   229篇
  国内免费   1篇
电工技术   9篇
综合类   3篇
化学工业   750篇
金属工艺   26篇
机械仪表   20篇
建筑科学   100篇
矿业工程   78篇
能源动力   39篇
轻工业   574篇
水利工程   21篇
石油天然气   6篇
无线电   137篇
一般工业技术   355篇
冶金工业   269篇
原子能技术   13篇
自动化技术   245篇
  2023年   34篇
  2022年   76篇
  2021年   102篇
  2020年   57篇
  2019年   58篇
  2018年   68篇
  2017年   104篇
  2016年   125篇
  2015年   111篇
  2014年   113篇
  2013年   201篇
  2012年   143篇
  2011年   155篇
  2010年   135篇
  2009年   104篇
  2008年   124篇
  2007年   143篇
  2006年   87篇
  2005年   77篇
  2004年   72篇
  2003年   58篇
  2002年   58篇
  2001年   45篇
  2000年   33篇
  1999年   30篇
  1998年   41篇
  1997年   40篇
  1996年   23篇
  1995年   25篇
  1994年   26篇
  1993年   19篇
  1992年   15篇
  1991年   8篇
  1990年   7篇
  1989年   6篇
  1988年   14篇
  1987年   12篇
  1986年   7篇
  1985年   6篇
  1984年   10篇
  1983年   13篇
  1982年   8篇
  1981年   7篇
  1980年   5篇
  1979年   8篇
  1977年   6篇
  1975年   6篇
  1970年   3篇
  1969年   2篇
  1968年   2篇
排序方式: 共有2645条查询结果,搜索用时 15 毫秒
91.
The irreversible capacity of negative electrode in a lithium-ion cell is a widely described the phenomenon. Irreversible capacity losses are connected with formation of a solid electrolyte interface layer. This layer is growing on the electrode-electrolyte interface during first several charging cycles. The layer is indispensable for proper functioning of a lithium-ion cell. However, during this layer formation, the atoms of lithium are consumed in a range from 18 to 45% of the total amount of lithium atoms presented in cell. Demonstration of possibilities to suppress this phenomenon that occurs on a negative electrode interface is the main aim of this paper.  相似文献   
92.
Food Science and Biotechnology - Quercus salicina Blume (QS) is an oak species that is indigenous to Japan and Korea. Historically, extracts of leaves, stems, barks and buds from the QS tree had...  相似文献   
93.
94.
Therapeutic approaches providing effective medication for Alzheimer’s disease (AD) patients after disease onset are urgently needed. Previous studies in AD mouse models suggested that physical exercise or changed lifestyle can delay AD-related synaptic and memory dysfunctions when treatment started in juvenile animals long before onset of disease symptoms, while a pharmacological treatment that can reverse synaptic and memory deficits in AD mice was thus far not identified. Repurposing food and drug administration (FDA)-approved drugs for treatment of AD is a promising way to reduce the time to bring such medication into clinical practice. The sphingosine-1 phosphate analog fingolimod (FTY720) was approved recently for treatment of multiple sclerosis patients. Here, we addressed whether fingolimod rescues AD-related synaptic deficits and memory dysfunction in an amyloid precursor protein/presenilin-1 (APP/PS1) AD mouse model when medication starts after onset of symptoms (at five months). Male mice received intraperitoneal injections of fingolimod for one to two months starting at five to six months. This treatment rescued spine density as well as long-term potentiation in hippocampal cornu ammonis-1 (CA1) pyramidal neurons, that were both impaired in untreated APP/PS1 animals at six to seven months of age. Immunohistochemical analysis with markers of microgliosis (ionized calcium-binding adapter molecule 1; Iba1) and astrogliosis (glial fibrillary acid protein; GFAP) revealed that our fingolimod treatment regime strongly down regulated neuroinflammation in the hippocampus and neocortex of this AD model. These effects were accompanied by a moderate reduction of Aβ accumulation in hippocampus and neocortex. Our results suggest that fingolimod, when applied after onset of disease symptoms in an APP/PS1 mouse model, rescues synaptic pathology that is believed to underlie memory deficits in AD mice, and that this beneficial effect is mediated via anti-neuroinflammatory actions of the drug on microglia and astrocytes.  相似文献   
95.
We report the anti-osteosarcoma and anti-osteosarcoma stem cell (OSC) properties of a nickel(II) complex, 1 . Complex 1 displays similar potency towards bulk osteosarcoma cells and OSCs, in the micromolar range. Notably, 1 displays similar or better OSC potency than the clinically approved platinum(II) anticancer drugs cisplatin and carboplatin in two- and three-dimensional osteosarcoma cell cultures. Mechanistic studies revealed that 1 induces osteosarcoma cell death by necroptosis, an ordered form of necrosis. The nickel(II) complex, 1 triggers necrosome-dependent mitrochondrial membrane depolarisation and propidium iodide uptake. Interestingly, 1 does not evoke necroptosis by elevating intracellular reactive oxygen species (ROS) or hyperactivation of poly ADP ribose polymerase (PARP-1). ROS elevation and PARP-1 activity are traits that have been observed for established necroptosis inducers such as shikonin, TRAIL and glutamate. Thus the necroptosis pathway evoked by 1 is distinct. To the best of our knowledge, this is the first report into the anti-osteosarcoma and anti-OSC properties of a nickel complex.  相似文献   
96.
97.
98.
Due to large knowledge gaps in chemical composition and toxicological data for substances involved, paper and board food-contact materials (P&B FCM) have been emerging as a FCM type of particular concern for consumer safety. This study describes the development of a step-by-step strategy, including extraction, high-performance liquid chromatography (HPLC) fractionation, tentative identification of relevant substances and in vitro testing of selected tentatively identified substances. As a case study, we used two fractions from a recycled pizza box sample which exhibited aryl hydrocarbon receptor (AhR) activity. These fractions were analysed by gas chromatography (GC) and ultra-HPLC (UHPLC) coupled to quadrupole time-of-flight mass spectrometers (QTOF MS) in order tentatively to identify substances. The elemental composition was determined for peaks above a threshold, and compared with entries in a commercial mass spectral library for GC-MS (GC-EI-QTOF MS) analysis and an in-house built library of accurate masses for substances known to be used in P&B packaging for UHPLC-QTOF analysis. Of 75 tentatively identified substances, 15 were initially selected for further testing in vitro; however, only seven were commercially available and subsequently tested in vitro and quantified. Of these seven, the identities of three pigments found in printing inks were confirmed by UHPLC tandem mass spectrometry (QqQ MS/MS). Two pigments had entries in the database, meaning that a material relevant accurate mass database can provide a fast tentative identification. Pure standards of the seven tentatively identified substances were tested in vitro but could not explain a significant proportion of the AhR-response in the extract. Targeted analyses of dioxins and PCBs, both well-known AhR agonists, was performed. However, the dioxins could explain approximately 3% of the activity observed in the pizza box extract indicating that some very AhR active substance(s) still remain to be identified in recycled low quality P&B.  相似文献   
99.
Background: The influence of dietary fat upon breast cancer mortality remains largely understudied despite extensive investigation into its influence upon breast cancer risk. Objective: To conduct meta-analyses of studies to clarify the association between dietary fat and breast cancer mortality. Design: MEDLINE and EMBASE were searched for relevant articles published up to March 2012. Risk of all-cause or breast-cancer-specific death was evaluated by combining multivariable adjusted estimates comparing highest versus lowest categories of intake; and per 20 g increase in intake of total and/or saturated fat (g/day) using random-effects meta-analyses. Results: Fifteen prospective cohort studies investigating total fat and/or saturated fat intake (g/day) and breast cancer mortality were included. There was no difference in risk of breast-cancer-specific death (n = 6; HR = 1.14; 95% CI: 0.86, 1.52; p = 0.34) or all-cause death (n = 4; HR = 1.73; 95% CI: 0.82, 3.66; p = 0.15) for women in the highest versus lowest category of total fat intake. Breast-cancer-specific death (n = 4; HR = 1.51; 95% CI: 1.09, 2.09; p < 0.01) was higher for women in the highest versus lowest category of saturated fat intake. Conclusions: These meta-analyses have shown that saturated fat intake negatively impacts upon breast cancer survival.  相似文献   
100.
Method validation for strobilurin fungicides in cereals and fruit   总被引:2,自引:0,他引:2  
Strobilurins are a new class of fungicides that are active against a broad spectrum of fungi. In the present work a GC method for analysis of strobilurin fungicides was validated. The method was based on extraction with ethyl acetate/cyclohexane, clean-up by gel permeation chromatography (GPC) and determination of the content by gas chromatography (GC) with electron capture (EC-), nitrogen/phosphorous (NP-), and mass spectrometric (MS-) detection. Three strobilurins, azoxystrobin, kresoxim-methyl and trifloxystrobin were validated on three matrices, wheat, apple and grapes. The validation was based on recovery tests at three or four spiking levels, determined as double determinations and repeated three times (n = 6). The mean recoveries for the three detectors were in the range of 70-114%, and the LODs were between 0.004mg/kg and 0.014mg/kg, for all three strobilurins. The values for repeatability and reproducibility were within the limits for repeatability and reproducibility given by the Horwitz equation. Validation was not accepted for azoxystrobin in grapes on all three detectors and for azoxystrobin in apple for the MS-detector. A comparison of matrix-matched standards versus standards in solvent showed varying differences  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