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   863篇
  免费   69篇
电工技术   3篇
综合类   2篇
化学工业   322篇
金属工艺   5篇
机械仪表   41篇
建筑科学   43篇
矿业工程   1篇
能源动力   16篇
轻工业   185篇
水利工程   9篇
石油天然气   8篇
无线电   22篇
一般工业技术   133篇
冶金工业   81篇
原子能技术   4篇
自动化技术   57篇
  2024年   3篇
  2023年   6篇
  2022年   29篇
  2021年   34篇
  2020年   30篇
  2019年   35篇
  2018年   32篇
  2017年   32篇
  2016年   36篇
  2015年   19篇
  2014年   37篇
  2013年   56篇
  2012年   71篇
  2011年   67篇
  2010年   59篇
  2009年   41篇
  2008年   55篇
  2007年   39篇
  2006年   33篇
  2005年   31篇
  2004年   23篇
  2003年   21篇
  2002年   19篇
  2001年   11篇
  2000年   8篇
  1999年   6篇
  1998年   11篇
  1997年   13篇
  1996年   9篇
  1995年   12篇
  1994年   7篇
  1993年   9篇
  1992年   3篇
  1991年   2篇
  1989年   2篇
  1987年   2篇
  1986年   2篇
  1985年   1篇
  1983年   1篇
  1982年   2篇
  1981年   4篇
  1980年   4篇
  1979年   1篇
  1978年   2篇
  1977年   4篇
  1976年   1篇
  1974年   1篇
  1973年   1篇
  1969年   1篇
  1968年   2篇
排序方式: 共有932条查询结果,搜索用时 78 毫秒
921.
Toxoplasma gondii causes severe disease both to man and livestock and its detection in meat after slaughtering requires PCR or biological tests. Meat packages contain retained exudate that could be used for serology due to its blood content. Similar studies reported false negative assays in those tests. We standardized an anti-T. gondii IgG ELISA in muscle juices from experimentally infected rabbits, with blood content determination by cyanhemoglobin spectrophotometry. IgG titers and immunoblotting profiles were similar in blood, serum or meat juice, after blood content correction. These assays were adequate regardless of the storage time up to 120 days or freeze-thaw cycles, without false negative results. We also found 1.35% (1/74) positive sample in commercial Brazilian rabbit meat cuts, by this assay. The blood content determination shows ELISA of meat juice may be useful for quality control for toxoplasmosis monitoring.  相似文献   
922.
Due to their redox reactivity, surface sorption characteristics, and ubiquity as corrosion products or as minerals in natural sediments, iron(II)-bearing minerals control to a large extent the environmental fate of actinides. Pu-L(III)-edge XANES and EXAFS spectra were used to investigate reaction products of aqueous (242)Pu(III) and (242)Pu(V) reacted with magnetite, mackinawite, and chukanovite under anoxic conditions. As Pu concentrations in the liquid phase were rapidly below detection limit, oxidation state and local structure of Pu were determined for Pu associated with the solid mineral phase. Pu(V) was reduced in the presence of all three minerals. A newly identified, highly specific Pu(III)-sorption complex formed with magnetite. Solid PuO(2) phases formed in the presence of mackinawite and chukanovite; in the case of chukanovite, up to one-third of plutonium was also present as Pu(III). This highlights the necessity to consider, under reducing anoxic conditions, Pu(III) species in addition to tetravalent PuO(2) for environmental risk assessment. Our results also demonstrate the necessity to support thermodynamic calculations with spectroscopic data.  相似文献   
923.
A fast and efficient method to determine molybdenum, Mo, in milk and other infant food by atomic absorption spectrometry with electrothermal atomization employing slurry sampling was developed. Slurries were prepared in ultrapure water with 5 to 20 min of sonication in concentrations of 10% w/v. The injection of 5.0 μL of a 0.1% (v/v) cetyl trimethyl ammonium chloride solution before the temperature program reduced the effect of build-up of carbonaceous residues within the atomizer. Europium (chemical modifier) and niobium (permanent modifier) were chosen for use from several potential modifiers. The parameters of merit were obtained in the optimized conditions T a  =  2,700 oC, T p  = 2,000 oC, tp = 20 s, and Eu 5.0 μg + permanent Nb 500.0 μg. These parameters were linear working range up to 100.0 μg/L, limit of detection (1.1 ± 0.1) μg/L, aqueous calibration, and standard addition curves with r 2 > 0.9900 and relative standard deviation of 0.6% to 8.7%. The accuracy was evaluated by recovery tests and by certified material analysis; the agreement among these numbers validated the method. The powdered sample concentrations were between 39 and 1,570 μg/kg.  相似文献   
924.
Early pregnancy loss (EPL) is a relatively common pathology of which almost 50% of cases remain idiopathic. In the search for novel biomarkers, differential scanning calorimetry (DSC) is intensively used to characterize the thermodynamic behavior of blood plasma/serum proteome in health and disease. Herein, for the first time, we investigate the DSC denaturation profiles of blood plasma derived from patients suffering EPL compared to healthy pregnant and non-pregnant women. Data analysis reveals that 58% of the EPL thermograms differ significantly from those of healthy pregnant women. Thermal stabilization of a fraction of albumin-assigned transition with concomitant suppression of the major and enhancement of the globulin-assigned transition are characteristic features of EPL calorimetric profiles that could be used as a new indicator of a risk pregnancy. The presented results suggest an altered composition or intermolecular interactions of the plasma proteome of women with EPL. In addition, the alterations of the EPL thermograms correlate with the increased blood levels of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) and a higher prevalence of the polymorphism in the plasminogen activator inhibitor type-1 (PAI-1) gene, suggesting an expression of an overall enhanced immune response. The concomitant changes in plasma thermograms confirm the potential of the DSC approach for distinguishing changes in the pathological state of the blood plasma proteome.  相似文献   
925.
Monolayer cultures, the less standard three-dimensional (3D) culturing systems, and xenografts are the main tools used in current basic and drug development studies of cancer research. The aim of biofabrication is to design and construct a more representative in vivo 3D environment, replacing two-dimensional (2D) cell cultures. Here, we aim to provide a complex comparative analysis of 2D and 3D spheroid culturing, and 3D bioprinted and xenografted breast cancer models. We established a protocol to produce alginate-based hydrogel bioink for 3D bioprinting and the long-term culturing of tumour cells in vitro. Cell proliferation and tumourigenicity were assessed with various tests. Additionally, the results of rapamycin, doxycycline and doxorubicin monotreatments and combinations were also compared. The sensitivity and protein expression profile of 3D bioprinted tissue-mimetic scaffolds showed the highest similarity to the less drug-sensitive xenograft models. Several metabolic protein expressions were examined, and the in situ tissue heterogeneity representing the characteristics of human breast cancers was also verified in 3D bioprinted and cultured tissue-mimetic structures. Our results provide additional steps in the direction of representing in vivo 3D situations in in vitro studies. Future use of these models could help to reduce the number of animal experiments and increase the success rate of clinical phase trials.  相似文献   
926.
In this study, the authors investigated whether psychotherapist bias related to client bisexuality is most likely to occur with respect to judgments about stereotype-relevant clinical issues. Participants were 108 psychotherapists who read a fictitious intake report about a male client who was portrayed as heterosexual, gay, or bisexual. Client sexual orientation was behaviorally operationalized through reference to the sex of the client's present and previous romantic partners. Participants rated the case for the salience of a variety of clinical issues (some of which were related to bisexual stereotypes), global psychological functioning, and anticipated reactions to the client. Client sexual orientation had no effect for outcomes unrelated to bisexual stereotypes. In contrast, clinical issues related to bisexual stereotypes were rated as most salient to the case when the client was portrayed as bisexual rather than when the client was portrayed as heterosexual or gay. This effect remained significant even when participants' self-reported ability to avoid bias, self-presentational concerns, and response set related to perceptions of psychopathology were controlled for. Exploratory analyses suggested that this effect was partially mediated by stereotypes of bisexual men as confused and conflicted. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
927.
Wisdom of the Crowd is the aggregation of many individual estimates to obtain a better collective one. Because of its enormous social potential, this effect has been thoroughly investigated, but predominantly on tasks that involve rational thinking (such as estimating a number). Here we tested this effect in the context of drawing geometrical shapes, which still enacts cognitive processes but mainly involves visuomotor control. We asked more than 700 school students to trace five patterns shown on a touchscreen and then aggregated their individual trajectories to improve the match with the original pattern. Our results show the characteristics of the strongest examples of Wisdom of the Crowd. First, the aggregate trajectory can be up to 5 times more accurate than the individual ones. Second, this great improvement requires aggregating trajectories from different individuals (rather than trials from the same individual). Third, the aggregate trajectory outperforms more than 99% of individual trajectories. Fourth, while older individuals outperform younger ones, a crowd of young individuals outperforms the average older one. These results demonstrate for the first time Wisdom of the Crowd in the realm of motor control, opening the door to further studies of human and also animal behavioural trajectories and their mechanistic underpinnings.  相似文献   
928.
Although cocoa butter (CB) has remarkable physical properties, its high price, growing difficulties, and increased consumption have been the main incentive to explore alternatives to replace or improve it. The potential of fats systems obtained from tropical butters, mixtures of them with vegetable oils, or marine fats as cocoa butter equivalent (CBE), extender (CBEx), substitute (CBS), replacer (CBR), or improver (CBI) have been deeply investigated and their physical chemical properties have been compared to those of CB. The TAGs composition of fats systems is a key factor that determines fats crystallization and polymorphic behaviors, and the suitability for an application. Fats with high concentrations of the TAGs StOSt, StOA, or StOB and low concentrations of POP compared to CB show some incompatibility with CB as analyzed by iso-solid diagrams and a more complex polymorphic behavior. The presence of low melting TAGs such as POO, StOO, and AOO also leads to significant differences in physical behavior compared to CB. In those fats systems, co-crystallization and polymorphic transitions of co-existing solid solutions were reported. A few of the studied fat systems may behave as CBE. However, most of them have potential as CBS, CBR, CBEx or CBI in confectionery products. Studies reported the relevance of fractionation and interesterification processes to modify TAGs composition and the need of finding the right processing conditions and additives to extend fats applications.  相似文献   
929.
930.
Copaiba oleoresin has sesquiterpenes and diterpenes with significant medicinal properties, including being antimicrobial, antiparasitic, and wound healing, among others. Thus, the objective of this work was to study the diterpene enrichment of the copaiba oleoresin from Copaifera officinalis via molecular distillation. Evaporator temperature (EVT) and feed flow rate (Q) were evaluated using an experimental design (22 with central point) considering the ratio of distillate and residue streams (DTR) as the response to optimize the residue recovery. EVT and Q were the main effects for diterpenes recovery, with the best experimental condition at 100°C (EVT) and 15 ml/min (Q) under 0.001 mbar, of which the residue stream had a diterpenes content of 99.25%. With the molecular distillation process, it was possible to add value to the copaiba streams, separating and purifying diterpenes with applicability in the biomedical and pharmaceutical industries since no solvent is used in this process (clean).  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