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   949篇
  免费   54篇
工业技术   1003篇
  2024年   2篇
  2023年   8篇
  2022年   104篇
  2021年   139篇
  2020年   29篇
  2019年   44篇
  2018年   25篇
  2017年   31篇
  2016年   36篇
  2015年   40篇
  2014年   53篇
  2013年   48篇
  2012年   53篇
  2011年   64篇
  2010年   36篇
  2009年   31篇
  2008年   34篇
  2007年   33篇
  2006年   34篇
  2005年   26篇
  2004年   18篇
  2003年   19篇
  2002年   9篇
  2001年   3篇
  2000年   11篇
  1999年   7篇
  1998年   7篇
  1997年   8篇
  1996年   3篇
  1995年   5篇
  1994年   7篇
  1993年   4篇
  1992年   4篇
  1991年   8篇
  1990年   1篇
  1989年   3篇
  1987年   2篇
  1985年   1篇
  1984年   3篇
  1983年   1篇
  1982年   2篇
  1981年   2篇
  1979年   1篇
  1977年   1篇
  1976年   1篇
  1941年   1篇
  1940年   1篇
排序方式: 共有1003条查询结果,搜索用时 15 毫秒
31.
Although seed quality and quantity, as well as reproductive performance are important life history stages of plants, little is known about the reproductive responses of trees to environmental changes such as increased anthropogenic deposition of nitrogen (N) and phosphorus (P). Dioecious plants are good models with which to test the environmental impact on female or male reproductive responses individually. We analysed effects of different long-term nutritional availability on the reproductive performance of two dioecious species (Taxus baccata L. and Juniperus communis L.) characterised by different life histories. By using pot experiments with vegetatively propagated plants grown in different fertilisation conditions, we observed an increase in plant growth and strobili production but a decrease in seed efficiency. Seeds produced by fertilised plants had greater seed mass. Fertiliser addition did not change C or N content nor the C/N ratio of T. baccata seeds, but increased N content and the N/P ratio; however, it did lower the C/N ratio in J. communis. Fertilisation did not change the metabolite profile in T. baccata but 18 metabolites were changed in J. communis. The study revealed new links between species life history, environmental changes, and reproduction. The findings imply that future environmental conditions may alter both seed productivity, and quality, as well as plant reproductive behaviour.  相似文献   
32.
This study investigated the influence of antioxidants of green tea aqueous extract (GTE) and green coffee aqueous extract (GCE) in concentrations of 0.25, 0.5 and 1 g·100 g? 1 on the nutritional properties of fine yeast pastry fried products such as donuts. Yeast donuts were made according to the traditional processing technology. In fried donuts physical properties (water activity, pH, hardness and color with the use of instrumental methods) as well as sensory properties were established. Moreover, quality of fat extracted from donuts (composition of fatty acids and peroxide value), content of acrylamide, composition of polyphenols and antioxidant activity were analyzed. Obtained extracts of GTE and GCE contained 26 and 41% of polyphenols, respectively, and the degree of polyphenol degradation during production of donuts was less when the dilution in dough was greater. Both tests indicated that the highest antioxidant activity had donuts with the highest analyzed addition of extract, however depending on the applied test or GTE or GCE had better antioxidant properties. Fatty acid composition was the most beneficial when the addition of GTE and GCE was on a level of 0.25 and 0.5 g·100 g? 1, respectively. In fried donuts relatively low amounts of acrylamide were obtained, amounting to 18–46 μg·kg? 1. Only the lowest addition of GTE and the highest addition of GCE caused an increase of acrylamide content in donuts, while all other levels of added extracts caused a decrease in the content of formed acrylamide.  相似文献   
33.
Large-scale applications can be expressed as a set of tasks with data dependencies between them, also known as application workflows. Due to the scale and data processing requirements of these applications, they require Grid computing and storage resources. So far, the focus has been on developing easy to use interfaces for composing these workflows and finding an optimal mapping of tasks in the workflow to the Grid resources in order to minimize the completion time of the application. After this mapping is done, a workflow execution engine is required to run the workflow over the mapped resources. In this paper, we show that the performance of the workflow execution engine in executing the workflow can also be a critical factor in determining the workflow completion time. Using Condor as the workflow execution engine, we examine the various factors that affect the completion time of a fine granularity astronomy workflow. We show that changing the system parameters that influence these factors and restructuring the workflow can drastically reduce the completion time of this class of workflows. We also examine the effect on the optimizations developed for the astronomy application on a coarser granularity biology application. We were able to reduce the completion time of the Montage and the Tomography application workflows by 90% and 50%, respectively.  相似文献   
34.
This paper proposes a new strategy for improving the localization capabilities of linear inverse solutions, based on the relationship between the real solution and the estimated solution as described by the resolution matrix equation. Specifically, we present two alternatives based on either the partial or total inversion of the resolution matrix and applied them to the minimum norm solution, which is known for its poor performance in three-dimensional (3-D) localization problems. The minimum norm transformed inverse showed a clear improvement in 3-D localization. The strong dependence of localization errors with the eccentricity of the sources, characteristic of this solution, disappears after the proposed transformation. A similar effect is illustrated, using a realistic example where multiple generators at striate areas are active. While the original minimum norm incorrectly places the generators at extrastriate cortex, the transformed minimum norm localizes, for the example considered, the sources at their correct eccentricity with very low spatial blurring.  相似文献   
35.
The paper presents the experimental results of positron annihilation measurements of the subsurface zones in aluminum and aluminum alloy exposed to the indentation of the small steel ball or blasting by the silicon carbide particles. The measurements of the Doppler broadening of the annihilation line and positron lifetime (PL) enabled the depth profile of open volume defects induced by indentation and blasting processes to be obtained. The coincidence of the von Mises criterion for yield with the onset of the increase of the defect concentration at certain depth was detected. It was established that the defects created in the pure aluminum and the aluminum alloy detected by positrons are different. However, the kinds of induced defects do not change with depth. The PL measurements indicate the presence of vacancy clusters in samples exposed to blasting. The vacancy clusters created in the aluminum alloy are larger than in the pure aluminum.  相似文献   
36.
The dynamic self‐organization of lipids in biological systems is a highly regulated process that enables the compartmentalization of living systems at micro‐ and nanoscopic scales. Consequently, quantitative methods for assaying the kinetics of supramolecular remodeling such as vesicle formation from planar lipid bilayers or multilayers are needed to understand cellular self‐organization. Here, a new nanotechnology‐based method for quantitative measurements of lipid–protein interactions is presented and its suitability for quantifying the membrane binding, inflation, and budding activity of the membrane‐remodeling protein Sar1 is demonstrated. Lipid multilayer gratings are printed onto surfaces using nanointaglio and exposed to Sar1, resulting in the inflation of lipid multilayers into unilamellar structures, which can be observed in a label‐free manner by monitoring the diffracted light. Local variations in lipid multilayer volume on the surface is used to vary substrate availability in a microarray format. A quantitative model is developed that allows quantification of binding affinity (K D) and kinetics (kon and koff). Importantly, this assay is uniquely capable of quantifying membrane remodeling. Upon Sar1‐induced inflation of single bilayers from surface supported multilayers, the semicylindrical grating lines are observed to remodel into semispherical buds when a critical radius of curvature is reached.  相似文献   
37.
Optimisation of the germination process of different cultivars of broccoli (Brassica oleracea var. italica cv. Lucky, cv. Tiburon and cv. Belstar) and radish (Raphanus sativus cv. Rebel and cv. Bolide) seeds in relation to the content of glucosinolates (GLS), vitamin C and total antioxidant capacity was carried out in order to maximise the health-promoting properties of Brassica sprouts. The content of total and individual GLS varied between species, among cultivars, and germination time. Glucoraphanin in broccoli and glucoraphenin in radish were the predominant GLS in raw seeds (61–77 and 63–129 μmol/g DM, respectively) and, although their content decreased during germination, they were maintained in rather large proportions in sprouts. Vitamin C was not detected in raw seeds and its content increased sharply in broccoli and radish sprouts (162–350 and 84–113 mg/100 g DM, respectively). Raw brassica seeds are an excellent source of antioxidant capacity (64–90 and 103–162 μmol Trolox/g DM in broccoli and radish, respectively) and germination led to a sharp increase. Germination of broccoli cv. Belstar and radish cv. Rebel for 4 days provided the largest glucoraphanin and glucoraphenin content, respectively, and also brought about large amounts of vitamin C and antioxidant capacity.  相似文献   
38.
The aim of this study was to investigate whether there are differences in technique between young adults with and without musculoskeletal symptoms when using a mobile phone for texting and whether there are differences in muscle activity and kinematics between different texting techniques. A total of 56 young adults performed a standardised texting task on a mobile phone. Their texting techniques were registered using an observation protocol. The muscular activity in six muscles in the right forearm/hand and both shoulders were registered by surface electromyography and the thumb abduction/adduction and flexion/extension were registered using a biaxial electrogoniometer. Differences in texting techniques were found between the symptomatic and the asymptomatic group, with a higher proportion of sitting with back support and forearm support and with a neutral head position in the asymptomatic group. Differences in muscle activity and kinematics were also found between different texting techniques. The differences in texting technique between symptomatic and asymptomatic subjects cannot be explained by them having symptoms but may be a possible contribution to their symptoms. STATEMENT OF RELEVANCE: There has been a dramatically increased use of mobile phones for texting especially among young people during the last years. A better understanding of the physical exposure associated with the intensive use is important in order to prevent the development of musculoskeletal disorders and decreased work ability related to this use.  相似文献   
39.
Polyetheretherketone (PEEK) is a highly biocompatible polymer widely used in medicine as an implant production material. In this article, the PEEK surface was characterized in terms of its wettabillity properties after the physicochemical modifications by treatment with the low-temperature air plasma and covering with the Langmuir–Blodgett (LB) monolayers of polypeptide (cyclosporine A, CsA) and/or phospholipid (1,2-dipalmitoyl-sn-glycero-3-phosphocholine, DPPC). The LB deposition was preceded by the analysis of miscibility and morphology of monolayers at the air/water interface by means of the Langmuir technique and Brewster angle microscopy (BAM). Then, wettability of the polymer-supported films was evaluated by the contact angle measurements of three probe liquids of different characters (two polar—water and formamide, one apolar—diiodomethane). The measured contact angles allowed for determination of the surface free energy and its components based on the Lifshitz-van der Waals/acid–base (LWAB) approach. Some relations between the kind and magnitude of interactions within the model membranes on the water subphase and those of the PEEK-supported membranes with the liquids were found out. The results allowed obtaining the interesting models of biological coatings with potential applications.  相似文献   
40.
Depending on the calcium:phosphorus molar ratio of the initial precipitates determined by precipitation conditions (calcium:phosphorus molar ratio of reactants and pH of reaction environment), after sintering at 1250°C, monophase, biphase, or triphase ceramics consisting of hydroxyapatite, β-tricalcium phosphate, α-tricalcium phosphate, and calcium oxide were obtained. The phase composition and properties—i.e., density, shrinkage, hardness, bending strength, and roughness—of the fractured surfaces of the isostatically re-pressed sinters were determined.  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