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   2810篇
  免费   145篇
  国内免费   8篇
电工技术   68篇
综合类   2篇
化学工业   572篇
金属工艺   84篇
机械仪表   52篇
建筑科学   58篇
矿业工程   3篇
能源动力   90篇
轻工业   340篇
水利工程   17篇
石油天然气   12篇
无线电   277篇
一般工业技术   470篇
冶金工业   493篇
原子能技术   32篇
自动化技术   393篇
  2024年   3篇
  2023年   24篇
  2022年   35篇
  2021年   71篇
  2020年   51篇
  2019年   44篇
  2018年   83篇
  2017年   77篇
  2016年   74篇
  2015年   53篇
  2014年   115篇
  2013年   202篇
  2012年   111篇
  2011年   171篇
  2010年   115篇
  2009年   166篇
  2008年   145篇
  2007年   104篇
  2006年   100篇
  2005年   84篇
  2004年   83篇
  2003年   61篇
  2002年   65篇
  2001年   54篇
  2000年   56篇
  1999年   65篇
  1998年   149篇
  1997年   117篇
  1996年   79篇
  1995年   51篇
  1994年   47篇
  1993年   41篇
  1992年   26篇
  1991年   17篇
  1990年   24篇
  1989年   16篇
  1988年   18篇
  1987年   15篇
  1986年   19篇
  1985年   17篇
  1984年   12篇
  1983年   11篇
  1982年   16篇
  1981年   20篇
  1980年   10篇
  1979年   6篇
  1978年   3篇
  1977年   10篇
  1976年   17篇
  1975年   4篇
排序方式: 共有2963条查询结果,搜索用时 0 毫秒
81.
Microseaming is a significant technological development in the can manufacturing process that has been employed in the packaging of tomato processed products in Brazil. It was developed by the Brazilian company Grupo Kramer in 1990. Due to its reduced dimensions in relation to the traditional can closing system, i.e. the conventional double seam, microseam mechanical resistance as well as its capability to guarantee package integrity when submitted to processing and distribution remain questionable. In this study microseam resistance was compared to conventional double seam resistance when submitted to mechanical abuse through a standardized impact on the seam region positioned at angles of 45 and 67°. As evaluation parameters of closing integrity loss after impact swelling resulting from the cans external contact with a bacterial suspension, internal vacuum loss and can centre depth changes were used. The microseam presented a performance comparable to the conventional double seam for the impact at 45°, whereas at 67° its performance was found to be superior. This superior microseam performance can be credited to its being more malleable, i.e., to its greater capability of deforming itself when submitted to a puncture-type impact, to its more compact structure and to the type of deformation resulting from this type of impact.  相似文献   
82.
Understanding the pathways involved in the formation and stability of the core and shell regions of a platelet-rich arterial thrombus may result in new ways to treat arterial thrombosis. The distinguishing feature between these two regions is the absence of fibrin in the shell which indicates that in vitro flow-based assays over thrombogenic surfaces, in the absence of coagulation, can be used to resemble this region. In this study, we have investigated the contribution of Syk tyrosine kinase in the stability of platelet aggregates (or thrombi) formed on collagen or atherosclerotic plaque homogenate at arterial shear (1000 s−1). We show that post-perfusion of the Syk inhibitor PRT-060318 over preformed thrombi on both surfaces enhances thrombus breakdown and platelet detachment. The resulting loss of thrombus stability led to a reduction in thrombus contractile score which could be detected as early as 3 min after perfusion of the Syk inhibitor. A similar loss of thrombus stability was observed with ticagrelor and indomethacin, inhibitors of platelet adenosine diphosphate (ADP) receptor and thromboxane A2 (TxA2), respectively, and in the presence of the Src inhibitor, dasatinib. In contrast, the Btk inhibitor, ibrutinib, causes only a minor decrease in thrombus contractile score. Weak thrombus breakdown is also seen with the blocking GPVI nanobody, Nb21, which indicates, at best, a minor contribution of collagen to the stability of the platelet aggregate. These results show that Syk regulates thrombus stability in the absence of fibrin in human platelets under flow and provide evidence that this involves pathways additional to activation of GPVI by collagen.  相似文献   
83.
Ozonation can improve the effluent characteristics of UASB (upflow anaerobic sludge blanket) reactors treating domestic sewage, by removing organic matter, solids, surfactants, color and microorganisms. In Brazil, part of the effluent of a 120 msup3; UASB reactor, fed with screened domestic sewage at an hydraulic retention time of 7 hours, was post-treated in a two-column ozonation system of 300 liters total volume. With a contact time of 50 minutes and ozone application dosage of 16.7 mg/L, the following removals were obtained at the ozonation step: 51‰ BOD, 56‰COD, 76‰ TSS, 62‰ color, and 91‰ surfactants. Pathogens and indicator organisms were inactivated to over 99.9‰. Ozonation completely destroyed Salmonella, protozoa cysts and helminth eggs and larvae.  相似文献   
84.
In this investigation, the characteristics and the rheological properties of two different nanocomposite systems were investigated. These systems consisted of a dispersion of carbon nanotubes (CNTs) and carbon nanofibers (CNFs) in a polypropylene (PP) matrix. The mixing process was carried out by melt compounding with a twin‐screw corotating extruder with different reinforcement amounts (0.2–20 wt %) from concentrated masterbatches (20 wt %) of PP/CNT and PP/CNF. The results show a remarkable increase in the viscosity for both blends as the reinforcement amount was increased. It was important to evaluate the rheological behavior to understand the effect of the nanocarbon particles on the internal structures and their processing properties of the obtained composites. CNFs were a more viable reinforcement from a processability point of view because the obtained viscosities of the PP/CNF blends were more manageable. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012  相似文献   
85.
Coherent hydrous vanadium pentoxide (V2O5·nH2O)-carbon cryogel (CC) nanocomposites were synthesized by electrodeposition of vanadium pentoxide onto the porous carbon scaffold which was derived from resorcinol (R) and formaldehyde (F) organic hydrogels. As-fabricated nanocomposites were characterized by scanning electron microscopy (SEM), along with EDAX and nitrogen sorption isotherms which suggested vanadium pentoxide incorporated in the pores of carbon cryogels. The nanocomposites showed much improved discharge capacity and better cyclic stability as compared to hydrous vanadium pentoxide films deposited on platinum foil. The discharge capacity of the nanocomposites reached 280 mAh g−1 based on the mass of the vandium pentoxide at a current density of 100 mA g−1 and it possessed good cycle stability at different discharge rates. The results demonstrated that electrochemical performances, such as specific discharge capacitance and reversibility of the composite electrode, could be greatly enhanced by the introduction of carbon cryogels (CCs) scaffold with three-dimensionally interconnected porous structure in which V2O5·nH2O homogeneously dispersed.  相似文献   
86.
An increase in the average herd size on Australian dairy farms has also increased the labor and animal management pressure on farmers, thus potentially encouraging the adoption of precision technologies for enhanced management control. A survey was undertaken in 2015 in Australia to identify the relationship between herd size, current precision technology adoption, and perception of the future of precision technologies. Additionally, differences between farmers and service providers in relation to perception of future precision technology adoption were also investigated. Responses from 199 dairy farmers, and 102 service providers, were collected between May and August 2015 via an anonymous Internet-based questionnaire. Of the 199 dairy farmer responses, 10.4% corresponded to farms that had fewer than 150 cows, 37.7% had 151 to 300 cows, 35.5% had 301 to 500 cows; 6.0% had 501 to 700 cows, and 10.4% had more than 701 cows. The results showed that farmers with more than 500 cows adopted between 2 and 5 times more specific precision technologies, such as automatic cup removers, automatic milk plant wash systems, electronic cow identification systems and herd management software, when compared with smaller farms. Only minor differences were detected in perception of the future of precision technologies between either herd size or farmers and service providers. In particular, service providers expected a higher adoption of automatic milking and walk over weighing systems than farmers. Currently, the adoption of precision technology has mostly been of the type that reduces labor needs; however, respondents indicated that by 2025 adoption of data capturing technology for monitoring farm system parameters would be increased.  相似文献   
87.
The present research focused on the biogenic amines (BAs) formation in skipjack tuna (Katsuwonus pelamis) throughout the whole canning process. In agreement with its wide employment on this species, on‐board brine immersion freezing (BIF) was tested as post‐mortem processing. The study included fish samples corresponding to different stages of the canning process such as frozen, thawed, cooked and canned; after cooking, two kinds of tuna muscles were considered, that is, whole fillets (main product) and grated muscle (off‐product arising from small pieces). For the BAs (tryptamine, putrescine, cadaverine, histamine, spermidine and spermine) assessment, an HPLC‐DAD method was developed and validated in skipjack tuna samples, in agreement with different parameters such as suitability, linearity, limits of detection and quantification, precision, accuracy and robustness. Tuna submitted on‐board to BIF procedure provided low levels of spermine and spermidine (up to 27.6 mg kg?1), while contents on the remaining BAs maintained below the limit of detection. Throughout the different stages of the canning process, skipjack tuna showed a low formation of most BAs; interestingly, histamine content was found below 10.6 mg kg?1 level. The highest values were obtained for spermidine, these related to cooked grated tuna (from 22.6 to 66.7 mg kg?1) and canned grated tuna (from 70.6 to 104.4 mg kg?1). Values for pH assessment in all kinds of tuna samples corroborated the results obtained for BAs determination. BIF procedure proved to be an amenable post‐mortem processing to guarantee the quality of canned skipjack tuna.  相似文献   
88.
89.
90.
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