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   2708篇
  免费   688篇
  国内免费   124篇
电工技术   94篇
综合类   206篇
化学工业   587篇
金属工艺   110篇
机械仪表   136篇
建筑科学   83篇
矿业工程   40篇
能源动力   21篇
轻工业   793篇
水利工程   17篇
石油天然气   52篇
武器工业   11篇
无线电   531篇
一般工业技术   449篇
冶金工业   39篇
原子能技术   5篇
自动化技术   346篇
  2024年   20篇
  2023年   87篇
  2022年   109篇
  2021年   143篇
  2020年   162篇
  2019年   136篇
  2018年   148篇
  2017年   130篇
  2016年   147篇
  2015年   133篇
  2014年   177篇
  2013年   191篇
  2012年   212篇
  2011年   211篇
  2010年   176篇
  2009年   148篇
  2008年   142篇
  2007年   187篇
  2006年   156篇
  2005年   157篇
  2004年   125篇
  2003年   111篇
  2002年   79篇
  2001年   61篇
  2000年   45篇
  1999年   20篇
  1998年   22篇
  1997年   21篇
  1996年   18篇
  1995年   8篇
  1994年   8篇
  1993年   11篇
  1992年   4篇
  1991年   1篇
  1990年   5篇
  1989年   2篇
  1988年   1篇
  1984年   1篇
  1983年   1篇
  1981年   1篇
  1980年   1篇
  1951年   2篇
排序方式: 共有3520条查询结果,搜索用时 31 毫秒
11.
The objective of this research was to investigate and compare the effect of different treatments including gaseous ozone (6-ppm/4-min), ultrasound (450 W/4 min) and coating of shellac, lysozyme–chitosan (L-C) on fresh eggs internal quality during storage for six weeks at ambient temperature. The internal quality attributes such as weight loss (WL), albumen viscosity, Haugh unit (HU), yolk index, total soluble solids, albumen and yolk's pH were monitored. Control groups had the worst HU (50.04), WL (8.35%), albumen pH (9.27) and viscosity (7.72 mPa·s) values after storage. The best interior qualities were obtained by shellac coating [HU (72.37), WL (1.37) and viscosity (30.10 mPa·s)] and sonication (albumen pH: 8.22). Thus, the shellac-coated eggs maintained all the internal quality parameters at the highest values, while the ozone and ultrasound only helped to keep the internal quality and enhance the shelf life of eggs.  相似文献   
12.
The modulating effect of ultrasound treatments at varying powers and times on the structural and functional properties of black bean protein isolate (BBPI) was investigated. Compared with native BBPI, low-power (150 W) and medium-power (300 W) ultrasound treatments increased the solubility, foaming and emulsifying properties of BBPI, especially at 300 W, 24 min. This effect arises predominantly due to increased exposure of hydrophobic groups, which serve to increase the interactions between the protein and water molecules. Additionally, an increase in the protein surface activity improved the absorption of protein molecules at the oil–water and air–water interfaces. Rheology data showed that increased hydrophobic and hydrogen-bonding interactions improved the water-holding capacity of BBPI gels following ultrasound treatment. However, high-power (450 W) ultrasound treatment weakened the functional properties of BBPI, and this was likely due to the formation of macromolecular BBPI aggregates. Overall, this study indicates that ultrasound treatment could be a promising approach for modulating other plant protein resources as well as expanding the application of black bean protein.  相似文献   
13.
Hydrogels are formed using various triggers, including light irradiation, pH adjustment, heating, cooling, or chemical addition. Here, a new method for forming hydrogels is introduced: ultrasound-triggered enzymatic gelation. Specifically, ultrasound is used as a stimulus to liberate liposomal calcium ions, which then trigger the enzymatic activity of transglutaminase. The activated enzyme catalyzes the formation of fibrinogen hydrogels through covalent intermolecular crosslinking. The catalysis and gelation processes are monitored in real time and both the enzyme kinetics and final hydrogel properties are controlled by varying the initial ultrasound exposure time. This technology is extended to microbubble–liposome conjugates, which exhibit a stronger response to the applied acoustic field and are also used for ultrasound-triggered enzymatic hydrogelation. To the best of the knowledge, these results are the first instance in which ultrasound is used as a trigger for either enzyme catalysis or enzymatic hydrogelation. This approach is highly versatile and can be readily applied to different ion-dependent enzymes or gelation systems. Moreover, this work paves the way for the use of ultrasound as a remote trigger for in vivo hydrogelation.  相似文献   
14.
在45钢表面以超声波辅助脉冲电沉积制备Ni-TiN复合镀层。研究了平均阴极电流密度、脉冲占空比、超声功率和TiN粒子(平均直径20~30 nm)添加量对复合镀层的TiN粒子含量和显微硬度的影响。得到较优的工艺参数为:NiSO4ꞏ6H2O 300 g/L,NiCl2ꞏ6H2O 30 g/L,H3BO330 g/L,十二烷基硫酸钠0.3 g/L,TiN 25 g/L,pH 4.1~4.3,温度40°C,平均阴极电流密度4 A/dm2,脉冲占空比40%,脉冲频率1000 Hz,超声功率300 W,机械搅拌速率200 r/min,时间60 min。该条件下所得Ni-TiN复合镀层的TiN质量分数为8.35%,显微硬度为819 HV,表面平整、致密,晶粒尺寸均匀。  相似文献   
15.
《Planning》2015,(3)
目的 评估腹腔脏器病变患者术前经腹超声检查报告并分析超声漏诊及误诊的原因。方法 通过病理工作站导出2013年3月1日至8月31日因腹腔脏器(肝脏、胆囊、胆管、胰腺、脾脏、肾脏、肾上腺和阑尾)病变于北京协和医院进行手术治疗的住院患者病理资料,评估相应超声报告,记录漏、误诊报告信息,分析漏、误诊原因。结果 共评估超声报告1081份,漏、误诊报告58份(5.37%,58/1081),其中肝脏病变6例(5.77%,6/104),均为误诊;胆囊和胆管病变6例(1.30%,6/462),漏诊5例、误诊1例;胰腺病变14例(19.72%,14/71),均为漏诊;肾脏和肾上腺病变20例(6.47%,20/309),漏诊11例、误诊9例;阑尾病变12例(16.00%,12/75),漏诊11例、误诊1例。漏诊结节样病变最大径平均值显著低于误诊病变(P=0.001)。结论 不同腹腔脏器病变因性质、部位、体积以及超声本身的局限性等原因导致超声漏诊或误诊,超声医师在临床工作中应做到全面、仔细、谨慎,了解各腹腔脏器病变的自身特点以及超声显像的局限性,不断积累经验,尽可能避免不必要的错误。  相似文献   
16.
The influence of ultrasound power (1000–3000 W/L), citric acid concentration (0–3%) and solid:liquid ratio (1:5–1:15) on the phenolic compounds recovery and antioxidant capacity of Syrah grape skin extracts were evaluated. Total phenolic compounds varied from 6485 to 11732 mg gallic acid/100 g and monomeric anthocyanin content from 453 to 685 mg malvidin-3-glucoside/100 g. The antioxidant capacity measured by ORAC and ABTS methods ranged from 230 to 516 μmol Trolox/g and from 442 to 939 μmol Trolox/g, respectively. The most suitable conditions chosen for extraction, within the studied ranges, were 3000 W/L of power, 2.5% citric acid and solid:liquid ratio of 1:15. The extraction yield was satisfactory, with a recovery of 59% of the quantified phenolic compounds, with only 3 min of processing. Ultrasound was considered a suitable method as compared to the conventional extraction, improving the extraction of phenolic acids and facilitating their release.  相似文献   
17.
In this study, the influence of sonication time on the biogenic amines formation as a critical point in uncured dry-fermented beef manufacturing was studied. Samples of musculus semimembranosus were sonicated at different times (5 and 10 min) using ultrasound cold bath (4 °C) in acid whey (US 40 kHz and acoustic power 480 W). The effect of sonication on biogenic amine (BA) formation was investigated during 93 days of ripening period. Other parameters (pH value, water activity, microbial counts) that might provide further information on the product under study were also determined. The use of ultrasound during beef marinating in acid whey has a positive effect on retarding histamine (HIS), cadaverine (CAD), tyramine (TYR) and putrescine (PUT) formation. Moreover, the sonication treatment did not inhibit the growth of lactic acid bacteria (LAB) in dry-fermented beef during the whole ripening period. The pathogen bacteria (Staphylococcus aureus, Clostridium sp., Listeria monocytogenes) were not detected in all samples neither after 31 nor after 93 days of ripening period.  相似文献   
18.
《Planning》2019,(5)
目的探讨大脑中动脉血流动力学相关指标及脑氧饱和度变化与感染性休克患者预后的相关性。方法前瞻性收集2018年5月至2019年3月在中南大学湘雅医院重症医学科住院治疗的感染性休克患者临床资料,根据28 d内是否死亡,将患者分为死亡组和存活组。比较两组患者一般资料,入重症监护室即刻和初始复苏治疗6 h后动脉和中心静脉血气指标,重症心脏超声指标,器官功能指标,Sepsis生物标志物指标,液体复苏治疗6 h后大脑中动脉血流速度、灌注指数、动态脑血管自动调节功能[瞬时脑充血反应率(transient hyperemic response ratio,THRR)]以及脑氧饱和度变化。采用多因素Logistic回归,分析影响感染性休克患者预后的危险因素。结果 51例符合纳入和排除标准的感染休克患者入选本研究,男性31例,女性20例,年龄(53±13)岁,28 d死亡率为43%。死亡组的序贯性器官衰竭评分(sequential organ failure assessment,SOFA)(P=0. 007)、入室急性生理和慢性健康状况评估(acute physiology and chronic health evaluationⅡ,APACHEⅡ)评分(P=0. 026)以及高峰APACHEⅡ评分(P<0. 001)均高于存活组。初始复苏治疗6 h后,死亡组的氧合指数低于存活组(P=0. 047),而中心静脉-动脉二氧化碳分压差(central venous-to-arterial carbon dioxide difference,Pcva CO_2)则高于存活组(P=0. 044)。死亡组动态脑血管自动调节功能受损者(THRR<1. 09)多于存活组(P=0. 025),脑氧饱和度(regional cerebral oxygen saturation,rSO_2)均值低于存活组(P=0. 031)且rSO_2均值<60%者多于存活组(P=0. 010)。多因素Logistic回归分析显示,高峰APACHEⅡ评分(OR=1. 099,95%CI:1. 009~1. 196,P=0. 030)、液体复苏治疗6 h后的Pcv-aCO_2(OR=1. 320,95%CI:1. 001~1. 742,P=0. 050)、THRR<1. 09 (OR=4. 952,95%CI:1. 130~21. 70,P=0. 034)和rSO_2均值<60%(OR=4. 817,95%CI:1. 392~16. 663,P=0. 013)是预测感染性休克患者28 d内死亡的独立危险因素。结论感染性休克患者死亡率高,脑血流动力学和rSO_2指标中动态脑血管自动调节功能障碍(THRR<1. 09)与rSO_2均值<60%是28 d死亡率增加的独立预测因素。  相似文献   
19.
《Planning》2019,(6)
目的应用床旁超声技术观察术前2 h饮用碳水化合物对老年胃肠道手术患者麻醉前胃容量的影响,并评估患者发生反流误吸的风险。方法前瞻性选取2017年12月至2018年10月,在四川省人民医院行胃肠道手术的老年患者(>65岁),随机分为试验组和对照组。试验组常规禁食8 h,术前2 h口服200 ml碳水化合物;对照组要求术前禁食8 h,禁饮4 h。麻醉前采用床旁超声技术测量45°半坐位及右侧卧位胃窦部头尾径及前后径,分别计算两种体位下的胃窦部横截面积(cross-sectional area,CSA)、胃容量(gastric volume,GV)及胃容量与体重比(GV/weight,GV/W)。采用GV超声半定量3分评估法及GV/W分级法评估患者发生反流误吸的风险。结果共纳入69例符合入选和排除标准的患者,其中试验组33例,对照组36例。两组基线资料、手术类别及美国麻醉医师学会分级无统计学差异(P均>0. 05)。半坐位下,试验组和对照组的GV/W分别为(0. 57±0. 23) ml/kg和(0. 44±0. 21) ml/kg;右侧卧位下,试验组和对照组的CSA分别为(578. 8±71. 5) mm2和(513. 3±53. 2) mm2,GV分别为(21. 2±11. 1) ml和(12. 9±6. 8) ml,GV/W分别为(0. 36±0. 17) ml/kg和(0. 20±0. 11) ml/kg,上述指标两组间均存在统计学差异(P均<0. 05)。GV超声半定量评分:试验组0分17例(51. 5%,17/33),1分15例(45. 5%,15/33),2分1例(3. 0%,1/33),对照组0分25例(69. 4%,25/36),1分11例(30. 6%,11/36),2分0例(0,0/33),两组评分构成比无统计学差异(P>0. 05)。反流误吸风险评估:试验组极低风险者占比81. 8%(27/33)、低风险18. 2%(6/33)、高风险0 (0/33),对照组极低风险者占比94. 4%(34/36)、低风险5. 6%(2/36)、高风险0 (0/33),两组间构成比亦无统计学差异(P>0. 05)。结论老年胃肠道手术患者术前2 h饮用200 ml碳水化合物虽可以增加麻醉前胃容量,但并不增加反流误吸的风险。  相似文献   
20.
《Planning》2019,(5)
目的探讨彩色多普勒超声测量肾脏叶间动脉阻力指数(resistance index,RI)对Ⅰ型心肾综合征(cardiorenal syndrome,CRS)的诊断价值。方法选取2017年6月1日至2018年3月1日收住民航总医院急诊综合病房并诊断为Ⅰ型CRS的20例患者作为试验组(CRS组),选取同期诊断为单纯急性心力衰竭的患者20例作为对照组,分析两组患者的临床特征、实验室检查及用药情况,并根据受试者工作特征(receiver operating characteristic,ROC)曲线评价肾动脉RI对Ⅰ型CRS的诊断价值。结果两组患者年龄、左心室射血分数、心功能分级、心率及脉压差差异无统计学意义(P均>0. 05),CRS组患者的氨基末端脑钠尿肽、肌酐水平、呋塞米剂量以及肾动脉RI均高于对照组,而肾小球滤过率低于对照组,差异具有统计学意义(P均<0. 05)。ROC曲线下面积为0. 78,取最佳截点值0. 70时预测Ⅰ型CRS的敏感度为80%,特异度为80%。结论作为一种新的手段,肾动脉RI可与传统方法相互补充,对诊断Ⅰ型心肾综合征患者具有潜在应用价值。  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