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   5214篇
  免费   160篇
  国内免费   76篇
电工技术   94篇
综合类   7篇
化学工业   976篇
金属工艺   125篇
机械仪表   204篇
建筑科学   101篇
矿业工程   3篇
能源动力   197篇
轻工业   304篇
水利工程   27篇
石油天然气   7篇
武器工业   1篇
无线电   917篇
一般工业技术   919篇
冶金工业   565篇
原子能技术   26篇
自动化技术   977篇
  2024年   8篇
  2023年   41篇
  2022年   87篇
  2021年   139篇
  2020年   56篇
  2019年   69篇
  2018年   77篇
  2017年   89篇
  2016年   106篇
  2015年   105篇
  2014年   188篇
  2013年   384篇
  2012年   277篇
  2011年   330篇
  2010年   236篇
  2009年   271篇
  2008年   277篇
  2007年   245篇
  2006年   230篇
  2005年   202篇
  2004年   163篇
  2003年   158篇
  2002年   129篇
  2001年   117篇
  2000年   87篇
  1999年   99篇
  1998年   250篇
  1997年   151篇
  1996年   115篇
  1995年   72篇
  1994年   97篇
  1993年   61篇
  1992年   45篇
  1991年   54篇
  1990年   36篇
  1989年   45篇
  1988年   53篇
  1987年   39篇
  1986年   32篇
  1985年   24篇
  1984年   28篇
  1983年   24篇
  1982年   11篇
  1981年   16篇
  1980年   15篇
  1979年   9篇
  1978年   12篇
  1977年   18篇
  1976年   34篇
  1974年   7篇
排序方式: 共有5450条查询结果,搜索用时 15 毫秒
991.
热蒸加工对大菱鲆过敏原免疫原性的影响   总被引:1,自引:0,他引:1  
目的 研究热蒸加工方式对大菱鲆(Scophthatmus maximus)过敏原免疫原性的影响。方法 利用热蒸处理对大菱鲆鱼肉进行了不同时间的加工, 利用SDS-PAGE测定大菱鲆蛋白质组分和蛋白质含量的变化, 并采用免疫印迹和间接ELISA分析热蒸加工对过敏原免疫原性的影响。结果 大菱鲆经过热蒸加工后, 其肌肉组分中分子量在40 ~65 kDa的蛋白有很大程度地降解, 而分子量在10 ~12 kDa的蛋白组分有增加的现象。免疫印迹的结果表明热蒸后的大菱鲆蛋白质组分与血清IgE特异性结合的能力减弱, 但与兔源小清蛋白抗体有强烈地反应, 特别是在分子量18 kDa的位置出现了一条能够与人血清IgE结合的蛋白质, 有可能是新的过敏原组分。结论 热蒸加工可以降低大菱鲆过敏原的免疫活性, 但在加工过程中可能有新的过敏原条带产生, 在进行过敏原检测时有必要考虑加工方式对过敏原结构和活性的影响, 以便得到更可靠的结果。  相似文献   
992.
993.
In this study, nondestructive test is developed to analyze the structure failure of LED package. The relationship between thermal resistance analysis and LED package failure structure is build with T3Ster thermal transient tester and scanning electron microscope (SEM). The failure LED device with defect in the attaching layer and gap between LED chip and copper are designed advisedly. The failure factors of LED package have been measured with thermal resistance analysis and SEM cross-section images. The thermal dissipation performance of LED with defect in the attaching layer is indicated by thermal resistance analysis combined with SEM cross-section images. The blister in attaching layer results in 4.4 K/W additional thermal resistance. The gap between LED chip and copper also makes high additional thermal resistance with 8.6 K/W. Different failures of LED packages are indicated obviously using thermal transfer analysis. The LED package failure structure such as interface defect between solder and cup-shaped copper is able to forecast without destructive measurement.  相似文献   
994.
Manganese-doped zinc oxide (Mn-doped ZnO) thin films were prepared using chemical bath deposition (CBD), and the impacts of the manganese dopant concentration on the structure, electrical resistivity, optical transmission, and magnetic properties were investigated using x-ray diffractometry, Hall-effect measurements, ultraviolet–visible–near-infrared (UV–Vis–IR) spectrophotometry, and vibrating sample magnetometry (VSM), respectively. The concentration of the manganese dopant in the ZnO thin film critically impacted the resulting properties, and the 4.0 at.% Mn-doped ZnO film had a resistivity of 5.8 × 10−2 Ωcm, transmittance of 75.6% in the visible light range, and bandgap of 3.30 eV when the film was annealed at 600°C in an Ar + H2 atmosphere. Annealing the film could enhance its magnetic properties such that the film had a saturation magnetization of 21.0 emu/cm3 and a coercivity of 45.7 Oe after annealing at 600°C. Because of these electrical, optical, and magnetic properties, Mn-doped thin films are promising for use in spintronic devices.  相似文献   
995.
Low-voltage-differential-signaling (LVDS) is one of the very popular technologies which simultaneously addresses low dynamic power consumption and high data rate transmission in modern high speed circuit applications. In this paper, system level integration design approach is applied to design LVDS transmitter featuring high off-chip data rate. Full wave electromagnetic simulation technique was adopted to accurately characterize possible couplings and parasitic effects induced from the off-chip components which then acted as the termination of the output circuitry. Common mode feedback was included to perform fine tuning on the offset leading to much higher overall precision. Meanwhile, generation of the controlled current and voltage across termination was guaranteed through the introduction of a constant transconductance bias network. The design was implemented using TSMC 3.3?V 0.35???m CMOS technology with overall chip size of 0.923?mm2. At a DC power consumption level of 29.4?mW, the LVDS transmitter exhibited an off-chip data rate of 1.3?Gb/s validated through measurements.  相似文献   
996.
Various user authentication schemes with smart cards have been proposed. Generally, researchers implicitly assume that the contents of a smart card cannot be revealed. However, this is not true. An attacker can analyze the leaked information and obtain the secret values in a smart card. To improve on this drawback, we involve a fingerprint biometric and password to enhance the security level of the remote authentication scheme Our scheme uses only hashing functions to implement a robust authentication with a low computation property. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   
997.
We report an effective way to produce nanoporous Pt counter electrodes of dye-sensitized solar cells by the glancing-angle deposition (GLAD) technique. By controlling the orientation of the substrate relative to the incident Pt vapor flux during the deposition, nanoporous films composed of inclined nm-scale columns were produced through the self-shadowing effect. Pt counter electrodes having varied nanoporous structures were characterized for their morphological and electrochemical properties, and were subjected to device studies to establish the correlation with DSSC characteristics/performances. The results suggest that the nanoporous GLAD Pt electrodes can effectively enhance active surface areas, the catalytic ability and charge exchange at the Pt/electrolyte interface of a DSSC. As a result, the quantum efficiency, short-circuit current, and power conversion efficiency of the DSSC can be enhanced by up to 12–13% with using the nanoporous GLAD Pt counter electrodes.  相似文献   
998.
A new class of ladder‐type dithienosilolo‐carbazole ( DTSC ), dithienopyrrolo‐carbazole ( DTPC ), and dithienocyclopenta‐carbazole ( DTCC ) units is developed in which two outer thiophene subunits are covalently fastened to the central 2,7‐carbazole cores by silicon, nitrogen, and carbon bridges, respectively. The heptacyclic multifused monomers are polymerized with the benzothiadiazole ( BT ) acceptor by palladium‐catalyzed cross‐coupling to afford three alternating donor‐acceptor copolymers poly(dithienosilolo‐carbazole‐alt‐benzothiadiazole) ( PDTSCBT) , poly(dithienocyclopenta‐carbazole‐alt‐benzothiadiazole) ( PDTCCBT), and poly(dithienopyrrolo‐carbazole‐alt‐benzothiadiazole) ( PDTPCBT) . The silole units in DTSC possess electron‐accepting ability that lowers the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of PDTSCBT , whereas stronger electron‐donating ability of the pyrrole moiety in DTPC increases the HOMO and LUMO energy levels of PDTPCBT . The optical bandgaps (Egopt) deduced from the absorption edges of thin film spectra are in the following order: PDTSCBT (1.83 eV) > PDTCCBT (1.64 eV) > PDTPCBT (1.50 eV). This result indicated that the donor strength of the heptacyclic arenes is in the order: DTPC > DTCC > DTSC . The devices based on PDTSCBT and PDTCCBT exhibited high hole mobilities of 0.073 and 0.110 cm2 V?1 s?1, respectively, which are among the highest performance from the OFET devices based on the amorphous donor‐acceptor copolymers. The bulk heterojunction photovoltaic device using PDTSCBT as the p‐type material delivered a promising efficiency of 5.2% with an enhanced open circuit voltage, Voc, of 0.82 V.  相似文献   
999.
The unprecedented liquefaction-related land damage during earthquakes has highlighted the need to develop a model that better interprets the liquefaction land damage vulnerability (LLDV) when determining whether liquefaction is likely to cause damage at the ground’s surface. This paper presents the development of a novel comprehensive framework based on select case history records of cone penetration tests using a Bayesian belief network (BBN) methodology to assess seismic soil liquefaction and liquefaction land damage potentials in one model. The BBN-based LLDV model is developed by integrating multi-related factors of seismic soil liquefaction and its induced hazards using a machine learning (ML) algorithm-K2 and domain knowledge (DK) data fusion methodology. Compared with the C4.5 decision tree-J48 model, naive Bayesian (NB) classifier, and BBN-K2 ML prediction methods in terms of overall accuracy and the Cohen’s kappa coefficient, the proposed BBN K2 and DK model has a better performance and provides a substitutive novel LLDV framework for characterizing the vulnerability of land to liquefaction-induced damage. The proposed model not only predicts quantitatively the seismic soil liquefaction potential and its ground damage potential probability but can also identify the main reasons and fault-finding state combinations, and the results are likely to assist in decisions on seismic risk mitigation measures for sustainable development. The proposed model is simple to perform in practice and provides a step toward a more sophisticated liquefaction risk assessment modeling. This study also interprets the BBN model sensitivity analysis and most probable explanation of seismic soil liquefied sites based on an engineering point of view.  相似文献   
1000.
Elevated levels of serum pancreatic enzymes are frequently observed in hemodialysis (HD) patients. The complex hemodynamic, biochemical, and physiological alterations in uremia were speculated to cause excessive release of pancreatic enzymes beyond decreased renal clearance. However, hemodynamic factors are seldom explored in this aspect. We performed the study to evaluate the association between intradialytic hemodynamic change and elevated serum pancreatic amylase (SPA). Eighty‐three prevalent HD patients without any clinical evidence of acute pancreatitis underwent pre‐HD and post‐HD blood sampling for serum pancreatic enzyme levels. Demographic, biochemical, and hematological data were collected from patient record review. Hemodialysis information including intradialytic blood pressure changes and ultrafiltration (UF) amount were collected and averaged for 1 month before the blood sampling day. Patients with elevated SPA during the HD session had greater mean systolic blood pressure and mean arterial pressure reduction, greater UF volume, greater pre‐HD blood urea nitrogen and serum creatinine, higher serum phosphorus, lower pre‐HD serum total CO2, and lower left ventricle ejection fraction (LVEF). Using multivariate linear and logistic regression analysis, the independent predictors of elevated SPA were determined to be mean arterial pressure reduction during HD, mean UF amount, pre‐HD serum total CO2, and LVEF. Greater blood pressure reduction during HD, greater UF volume, lower pre‐HD serum total CO2, and lower LVEF were significantly associated with elevated SPA during HD. This suggests that hemodynamic factors contribute to elevated serum pancreatic enzymes in HD patients.  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