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   1105篇
  免费   47篇
电工技术   14篇
化学工业   286篇
金属工艺   8篇
机械仪表   31篇
建筑科学   23篇
能源动力   28篇
轻工业   109篇
水利工程   2篇
石油天然气   6篇
无线电   65篇
一般工业技术   158篇
冶金工业   284篇
原子能技术   7篇
自动化技术   131篇
  2023年   5篇
  2022年   51篇
  2021年   51篇
  2020年   25篇
  2019年   11篇
  2018年   32篇
  2017年   27篇
  2016年   20篇
  2015年   19篇
  2014年   22篇
  2013年   46篇
  2012年   42篇
  2011年   60篇
  2010年   28篇
  2009年   45篇
  2008年   48篇
  2007年   27篇
  2006年   33篇
  2005年   26篇
  2004年   23篇
  2003年   28篇
  2002年   34篇
  2001年   23篇
  2000年   13篇
  1999年   22篇
  1998年   97篇
  1997年   58篇
  1996年   38篇
  1995年   24篇
  1994年   13篇
  1993年   25篇
  1992年   10篇
  1991年   4篇
  1990年   8篇
  1989年   5篇
  1988年   6篇
  1987年   11篇
  1986年   8篇
  1985年   7篇
  1984年   4篇
  1983年   9篇
  1982年   5篇
  1981年   9篇
  1980年   7篇
  1979年   5篇
  1978年   4篇
  1977年   7篇
  1976年   8篇
  1975年   3篇
  1971年   4篇
排序方式: 共有1152条查询结果,搜索用时 62 毫秒
61.
We describe a collective episode of psychogenic illness in an indigenous group (Embera) of Colombia, geographically isolated from its native homeland and surrounded by non-indigenous settlers. The condition, which affected three young adult men and six adolescent women, was attributed by them to a spell (maleficio). It was designated as ataques de locura (madness attacks) according to their traditional medical system; and as a conversive disorder with dissociative features by psychiatrists. Different therapeutic approaches, including antipsychotic medication, religious healers and traditional herbal remedies were unsuccessful. Contact with shamans of the same ethnic origin, on the other hand, proved to be an effective way of dealing with the symptoms. We interpret the situation as an expression of psychosocial stress secondary to cultural change. This medical problem bears close resemblance to other specific culture-bound syndromes such as ataques de nervios or possession syndromes and gives clues to ways of dealing with psychogenic expressions of cultural stress.  相似文献   
62.
C++ uses inheritance as a substitute for subtype polymorphism. We give examples where this makes the type system too inflexible. We then describe a conservative language extension that allows a programmer to define an abstract type hierarchy independent of any implementation hierarchies, to retroactively abstract over an implementation, and to decouple subtyping from inheritance. This extension gives the user more of the flexibility of dynamic typing while retaining the efficiency and security of static typing. With default implementations and views flexible mechanisms are provided for implementing an abstract type by different concrete class types. We first show how the language extension can be implemented in a preprocessor to a C++ compiler, and then detail and analyse the efficiency of an implementation we directly incorporated in the GNU C++ compiler.  相似文献   
63.
OBJECTIVE: Free radical production has been reported to be increased in diabetic patients and to be involved in the pathogenesis of diabetic complications. In this study, a standardized meal was administered to 10 type 2 diabetic patients and 10 healthy matched normal subjects to evaluate its effects on plasma oxidative stress generation. RESEARCH DESIGN AND METHODS: In diabetic patients, at baseline and after the meal, plasma malondialdehyde (MDA), vitamin C, protein SH groups, uric acid, vitamin E, and total plasma radical-trapping parameter, which evaluates plasma antioxidant capacity due to known and unknown antioxidants present in the plasma as well as their mutual cooperation, were measured. RESULTS: After the meal, plasma MDA and vitamin C increased, while protein SH groups, uric acid, vitamin E, and total plasma radical-trapping parameter decreased more significantly in the diabetic subjects than in control subjects. CONCLUSIONS: This finding shows that in the absorptive phase, free radicals are produced in diabetic patients. Since plasma glucose, but not insulin, rose significantly more in diabetic subjects than in control subjects, hyperglycemia may play an important role in the generation of postprandial oxidative stress in diabetic patients.  相似文献   
64.
Acute toxicity bioassays in which fish were exposed to short-term cyclic fluctuations of ammonia were conducted on rainbow trout (Salmo gairdneri) and on cutthroat trout (S. clarki). Companion tests were also conducted in which test fish were subjected to ammonia at constant concentrations. The tests ranged in duration from 96 h to 4 weeks. Median lethal concentration (LC 50) values in terms of both average and peak concentrations of ammonia for the fluctuating concentration tests were compared with LC 50 values for the constant concentration (conventional) tests. Based on comparisons of total dose exposure, results showed that fish were more tolerant of constant concentrations of ammonia than of fluctuating concentrations. Fish subjected to fluctuating concentrations of ammonia at levels below those acutely toxic were subsequently better able to withstand exposure to higher fluctuating concentrations than fish not previously so acclimated.  相似文献   
65.
We compared the analytical performance of ultraviolet femtosecond and nanosecond laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). The benefit of ultrafast lasers was evaluated regarding thermal-induced chemical fractionation, that is otherwise well known to limit LA-ICPMS. Both lasers had a Gaussian beam energy profile and were tested using the same ablation system and ICPMS analyzer. Resulting crater morphologies and analytical signals showed more straightforward femtosecond laser ablation processes, with minimal thermal effects. Despite a less stable energy output, the ultrafast laser yielded elemental (Pb/U, Pb/Th) and Pb isotopic ratios that were more precise, repeatable, and accurate, even when compared to the best analytical conditions for the nanosecond laser. Measurements on NIST glasses, monazites, and zircon also showed that femtosecond LA-ICPMS calibration was less matrix-matched dependent and therefore more versatile.  相似文献   
66.
Dissimilar resistance spot welding of twinning induced plasticity (TWIP) and quenching and partitioning (Q&P) steel grades has been investigated by evaluating the effects of clamping force, welding current, and welding time on the microstructure, shear tension strength, and fracture of welded samples. The spot welding of TWIP and Q&P steels promotes the occurrence of an asymmetrical weld nugget with a greater dilution of TWIP steel because of its lower melting temperature and thermal conductivity. As a result, weld nuggets exhibit an austenitic microstructure. TWIP steel undergoes a grain coarsening in the HAZ, whereas Q&P steel undergoes some phase transformations. Welded samples tend to exhibit higher shear tension strength as they are joined at the highest welding current, even though an improper clamping force can promote excessive metal expulsion, thereby reducing the mechanical strength of the welded joints. Shear tension welded samples failed through interfacial fracture with partial thickness fracture mode for a low welding current, while partial thickness with button pull fractures were observed when a high welding current was used. The weld spots predominantly failed at the TWIP side. However, as TWIP steel can work harden significantly in the more resistant welded joints, the failures occur, instead, at the Q&P side.  相似文献   
67.
68.
In this work, the use of a film of an organometallic polymer, namely Pt‐DEBP, has been tested for the selective capture of sulfides with the aim of protecting silver object. Ag foils were exposed to different environmental conditions in the presence of Pt‐DEBP films. Scanning electron microscopy, energy dispersive spectrometry, and colorimetric studies allowed to assess that the polymeric layer selectively captures H2S, preventing the tarnishing of the silver substrate over a period at least of 2 months, without any manipulation of the sample. This approach open new perspectives for the prevention of aging effects on silver objects of artistic interest, for which cleaning or coating procedures should be avoid. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013  相似文献   
69.
Policy-based management provides the ability to (re-)configure differentiated services networks so that desired Quality of Service (QoS) goals are achieved. This requires implementing network provisioning decisions, performing admission control, and adapting bandwidth allocation to emerging traffic demands. A policy-based approach facilitates flexibility and adaptability as policies can be dynamically changed without modifying the underlying implementation. However, inconsistencies may arise in the policy specification. In this paper we provide a comprehensive set of QoS policies for managing Differentiated Services (DiffServ) networks, and classify the possible conflicts that can arise between them. We demonstrate the use of Event Calculus and formal reasoning for the analysis of both static and dynamic conflicts in a semi-automated fashion. In addition, we present a conflict analysis tool that provides network administrators with a user-friendly environment for determining and resolving potential inconsistencies. The tool has been extensively tested with large numbers of policies over a range of conflict types.  相似文献   
70.
In this paper, novel integer programming formulations are developed for solving the optimal scheduling of patients waiting for radiotherapy treatment. In this specific clinical domain, the suitable management and control of a patients’ waiting list strongly affect both the quality of the therapeutical outcome, in terms of effectiveness, and the cost-saving use of the overall therapeutical resources, in terms of efficiency. The proposed models allow the best scheduling strategy to be devised by taking into account the quality of the health care service offered to the patient as well as the status and the preferences of the patient. The computational experiments, carried out on realistic scenarios and considering real data, are very promising and show the efficiency and robustness of the proposed models to address the problem under consideration.  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