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   2145篇
  免费   26篇
电工技术   17篇
化学工业   197篇
金属工艺   83篇
机械仪表   23篇
建筑科学   66篇
能源动力   47篇
轻工业   154篇
水利工程   4篇
石油天然气   5篇
无线电   147篇
一般工业技术   231篇
冶金工业   1025篇
原子能技术   6篇
自动化技术   166篇
  2023年   5篇
  2022年   10篇
  2021年   17篇
  2020年   11篇
  2019年   12篇
  2018年   16篇
  2017年   22篇
  2016年   20篇
  2015年   32篇
  2014年   35篇
  2013年   65篇
  2012年   43篇
  2011年   69篇
  2010年   57篇
  2009年   56篇
  2008年   57篇
  2007年   59篇
  2006年   44篇
  2005年   46篇
  2004年   45篇
  2003年   43篇
  2002年   43篇
  2001年   30篇
  2000年   26篇
  1999年   64篇
  1998年   299篇
  1997年   180篇
  1996年   131篇
  1995年   92篇
  1994年   93篇
  1993年   73篇
  1992年   21篇
  1991年   20篇
  1990年   36篇
  1989年   36篇
  1988年   25篇
  1987年   23篇
  1986年   13篇
  1985年   19篇
  1984年   11篇
  1983年   6篇
  1982年   11篇
  1981年   14篇
  1980年   8篇
  1979年   7篇
  1978年   7篇
  1977年   34篇
  1976年   59篇
  1975年   4篇
  1973年   5篇
排序方式: 共有2171条查询结果,搜索用时 500 毫秒
11.
This paper describes the spatial distribution of customer demand, supply of customer services and facility investment, as the outcome of a three-level game-like interaction between customers (e.g., shoppers), suppliers (e.g., retailers) and developers (e.g., landlords). Treating both the suppliers and developers at each centre as competitors, oligopolistic equilibria of the Nash-Stackelberg type are developed, and conditions for their existence and uniqueness established. Uncertain customer demand is specified in probabilistic terms, representing the suppliers' perception of expected customer behaviour.  相似文献   
12.
A sampled grating distributed Bragg reflector-laser integrated with a waveguide Franz-Keldysh modulator is investigated for high optical power applications. The EAM modulation efficiency is demonstrated to asymptotically approach a limit determined by the internal differential photodetector efficiency. Linear photocurrent and 1 dB small signal AC compression point both exceed 70 mA, indicating high saturation power.  相似文献   
13.
A combustion method, relying on the Dumas principle, for the determination of total nitrogen in barley and malt, has been collaboratively tested by the Analysis Committee of the European Brewery Convention. Repeatability, r95, and reproducibility, R95, values were 0.063 and 0.116% of dry matter, respectively, for samples with nitrogen contents in the range 1.23 to 1.86% N of dry matter. There was no significant difference between these values for barley and malt. The Analysis Committee approved the adoption of the combustion method for inclusion in Analytica EBC as an alternative method.  相似文献   
14.
The objective of this study is to describe usual medical management and costs associated with recurrent respiratory infections in subjects with chronic obstructive bronchitis in France. A prospective survey was performed in Autumn 1994 on a national sample of private practice pulmonologists (N = 71). Two hundred forty-four patients, presenting at least one infection of the lower respiratory tract, were included. Bronchitis was the most frequent acute exacerbation observed (94%). Pneumonia concerned 9% of the patients. Biological tests, X-rays and pulmonary function tests were prescribed for, respectively, 59, 65 and 45% of the patients. Following the visit, 15 patients were hospitalized (6%). The direct medical cost per acute exacerbation was estimated 3,289 francs (1994 value) of which 60% were hospital-related. An average 10.4 day sick-leave was prescribed to 21% of patients in employment. For those patients, this sick-leave was associated to an extra-cost of 1,264-1,876 francs for Social Security and of 0-2,553 francs out of pocket per episode varying according to their Benefit Regimen.  相似文献   
15.
Southern blot analysis was performed with a panel of DNA probes to detect rearrangements of c-myc, bcl-1, bcl-2 and bcl-3 in 14 cases of B-cell non-Hodgkin's lymphoma (NHL) with a clonal cytogenetic rearrangement involving the chromosome 14q32 locus and no known donor chromosome [t(14;?)(q32;?)]. In our experience, 21% of all chromosomal abnormalities involving the 14q32 locus in B-cell NHL are of this type. We found oncogene rearrangements in five of the 14 cases: bcl-1 rearrangement on one mantle zone lymphoma, bcl-2 rearrangements in two follicular lymphomas, and c-myc rearrangements in two small noncleaved cell lymphomas. We conclude that a 14q32+ abnormality of unknown origin is a relatively frequent karyotypic finding in B-cell NHL. In one third of the cases, known oncogenes that have been previously described in reciprocal translocations involving the immunoglobulin heavy chain locus were shown to be involved in the 14q32+ abnormality. The translocations in the other cases are likely to have involved one of the above oncogenes with breakpoints not revealed by the probes employed, other known oncogenes, or oncogenes that have not yet been identified.  相似文献   
16.
The purpose of all injury care is to restore patients' pre-injury functioning and to facilitate the return to normal activities. The aim of this prospective study was to describe and analyse psychiatric factors and other patient-related characteristics which influence long-term results after moderate injuries. One hundred and sixty-nine injured patients were randomized to go through a comprehensive psychosocial research protocol and to participate in the 12 month follow up. The 49 patients lost to follow-up differed significantly from all other patients. They were more often single, blue-collar workers with a lower educational level and had a less favourable psychosocial background, including alcohol abuse. The 120 patients who completed the follow-up were divided in two groups: the non-recovered group (NR, N = 58), patients reporting limitations in performing their work and/or limitations in carrying out housework and/or in social life, and the recovered group (R, N = 62), patients reporting full recovery or only minor limitations in exercise or sports 12 months after the injury. The NR patients were older (P < 0.05), had a slightly higher injury Severity Score (P < 0.01) and showed signs of depression both during the acute post-injury period and at 1 year follow up (P < 0.001). The multivariate analysis showed that measurements of pain and depression during the acute post-injury period were associated with the functional outcome after 12 months. Co-operation between injury and psychiatric units should be developed to identify patients needing psychosocial or psychiatric support during the early phase of rehabilitation.  相似文献   
17.
Wheat proteins, soluble in diluted acid (glutenins), have been fractionated by counter-current distribution (CCD) using an aqueous two-phase system. The phase system is based on poly(ethylene glycol) and dextran but contains also 1% propionic acid and 6 mM magnesium sulfate. Approximately half of the bulk proteins partitioned to the upper phase while starch and other particles were recovered only into the lower phase. Whole wheat flour could be applied as sample for the CCD and 57 transfers were carried out. Starch and insoluble proteins remained stationary, while proteins followed the mobile phase to various degrees giving rise to a distribution pattern. The CCD pattern of the proteins showed distinct differences when various kinds of wheat flour were analysed. The patterns indicate that at least six subpopulations of proteins can be obtained by using two-phase extraction.  相似文献   
18.
Mass transport in wood during drying can have different mechanisms at different periods of drying. Depending on the current moisture content (MC) and the structure of the wood, the driving forces for the mass transport are essentially different. Above the fiber saturation point (FSP), the lumens are partially saturated and the transport of liquid (free) water occurs as a consequence of capillary action. On the other hand, below the FSP, bound water within the cell walls is conveyed by diffusion, and water vapor in the lumens moves under influence of pressures gradient. Based on these considerations, a unified model is presented that takes into account the transport of the different moisture phases. Simulation of the drying of a Norway spruce sample at 50°C from about 135 to 7% MC is carried out using the finite element method (FEM). Comparison between the simulated average MC and the experimental observations obtained from X-ray computed tomography (CT) shows reasonable agreement. Possible simplifications in the model are briefly discussed as well as some aspects of the numerical implementation. Finally, the influence of absolute permeability on the average MC is studied.  相似文献   
19.
20.
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