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   8903篇
  免费   276篇
  国内免费   11篇
电工技术   100篇
综合类   1篇
化学工业   1451篇
金属工艺   154篇
机械仪表   152篇
建筑科学   418篇
矿业工程   22篇
能源动力   223篇
轻工业   738篇
水利工程   64篇
石油天然气   41篇
武器工业   1篇
无线电   632篇
一般工业技术   1454篇
冶金工业   2157篇
原子能技术   65篇
自动化技术   1517篇
  2022年   50篇
  2021年   105篇
  2020年   94篇
  2019年   97篇
  2018年   135篇
  2017年   120篇
  2016年   154篇
  2015年   128篇
  2014年   235篇
  2013年   529篇
  2012年   317篇
  2011年   438篇
  2010年   327篇
  2009年   294篇
  2008年   363篇
  2007年   354篇
  2006年   280篇
  2005年   273篇
  2004年   220篇
  2003年   223篇
  2002年   216篇
  2001年   170篇
  2000年   154篇
  1999年   172篇
  1998年   425篇
  1997年   299篇
  1996年   227篇
  1995年   180篇
  1994年   152篇
  1993年   165篇
  1992年   132篇
  1991年   99篇
  1990年   100篇
  1989年   111篇
  1988年   102篇
  1987年   101篇
  1986年   91篇
  1985年   115篇
  1984年   118篇
  1983年   121篇
  1982年   92篇
  1981年   84篇
  1980年   96篇
  1979年   116篇
  1978年   87篇
  1977年   100篇
  1976年   130篇
  1975年   77篇
  1974年   49篇
  1973年   46篇
排序方式: 共有9190条查询结果,搜索用时 46 毫秒
81.
Retail samples of livers from calf (23), ox (18), lamb (17), pig (15), chicken (16) and turkey (1) were analysed to determine levels of vitamin A (all trans-retinol) and to aid assessment of the effects of using vitamin supplemented compound feedingstuffs for livestock. For comparison, 22 liver samples from lambs reared on diets not containing vitamin-supplemented compound feedingstuffs and four samples of liver from ox which had received supplemented feed but not during the last four months prior to slaughter were also analysed. The chosen method of analysis utilized saponification, solvent extraction and normal-phase high performance liquid chromatography with fluorescence detection. For all species analysed, the levels of vitamin A ranged from 10 to 1100 mg/kg, with all but seven at or below 400 mg/kg. For lamb and ox livers, the mean levels were 310 mg/kg and 200 mg/kg respectively for retail samples. The mean levels were 220 mg/kg (lamb) and 120 mg/kg (ox) in liver samples from animals fed controlled diets. The results are of the same order as those reported over recent years.  相似文献   
82.
Examined intake profiles of 54 depressed women survivors of child sexual abuse presenting for a specialized group therapy program at a community mental health center. The 32 therapy completers were compared with the 22 dropouts. Both groups possessed extensive and severe childhood and adult abuse histories. Both were extremely socially disadvantaged and clinically impaired as measured on the Millon Clinical Multiaxial Inventory (MCMI). Dropouts were more likely to have been battered as children and to have been sexually abused only within the family. Completers were more likely to have been multiply offended both by intrafamilial and extrafamilial perpetrators. The groups differed in terms of marital status and extent of economic dependence on spouse. Dropouts appeared to be more actively enmeshed in the abuse cycle at the time of therapy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
83.
Addressed conflicting views of depressives' interpersonal accuracy in an investigation of the accuracy of mild depressives (dysphorics) across differing social contexts. Women who were either friends or strangers and who were either similar or dissimilar in level of dysphoria conversed about 3 topics: a neutral topic, their own disclosure of a personal problem, and their partner's disclosure. Dysphorics were not more accurate in general than nondysphorics. After self-disclosure, all women more accurately detected sympathy from a similar stranger. After the partner's disclosure, women also better detected the mood of a similar partner. When interacting with nondysphoric strangers, however, dysphorics underestimated their partner's sympathy toward them. Implications for cognitive and interpersonal theories of depression and for depressives' relationships are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
84.
An estimate is made of the motion of a rigid body from two noisy 2-D perspective projections using the least-squares method and the algebra of R.Y. Tsai and T.S. Huang (1984). The accuracy of the estimated motion parameters is influenced by the position of the features of the object used in the calculation. Four test variables are derived that indicate how the accuracy is affected, and they are used for discarding inaccurate estimates. Monte Carlo tests demonstrate the obtained accuracy  相似文献   
85.
The authors describe an integrated processor that performs addition and subtraction of 30-b numbers in the logarithmic number system (LNS). This processor offers 5-MOPS performance in 3-μm CMOS technology, and is implemented in a two-chip set comprising 170 K transistors. Two techniques are used to achieve this precision in a moderate circuit area. Linear approximation of the LNS arithmetic functions using logarithmic arithmetic is shown to be simple due to the particular functions involved. A segmented approach to linear approximation minimizes the amount of table space required. Subsequent nonlinear compression of each lookup table leads to a further reduction in table size. The result is that a factor of 285 reduction in table size is achieved, compared to previous techniques. The circuit area of the implementation is minimized by optimizing the table parameters, using a computer program that accurately models ROM area. The implementation is highly pipelined, and produces one result per clock cycle using a ten-stage pipeline  相似文献   
86.
The Modular High Temperature Gas-Cooled Reactor (MHTGR) is a candidate design for new production and commercial power nuclear reactors. The MHTGR has inherent safety features including: (1) passive shutdown and decay heat removal, (2) reduced requirements for operator intervention, thereby reducing sensitivity to operator error, and (3) long time intervals for corrective action. In support of the Department of Energy's (DOE) initial development of the design, the authors have completed an evaluation of the thermal-hydraulic phenomena that will dominate the plant response during representative normal, off-normal and accident conditions. Phenomena having significance to the plant behavior have been identified, and ranked with respect to their relative importance in satisfying operational, investment and/or safety criteria. The resulting information provides the basis for evaluating the applicability of existing computer codes, and defines the requirements for the development of new codes, for thermal-hydraulic systems analysis. The phenomena-based requirements also support the quality assurance related verification and validation of these codes. This paper briefly describes the methodology employed, and gives illustrative examples of the resulting requirements. References are cited for reports that document the full body of requirements and provide additional information for the methodology.  相似文献   
87.
Standard commercial pallet racking is used in warehouses, factories, shops and a multitude of other places where palletised goods are to be stored. The structural analysis of this type of structure is complicated by the semi-rigid nature of the beam-to-upright connection, which is different from one manufacturer to another.In the present paper an attempt has been made to provide a simple design approach to the stability of pallet rack structures, and the effect that the form of the moment-rotation characteristic has on the type of stability demonstrated by the system.Finally the role of small imperfections is studied, and the effect that they have on the maximum load carrying capacity of the structure is shown.  相似文献   
88.
The morphology of nickel crystals can be quantified using measurements of fractal structure. In the study described in this article, fractal dimensions of cross sections of 16 nickel samples were determined, and the numerical analysis indicates that the more rugged surfaces are characterized by higher fractal dimensions although the relationship between morphology and fractal dimension is relatively weak. However, the data also show that fractal dimension is a better predictor of morphology than apparent density, which is the measurement currently used. The nickel samples were also subjected to an avalanching disc technique that has the potential to separate out the differences in flow in the different types of nickel powder. The differences in flow between powders were ascribed to the similar gross morphologies of the particles, and the presence of shattered individual particles in the mix. For more information, contact A.E. Lewis, University of Cape Town, Precipitation and Crystallisation Research Facility, Department of Chemical Engineering, Rondebosch, 7701, South Africa; +27-21-650-4091; fax +27-21-689-7479; e-mail alison@chemeng.uct.ac.za.  相似文献   
89.
90.
Pulsed field-gradient spin-echo (PGSE) nuclear magnetic resonance (NMR) diffusion experiments conducted on some heterogeneous systems have been observed to show periodicities in the data. These “coherence patterns” are manifest in the normalized PGSE signal intensities as a function of the spatial wave vector q in so-called q-space plots. The sample that to our knowledge best reveals these coherence patterns is suspensions of red blood cells (RBC). The origin of these patterns and their mathematical and physical underpinnings are now well established. We have used computer simulations of molecular diffusion in lattices of RBC and other cells to aid in the interpretation and analysis of the corresponding experimental data. The aim of this review is to present the current status of NMR q-space studies of RBC suspensions that show the diffusion-coherence effect.  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