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   373篇
  免费   8篇
化学工业   62篇
金属工艺   23篇
机械仪表   6篇
建筑科学   10篇
能源动力   10篇
轻工业   15篇
水利工程   1篇
无线电   44篇
一般工业技术   68篇
冶金工业   94篇
原子能技术   7篇
自动化技术   41篇
  2023年   3篇
  2022年   4篇
  2021年   6篇
  2019年   2篇
  2018年   4篇
  2017年   8篇
  2016年   10篇
  2015年   6篇
  2014年   8篇
  2013年   11篇
  2012年   13篇
  2011年   27篇
  2010年   14篇
  2009年   22篇
  2008年   17篇
  2007年   8篇
  2006年   11篇
  2005年   8篇
  2004年   7篇
  2003年   6篇
  2002年   6篇
  2001年   4篇
  2000年   4篇
  1999年   3篇
  1998年   39篇
  1997年   28篇
  1996年   10篇
  1995年   10篇
  1994年   8篇
  1993年   10篇
  1992年   5篇
  1991年   5篇
  1989年   4篇
  1987年   4篇
  1986年   3篇
  1985年   5篇
  1984年   3篇
  1983年   3篇
  1982年   6篇
  1981年   2篇
  1980年   3篇
  1979年   3篇
  1977年   3篇
  1976年   6篇
  1974年   1篇
  1973年   1篇
  1970年   1篇
  1967年   1篇
  1963年   2篇
  1960年   1篇
排序方式: 共有381条查询结果,搜索用时 15 毫秒
21.
This study reports the fatty acid composition of subcutaneous adipose tissue in French women with special emphasis on the content of trans fatty acids originating from two main dietary sources, ruminant fats and partially hydrogenated vegetable oils (PHVO). Adipose tissue trans fatty acid levels from 71 women, recruited between 1997 and 1998, were determined using a combination of capillary gas chromatography and silver nitrate thin-layer chromatography. Results indicate that on average cis monounsaturates accounted for 47.9% of total fatty acids, saturates for 32.2%, and linoleic acid for 14.4%. Cis n−3 polyunsaturates represented only 0.7%. Total content of trans fatty acids was 2.32±0.50%, consisting of trans 18∶1 (1.97±0.49%), trans 18∶2 (0.28±0.08%), and trans 16∶1 (0.06±0.03%). Trans 18∶3 isomers were not detectable. The level of trans fatty acids found in adipose tissue of French women was lower than those reported for Canada, the United States, and Northern European countries but higher than that determined in Spain. Therefore, trans fatty acid consumption in France appears to be intermediate between that of the United States or North Europe and that of Spain. Based on the equation of Enig et al., we estimated the mean daily trans 18∶1 acid intake of French women at 1.9 g per person. The major trans 18∶1 isomer in adipose tissue was Δ11trans, as in ruminant fats. Estimates of relative contribution of trans fatty acid intake were 55% from ruminant fats and 45% from PHVO. This pattern contrasts sharply with those established for Canada and the United States where PHVO is reported to be the major dietary source of trans fatty acids.  相似文献   
22.
23.
New applications have been found for advanced best estimate codes, due to the needs for industrial studies and safety studies, and due also to the appearance of new generations of computers, such as powerful work stations. Thus developments have been focused on the optimization of the numerical performance of thermal-hydraulics codes based on the two-fluid six equation model.One important goal is that of minimizing the computing time. Comparisons of existing methods demonstrate that a fully implicit scheme is well suitable for optimization.A second field of investigation is to develop powerful three-dimensional modules with advanced numerical methods, as multistep method, conjugate gradient method for the solver and, in future, non-structured meshing.  相似文献   
24.
To facilitate materials research by thin film techniques, we have built a compact multi-source multi-substrate evaporator. We have successfully prepared crystalline binary EuS (Tc = 16 K), SmS and Sm2S3 as well as ternary Sm1?xLnxS (Ln = Tm, Yb) compounds by tenchnique of co-evaporation. Special precautions were taken to avoid sulphur contamination. The X-ray, optical and magnetic properties of these films confirmed the good quality of the samples. Optical data obtained on Sm1?xYbxS indicate a stable valency of 2 for Sm and Yb for all values of x.  相似文献   
25.
Considers the question of how the payment of fees by clients for psychotherapy and related psychological services influences therapeutic outcomes. Psychoanalytic theory and cognitive dissonance theory suggest that clients who pay for psychotherapy will benefit more than those who pay nothing. This question and related issues are discussed with reference to observations and experimental studies that have explored how fees influence psychotherapy. Presently, sufficient evidence does not exist either to support or refute most of the hypotheses that have been generated, including the one that clients who pay a fee benefit more than those who pay nothing. Explanations for this void in the research literature and suggestions for expanding the understanding of this domain are provided. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
26.
A new approach to modeling using semi-quantum dielectric function models is proposed for the retrieval of the optical functions from infrared spectra. The powerful points of the method are shown throughout the analysis of two semitransparent materials, MgO and KBr. All the results are discussed in light of those obtained with classical techniques. This type of model is able to retrieve, for example, the extinction index in a range that covers at least six orders of magnitude and gives access to highly valuable information about high-order phonon processes.  相似文献   
27.
A cluster operator takes a set of data points and partitions the points into clusters (subsets). As with any scientific model, the scientific content of a cluster operator lies in its ability to predict results. This ability is measured by its error rate relative to cluster formation. To estimate the error of a cluster operator, a sample of point sets is generated, the algorithm is applied to each point set and the clusters evaluated relative to the known partition according to the distributions, and then the errors are averaged over the point sets composing the sample. Many validity measures have been proposed for evaluating clustering results based on a single realization of the random-point-set process. In this paper we consider a number of proposed validity measures and we examine how well they correlate with error rates across a number of clustering algorithms and random-point-set models. Validity measures fall broadly into three classes: internal validation is based on calculating properties of the resulting clusters; relative validation is based on comparisons of partitions generated by the same algorithm with different parameters or different subsets of the data; and external validation compares the partition generated by the clustering algorithm and a given partition of the data. To quantify the degree of similarity between the validation indices and the clustering errors, we use Kendall's rank correlation between their values. Our results indicate that, overall, the performance of validity indices is highly variable. For complex models or when a clustering algorithm yields complex clusters, both the internal and relative indices fail to predict the error of the algorithm. Some external indices appear to perform well, whereas others do not. We conclude that one should not put much faith in a validity score unless there is evidence, either in terms of sufficient data for model estimation or prior model knowledge, that a validity measure is well-correlated to the error rate of the clustering algorithm.  相似文献   
28.
Bioactive glasses are used as coating biomaterials to facilitate anchorage of metallic prostheses implanted into the body. The aim of this work is to study the behavior of gel formed in contact with alloys and BVA and BVH bioactive glasses implanted. Cylinders of metallic implants composed by Ti, Al and V, are coated with bioactive glass. Three sheep were implanted for different time length: 3, 6 and 12 months in the femoral epiphysis. Results obtained with particle induced X-ray emission and scanning electron microscopy show that BVA coating induces a better contact between the metallic implant and bone. On the other hand, BVH coating prevents corrosion from the metallic implant.  相似文献   
29.
One of the key purposes of bone tissue engineering is the development of new biomaterials that can stimulate the body's own regenerative mechanism for patient's anatomical and functional recovery. Bioactive glasses, due to their versatile properties, are excellent candidates to fabricate porous 3-D architectures for bone replacement. In this work, morphological and structural investigations are carried out on Bioglass®- and CEL2-derived scaffolds produced by sponge replication (CEL2 is an experimental glass developed at Politecnico di Torino). Synchrotron radiation X-ray microtomography is used to study the samples 3-D architecture, pores size, shape, distribution and interconnectivity, as well as the growth kinetics on scaffolds struts of a newly formed apatitic phase during in vitro treatment in simulated body fluid, in order to describe from a quantitative viewpoint the bioactive potential of the analyzed biomaterials. An accurate comparison between architectural features and bioactive behaviour of Bioglass®- and CEL2-derived scaffolds is presented and discussed.  相似文献   
30.
We present a general theory of entanglement-assisted quantum convolutional coding. The codes have a convolutional or memory structure, they assume that the sender and receiver share noiseless entanglement prior to quantum communication, and they are not restricted to possess the Calderbank–Shor–Steane structure as in previous work. We provide two significant advances for quantum convolutional coding theory. We first show how to “expand” a given set of quantum convolutional generators. This expansion step acts as a preprocessor for a polynomial symplectic Gram–Schmidt orthogonalization procedure that simplifies the commutation relations of the expanded generators to be the same as those of entangled Bell states (ebits) and ancilla qubits. The above two steps produce a set of generators with equivalent error-correcting properties to those of the original generators. We then demonstrate how to perform online encoding and decoding for a stream of information qubits, halves of ebits, and ancilla qubits. The upshot of our theory is that the quantum code designer can engineer quantum convolutional codes with desirable error-correcting properties without having to worry about the commutation relations of these generators.  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