全文获取类型
收费全文 | 2868篇 |
免费 | 34篇 |
专业分类
电工技术 | 12篇 |
综合类 | 1篇 |
化学工业 | 208篇 |
金属工艺 | 17篇 |
机械仪表 | 16篇 |
建筑科学 | 46篇 |
矿业工程 | 1篇 |
能源动力 | 14篇 |
轻工业 | 109篇 |
水利工程 | 9篇 |
石油天然气 | 9篇 |
无线电 | 135篇 |
一般工业技术 | 226篇 |
冶金工业 | 1981篇 |
原子能技术 | 18篇 |
自动化技术 | 100篇 |
出版年
2021年 | 12篇 |
2020年 | 9篇 |
2019年 | 9篇 |
2018年 | 10篇 |
2017年 | 22篇 |
2016年 | 16篇 |
2015年 | 14篇 |
2014年 | 30篇 |
2013年 | 50篇 |
2012年 | 34篇 |
2011年 | 41篇 |
2010年 | 29篇 |
2009年 | 34篇 |
2008年 | 35篇 |
2007年 | 43篇 |
2006年 | 24篇 |
2005年 | 37篇 |
2004年 | 31篇 |
2003年 | 34篇 |
2002年 | 35篇 |
2001年 | 32篇 |
2000年 | 25篇 |
1999年 | 78篇 |
1998年 | 598篇 |
1997年 | 381篇 |
1996年 | 249篇 |
1995年 | 122篇 |
1994年 | 108篇 |
1993年 | 120篇 |
1992年 | 30篇 |
1991年 | 32篇 |
1990年 | 36篇 |
1989年 | 47篇 |
1988年 | 42篇 |
1987年 | 43篇 |
1986年 | 31篇 |
1985年 | 34篇 |
1984年 | 17篇 |
1983年 | 19篇 |
1982年 | 18篇 |
1981年 | 14篇 |
1980年 | 27篇 |
1979年 | 14篇 |
1978年 | 24篇 |
1977年 | 39篇 |
1976年 | 87篇 |
1974年 | 6篇 |
1973年 | 8篇 |
1972年 | 10篇 |
1968年 | 7篇 |
排序方式: 共有2902条查询结果,搜索用时 15 毫秒
1.
Barbara M. Johnston Peter R. Johnston 《International journal for numerical methods in engineering》2003,56(4):589-607
Accurate numerical evaluation of integrals arising in the boundary element method is fundamental to achieving useful results via this solution technique. In this paper, a number of techniques are considered to evaluate the weakly singular integrals which arise in the solution of Laplace's equation in three dimensions and Poisson's equation in two dimensions. Both are two‐dimensional weakly singular integrals and are evaluated using (in a product fashion) methods which have recently been used for evaluating one‐dimensional weakly singular integrals arising in the boundary element method. The methods used are based on various polynomial transformations of conventional Gaussian quadrature points where the transformation polynomial has zero Jacobian at the singular point. Methods which split the region of integration into sub‐regions are considered as well as non‐splitting methods. In particular, the newly introduced and highly accurate generalized composite subtraction of singularity and non‐linear transformation approach (GSSNT) is applied to various two‐dimensional weakly singular integrals. A study of the different methods reveals complex relationships between transformation orders, position of the singular point, integration kernel and basis function. It is concluded that the GSSNT method gives the best overall results for the two‐dimensional weakly singular integrals studied. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
2.
The kinetics of substrate removal by the liver and the resulting nonlinear changes in unbound fraction along the flow path at varying input drug concentrations were examined by a model simulation study. Specifically, we varied the binding association constant, KA, and the Michaelis-Menten constants (Km and Vmax) to examine the steady state drug removal (expressed as hepatic extraction ratio E) and changes in drug binding for (i) unienzyme systems and (ii) simple, parallel metabolic pathways; zonal metabolic heterogeneity was also added as a variable. At low KA, E declined with increasing input drug concentration, due primarily to saturation of enzymes; only small differences in binding were present across the liver. At high KA, a parabolic profile for E with concentration was observed; changes in unbound fraction between the inlet and the outlet of the liver followed in parallel fashion. Protein binding was the rate-determining step at low input drug concentrations, whereas enzyme saturation was the rate-controlling factor at high input drug concentration. Heterogeneous enzymic distribution modulated changes in unbound fraction within the liver and at the outlet. Despite marked changes in unbound fraction occurring within the liver for different enzymic distributions, the overall transhepatic differences were relatively small. We then investigated the logarithmic average unbound concentration and the length averaged concentration as estimates of substrate concentration in liver in the presence of nonlinear drug binding. Fitting of simulated data, with and without assigned random error (10%), to the Michaelis-Menten equation was performed; fitting was repeated for simulated data obtained with presence of a specific inhibitor of the high-affinity, anteriorly distributed pathway. Results were similar for both concentration terms: accurate estimates were obtained for anterior, high affinity pathways; an overestimation of parameters was observed for the lower affinity posteriorly distributed pathways. Improved estimations were found for posteriorly distributed pathways upon inhibition with specific inhibitors; with added random error, however, the improvement was much decreased. We applied the method for fitting of several sets of metabolic data obtained from rat liver perfusion studies performed with salicylamide (SAM) (i) without and (ii) with the presence of 2,6-dichloro-4-nitrophenol (DCNP), a SAM sulfation inhibitor. The fitted results showed that SAM sulfation was a high-affinity high-capacity pathway; SAM glucuronidation was of lower affinity but comparable capacity as the sulfation pathway, whereas SAM hydroxylation was of lower affinity and lower capacity. 相似文献
3.
The evaluation of microcomputer programs: an area of debate 总被引:1,自引:0,他引:1
V. M. Johnston 《Journal of Computer Assisted Learning》1987,3(1):40-50
4.
Letters to the editor 总被引:1,自引:0,他引:1
5.
6.
[Correction Notice: An erratum for this article was reported in Vol 31(2) of Canadian Psychology Psychologie Canadienne (see record 2007-08913-001). In the October 1989 issue (Vol. 30, No. 4, p. 697), Arnold Rincover's affiliation with the Ontario Institute for Studies in Education was incorrectly given as Associate Professor. He has been an Extramural Instructor at O.I.S.E.] Reviews the book, The parent-child connection by Arnold Rincover (1988). The parent-child connection is a well written book that offers valuable advice to help parents of young children evaluate and understand their children's behaviour. It also offers useful suggestions on managing child behaviour, although these parenting tips are most likely to be useful to those parents who least need them (i.e., those with numerous personal and social resources, whose children are presenting only minor behavioural difficulties). The two general themes of the book, child behaviour as communication and developmental norms as guidelines for deciding if behaviour is problematic, are well-suited to the purposes of a parent reference book. They offer an appropriate framework for discussing specific child behaviours and helping parents to determine if these behaviours are problematic in their children. This book is a welcome addition to the list of available parenting books, and may prove particularly useful for younger parents in need of accurate and understandable information about normal child development and behaviour. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
7.
KS Atia AI El‐Batal 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(7):805-811
Glucose oxidase (EC 1.1.3.4) was immobilized on different polymeric materials using different immobilization techniques (entrapping by γ‐irradiation, and covalent binding using epichlorohydrin). Studies were carried out to increase the thermal stability of glucose oxidase (GOD) for different applications. The activity and stability of the resulting biopolymers have been compared with those of free GOD. The effect of different polyvinyl alcohol/polyacrylamide (PVA/PAAm) compositions of the copolymer carrier on the enzymatic activity of the immobilized GOD was studied. The maximum enzymatic activity was obtained with the composition ratio of PVA/PAAm of 60:40. The behaviour of the free and immobilized enzyme was analysed as a function of pH. A broadening in the pH profile (5.5–8) was observed for immobilized preparations. The activity and stability of the resulting biopolymers produced by immobilization of GOD onto different carriers have been compared, in both aqueous and organic media, with those of the free GOD. The enzyme's tolerance toward both heat and organic solvent was enhanced by immobilization onto polymers. The addition of different concentrations of organic solvents (10–50%, v/v) to the enzyme at higher temperature (60 °C) was found to stabilize the enzyme molecule. The strongest stabilizing effect on the enzymatic activity was achieved at a concentration of 10%. Copyright © 2005 Society of Chemical Industry 相似文献
8.
9.
How senile plaques and neurofibrillary tangles are linked represents a major gap in our understanding of the pathophysiology of Alzheimer's disease. We characterized a hippocampal neuronal culture system in which tau undergoes maturation in vivo; rat neurons maintained in culture for more than 3 weeks replicated the splicing and phosphorylation changes that tau undergoes upon maturation in situ. Using this model system, we induced an Alzheimer-like neuritic dystrophy following the application of fibrillar beta-amyloid. The dystrophy consisted of focal distortions and swellings within the neurites and an altered phosphorylation of the adult tau isoforms. Fibrillar beta-amyloid induced the concomitant activation of MAP kinase and GSK3 beta. The aberrant activation of several signaling pathways may lead to the abnormal phosphorylation of tau and neuritic degeneration. 相似文献
10.
The memory of hamsters (Mesocricetus auratus) for the flank scent of older male hamsters was investigated in a series of habituation experiments. In 2 types of habituation tasks (Exps 1 and 2), male hamsters habituated to the flank scent of 1 male and then increased their level of investigation to that of a novel male; similar results were obtained when the intervals between trials ranged from 1 sec to 2 days. When the test trial was 10 or 21 days after habituation (Exp 3), males discriminated between familiar and novel flank scents at 10 days but not at 21 days. The results demonstrate recognition of familiar and unfamiliar individual odors and excellent memory for these differences. Habituation techniques yield extremely robust results and may be useful for investigations of other aspects of individual signatures. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献