全文获取类型
收费全文 | 3378篇 |
免费 | 48篇 |
专业分类
电工技术 | 31篇 |
综合类 | 3篇 |
化学工业 | 280篇 |
金属工艺 | 30篇 |
机械仪表 | 36篇 |
建筑科学 | 81篇 |
矿业工程 | 5篇 |
能源动力 | 30篇 |
轻工业 | 89篇 |
水利工程 | 36篇 |
石油天然气 | 1篇 |
无线电 | 232篇 |
一般工业技术 | 333篇 |
冶金工业 | 2048篇 |
原子能技术 | 22篇 |
自动化技术 | 169篇 |
出版年
2022年 | 18篇 |
2021年 | 26篇 |
2019年 | 14篇 |
2018年 | 22篇 |
2017年 | 16篇 |
2016年 | 21篇 |
2015年 | 24篇 |
2014年 | 27篇 |
2013年 | 58篇 |
2012年 | 47篇 |
2011年 | 71篇 |
2010年 | 50篇 |
2009年 | 53篇 |
2008年 | 71篇 |
2007年 | 66篇 |
2006年 | 63篇 |
2005年 | 44篇 |
2004年 | 63篇 |
2003年 | 52篇 |
2002年 | 39篇 |
2001年 | 42篇 |
2000年 | 52篇 |
1999年 | 71篇 |
1998年 | 547篇 |
1997年 | 341篇 |
1996年 | 244篇 |
1995年 | 148篇 |
1994年 | 108篇 |
1993年 | 138篇 |
1992年 | 24篇 |
1991年 | 31篇 |
1990年 | 31篇 |
1989年 | 29篇 |
1988年 | 21篇 |
1987年 | 29篇 |
1986年 | 33篇 |
1985年 | 24篇 |
1984年 | 23篇 |
1983年 | 22篇 |
1982年 | 26篇 |
1981年 | 39篇 |
1980年 | 49篇 |
1979年 | 17篇 |
1978年 | 20篇 |
1977年 | 112篇 |
1976年 | 227篇 |
1975年 | 20篇 |
1974年 | 11篇 |
1973年 | 10篇 |
1971年 | 13篇 |
排序方式: 共有3426条查询结果,搜索用时 203 毫秒
91.
Fracture mechanics‐based progressive damage modelling of adhesively bonded fibre‐reinforced polymer joints
下载免费PDF全文
![点击此处可从《Fatigue & Fracture of Engineering Materials & Structures》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Aida Cameselle‐Molares Roohollah Sarfaraz Moslem Shahverdi Thomas Keller Anastasios P. Vassilopoulos 《Fatigue & Fracture of Engineering Materials & Structures》2017,40(12):2183-2193
A quasi‐static progressive damage model for prediction of the fracture behaviour and strength of adhesively bonded fibre‐reinforced polymer joints is introduced in this paper. The model is based on the development of a mixed‐mode failure criterion as a function of a master R‐curve derived from the experimental results obtained from standard fracture mechanics joints. Consequently, the developed failure criterion is crack‐length and mode‐mixity dependent, and it takes into account the contribution of the fibre‐bridging effect. Energy release rate values for adhesively bonded double‐lap joints are obtained by using the virtual crack closure technique method in a finite element model, and the numerically obtained strain energy release rate is compared to the critical strain energy release rate given by the mixed‐mode failure criterion. The entire procedure is implemented in a numerical algorithm, which was successfully used for predicting the strength and R‐curve response of adhesively bonded double‐lap structural joints made of pultruded glass fibre‐reinforced polymers and epoxy adhesives. 相似文献
92.
Use of fuzzy-logic-inspired features to improve bacterialrecognition through classifier fusion 总被引:1,自引:0,他引:1
Dayou Wang Keller J.M. Carson C.A. McAdo-Edwards K.K. Bailey C.W. 《IEEE transactions on systems, man, and cybernetics. Part B, Cybernetics》1998,28(4):583-591
Escherichia coli O157:H7 has been found to cause serious health problems. Traditional methods to identify the organism are quite slow, pulsed-held gel electrophoresis (PFGE) images contain "banding pattern" information which can be used to recognize the bacteria. A fuzzy logic rule-based system is used as a guide to find a good feature set for the recognition of E. coli O157:H7. While the fuzzy rule-based system achieved good recognition, the human inspired features used in the rules were incorporated into a multiple neural network fusion approach which gave excellent separation of the target bacteria. The fuzzy integral was utilized in the fusion of neural networks trained with different feature sets to reach an almost perfect classification rate of E. coli O157:H7 PFGE patterns made available for the experiments. 相似文献
93.
AM Jackson AV Ivshina O Senko A Kuznetsova A Sundan MA O'Donnell S Clinton AB Alexandroff PJ Selby K James VA Kuznetsov 《Canadian Metallurgical Quarterly》1998,159(3):1054-1063
PURPOSE: The goal of this research was to discover new biological indicators in urine which could be used for short-term prognosis of local Bacillus Calmette-Guerin (BCG) therapy outcome in patients with superficial bladder cancer. PATIENTS AND METHODS: We measured and statistically evaluated soluble immunological molecules in urine from bladder cancer patients (n = 34) receiving BCG intravesically. Urine was collected following each of 6 weekly treatments, processed and assayed. The data base included measurements of interleukin-1 (IL-2, IL-4, IL-6, IL-10, IL-12, soluble intercellular adhesion molecule-1 (sICAM-1), tumour necrosis factor-alpha (TNF alpha), soluble CD14 (sCD14), interferon-gamma (IFN gamma), GM-CSF, volume of urine and its pH. The clinical response was evaluated by urine histology and random quadrant biopsy 3 months after the start of therapy. Patients were divided into 2 groups, with good and poor therapeutic effect. The initial complete response rate was 62% (21/34). The data base was analyzed using traditional multivariate statistical methods and a pattern recognition method which deals with combinatorial-statistical analysis (statistically weighted syndromes (SWS) method) of the gradated features. The SWS method is capable of identifying robust patterns in small "fuzzy" sets with high dimensional objects and some missing values. RESULTS: Only one parameter gave significant differences at p < 0.05, GM-CSF at instillation 6. Repeated measurement analysis of variance, backward stepwise multiple logistic regression and linear discriminant analysis failed to show any significance. However, significant differences in the structure of correlation between features in the groups with and without therapeutic effect were observed and four highly informative variables (the masses of sICAM-1, TNF alpha, sCD14 and pH) relating to 5th-6th installations were selected by SWS. These features provided accurate individual prediction of therapeutic outcome for all our patients. Cross-validation analysis and computer simulation showed the statistically significant stability of the prediction. CONCLUSION: We have selected a set of urinary variables that could be considered as a perspective combination of indicators (syndromes) of outcome of pre-operation BCG therapy of patients with superficial bladder cancer. A larger patient database will provide testing and evaluation of the biological and clinical significance of selected features. The computational syndrome-disease approach should be applicable for the solution of decision-making problems for management of cancer. 相似文献
94.
We demonstrate the use of a single prism for adjustable dispersion compensation in a mode-locked laser cavity, instead of the standard approach with a prism pair. A simple model based on the prism-pair configuration is presented to determine the group-velocity dispersion by use of ray optics to trace the wavelength-dependent optical axes through the cavity. We experimentally demonstrated this concept with a passively mode-locked diode-pumped Nd:glass laser producing 200-fs pulses with a 200-mW average output power, using only one intracavity prism. The advantages of such a cavity design are simple alignment, reduced loss, and lossless wavelength tunability This technique can be generalized to other angularly dispersive elements such as prismatic output couplers. 相似文献
95.
Behnke B Schlotterbeck G Tallarek U Strohschein S Tseng LH Keller T Albert K Bayer E 《Analytical chemistry》1996,68(7):1110-1115
Coupling HPLC and NMR is one of the most powerful techniques for simultaneous separation and structural elucidation of unknown compounds in mixtures. To date, however, minimizing the detection volume, as is required when coupling NMR with miniaturized separation techniques, has been accompanied by a dramatic loss in resolution of the NMR spectra. Here, we report on the coupling of gradient capillary HPLC with on-column, high-resolution NMR detection. On-line stopped-flow and static (1)H NMR spectra were acquired with capillary columns of 75-315 μm i.d. With detection over a length of 1.2 cm, cell volumes cover a range of 50-900 nL. An on-line-detected NMR separation of dansylated amino acids was carried out in a 315 μm i.d. fused silica capillary packed to a length of 12 cm with C(18) stationary phase. The low solvent consumption makes the use of fully deuterated solvents economically feasible. NMR spectra with resolution on the order of 3 Hz were obtained using a 50 nL detection cell to measure 1.1 nmol of dansylated γ-aminobutyric acid under static conditions in a 75 μm i.d. capillary. 相似文献
96.
With the increasing power of computers, new methods in synthesis of optical multilayer systems have appeared. Among these, the simulated-annealing algorithm has proved its efficiency in several fields of physics. We propose to show its performances in the field of optical multilayer systems through different filter designs. 相似文献
97.
JM Warnecke JP Fürste WD Hardt VA Erdmann RK Hartmann 《Canadian Metallurgical Quarterly》1996,93(17):8924-8928
To study the cleavage mechanism of bacterial Nase P RNA, we have synthesized precursor tRNA substrates carrying a single Rp- or Sp-phosphorothioate modification at the RNase P cleavage site. Both the Sp- and the Rp-diastereomer reduced the rate of processing by Escherichia coli RNase P RNA at least 1000-fold under conditions where the chemical step is rate-limiting. The Rp-modification had no effect and the Sp-modification had a moderate effect on precursor tRNA ground state binding to RNase P RNA. Processing of the Rp-diastereomeric substrate was largely restored in the presence of the "thiophilic" Cd2+ as the only divalent metal ion, demonstrating direct metal ion coordination to the (pro)-Rp substituent at the cleavage site and arguing against a specific role for Mg(2+)-ions at the pro-Sp oxygen. For the Rp-diastereomeric substrate, Hill plot analysis revealed a cooperative dependence upon [Cd2+] of nH = 1.8, consistent with a two-metal ion mechanism. In the presence of the Sp-modification, neither Mn2+ nor Cd2+ was able to restore detectable cleavage at the canonical site. Instead, the ribozyme promotes cleavage at the neighboring unmodified phosphodiester with low efficiency. Dramatic inhibition of the chemical step by both the Rp- and Sp-phosphorothioate modification is unprecedented among known ribozymes and points to unique features of transition state geometry in the RNase P RNA-catalyzed reaction. 相似文献
98.
ML Jensen OM Jensen W Michalski OS Nielsen J Keller 《Canadian Metallurgical Quarterly》1996,23(5):458-463
Superficial leiomyosarcomas are rare tumours. The lesions confined to the dermis, contrary to those involving the subcutis, have been reported to carry a favourable prognosis. A retrospective study of 41 consecutive cases of surgically treated intradermal and subcutaneous leiomyosarcomas was undertaken in order to determine the prognostic factors that may influence the survival of these patients. Seven tumours were predominantly intradermal and 34 involved the subcutaneous tissue. Fifty-four percent of the tumours were located in the lower extremities. All cases stained positively for smooth muscle antigen and 66% for desmin. The tumours were classified with regard to tumour grade I (low grade, 3%), II (intermediate, 12%), IIIA (high grade, 46%) and IIIB (high grade, 39%). In all patients, follow-up information was available. Mean follow-up time was 5 years. The patients with intradermal tumours were all alive without signs of recurrence, whereas 14 of those with leiomyosarcomas involving the subcutis have died with pulmonary metastases. Our study confirms that "pure" intradermal leiomyosarcomas independent of tumour grade behave in a benign fashion, probably due to small tumour size. Tumour size > or = 5 cm, deep localization with fascia involvement, and high malignancy grade (IIIB) were found to deteriorate survival based on a univariate analysis. However, in a multivariate analysis only tumour size was found to be an independent prognostic factor. 相似文献
99.
Sven A. Carlsson Stefan Henningsson Stefan Hrastinski Christina Keller 《Information Systems and E-Business Management》2011,9(1):109-131
Design science research is an essential part of IS research since the field should not only try to understand how the world
is, but also how to change it. We argue that the aim of IS design science research should be to develop practical knowledge
not only for the design of novel information technology (IT), but also for IS governance and management. Whereas at least
some methodological support exists for researchers engaged in IT-centric design science research, limited support is available
for researchers who want to develop design knowledge and theory for IS governance and management. To overcome this shortcoming,
we suggest a socio-technical IS design science research approach. The approach has four main activities: (1) identifying problem
situations and desired outcomes, (2) reviewing extant theories, knowledge and data, (3) proposing/refining design theory and
knowledge, and (4) testing design theory and knowledge. The applicability and usefulness of the proposed approach is shown
by means of a design science research project concerning IS integration management in the context of mergers and acquisitions. 相似文献
100.
In numerous modern stream ciphers, the internal state consists of a large array of pseudo-random words, while the output key-stream is a relatively simple function of the state. It has been heuristically shown in several situations [3], [8], [9], [10], [11] and [14] that this structure may lead to distinguishing attacks on the cipher. In this note we present a more rigorous treatment of this structural attack. First, we present a rigorous proof of the main probabilistic claim behind it in the basic cases. We then apply it concretely to the cipher sn3 [12], and demonstrate that the heuristic assumptions of the attack are remarkably precise in more complicated cases. 相似文献