全文获取类型
收费全文 | 32174篇 |
免费 | 1467篇 |
国内免费 | 35篇 |
专业分类
电工技术 | 337篇 |
综合类 | 58篇 |
化学工业 | 6996篇 |
金属工艺 | 600篇 |
机械仪表 | 581篇 |
建筑科学 | 1895篇 |
矿业工程 | 78篇 |
能源动力 | 875篇 |
轻工业 | 2698篇 |
水利工程 | 296篇 |
石油天然气 | 165篇 |
武器工业 | 3篇 |
无线电 | 2300篇 |
一般工业技术 | 5950篇 |
冶金工业 | 5258篇 |
原子能技术 | 205篇 |
自动化技术 | 5381篇 |
出版年
2023年 | 278篇 |
2022年 | 449篇 |
2021年 | 701篇 |
2020年 | 507篇 |
2019年 | 593篇 |
2018年 | 726篇 |
2017年 | 693篇 |
2016年 | 910篇 |
2015年 | 818篇 |
2014年 | 1034篇 |
2013年 | 1927篇 |
2012年 | 1680篇 |
2011年 | 2126篇 |
2010年 | 1516篇 |
2009年 | 1469篇 |
2008年 | 1767篇 |
2007年 | 1654篇 |
2006年 | 1444篇 |
2005年 | 1235篇 |
2004年 | 1103篇 |
2003年 | 949篇 |
2002年 | 915篇 |
2001年 | 545篇 |
2000年 | 526篇 |
1999年 | 535篇 |
1998年 | 503篇 |
1997年 | 464篇 |
1996年 | 466篇 |
1995年 | 442篇 |
1994年 | 428篇 |
1993年 | 431篇 |
1992年 | 385篇 |
1991年 | 229篇 |
1990年 | 321篇 |
1989年 | 323篇 |
1988年 | 274篇 |
1987年 | 297篇 |
1986年 | 286篇 |
1985年 | 307篇 |
1984年 | 267篇 |
1983年 | 257篇 |
1982年 | 240篇 |
1981年 | 209篇 |
1980年 | 176篇 |
1979年 | 183篇 |
1978年 | 165篇 |
1977年 | 140篇 |
1976年 | 124篇 |
1975年 | 136篇 |
1974年 | 109篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Ioannis K. Karabagias Evangelia Z. Halatsi Stavros Kontakos Sofia Karabournioti Michael G. Kontominas 《International Journal of Food Properties》2017,20(11):2699-2710
The aim of the present study was to investigate the volatile fraction and discriminate 34 commercial thyme honeys from Morocco, Egypt, Spain, and Greece according to geographical origin, using key volatile compounds in combination with chemometrics. Sixty-two volatile compounds belonging to different classes were identified and semi-quantified using headspace solid phase micro-extraction coupled to gas chromatography/mass spectrometry (HS-SPME-GC/MS). Applying chemometric analyses to 17 volatiles (p < 0.05), honeys were successfully discriminated according to geographical origin. Correct classification rate was 88.2% using the cross-validation method. Volatile compounds proved to be a powerful tool for discriminating commercial thyme honeys from different countries. 相似文献
992.
The potential of industrial porous concrete for using as a template for the synthesis of porous carbon materials has been investigated. Carbon replicas of porous concrete have been prepared by carbonization of sucrose. The pores of the resulting carbon materials range from the macropore to the micropore region, pointing to a hierarchy. 相似文献
993.
This paper examines the interaction between the electric double layers of aggregates. Commonly, rather simplified models are used like the approximation of primary particle interaction (APPI), which just considers the interaction of the closest pair of primary particles having a double layer as if they were isolated. However, for nanoparticles the double layer thickness may be in the same order of magnitude as the particle size or even larger, what leads to a considerable double layer overlap inside the aggregates and between two interacting aggregates. Consequently, such approximations will fail. The paper presents a numerical scheme for the double layer interaction of arbitrarily shaped aggregates, which can e.g. help to establish criteria for the applicability of approximate models. The calculation employs a singularity method, which is based on the linearised Poisson–Boltzmann equation. Additionally, a linear model for charge regulation is implemented. The impact of charge regulation and double layer thickness were studied for fractal DLCA aggregates and hexagonal closed-packed aggregates. 相似文献
994.
Giovanni Caprioli Michael G. Cahill Sauro Vittori Kevin J. James 《Food Analytical Methods》2014,7(7):1367-1372
Potatoes produce biologically active secondary metabolites like glycoalkaloids and their aglycons, which may have both adverse and beneficial effects in the diet. A new analytical method that uses liquid chromatography–mass spectrometry (LTQ-Orbitrap) has been developed for the analysis of glycoalkaloids and their aglycons in potato samples. Two glycoalkaloids, α-solanine and α-chaconine, and two aglycons, demissidine and solasodine, were quantified in potato samples. Samples were extracted using methanol, purified on an SPE Strata C18 cartridge, and then analyzed in HPLC–mass spectrometry (LTQ-Orbitrap) with the FTMS operating in full scan at a resolving power of 30,000 (FWHM), enabling the detection and accurate mass measurement and with the ITMS mode operating in MRM (multiple reaction monitoring) for glycoalkaloids and their aglycons using the [M + H]+ ions and their optimized collision energies. After validation, the method was applied to screen different type of potatoes, and some cooking experiment were conducted. 相似文献
995.
Modern vehicles are proficient in establishing a spontaneous connection over a wireless radio channel, synchronizing actions and information. Security infrastructure is most important in such a sensitive scope of vehicle communication for coordinating actions and avoiding accidents on the road. One of the first security issues that need to be established is authentication via IEEE 1609.2 security infrastructure. According to our preliminary work, vehicle owners are bound to preprocess a certificate from the certificate authority. The certificate carries vehicle static attributes (e.g., licence number, brand and color) certified together with the vehicle public key in a monolithic manner. Nevertheless, a malicious vehicle might clone the static attributes to impersonate a specific vehicle. Therefore, in this paper we consider a resource expensive attack scenario involving multiple malicious vehicles with identical visual static attributes. Apparently, dynamic attributes (e.g., location and direction) can uniquely define a vehicle and can be utilized to resolve the true identity of the vehicle. However, unlike static attributes, dynamic attributes cannot be signed by a trusted authority beforehand. We propose an approach to verify the coupling between non-certified dynamic attributes and certified static attributes on an auxiliary communication channel, for example, a modulated laser beam. Furthermore, we illustrate that the proposed approach can be used to facilitate the usage of existing authentication protocols such as NAXOS, in the new scope of ad-hoc vehicle networks. We use BAN logic to verify the security claims of the protocol against the passive and active interception. 相似文献
996.
Adam J. Hall Michael J. Chappell John A.D. Aston Stephen A. Ward 《Computer methods and programs in biomedicine》2014
A four compartment mechanistic mathematical model is developed for the pharmacokinetics of the commonly used anti-malarial drug artesunate and its principle metabolite dihydroartemisinin following oral administration of artesunate. The model is structurally unidentifiable unless additional constraints are imposed. Combinations of mechanistically derived constraints are considered to assess their effects on structural identifiability and on model fits. Certain combinations of the constraints give rise to locally or globally identifiable model structures. 相似文献
997.
In this paper, we identify two cases in which the proposition for calculating time window penalties presented in Nagata, Y., Bräysy, O. and Dullaert, W. A penalty-based edge assembly memetic algorithm for the vehicle routing problem with time windows, Computers & Operations Research 2010;37(4): 724–37 yields incorrect results. We derive the corrected proposition and use numerical studies to show that a significant proportion of the evaluations performed by a Tabu Search for VRPTW falls under the two incorrect cases. Moreover, we demonstrate that the incorrect time window handling has a significant negative impact on the solution quality of the Tabu Search. 相似文献
998.
Michael J. Best Robert R. Grauer Jaroslava Hlouskova Xili Zhang 《Computational Economics》2014,44(1):45-65
Prospect theory postulates that the utility function is characterized by a kink (a point of non-differentiability) that distinguishes gains from losses. In this paper we present an algorithm that efficiently solves the linear version of the kinked-utility problem. First, we transform the non-differentiable kinked linear-utility problem into a higher dimensional, differentiable, linear program. Second, we introduce an efficient algorithm that solves the higher dimensional linear program in a smaller dimensional space. Third, we employ a numerical example to show that solving the problem with our algorithm is 15 times faster than solving the higher dimensional linear program using the interior point method of Mosek. Finally, we provide a direct link between the piece-wise linear programming problem and conditional value-at-risk, a downside risk measure. 相似文献
999.
Different concepts and designs of photovoltaic thermal (PV/T) collectors were developed for the past few decades to improve the electrical and thermal efficiencies. Several of those designs have become successful and are being commercialized along with other solar collectors. This paper discusses the experimental studies on a novel PV/T water-based collector constructed by laminating the PV cells on a copper thermal absorber. This modification reduced the thermal resistance by 9.93 %, thereby enabling better heat transfer from the PV cells to the heat transfer fluid. Water was passed through a single water channel connected to an open reservoir. Experiments were conducted with and without glazing, with two different water mass flow rates and stagnant conditions, and with load and no-load conditions and thermal stress test. Results show that an overall efficiency of 87.52 % was achieved in the presence of glazing at a mass flow rate of 0.1 kg/s. Few conformance tests according to IEC standards are also presented to check the electrical insulation and structural integrity of the PV/T collector. 相似文献
1000.
Battery cells being electrically disconnected resulting from degradation, mechanical stress, or corrosion can lead to hazardous situations during operation of electric vehicles or storage systems in stationary applications. The mentioned errors can be acceptable in some cases when cells or cell strings are connected in parallel, but the failure is to be detected in order to guarantee the reliable and safe operation of the battery system. A method enabling the estimation whether individual battery cells are faulty (cell error or electrically disconnected) by evaluating the mean impedance and capacity information of cell groups is introduced and validated. 相似文献