全文获取类型
收费全文 | 1972篇 |
免费 | 121篇 |
国内免费 | 2篇 |
学科分类
工业技术 | 2095篇 |
出版年
2024年 | 2篇 |
2023年 | 9篇 |
2022年 | 24篇 |
2021年 | 218篇 |
2020年 | 80篇 |
2019年 | 88篇 |
2018年 | 104篇 |
2017年 | 88篇 |
2016年 | 120篇 |
2015年 | 78篇 |
2014年 | 127篇 |
2013年 | 149篇 |
2012年 | 108篇 |
2011年 | 110篇 |
2010年 | 93篇 |
2009年 | 89篇 |
2008年 | 87篇 |
2007年 | 77篇 |
2006年 | 65篇 |
2005年 | 50篇 |
2004年 | 51篇 |
2003年 | 39篇 |
2002年 | 36篇 |
2001年 | 21篇 |
2000年 | 16篇 |
1999年 | 17篇 |
1998年 | 12篇 |
1997年 | 14篇 |
1996年 | 8篇 |
1995年 | 9篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 4篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 2篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1973年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有2095条查询结果,搜索用时 16 毫秒
11.
Piotr Piecuch Stanis?aw A. KucharskiKarol Kowalski Monika Musia? 《Computer Physics Communications》2002,149(2):71-96
The recently proposed renormalized (R) and completely renormalized (CR) coupled-cluster (CC) methods of the CCSD[T] and CCSD(T) types have been implemented using recursively generated intermediates and fast matrix multiplication routines. The details of this implementation, including the complete set of equations that have been used in writing efficient computer codes, memory requirements, and typical CPU timings, are discussed. The R-CCSD[T], R-CCSD(T), CR-CCSD[T], and CR-CCSD(T) computer codes and similar codes for the standard CC methods, including the LCCD, CCD, CCSD, CCSD[T], and CCSD(T) approaches, have been incorporated into the gamess package. Information about the main features of this new set of CC programs is provided. 相似文献
12.
High-density structures with relatively well-ordered nanopore arrays have been obtained by the self-ordering growth of nanopores occurring during anodisation of aluminium in sulphuric acid. The resulting array of well-ordered nanopores strongly depends on an applied voltage of anodising, temperature and a procedure of synthesis. Regular arranged hexagonal arrays on aluminium with a relatively uniform pore diameter, interpore distance, and depth of pores exceeding 90 μm, can be formed by the self-ordering two-step anodising at 1 °C. The interpore distance and the pore diameter were evaluated on anodised aluminium layers obtained at different cell potentials ranging from 15 to 25 V. The detailed analyses of their uniformity were performed from SEM images. The analysis of a pore arrangement defects was made from SEM top view images taken on samples anodised at various cell potentials. The defect maps, known as Delaunay triangulations, of the arrangement of about 1000 pores were constructed for different applied anodising potentials. The percentage of pores that are not six-fold coordinated by the neighbouring pores indicates the percentage of defected surface. 相似文献
13.
We describe a formal language/notation for DNA molecules that may contain nicks and gaps. The elements of the language, DNA
expressions, denote formal DNA molecules. Different DNA expressions may denote the same formal DNA molecule. We analyse the
shortest DNA expressions denoting a given formal DNA molecule. We determine lower bounds on their lengths and explain how
we construct these minimal DNA expressions. 相似文献
14.
James Mark William Brownjohn Pilate Moyo Piotr Omenzetter Yong Lu 《Canadian Metallurgical Quarterly》2003,8(3):162-172
The Land Transport Authority of Singapore has a continuing program of highway bridge upgrading for refurbishing and strengthening bridges to allow for increasing vehicle traffic and increasing axle loads. One subject of this program has been a short-span bridge taking a busy main road across a coastal inlet near a major port facility. Experiment-based structural assessments of the bridge were conducted before and after upgrading works including strengthening. Each assessment exercise comprised three separate components: (1) a strain and acceleration monitoring exercise lasting approximately one month; (2) a full-scale dynamic test carried out in a single day without closing the bridge; and (3) a finite-element model updating exercise to identify structural parameters and mechanisms. This paper presents the dynamic testing and the modal analysis used to identify the vibration properties and the quantification of the effectiveness of the upgrading through the subsequent model updating. Before and after upgrade, similar sets of vibration modes were identified, resembling those of an orthotropic plate with relatively weak transverse bending stiffness. Conversion of bearings from nominal simple supports to nominal full fixity was shown via model updating to be the principal cause of natural frequency increases of up to 50%. The utility of the combined experimental and analytical process in direct identification of structural properties has been proven, and the procedure can be applied to other structures and their capacity assessments. 相似文献
15.
The cognitive exhaustion model of helplessness (predicting withdrawal from constructive effortful processing after uncontrollability) was applied to decision making. After unsolvable problems (or no preexposure), Ss requested information from a matrix with 5 alternatives (films)?×?10 attributes and then chose the best film. Films in a set were either similar (difficult decision) or dissimilar (easy decision) in attractiveness. As predicted, Ss with an uncontrollable preexposure spent less time on predecisional information search, disregarded their own importance criteria when asking for information, and had attention highly focused on a selected option for the easy decision condition but diffused across options for the difficult decision condition. The implications of these findings for understanding cognitive mechanisms of learned helplessness and depression are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
16.
Agnieszka J. Klemm Piotr Klemm Kazimierz Rozniakowski Tomasz W. Wojtatowicz 《Building and Environment》2002,37(12):1233-1240
This paper presents the results of the larger study into a potential application of laser radiation for the detection of phase transition processes in low temperatures occurring on the surface layers of cementitious materials. An attempt was made to identify relationships between the environmental conditions—temperature and air humidity, and the selected parameters of the reflected light. Onset of the condensation process and formation of water microdrops on the surface of the material leads to the phase displacement of individual laser rays, which are represented by different speckle images.
Although the analysis of parameters of the reflected light are very difficult in the case of porous materials because of highly developed roughness of the surface structure it has been proved that a dynamic study of the phase transition phenomena can be successfully carried out without mechanical intervention. 相似文献
17.
Agnieszka J Klemm Piotr Klemm Kazimierz Rozniakowski Tomasz W Wojtatowicz 《Building and Environment》2002,37(12):1221-1232
This paper present the results of the investigation into a potential application of laser radiation for the detection of phase transition processes occurring on the surface layers of porous materials. An attempt was made to discuss in the approximation equations, the relationships between coefficients of the reflected light, the temperature and humidity of the surrounding environment. Laser light reflected from the porous surface carries information about the roughness of the structure. The presence of water microdrop on the surface of the porous material, as a result of condensation and thus a phase transition, leads to the phase displacement of individual rays, which is represented by different images. Therefore, a comprehensive analysis of the reflected light parameters allows a dynamic study of the phase transition phenomena without mechanical intervention. 相似文献
18.
A grid (or a mesh) is a two-dimensional permutation: an m× n-grid of size mn is an m× n-matrix where the entries run through the elements {1,2, …, mn}. We prove that if δ1 and δ2 are any two linear orders on {1,2, …, N}, then they can be simultaneously embedded (in a well defined sense) into a unique grid having the smallest size. 相似文献
19.
Piotr Furma
ski 《International Journal of Heat and Mass Transfer》1994,37(18):2993-3002
A mixture theory based on the ensemble-averaging technique is proposed for studying the thermal behaviour of heterogeneous media. Balance equations with partial heat fluxes and interaction terms are introduced for a two-component medium. Relations between these quantities and the ensemble-averaged (mean) temperatures of separate components are derived. The limits of application of widely used postulates of proportionality of the interaction term of difference in mean temperature of components is discussed. The effective conductivities of components in the mixture and the interaction coefficient are introduced and related to the so-called microstructure functions, which are functions of the microgeometry of the medium and the thermal properties of its components. Examples of the application of the theory to the calculation of the mean properties of a heterogeneous medium are presented. 相似文献
20.
Renata Gruszka Krzysztof Zakrzewski Pawe Piotr Liberski Magdalena Zakrzewska 《International journal of molecular sciences》2021,22(2)
Numerous molecular factors disrupt the correctness of the cell cycle process leading to the development of cancer due to increased cell proliferation. Among known causative factors of such process is abnormal gene expression. Nowadays in the light of current knowledge such alterations are frequently considered in the context of mRNA–miRNA correlation. One of the molecular factors with potential value in tumorigenesis is the feedback loop between MYC and E2F genes in which miR-17-5p and miR-20a from the miR-17-92 cluster are involved. The current literature shows that overexpression of the members of the OncomiR-1 are involved in the development of many solid tumors. In the present work, we investigated the expression of components of the MYC/E2F/miR-17-92 network and their closely related elements including members of MYC and E2F families and miRNAs from two paralogs of miR-17-92: miR-106b-25 and miR-106a-363, in the most common brain tumors of childhood, pilocytic astrocytoma (PA), WHO grade 1; ependymoma (EP), WHO grade 2; and medulloblastoma (MB), WHO grade 4. We showed that the highest gene expression was observed in the MYC family for MYCN and in the E2F family for E2F2. Positive correlation was observed between the gene expression and tumor grade and type, with the highest expression being noted for medulloblastomas, followed by ependymomas, and the lowest for pilocytic astrocytomas. Most members of miR-17-92, miR-106a-363 and miR-106b-25 clusters were upregulated and the highest expression was noted for miR-18a and miR-18b. The rest of the miRNAs, including miR-19a, miR-92a, miR-106a, miR-93, or miR-25 also showed high values. miR-17-5p, miR-20a obtained a high level of expression in medulloblastomas and ependymomas, while close to the control in the pilocytic astrocytoma samples. miRNA expression also depended on tumor grade and histology. 相似文献