全文获取类型
收费全文 | 27130篇 |
免费 | 1137篇 |
国内免费 | 39篇 |
专业分类
电工技术 | 191篇 |
综合类 | 28篇 |
化学工业 | 6591篇 |
金属工艺 | 522篇 |
机械仪表 | 514篇 |
建筑科学 | 934篇 |
矿业工程 | 61篇 |
能源动力 | 1131篇 |
轻工业 | 5029篇 |
水利工程 | 218篇 |
石油天然气 | 140篇 |
武器工业 | 2篇 |
无线电 | 1205篇 |
一般工业技术 | 3721篇 |
冶金工业 | 4067篇 |
原子能技术 | 216篇 |
自动化技术 | 3736篇 |
出版年
2024年 | 60篇 |
2023年 | 229篇 |
2022年 | 708篇 |
2021年 | 917篇 |
2020年 | 574篇 |
2019年 | 656篇 |
2018年 | 822篇 |
2017年 | 820篇 |
2016年 | 906篇 |
2015年 | 749篇 |
2014年 | 1039篇 |
2013年 | 1932篇 |
2012年 | 1489篇 |
2011年 | 1868篇 |
2010年 | 1430篇 |
2009年 | 1434篇 |
2008年 | 1237篇 |
2007年 | 1097篇 |
2006年 | 881篇 |
2005年 | 749篇 |
2004年 | 692篇 |
2003年 | 623篇 |
2002年 | 560篇 |
2001年 | 390篇 |
2000年 | 382篇 |
1999年 | 412篇 |
1998年 | 1429篇 |
1997年 | 916篇 |
1996年 | 675篇 |
1995年 | 370篇 |
1994年 | 325篇 |
1993年 | 324篇 |
1992年 | 124篇 |
1991年 | 120篇 |
1990年 | 85篇 |
1989年 | 114篇 |
1988年 | 92篇 |
1987年 | 84篇 |
1986年 | 67篇 |
1985年 | 105篇 |
1984年 | 66篇 |
1983年 | 52篇 |
1982年 | 55篇 |
1981年 | 59篇 |
1980年 | 58篇 |
1979年 | 36篇 |
1977年 | 97篇 |
1976年 | 186篇 |
1975年 | 31篇 |
1973年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
This paper attempts to shed light on the determinants of energy demand in Turkey. Energy demand model is first proposed using the ant colony optimization (ACO) approach. It is multi-agent systems in which the behavior of each ant is inspired by the foraging behavior of real ants to solve optimization problem. ACO energy demand estimation (ACOEDE) model is developed using population, gross domestic product (GDP), import and export. All equations proposed here are linear and quadratic. Quadratic_ACOEDE provided better-fit solution due to fluctuations of the economic indicators. The ACOEDE model plans the energy demand of Turkey until 2025 according to three scenarios. The relative estimation errors of the ACOEDE model are the lowest when they are compared with the Ministry of Energy and Natural Resources (MENR) projection. 相似文献
42.
A new definition of the flooding point in a two-phase counter-current trickle bed column has been proposed. Based on this point a versatile correlation of liquid hold-up has been formulated. The coefficients of this correlation are invariant to the change of physical properties of liquid, type and size of the packing forming the bed and gas velocity. This conclusion has been reached from the analysis of experiments with four different liquids irrigating the bed and three types of packing of various size. The versatile correlation can be used also re-currently to calculate flooding hold-up and flooding liquid rate from two known values of liquid hold-up for a given gas rate. 相似文献
43.
Summary The nucleophilic substitution with C6H5SNa, at -30°C, is compared for five PVC samples with various contents of isotactic triads. The conversion curves consist of a very fast stage followed by a steady one. All the samples are found to behave in the same way except for the content of the structures involved in the fast period. This content is estimated by extrapolating the straight lines of the steady stages to zero time. The obtained values are found to be a linear function of the content of isotactic triads. The results, together with some earlier ones, allow for the content of the labile non-defect structures in PVC to be determined. 相似文献
44.
Staub Adrian; Rayner Keith; Pollatsek Alexander; Hy?n? Jukka; Majewski Helen 《Canadian Metallurgical Quarterly》2007,33(6):1162
Readers' eye movements were monitored as they read sentences containing noun-noun compounds that varied in frequency (e.g., elevator mechanic, mountain lion). The left constituent of the compound was either plausible or implausible as a head noun at the point at which it appeared, whereas the compound as a whole was always plausible. When the head noun analysis of the left constituent was implausible, reading times on this word were inflated, beginning with the first fixation. This finding is consistent with previous demonstrations of very rapid effects of plausibility on eye movements. Compound frequency did not modulate the plausibility effect, and all disruption was resolved by the time readers' eyes moved to the next word. These findings suggest (contra Kennison, 2005) that the parser initially analyzes a singular noun as a head instead of a modifier. In addition, the findings confirm that the very rapid effect of plausibility on eye movements is not due to strategic factors, because in the present experiment, unlike in previous demonstrations, this effect appeared in sentences that were globally plausible. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
45.
J. R. Díaz-Estrada E. Camps L. Escobar-Alarcón J. A. Ascencio 《Journal of Materials Science》2007,42(4):1360-1368
Deposition of Ti was carried out by laser ablation onto hydroxyapatite porous discs in an Ar atmosphere. Ti nanoparticles
were deposited onto HAp surface in order to modify its roughness and morphology as it is observed by scanning electron microscopy
(SEM) and scanning probe microscopy (SPM). A homogeneous distribution of Ti over the disc surface was corroborated by elemental
mapping. A comparison of the hydroxyapatite hardness before and after deposition was performed using SPM nanoindentation.
Transmission Electron Microscopy (TEM) showed that the Ti nanoparticles obtained were covered by an oxygen shell. It is shown
that surface modifications of the covered HAp by Ti result in better mechanical properties, reducing the possible damage to
the HAp ceramic by friction or impacts as it often happens in meniscus, bone junctions and the inclusion of prosthesis for
human treatments. 相似文献
46.
In this paper we consider A(θ)-stable finite difference methods for numerical solutions of dissipative partial differential equations of parabolic type.
Combining two rational approximation methods with different orders of accuracy, where the lower order method is applied n
0 times (n
0 fixed) at each time step, we prove the existence of a second order method which is contractive for all time steps. Moreover,
we shed light on the conditions on the lower order method which are sufficient (and sometimes necessary) to obtain the optimal
order of accuracy. For the one-dimensional heat equation we construct a family of numerical methods which are contractive
in the maximum norm for all values of the discretization parameters. We also present numerical examples to illustrate our
results.
Received: May 2002 / Accepted: January 2003 相似文献
47.
Peter Eaton Andrea Ragusa Caroline Clavel Cristina T Rojas Paul Graham Raúl V Durán Soledad Penadés 《IEEE transactions on nanobioscience》2007,6(4):309-318
Glyconanoparticles which present carbohydrate and amino groups motifs at their surface were produced. These particles were highly stable and soluble in aqueous solutions. The presence of the carbohydrate groups also allowed the inclusion of more strongly binding groups, without affecting solubility. The binding of a model DNA, plasmid by these nanoparticles was studied by atomic force microscopy, transmission electron microscopy, and gel electrophoresis. Significant differences between the nanoparticles based on their affinities for the DNA were found, with implications for their potential use as nonviral gene delivery agents. 相似文献
48.
Alfredo Bone´ 《国际水资源开发杂志》2003,19(3):413-435
The present paper outlines the views of the Government of Aragon on the National Hydrological Plan of Spain. It concludes that the transfer of water from the Ebro River will accentuate the differences among some regions of Spain in terms of their development potentials. It will unquestionably constrain the future development of regions that are already disadvantaged, such as Aragon. Alternatives are proposed where the regions in need of water can obtain it, but without adversely affecting the economic, social and environmental sustainability of the region and the people of Aragon. 相似文献
49.
We present some new lower bounds on the optimal information rate and on the optimal average information rate of secret sharing schemes with homogeneous access structure. These bounds are found by using some covering constructions and a new parameter, the k-degree of a participant, that is introduced in this paper. Our bounds improve the previous ones in almost all cases. 相似文献
50.
Francisco Jos Alguacil Concepcin Caravaca María Isabel Martín 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2003,78(10):1048-1053
The transport of chromium(VI) through a flat‐sheet supported liquid membrane containing Cyanex 921 as a carrier has been investigated. The permeation of the metal is investigated as a function of various experimental variables: hydrodynamic conditions, concentration of chromium(VI) and HCl in the feed phase, carrier concentration and diluent in the membrane and strippant concentration in the stripping phase. The mass transfer coefficient and the thickness of the aqueous boundary layer were calculated from the experimental data. Furthermore, the selectivity of Cyanex 921‐based flat‐sheet supported liquid membrane towards different metal ions and the behaviour of the system against other carriers are presented. Copyright © 2003 Society of Chemical Industry 相似文献