全文获取类型
收费全文 | 41857篇 |
免费 | 1987篇 |
国内免费 | 78篇 |
专业分类
电工技术 | 284篇 |
综合类 | 139篇 |
化学工业 | 10711篇 |
金属工艺 | 899篇 |
机械仪表 | 816篇 |
建筑科学 | 1435篇 |
矿业工程 | 94篇 |
能源动力 | 1655篇 |
轻工业 | 8031篇 |
水利工程 | 339篇 |
石油天然气 | 259篇 |
武器工业 | 3篇 |
无线电 | 1813篇 |
一般工业技术 | 5911篇 |
冶金工业 | 5616篇 |
原子能技术 | 329篇 |
自动化技术 | 5588篇 |
出版年
2024年 | 99篇 |
2023年 | 366篇 |
2022年 | 1184篇 |
2021年 | 1560篇 |
2020年 | 972篇 |
2019年 | 1080篇 |
2018年 | 1382篇 |
2017年 | 1357篇 |
2016年 | 1497篇 |
2015年 | 1148篇 |
2014年 | 1691篇 |
2013年 | 3297篇 |
2012年 | 2457篇 |
2011年 | 2907篇 |
2010年 | 2244篇 |
2009年 | 2235篇 |
2008年 | 1892篇 |
2007年 | 1667篇 |
2006年 | 1331篇 |
2005年 | 1099篇 |
2004年 | 1020篇 |
2003年 | 946篇 |
2002年 | 817篇 |
2001年 | 602篇 |
2000年 | 570篇 |
1999年 | 602篇 |
1998年 | 2016篇 |
1997年 | 1293篇 |
1996年 | 951篇 |
1995年 | 529篇 |
1994年 | 475篇 |
1993年 | 427篇 |
1992年 | 186篇 |
1991年 | 154篇 |
1990年 | 126篇 |
1989年 | 156篇 |
1988年 | 137篇 |
1987年 | 121篇 |
1986年 | 90篇 |
1985年 | 141篇 |
1984年 | 89篇 |
1983年 | 74篇 |
1982年 | 78篇 |
1981年 | 72篇 |
1980年 | 93篇 |
1979年 | 48篇 |
1978年 | 45篇 |
1977年 | 121篇 |
1976年 | 230篇 |
1973年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
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
62.
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
63.
A. Cardador-Martí nez E. Casta o-Tostado G. Loarca-Pi a 《Food Additives & Contaminants》2002,19(1):62-69
Polyphenols with antimutagenic and anticarcinogenic properties are present in fruits, vegetables and legumes. In this study, the Salmonella typhimurium tester strains TA98 and TA100 were used in the microsuspension assay to examine the antimutagenic effect of phenolic compounds extracted from the common bean (Phaseolus vulgaris) against mutagenicity induced by aflatoxin B 1 (AFB 1 ). A dose-response curve was constructed for AFB 1 ; from which a level of 40ng AFB 1 /tube was selected for all antimutagenicity assays. The AFB 1 and phenolic extract (PE) were not toxic to the bacteria at concentrations tested. In the case of PE, results were similar to the number of spontaneous revertants for TA98 and TA100. The inhibitory effect of PE against AFB 1 mutagenicity was dose-dependent at the lower concentrations tested (2.5, 5, 10, 12.5, 15 and 25 μg-equivalent ( + )-catechin/tube for TA98; 0.5, 1, 1.5, 2.5, 5, 10 and 25 μg-equivalent ( + )-catechin/ tube for TA100). Further, a two-stage incubation procedure was used to investigate the potential interaction between PE and AFB 1 . The greatest inhibitory effect of the PE on AFB 1 mutagenicity occurred when PE and AFB 1 were incubated together. When the bacteria were first incubated with PE followed by a second incubation with AFB 1 , lower inhibition was observed. Lower inhibition was also observed when the bacteria were first incubated with AFB 1 followed by a second incubation with PE. The results suggest that the mechanism of inhibition could involve the formation of a chemical complex between of PE and AFB 1 . 相似文献
64.
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
65.
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
66.
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
67.
68.
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
69.
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
70.
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