全文获取类型
收费全文 | 19685篇 |
免费 | 1229篇 |
国内免费 | 25篇 |
专业分类
电工技术 | 226篇 |
综合类 | 13篇 |
化学工业 | 4978篇 |
金属工艺 | 281篇 |
机械仪表 | 534篇 |
建筑科学 | 785篇 |
矿业工程 | 40篇 |
能源动力 | 757篇 |
轻工业 | 3870篇 |
水利工程 | 229篇 |
石油天然气 | 100篇 |
武器工业 | 2篇 |
无线电 | 1113篇 |
一般工业技术 | 3297篇 |
冶金工业 | 1139篇 |
原子能技术 | 119篇 |
自动化技术 | 3456篇 |
出版年
2024年 | 55篇 |
2023年 | 211篇 |
2022年 | 575篇 |
2021年 | 836篇 |
2020年 | 585篇 |
2019年 | 647篇 |
2018年 | 841篇 |
2017年 | 870篇 |
2016年 | 930篇 |
2015年 | 667篇 |
2014年 | 879篇 |
2013年 | 1713篇 |
2012年 | 1318篇 |
2011年 | 1504篇 |
2010年 | 1044篇 |
2009年 | 1100篇 |
2008年 | 1042篇 |
2007年 | 902篇 |
2006年 | 740篇 |
2005年 | 496篇 |
2004年 | 456篇 |
2003年 | 410篇 |
2002年 | 398篇 |
2001年 | 257篇 |
2000年 | 234篇 |
1999年 | 213篇 |
1998年 | 416篇 |
1997年 | 296篇 |
1996年 | 214篇 |
1995年 | 163篇 |
1994年 | 117篇 |
1993年 | 103篇 |
1992年 | 61篇 |
1991年 | 52篇 |
1990年 | 54篇 |
1989年 | 44篇 |
1988年 | 42篇 |
1987年 | 34篇 |
1986年 | 32篇 |
1985年 | 41篇 |
1984年 | 62篇 |
1983年 | 47篇 |
1982年 | 33篇 |
1981年 | 27篇 |
1980年 | 31篇 |
1979年 | 19篇 |
1978年 | 15篇 |
1977年 | 18篇 |
1976年 | 33篇 |
1975年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
Renato Cataluña Rosângela da Silva Eliana Weber de Menezes Ricardo Boeira Ivanov 《Fuel》2008,87(15-16):3362-3368
Oxygenated fuels increase fuel consumption due to their low enthalpy of combustion; however, their high antiknock index renders them suitable for use in engines with a high compression rate, increasing their thermal yield. This study evaluated the performance of biorenewable oxygenated fuels (ethanol and isoamyl alcohol) and partially renewable fuels (ETBE: ethyl tert-butyl ether, TAEE: tert-amyl ethyl ether and di-TAE: di-tert-amyl ether) with high degree of purity and in mixtures with automotive gasoline, based on tests with Otto cycle engines. Among the oxygenated fuels evaluated here, di-TAE was found to present the best characteristics of performance, both individually and in mixtures with gasoline. 相似文献
33.
The nonisothermal crystallization kinetics of a metallocene-made isotactic polypropylene (m-iPP) and its compounds with 0.1 wt % and 0.3 wt % of a sorbitol derivative [1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (DMDBS); an α nucleator] were investigated by differential scanning calorimetry at different cooling rates from the melt. The nucleation efficiency was proved by a significant increase in the crystallization temperatures (accompanied by a slight augmentation of the degree of crystallinity and a decrease in the crystal sizes). This increase in the crystallization temperatures led to higher amounts of fractional content in the γ polymorph, even though DMDBS was supposed to be a nucleator for the α form. The Avrami and Ozawa methods effectively described only the early stage of crystallization, whereas a combined Avrami–Ozawa method was valid for the whole crystallization process. The values of the exponent for this method decreased for nucleated samples in the later stage of crystallization, especially in the case of m-iPP with 0.3 wt % DMDBS added (m-iPP03). The activation energy of the process and the surface free energy were also estimated. The production of considerable proportions of the γ polymorph in m-iPP03 corresponded to higher values of the activation energy and lower values of the surface free energy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
34.
Reda Karoum Antonio de Lucas-Consuegra Fernando Dorado Jose Luis Valverde Alain Billard Philippe Vernoux 《Journal of Applied Electrochemistry》2008,38(8):1083-1088
The electrochemical promotion of catalysis (EPOC) of propene combustion was investigated using Pt sputtered thin film on an
O2− conductor, 8 mol% Y2O3-stabilized-ZrO2 (YSZ). In order to separate the influence of the thermal migration of the O2− oxide ions from the electrolyte to the catalyst surface and the impact of an electrical polarization on the catalytic activity,
several light-off experiments (cool down and heat up procedures) were successively performed under different polarizations,
i.e. OCV, +2 and −2 V. These experiments have clearly shown that the presence of O2− (thermally or electrochemically induced) inhibits the catalytic activity of the platinum for the propene deep oxidation.
These results demonstrate the importance to define a normalized rate enhancement ratio, ρ
n
, from a reference value of the catalytic rate corresponding to a Pt surface state free of O2− ions. 相似文献
35.
The Humanitarian Engineering initiative, sponsored by the William and Flora Hewlett Foundation, at the Colorado School of Mines, is creating a program that will support engineering students in understanding their responsibility for solving community development problems that exist throughout the world. As part of this effort, data has been collected on faculty and student attitudes using the ‘Community Service Attitudes Scale,” developed and validated by Shiarella, McCarthy, and Tucker. During the fall 2004, 78 students and 34 faculty members responded to this instrument. Statistically significant differences were found between the attitudes of students and faculty, males and females, and among different age groupings with respect to service activities. A general finding was that faculty displayed better attitudes toward community service than the students. 相似文献
36.
37.
This article presents the first application of the Finite Calculus (FIC) in a Ritz-FEM variational framework. FIC provides a steplength parametrization of mesh dimensions, which is used to modify the shape functions. This approach is applied to the FEM discretization of the steady-state, one-dimensional, diffusion–absorption and Helmholtz equations. Parametrized linear shape functions are directly inserted into a FIC functional. The resulting Ritz-FIC equations are symmetric and carry a element-level free parameter coming from the function modification process. Both constant- and variable-coefficient cases are studied. It is shown that the parameter can be used to produce nodally exact solutions for the constant coefficient case. The optimal value is found by matching the finite-order modified differential equation (FOMoDE) of the Ritz-FIC equations with the original field equation. The inclusion of the Ritz-FIC models in the context of templates is examined. This inclusion shows that there is an infinite number of nodally exact models for the constant coefficient case. The ingredients of these methods (FIC, Ritz, MoDE and templates) can be extended to multiple dimensions 相似文献
38.
We compute the temperature dependent magnetic susceptibility of the single-impurity, two-channel Anderson model with an alternative multi-step numerical renormalization-group transformation, previously applied only to the two-impurity single-channel Kondo model. Compared with the traditional transformation, the new procedure requires substantially less memory and computational time, and opens therefore perspectives for the application of the numerical renormalization-group procedure to more complex Hamiltonians. 相似文献
39.
Raquel Alves dos Santos Teresinha Rosa Cabral Isabel Rosa Cabral Lusania Maria Greggi Antunes Cristiane Pontes Andrade Plínio Cerqueira dos Santos Cardoso Marcelo de Oliveira Bahia Claudia Pessoa José Luis Martins do Nascimento Rommel Rodríguez Burbano Catarina Satie Takahashi 《Biocell》2008,32(2):195-200
Physalis angulata L (Solanaceae) is a medicinal plant from North of Brazil, whose different extracts and infusions are commonly used in the popular medicine for the treatment of malaria, asthma, hepatitis, dermatitis and rheumatism. However, the genotoxic effects of P. angulata on human cells is not well known. The main purpose of the present study was to evaluate the in vitro genotoxic effects of aqueous extract of P. angulata using the comet assay and the micronucleus assay in human lymphocytes provided from 6 healthy donors. Treatments with P. angulata extracts were performed in vitro in order to access the extent of DNA damage. The comet assay has shown that treatments with P. angulata at 0.5, 1.0, 2.0, 3.0 and 6.0 microg/mL in culture medium were genotoxic. Lymphocytes treated with P. angulata at the concentrations of 3.0 and 6.0 microg/mL in culture medium showed a statistically significant increase in the frequency of micronucleus (p<0.05), however, the cytokinesis blocked proliferation index (CBPI) was not decreased after P. angulata treatment. In conclusion, the present work demonstrated the genotoxic effects of P. angulata extract on human lymphocytes in vitro. 相似文献
40.