全文获取类型
收费全文 | 15133篇 |
免费 | 1061篇 |
国内免费 | 14篇 |
专业分类
电工技术 | 135篇 |
综合类 | 11篇 |
化学工业 | 5576篇 |
金属工艺 | 196篇 |
机械仪表 | 339篇 |
建筑科学 | 502篇 |
矿业工程 | 20篇 |
能源动力 | 369篇 |
轻工业 | 3401篇 |
水利工程 | 123篇 |
石油天然气 | 79篇 |
无线电 | 754篇 |
一般工业技术 | 2074篇 |
冶金工业 | 984篇 |
原子能技术 | 66篇 |
自动化技术 | 1579篇 |
出版年
2024年 | 42篇 |
2023年 | 206篇 |
2022年 | 942篇 |
2021年 | 1084篇 |
2020年 | 466篇 |
2019年 | 493篇 |
2018年 | 559篇 |
2017年 | 581篇 |
2016年 | 632篇 |
2015年 | 513篇 |
2014年 | 686篇 |
2013年 | 1014篇 |
2012年 | 934篇 |
2011年 | 1081篇 |
2010年 | 804篇 |
2009年 | 778篇 |
2008年 | 687篇 |
2007年 | 689篇 |
2006年 | 527篇 |
2005年 | 396篇 |
2004年 | 336篇 |
2003年 | 289篇 |
2002年 | 280篇 |
2001年 | 180篇 |
2000年 | 129篇 |
1999年 | 176篇 |
1998年 | 254篇 |
1997年 | 202篇 |
1996年 | 165篇 |
1995年 | 115篇 |
1994年 | 97篇 |
1993年 | 102篇 |
1992年 | 95篇 |
1991年 | 68篇 |
1990年 | 54篇 |
1989年 | 49篇 |
1988年 | 54篇 |
1987年 | 53篇 |
1986年 | 53篇 |
1985年 | 44篇 |
1984年 | 36篇 |
1983年 | 34篇 |
1982年 | 23篇 |
1981年 | 28篇 |
1980年 | 30篇 |
1979年 | 25篇 |
1978年 | 26篇 |
1977年 | 20篇 |
1976年 | 20篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
C sar Ovalles Carlos Vallejos Tito Vasquez Iraima Rojas Ursula Ehrman Jose Luis Benitez Ronald Martinez 《Petroleum Science and Technology》2003,21(1):255-274
An extra-heavy crude oil underground upgrading process is described which involves the downhole addition of a hydrogen donor additive under steam injection conditions (280-315°C and residence times of at least 24-h). Laboratory experiments showed a 4° increase in the API gravity (from 9 to 12°) of the upgraded product, a two-fold reduction in the viscosity and, an approximately 8% decrease in the asphaltene content with respect to the original crude. Further increases on the temperature led to products with improved properties reaching 15°API at 315°C. It was found that the presence of the natural formation (catalysts) and methane (natural gas) is necessary to enhance the properties of the upgraded crude oil. From GC and GC-MS results a reaction pathway is proposed that involves hydrogen transfers from tetralin to the extra-heavy crude oil resulting in the formation of 1,2-dihydronaphthalene. This compound is then transformed into naphthalene, further upgrading of crude oil through hydrogen donation. The results of the experiments carried out in the presence and absence of the mineral formation and with an inert solid (SiC) strongly indicate that the former acts as a catalyst and not as a heat transfer matrix. Isotopic labeling studies (CD4 and 13CH4) give evidences that, most probably, methane is involved in the upgrading reactions. 相似文献
42.
43.
An optical nondestructive strain measurement technique was performed to analyze the mechanical deformation induced by an electrical field within the insulating materials. Poly(ethylene naphthalene 2,6‐dicarboxylate) (PEN) films were then subjected to constant electrical fields right up to their electrical breakdown. The experimental technique made it possible to follow the various stages of the mechanical behavior of PEN in real time. The final breakdown occurred in the observation zone and the related mechanical deformation was captured. A “margarita” structure was observed with a hole at the center. The experimental results indicated that the level of the induced‐mechanical deformations depended on the local environment. We defined two different zones representing the inside and the outside of the damaged area. The induced‐deformations were larger in the damaged zone. It was also observed that deformations increased when the sample had a lower degree of crystallinity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
44.
On-Chip Optical Technology in Future Bus-Based Multicore Designs 总被引:1,自引:0,他引:1
Kirman N. Kirman M. Dokania R.K. Martinez J.F. Apsel A.B. Watkins M.A. Albonesi D.H. 《Micro, IEEE》2007,27(1):56-66
This work investigates the integration of CMOS-compatible optical technology to on-chip coherent buses for future CMPs. The analysis results in a hierarchical optoelectrical bus that exploits the advantages of optical technology while abiding by projected limitations. This bus achieves significant performance improvement for high-bandwidth applications relative to a state-of-the-art fully electrical bus 相似文献
45.
Kerstin Skog Åsa Eneroth & Maria Svanberg 《International Journal of Food Science & Technology》2003,38(3):313-323
Hamburgers and chicken fillets were cooked in convection ovens, deep‐fried or contact fried and analysed for mutagenic activity using the Ames test. For the three different convection ovens, the cooking parameters studied included the presence of steam, air velocity, air temperature and holding time. For deep‐frying and contact frying, the cooking parameters included cooking temperature and cooking time. In cooked hamburgers, mutagenic activity was only detected in those that had been deep‐fried. In chicken fillets, mutagenic activity was detected in samples prepared with all cooking methods, being highest in the deep‐fried samples. Factorial analysis indicated that heat transfer was the most important factor affecting mutagenic activity. High temperature and high air velocity in the convection ovens enhanced mutagenic activity. The presence of steam reduced the mutagenic activity, except when high temperature was used in combination with high air velocity. In chicken fillets, high mutagenic activity correlated to high weight loss during cooking. Pan‐fried chicken fillets were analysed using high performance liquid chromatography (HPLC) and the mutagenic/carcinogenic heterocyclic amines 2‐amino‐3,8‐dimethylimidazo[4,5‐f ]‐quinoxaline (MeIQx), 2‐amino‐1‐methyl‐6‐phenylimidazo‐[4,5‐b]‐pyridine (PhIP) and the co‐mutagenic heterocyclic amine Norharman (9H‐pyrido[3,4‐b]‐indole) were identified. The HPLC fractions were tested for mutagenic activity and, apart from the mutagenic fractions corresponding to MeIQx and PhIP, several mutagenic fractions were detected that did not correspond to known heterocyclic amines. 相似文献
46.
Maria E. Nadal Edward A. Early Will Weber Robert Bousquet 《Color research and application》2008,33(2):94-99
The NIST 0:45 reflectometer measures the spectral reflectance factor at an influx angle of 0° and an efflux angle of 45° of colored, nonfluorescent specimens at room temperature, with widths ranging from 3 to 10 cm and heights from 3 to 20 cm and with an uncertainty of less than 0.5 in color difference units. Published in 2008 by John Wiley & Sons, Inc. Col Res Appl, 33, 94–99, 2008 相似文献
47.
Sets of color tiles are available from the National Institute of Standards and Technology calibrated using the NIST 0:45 Reflectometer. The uncertainties associated with the measured values for the color tiles are an indispensable component of the calibration report that accompanies these tiles. A systematic, analytical approach developed previously was applied to the particular case of the reference instrument and color tile set, taking into account the operation and characteristics of the instrument and the spectral properties of the set. The primary sources of uncertainty were identified, and the resulting uncertainties in the color space values L*, a*, and b* were determined. In general, the uncertainties are lowest for those color tiles whose reflectance factors are nearly constant with wavelength. Published in 2008 by John Wiley & Sons, Inc. Col Res Appl, 33, 100–107, 2008 相似文献
48.
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
49.
People have knowledge about relationships (i.e., relational schemas) that is based on their experiences. Because most people have experience with complementary behavior (interaction partners behaving similarly in terms of affiliation but oppositely in terms of control), they expect complementary behavior in their relationships. Like other beliefs about relationships, expectations of complementarity affect self-construal. The authors provide evidence for complementary self-construal; people assimilate to relevant relationship partners on the affiliation dimension and contrast on the control dimension. Consistent with the proposed role of relationship knowledge in these effects, complementary self-construal was moderated by the familiarity of the target, whether people focused on their relationship with or the appearance of the target, and whether the context was relevant for the interpersonal dimension. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
50.