全文获取类型
收费全文 | 49952篇 |
免费 | 2443篇 |
国内免费 | 49篇 |
专业分类
电工技术 | 324篇 |
综合类 | 41篇 |
化学工业 | 10148篇 |
金属工艺 | 859篇 |
机械仪表 | 914篇 |
建筑科学 | 1595篇 |
矿业工程 | 108篇 |
能源动力 | 1169篇 |
轻工业 | 7522篇 |
水利工程 | 450篇 |
石油天然气 | 236篇 |
武器工业 | 4篇 |
无线电 | 2744篇 |
一般工业技术 | 8235篇 |
冶金工业 | 11141篇 |
原子能技术 | 234篇 |
自动化技术 | 6720篇 |
出版年
2023年 | 448篇 |
2022年 | 784篇 |
2021年 | 1353篇 |
2020年 | 996篇 |
2019年 | 990篇 |
2018年 | 1782篇 |
2017年 | 1755篇 |
2016年 | 1860篇 |
2015年 | 1337篇 |
2014年 | 1804篇 |
2013年 | 3404篇 |
2012年 | 2909篇 |
2011年 | 2855篇 |
2010年 | 2246篇 |
2009年 | 2101篇 |
2008年 | 2284篇 |
2007年 | 2005篇 |
2006年 | 1508篇 |
2005年 | 1260篇 |
2004年 | 1149篇 |
2003年 | 1036篇 |
2002年 | 897篇 |
2001年 | 584篇 |
2000年 | 582篇 |
1999年 | 741篇 |
1998年 | 3575篇 |
1997年 | 2165篇 |
1996年 | 1427篇 |
1995年 | 845篇 |
1994年 | 719篇 |
1993年 | 694篇 |
1992年 | 251篇 |
1991年 | 243篇 |
1990年 | 235篇 |
1989年 | 244篇 |
1988年 | 216篇 |
1987年 | 202篇 |
1986年 | 202篇 |
1985年 | 234篇 |
1984年 | 200篇 |
1983年 | 143篇 |
1982年 | 169篇 |
1981年 | 187篇 |
1980年 | 164篇 |
1979年 | 134篇 |
1978年 | 124篇 |
1977年 | 206篇 |
1976年 | 430篇 |
1975年 | 92篇 |
1973年 | 86篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
131.
The validity for a domain-specific model of self-perceived peer and school competence was examined in a sample of young Black adolescents of lower socioeconomic status. Three methods were used to gauge peer and school competence: self-ratings, via the Perceived Social Competence Scale for Children; peer-ratings, based on nominations; and objective criteria, such as grade point average, achievement test scores, and number of reciprocated friendship choices. More generally defined measures of social competence (i.e., perceived general competence and the Social Competence Nomination Form) were included in some analyses for purposes of comparison. Correlations within and between competence domains were examined via both a multitrait-multimethod matrix and factor analysis. Findings supported the distinctness of perceived peer and school competence domains, providing support for a domain-specific model of self-concept. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
132.
The possibility of long-term safe disposal of radioactive wastes based on their radiation and radiation-migration balance with the initial fuel component and taking account of the thermal, radiation, and elastic loads due to waste dispoasl on the natural medium is examined. The specific radiation and radiation-migration equivalence is established on the basis of the radiotoxicity of uranium and the components of the decay of uranium and individual radionuclides as well as the sum of the latter. 相似文献
133.
Electron Spin Resonance, Differential Scanning Calorimetry and rheological techniques have been used to study the physical
changes induced by temperature in lard and in the solid and liquid fractions obtained by fractionation of lard at 15 C. The
mobilization process of a C18 fatty acid nitroxide derivative dispersed in the molten fat has been observed in the temperature
range −50 to +70 C.
The mobilization of the probe seemed to be concomitant with the melting of the low melting point glycerides. Above this temperature,
all the probes were in the liquid phase and their mobility reflected the viscosity of their liquid environment, or the viscosity
of the bulk fat when crystal was no longer present.
Probe mobility was temperature dependent, and it was identical for the three fats at the same temperature, despite their different
triglyceride compositions. 相似文献
134.
Phillips Dorothy A.; Hearty Paul J.; Latrémouille Susane; Treurniet William C.; Whalen Thomas E. 《Canadian Metallurgical Quarterly》1985,26(3):219
Discusses telematics, a new field of behavioral research in Canada that has grown with the technical developments in which computers and telecommunications have been combined. Three domains of behavioral research reflect relationships between humans and the technology and use the evidence and methods of different areas of psychology: (1) interface studies address perception and performance questions, (2) dialog studies focus on cognitive processes, and (3) impact studies investigate social relations and how institutions and individuals are affected by telematics. Studies conducted during the past 5 yrs by the Behavioural Research and Evaluation division of the Department of Communications, Government of Canada, are described in each of these 3 domains. Behavioral research in telematics is expected to be an increasingly important activity in which psychologists may play an active part as the technology disseminates. (French abstract) (47 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
135.
Adjuvant-induced arthritis is an animal model of chronic inflammatory disease widely used in anti-inflammatory and immunosuppressive drugs testing. When the development and the inhibition of the induced arthritis are measured by the injected paw oedema, it is difficult to delineate the immunological contribution from the persistent non-specific primary section. To study the influence of volume and composition of the injected adjuvant upon the primary non-specific inflammation, we devised a 3X4 factorial experiment on a strain of inbred rats with a low susceptibility to adjuvant-induced arthritis. The injection of mineral oil alone produces a persistent oedema. The injection of mycobacteriae in suspension in saline induces a rapid inflammatory response followed by a fast decrease of the oedema. When complete adjuvant is used, there is always a very strong interaction between the effects of the two components of the adjuvant, i.e. the measured oedemas are much greater than the calculated values, For a given injected volume, the inflammation is maximum when the concentration of mycobacteriae is 2.5 mg/ml. All the rats injected with complete adjuvant present a transient oedema of the non-injected hind paw. This oedema is very small and proportional to the amount of mycobacteria injected. 相似文献
136.
V. Recarte R. B. Pérez-Sáez J. San Juan E. H. Bocanegra M. L. Nó 《Metallurgical and Materials Transactions A》2002,33(8):2581-2591
The martensitic transformation temperatures and the types of martensitic phases have been determined in a wide concentration
range of technological interest for Cu-Al-Ni shape-memory alloys (SMAs) A stability diagram of martensitic phases as a function
of alloy concentration has been determined. It is found that when the aluminum content increases, the transformation changes
from β
3 ⇒ β′3 to β
3 ⇒ γ′3, with an intermediate concentration range where both martensites coexist due to a β
3 ⇒ γ′3+β′3 transformation. On the other hand, an increase of nickel content stabilizes the martensite β′3, changing from a mixed β
3 ⇒ γ′3 + β′3 to a single β
3 ⇒ β′3 transformation. Furthermore, linear relationships between M
s
and Al and Ni concentrations have been obtained for all types of martensitic phases. 相似文献
137.
Mathematical models for liquid-liquid extraction processes are not widely available. The correlation of liquid-liquid equilibrium for such a model is often difficult. One correlation, based upon the Redlich-Kister expansion for the molar excess Gibb's free energy, has been shown to accurately represent ternary liquid-liquid equilibrium systems used in liquid-liquid extraction operations.
The use of this correlation in an extraction model was investigated and found to be suitable for a ternary liquid-liquid extraction model with only minor limitations. A successful ternary liquid-liquid extraction model was developed using this equilibrium correlation. 相似文献
The use of this correlation in an extraction model was investigated and found to be suitable for a ternary liquid-liquid extraction model with only minor limitations. A successful ternary liquid-liquid extraction model was developed using this equilibrium correlation. 相似文献
138.
New ternary stannides are reported: RE1+xRh2Sn4?x, 0 ? x ? 0,5 (RE = La ? Sm). NdRh2Sn4 has been characterized by single - crystal X-ray diffraction analysis. Its structure is of a new type with space group Pnma and Z = 4: a = 18,535(3), b = 4,463(1), , Dx = 9,16 g.cm?1, μ(AgKα) = 13,6 mm?1, F(000) = 1300, R = 0,040 for 496 independent reflexions (Rw = 0,047). One of the tin sites can be partly occupied by rare earths atoms. The structure types of NdRh2Sn4 and Y2Rh3Sn5 are closely related. LaRh2Sn4 does not exhibit superconductivity above 1.4 K. 相似文献
139.
140.