全文获取类型
收费全文 | 2887篇 |
免费 | 86篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 40篇 |
综合类 | 5篇 |
化学工业 | 400篇 |
金属工艺 | 57篇 |
机械仪表 | 53篇 |
建筑科学 | 117篇 |
矿业工程 | 10篇 |
能源动力 | 104篇 |
轻工业 | 338篇 |
水利工程 | 17篇 |
石油天然气 | 19篇 |
无线电 | 237篇 |
一般工业技术 | 362篇 |
冶金工业 | 791篇 |
原子能技术 | 24篇 |
自动化技术 | 411篇 |
出版年
2022年 | 29篇 |
2021年 | 35篇 |
2020年 | 27篇 |
2019年 | 20篇 |
2018年 | 43篇 |
2017年 | 35篇 |
2016年 | 44篇 |
2015年 | 44篇 |
2014年 | 79篇 |
2013年 | 128篇 |
2012年 | 93篇 |
2011年 | 113篇 |
2010年 | 93篇 |
2009年 | 83篇 |
2008年 | 102篇 |
2007年 | 113篇 |
2006年 | 100篇 |
2005年 | 63篇 |
2004年 | 69篇 |
2003年 | 80篇 |
2002年 | 60篇 |
2001年 | 62篇 |
2000年 | 60篇 |
1999年 | 62篇 |
1998年 | 266篇 |
1997年 | 164篇 |
1996年 | 108篇 |
1995年 | 67篇 |
1994年 | 82篇 |
1993年 | 83篇 |
1992年 | 38篇 |
1991年 | 37篇 |
1990年 | 32篇 |
1989年 | 36篇 |
1988年 | 30篇 |
1987年 | 31篇 |
1986年 | 18篇 |
1985年 | 25篇 |
1984年 | 20篇 |
1983年 | 23篇 |
1982年 | 14篇 |
1981年 | 17篇 |
1980年 | 22篇 |
1979年 | 13篇 |
1978年 | 15篇 |
1977年 | 29篇 |
1976年 | 47篇 |
1974年 | 14篇 |
1973年 | 18篇 |
1972年 | 13篇 |
排序方式: 共有2985条查询结果,搜索用时 15 毫秒
11.
Wood has long traditions as a building material, and is often used in construction elements, and as interior and exterior surfaces in the Nordic countries. In most applications, there are reaction to fire requirements to products used as surfaces, e.g. in escape routes and larger public spaces. Most wood products will therefore have to be treated with fire retardant (FR) agents to fulfil the strict requirements to properties connected to heat release and flame spread. Unfortunately, FR agents usually also increase the smoke production, as they cause a more incomplete combustion of the wood. The wood product manufacturers seek to find the optimal amount of FR additives where both heat release and smoke production in the classifying test are within the requirements given in the building regulations. This paper describes models for prediction of the European reaction to fire classes of wood products. The models are based on multivariate statistical analysis, and use test results from the cone calorimeter test as input. The presented models are, with very good precision, able to predict which Euroclass and additional smoke class a wood based product would obtain if it were to be tested in the single burning item test. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
12.
13.
Response to selection for milk yield in Holsteins was examined by a controlled selection experiment initiated in 1964. Foundation cows were paired by sire and divided randomly into two breeding groups, selection and control. Selection group was mated to four sires each year highest for Predicted Difference milk. Twenty bulls selected in 1964 as near breed average for milk sired all control cows. Milk yield was recorded for each lactation, and height of udder from ground, distances between teats, and perimeter and area bound by the four teats were measured at 30 to 75 days postpartum on 153 selection and 202 control cows over 14 yr. Most estimates of repeatability and heritability of udder dimensions before and after milking were .45 or larger. Correlations with milk yield were negative for udder height and positive for other udder measurements. Selection cows exceeded controls for lactational milk yield. Daughters of high milk bulls had greater distances between teats, greater perimeters, and larger areas of udder floor. Selection cows did not differ from controls in udder height for first parity but were below controls in udder height and had udders that collapsed more for all parities. 相似文献
14.
With the object of assessing the long-term prognosis and the frequencies of recurrence and remission in women chronic low abdominal pain without laparoscopically visible cause, questionnaire were sent in 1985 and 1991 to 55 women who had been submitted to laparoscopy in 1982-1984 for this reason. These women had been told that there was no demonstrable explanation of the pain experienced and were then discharged. 65% and 55% respectively had experienced and unfavourable course with considerable and continued symptoms. Only 22% stated in both investigations that they had experienced a favourable course and that they were, by and large, free from pain. 36% changed from an unfavourable to a favourable course or the reverse. The assessment made by the women was confirmed by a series of subordinate questions and this demonstrated a marked difference between the favourable and unfavourable courses of the condition. It is concluded that laparoscopy with exclusion of significant pathology is not, in itself, satisfactory as treatment of this patient group and that no improvement occurs in the course of time. The condition varies greatly with many recurrences and remissions and, for this reason, uncontrolled reports of the therapeutic effects are of no significance. When compared with the literature, it is suggested that this patient group should be referred early in the course of the condition to a therapist with specialist psychological/sexological insight and/or to a physiotherapist with interest in this patient group. 相似文献
15.
16.
A. Celaya Sanfiz T. W. Hansen F. Girgsdies O. Timpe E. Rödel T. Ressler A. Trunschke R. Schlögl 《Topics in Catalysis》2008,50(1-4):19-32
This work presents a detailed investigation of the preparation of MoVTeNbO x catalysts by hydrothermal synthesis. Phase-pure synthesis of M1 has been achieved applying the metals in a molar ratio Mo/V/Te/Nb = 1/0.25/0.23/0.12. Raman, UV/Vis spectroscopy, and SEM/EDX analysis show that the elements are inhomogeneously distributed in the initial suspension that is formed after mixing the metal salts in an aqueous medium. Iso- and heteropoly anions of molybdenum, free telluric acid as well as supra-molecular polyoxometalate clusters are observed in the solution, whereas all metals have been found in the precipitate. Complete rearrangement of molecular building blocks under hydrothermal conditions is essential for formation of phase-pure materials. Optimized synthesis conditions with respect to temperature and time result in the formation of a precursor consisting of nano-structured M1 characterized by an extended periodic organization in the [001] direction and a fairly homogeneous distribution of the elements. Residual ammonium containing supra-molecular species in the precursor result in the formation of phase mixtures during the subsequent crystallization by heat treatment in inert gas. Phase-pure M1 exhibits a distinct degree of flexibility with respect to the chemical composition that becomes obvious by incorporating Nb not exclusively into pentagonal bi-pyramidal units, but also into octahedral coordinated positions as shown by EXAFS. Anisotropic growth of the needle-like M1 crystals has been observed during the final heat treatment performed at 873–923 K in inert atmosphere disclosing a potential method to control the catalytic properties of MoVTeNbO x catalysts. 相似文献
17.
A semiautomated electron backscatter diffraction technique for extracting reliable twin statistics 总被引:2,自引:0,他引:2
B. L. Henrie T. A. Mason B. L. Hansen 《Metallurgical and Materials Transactions A》2004,35(12):3745-3751
A framework has been developed for extracting reliable twin statistics from a deformed microstructure using crystallographic
twin identification techniques with spatially correlated electron backscatter diffraction (EBSD) data. The key features of
this analysis are the use of the mathematical definition of twin relationships, the inclination of the common K
1 plane at a twin boundary, and the correct identification of the parent orientation in a parent/twin pair. Methods for identifying
the parent in a parent/twin pair will be briefly discussed and compared. Twin area fractions are then categorized by operative
twin systems, number of active twin variants in each system, and corrected twin widths. These statistics are reported here
for α-zirconium samples deformed in quasi-static four-point bend beams and in a 100 m/s Taylor cylinder impact test. Analysis of
the statistics also begins to reveal the roles that deformation rate and relative orientation of the boundary conditions to
the material’s symmetry axes play in determining the twinning activity that accommodates the imposed boundary conditions.
These improved twin statistics can help quantify the deformation processes in materials that deform by twinning as well as
serve to provide better validation of proposed models of the deformation processes. 相似文献
18.
Two cases of adverse reactions to intravesical treatment with bacillus Calmette-Guérin are reported. The first patient presented with a severe suppurating epididymo-orchitis three months after his last treatment. The second patient developed Reiter's disease with arthritis of one knee and conjunctivitis 1 week after the fourth instillation. 相似文献
19.
Current sanitation concepts of decentralised wastewater treatment and reuse raise the issue of monitoring and maintenance of such systems. To guarantee high quality of the recycled water, systems with high requirements concerning process technology are essential. With increasing numbers of decentralised treatment systems spread over far distances it will become more and more impossible and uneconomic to have expert personnel on site. Therefore, new visualisation and intelligent information systems are necessary. The paper describes the structure and 3D-demonstrations as a base for information visualisation. Up-to-date visualisation techniques, facilitating the cognition of context-adapted information, make it possible to maximise the amount of information presented to the user without overwhelming her or him. Concerning diagnosis and decision support systems in the domain of wastewater treatment, several interesting approaches are presented, estimating their applicability for decentralised wastewater treatment systems. The intelligent decision support system presented here consists of a combined ontology- and case-based reasoning system in addition to a process monitoring system. It is responsible for plausibility checks, error diagnosis, solution proposals, and optimisation suggestions. 相似文献
20.
Combined-Stage Sintering Model 总被引:8,自引:0,他引:8
James D. Hansen Richard P. Rusin Mao-Hua Teng D. Lynn Johnson 《Journal of the American Ceramic Society》1992,75(5):1129-1135
By focusing on the similarities between the three stages of sintering, a single equation is derived that quantifies sintering as a continuous process from beginning to end. The microstructure is characterized by two separate parameters representing geometry and scale. The dimensionless geometry parameter, denoted T, comprises five scaling factors that relate specific microstructural featuers (e.g., surface curvature) to the scale (grain diameter). Calculations of T from experimental data show (a) agreement with computer simulations of initial-stage sintering, (b) the effect of surface diffusion on T, and (c) changes in T with microstructural evolution during sintering. Application of the model to the design of firing schedules and the study of microstructural geometry effects on sintering is discussed. 相似文献