全文获取类型
收费全文 | 3186篇 |
免费 | 148篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 28篇 |
综合类 | 2篇 |
化学工业 | 649篇 |
金属工艺 | 71篇 |
机械仪表 | 86篇 |
建筑科学 | 144篇 |
矿业工程 | 12篇 |
能源动力 | 127篇 |
轻工业 | 277篇 |
水利工程 | 32篇 |
石油天然气 | 6篇 |
无线电 | 207篇 |
一般工业技术 | 655篇 |
冶金工业 | 630篇 |
原子能技术 | 25篇 |
自动化技术 | 395篇 |
出版年
2023年 | 51篇 |
2022年 | 71篇 |
2021年 | 104篇 |
2020年 | 107篇 |
2019年 | 103篇 |
2018年 | 101篇 |
2017年 | 92篇 |
2016年 | 92篇 |
2015年 | 69篇 |
2014年 | 100篇 |
2013年 | 181篇 |
2012年 | 145篇 |
2011年 | 208篇 |
2010年 | 143篇 |
2009年 | 143篇 |
2008年 | 185篇 |
2007年 | 150篇 |
2006年 | 107篇 |
2005年 | 101篇 |
2004年 | 75篇 |
2003年 | 70篇 |
2002年 | 44篇 |
2001年 | 48篇 |
2000年 | 47篇 |
1999年 | 54篇 |
1998年 | 52篇 |
1997年 | 43篇 |
1996年 | 51篇 |
1995年 | 43篇 |
1994年 | 28篇 |
1993年 | 19篇 |
1992年 | 26篇 |
1991年 | 15篇 |
1990年 | 26篇 |
1989年 | 25篇 |
1988年 | 17篇 |
1987年 | 21篇 |
1986年 | 23篇 |
1985年 | 27篇 |
1984年 | 15篇 |
1983年 | 18篇 |
1982年 | 21篇 |
1981年 | 23篇 |
1980年 | 28篇 |
1979年 | 18篇 |
1978年 | 24篇 |
1977年 | 19篇 |
1976年 | 20篇 |
1975年 | 16篇 |
1973年 | 18篇 |
排序方式: 共有3346条查询结果,搜索用时 437 毫秒
21.
W Samuel M Dryden M Sampson A Page H Shepherd 《Canadian Metallurgical Quarterly》1997,22(23):2763-2765
STUDY DESIGN: A case of paraspinal abscess formation from Haemophilus paraphrophilus is presented. OBJECTIVES: To describe a case of paraspinal abscess formation from H. paraphrophilus, a fastidious commensal organism of the mouth and pharynx. A precise bacteriologic identification can be difficult; techniques for such identification are discussed. SUMMARY OF BACKGROUND DATA: Spinal abscess caused by H. paraphrophilus is unusual and can be very difficult to diagnose. METHODS: The etiology, clinical presentation, technical examinations, and treatment are reviewed. RESULTS: Prolonged antibiotic treatment was curative, although surgery was considered. CONCLUSIONS: Bacteriologic diagnoses in these rare infections are difficult. Antibiotic therapy was curative in the patient described. 相似文献
22.
Effect of alloying elements on the solidification characteristics and microstructure of Al- Si- Cu- Mg- Fe 380 alloy 总被引:1,自引:0,他引:1
The effect of varying the major alloying elements within the limits of specification on the solidification behavior, fluidity,
and microstructure of a 380 alloy has been studied at two cooling rates. The thermal analysis technique has been used to study
the solidification behavior. The alloying elements investigated ranged from 3.22 to 4.09 pct copper, 1.01 to 1.70 pct iron,
0.06 to 0.50 pct magnesium, 1.69 to 3.00 pct zinc, and 0.16 to 0.46 pct manganese. The results show that the solidification
behavior of the 380 alloys is complicated, and the cooling curve at 0.4 ‡C/s indicates six reactions taking place during the
process of solidification. Cooling curves obtained for each of the alloying element additions, their analysis, and the resultant
microstructures are discussed. 相似文献
23.
The problem of tracking a periodic trajectory of the well-known cart-pendulum system is solved. After a change of coordinates and a change of feedback, the equations of this system are nonlinear but feedforward. This property is extensively used to carry out for this system the design of uniformly asymptotically stabilizing time-varying state feedbacks by using the forwarding approach. 相似文献
24.
Amplification of a 340 bp sequence of the 38 kDa protein gene of Mycobacterium tuberculosis by the polymerase chain reaction has been developed. The sensitivity of this PCR was shown to be 10 fg both by agarose gel electrophoresis and Southern blot hybridisation being equivalent to 2-3 organisms and highly specific to M. tuberculosis and excluding even M. tuberculosis H37Ra and Mycobacterium bovis BCG. Sputum samples from patients with pulmonary tuberculosis gave a positivity rate of 45%. PCR was also performed using pt8 and pt9 primers which amplified a 541 bp sequence of IS6110. 41% of the above samples gave positive amplification. Three samples that were positive for 38 kDa sequence were negative for IS6110. 相似文献
25.
The traditional conception of validity divides it into three separate and substitutable types: content, criterion, and construct validities. This view is fragmented and incomplete, especially because it fails to take into account both evidence of the value implications of score meaning as a basis for action and the social consequences of score use. The new unified concept of validity interrelates these issues as fundamental aspects of a more comprehensive theory of construct validity that addresses both score meaning and social values in test interpretation and test use. That is, unified validity integrates considerations of content, criteria, and consequences into a construct framework for the empirical testing of rational hypotheses about score meaning and theoretically relevant relationships, including those of an applied and a scientific nature. Six distinguishable aspects of construct validity are highlighted as a means of addressing central issues implicit in the notion of validity as a unified concept. These are content, substantive, structural, generalizability, external, and consequential aspects of construct validity. In effect, these six aspects function as general validity criteria or standards for all educational and psychological measurement, including performance assessments, which are discussed in some detail because of their increasing emphasis in educational and employment settings. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
26.
A sample of 1,411 older adults (age 55+) who had been interviewed both prior to and after bereavement was studied, allowing for pre-event controls. Those who had lost a parent, spouse, or child had the strongest depressive reactions, as predicted by an attachment-bonding hypothesis; however, material losses were also related to depression. Although bereavement/loss events were clearly related to subsequent depression even after pre-event depression, resources, and events were controlled, certain pre-event characteristics were predictive of the bereavement/loss events, including prior undesirable events, age, and urban/rural residency. A further analysis of 1,007 persons with two post-event interviews (at 6-month to 1-year follow-up) revealed an initial depressive reaction to a bereavement/loss event, which then dissipated completely within 1 year's time. Generally, bereavement appeared to have limited etiologic importance. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
27.
28.
The data obtained on inclusion types and concentrations has been analysed in the present part in terms of their effect on
filtration time and fluidity (measured by the length of solidified metal in quartz tubes). The dross, i.e., the oxide layer
that formed on the surface of the molten metal, was carefully collected and its mass determined; then it was examined in a
scanning electron microscope equipped with an energy-dispersive X-ray system. The results show that inclusions are not the
only parameter to be considered. More importantly, it is Al2O3 (films or particles), which seems to be the deciding factor.
It is found, however, that it is quite difficult to separate the individual role of each parameter using the porous disc filtration
apparatus (PoDFA) technique, i.e., sampling, without disturbing the molten metal. Sampling would introduce undesirable oxides
into the PoDFA crucible, resulting in an artificial increase in the filtration time. Increasing the holding periods of the
molten metal increases the quantity of dross. In all cases, the skimmed dross is wet, i.e., it contains an appreciable amount
of molten metal. The main types of oxides in the dross are MgO, MgAl2O4, Al4C3 and Al2O3.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
29.
The solidification behavior of two composites based on Al-Si alloy has been investigated as a function of cooling rate. Thermal
analysis techniques have been used to establish the relationship between solidification history and the microstructure developed.
The results of thermal analysis show that the characteristic parameters are influenced by the cooling rate. A marked difference
in these parameters is observed between the reinforced and the unreinforced materials at all cooling rates studied. The cooling
rates used in the present study range from 0.3 to 20 K/s. Increasing the cooling rate is shown to affect the undercooling
parameters both in the liquidus and eutectic solidification region. The eutectic growth temperature of the composites is observed
to be higher than that of the base alloy at all cooling rates. The depression in eutectic temperature ΔT is found to decrease
by 27 K for the unreinforced alloy (A356) and by 17 K for the composites (A356 + 10, 20 vol pct SiC) at a higher cooling rate
of ≃16 K/s. The presence of SiC reinforcement is observed to suppress the Mg2Si precipitate formation and decrease the amount of heat liberated during both primary and eutectic phase formation. Dendrite
arm spacing (DAS) is correlated to the cooling rate by a relationship of the form DAS =AT
-n, wheren is found to be of the order of 0.33. 相似文献
30.
Yaping Liu James D. Livingston Samuel M. Allen 《Metallurgical and Materials Transactions A》1992,23(12):3303-3308
The microstructure within particles of the Laves phase Fe2Zr in a two-phase Fe-10 at. pct Zr alloy after compression was investigated using X-ray diffraction and electron microscopy.
Stressinduced phase transformation between C36 and C15 structures was found to be a major deformation mode for the Laves phase.
Twinning and stacking faults were also found within C15 regions. Phase transformation models based on partial dislocations
are discussed. 相似文献