全文获取类型
收费全文 | 40604篇 |
免费 | 2374篇 |
国内免费 | 36篇 |
专业分类
电工技术 | 280篇 |
综合类 | 31篇 |
化学工业 | 7402篇 |
金属工艺 | 730篇 |
机械仪表 | 773篇 |
建筑科学 | 1260篇 |
矿业工程 | 75篇 |
能源动力 | 804篇 |
轻工业 | 5496篇 |
水利工程 | 373篇 |
石油天然气 | 170篇 |
武器工业 | 4篇 |
无线电 | 2286篇 |
一般工业技术 | 7183篇 |
冶金工业 | 10432篇 |
原子能技术 | 200篇 |
自动化技术 | 5515篇 |
出版年
2023年 | 351篇 |
2022年 | 336篇 |
2021年 | 887篇 |
2020年 | 741篇 |
2019年 | 678篇 |
2018年 | 1511篇 |
2017年 | 1511篇 |
2016年 | 1556篇 |
2015年 | 1111篇 |
2014年 | 1415篇 |
2013年 | 2743篇 |
2012年 | 2378篇 |
2011年 | 2202篇 |
2010年 | 1737篇 |
2009年 | 1540篇 |
2008年 | 1801篇 |
2007年 | 1568篇 |
2006年 | 1169篇 |
2005年 | 969篇 |
2004年 | 913篇 |
2003年 | 810篇 |
2002年 | 715篇 |
2001年 | 462篇 |
2000年 | 461篇 |
1999年 | 613篇 |
1998年 | 3351篇 |
1997年 | 2002篇 |
1996年 | 1297篇 |
1995年 | 754篇 |
1994年 | 650篇 |
1993年 | 634篇 |
1992年 | 212篇 |
1991年 | 223篇 |
1990年 | 220篇 |
1989年 | 212篇 |
1988年 | 192篇 |
1987年 | 166篇 |
1986年 | 181篇 |
1985年 | 212篇 |
1984年 | 184篇 |
1983年 | 130篇 |
1982年 | 170篇 |
1981年 | 174篇 |
1980年 | 158篇 |
1979年 | 130篇 |
1978年 | 119篇 |
1977年 | 204篇 |
1976年 | 417篇 |
1975年 | 91篇 |
1973年 | 96篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
P Klein R Béliard A Glacet S Moitel T Ducrot D Bourel 《Canadian Metallurgical Quarterly》1997,8(1):17-25
The aim of this study was to investigate how intrauterine growth retardation affects body proportions in VLBW infants. The cohort consisted of 135 surviving and 80 deceased preterm infants weighing less than 1250 grams at birth. Gestational age varied between 24 and 36 weeks (mean age 29.7 and 27.5 weeks, respectively). Birth weight was more than 2 SD below the mean birth standard values in 32% of the surviving, and in 27% of the deceased infants. Reduction of weight, length and head circumference at birth was analysed using Z scores based on Swedish birth standards. Z scores of weight, length and head circumference were highly correlated in the surviving and the deceased infants (r = 0.78 to 0.94 and 0.65 to 0.97, respectively). Length was significantly more affected by growth retardation than weight. Weight and head circumference were proportionately reduced. Intrauterine growth retardation influences body proportions in VLBW infants differently than in larger preterm and term infants. 相似文献
72.
JC Métraux 《Canadian Metallurgical Quarterly》1997,117(5):419-423
The purpose of this study was to assess cortical and cancellous bone responses to unilateral limb immobilization and, subsequently, to remobilization with exercise, in a young adult canine model. Right forelimbs of 14 1-2-year old mongrel dogs were immobilized in a non-weight-bearing position by a bandage for 16 weeks. Six control dogs were untreated. At 16 weeks, seven immobilized and three control dogs were euthanized. The remaining seven immobilized dogs began a recovery protocol consisting of 16 weeks of kennel confinement (without the right forelimb bandaged) followed by 16 weeks of treadmill exercise conducted three times per week. These seven dogs and three control dogs were euthanized at 48 weeks. Bone mineral density of the proximal radii was determined with dual-energy X-ray absorptiometry and humeral middiaphyseal cross-sectional areas were determined with computed tomography. Humeri were tested in cranio-caudal three-point bending to failure. Cancellous bone cores from the lateral humeral condyles had wet apparent density determined and were tested to failure in compression. Mechanical properties, bone density, and cross-sectional areas were compared between immobilized (right forelimb), contralateral weight bearing (left forelimb), and control forelimbs with Kruskal-Wallis and post hoc tests. At 16 weeks, bone mineral density, cortical load, yield, and stiffness as well as cancellous bone failure stress, yield stress, and modulus were significantly lower (p < 0.02) for immobilized limbs than control limbs. Immobilized limb cancellous bone mechanical properties were 28%-74% of control values, and cortical bone mechanical properties were 71%-98% of control values. After 32 weeks of remobilization, cortical and cancellous bone mechanical properties were not different from control values except that cortical bone failure stress and modulus were significantly higher (p < 0.01) between remobilized and control limbs. In summary, 16 weeks of forelimb immobilization was associated with significantly lower mechanical properties, and with greater differences in cancellous than cortical bone properties. Mechanical properties were not different from control values after 32 weeks of recovery that included 16 weeks of treadmill exercise. 相似文献
73.
74.
75.
The objective of this study was to determine the disturbances of urea in serum and urine of endurance trained volunteers during prolonged exposure to hypokinesia (decreased number of km/day). The studies during hypokinesia (HK) were performed for 364 days on twenty long-distance runners in the age of 23 to 26 years, with an average peak oxygen uptake, of 66 ml.kg.min-1. All volunteers were divided into two equal groups: Ten volunteers were placed on a continuous regime of exercise 14.8 km/day and served as control subjects (CS). The remaining volunteers were subjected to continuous HK without the use of any preventive measures and were considered as the hypokinetic subjects (HS). For the simulation of the hypokinetic effect, the HS were kept continuously under an average of 2.7 km/day for the duration of the study. Prior to exposure to HK, the HS were on the same exercise regime as the CS. During a 60 day pre-HK period and during the experimental period, urinary excretion of urea, creatinine, sodium, potassium and calcium and concentrations thereof in serum were measured. In the HS the concentrations of urea, creatinine, sodium, potassium and calcium in serum and the rate of excretion thereof in urine increased significantly when compared to the CS. It was concluded that prolonged restriction of muscular activity induces significant disturbances of urea in serum and urine of endurance trained volunteers. 相似文献
76.
77.
Frédéric Gaschet 《Papers in Regional Science》2002,81(1):63-81
This article examines the relationships between the employment suburbanisation from central cities towards their suburbs,
and the process of intra-urban specialisation that occurred simultaneously in the fifty largest French metropolitan areas.
A methodology is proposed to identify urban subcentres and to analyse the effects of the intra-urban specialisations on suburbanisation
patterns. We conclude that the specialisation of both subcentres and central cities has a significant effect on suburbanisation
rates. Lastly, an intra-metropolitan shift/share analysis provides additional insights into the employment dynamics of central
cities and suburbs during the last twenty years.
Received: 25 July 2000 / Accepted: 29 May 2001 相似文献
78.
79.
Numerical simulation of Zn coating solidification 总被引:2,自引:0,他引:2
A. Sémoroz Ph.D L. Strezov M. Rappaz 《Metallurgical and Materials Transactions A》2002,33(8):2685-2694
A numerical model, which simulates nucleation and growth of Zn grains, has been developed in order to describe quantitatively
the solidification of Zn coatings during the hot-dipping process. The inputs of the model are the nucleation distribution,
which has been measured by electron backscattered diffraction (EBSD), and the dendritic growth kinetics, calculated with an
analytical model of a parabolic dendrite tip modified to account for the interactions with the coating interfaces. The model
predicts the shapes of the grain envelopes as a function of the grain orientation and the texture induced by growth. Three
types of grain envelopes have been evidenced, depending on the angle between the c-axis and the normal to the coating plane.
Moreover, it has been shown that growth reinforces the already existing {00.1} nucleation texture, in good agreement with
experimental data. The model also predicts the cooling curve, including recalescence, and the grain size. Thus, it is used
to describe the effects of Pb additions on solidification. In particular, it has been shown that Pb increases the nucleation
undercooling and strongly decreases the density of active nuclei, thus resulting in a much larger grain size. 相似文献
80.
The extinction coefficient ? at 2.9 μm for OH in fluoride glasses is measured by determining the amount of HF evolved during heating of the glass under steam and the corresponding intensity of the OH absorption band. This coefficient is respectively equal to 31 litre mole?1 cm?1 for BTYbZ glass (15 BaF2 - 29 ThF4 - 28 YbF3 - 28 ZnF2) and 19.5 litre mole?1 cm?1 for BALLA glass (34 BaF2 - 57 ZrF4 - 4 AlF3 - 5 LaF3). 相似文献