全文获取类型
收费全文 | 470篇 |
免费 | 11篇 |
国内免费 | 13篇 |
专业分类
电工技术 | 3篇 |
综合类 | 3篇 |
化学工业 | 16篇 |
金属工艺 | 18篇 |
机械仪表 | 6篇 |
建筑科学 | 19篇 |
矿业工程 | 2篇 |
能源动力 | 1篇 |
轻工业 | 69篇 |
水利工程 | 1篇 |
石油天然气 | 1篇 |
无线电 | 14篇 |
一般工业技术 | 14篇 |
冶金工业 | 297篇 |
自动化技术 | 30篇 |
出版年
2022年 | 4篇 |
2021年 | 5篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2013年 | 41篇 |
2012年 | 2篇 |
2011年 | 5篇 |
2010年 | 5篇 |
2009年 | 4篇 |
2008年 | 8篇 |
2007年 | 10篇 |
2006年 | 10篇 |
2005年 | 9篇 |
2004年 | 5篇 |
2003年 | 2篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 8篇 |
1998年 | 70篇 |
1997年 | 64篇 |
1996年 | 34篇 |
1995年 | 18篇 |
1994年 | 12篇 |
1993年 | 19篇 |
1992年 | 11篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1977年 | 9篇 |
1976年 | 35篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1964年 | 2篇 |
1963年 | 1篇 |
1959年 | 2篇 |
1957年 | 2篇 |
1956年 | 3篇 |
排序方式: 共有494条查询结果,搜索用时 15 毫秒
71.
在市區進行夜間隧道鑽挖工程所產生的土傳噪音及震動,容易引起投訴。現時的技術難以準確預測噪音及震動的級數,而隧道工程的進度也常因進行隧道鑽挖工程時產生過大的土傳噪音及震動而延誤。本文所提述的新技術,可以更準確地量度及預測鑽機震動強度及土壤傳震的特性@個技術包括測量單位衝擊力及隧道鑽機摩擦力所產生的震動級數鋵嵲珈?80於代,美國政府運輸部門(U.S.DeptofTransportationFederalTransitAdministrative)已研發相關的技術,並將該技術應用於鐵路土傳噪音量度及預測上。本文報告隧道鑽機所產生的土傳噪音及震動級數1/3倍頻帶數值的量度及預測。比較地面震動峰值速度(PPV)、最高(Lmax)噪聲和振動級數按快速和緩慢的時間常數和整體百分比(Percentile)數值列出。 相似文献
72.
Hormone replacement therapy and the risk of stroke. Follow-up of a population-based cohort in Sweden
M Falkeborn I Persson A Terént HO Adami H Lithell R Bergstr?m 《Canadian Metallurgical Quarterly》1993,153(10):1201-1209
BACKGROUND: The protective effect of postmenopausal estrogen replacement therapy on coronary heart disease has been shown in several studies. However, the effect on stroke is more controversial, and data on estrogen-progestin combinations are sparse. METHODS: A total of 23,088 women living in the Uppsala (Sweden) Health Care Region were identified from pharmacy records as having been prescribed noncontraceptive estrogens during 1977 through 1980. They were followed up from 1977 to 1983 for admissions to the hospital because of a first stroke (International Classification of Diseases, Eighth Revision, codes 430 through 438 and 344). The mean observation time was 5.8 years. The expected number was based on person-years in the cohort and incidence rates in the population of the region. RESULTS: Overall, 361 cases of first stroke were observed in the cohort, as compared with 403.2 expected (relative risk [RR], 0.90; 95% confidence limits, 0.81, 0.99). The RR for acute stroke (International Classification of Diseases, Eighth Revision, codes 431 through 436) was 0.85 (0.75, 0.97). In women younger than 60 years at entry who were prescribed estradiol compounds (1 to 2 mg) or conjugated equine estrogens (0.625 to 1.25 mg), the risk of any stroke was reduced by almost 30% (RR, 0.72; 0.58, 0.88) and the risk of acute stroke was reduced by 40% (RR, 0.61; 0.46, 0.79). Women prescribed a combined estradiol-levonorgestrel brand also had a lowered risk of stroke (RR, 0.61; 0.40, 0.88). Weak compounds (mainly estriol) showed no stroke-protective effect, nor was there any relationship between hormone replacement and risk of subarachnoid hemorrhage. CONCLUSION: Hormone replacement therapy with potent estrogens alone or cyclically combined with progestins can, particularly when started shortly after menopause, reduce the risk of stroke. 相似文献
73.
In the Copenhagen Male Study we found an increased risk of ischaemic heart disease (IHD) in men with the Lewis phenotype Le(a-b-). This study investigated whether, within the group of Le(a-b-) men, any conventional risk factors modified their increased risk. Three thousand, three hundred and eighty-three men aged 53 to 75 years were examined in 1985/86 and their morbidity and mortality over the next four years recorded. Three hundred and forty-three men with cardiovascular diseases were excluded at baseline. Potential risk factors examined were: alcohol consumption, physical activity, tobacco smoking, serum cotinine, serum lipids, body mass index, blood pressure, hypertension, non-insulin dependent diabetes mellitus and social class. In eligible men with Le(a-b-), N = 280 (9.6%), alcohol was the only risk factor associated with risk of IHD. There was a significant inverse dose-effect relationship between alcohol consumption and risk. The age-adjusted p-values of trend tests were for risk of non-fatal + fatal IHD: p = 0.03; for risk of fatal IHD: p = 0.02. In eligible men with other phenotypes, N = 2,649 (90.4%) only a limited and non-significant negative association with alcohol. In Le(a-b-) men, a group genetically at increased risk of IHD, the risk was strongly and significantly negatively correlated with alcohol consumption. 相似文献
74.
75.
Sea urchins of the genus Arbacia (order Stirodonta) have discontinuous allopatric distributions ranging over thousands of kilometers. Mitochondrial DNA (mtDNA) sequences were used to reconstruct phylogenetic relationships of four Arbacia species and their geographic populations. There is little evidence of genetic structuring of populations within species, except in two cases at range extremes. The mtDNA sequence differentiation between species suggests that divergence occurred about 4-9 MYA. Gene sequences encoding the sperm protein bindin and its intron were obtained and compared with the mtDNA phylogeny. Sea urchins among the well-studied echinoid order Camarodonta, with degrees of mtDNA divergence similar to those of Arbacia species, are known to have remarkable variation in bindin. However, in Arbacia, little variation in deduced amino acid sequences of bindin was found, indicating that purifying selection acts on the protein. In contrast, bindin intron sequences showed much differentiation, including numerous insertion/deletions. Fertilization experiments performed between a divergent pair of Arbacia species from the Atlantic and Pacific Oceans revealed no evidence of blocks to gamete recognition. In Arbacia, fertilization specificities may have evolved relatively slowly as a result of extensive gene flow within species, greater functional constraint on the bindin polypeptide, or reduced selective pressure for species recognition in singly occurring species. 相似文献
76.
77.
HO Curth 《Canadian Metallurgical Quarterly》1976,15(8):592-593
78.
79.
Tamponade treatment in epistaxis is painful and the patient needs hospitalisation. Irrigation with hot water was introduced as a treatment of epistaxis 100 years ago. This study compares the two treatments with respect to effect, recurrence, pain, and length of hospital stay. Forty-four consecutive patients with posterior epistaxis were randomized to receive treatment with either hot water (HWI) or tamponade. In the group of patients treated with HWI, the treatment had to be stopped in seven patients (33%) because of lack of cooperation; nine patients (43%) could be discharged from hospital with no need for further treatment, whereas five patients (24%) had recurrent epistaxis requiring additional tamponade treatment. Among patients treated with tamponade, 14 patients (61%) could be discharged from hospital with no need for further treatment, while nine patients (39%) had recurrent epistaxis requiring additional tamponade treatment. Compared with the tamponade treatment, HWI is almost as effective, the hospital stay is shorter, and the treatment is significantly less painful. 相似文献
80.
Regenerative and degenerative changes of cartilage were studied in animals by micromorphological methods and autoradiography. Cartilage lesions of defined size were set in the femoral condyle of rabbits of variing age by means of an electrical drill developed by us. We used juvenile animals, 3 months old, and senile animals 4 years old. The lesions were studied by lightmicroscopy, electronmicroscopy and scanning electron microscopy. In young animals we were able to demonstrate prevailing reparative changes after injury and the potency for genuine regeneration originating from cartilage. Isolated chondral lesions develop reactive tissue originating mainly from superficial parts of the cartilage. When subchondral bone is exposed we see granulation tissue filling up the defect and change by metaplasia. The replacing tissue originating from superficial cartilage as well as from subchondral bone is able to fill the defect within 3 months. In the replacing tissue originating from cartilage we find fibroblasts and fibrocytes with many mitoses. Consecutively the cells are rounding increasingly. Finally chondrocytes are developing. At the same time as these reparative changes occur we see degenerative changes with decreased mucopolysaccharide synthesis, cell necroses with consecutive decrease in number of cells and singular small cluster. In old animals we could not demonstrate any reparative or regenerative changes after injuries; the artificial defect in cartilage persists. Instead, degenerative changes with signs of arthrosis are developing rapidly: chondroitin sulfate synthesis is decreased, there is ample cluster formation, cell necrosis, decrease in number of cells, and incorporation of paraplasmatic substances in cartilage. We could not demonstrate any mitoses. The causes for the inability of cartilage of aged individuals for reparative changes are discussed. 相似文献