全文获取类型
收费全文 | 12376篇 |
免费 | 368篇 |
国内免费 | 106篇 |
专业分类
电工技术 | 231篇 |
综合类 | 193篇 |
化学工业 | 1884篇 |
金属工艺 | 350篇 |
机械仪表 | 354篇 |
建筑科学 | 347篇 |
矿业工程 | 104篇 |
能源动力 | 325篇 |
轻工业 | 598篇 |
水利工程 | 107篇 |
石油天然气 | 156篇 |
武器工业 | 16篇 |
无线电 | 1099篇 |
一般工业技术 | 2163篇 |
冶金工业 | 3892篇 |
原子能技术 | 107篇 |
自动化技术 | 924篇 |
出版年
2023年 | 91篇 |
2022年 | 170篇 |
2021年 | 221篇 |
2020年 | 190篇 |
2019年 | 147篇 |
2018年 | 249篇 |
2017年 | 200篇 |
2016年 | 215篇 |
2015年 | 202篇 |
2014年 | 264篇 |
2013年 | 572篇 |
2012年 | 377篇 |
2011年 | 447篇 |
2010年 | 384篇 |
2009年 | 365篇 |
2008年 | 361篇 |
2007年 | 328篇 |
2006年 | 306篇 |
2005年 | 260篇 |
2004年 | 234篇 |
2003年 | 218篇 |
2002年 | 200篇 |
2001年 | 171篇 |
2000年 | 220篇 |
1999年 | 307篇 |
1998年 | 1208篇 |
1997年 | 748篇 |
1996年 | 564篇 |
1995年 | 377篇 |
1994年 | 320篇 |
1993年 | 316篇 |
1992年 | 165篇 |
1991年 | 194篇 |
1990年 | 133篇 |
1989年 | 140篇 |
1988年 | 146篇 |
1987年 | 154篇 |
1986年 | 126篇 |
1985年 | 148篇 |
1984年 | 122篇 |
1983年 | 137篇 |
1982年 | 106篇 |
1981年 | 112篇 |
1980年 | 103篇 |
1979年 | 90篇 |
1978年 | 76篇 |
1977年 | 122篇 |
1976年 | 205篇 |
1975年 | 62篇 |
1974年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
A trade-off analysis on the cost and system packaging metrics of an electronic product aimed at the commercial/retail industry has been carried out. By comparing the system cost and packaging metrics with those of comparable consumer products, we have determined that there is opportunity for significant cost, size, and weight reduction of the overall electronics packaging system. These include the use of fine pitch IC packages, smaller discrete components, denser PCB wiring technology, double sided IC package surface mount, surface mount connectors, and improved plastics for the product housing. The analysis concluded that PCB area reduction of 40%, using a single PCB instead of three boards, reduction in board cost of over 50% and product weight reduction of over 28% are possible using available technologies. 相似文献
102.
A semi-quantitative right coronary artery score (RCA score) was derived from the ratio of the number of the major left ventricular branches of the right coronary artery to the total of the right coronary and left circumflex arteries, to stratify the extent of perfusion in patients with right coronary artery dominance. Thirty-seven patients with one-vessel coronary disease involving a dominant right coronary artery proximal to the left ventricular branches were selected for study. Thallium scintigraphy was performed after right intracoronary injection in 11 patients, and 26 patients underwent conventional stress thallium scintigraphy (24 exercise thallium and two dipyridamole thallium scintigraphy). Thallium scores of perfusion region size after right intracoronary thallium injection and perfusion defect size in stress thallium studies were quantitated from planar thallium images. Both the RCA score and the regional thallium scores spanned over a wide range. The RCA score (range 0.23-0.85) correlated best with the posterior (70 degrees left anterior oblique view) plus lateral segment (40 degrees left anterior oblique view) thallium score (r = 0.88 and 0.53 for intracoronary and stress thallium studies respectively). It also correlated with the summed thallium scores in the posterior, lateral, apical and inferior segments (r = 0.73 and 0.54 respectively) but not with thallium scores in the apex or inferior segment alone. The proposed RCA score quantitates the variable posterolateral perfusion territory of the right coronary artery, and could stratify the area of myocardium at risk from coronary stenosis in the majority of patients with right coronary dominance. 相似文献
103.
We report an unusual case of a 1 cm papillary renal cell carcinoma arising from the outer surface of the free wall of a radiographically simple renal cyst. Most malignancies arising from the wall of a renal cyst are present along the inner surface, usually adjacent to underlying renal parenchyma. While this is a rare occurrence, it does reinforce the need to explore even small solid renal masses. 相似文献
104.
B Rau C Below W Haensch W Liebrich C von Schilling PM Schlag 《Canadian Metallurgical Quarterly》1995,380(6):359-364
We performed BAEP study to evaluate acoustic nerve involvement in 102 patients affected by peripheral neuropathies of different etiology, predominantly hereditary and inflammatory acquired neuropathies. Prolonged latency of early waves, indicative of slowing in VIII nerve conduction, was found in a high percentage of cases. Abnormalities were far more frequent (44% vs 14%) and severe in patients with demyelinating rather than axonal neuropathy. Among demyelinating neuropathy, the most severe latency delay was found in Hereditary Motor and Sensory Neuropathy type III. The pattern of acoustic nerve involvement differed slightly between Hereditary Motor and Sensory Neuropathy type I and acquired inflammatory demyelinating polyradiculoneuropathy, perhaps reflecting different pathogenetic mechanisms and different sites of VIII nerve demyelination. 相似文献
105.
The serum amyloid A (SAA) superfamily comprises a number of genes and proteins characterized from a range of mammalian species. The majority of members described to date are dramatically induced during the acute-phase response, suggesting an important short-term beneficial role in the response to tissue injury and inflammation. However, important disease associations have also been proposed for certain SAAs during chronic inflammation. The nomenclature of many of the superfamily members has been the result of comparisons with previously reported sequences implying disease association and/or functional relatedness between such members. The evolutionary relationships of the SAA superfamily members have been investigated by comparisons at both the amino acid and the nucleotide level. The results indicate that all members of the superfamily within a species have been undergoing concerted evolution. This has important implications in ascribing functions and disease associations to individual SAA superfamily members and indicates that designations should not be based on the extent of amino acid identity alone but should be made only following direct experimental observation of the proteins themselves. 相似文献
106.
研究了气氛加压烧成ZrO2(Y-TZP)-Si3N4复合材料中抑制ZrN生成工艺问题,相组成分析表明:无论添加20wt%工业ZrO2或者Y-TZP(3mol%Y。O。)的氯化硅复合材料,在低于1850℃,3MPak气压力下烧成,表面无ZrN生成.通过加入有效的烧结助剂(Y。Oa+AI。Os)、增加埋粉中SIO分压以及增加保护气氛氮气压力,适当的烧成条件等工艺措施可有效地抑制ZrN的生成.实验还证实了ZrN很容易氧化,含有ZrN的ZrO。(Y-TZP)-SisN。复合材料试样经900℃,0.sh热处理已粉碎性裂开. 相似文献
107.
In the present study, the effect of bradykinin on basal and precontracted mouse-isolated trachea was investigated. In basal conditions mouse-isolated tracheal rings do not respond to bradykinin. However, when the tracheal rings were precontracted with carbachol (10(-7) M) a relaxation with bradykinin (3 x 10(-9)-3 x 10(-7)) was found. The maximal response amounted 69.7+/-4.1% (n=15) with a pD2 value of 7.2+/-0.21. The selective bradykinin B2 receptor antagonist HOE 140 (10(-10)-10(-8) M) antagonized the bradykinin-induced relaxation, while the bradykinin B1 receptor antagonist des-Arg9-Leu8-bradykinin (10(-6) M) had no influence. The selective bradykinin B1 receptor agonist des-Arg9-bradykinin (10(-6) M) caused a small relaxation (8.4+/-2.5%, n=6), which could be antagonized completely by the selective bradykinin B1 receptor antagonist des-Arg9-Leu8-bradykinin (10(-6) M) while addition of the selective bradykinin B2 receptor antagonist HOE 140 (10(-8) M) was without effect. In the presence of indomethacin (10(-6) M) the relaxation of bradykinin was completely abolished. Pretreatment of the tracheal rings with capsaicin, or the presence of the selective NK1 receptor antagonist RP 67851 (10(-6) M) or the presence of the nitric oxide synthase inhibitor L-NAME (3 x 10(-4) M) had no effect on the bradykinin-induced relaxation. In conclusion, these results demonstrate that the mouse-isolated tracheal is a preparation in which bradykinin exerts a relaxant response via stimulation of bradykinin B2 receptors. This response is probably mediated by prostaglandins. 相似文献
108.
109.
Barium copper oxalate was grown in silica hydrogel at ambient temperature. The effect of various parameters like gel pH, gel
density, gel aging and concentrations of reactants on the growth of these crystals was studied. The crystals grown were characterized
by chemical analysis, X-ray powder diffractometry, infrared spectroscopy, thermogravimetric and differential thermal analysis.
The results of these observations are described and discussed. 相似文献
110.