全文获取类型
收费全文 | 42787篇 |
免费 | 931篇 |
国内免费 | 178篇 |
专业分类
电工技术 | 532篇 |
综合类 | 631篇 |
化学工业 | 4565篇 |
金属工艺 | 581篇 |
机械仪表 | 859篇 |
建筑科学 | 829篇 |
矿业工程 | 390篇 |
能源动力 | 421篇 |
轻工业 | 2040篇 |
水利工程 | 612篇 |
石油天然气 | 48篇 |
武器工业 | 4篇 |
无线电 | 1835篇 |
一般工业技术 | 3354篇 |
冶金工业 | 21401篇 |
原子能技术 | 189篇 |
自动化技术 | 5605篇 |
出版年
2024年 | 55篇 |
2023年 | 190篇 |
2022年 | 122篇 |
2021年 | 110篇 |
2018年 | 452篇 |
2017年 | 674篇 |
2016年 | 1050篇 |
2015年 | 777篇 |
2014年 | 423篇 |
2013年 | 420篇 |
2012年 | 2138篇 |
2011年 | 2436篇 |
2010年 | 668篇 |
2009年 | 765篇 |
2008年 | 602篇 |
2007年 | 630篇 |
2006年 | 563篇 |
2005年 | 3339篇 |
2004年 | 2554篇 |
2003年 | 2047篇 |
2002年 | 843篇 |
2001年 | 729篇 |
2000年 | 279篇 |
1999年 | 614篇 |
1998年 | 6146篇 |
1997年 | 3804篇 |
1996年 | 2505篇 |
1995年 | 1446篇 |
1994年 | 1067篇 |
1993年 | 1096篇 |
1992年 | 244篇 |
1991年 | 303篇 |
1990年 | 301篇 |
1989年 | 273篇 |
1988年 | 290篇 |
1987年 | 219篇 |
1986年 | 198篇 |
1985年 | 166篇 |
1984年 | 68篇 |
1983年 | 80篇 |
1982年 | 127篇 |
1981年 | 176篇 |
1980年 | 191篇 |
1979年 | 60篇 |
1978年 | 97篇 |
1977年 | 609篇 |
1976年 | 1322篇 |
1975年 | 98篇 |
1973年 | 47篇 |
1971年 | 49篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
Head and eye movements were simultaneously recorded during locomotory and pecking behavior of 4 pigeons, which were trained to traverse a conditioning chamber, with a pecking key and a food dispenser at each end. Each trial involved key pecking, walking, and feeding. Head movements were registered with a skull-mounted miniature accelerometer, and eye movements were recorded with implanted electrooculogram (EOG) electrodes. An almost perfect temporal coordination between head and eye movements was observed during both walking and feeding bouts. During walking, head movements primarily provide retinal image stability, and eye movements support visual scanning. During feeding, head movements mainly subserve the grasping of food items, and eye movements maintain visual fixation on them. Because the eyes are reflexively closed during the middle phase of pecks, the head and eye movements are then under ballistic control. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
53.
F Jónsson P Madsen LG J?rgensen M Lunding NH Secher 《Canadian Metallurgical Quarterly》1996,158(44):6256-6259
Indices of fluid balance were evaluated during and after aortic surgery in 16 consecutive patients. Thoracic electrical impedance (TI), heart rate (HR), central venous (CVP), pulmonary artery mean (PAMP), pulmonary wedge (PWP) and mean arterial (MAP) pressures as well as fourteen arterial and venous blood gas variables were followed. Consistent with a reduction of TI during the operation, fluid balance was in excess, and it remained elevated on the first postoperative morning. The HR, MAP and PWP remained stable, while CVP and PAMP decreased. Of the determined variables only TI revealed a meaningful correlation to fluid balance (rho = -0.41; p < 0.01). The results indicate that while central venous and pulmonary artery mean pressures gave the impression of a volume deficit, the positive fluid balance was mirrored by thoracic electrical impedance. 相似文献
54.
55.
56.
A modified natural surfactant was administered to a patient with life-threatening adult respiratory distress syndrome caused by viral pneumonia. Subsequently, there was a marked improvement in gas exchange. In order to assess the mechanism for improved oxygenation, computed tomography of the lungs was done. Quantitative analysis of the scans taken before and after surfactant administration indicates that improvement in gas exchange was largely due to the expansion of underinflated and collapsed lung areas. Although this is a single case report, it provides insight into the possible beneficial effect of instilled surfactant in severe respiratory distress from viral pneumonia. 相似文献
57.
J Botling F Oberg H T?rm? P Tuohimaa M Bl?uer K Nilsson 《Canadian Metallurgical Quarterly》1996,7(9):1239-1249
58.
59.
Overproduction of proteinase A by recombinant Saccharomyces cerevisiae was investigated by cultivations in a cell-recycling bioreactor. Membrane filtration was used to separate cells from the broth. Recycling ratios and dilution rates were varied and the effect on enzyme production was studied both experimentally and by computer simulations. Experiments and simulations showed that cell mass and product concentration were enhanced by high ratios of recycling. Additional simulations showed that the proteinase A concentration decreased drastically at high dilution rates and the optimal volumetric productivities were at high dilution rates just below washout and at high ratios of recycling. Cell-recycling fermentation gave much higher volumetric productivities and stable product concentrations in contrast to simple continuous fermentation. 相似文献
60.
Increased concentrations of octachlorodibenzo-p-dioxin in cases with breast cancer--results from a case-control study 总被引:1,自引:0,他引:1
L Hardell G Lindstr?m G Liljegren P Dahl A Magnuson 《Canadian Metallurgical Quarterly》1996,5(5):351-357
Organochlorines are persistent and highly lipophilic environmental contaminants which bioaccumulate in the food chain. Some of these chemicals, 2,2-bis(p-chlorophenyl)-1,1,1-trichloroethane (DDT) and polychlorinated biphenyls (PCBs), have been suggested to be of significance in the aetiology of breast cancer. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is an anti-oestrogen in animal studies and should be thus lower the risk of breast cancer. The other isomers of polychlorinated dibenzo-p-dioxins (PCDDs) or the chemically related polychlorinated dibenzofurans (PCDFs) have not been tested regarding carcinogenesis of the breast. The purpose of this study was to investigate whether PCDDs or PCDFs influence the risk for breast cancer. Consecutive patients who underwent surgery for a breast disease between 1993 and 1995 were recruited for the study. Cases were 22 patients with infiltrative breast cancer and controls were 19 patients operated for a benign breast disease during the same time period. Approximately 10 g of breast tissue free from tumour was taken from the specimen and frozen until analysis. Fat was extracted, cleaned and analysed with a high-resolution gas chromatograph coupled to a high-resolution mass spectrometer. Median concentrations of octachlorinated dibenzo-p-dioxin (OCDD) were 598 (170-14,880) and 396 (103-1,847) pg/g lipid in the cases and in the controls, respectively. In a multivariate logistic regression analysis controlling for other risk factors for breast cancer increased odds ratio (OR) was obtained for OCDD: 401-1000 pg/g lipid yielded OR 3.8, 95% confidence interval (CI) 0.4-39, > 1000 pg/g lipid gave OR 5.2, CI 0.4-72. When the lipid OCDD variable was examined as a continuous risk factor there was a 1.09 (9%), CI 0.95-1.25, increase in the adjusted OR for breast cancer per 100 unit (pg/g lipid) increase in OCDD. No differences were found between cases and controls for the other six tested PCDDs. Mean concentration of TCDD was in the cases 3.6 (1.0-7.9) and in the controls 3.3 (1.1-6.3) pg/g lipid. For PCDFs no significant differences were found between cases and controls. The results were not changed if oestrogen or progesterone receptor status, S-phase fraction and DNA ploidy were considered. Breast tissue concentration of OCDD was increased in cancer patients, whereas the concentrations of other PCDDs and PCDFs were equal in cases and controls. 相似文献