全文获取类型
收费全文 | 3300篇 |
免费 | 27篇 |
专业分类
电工技术 | 14篇 |
化学工业 | 181篇 |
金属工艺 | 17篇 |
机械仪表 | 33篇 |
建筑科学 | 32篇 |
矿业工程 | 2篇 |
能源动力 | 13篇 |
轻工业 | 44篇 |
水利工程 | 11篇 |
石油天然气 | 1篇 |
无线电 | 159篇 |
一般工业技术 | 168篇 |
冶金工业 | 2543篇 |
原子能技术 | 9篇 |
自动化技术 | 100篇 |
出版年
2021年 | 10篇 |
2019年 | 11篇 |
2018年 | 14篇 |
2017年 | 12篇 |
2016年 | 13篇 |
2015年 | 8篇 |
2014年 | 15篇 |
2013年 | 32篇 |
2012年 | 30篇 |
2011年 | 44篇 |
2010年 | 26篇 |
2009年 | 29篇 |
2008年 | 38篇 |
2007年 | 31篇 |
2006年 | 31篇 |
2005年 | 23篇 |
2004年 | 25篇 |
2003年 | 19篇 |
2002年 | 15篇 |
2001年 | 14篇 |
2000年 | 14篇 |
1999年 | 93篇 |
1998年 | 703篇 |
1997年 | 411篇 |
1996年 | 301篇 |
1995年 | 182篇 |
1994年 | 140篇 |
1993年 | 156篇 |
1992年 | 40篇 |
1991年 | 66篇 |
1990年 | 48篇 |
1989年 | 59篇 |
1988年 | 65篇 |
1987年 | 59篇 |
1986年 | 38篇 |
1985年 | 56篇 |
1984年 | 29篇 |
1983年 | 22篇 |
1982年 | 28篇 |
1981年 | 30篇 |
1980年 | 25篇 |
1979年 | 20篇 |
1978年 | 12篇 |
1977年 | 59篇 |
1976年 | 123篇 |
1975年 | 9篇 |
1974年 | 14篇 |
1973年 | 10篇 |
1972年 | 8篇 |
1966年 | 12篇 |
排序方式: 共有3327条查询结果,搜索用时 15 毫秒
1.
2.
MB Heyman JM LaBerge KA Somberg P Rosenthal C Mudge EJ Ring JD Snyder 《Canadian Metallurgical Quarterly》1997,131(6):914-919
The transjugular intrahepatic portosystemic shunt procedure is an accepted treatment for adults with complications of portal hypertension. We performed a retrospective review of all pediatric TIPS placements performed at the University of California, San Francisco between 1990 and 1996. Twelve procedures were attempted in nine children, with a mean age (+/- SD) of 9.4 +/- 3.9 years (range, 5 to 15 years) and a mean weight of 31 +/- 18 kg (range, 16 to 70 kg). The indications for TIPS placement were portal hypertension complicated by chronic variceal hemorrhage not controlled with sclerotherapy (n = 7) and hypersplenism with thrombocytopenia (n = 2). TIPS placement was successfully completed initially in seven of nine (78%) patients. Unfavorable vascular anatomy was the cause of failure in two cases. The seven patients who underwent successful TIPS placement were followed up for an average of 136 days (range, 1 to 800 days); two still have patent shunts, three underwent liver transplantation, one had a splenorenal shunt after stenosis, and one died of underlying liver disease. Variceal bleeding was controlled in four of five patients who successfully underwent TIPS placement. Shunt occlusion occurred in four patients; patency was restored by transjugular shunt revision in three, and a splenorenal shunt was performed in one. 相似文献
3.
BF Habbick JL Nanson RE Snyder RE Casey AL Schulman 《Canadian Metallurgical Quarterly》1996,87(3):204-207
Ethers and thioethers of monosaccharides have been synthesised which show potent toxicity to mouse (LD50 > or = 4 g.kg-1 O.W. and 0.2 to 1.5 g.kg-1 I.P.W.). A study of calcium antagonist activity for the full series of compounds indicated that the activity was similar for both O- and S- ethers and maximum activities were observed for monoacetoneglucose ethers possessing carbon chain close to 8 carbons. 相似文献
4.
PE Sipila VJ Wiebe GB Hubbard SK Koester VD Emshoff JU Maenpaa GT Wurz RC Seymour MW DeGregorio 《Canadian Metallurgical Quarterly》1993,(15):2138-2144
The effects of long-term tamoxifen exposure on cell growth and cell cycle kinetics were compared between oestrogen receptor (ER)-positive (MCF-7) and ER-negative (MDA-MB-231) cell lines. In the MCF-7 cell line, prolonged tamoxifen exposure (0.5 mumol/l for > 100 days) blocked cells in G0-G1 of the cell cycle, and slowed the doubling time of cells from 30 to 59 h. These effects corresponded to an increase in the cellular accumulation of tamoxifen over time [mean area under concentration curve (AUC) = 77.92 mumoles/10(6)/cells/day]. In contrast, in the MDA-MB-231 cell line, long-term tamoxifen exposure had no obvious effect on the doubling time, and reduced cellular tamoxifen accumulation (mean AUC = 50.50 mumoles/10(6)/cells/day) compared to the MCF-7 cells. Flow cytometric analysis of MDA-MB-231 cells demonstrated that a new tetraploid clone emerged following 56 days of tamoxifen exposure. Inoculation of the MDA-MB-231 tetraploid clone and MDA-MB-231 wildtype cells into the opposite flanks of athymic nude mice resulted in the rapid growth of tetraploid tumours. The tetraploid tumours maintained their ploidy following tamoxifen treatment for nine consecutive serial transplantations. Histological examination of the fifth transplant generation xenografts revealed that the tetraploid tumour had a 25-30 times greater mass, area of haemorrhage and necrosis, a slightly higher mitotic index and was more anaplastic than the control neoplasm. The control wildtype MDA-MB-231 tumours maintained a stable ploidy following tamoxifen treatment until the eighth and ninth transplantation, when a tetraploid population appeared, suggesting that tamoxifen treatment may select for this clone in vivo. These studies suggest that prolonged tamoxifen exposure may select for new, stable, fast growing cell clones in vitro as well as in vivo. 相似文献
5.
6.
7.
8.
9.
The purpose of the present study was to evaluate the accuracy of data regarding diagnoses of spinal disorders in administrative databases at eight different institutions. The records of 189 patients who had been managed for a disorder of the lumbar spine were independently reviewed by a physician who assigned the appropriate diagnostic codes according to the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM). The age range of the 189 patients was seventeen to eighty-four years. The six major diagnostic categories studied were herniation of a lumbar disc, a previous operation on the lumbar spine, spinal stenosis, cauda equina syndrome, acquired spondylolisthesis, and congenital spondylolisthesis. The diagnostic codes assigned by the physician were compared with the codes that had been assigned during the ordinary course of events by personnel in the medical records department of each of the eight hospitals. The accuracy of coding was also compared among the eight hospitals, and it was found to vary depending on the diagnosis. Although there were both false-negative and false-positive codes at each institution, most errors were related to the low sensitivity of coding for previous spinal operations: only seventeen (28 per cent) of sixty-one such diagnoses were coded correctly. Other errors in coding were less frequent, but their implications for conclusions drawn from the information in administrative databases depend on the frequency of a diagnosis and its importance in an analysis. This study demonstrated that the accuracy of a diagnosis of a spinal disorder recorded in an administrative database varies according to the specific condition being evaluated. It is necessary to document the relative accuracy of specific ICD-9-CM diagnostic codes in order to improve the ability to validate the conclusions derived from investigations based on administrative databases. 相似文献
10.
This multiple baseline study investigated the effectiveness of a cognitive-behavioral self-management training package on the consistent use of specific classroom survival skills. Participants were three adolescent males with learning disabilities in Grades 7 and 8. The training package involved a multicomponent strategy focused on the improvement, maintenance, and cross-classroom generalization of targeted classroom preparedness skills. Following intervention, the training procedures were systematically faded. Results demonstrated more consistent use of targeted classroom survival skills by all three students in both learning support and mainstream generalization settings. Long-term maintenance of the intervention effects was observed for two students in both settings. Three social validity measures revealed positive results. Implications for self-management in secondary education settings are discussed. 相似文献