全文获取类型
收费全文 | 3858篇 |
免费 | 41篇 |
学科分类
工业技术 | 3899篇 |
出版年
2021年 | 14篇 |
2020年 | 10篇 |
2019年 | 19篇 |
2018年 | 16篇 |
2017年 | 16篇 |
2016年 | 26篇 |
2015年 | 20篇 |
2014年 | 19篇 |
2013年 | 48篇 |
2012年 | 42篇 |
2011年 | 55篇 |
2010年 | 40篇 |
2009年 | 34篇 |
2008年 | 45篇 |
2007年 | 47篇 |
2006年 | 35篇 |
2005年 | 39篇 |
2004年 | 37篇 |
2003年 | 31篇 |
2002年 | 35篇 |
2001年 | 35篇 |
2000年 | 26篇 |
1999年 | 89篇 |
1998年 | 864篇 |
1997年 | 525篇 |
1996年 | 321篇 |
1995年 | 228篇 |
1994年 | 146篇 |
1993年 | 201篇 |
1992年 | 36篇 |
1991年 | 38篇 |
1990年 | 44篇 |
1989年 | 39篇 |
1988年 | 42篇 |
1987年 | 44篇 |
1986年 | 30篇 |
1985年 | 23篇 |
1984年 | 13篇 |
1983年 | 16篇 |
1982年 | 24篇 |
1981年 | 39篇 |
1980年 | 27篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 93篇 |
1976年 | 182篇 |
1975年 | 20篇 |
1974年 | 10篇 |
1973年 | 8篇 |
1972年 | 8篇 |
排序方式: 共有3899条查询结果,搜索用时 15 毫秒
21.
RG Wilde JT Billheimer SJ Germain EA Hausner PC Meunier DA Munzer JK Stoltenborg PJ Gillies DL Burcham SM Huang JD Klaczkiewicz SS Ko RR Wexler 《Canadian Metallurgical Quarterly》1996,4(9):1493-1513
Acyl-CoA:cholesterol acyltransferase (ACAT) is the enzyme largely responsible for intracellular cholesterol esterification. A systemic inhibitor of ACAT is believed to be able to slow or even reverse the atherosclerotic process. Towards that goal, a series of cyclic sulfides, derived from the hetero-Diels-Alder reaction of thioaldehydes with 1,3-dienes, and bearing carboxamide substituents, were prepared and evaluated for in vitro (in several tissues and species) and ex vivo ACAT inhibition. Minor changes in subsequent structure were found to have a significant effect in optimization of the biological activity of this series of compounds. 相似文献
22.
MK Atalay JR Forder VP Chacko S Kawamoto EA Zerhouni 《Canadian Metallurgical Quarterly》1993,189(3):759-764
PURPOSE: To determine the feasibility of using hemoglobin (Hb) desaturation as an indicator of myocardial oxygenation. MATERIALS AND METHODS: High-resolution gradient-echo nuclear magnetic resonance (MR) images of isolated, blood-perfused rabbit hearts were obtained at various blood oxygenation levels. The hearts were perfused at 37 degrees C with a Langendorff apparatus modified for nuclear MR imaging. The perfusate contained bovine red blood cells in a cardioplegic solution that eliminated motion artifacts and minimized arteriovenous oxygenation differences. Hb saturation was varied (7%-100%) randomly. Perfusion pressure was continuously monitored, and blood samples were obtained. RESULTS: There was a substantial correlation between image signal intensity in the myocardium and Hb saturation in the blood, believed to be due to susceptibility effects of the paramagnetic species deoxyhemoglobin. CONCLUSION: Direct and noninvasive determination of regional Hb saturation with susceptibility-dependent MR imaging may provide information regarding regional myocardial O2 content. 相似文献
23.
The Uniform Covering by Probabilistic Rejection (UCPR) algorithm was used, in conjunction with the Soil and Water Assessment Tool (SWAT) model, to identify P loads from point source and nonpoint source polluters in the upper Etowah River basin (UERB) in Georgia. The key findings of the research are as follows. The mean absolute error was preferred over the root mean square error as a search criterion for the UCPR algorithm when water quality observations are scarce. The undocumented P load from point sources in the UERB was consistently estimated as about 43 kg/d by the proposed method; but the method was not able to identify the broiler litter application rate to the poultry/beef operation pastures. Point sources (both documented and undocumented), poultry/beef operation pastures, and forests are the three major contributors of P. During 1992-1996, on average they accounted for 36.4, 31.7, and 17.2% of P load from the UERB, respectively. 相似文献
24.
25.
26.
27.
28.
Beck J. Gayle; Novy Diane M.; Diefenbach Gretchen J.; Stanley Melinda A.; Averill Patricia M.; Swann Alan C. 《Canadian Metallurgical Quarterly》2003,15(2):184
To examine affect and cognition in differentiating anxiety and depression, 83 older participants with generalized anxiety disorder completed the Cognitive Checklist (CCL) and the Positive and Negative Affect Schedule (PANAS). A 3-factor solution was found for the PANAS: positive affect (PA), anxiety and anger (Negative Affect 1 [NA-1]), and guilt and shame (Negative Affect 2 [NA-2]). A 2-factor structure was noted for the CCL. Correlations with anxiety and depression measures suggested that the CCL Depression (CCL-D) subscale showed stronger correlations with depression, whereas the CCL Anxiety subscale did not uniquely correlate with anxiety. The NA-1 subscale correlated positively with measures of depression and anxiety, whereas the PA subscale showed negative correlations. Hierarchical regression suggested that the CCL-D subscale was a significant predictor of self-reported depression. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
29.
30.
Cell cycle. The NIMA kinase joins forces with Cdc2 总被引:1,自引:0,他引:1
The NIMA and Cdc2 protein kinases cooperate to regulate mitosis in Aspergillus nidulans. NIMA-related pathways have now begun to emerge in higher eukaryotes. 相似文献