全文获取类型
收费全文 | 2235篇 |
免费 | 24篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 23篇 |
综合类 | 1篇 |
化学工业 | 106篇 |
金属工艺 | 46篇 |
机械仪表 | 7篇 |
建筑科学 | 60篇 |
矿业工程 | 4篇 |
能源动力 | 33篇 |
轻工业 | 104篇 |
水利工程 | 8篇 |
石油天然气 | 4篇 |
无线电 | 108篇 |
一般工业技术 | 224篇 |
冶金工业 | 1355篇 |
原子能技术 | 11篇 |
自动化技术 | 166篇 |
出版年
2022年 | 8篇 |
2021年 | 13篇 |
2020年 | 7篇 |
2019年 | 10篇 |
2018年 | 13篇 |
2017年 | 15篇 |
2016年 | 20篇 |
2015年 | 17篇 |
2014年 | 16篇 |
2013年 | 58篇 |
2012年 | 25篇 |
2011年 | 39篇 |
2010年 | 28篇 |
2009年 | 27篇 |
2008年 | 40篇 |
2007年 | 47篇 |
2006年 | 40篇 |
2005年 | 35篇 |
2004年 | 50篇 |
2003年 | 34篇 |
2002年 | 36篇 |
2001年 | 44篇 |
2000年 | 29篇 |
1999年 | 57篇 |
1998年 | 407篇 |
1997年 | 224篇 |
1996年 | 145篇 |
1995年 | 100篇 |
1994年 | 94篇 |
1993年 | 80篇 |
1992年 | 28篇 |
1991年 | 21篇 |
1990年 | 20篇 |
1989年 | 32篇 |
1988年 | 31篇 |
1987年 | 23篇 |
1986年 | 27篇 |
1985年 | 30篇 |
1984年 | 19篇 |
1983年 | 14篇 |
1982年 | 10篇 |
1981年 | 18篇 |
1980年 | 18篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 46篇 |
1976年 | 93篇 |
1975年 | 10篇 |
1973年 | 8篇 |
1972年 | 5篇 |
排序方式: 共有2260条查询结果,搜索用时 62 毫秒
1.
2.
3.
McDonald K.C. Zimmermann R. Kimball J.S. 《Geoscience and Remote Sensing, IEEE Transactions on》2002,40(9):2063-2082
Spatial and temporal variations in vegetation dielectric properties strongly influence the microwave backscatter characteristics of forested landscapes. This paper examines the relationship between xylem tissue dielectric constant, xylem sap flux density, and xylem sap chemical composition as measured in the stems of two Norway Spruce (Picea abies [L.] Karst.) trees in the Fichtelgebirge region of Northern Bavaria, Germany. Dielectric constant and xylem sap flux were monitored continuously from June through October 1995, at several heights along the tree trunks. At the end of the measurement series, each tree was harvested, and its xylem sap extracted and analyzed to determine the concentrations of amino acids and cations. Results show that the sap flux density was correlated with vapor pressure deficit (VPD) at all heights in the stem. In contrast, the xylem tissue dielectric constant is influenced by VPD but can exhibit a significant temporal lag relative to changes in VPD. This lag varies with position along the tree trunk. The temporal variability of the dielectric constant is compared with both trees at several positions along the tree trunks. Results of xylem sap chemical analysis are presented. We show that spatial and temporal variability in the xylem tissue dielectric constant is influenced not only by water content, but by variations in xylem sap chemistry as well. This has important implications for microwave remote sensing of forested landscapes, as useful information may be acquired regarding stand physiology and water relations and where variations in dielectric properties within individual trees and across geographic areas can be significant error sources for forest inventory mapping. 相似文献
4.
GN Mozhokina GB Sokolova OV Makarova LP Mikha?lova 《Canadian Metallurgical Quarterly》1996,41(7-8):31-33
The effect of lomefloxacin was studied on mice with experimental infection due to Mycobacterium tuberculosis. The antibiotic was administered in doses of 100 and 200 mg/kg. It was shown that the use of lomefloxacin for a month provided a lower death rate of the animals with progressing acute generalized tuberculosis, a lower level of the lesions in the internal organs and a lower number of the Mycobacterium isolates from them. The efficacy of the treatment depended on the drug dose. When lomefloxacin was used in a dose of 200 mg/kg, the survival rate was much higher and the number of the epithelial unicellular granulomas in the tissue of the lung and spleen was markedly decreased while with the lower dose the indices did not differ from those in the control. 相似文献
5.
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
6.
7.
8.
9.
10.
Welsh Kathleen A.; Hoffman John M.; McDonald William M.; Earl Nancy L.; Breitner John C. S. 《Canadian Metallurgical Quarterly》1993,7(2):158
To illustrate the utility of the twin method in Alzheimer's disease (AD) research, a pair of monozygotic twins, concordant for the disease but markedly different in their clinical presentations, was studied in detail. Neuropsychological evaluation, magnetic resonance imaging (MRI), and cerebral glucose metabolic studies revealed a typical behavioral presentation for AD in Twin A. In contrast, Twin B showed prominent visuospatial impairments. Although there was no identified cause for the disparate presentations, a close correspondence was observed between the neuropsychological findings and the regional brain measures. The results suggest that the trajectory of AD may vary widely even in genetically identical individuals. Factors accounting for the variability include potential intrauterine, early developmental, and environmental differences. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献