全文获取类型
收费全文 | 4790篇 |
免费 | 568篇 |
国内免费 | 371篇 |
专业分类
电工技术 | 582篇 |
综合类 | 462篇 |
化学工业 | 569篇 |
金属工艺 | 319篇 |
机械仪表 | 289篇 |
建筑科学 | 286篇 |
矿业工程 | 193篇 |
能源动力 | 174篇 |
轻工业 | 465篇 |
水利工程 | 183篇 |
石油天然气 | 206篇 |
武器工业 | 101篇 |
无线电 | 512篇 |
一般工业技术 | 281篇 |
冶金工业 | 322篇 |
原子能技术 | 78篇 |
自动化技术 | 707篇 |
出版年
2024年 | 24篇 |
2023年 | 71篇 |
2022年 | 209篇 |
2021年 | 214篇 |
2020年 | 151篇 |
2019年 | 140篇 |
2018年 | 127篇 |
2017年 | 128篇 |
2016年 | 137篇 |
2015年 | 222篇 |
2014年 | 289篇 |
2013年 | 350篇 |
2012年 | 439篇 |
2011年 | 416篇 |
2010年 | 374篇 |
2009年 | 397篇 |
2008年 | 344篇 |
2007年 | 322篇 |
2006年 | 332篇 |
2005年 | 222篇 |
2004年 | 179篇 |
2003年 | 135篇 |
2002年 | 126篇 |
2001年 | 95篇 |
2000年 | 84篇 |
1999年 | 32篇 |
1998年 | 58篇 |
1997年 | 39篇 |
1996年 | 16篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1976年 | 5篇 |
1959年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有5729条查询结果,搜索用时 0 毫秒
1.
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
2.
LILin LIUWen-li LUBin JUGuo-xian ZHANGYong-ming HAOYong-qin SUWei ZHONGJing-chang 《半导体光子学与技术》2004,10(3):179-181,193
Spectral and structural characteristics of distributed Bragg reflector (DBR) in vertical-cavity surface-emitting lasers were studied with photoluminescence and double- crystal X- ray diffraction measurement. The expected high quality epitaxial DBR structure was verified. In the X- ray double- crystal rocking curves of DBR the zeroth- order peak, the first and second order satellite peaks were measured. Splitting of diffraction peak appeared in the rocking curves was analyzed. The effects of introduced deep energy levels on the structural perfection and optical properties were discussed. 相似文献
3.
STUDY DESIGN: Utility of using computed tomography to predict pedicle screw misplacement. OBJECTIVE: This study defines the sensitivity and specificity of predicting pedicle screw placement by experienced clinicians using a CT scan image. SUMMARY OF BACKGROUND DATA: In clinical and research settings, the method most commonly used to evaluate pedicle screws placement has been computed tomography. However, no current literature describes the accuracy of this method of evaluating screw placement. METHOD: Cobalt-chrome and titanium alloy pedicle screws of identical size were placed in six cadaveric human lumbar spine. Wide laminectomy was performed to allow complete visualization of the pedicles. Three consecutive lumbar levels were instrumented in each spine, giving 36 pedicle screw placements to identify. The instrumented spines were imaged, and four orthopaedic spine surgeons and a musculoskeletal radiologist were asked to read the images to identify the accuracy of screw placement within the pedicles. RESULTS: The sensitivity rate of identifying a misplaced screw was 67 +/- 6% for cobalt-chrome screws compared with 86 +/- 5% for titanium screws (P < 0.005). The specificity rates of radiographic diagnosis of misplaced pedicle screws were 66 +/- 10% for cobalt-chrome screws and 88 +/- 8% for titanium screws (P < 0.005). Similarly, a statistically significant difference was found in the sensitivity rates of identifying screws placed correctly in the pedicle: 70 +/- 10% for cobalt-chrome screws versus 89 +/- 8% for titanium screws (P < 0.005). Overall accuracy rates were 68 +/- 7% for cobalt chrome screws versus 87 +/- 3% for titanium screws (P < 0.002). CONCLUSION: Reliance on the computed tomography scan data alone in determining accuracy of pedicle screws can lead to inaccuracies in both clinical and research conditions. 相似文献
4.
5.
材质对蜂窝纸板缓冲性能的影响 总被引:2,自引:1,他引:1
对两种不同材质的蜂窝纸板静态应力应变性能和动态缓冲结果进行了比较分析。讨论了蜂窝纸板力学性能对应变速度的敏感性及两种纸板的缓冲性能差异。缓冲试验结果表明。在不同的冲击应变率下蜂窝纸板的材质影响蜂窝纸板缓冲性能。 相似文献
6.
7.
ECAP细化晶粒法的仿真与分析 总被引:7,自引:0,他引:7
ECAP(Equal Channel Angular Extrusion)方法,是实现材料纯剪切变形的有效方法。本文采用有限元(FEA)分析软件ANSYS对Al的挤压过程进行仿真与分析。分析结果表明:外切角Φ、圆角半径、试样与凹模之间的摩擦系数、凹模本身的特性(如弹性模量、泊松比等)等等,对材料的变形量都有不同程度的影响。 相似文献
8.
9.
MR Fibi P Hermentin JU Pauly L Lauffer G Zettlmeissl 《Canadian Metallurgical Quarterly》1995,85(5):1229-1236
Single-site glycomuteins of recombinant human erythropoietin (rhuEpo) were constructed and transiently and stably expressed in BHK-21 cells. The transient expression levels varied among muteins, being highest for mutein rhuEpoGln24 followed by wild-type rhuEpo (rhuEpowt). All other glycomuteins, including rhuEpoGln38, rhuEpoGln83, rhuEpoThr126, and rhuEpoGly126, were secreted at lower levels than rhuEpowt. Muteins expressed in stable cell lines showed similar differences in expression levels. Also each mutein could be affinity-purified from culture supernatants, and was biologically active in vivo. Based on secretion rates from BHK-21 cells, the most potent erythropoietin was rhuEpoGln24. This mutein is also considered to have biologic activities that are superior to rhuEpowt. 相似文献
10.