全文获取类型
收费全文 | 37521篇 |
免费 | 2799篇 |
国内免费 | 1429篇 |
专业分类
电工技术 | 1961篇 |
综合类 | 2141篇 |
化学工业 | 6673篇 |
金属工艺 | 1834篇 |
机械仪表 | 2118篇 |
建筑科学 | 3593篇 |
矿业工程 | 729篇 |
能源动力 | 1165篇 |
轻工业 | 2249篇 |
水利工程 | 595篇 |
石油天然气 | 2062篇 |
武器工业 | 254篇 |
无线电 | 4479篇 |
一般工业技术 | 4791篇 |
冶金工业 | 1966篇 |
原子能技术 | 557篇 |
自动化技术 | 4582篇 |
出版年
2024年 | 155篇 |
2023年 | 539篇 |
2022年 | 985篇 |
2021年 | 1369篇 |
2020年 | 1053篇 |
2019年 | 859篇 |
2018年 | 953篇 |
2017年 | 1109篇 |
2016年 | 986篇 |
2015年 | 1292篇 |
2014年 | 1652篇 |
2013年 | 2137篇 |
2012年 | 2232篇 |
2011年 | 2448篇 |
2010年 | 2040篇 |
2009年 | 2016篇 |
2008年 | 1965篇 |
2007年 | 1920篇 |
2006年 | 1973篇 |
2005年 | 1755篇 |
2004年 | 1225篇 |
2003年 | 1090篇 |
2002年 | 1050篇 |
2001年 | 907篇 |
2000年 | 993篇 |
1999年 | 1070篇 |
1998年 | 1018篇 |
1997年 | 845篇 |
1996年 | 820篇 |
1995年 | 669篇 |
1994年 | 534篇 |
1993年 | 475篇 |
1992年 | 335篇 |
1991年 | 241篇 |
1990年 | 249篇 |
1989年 | 170篇 |
1988年 | 140篇 |
1987年 | 97篇 |
1986年 | 79篇 |
1985年 | 58篇 |
1984年 | 48篇 |
1983年 | 35篇 |
1982年 | 32篇 |
1981年 | 20篇 |
1980年 | 23篇 |
1979年 | 10篇 |
1977年 | 10篇 |
1976年 | 12篇 |
1973年 | 8篇 |
1970年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
Harringtonine (HT), an anticancer drug with high chemotherapeutic efficiency to human chronic granulocytic/myelomonocytic leukemia, has been reported to rapidly induce apoptosis in HL-60 cells in a wide scope/range of dosage by investigators from our lab and others. In the present studies, by using video enhancement contrast (VEC) microscopy, we dynamically analyzed changes in intracellular calcium distribution in a single HL-60 cell over the period from the initiation of apoptosis to the obvious appearance of chromatin condensation. The results from this paper demonstrated the striking distinction of intracellular calcium distribution at different time points after treatment with HT. Before treatment in normal HL-60 cells the highest [Ca2+]i accumulation was observed in the peri-nuclear area and the lowest was observed in the nucleus; after treatment with 1 microg/ml HT for 30 min intracellular calcium diffused all over the cell compartments, while intranuclear calcium increased comparatively and significantly. The phenomenon of intranuclear calcium accumulation was further confirmed by using laser scanning confocal microscopy (LSCM). In addition, co-localization of the highest calcium region with condensed chromatin in apoptotic HL-60 cells was also observed by LSCM. Our results suggest that two sequential alterations of intracellular calcium distribution occurred in apoptotic HL-60 cells induced by HT, i.e. (a) accumulation of calcium in the nucleus and (b) regionalization in a specific nuclear region. 相似文献
162.
An evaluation of ruminally degradable intake protein and metabolizable amino acid requirements of feedlot calves 总被引:1,自引:0,他引:1
Ruminally degradable intake protein (DIP) and metabolizable indispensable amino acid (MIAA) requirements of feedlot steers were evaluated. Dietary treatments consisted of isocaloric 80% concentrate steam-flaked corn-based diets containing either .8% urea, 1.5% fish meal (FM), 3.0% FM, 4.5% FM, or 4.5% soybean meal (SBM). Treatment effects on characteristics of ruminal and total tract digestion were evaluated using four Holstein steers (249 kg) with cannulas in the rumen and proximal duodenum. Ruminal digestibility of OM (RDOM; P < .05) and feed N (P < .01) and microbial N flow (MNF; P < .01) to the small intestine were greater with urea as the supplemental N source. The level of DIP was closely associated (R2 = .89) with MNF. Postruminal digestibility of OM was greater (P < .05) for FM than for urea-supplemented diets, compensating for lower RDOM. There were no treatment effects (P > .10) on DOM. As the level of FM was increased, MIAA increased linearly (P < .01). Intestinal MIAA were similar (P > .10) for urea- and SBM-supplemented diets. Treatment effects on 56-d growth performance were evaluated using 100 medium-framed crossbred steers (231 kg). Daily weight gain (linear effect; P < .01), DM intake (linear effect; P < .10), feed efficiency (linear effect; P < .05), and diet NE (linear effect; P < .05) increased with level of FM supplementation. Daily weight gain (P < .10) and DM intake (P < .05) were greater for urea- than for SBM-supplemented diets. Using bovine tissue as the reference protein, the biological value (based on chemical score) of the intestinal chyme protein averaged 73%; methionine was first-limiting. There was a close association (R2 = .99) between methionine supply to the small intestine and observed/expected dietary NE. The metabolizable methionine requirement (MMETR, g/d) of medium-framed feedlot steers can be reliably predicted from measures of BW and ADG (MMETR = 1.565 + .0234ADG[268 - (29.4 x .0557BW(.75)ADG(1.097))/ADG] + .0896BW(.75)). There was a very close association (R2 = .89) between DIP and MNF (MNF = 13.7DIP - .66DIP(2) + 25.9). At maximal observed synthesis, DIP accounted for 76% of the MNF. A minimum of 100 g DIP/kg of total tract digestible OM was required to maximize RDOM and MNF. 相似文献
163.
叙述了体吸收激光能量计的特点,介绍了其标定方法,给出了其技术参数。体吸收激光地的推广应用取得了广泛的社会效益。 相似文献
164.
双重孔隙介质的碳酸盐岩油藏在稳定注水采油后岩块系统还存在大量剩余油,而不稳定注水方法可在一定程度上提高水驱油效率。室内物理模型实验、数值模拟计算及现场试验结果一致表明:在碳酸盐岩油藏注水开发后期采用衰竭式降压开采,周期注水等不稳定注水方式,能够提高水驱油效率,改善油藏开发效果,获得良好的经济效益。 相似文献
165.
166.
Pre-bainitic Transformation in Fe-Ni Alloy 总被引:1,自引:0,他引:1
Thepre-bainiticphenomenonisoneoftheim-portantsubjectsofbainitictransformationwhichisstilcontroversial.Oneviewisthatthesolutea... 相似文献
167.
通过对某特钢厂破裂的结晶器铜管进行金相实验、扫描电镜和能谱分析,并结合结晶器的生产、使用及失效过程情况,综合受力分析,认为铜管破裂原因主要是环境介质硫渗入形成硫化物,在拉应力作用下,裂纹沿脆性质点扩展导致的破坏。 相似文献
168.
羧酸酯稀土对聚氯乙烯的热老化稳定作用研究 总被引:11,自引:1,他引:10
用热烘法研究了羧酸酯稀土对聚氯乙烯的热老化稳定作用。利用紫外/可见光谱分析跟踪共轭双键在热老化过程中的变化,比较CERES,有机锡及两者的复合稳定剂的热老化稳定性能,发现CERES与有机锡的稳定性能相当,复合稳定剂具有协同效应。 相似文献
169.
针对塑料挤出机控制系统成本高、速度低、精度低的问题,提出采用UniMATPLC控制方式,实践证明效果良好。 相似文献
170.
隐写算法的评估是以隐写系统安全性角度出发,总结出了抗检测性、鲁棒性、抗容量探测性等多个性能指标,构建了评估指标集.并采用解释结构模型法对评估指标体系进行分析。重点讨论了方法的应用和结果的分析,给出了对图像隐写算法评估体系建立和分析的思路与方法。 相似文献