全文获取类型
收费全文 | 9016篇 |
免费 | 976篇 |
国内免费 | 202篇 |
专业分类
电工技术 | 652篇 |
综合类 | 272篇 |
化学工业 | 1785篇 |
金属工艺 | 375篇 |
机械仪表 | 605篇 |
建筑科学 | 779篇 |
矿业工程 | 355篇 |
能源动力 | 290篇 |
轻工业 | 769篇 |
水利工程 | 135篇 |
石油天然气 | 472篇 |
武器工业 | 33篇 |
无线电 | 865篇 |
一般工业技术 | 1175篇 |
冶金工业 | 382篇 |
原子能技术 | 37篇 |
自动化技术 | 1213篇 |
出版年
2024年 | 58篇 |
2023年 | 212篇 |
2022年 | 314篇 |
2021年 | 487篇 |
2020年 | 377篇 |
2019年 | 357篇 |
2018年 | 422篇 |
2017年 | 415篇 |
2016年 | 351篇 |
2015年 | 446篇 |
2014年 | 625篇 |
2013年 | 735篇 |
2012年 | 812篇 |
2011年 | 819篇 |
2010年 | 705篇 |
2009年 | 581篇 |
2008年 | 556篇 |
2007年 | 489篇 |
2006年 | 511篇 |
2005年 | 380篇 |
2004年 | 174篇 |
2003年 | 122篇 |
2002年 | 72篇 |
2001年 | 38篇 |
2000年 | 32篇 |
1999年 | 27篇 |
1998年 | 9篇 |
1997年 | 8篇 |
1996年 | 12篇 |
1995年 | 11篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1979年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
An approach is proposed for producing compressed sensing (CS) matrices via multidimensional pseudo-random sequences. The columns of these matrices are binary Gold code vectors where zeros are replaced by ?1. This technique is mainly applied to restore sub-Nyquist-sampled sparse signals, especially image reconstruction using block CS. First, for the specific requirements of message length and compression ratio, a set Λ which includes all preferred pairs of m-sequences is obtained by a searching algorithm. Then a sensing matrix A M×N is produced by using structured hardware circuits. In order to better characterize the correlation between any two columns of A, the average coherence is defined and the restricted isometry property (RIP) condition is described accordingly. This RIP condition has strong adaptability to different sparse signals. The experimental results show that with constant values of N and M, the sparsity bound of A is higher than that of a random matrix. Also, the recovery probability may have a maximum increase of 20 % in a noisy environment. 相似文献
992.
Inappropriately elevated endothelin‐1 plays a role in the pathogenesis of intradialytic hypertension 下载免费PDF全文
Jie Teng Jie Tian Wen‐Lv Lv Xiao‐Yan Zhang Jian‐Zhou Zou Yi Fang Jinbo Yu Bo Shen Zhong‐Hua Liu Xiao‐Qiang Ding 《Hemodialysis international. International Symposium on Home Hemodialysis》2015,19(2):279-286
The aim of this study is to investigate the effects of endogenous vasoactive substances on the occurrence of intradialytic hypertension (IDH) in patients during maintenance hemodialysis. Thirty‐four maintenance hemodialysis patients were enrolled in this trial, and 17 of them were diagnosed with IDH (defined as an increase in blood pressure of at least 10 mmHg during or immediately after a hemodialysis session), while 17 age‐matched and sex‐matched controls without IDH were selected for a retrospective comparison. We collected patients' blood samples before and after a dialysis session and measured the plasma levels of N‐terminal fragment brain natriuretic peptide, renin, angiotensin‐II, aldosterone (ALD), angiotensin‐converting enzyme (ACE), endothelin‐1 (ET‐1), nitric oxide (NO), norepinephrine (NOR), and adrenomedullin. The post‐dialysis serum ET‐1 concentrations were significantly higher (4.09 ± 2.06 vs. 2.75 ± 1.34 pg/mL, P < 0.05), while the post‐dialysis ratio of NO to ET‐1 was lower (17.79 ± 5.65 vs. 24.78 ± 12.04, P < 0.05) in IDH patients compared with the control group. Post‐dialysis ALD and NOR values were significantly lower (P < 0.01) and ACE levels were significantly higher (P < 0.01) than the pre‐dialysis concentrations only in the control and not in the IDH group. All other measured factors did not differ significantly between the groups and between pre‐dialysis and post‐dialysis determinations. Compared with blood angiotensin‐II, ALD, ACE, NOR, adrenomedullin, N‐terminal fragment brain natriuretic peptide, and NO status, inappropriately elevated ET‐1 plasma concentrations may play a predominant role in the pathogenesis of IDH. 相似文献
993.
对某公司石化污水处理系统运行情况及其易发生的问题进行了系统的分析和总结。重点针对反渗透膜的硅垢问题、活性污泥法的泡沫问题及重度污染含油污水预处理不足等现场运行中的突出问题进行分析,提出了相应的解决对策,同时对装置的运行提出一些建议,以此供相关同行借鉴和参考。 相似文献
994.
以核-壳结构的复合分子筛Al SBA-15/Y为催化剂的主要载体组分,以Ni,W为加氢成分,合成了高活性中间馏分油型加氢裂化催化剂Ni W/Al SBA-15/Y-HK,并对其催化性能进行了评价。实验结果表明,该催化剂具有中油选择性高、产品质量优等特点。在控制原料370℃馏分油转化率为67%的条件下,中间馏分油选择性为81.5%,其中柴油馏分的收率为54.7%,凝点为-40℃,是优质-10#柴油调和组分;重石脑油芳潜为54.6%,是优质的重整进料;尾油芳烃指数为11.2,是良好的乙烯裂解原料。 相似文献
995.
996.
确定性分析方法无法解释边坡安全系数处于安全值时出现结构失稳的状况,因此不确定性分析方法在边坡稳定性评价方面逐渐被广泛应用。提出基于可靠度理论的边坡不确定性分析方法,并对金堆城露天钼矿南帮9-9剖面处边坡体进行边坡稳定性分析。首先采用拉丁超立方蒙特卡洛抽样技术选取样本参数,然后用二维有限差分法对安全系数和失效概率进行求解,最后对计算结果进行Z假设检验。结果表明,在置信度为95%的情况下,边坡的安全系数是大于1.3的,此时边坡处于稳定状态。 相似文献
997.
We put forward a novel single selection transmission scheme based on maximum desired signal criterion and investigate the capacity of distributed antenna systems in multicell environment. However, for most of the recent literatures, the interference plus noise is treated as Gaussian random variable with fixed variance by the central limit theorem, which ignores the effect of the short‐term fading on interference. To avoid it, non‐central limit theorem is adopted in which the variance of interference plus noise is considered as a random variable with changeable variance influenced by the short‐term fading. Moreover, channels are assumed to suffer from independent identical Rayleigh fading together with propagation path loss, and the closed‐form expression of capacity for distributed antenna systems is derived. Finally, extensive simulations are carried out to validate the theoretical analysis. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
998.
以丙烯酸(AA)和聚乙二醇单烯丙基醚(APEG)为聚合单体,S-正十二烷基-S'-(2-甲基-2-丙酸基)三硫代碳酸酯(DDMAT)为链转移剂,偶氮二异丁腈(AIBN)为引发剂,采用可逆加成-断裂链转移(RAFT)活性自由基聚合方法,合成超分散剂P(AA-b-APEG),并通过FT-IR,GPC进行表征。研究发现聚合反应12h合成的超分散剂P3加入量为2g/L可以使TiO2颗粒在水体系中悬浮率达到99.89%,25℃静置沉降7d后,沉降率仅为4%。 相似文献
999.
1000.