全文获取类型
收费全文 | 241416篇 |
免费 | 26005篇 |
国内免费 | 14184篇 |
专业分类
电工技术 | 18162篇 |
技术理论 | 8篇 |
综合类 | 26224篇 |
化学工业 | 35059篇 |
金属工艺 | 10957篇 |
机械仪表 | 15953篇 |
建筑科学 | 25941篇 |
矿业工程 | 9991篇 |
能源动力 | 7200篇 |
轻工业 | 18263篇 |
水利工程 | 9380篇 |
石油天然气 | 10396篇 |
武器工业 | 3070篇 |
无线电 | 18110篇 |
一般工业技术 | 29486篇 |
冶金工业 | 9264篇 |
原子能技术 | 3293篇 |
自动化技术 | 30848篇 |
出版年
2024年 | 758篇 |
2023年 | 3390篇 |
2022年 | 6712篇 |
2021年 | 8992篇 |
2020年 | 7551篇 |
2019年 | 6754篇 |
2018年 | 6578篇 |
2017年 | 8381篇 |
2016年 | 10123篇 |
2015年 | 10899篇 |
2014年 | 15451篇 |
2013年 | 15276篇 |
2012年 | 17329篇 |
2011年 | 16816篇 |
2010年 | 13253篇 |
2009年 | 13807篇 |
2008年 | 12751篇 |
2007年 | 16323篇 |
2006年 | 15065篇 |
2005年 | 12745篇 |
2004年 | 10034篇 |
2003年 | 8717篇 |
2002年 | 7179篇 |
2001年 | 5861篇 |
2000年 | 5136篇 |
1999年 | 4244篇 |
1998年 | 3216篇 |
1997年 | 2782篇 |
1996年 | 3349篇 |
1995年 | 2566篇 |
1994年 | 2142篇 |
1993年 | 1299篇 |
1992年 | 1191篇 |
1991年 | 886篇 |
1990年 | 775篇 |
1989年 | 692篇 |
1988年 | 522篇 |
1987年 | 310篇 |
1986年 | 262篇 |
1985年 | 175篇 |
1984年 | 213篇 |
1983年 | 114篇 |
1982年 | 124篇 |
1981年 | 127篇 |
1980年 | 108篇 |
1979年 | 75篇 |
1978年 | 47篇 |
1964年 | 43篇 |
1962年 | 65篇 |
1959年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
The Interplay of Modulus,Strength, and Ductility in Adhesive Design Using Biomimetic Polymer Chemistry 下载免费PDF全文
High‐performance adhesives require mechanical properties tuned to demands of the surroundings. A mismatch in stiffness between substrate and adhesive leads to stress concentrations and fracture when the bonding is subjected to mechanical load. Balancing material strength versus ductility, as well as considering the relationship between adhesive modulus and substrate modulus, creates stronger joints. However, a detailed understanding of how these properties interplay is lacking. Here, a biomimetic terpolymer is altered systematically to identify regions of optimal bonding. Mechanical properties of these terpolymers are tailored by controlling the amount of a methyl methacrylate stiff monomer versus a similar monomer containing flexible poly(ethylene glycol) chains. Dopamine methacrylamide, the cross‐linking monomer, is a catechol moiety analogous to 3,4‐dihydroxyphenylalanine, a key component in the adhesive proteins of marine mussels. Bulk adhesion of this family of terpolymers is tested on metal and plastic substrates. Incorporating higher amounts of poly(ethylene glycol) into the terpolymer introduces flexibility and ductility. By taking a systematic approach to polymer design, the region in which material strength and ductility are balanced in relation to the substrate modulus is found, thereby yielding the most robust joints. 相似文献
93.
Karim Gharbi Louise Matthews James Bron Ron Roberts Alan Tinch Michael Stear 《Journal of the Royal Society Interface》2015,12(110)
Sea lice threaten the welfare of farmed Atlantic salmon and the sustainability of fish farming across the world. Chemical treatments are the major method of control but drug resistance means that alternatives are urgently needed. Selective breeding can be a cheap and effective alternative. Here, we combine experimental trials and diagnostics to provide a practical protocol for quantifying resistance to sea lice. We then combined quantitative genetics with epidemiological modelling to make the first prediction of the response to selection, quantified in terms of reduced need for chemical treatments. We infected over 1400 young fish with Lepeophtheirus salmonis, the most important species in the Northern Hemisphere. Mechanisms of resistance were expressed early in infection. Consequently, the number of lice per fish and the ranking of families were very similar at 7 and 17 days post infection, providing a stable window for assessing susceptibility to infection. The heritability of lice numbers within this time window was moderately high at 0.3, confirming that selective breeding is viable. We combined an epidemiological model of sea lice infection and control on a salmon farm with genetic variation in susceptibility among individuals. We simulated 10 generations of selective breeding and examined the frequency of treatments needed to control infection. Our model predicted that substantially fewer chemical treatments are needed to control lice outbreaks in selected populations and chemical treatment could be unnecessary after 10 generations of selection. Selective breeding for sea lice resistance should reduce the impact of sea lice on fish health and thus substantially improve the sustainability of Atlantic salmon production. 相似文献
94.
《Intermetallics》2015
An equiatomic CoCrFeNiMn high-entropy alloy was synthesized by mechanical alloying (MA) and spark plasma sintering (SPS). During MA, a solid solution with refined microstructure of 10 nm which consists of a FCC phase and a BCC phase was formed. After SPS consolidation, only one FCC phase can be detected in the HEA bulks. The as-sintered bulks exhibit high compressive strength of 1987 MPa. An interesting magnetic transition associated with the structure coarsening and phase transformation was observed during SPS process. 相似文献
95.
孙希东 《自动化技术与应用》2015,34(4)
本文给出一种采用DPT估计SNCK信号时宽—带宽积的方法,并通过仿真该估计方法的性能与其它估计方法进行比较.首先给出SNCK信号参数估计的一般过程.为了便于计算和理论推导,根据估计出的中心频率将接收到的SNCK信号搬移到零频,从而进一步估计其它参数,如采用DPT估计SNCK信号时宽带宽积.本文将重点研究采用DPT算法估计SNCK信号值的方法. 相似文献
96.
本文基于横向积分离散纵标方程,解析得到横向积分通量中出射通量与入射通量的关系,并根据类似于扩散方程节块展开法的输运节块中子平衡方程形式,得到了一种高效的节块离散纵标法数值迭代策略。数值结果表明,本文提出的方法可行且数值结果正确。此外,粗网有限差分(CMFD)加速技术在节块离散纵标法中也取得了非常好的应用效果。 相似文献
97.
98.
The ensemble learning paradigm has proved to be relevant to solving most challenging industrial problems. Despite its successful application especially in the Bioinformatics, the petroleum industry has not benefited enough from the promises of this machine learning technology. The petroleum industry, with its persistent quest for high-performance predictive models, is in great need of this new learning methodology. A marginal improvement in the prediction indices of petroleum reservoir properties could have huge positive impact on the success of exploration, drilling and the overall reservoir management portfolio. Support vector machines (SVM) is one of the promising machine learning tools that have performed excellently well in most prediction problems. However, its performance is a function of the prudent choice of its tuning parameters most especially the regularization parameter, C. Reports have shown that this parameter has significant impact on the performance of SVM. Understandably, no specific value has been recommended for it. This paper proposes a stacked generalization ensemble model of SVM that incorporates different expert opinions on the optimal values of this parameter in the prediction of porosity and permeability of petroleum reservoirs using datasets from diverse geological formations. The performance of the proposed SVM ensemble was compared to that of conventional SVM technique, another SVM implemented with the bagging method, and Random Forest technique. The results showed that the proposed ensemble model, in most cases, outperformed the others with the highest correlation coefficient, and the lowest mean and absolute errors. The study indicated that there is a great potential for ensemble learning in petroleum reservoir characterization to improve the accuracy of reservoir properties predictions for more successful explorations and increased production of petroleum resources. The results also confirmed that ensemble models perform better than the conventional SVM implementation. 相似文献
99.
以从自然腐败的樱桃上分离的链格孢霉(Alternaria sp.)LD3.0086为指示菌,研究苯乳酸对链格孢霉的主要抑制作用靶位。应用分光光度法测定苯乳酸对链格孢霉的最小抑菌浓度,通过卡尔科弗卢尔荧光增白剂染液(calcofluor white,CFW)染色观察苯乳酸对菌丝顶端生长的破坏作用,利用扫描电子显微镜和透射电子显微镜观察链格孢霉的超微结构变化,通过测定苯乳酸作用前后链格孢霉上清液中N-乙酰葡萄糖胺质量浓度变化研究苯乳酸对菌丝细胞壁的破坏作用,应用荧光双染色法观察苯乳酸对链格孢霉菌丝细胞膜的损伤作用。结果表明,12.5 mmol/L的苯乳酸能有效抑制链格孢霉的生长;与对照组(无菌水处理)相比,苯乳酸处理后链格孢霉顶端生长细胞无明显形变,经12.5 mmol/L苯乳酸处理的链格孢霉上清液中N-乙酰葡萄糖胺质量浓度基本不变;苯乳酸处理24 h,链格孢霉菌丝细胞壁表面无明显损伤,细胞内结构发生明显变化;苯乳酸短时间(4 h)处理链格孢霉,菌丝细胞膜仍较为完整,加入苯乳酸较长时间(8 h)后细胞膜发生破裂。综合分析可知,苯乳酸对链格孢霉的主要作用靶位应不是菌丝体的细胞壁和细胞膜,而是在菌丝体内部,通过破坏菌丝内部细胞器结构或引起细胞内的生化反应,从而抑制链格孢霉的生长和繁殖,发挥抑菌活性。 相似文献
100.