全文获取类型
收费全文 | 22610篇 |
免费 | 1586篇 |
国内免费 | 639篇 |
专业分类
电工技术 | 1002篇 |
技术理论 | 2篇 |
综合类 | 868篇 |
化学工业 | 3670篇 |
金属工艺 | 1066篇 |
机械仪表 | 1194篇 |
建筑科学 | 1520篇 |
矿业工程 | 517篇 |
能源动力 | 598篇 |
轻工业 | 1225篇 |
水利工程 | 262篇 |
石油天然气 | 1215篇 |
武器工业 | 105篇 |
无线电 | 3348篇 |
一般工业技术 | 3147篇 |
冶金工业 | 1997篇 |
原子能技术 | 183篇 |
自动化技术 | 2916篇 |
出版年
2024年 | 82篇 |
2023年 | 342篇 |
2022年 | 558篇 |
2021年 | 760篇 |
2020年 | 591篇 |
2019年 | 538篇 |
2018年 | 648篇 |
2017年 | 616篇 |
2016年 | 601篇 |
2015年 | 733篇 |
2014年 | 931篇 |
2013年 | 1290篇 |
2012年 | 1287篇 |
2011年 | 1385篇 |
2010年 | 1161篇 |
2009年 | 1187篇 |
2008年 | 1233篇 |
2007年 | 1109篇 |
2006年 | 1112篇 |
2005年 | 922篇 |
2004年 | 763篇 |
2003年 | 685篇 |
2002年 | 612篇 |
2001年 | 557篇 |
2000年 | 538篇 |
1999年 | 613篇 |
1998年 | 796篇 |
1997年 | 570篇 |
1996年 | 470篇 |
1995年 | 402篇 |
1994年 | 286篇 |
1993年 | 256篇 |
1992年 | 185篇 |
1991年 | 132篇 |
1990年 | 119篇 |
1989年 | 96篇 |
1988年 | 78篇 |
1987年 | 67篇 |
1986年 | 58篇 |
1985年 | 76篇 |
1984年 | 44篇 |
1983年 | 31篇 |
1982年 | 46篇 |
1981年 | 42篇 |
1980年 | 32篇 |
1979年 | 28篇 |
1978年 | 19篇 |
1977年 | 23篇 |
1976年 | 45篇 |
1973年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 20 毫秒
1.
The process characteristics and control strategy of a high-purity IPA reactive distillation column were investigated. A robust nominal operation was found by maintaining an excess of propylene feed to the column and recycling the unreacted propylene to the feed instead of the top stage. Stage temperature and propylene composition with one-to-one relationship with reboiler duty and propylene feed are selected as controlled variables for maintaining bottom purity and feed ratio in the presence of possible measurement bias respectively. High nonlinearity between selected input–output pair was reduced by using variable transformation. Dynamic simulations demonstrated that such a control scheme with nonlinear transformed variable was capable of providing much superior control performance than the one using natural variable. 相似文献
2.
文中对万家寨引黄工程北干线1号隧洞Ⅳ标使用的155—274型TBM主轴承总成各部件组装过程及其相应的技术要求进行了概要的描述,目的是进一步熟悉155—274型TBM主轴承总成的各个部件并加深对主轴承工作原理的理解。 相似文献
3.
A stochastic model for local disturbances, particularly for a temporal harmonic with random modulations in amplitude and/or phase, is proposed in this paper. Results for the second moment responses of a linear single-degree-of-freedom system to this type of stochastic loading demonstrate a significant change in response characteristics due to a small uncertainty. A local phenomenon may last much longer and resonance may be smeared to a broad range. Integrated with wavelet transform, the proposed approach may be used to model a random process with non-stationary frequency content. Especially, it can be effectively used for Monte Carlo simulation to generate large size of samples that have similar characteristics in time and frequency domains as a pre-selected mother sample has. The technique has a great potential for the case where uncertainty study is warranted but the available samples are limited. 相似文献
4.
5.
6.
N. Mitchell A. Alekseev R. Gallix D. Holland R. Meyder A. Panin M. Shimada F. Wong E. Zapretelina 《Journal of Fusion Energy》1997,16(1-2):25-35
The ITER magnet system consists of structurally linked sets of toroidal (TF) and poloidal (PF) field coils, central solenoid (CS), and various support structures. The coils are superconducting, force flow Helium cooled with a Kapton-Glass-Epoxy multilayer insulation system. The stored magnetic energy is about 100GJ in the TF system and 20GJ in the PF-CS. Coils and structure are maintained at 4 K by enclosing them in a vacuum cryostat. The cryostat, comprising an outer envelope to the magnets, forms most of the second radioactivity confinement barrier. The inner primary barrier is formed by the vacuum vessel, its ports and their extensions. To keep the machine size within acceptable bounds, it is essential that the magnets are in close proximity to both of the nuclear confinement barriers. The objective of the magnet design is that, although local damage to one of the barriers may occur in very exceptional circumstances, large scale magnet structural or thermal failure leading to simultaneous breaching of both barriers is not credible. Magnet accidents fall into three categories: thermal (which includes arcing arising from insulation failure and local overheating due to discharge failure in the event of a superconductor quench), structural (which includes component mechanical failure arising from material inadequacies, design errors and exceptional force patterns arising from coil shorts or control failures), and fluid (Helium release due to cooling line failure). After a preliminary survey to select initial faults conceivable within the present design, these faults are systematically analyzed to provide an assessment of the damage potential. The results of this damage assessment together with an assessment of the reliability of the monitoring and protective systems, shows that the magnets can operate with the required safety condition. 相似文献
7.
8.
Three sporulation-specific genes (orfA, sigE, sigG) from clostridium acetobutylicum ATCC 824 are arranged in a cluster, encoding the putative sigma E-processing enzyme, sigma E, and sigma sigma G respectively. When they were transformed into Clostridium acetobutylicum while on a plasmid functional in this organism, transformants did not survive. Three kinds of recombinations were then attempted with nonreplicative plasmids: duplication of orfA and sigE, replacement of all of the three genes, and inactivation of orfA. While the wild-type strain ceased to grow and produce solvents in batch cultures after approximately 24 h, mutant strains were isolated that showed sustained growth for a much longer time and produced a threefold increase in acetone and butanol in test tube cultures. In addition, one of the derived strains showed a significantly higher growth rate. Features of the restriction maps of the recombinants did not correlate with expected maps, indicating possible complications occurring during the recombination events. 相似文献
9.
The phenotypic characteristics of three Serpulina pilosicoli strains isolated from humans with diarrhoea (WesB, Kar, Hrm7) and two porcine S. pilosicoli strains isolated from pigs with intestinal spirochaetosis (1648, 3295), were compared with the type strain of the species P43/6/78T (T = type strain) and other intestinal spirochaetes within the genus Serpulina. All S. pilosicoli strains had a characteristic ultrastructural appearance, displayed similar growth rates, hydrolysed hippurate, lacked beta-glucosidase activity, utilised D-ribose as a growth substrate, and had similar sensitivities to rifampicin and spiramycin. The only consistent phenotypic characteristic that differentiated human strains from porcine strains of S. pilosicoli was that the human strains all utilised the pentose sugar D-xylose. These distinguishing phenotypic traits appear useful for identifying S. pilosicoli. 相似文献
10.
摩托罗拉微控制器(MCU)具有编程语言简单、外围设备齐全、存储器模型用户友好、选择广及供应多、性能价格比高等优点,被设计者评为最容易使用的产品之一。在全球顶级的原始设备制造厂商(OEM)的无数嵌入式系统和用户最终产品中都可找到摩托罗拉的MCU,包括键盘、传呼机、电子游戏机、洗衣机、安全系统及汽车等。 相似文献