全文获取类型
收费全文 | 331940篇 |
免费 | 6182篇 |
国内免费 | 875篇 |
专业分类
电工技术 | 5334篇 |
综合类 | 199篇 |
化学工业 | 55498篇 |
金属工艺 | 12703篇 |
机械仪表 | 9497篇 |
建筑科学 | 8336篇 |
矿业工程 | 1939篇 |
能源动力 | 8002篇 |
轻工业 | 34082篇 |
水利工程 | 3638篇 |
石油天然气 | 7285篇 |
武器工业 | 19篇 |
无线电 | 33334篇 |
一般工业技术 | 63706篇 |
冶金工业 | 59698篇 |
原子能技术 | 7757篇 |
自动化技术 | 27970篇 |
出版年
2021年 | 3413篇 |
2020年 | 2594篇 |
2019年 | 3099篇 |
2018年 | 5280篇 |
2017年 | 5240篇 |
2016年 | 5675篇 |
2015年 | 3818篇 |
2014年 | 5953篇 |
2013年 | 15451篇 |
2012年 | 9490篇 |
2011年 | 12036篇 |
2010年 | 9760篇 |
2009年 | 10753篇 |
2008年 | 10923篇 |
2007年 | 10562篇 |
2006年 | 9122篇 |
2005年 | 8430篇 |
2004年 | 7870篇 |
2003年 | 7494篇 |
2002年 | 7491篇 |
2001年 | 7102篇 |
2000年 | 6737篇 |
1999年 | 6841篇 |
1998年 | 17532篇 |
1997年 | 12842篇 |
1996年 | 9779篇 |
1995年 | 7206篇 |
1994年 | 6485篇 |
1993年 | 6367篇 |
1992年 | 4669篇 |
1991年 | 4641篇 |
1990年 | 4441篇 |
1989年 | 4472篇 |
1988年 | 4423篇 |
1987年 | 3758篇 |
1986年 | 3728篇 |
1985年 | 4318篇 |
1984年 | 4087篇 |
1983年 | 3709篇 |
1982年 | 3531篇 |
1981年 | 3688篇 |
1980年 | 3551篇 |
1979年 | 3428篇 |
1978年 | 3514篇 |
1977年 | 4142篇 |
1976年 | 5465篇 |
1975年 | 3212篇 |
1974年 | 3051篇 |
1973年 | 3080篇 |
1972年 | 2663篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Multimedia Tools and Applications - Remote Sensing categorical signature classification has gained significant implications on spatial resolution image analysis due to differences in the... 相似文献
2.
3.
Chumakov Yu. A. Knyazeva A. G. Pribytkov G. A. 《Theoretical Foundations of Chemical Engineering》2021,55(3):490-503
Theoretical Foundations of Chemical Engineering - On the basis of the classic concepts of the theory of solid-phase combustion, for the first time, a model with a detailed scheme of chemical... 相似文献
4.
Engineering new glass compositions have experienced a sturdy tendency to move forward from (educated) trial-and-error to data- and simulation-driven strategies. In this work, we developed a computer program that combines data-driven predictive models (in this case, neural networks) with a genetic algorithm to design glass compositions with desired combinations of properties. First, we induced predictive models for the glass transition temperature (Tg) using a dataset of 45,302 compositions with 39 different chemical elements, and for the refractive index (nd) using a dataset of 41,225 compositions with 38 different chemical elements. Then, we searched for relevant glass compositions using a genetic algorithm informed by a design trend of glasses having high nd (1.7 or more) and low Tg (500 °C or less). Two candidate compositions suggested by the combined algorithms were selected and produced in the laboratory. These compositions are significantly different from those in the datasets used to induce the predictive models, showing that the used method is indeed capable of exploration. Both glasses met the constraints of the work, which supports the proposed framework. Therefore, this new tool can be immediately used for accelerating the design of new glasses. These results are a stepping stone in the pathway of machine learning-guided design of novel glasses. 相似文献
5.
Journal of Chemical Ecology - Biocontrol agents such as parasitic wasps use long-range volatiles and host-associated cues from lower trophic levels to find their hosts. However, this chemical... 相似文献
6.
David Diaz Elisa Lopez-Dolado Sergio Haro Jorge Monserrat Carlos Martinez-Alonso Dimitrios Balomeros Agustín Albillos Melchor Alvarez-Mon 《International journal of molecular sciences》2021,22(2)
Our aim was to investigate the subset distribution and function of circulating monocytes, proinflammatory cytokine levels, gut barrier damage, and bacterial translocation in chronic spinal cord injury (SCI) patients. Thus, 56 SCI patients and 28 healthy donors were studied. The levels of circulating CD14+highCD16−, CD14+highCD16+, and CD14+lowCD16+ monocytes, membrane TLR2, TLR4, and TLR9, phagocytic activity, ROS generation, and intracytoplasmic TNF-α, IL-1, IL-6, and IL-10 after lipopolysaccharide (LPS) stimulation were analyzed by polychromatic flow cytometry. Serum TNF-α, IL-1, IL-6 and IL-10 levels were measured by Luminex and LPS-binding protein (LBP), intestinal fatty acid-binding protein (I-FABP) and zonulin by ELISA. SCI patients had normal monocyte counts and subset distribution. CD14+highCD16− and CD14+highCD16+ monocytes exhibited decreased TLR4, normal TLR2 and increased TLR9 expression. CD14+highCD16− monocytes had increased LPS-induced TNF-α but normal IL-1, IL-6, and IL-10 production. Monocytes exhibited defective phagocytosis but normal ROS production. Patients had enhanced serum TNF-α and IL-6 levels, normal IL-1 and IL-10 levels, and increased circulating LBP, I-FABP, and zonulin levels. Chronic SCI patients displayed impaired circulating monocyte function. These patients exhibited a systemic proinflammatory state characterized by enhanced serum TNF-α and IL-6 levels. These patients also had increased bacterial translocation and gut barrier damage. 相似文献
7.
Journal of Communications Technology and Electronics - A statistical study of the effectiveness of the non-threshold search procedure for a noise-like phase-shift keyed signal by the delay time is... 相似文献
8.
Golam Haider Krishna Sampathkumar Tim Verhagen Lukáš Nádvorník Farjana J. Sonia Václav Valeš Jan Sýkora Peter Kapusta Petr Němec Martin Hof Otakar Frank Yang-Fang Chen Jana Vejpravová Martin Kalbáč 《Advanced functional materials》2021,31(29):2102196
Recent advancements in isolation and stacking of layered van der Waals materials have created an unprecedented paradigm for demonstrating varieties of 2D quantum materials. Rationally designed van der Waals heterostructures composed of monolayer transition-metal dichalcogenides (TMDs) and few-layer hBN show several unique optoelectronic features driven by correlations. However, entangled superradiant excitonic species in such systems have not been observed before. In this report, it is demonstrated that strong suppression of phonon population at low temperature results in a formation of a coherent excitonic-dipoles ensemble in the heterostructure, and the collective oscillation of those dipoles stimulates a robust phase synchronized ultra-narrow band superradiant emission even at extremely low pumping intensity. Such emitters are in high demand for a multitude of applications, including fundamental research on many-body correlations and other state-of-the-art technologies. This timely demonstration paves the way for further exploration of ultralow-threshold quantum-emitting devices with unmatched design freedom and spectral tunability. 相似文献
9.
Ahmed Fathy Mohammad Ali Abdelkareem A.G. Olabi Hegazy Rezk 《International Journal of Hydrogen Energy》2021,46(8):6087-6099
Cell temperature and water content of the membrane have a significant effect on the performance of fuel cells. The current-power curve of the fuel cell has a maximum power point (MPP) that is needed to be tracked. This study presents a novel strategy based on a salp swarm algorithm (SSA) for extracting the maximum power of proton-exchange membrane fuel cell (PEMFC). At first, a new formula is derived to estimate the optimal voltage of PEMFC corresponding to MPP. Then the error between the estimated voltage at MPP and the actual terminal voltage of the fuel cell is fed to a proportional-integral-derivative controller (PID). The output of the PID controller tunes the duty cycle of a boost converter to maximize the harvested power from the PEMFC. SSA determines the optimal gains of PID. Sensitivity analysis is performed with the operating fuel cell at different cell temperature and water content of the membrane. The obtained results through the proposed strategy are compared with other programmed approaches of incremental resistance method, Fuzzy-Logic, grey antlion optimizer, wolf optimizer, and mine-blast algorithm. The obtained results demonstrated high reliability and efficiency of the proposed strategy in extracting the maximum power of the PEMFC. 相似文献
10.
Paola Leonor Quan Marina Sabat-Bresc Yanru Guo Margarita Martín Gabriel Gastaminza 《International journal of molecular sciences》2021,22(9)
Recent research on mast cell biology has turned its focus on MRGPRX2, a new member of the Mas-related G protein-coupled subfamily of receptors (Mrgprs), originally described in nociceptive neurons of the dorsal root ganglia. MRGPRX2, a member of this group, is present not only in neurons but also in mast cells (MCs), specifically, and potentially in other cells of the immune system, such as basophils and eosinophils. As emerging new functions for this receptor are studied, a variety of both natural and pharmacologic ligands are being uncovered, linked to the ability to induce receptor-mediated MC activation and degranulation. The diversity of these ligands, characterized in their human, mice, or rat homologues, seems to match that of the receptor’s interactions. Natural ligands include host defense peptides, basic molecules, and key neuropeptides such as substance P and vasointestinal peptide (known for their role in the transmission of pain and itch) as well as eosinophil granule-derived proteins. Exogenous ligands include MC secretagogues such as compound 48/80 and mastoparan, a component of bee wasp venom, and several peptidergic drugs, among which are members of the quinolone family, neuromuscular blocking agents, morphine, and vancomycin. These discoveries shed light on its capacity as a multifaceted participant in naturally occurring responses within immunity and neural stimulus perception, as in responses at the center of immune pathology. In host defense, the mice Mrgprb2 has been proven to aid mast cells in the detection of peptidic molecules from bacteria and in the release of peptides with antimicrobial activities and other immune mediators. There are several potential actions described for it in tissue homeostasis and repair. In the realm of pathologic response, there is evidence to suggest that this receptor is also involved in chronic inflammation. Furthermore, MRGPRX2 has been linked to the pathophysiology of non-IgE-mediated immediate hypersensitivity drug reactions. Different studies have shown its possible role in other allergic diseases as well, such as asthma, atopic dermatitis, contact dermatitis, and chronic spontaneous urticaria. In this review, we sought to cover its function in physiologic processes and responses, as well as in allergic and nonallergic immune disease. 相似文献