全文获取类型
收费全文 | 571444篇 |
免费 | 61854篇 |
国内免费 | 47987篇 |
专业分类
电工技术 | 45152篇 |
技术理论 | 66篇 |
综合类 | 65538篇 |
化学工业 | 77870篇 |
金属工艺 | 21315篇 |
机械仪表 | 34240篇 |
建筑科学 | 57300篇 |
矿业工程 | 21578篇 |
能源动力 | 19603篇 |
轻工业 | 33518篇 |
水利工程 | 24105篇 |
石油天然气 | 22420篇 |
武器工业 | 6291篇 |
无线电 | 56774篇 |
一般工业技术 | 49884篇 |
冶金工业 | 23912篇 |
原子能技术 | 6802篇 |
自动化技术 | 114917篇 |
出版年
2024年 | 2531篇 |
2023年 | 7904篇 |
2022年 | 14776篇 |
2021年 | 17156篇 |
2020年 | 17601篇 |
2019年 | 15365篇 |
2018年 | 14494篇 |
2017年 | 18327篇 |
2016年 | 20938篇 |
2015年 | 22927篇 |
2014年 | 31678篇 |
2013年 | 33798篇 |
2012年 | 40246篇 |
2011年 | 43950篇 |
2010年 | 33738篇 |
2009年 | 34415篇 |
2008年 | 34458篇 |
2007年 | 41380篇 |
2006年 | 38608篇 |
2005年 | 33513篇 |
2004年 | 28063篇 |
2003年 | 24151篇 |
2002年 | 19299篇 |
2001年 | 15775篇 |
2000年 | 13351篇 |
1999年 | 10866篇 |
1998年 | 8639篇 |
1997年 | 7298篇 |
1996年 | 6489篇 |
1995年 | 5552篇 |
1994年 | 4805篇 |
1993年 | 3537篇 |
1992年 | 3020篇 |
1991年 | 2344篇 |
1990年 | 1993篇 |
1989年 | 1655篇 |
1988年 | 1260篇 |
1987年 | 846篇 |
1986年 | 685篇 |
1985年 | 651篇 |
1984年 | 613篇 |
1983年 | 423篇 |
1982年 | 464篇 |
1981年 | 281篇 |
1980年 | 259篇 |
1979年 | 180篇 |
1978年 | 89篇 |
1977年 | 104篇 |
1976年 | 72篇 |
1959年 | 74篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Xiao-juan Li Yi-xiang Xu Xiang Li Zhi-jiang Jin Jin-yuan Qian 《International Journal of Hydrogen Energy》2021,46(7):5537-5547
Ambient condition, especially the wind condition, is an important factor to determine the behavior of hydrogen diffusion during hydrogen release. However, only few studies aim at the quantitative study of the hydrogen diffusion in a wind-exist condition. And very little researches aiming at the variable wind condition have been done. In this paper, the hydrogen diffusion in different wind condition which including the constant wind velocity and the variable wind velocity is investigated numerically. When considering the variable wind velocity, the UDF (user defined function) is compiled. Characteristics of the FGC (flammable gas cloud) and the HMF (hydrogen mass fraction) are analyzed in different wind condition and comparisons are made with the no-wind condition. Results indicate that the constant wind velocity and the variable wind velocity have totally different effect for the determination of hydrogen diffusion. Comparisons between the constant wind velocity and the variable wind velocity indicate that the variable wind velocity may cause a more dangerous situation since there has a larger FGC volume. More importantly, the wind condition has a non-negligible effect when considering the HMF along the radial direction. As the wind velocity increases, the distribution of the HMF along the radial direction is not Gaussian anymore when the distance between the release hole and the observation line exceeds to a critical value. This work can be a supplement of the research on the hydrogen release and diffusion and a valuable reference for the researchers. 相似文献
32.
Poly(l ‐lactic acid) (PLLA) is a biodegradable and biocompatible thermoplastic polyester produced from renewable sources, widely used for biomedical devices, in food packaging and in agriculture. It is a semicrystalline polymer, and as such its properties are strongly affected by the developed semicrystalline morphology. As a function of the crystallization temperature, PLLA can form different crystal modifications, namely α′‐crystals below about 120 °C and α‐crystals at higher temperatures. The α′ modification is therefore of special importance as it may be the preferred polymorph developing at processing‐relevant conditions. It is a metastable modification which typically transforms into the more stable α‐crystals on annealing at elevated temperature. The structure, kinetics of formation and thermodynamics of α′‐ and α‐crystals of PLLA are reviewed in this contribution, together with the effect of α′‐/α‐crystal polymorphism on the properties of PLLA. © 2018 Society of Chemical Industry 相似文献
33.
Sehar Tasleem Muhammad Tahir Wesam Alsayeh Khalifa 《International Journal of Hydrogen Energy》2021,46(27):14148-14189
Photocatalytic H2 generation using semiconductor photocatalysts is considered as a cost-effective and eco-friendly technology for solar to energy conversion; however, the present photocatalysts have been recognized to depict low efficiency. Currently, porous coordination polymers known as metal-organic frameworks (MOFs) constituting flexible and modifiable porous structure and having excess active sites are considered to be appropriate for photocatalytic H2 production. This review highlights current progress in structural development of MOF materials along with modification strategies for enhanced photoactivity. Initially, the review discusses the photocatalytic H2 production mechanism with the concepts of thermodynamics and mass transfer with particular focus on MOFs. Elaboration of the structural categories of MOFs into Type I, Type II, Type III and classification of MOFs for H2 generation into transition metal based, post-transition metal based, noble-metal based and hetero-metal based has been systematically discussed. The review also critically deliberate various modification approaches of band engineering, improvement of charge separation, efficient irradiation utilization and overall efficiency of MOFs including metal modification, heterojunction formation, Z-scheme formation, by introducing electron mediator, and dye based composites. Also, the MOF synthesized derivatives for photocatalytic H2 generation are elaborated. Finally, future perspectives of MOFs for H2 generation and approaches for efficiency improvement have been suggested. 相似文献
34.
Elli Ntakou Ralph Masiello Farnaz Farzan Shay Bahramirad Aleksi Paaso M.A. Nayeem Maigha Maigha Daniel Kushner 《The Electricity Journal》2019,32(4):45-49
This paper presents part of the work ComEd and Quanta Technology have performed to quantify the locational and temporal value of DER to avoid distribution grid upgrade investments. It focuses on the formulation of a robust and efficient algorithm for DER optimal dispatch on a distribution feeder to mitigate the violation of current and voltage limits using the allocated cost of capacity and locational marginal value of real and reactive DER injection/withdrawal. 相似文献
35.
36.
37.
An electrolyte Equation of State is presented by combining the Cubic Plus Association Equation of State,Mean Spherical Approximation and the Born equation.This new model uses experimental relative static permittivity,intend to predict well the activity coefficients of individual ions (ACI) and liquid densities of aqueous solutions.This new model is applied to model water + NaCl binary system and water + gas +NaCl ternary systems.The cation/anion-water interaction parameters of are obtained by fitting the exper-imental data of ACI,mean ionic activity coefficients (MIAC) and liquid densities of water + NaCl binary system.The cation/anion-gas interaction parameters are obtained by fitting the experimental data of gas solubilities in aqueous NaCl solutions.The modeling results show that this new model can correlate well with the phase equilibrium and volumetric properties.Without gas,predictions for ACI,MIAC,and liquid densities present relative average deviations of 1.3%,3.6% and 1.4% compared to experimental ref-erence values.For most gas-containing systems,predictions for gas solubilities present relative average deviations lower than 7.0%.Further,the contributions of ACI,and salting effects of NaCl on gases are ana-lyzed and discussed. 相似文献
38.
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
39.
The effect of the emergency perception of bystanders of cyberbullying victims on helping behaviors is often neglected in research on cyberbullying. In this study, we explored the influence of this cognitive factor on cyber-bystanders’ helping tendencies as well as elucidated possible underlying processes. The results of two studies were reported. In Study 1, 150 undergraduates read a true case of a girl experiencing cyberbullying. The results indicated that when the participants perceived the victim’s situation to be more critical (i.e., higher emergency perception), their helping tendencies were stronger, partly through increased state empathy followed by feelings of responsibility to help. In Study 2, we randomly assigned 300 undergraduates to two groups. The low emergency group read the same cyberbullying case as Study 1, whereas the cyberbullying case read by the high emergency group contained additional emergency information of the victim. The results indicated that the high emergency group expressed stronger helping tendencies than did the low emergency group. This effect was caused by a stronger perception that the victim was in an emergency situation, which not only strengthened the participants’ helping tendencies directly but also indirectly through increasing their state empathy and feelings of responsibility to help. 相似文献
40.