全文获取类型
收费全文 | 468569篇 |
免费 | 47219篇 |
国内免费 | 26977篇 |
专业分类
电工技术 | 31810篇 |
技术理论 | 43篇 |
综合类 | 49928篇 |
化学工业 | 55361篇 |
金属工艺 | 16792篇 |
机械仪表 | 24546篇 |
建筑科学 | 63683篇 |
矿业工程 | 22524篇 |
能源动力 | 18884篇 |
轻工业 | 37670篇 |
水利工程 | 33408篇 |
石油天然气 | 26795篇 |
武器工业 | 5324篇 |
无线电 | 28651篇 |
一般工业技术 | 33862篇 |
冶金工业 | 21697篇 |
原子能技术 | 4085篇 |
自动化技术 | 67702篇 |
出版年
2024年 | 2220篇 |
2023年 | 6410篇 |
2022年 | 12014篇 |
2021年 | 14947篇 |
2020年 | 15428篇 |
2019年 | 12440篇 |
2018年 | 11841篇 |
2017年 | 14505篇 |
2016年 | 17044篇 |
2015年 | 18073篇 |
2014年 | 30800篇 |
2013年 | 28785篇 |
2012年 | 33997篇 |
2011年 | 36578篇 |
2010年 | 27836篇 |
2009年 | 28711篇 |
2008年 | 26788篇 |
2007年 | 32222篇 |
2006年 | 28981篇 |
2005年 | 25299篇 |
2004年 | 20804篇 |
2003年 | 18361篇 |
2002年 | 15150篇 |
2001年 | 12279篇 |
2000年 | 10452篇 |
1999年 | 8125篇 |
1998年 | 6045篇 |
1997年 | 5061篇 |
1996年 | 4316篇 |
1995年 | 3682篇 |
1994年 | 3020篇 |
1993年 | 2164篇 |
1992年 | 1775篇 |
1991年 | 1303篇 |
1990年 | 1055篇 |
1989年 | 964篇 |
1988年 | 596篇 |
1987年 | 472篇 |
1986年 | 366篇 |
1985年 | 390篇 |
1984年 | 327篇 |
1983年 | 220篇 |
1982年 | 165篇 |
1981年 | 123篇 |
1980年 | 155篇 |
1979年 | 96篇 |
1978年 | 43篇 |
1977年 | 43篇 |
1975年 | 25篇 |
1959年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Somnath Karmakar 《Polycyclic Aromatic Compounds》2019,39(2):159-171
Eigensolutions of {X( = C,B,N),Y( = C,B,N)}-cyclacene graphs with next nearest neighbor (nnn) interactions have been obtained in analytical forms by adapting n-fold rotational symmetry followed by two-fold rotational symmetry (or a plane of symmetry). Expressions of eigensolution indicate the subspectral relationship among such cyclacenes with an even number of hexagonal rings e.g., eigenvalues of {X,Y}-di-cyclacene are found in the eigenspectra of all such even cyclacenes. Total π-electron energies and highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO–LUMO) gaps are calculated using the analytical expressions obtained and are found to vary negligibly with the variation of nnn interactions in such cyclacenes. Total π-electron energy is found to increase due to increase in restriction intensity of nnn interactions, whereas the HOMO–LUMO gap of polyacenecs having the even number of hexagonal rings and with one electron at each site (atom) decreases with increase in the restriction intensity since such systems contain degenerate half-filled HOMO (bonding or nonbonding) that are much more vulnerable for perturbations imposed through nnn interactions. 相似文献
72.
73.
Mahmoud Elsisi 《国际智能系统杂志》2020,35(11):1857-1878
The controller design for the robotic manipulator faces different challenges such as the system's nonlinearities and the uncertainties of the parameters. Furthermore, the tracking of different linear and nonlinear trajectories represents a vital role by the manipulator. This paper suggests an optimal design for the nonlinear model predictive control (NLMPC) based on a new improved intelligent technique and it is named modified multitracker optimization algorithm (MMTOA). The proposed modification of the MTOA is carried out based on opposition-based learning (OBL) and quasi OBL approaches. This modification improves the exploration behavior of the MTOA to prevent it from becoming trapped in a local optimum. The proposed method is applied on the robotic manipulator to track different linear and nonlinear trajectories. The NLMPC parameters are tuned by the MMTOA rather than the trial and error method of the designer. The proposed NLMPC based on MMTOA is compared with the original MTOA, genetic algorithm, and cuckoo search algorithm in literature. The superiority and effectiveness of the proposed controller are confirmed to track different linear and nonlinear trajectories. Furthermore, the robustness of the proposed method is emphasized against the uncertainties of the parameters. 相似文献
74.
75.
76.
《International Journal of Hydrogen Energy》2019,44(5):2905-2917
In this study, a multi-tubular thermally coupled packed bed reactor in which simultaneous production of ammonia and methyl ethyl ketone (MEK) takes place is simulated. The simulation results are presented in two co-current and counter-current flow modes. Based on this new configuration, the released heat from the ammonia synthesis reaction as an extremely exothermic reaction in the inner tube is employed to supply the required heat for the endothermic 2-butanol dehydrogenation reaction in the outer tube. On the other hand, MEK and hydrogen are produced by the dehydrogenation reaction of 2-butanol in the endothermic side, and the produced hydrogen is used to supply a part of the ammonia synthesis feed in the exothermic side. Thus, 30.72% and 31.88% of the required hydrogen for the ammonia synthesis are provided by the dehydrogenation reaction in the co-current and counter-current configurations, respectively. Also, according to the thermal coupling, the required cooler and furnace for the ammonia synthesis and 2-butanol dehydrogenation conventional plants are eliminated, respectively. As a result, operational costs, energy consumption and furnace emissions are considerably decreased. Finally, a sensitivity analysis and optimization are applied to study the effect of the main process parameters variation on the system performance and obtain the minimum hydrogen make-up flow rate, respectively. 相似文献
77.
《Food Control》2015
The main objective of this study was to develop the primary and secondary models to describe the growth kinetics of Salmonella as well as background microorganisms in raw, shucked oysters. Samples, inoculated with a cocktail of two Salmonella serotypes, S. Typhimurium (CICC22956) and S. Enteritidis (CICC21482), were incubated at 4, 8, 12, 16, 20, 25, 30, 33, 37, 40, and 43 °C. Growth of Salmonella was observed at all temperatures, except at 4 °C. The background microorganisms grew at all temperatures. All growth curves clearly exhibited lag, exponential and stationary phases, and were analyzed using the Huang growth model. Three secondary models (Ratkowsky square-root, Huang square-root, and Cardinal parameter models) were compared for evaluating the effect of temperature on bacterial growth rates. Data analysis was performed using IPMP 2013, a free predictive microbiology software tool developed by the USDA ARS.The Cardinal parameters model underestimated the specific rates of the microorganisms at low temperatures. The Huang square-root model was more suitable than the Ratkowsky square-root model for describing the effect of temperature on growth of Salmonella, while the Ratkowsky square-root model, on the other hand, was more suitable for background microorganisms. For both Salmonella and background microorganisms, the logarithms of the lag phase were expressed as linear functions of the logarithms of specific growth rates. The results of this study can be used by the food retailers and regulatory agencies to estimate the microbial shelf-life of raw, shucked oysters. 相似文献
78.
A 2D computational fluid dynamics (Eulerian–Eulerian) multiphase flow model coupled with a population balance model (CFD-PBM) was implemented to investigate the fluidization structure in terms of entrance region in an industrial-scale gas phase fluidized bed reactor. The simulation results were compared with the industrial data, and good agreement was observed. Two cases including perforated distributor and complete sparger were applied to examine the flow structure through the bed. The parametric sensitivity analysis of time step, number of node, drag coefficient, and specularity coefficient was carried out. It was found that the results were more sensitive to the drag model. The results showed that the entrance configuration has significant effect on the flow structure. While the dead zones are created in both corners of the distributors, the perforated distributor generates more startup bubbles, heterogeneous flow field, and better gas–solid interaction above the entrance region due to jet formation. 相似文献
79.
80.
本文以云杉八齿小蠹Ips typographus Linnaeus为例,经标本选取,观察虫体整体形态,绘制整体结构草图,电子显微镜观察局部、得到局部数字图像,分别建立虫体每一部分的高精度细节。把模型每部分拼装在一起组成整体模型,构建出了云杉八齿小蠹三维虚拟昆虫数字化模型。 相似文献