全文获取类型
收费全文 | 53686篇 |
免费 | 6575篇 |
国内免费 | 3938篇 |
专业分类
电工技术 | 6068篇 |
技术理论 | 6篇 |
综合类 | 6239篇 |
化学工业 | 5165篇 |
金属工艺 | 2942篇 |
机械仪表 | 4047篇 |
建筑科学 | 5717篇 |
矿业工程 | 1669篇 |
能源动力 | 1253篇 |
轻工业 | 1963篇 |
水利工程 | 1410篇 |
石油天然气 | 2173篇 |
武器工业 | 713篇 |
无线电 | 6454篇 |
一般工业技术 | 5980篇 |
冶金工业 | 2162篇 |
原子能技术 | 494篇 |
自动化技术 | 9744篇 |
出版年
2024年 | 310篇 |
2023年 | 878篇 |
2022年 | 1615篇 |
2021年 | 1832篇 |
2020年 | 2063篇 |
2019年 | 1737篇 |
2018年 | 1466篇 |
2017年 | 1965篇 |
2016年 | 2109篇 |
2015年 | 2202篇 |
2014年 | 3682篇 |
2013年 | 3387篇 |
2012年 | 4167篇 |
2011年 | 4420篇 |
2010年 | 3276篇 |
2009年 | 3412篇 |
2008年 | 3104篇 |
2007年 | 3720篇 |
2006年 | 3082篇 |
2005年 | 2719篇 |
2004年 | 2275篇 |
2003年 | 1934篇 |
2002年 | 1604篇 |
2001年 | 1406篇 |
2000年 | 1111篇 |
1999年 | 928篇 |
1998年 | 705篇 |
1997年 | 638篇 |
1996年 | 487篇 |
1995年 | 440篇 |
1994年 | 330篇 |
1993年 | 234篇 |
1992年 | 226篇 |
1991年 | 160篇 |
1990年 | 139篇 |
1989年 | 129篇 |
1988年 | 80篇 |
1987年 | 40篇 |
1986年 | 20篇 |
1985年 | 22篇 |
1984年 | 33篇 |
1983年 | 20篇 |
1982年 | 19篇 |
1981年 | 11篇 |
1980年 | 16篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1966年 | 4篇 |
1961年 | 6篇 |
1959年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
吴敬东 《湖南工业职业技术学院学报》2015,(2):137-140
高校是培养人才的摇篮,肩负着科教兴国、人才强国两大历史性战略任务。由于社会环境的复杂化,人际关系的交错性,新时代的大学生行为状况给高校学生管理工作带来了新的挑战。针对新时期大学生行为特点,我们通过加强党建工作、强化学风建设、做好班级自主管理和深化社会服务四个方面工作进行分析,提出了全面引导、约束、规范和优化大学生的行为的建议和对策,从而有效解决新形势下普通高校学生管理工作的实际困难。 相似文献
2.
3.
Three N-heteroleptic Pt(II) complexes, [Pt(C^C)(O^O)] [O^O = acetylacetonate, C^C = 1-phenyl-1,2,4-triazol-5-ylidene (1), C^C = 4-phenyl-1,2,4-triazol-5-ylidene (2), C^C = 2-phenylpyrazine (3)] have been investigated with density functional theory (DFT) and time-dependent density functional theory (TDDFT). The radiative decay rate constants of complexes 1–3 have been discussed with the oscillator strength (fn), the strength of spin–orbit coupling (SOC) interaction between the lowest energy triplet excited state (T1) and singlet excited states (Sn), and the energy gaps between E(T1) and E(Sn). To illustrate the nonradiative decay processes, the transition states between triplet metal-centered (3MC) and T1 states have been optimized and were verified with the calculations of vibrational frequencies and intrinsic reaction coordinate (IRC). In addition, the minimum energy crossing points (MECPs) between 3MC and ground states (S0) were optimized. At last, the potential energy curves relevant to the nonradiative decay pathways are simulated. The results show that complex 3 has the biggest photoluminescence quantum yield because the complex 3 has the biggest radiative decay rate constant and the smallest nonradiative decay rate constant in complexes 1–3. 相似文献
4.
This study demonstrates the application of an improved Evolutionary optimization Algorithm (EA), titled Multi-Objective Complex Evolution Global Optimization Method with Principal Component Analysis and Crowding Distance Operator (MOSPD), for the hydropower reservoir operation of the Oroville–Thermalito Complex (OTC) – a crucial head-water resource for the California State Water Project (SWP). In the OTC's water-hydropower joint management study, the nonlinearity of hydropower generation and the reservoir's water elevation–storage relationship are explicitly formulated by polynomial function in order to closely match realistic situations and reduce linearization approximation errors. Comparison among different curve-fitting methods is conducted to understand the impact of the simplification of reservoir topography. In the optimization algorithm development, techniques of crowding distance and principal component analysis are implemented to improve the diversity and convergence of the optimal solutions towards and along the Pareto optimal set in the objective space. A comparative evaluation among the new algorithm MOSPD, the original Multi-Objective Complex Evolution Global Optimization Method (MOCOM), the Multi-Objective Differential Evolution method (MODE), the Multi-Objective Genetic Algorithm (MOGA), the Multi-Objective Simulated Annealing approach (MOSA), and the Multi-Objective Particle Swarm Optimization scheme (MOPSO) is conducted using the benchmark functions. The results show that best the MOSPD algorithm demonstrated the best and most consistent performance when compared with other algorithms on the test problems. The newly developed algorithm (MOSPD) is further applied to the OTC reservoir releasing problem during the snow melting season in 1998 (wet year), 2000 (normal year) and 2001 (dry year), in which the more spreading and converged non-dominated solutions of MOSPD provide decision makers with better operational alternatives for effectively and efficiently managing the OTC reservoirs in response to the different climates, especially drought, which has become more and more severe and frequent in California. 相似文献
6.
7.
针对甲醇液相氧化羰基化法合成碳酸二甲酯(DMC)工艺,开发了新型Cu基络合催化剂(CuB rnLm)。对CuB rnLm催化剂的活性及其稳定性进行了研究。实验结果表明,采用该催化剂,甲醇转化率和DMC选择性较高;元素价态和物质结构分析表明,CuB rnLm催化剂循环使用5次后仍保持较好的稳定性。采用正交设计和中心响应曲面法设计实验,并使用S tatistica软件进行统计分析,寻求出反应的主要影响因素,并得到优化的工艺条件:反应温度100~110℃、反应压力3.0~3.5M Pa、反应时间4~6h、CuB rnLm催化剂质量浓度(以甲醇的体积计)0.15~0.20g/mL。在此工艺条件下,甲醇转化率可达23%以上,DMC的选择性为96%~98%。 相似文献
8.
Aqueous solutions of poly(vinyl pyrrolidone)-fullerene complexes (PVP-C70) have been studied using static and dynamic light scattering methods. Two diffusive processes were detected. The slow diffusion was interpreted as dynamics of large intermolecular PVP-C70 complexes while the fast diffusion was associated with the presence of individual PVP molecules in solution. It was also shown that the molecular weights and dimensions of PVP-C70 complexes are smaller than for PVP-C60 by a factor of 2.5-3. In aqueous solutions of PVP-C70 complex the depolarization and dissymmetry of scattered light were observed in contrast to PVP-C60 solutions. It reveals the existence of anisotropic structures in PVP-C70 solutions. Intermolecular interactions within PVP-C70 complexes are weak and a hydrodynamic field can destroy complexes. 相似文献
9.
10.
The microstructural aspects of compressive inelastic deformation in balsa wood are investigated with emphasis on the failure mode transition and its effects on energy dissipation characteristics. The architectural features as well as the composite character of cell wall ultrastructure are discussed in a framework to understand the complex interrelationship between microstructure and macroscopic behavior in this extremely lightweight cellular biocomposite. Based on this discussion and experimental results, it is concluded that the biomimetic approach may prove to be a viable strategy in designing composite structures with high specific energy absorption capacity. 相似文献