全文获取类型
收费全文 | 76837篇 |
免费 | 8813篇 |
国内免费 | 8491篇 |
专业分类
电工技术 | 5921篇 |
技术理论 | 2篇 |
综合类 | 4939篇 |
化学工业 | 19484篇 |
金属工艺 | 3564篇 |
机械仪表 | 4421篇 |
建筑科学 | 3025篇 |
矿业工程 | 868篇 |
能源动力 | 2360篇 |
轻工业 | 4846篇 |
水利工程 | 885篇 |
石油天然气 | 1851篇 |
武器工业 | 604篇 |
无线电 | 11788篇 |
一般工业技术 | 8661篇 |
冶金工业 | 1919篇 |
原子能技术 | 2131篇 |
自动化技术 | 16872篇 |
出版年
2024年 | 319篇 |
2023年 | 1342篇 |
2022年 | 2154篇 |
2021年 | 2610篇 |
2020年 | 2668篇 |
2019年 | 2441篇 |
2018年 | 2146篇 |
2017年 | 3085篇 |
2016年 | 3145篇 |
2015年 | 3593篇 |
2014年 | 3663篇 |
2013年 | 4892篇 |
2012年 | 5825篇 |
2011年 | 4950篇 |
2010年 | 4363篇 |
2009年 | 4464篇 |
2008年 | 4686篇 |
2007年 | 5667篇 |
2006年 | 5480篇 |
2005年 | 4578篇 |
2004年 | 3865篇 |
2003年 | 3167篇 |
2002年 | 2560篇 |
2001年 | 1991篇 |
2000年 | 1738篇 |
1999年 | 1610篇 |
1998年 | 1280篇 |
1997年 | 1090篇 |
1996年 | 881篇 |
1995年 | 725篇 |
1994年 | 636篇 |
1993年 | 504篇 |
1992年 | 400篇 |
1991年 | 317篇 |
1990年 | 279篇 |
1989年 | 200篇 |
1988年 | 193篇 |
1987年 | 122篇 |
1986年 | 104篇 |
1985年 | 105篇 |
1984年 | 82篇 |
1983年 | 43篇 |
1982年 | 60篇 |
1981年 | 23篇 |
1980年 | 23篇 |
1979年 | 17篇 |
1978年 | 7篇 |
1977年 | 20篇 |
1976年 | 8篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
991.
We address the problem of robust and efficient treatment of element collapse and inversion in corotational FEM simulations of deformable objects in two and three dimensions, and show that existing degeneration treatment methods have previously unreported flaws that seriously threaten robustness and physical plausibility in interactive applications. We propose a new method that avoids such flaws, yields faster and smoother degeneration recovery and extends the range of well‐behaved degenerate configurations without adding significant complexity or computational cost to standard explicit and quasi‐implicit solvers. 相似文献
992.
Jens Cornelis Markus Ihmsen Andreas Peer Matthias Teschner 《Computer Graphics Forum》2014,33(2):255-262
We propose to use Implicit Incompressible Smoothed Particle Hydrodynamics (IISPH) for pressure projection and boundary handling in Fluid‐Implicit‐Particle (FLIP) solvers for the simulation of incompressible fluids. This novel combination addresses two issues of existing SPH and FLIP solvers, namely mass preservation in FLIP and efficiency and memory consumption in SPH. First, the SPH component enables the simulation of incompressible fluids with perfect mass preservation. Second, the FLIP component efficiently enriches the SPH component with detail that is comparable to a standard SPH simulation with the same number of particles, while improving the performance by a factor of 7 and significantly reducing the memory consumption. We demonstrate that the proposed IISPH‐FLIP solver can simulate incompressible fluids with a quantifiable, imperceptible density deviation below 0.1%. We show large‐scale scenarios with up to 160 million particles that have been processed on a single desktop PC using only 15GB of memory. One‐ and two‐way coupled solids are illustrated. 相似文献
993.
Since the mid-1970s new types of forest damage are observed in the Federal Republic of Germany. Typical damage symptoms in coniferous tree species are needle yellowing, reddening and premature loss of older foliage. Needle analysis carried out in damaged Norway spruce stands indicated that these phenomena, most of all needle yellowing, are influenced by the nutritional status of the trees. For the investigated sites Mg but also other elements, particularly P, S, K, Ca and Zn may play a causal role. As N is the most abundant element in the plant its form of uptake is important for a balanced nutrition. On the contrary to NO3-N high NH4-N uptake reduces the uptake of cations, particularly Mg and Ca, eventually inducing foliar discoloration symptoms on specific sites. Fertilizer experiments indicated that Mg fertilization is an appropriate tool to mitigate forest damages associated with Mg deficiency for a sustained time period. The application of N in the form of NH4-N may impede Mg uptake. This mechanism may cause severe damage in forest areas receiving continuously high NH4-N deposition. 相似文献
994.
Michael Birsak Przemyslaw Musialski Peter Wonka Michael Wimmer 《Computer Graphics Forum》2014,33(2):449-458
We present a novel framework for the automatic generation of tourist brochures that include routing instructions and additional information presented in the form of so‐called detail lenses. The first contribution of this paper is the automatic creation of layouts for the brochures. Our approach is based on the minimization of an energy function that combines multiple goals: positioning of the lenses as close as possible to the corresponding region shown in an overview map, keeping the number of lenses low, and an efficient numbering of the lenses. The second contribution is a route‐aware simplification of the graph of streets used for traveling between the points of interest (POIs). This is done by reducing the graph consisting of all shortest paths through the minimization of an energy function. The output is a subset of street segments that enable traveling between all the POIs without considerable detours, while at the same time guaranteeing a clutter‐free visualization. 相似文献
995.
996.
997.
Catherine J Watson 《Nutrient Cycling in Agroecosystems》1987,14(3):193-204
The15N isotope was used to study the mode of action of individual nitrogen sources in a 30% urea:30% ammonium nitrate: 10% ammonium sulphate:30% filler (w/w) granular fertilizer for perennial ryegrass in a greenhouse pot experiment. The fertilizer consisted of two types of granules, one containing 80% urea and 20% filler and the second containing 48% ammonium nitrate (AN), 16% ammonium sulphate (AS) and 36% filler. In addition the effect of dolomite compared with silica as the filler was investigated on nitrogen recovery from the 30:30:10:30 formulation.Dolomite adversely affected the recovery of nitrate N from the system and evidence suggested that MgCO3 was the active component. Granules containing dolomite resulted in a lower dry-matter yield than those containing silica, however the difference was not significant as nitrate contributed only 20% of the N in the formulation. AN gave the greatest DM yield and urea the lowest with AS being intermediate. The15N budget in shoots, roots and soil indicated that only 65% of the N from urea was recovered at the end of the experiment compared with 86% for AN and 91% for AS. The dry-matter yield of the 30:30:10:30 formulation using silica as the filler was intermediate between urea and AN; however, the apparent N recovery was significantly higher than expected from the sum of the individual components. The use of15N labelling indicated that using separate granules for ammonium N and urea the recovery of urea was improved by 11% in the triple N mixture when both AN and AS were present in the second granule compared to the recovery on its own. The enhanced recovery of urea appeared to be a function of AN and AS acting together as neither source in double combination with urea had any effect on urea N recovery.Urea enhanced the recovery of nitrate N by 10% but decreased the recovery of AS by 6% (in the 30:30:10:30 formulation) in comparison with the single sources on their own. The results indicate that interactions can occur between N sources even when they are physically separated by being in different granules. 相似文献
998.
999.
Ink‐eliminated sludge flour (IESF), waste residue from the recycling treatments of waste paper, was utilized as a new kind of filler to reinforce polypropylene (PP) in this research work. Different coupling agents, including maleated anhydride grafted PP (MAPP), stearic acid (SA), and titanate (NDZ‐101), were used to increase the compatibility between IESF and PP. By using different measurements, the microstructure, morphology, thermal behaviors, and mechanical properties of the IESF/PP composites were investigated in detail. It was found that IESF, as a nucleation agent, not only induced the crystallization orientation of PP but also accelerate the crystallization rate of PP. Just as indicated in the experiments, the presence of IESF has shown the advantages of increasing the dimensional stability, the hardness and the flexural property, and the presence of coupling agents has a favorable effect on the improvement of dimensional stability. Moreover, the coupling agent has minor influence on the mechanical property, even causes some decrease in the impact strength. Among these three coupling agents, MAPP is found to be the best coupling agent for increasing the interfacial adhesion between IESF and PP, and the MAPP addition makes the PP composite possess the quickest crystallization rate and greatest tensile strength. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 513–520, 2003 相似文献
1000.
环氧树脂/蒙脱土纳米复合材料性能的研究 总被引:7,自引:0,他引:7
用一种新型的热稳定性较好的改性剂2,2’-二[4-(4-氨基苯氧基)苯基]-丙烷(BAPP)改性钠基蒙脱土,再与环氧树脂进行纳米复合制备了环氧树脂/蒙脱土纳米复合材料。讨论了蒙脱土用量对环氧树脂/蒙脱土纳米复合材料性能的影响,并对其结构和性能进行了表征和测试。结果表明:改性使蒙脱土层间距变大,制备出的环氧树脂/蒙脱土纳米复合材料剥离结构较好,环氧树脂/蒙脱土纳米复合材料的玻璃化转变温度和动态储能模量随改性蒙脱土用量的增加呈现较好的递增趋势。 相似文献