全文获取类型
收费全文 | 13582篇 |
免费 | 798篇 |
国内免费 | 198篇 |
专业分类
电工技术 | 30篇 |
综合类 | 395篇 |
化学工业 | 2700篇 |
金属工艺 | 204篇 |
机械仪表 | 217篇 |
建筑科学 | 163篇 |
矿业工程 | 89篇 |
能源动力 | 635篇 |
轻工业 | 7138篇 |
水利工程 | 138篇 |
石油天然气 | 336篇 |
武器工业 | 2篇 |
无线电 | 442篇 |
一般工业技术 | 1120篇 |
冶金工业 | 124篇 |
原子能技术 | 60篇 |
自动化技术 | 785篇 |
出版年
2024年 | 71篇 |
2023年 | 460篇 |
2022年 | 545篇 |
2021年 | 654篇 |
2020年 | 639篇 |
2019年 | 506篇 |
2018年 | 487篇 |
2017年 | 517篇 |
2016年 | 645篇 |
2015年 | 774篇 |
2014年 | 958篇 |
2013年 | 892篇 |
2012年 | 1241篇 |
2011年 | 1201篇 |
2010年 | 802篇 |
2009年 | 718篇 |
2008年 | 312篇 |
2007年 | 795篇 |
2006年 | 537篇 |
2005年 | 269篇 |
2004年 | 128篇 |
2003年 | 156篇 |
2002年 | 184篇 |
2001年 | 142篇 |
2000年 | 88篇 |
1999年 | 128篇 |
1998年 | 77篇 |
1997年 | 42篇 |
1996年 | 64篇 |
1995年 | 35篇 |
1994年 | 30篇 |
1993年 | 27篇 |
1992年 | 30篇 |
1991年 | 24篇 |
1990年 | 18篇 |
1989年 | 23篇 |
1988年 | 55篇 |
1987年 | 137篇 |
1986年 | 99篇 |
1985年 | 40篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
111.
为了改善苹果酒生产中酸度低、单宁少的缺陷,以红富士苹果为原料,经榨汁、护色、海红果汁调整成分、发酵、澄清等工艺生产苹果酒,并与柠檬酸调整苹果汁成分的发酵进行对比,得出海红果汁调节苹果汁酸度酿造苹果酒优于传统的柠檬酸调酸,其优化工艺条件为:初始pH3.6,初始糖度24°Brix,发酵温度20℃,酵母接种量为0.3‰,在此条件下所得苹果酒金黄色,果香酒香协调浓郁,酒体复杂丰满. 相似文献
112.
LIU Si-mian TIAN Da-lun XIANG Wen-hua YAN Wen-de LIU Yun-guo HU Xin-jiang 《中南工业大学学报(英文版)》2014,(2):694-700
Acidic deposition,which is mainly caused by atmospheric pollution,is one of the global environmental problems.Thinning is an effective management to improve the tree productivity,reduce the wildfire risk and maintain a healthy forest.Since thinning may reduce the effect of acidic deposition,the effect of thinning on acidic deposition was estimated.The biomass,soil properties,pH value of runoff and groundwater in both unthinned and thinned Chinese fir plantations were measured and compared over a 5-year period(2-6 years after thinning).The results indicated that acidic deposition in the Huitong State Ecosystem Research Station was serious,and it got worse with time.Forest thinning resulted in a huge change in biomass and soil properties.During the 5-year monitoring period,biomasses of understory and litter,plant species richness,coverage of undergrowth plant layer were significantly higher in thinned site than in unthinned site.Moreover,higher soil fertility as well as lower amounts of runoff and groundwater were found in thinned site.It was suggested that thinning could improve the structure of forest,leading to restoring the effluent(runoff and groundwater) pH to the normal value. 相似文献
113.
Qianyu Yang Chen Gao Xuemei Zhang Xingyu Zhao Yiqing Fu Chihui Tsou Chunyan Zeng Li Yuan Zejun Pu Yiqing Xia Yuping Sheng Yu Fang 《应用聚合物科学杂志》2021,138(13):50308
Shape memory hydrogels (SMHs) can fix the hydrogels in a provisional shape and restore the initial shape under external stimulation. Herein, a dual-responsive shape memory hydrogel with dual-responsive swelling and self-healing properties is presented in this work. The SMHs were fabricated by one-step emulsion copolymerization of acrylic acid (AAc), acrylamide (AAm) and stearyl methacrylate (SMA). Sodium alginate (SA) was introduced as an interpenetrating polymer in the network. With ionic cross-linking between -COO− and Fe3+ or saline-reinforced hydrophobic association, the hydrogels can be fixed in a provisional shape, which can be restored by immersing the hydrogels in vitamin C solution or pure water, respectively. When the as-prepared hydrogels were immersed in FeCl3 solutions, additional ionic cross-linking between Fe3+ and -COO− could be formed, thus constructing the dual physically cross-linked (DPC) network, which endows the hydrogels with excellent fracture stress (2.6 MPa) and toughness (5.47 MJ/m3). Besides, the reversible physical cross-linkings endowed the hydrogel with outstanding self-healing capability. Furthermore, the pH and saline responsive swelling properties of the SMHs are additional fantastic properties. Therefore, we believe that this simple strategy provides a great opportunity for the preparation of SMHs with multiple intellectual performances. 相似文献
114.
Maolan Zhang Yuanliang Wang Guoming Zeng Shuang Yang Xiaoling Liao Da Sun 《应用聚合物科学杂志》2021,138(20):50451
Piperazine polymers poly(ethylenediaminetetraacetic dianhydride-co-piperazine) (PE) and MGF-Ct24E-modified poly(ethylenediaminetetraacetic dianhydride-co-piperazine) (PEM) showed good antibacterial activity. Considering their different applications, the effects of time, pH, and inoculation concentration of these antibacterials against Escherichia coli (E. coli) in unique environments were evaluated in this study. The results indicated that the MIC and MBC values of the polymers increased after the introduction of MGF-Ct24E into PE, but the two types of polymers still exhibited good antibacterial activity in a short time period under acidic conditions. In addition, we investigated the effect of the piperazine polymers on bacterial cell structure. It was clear that PE and PEM could destroy the bacterial cell wall, cell membrane and DNA, and their specific mechanism may be different. For PE, its carboxyl group could react with peptidoglycans on the E.coli cell wall to form holes on the bacterial surface, allowing PE to penetrate into the bacterial cell to damage DNA. For PEM, the alkaline MGF-Ct24E could adsorb E.coli and make it shrink, meanwhile, the PE component created small holes on the bacterial walls and membranes, and inserted into the bacteria to result in bactericidal effect. These findings reveal the potential usefulness of PE and PEM in biomedical applications. 相似文献
115.
Many efficient exact branch and bound maximum clique solvers use approximate coloring to compute an upper bound on the clique number for every subproblem. This technique reasonably promises tight bounds on average, but never tighter than the chromatic number of the graph.Li and Quan, 2010, AAAI Conference, p. 128–133 describe a way to compute even tighter bounds by reducing each colored subproblem to maximum satisfiability problem (MaxSAT). Moreover they show empirically that the new bounds obtained may be lower than the chromatic number.Based on this idea this paper shows an efficient way to compute related “infra-chromatic” upper bounds without an explicit MaxSAT encoding. The reported results show some of the best times for a stand-alone computer over a number of instances from standard benchmarks. 相似文献
116.
For the analysis of noise problems in medium-to-high frequency ranges, the energy flow boundary element method (EFBEM) has been studied. EFBEM is numerical analysis method of energy flow analysis (EFA), and solves energy governing equations using a boundary element method in complex structures. Based on EFBEM, a noise prediction software, “noise analysis system by energy flow analysis” (NASEFA), was developed. For effective maintenance, NASEFA is composed of three main modules: the translator, the model converter, and the main solver. The translator changes the FE model to the NASEFA BE model, and the model converter changes the BE model to an EFBE model, including various data, such as structural materials, medium properties, sources, and boundary conditions. NASEFA then solves the acoustic energy density and intensity on boundary and in the field. Moreover, it analyzes interior and exterior noise problems for single and multiple domains in two and three dimensions. Finally, for the validation of the software developed, interior and exterior noise predictions of various structures were performed. The results obtained with NASEFA were compared with those of the commercial SEA program and experiment. From these comparative studies, the usefulness of NASEFA was established. 相似文献
117.
Sustainable management of groundwater-dependent vegetation (GDV) requires the accurate identification of GDVs, characterisation of their water use dynamics and an understanding of associated errors. This paper presents sensitivity and uncertainty analyses of one GDV mapping method which uses temperature differences between time-series of modelled and observed land surface temperature (LST) to detect groundwater use by vegetation in a subtropical woodland. Uncertainty in modelled LST was quantified using the Jacobian method with error variances obtained from literature. Groundwater use was inferred where modelled and observed LST were significantly different using a Student's t-test. Modelled LST was most sensitive to low-range wind speeds (<1.5 m s−1), low-range vegetation height (<=0.5 m), and low-range leaf area index (<=0.5 m2 m−2), limiting the detectability of groundwater use by vegetation under such conditions. The model-data approach was well-suited to detection of GDV because model-data errors were lowest for climatic conditions conducive to groundwater use. 相似文献
118.
119.
Multi-objective model optimization methods have been extensively studied based on evolutionary algorithms, but less on gradient-based algorithms. This study demonstrates a framework for multi-objective model calibration/optimization using gradient-based optimization tools. Model-independent software Parameter ESTimation (PEST) was used to auto-calibrate ISWAT, a modified version of the distributed hydrologic model Soil and Water Assessment Tool (SWAT2005), in the Shenandoah River watershed. The time-series processor TSPROC was used to combine multiple objectives into the auto-calibration process. Two sets of roughness coefficients for main channels, one assigned and calibrated according on soil types and one determined via empirical equations, were examined for stream discharge simulation. Five different weighting alternatives were investigated for their effects on ISWAT calibrations. Results showed that using Manning's roughness coefficients obtained from empirical equations improves simulation results and calibration efficiency. Applying a two-step weighting alternative to different observation groups would provide the best calibration results. 相似文献
120.
Plasmodium falciparum causes the most fatal form of malaria and accounts for over 1 million deaths annually, yet currently used drug therapies are compromised by resistance. The malaria parasite cannot salvage pyrimidines and relies on de novo biosynthesis for survival. The enzyme dihydrooratate dehydrogenase (DHODH), a mitochondrial flavoenzyme, catalyzes the rate-limiting step of this pathway and is therefore an attractive anti-malarial chemotherapeutic target. In an effort to design new and potential anti-malarials, structure-based pharmacophore mapping, molecular docking, binding energy calculations and binding affinity predictions were employed in a virtual screening strategy to design new and potent P. falciparum dihydrooratate dehydrogenase (PfDHODH) inhibitors. A structure-based pharmacophore model was generated which consist of important interactions as observed in co-crystal of PfDHODH enzyme. The developed model was used to retrieve molecules from ChemBridge database, a freely available commercial database. A total of 87 molecules mapped on the modeled pharmacophore from the database. The retrieved hits were further screened by docking simulation, binding energy calculations and biding affinity predictions using genetic optimization for ligand docking (GOLD) and MOE. Based on these results, finally 26 chemo-types molecules were predicted as new, potential and structurally diverse PfDHODH inhibitors. 相似文献