全文获取类型
收费全文 | 87515篇 |
免费 | 18489篇 |
国内免费 | 2008篇 |
专业分类
电工技术 | 3307篇 |
技术理论 | 2篇 |
综合类 | 2507篇 |
化学工业 | 25918篇 |
金属工艺 | 3221篇 |
机械仪表 | 4150篇 |
建筑科学 | 4852篇 |
矿业工程 | 1282篇 |
能源动力 | 2337篇 |
轻工业 | 10568篇 |
水利工程 | 965篇 |
石油天然气 | 2508篇 |
武器工业 | 337篇 |
无线电 | 12815篇 |
一般工业技术 | 18223篇 |
冶金工业 | 3522篇 |
原子能技术 | 587篇 |
自动化技术 | 10911篇 |
出版年
2024年 | 201篇 |
2023年 | 949篇 |
2022年 | 1680篇 |
2021年 | 2682篇 |
2020年 | 3090篇 |
2019年 | 4615篇 |
2018年 | 4750篇 |
2017年 | 5025篇 |
2016年 | 5461篇 |
2015年 | 5875篇 |
2014年 | 6308篇 |
2013年 | 8018篇 |
2012年 | 5931篇 |
2011年 | 6075篇 |
2010年 | 5439篇 |
2009年 | 5283篇 |
2008年 | 4859篇 |
2007年 | 4334篇 |
2006年 | 4181篇 |
2005年 | 3405篇 |
2004年 | 2842篇 |
2003年 | 2653篇 |
2002年 | 2523篇 |
2001年 | 2209篇 |
2000年 | 2107篇 |
1999年 | 1556篇 |
1998年 | 1096篇 |
1997年 | 908篇 |
1996年 | 741篇 |
1995年 | 623篇 |
1994年 | 504篇 |
1993年 | 348篇 |
1992年 | 295篇 |
1991年 | 260篇 |
1990年 | 217篇 |
1989年 | 185篇 |
1988年 | 119篇 |
1987年 | 115篇 |
1986年 | 79篇 |
1985年 | 72篇 |
1984年 | 59篇 |
1983年 | 55篇 |
1982年 | 35篇 |
1981年 | 31篇 |
1980年 | 37篇 |
1979年 | 29篇 |
1978年 | 20篇 |
1977年 | 21篇 |
1976年 | 33篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The copolymerization of carbazole (CZ) and 3‐methylthiophene (3MeT) was successfully performed electrochemically in freshly distilled boron trifluoride diethyl etherate by direct anodic oxidation of the monomer mixtures, although the oxidation potentials of CZ and 3MeT were quite different. The electrochemical properties of the copolymers were studied with cyclic voltammetry. The influence of the applied polymerization potential on the synthesis of the copolymers was investigated. The higher potential favored the incorporation of 3MeT units into the copolymers. The insertion of 3MeT units into polycarbazole (PCZ) was helpful in improving the conductivity of PCZ. The novel copolymers had the advantages of both PCZ and poly(3‐methylthiophene), that is, good redox activity, good thermal stability, and high conductivity. The structure and morphology of the copolymers were investigated with ultraviolet–visible, infrared spectroscopy, thermal analysis, and scanning electron microscopy. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1877–1885, 2006 相似文献
992.
Sykes EC Han P Kandel SA Kelly KF McCarty GS Weiss PS 《Accounts of chemical research》2003,36(12):945-953
Adsorbate interactions and reactions on metal surfaces have been investigated using scanning tunneling microscopy. The manners in which adsorbates perturb the surface electronic structure in their vicinity are discussed. The effects these perturbations have on other molecules are shown to be important in overlayer growth. Interactions of molecules with surface steps are addressed, and each molecule's electron affinity is shown to dictate its adsorption sites at step edges. Standing waves emanating from steps are demonstrated to effect transient molecular adsorption up to 40 A away from the step edge. Halobenzene derivatives are used to demonstrate how the surface is important in aligning reactive intermediates. 相似文献
993.
994.
为实现遭受重大火灾等灾害后,对伤员皮肤烧伤自动化分级,加快诊断效率,提出提出一种用于皮肤烧伤分类的轻量化模型BI-YOLOv5算法。替换Swish激活函数,提高模型收敛能力及检测效率;使用K-means++算法对anchors聚类分析,增强对不同尺度目标的适应能力;修改特征提取网络,提取多个尺度的特征信息,建立多尺度特征融合网络,提高模型对深层特征信息的利用率,提高小面积烧伤的识别精度。实验结果表明,BI-YOLOv5算法在检测并区分不同烧伤类别及环境干扰下烧伤检测有较高的精度和效率,mAP达到97.6,对比YOLOv5提升8.4个百分点。 相似文献
995.
The impact that some membrane preparation steps had on ultrafiltration (UF) membrane characteristics and performance was studied. Polyethersulfone (PES) was employed as base polymer, while N‐methyl pyrrolidone (NMP) was used as a solvent, and polyvinylpyrrolidone (PVP) was used as a nonsolvent pore‐forming additive. The manufacturing variables studied were solvent evaporation time and membrane surface modification, using a fluorine‐based copolymer referred to as surface‐modifying macromolecule (SMM). The flat sheet membranes, prepared via phase inversion, were characterized using solute transport data, X‐ray photoelectron spectroscopy (XPS), and contact angle measurements. Membrane performance was evaluated via filtration test protocol that included a 6‐day filtration of concentrated river water. The flux reduction with time was modeled using single and dual mechanisms of fouling. The pore blockage/cake filtration model described better the behavior of the permeation rate along the experiments. Increasing the solvent evaporation time decreased the size of the pores and the permeation rate. However, it did not significantly affect the removal of the organic compounds naturally present in the river water used as feed. XPS and contact angle measurements proved that the short evaporation periods did not allow enough SMM migration to the surface to provoke a significant effect on the membrane performance. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci, 2006 相似文献
996.
The transitions and reactions involved in the thermal processing of binary mixtures of polyethylene and poly(ethylene‐co‐vinyl acetate) copolymers with different concentrations of a foaming agent (azodicarbonamide) were studied using differential scanning calorimetry (DSC). The effect of ZnO as a kicker also was discussed. The temperature at the maximum rate and the heat evolved were measured for all the processes—melting, transitions, and reactions—all the mixtures prepared were measured and compared. Azodicarbonamide decomposed differently depending on the polymeric matrix. These data can be very useful for the plastic processing industry. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2015–2025, 2006 相似文献
997.
Ti‐based Ziegler–Natta catalysts supported on MgCl2 doped with AlCl3 were prepared by the reaction of MgCl2/AlCl3–ethanol adduct with TiCl4. No AlCl3 crystallites were found in the AlCl3‐doped catalysts by WAXD analysis, suggesting that AlCl3/MgCl2 solid solution was formed. The effect of doping on the catalyst performance in ethylene polymerization was investigated. The results showed that the catalysts based on AlCl3‐doped MgCl2 support exhibited a slightly higher activity than did the MgCl2‐supported catalyst and the molecular weight distribution (MWD) of polyethylene (PE) markedly increased (from 10.8 to 47.9) with the increase of AlCl3 content in catalysts. The changes in catalyst's active center distribution were studied based on nonlinear fitting of the polymer GPC curves by multiple Flory functions. It was found that increase of types of active centers by introducing AlCl3 into the support should be responsible for the broadening of MWD of PE. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1768–1772, 2006 相似文献
998.
Leonel F. Murga Ying Wei Pierrette André James G. Clifton Dagmar Ringe Mary Jo Ondrechen 《Israel journal of chemistry》2004,44(1-3):299-308
Structural genomics initiatives are determining thousands of new protein structures. Many of these structures are of unknown function, and computational methods for the rapid determination of functional information from protein structure are needed. We present details of how functional information is obtained from the structure using THEMATICS (Theoretical Microscopic Titration Curves). THEMATICS is a computational procedure that gives information about chemical reactivity, based on solution of the Poisson-Boltzmann equations for the electrical potential function. We show how anomalies in predicted titration curves are established. We show further that when residues with anomalous predicted titration curves form a cluster in physical space, these residues tend to be very highly conserved across species and such clusters are reliable predictors of the active site. Results are given for ten enzymes; detailed results are shown for the enzymes triosephosphate isomerase (from chicken), 6-hydroxymethyl-7,8-dihydropterin pyrophosphokinase (from E. coli), and papain (from papaya). 相似文献
999.
1000.
针对现有三维形状配准方法中存在左右翻转的错误匹配问题,提出了基于内蕴对称特征检测的高效形状配准算法。首先,通过热核与几何约束构建模型的内蕴自对称点对;其次,基于谱嵌入特征空间分析提取模型的内蕴对称平面,并依据模型表面法向量有效识别模型的左右结构属性;然后,根据内蕴对称点对获得模型的一致性谱对称结构描述;最后,引入一致性点漂移算法(CPD),实现基于谱对称的非刚性模型的形状配准,有效避免了模型配准中的左右结构翻转问题。实验进一步论证了这种方法不仅有效提高了模型匹配的效率,而且能有效识别同类模型的结构特征,对于非刚性模型的配准具有较强的鲁棒性。 相似文献