全文获取类型
收费全文 | 9304篇 |
免费 | 586篇 |
国内免费 | 386篇 |
专业分类
电工技术 | 378篇 |
综合类 | 554篇 |
化学工业 | 1520篇 |
金属工艺 | 681篇 |
机械仪表 | 453篇 |
建筑科学 | 357篇 |
矿业工程 | 116篇 |
能源动力 | 237篇 |
轻工业 | 556篇 |
水利工程 | 100篇 |
石油天然气 | 173篇 |
武器工业 | 50篇 |
无线电 | 1040篇 |
一般工业技术 | 1414篇 |
冶金工业 | 526篇 |
原子能技术 | 251篇 |
自动化技术 | 1870篇 |
出版年
2024年 | 9篇 |
2023年 | 91篇 |
2022年 | 187篇 |
2021年 | 191篇 |
2020年 | 183篇 |
2019年 | 175篇 |
2018年 | 164篇 |
2017年 | 217篇 |
2016年 | 229篇 |
2015年 | 244篇 |
2014年 | 432篇 |
2013年 | 493篇 |
2012年 | 507篇 |
2011年 | 663篇 |
2010年 | 495篇 |
2009年 | 563篇 |
2008年 | 579篇 |
2007年 | 602篇 |
2006年 | 591篇 |
2005年 | 494篇 |
2004年 | 421篇 |
2003年 | 384篇 |
2002年 | 315篇 |
2001年 | 300篇 |
2000年 | 336篇 |
1999年 | 212篇 |
1998年 | 137篇 |
1997年 | 131篇 |
1996年 | 124篇 |
1995年 | 119篇 |
1994年 | 123篇 |
1993年 | 95篇 |
1992年 | 81篇 |
1991年 | 64篇 |
1990年 | 54篇 |
1989年 | 44篇 |
1988年 | 29篇 |
1987年 | 25篇 |
1986年 | 32篇 |
1985年 | 32篇 |
1984年 | 22篇 |
1983年 | 16篇 |
1982年 | 17篇 |
1981年 | 18篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1975年 | 7篇 |
1956年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
摘要:为了研究300M超高强钢在中性盐雾环境中的腐蚀行为及腐蚀机制,采用失重法,宏观、微观腐蚀形貌分析,三维表面轮廓分析及电化学分析的研究方法,来表征腐蚀实验现象并进行分析。结果表明:300M超高强钢在中性盐雾环境中的腐蚀产物为FeOOH、Fe2O3、Fe(OH)3和Fe3O4;腐蚀速率随着腐蚀时间逐渐降低,腐蚀后期(72h)腐蚀速率降低50%;腐蚀初期以点蚀为主,点蚀坑通过横向扩展,逐渐发展为后期的均匀腐蚀,腐蚀表面形貌呈沟壑状;外腐蚀层对基体的保护能力很弱,Cr元素在锈层靠近基体的一侧偏聚使内腐蚀层具有一定的抗腐蚀性。 相似文献
3.
电器外壳制品形状结构复杂,有两处侧凸(孔)较难处理。通过对矩形孔内侧凸的结构分析,在其局部设计了分型面,避免了使用侧向抽芯机构;对侧孔部位设计了斜顶杆侧向抽芯机构,其结构简单、紧凑。模具采用一模二腔、平衡式布局,采用经扁推杆由制品内部进料的潜伏式浇口,S型流道。在NX 8.0中完成了模具结构设计。经实践证明,该模具结构合理,产品合格。 相似文献
4.
During restructuring processes, due to mergers and acquisitions, banks frequently face the problem of having redundant branches competing in the same market. In this work, we introduce a new Capacitated Branch Restructuring Model which extends the available literature in delocation models. It considers both closing down and long term operations׳ costs, and addresses the problem of resizing open branches in order to maintain a constant service level. We consider, as well, the presence of competitors and allow for ceding market share whenever the restructuring costs are prohibitively expensive.We test our model in a real life scenario, obtaining a reduction of about 40% of the network size, and annual savings over 45% in operation costs from the second year on. We finally perform a sensitivity analysis on critical parameters. This analysis shows that the final design of the network depends on certain strategic decisions concerning the redundancy of the branches, as well as their proximity to the demand nodes and to the competitor׳s branches. At the same time, this design is quite robust to changes in the parameters associated with the adjustments on service capacity and with the market reaction. 相似文献
5.
The aim of this paper is to assess the closeness of agreement between results of ELISA and LC-MS/MS methods for determination of aflatoxin B1 in corn and aflatoxin M1 in milk. Samples of corn (n=100) and milk (n=250) were simultaneously analyzed using ELISA and LC-MS/MS methods, after the severe drought that affected Serbia in summer 2012 resulting in occurrence of aflatoxin B1 in corn and aflatoxin M1 in milk. Regression analysis showed higher level of agreement between aflatoxin B1 samples (R2=0.994), compared to aflatoxin M1 samples (R2=0.920). However, both techniques were satisfactory in meeting the requirements for official control purposes. 相似文献
6.
Hiroshi Takamatsu Hikaru Yamashiro Nobuo Takata Hiroshi Honda 《International Journal of Refrigeration》2003,26(6):79
Heat and mass transfer in a falling film vertical in-tube absorber was studied experimentally with LiBr aqueous solution. The presented results include the effect of solution flow rate, solution subcooling and cooling water temperature on the absorption in a smooth copper tube 16.05 mm I.D. and 400 mm long. The experimental data in the previous report for a 1200-mm-long tube was also re-examined and compared. It was demonstrated by the observation of the flow in the tube that the break down of the liquid film into rivulets leads to deterioration of heat and mass transfer at lower film Reynolds number or in longer tubes. An attempt to evaluate physically acceptable heat and mass transfer coefficients that are defined with estimated temperature and concentration at the vapor–liquid interface was also presented. 相似文献
7.
Kelson C. Lopes Flvia S. Pereira Regiane C. M. U. Araújo Mozart N. Ramos Roy E. Bruns 《Chemometrics and Intelligent Laboratory Systems》2004,70(2):157-163
Factorial design and principal component models are used to determine how ab initio H-bond stretching frequencies depend on characteristics of the molecular orbital wave functions of acetylene–HX, ethylene–HX and cyclopropane–HX π-type hydrogen complexes with X=F, Cl, CN, NC and CCH. The results obtained for the three sets of complexes show that factorial design and principal component analyses complement each other. Factorial design calculations clearly show that these frequencies are affected mostly by inclusion of electron correlation on the calculation level. On average, their values are increased by about 25 cm−1 due to a change from the Hartree–Fock (HF) to Möller–Plesset 2 (MP2) level. Valence, diffuse and polarization main effects as well as valence–diffuse, diffuse–correlation and polarization–correlation interaction effects are also important to better describe a factorial model to the H-bond stretching frequencies of these hydrogen complexes. This simplified model has been successful in reproducing the complete ab initio results, which correspond to two hundred and forty calculations. Principal component analyses applied only to hydrogen-bonded complexes whose experimental frequencies are known, has revealed that the six-dimensional original space can be accurately represented by a bidimensional space defined by two principal components. Its graphical representation reveals that the experimental intermolecular stretching frequencies are in closest agreement with the MP2/6–31+G and MP2/6–311+G ab initio results. 相似文献
8.
9.
进入WTO后的企业设备管理思考 总被引:1,自引:0,他引:1
本文从企业设备管理战略、设备工程要成为培养“企业核心竞争能力”的平台、发挥行业协会作用三方面,提出了入世后企业设备管理的应对措施。 相似文献
10.
Morten
rregaard Nielsen 《时间序列分析杂志》2005,26(2):279-304
Abstract. We consider semiparametric estimation in time‐series regression in the presence of long‐range dependence in both the errors and the stochastic regressors. A central limit theorem is established for a class of semiparametric frequency domain‐weighted least squares estimates, which includes both narrow‐band ordinary least squares and narrow‐band generalized least squares as special cases. The estimates are semiparametric in the sense that focus is on the neighbourhood of the origin, and only periodogram ordinates in a degenerating band around the origin are used. This setting differs from earlier studies on time‐series regression with long‐range dependence, where a fully parametric approach has been employed. The generalized least squares estimate is infeasible when the degree of long‐range dependence is unknown and must be estimated in an initial step. In that case, we show that a feasible estimate which has the same asymptotic properties as the infeasible estimate, exists. By Monte Carlo simulation, we evaluate the finite‐sample performance of the generalized least squares estimate and the feasible estimate. 相似文献