全文获取类型
收费全文 | 11076篇 |
免费 | 1199篇 |
国内免费 | 598篇 |
专业分类
电工技术 | 846篇 |
综合类 | 903篇 |
化学工业 | 1929篇 |
金属工艺 | 196篇 |
机械仪表 | 359篇 |
建筑科学 | 956篇 |
矿业工程 | 307篇 |
能源动力 | 372篇 |
轻工业 | 3219篇 |
水利工程 | 498篇 |
石油天然气 | 484篇 |
武器工业 | 42篇 |
无线电 | 592篇 |
一般工业技术 | 830篇 |
冶金工业 | 413篇 |
原子能技术 | 193篇 |
自动化技术 | 734篇 |
出版年
2024年 | 37篇 |
2023年 | 138篇 |
2022年 | 277篇 |
2021年 | 342篇 |
2020年 | 427篇 |
2019年 | 384篇 |
2018年 | 376篇 |
2017年 | 435篇 |
2016年 | 462篇 |
2015年 | 509篇 |
2014年 | 756篇 |
2013年 | 900篇 |
2012年 | 975篇 |
2011年 | 995篇 |
2010年 | 644篇 |
2009年 | 656篇 |
2008年 | 570篇 |
2007年 | 660篇 |
2006年 | 609篇 |
2005年 | 429篇 |
2004年 | 363篇 |
2003年 | 270篇 |
2002年 | 260篇 |
2001年 | 224篇 |
2000年 | 163篇 |
1999年 | 156篇 |
1998年 | 143篇 |
1997年 | 114篇 |
1996年 | 97篇 |
1995年 | 90篇 |
1994年 | 64篇 |
1993年 | 41篇 |
1992年 | 50篇 |
1991年 | 45篇 |
1990年 | 38篇 |
1989年 | 41篇 |
1988年 | 29篇 |
1987年 | 18篇 |
1986年 | 15篇 |
1985年 | 18篇 |
1984年 | 19篇 |
1983年 | 18篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
1.
Somnath Karmakar 《Polycyclic Aromatic Compounds》2019,39(2):159-171
Eigensolutions of {X( = C,B,N),Y( = C,B,N)}-cyclacene graphs with next nearest neighbor (nnn) interactions have been obtained in analytical forms by adapting n-fold rotational symmetry followed by two-fold rotational symmetry (or a plane of symmetry). Expressions of eigensolution indicate the subspectral relationship among such cyclacenes with an even number of hexagonal rings e.g., eigenvalues of {X,Y}-di-cyclacene are found in the eigenspectra of all such even cyclacenes. Total π-electron energies and highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO–LUMO) gaps are calculated using the analytical expressions obtained and are found to vary negligibly with the variation of nnn interactions in such cyclacenes. Total π-electron energy is found to increase due to increase in restriction intensity of nnn interactions, whereas the HOMO–LUMO gap of polyacenecs having the even number of hexagonal rings and with one electron at each site (atom) decreases with increase in the restriction intensity since such systems contain degenerate half-filled HOMO (bonding or nonbonding) that are much more vulnerable for perturbations imposed through nnn interactions. 相似文献
2.
3.
Kevin J. Hanley 《International journal for numerical methods in engineering》2020,121(21):4865-4877
An algorithm is presented for discrete element method simulations of energy-conserving systems of frictionless, spherical particles in a reversed-time frame. This algorithm is verified, within the limits of round-off error, through implementation in the LAMMPS code. Mechanisms for energy dissipation such as interparticle friction, damping, rotational resistance, particle crushing, or bond breakage cannot be incorporated into this algorithm without causing time irreversibility. This theoretical development is applied to critical-state soil mechanics as an exemplar. It is shown that the convergence of soil samples, which differ only in terms of their initial void ratio, to the same critical state requires the presence of shear forces and frictional dissipation within the soil system. 相似文献
4.
本文提出了将智能全站仪这种精密测量仪器广泛应用于田赛项目测量中,并结合其他科技元素用于解决田赛项目中跳远、投掷等项目的测量及数据管理问题,实现实时、自动、准确地裁定和报告比赛成绩。 相似文献
5.
Jeong Ha-Ram Cho Hye-Seung Cho Youn-Sup Kim Dae-Ok 《Food science and biotechnology》2020,29(12):1763-1770
Food Science and Biotechnology - Hardy kiwifruits (Actinidia arguta) contain various bioactive compounds such as vitamin C and phenolics and can withstand cold temperatures. Changes in soluble... 相似文献
6.
介绍了循环伏安法的产生背景、原理。应用该技术可以快速、方便地对润滑油中抗氧剂、总酸(碱)值进行测定,并且可以对不同厂家润滑油的抗氧剂包进行区别。该技术还可以有效地评价润滑油的使用寿命和设备工作状况。 相似文献
7.
集输系统热回水管线腐蚀分析 总被引:2,自引:0,他引:2
中国石油天然气股份有限公司华北分公司第三采油厂油气集输系统热回水管线普遍存在着腐蚀问题,影响原油生产和集输的正常运行。介绍了腐蚀较严重的13个站点的水质普查、水质结垢倾向和腐蚀性情况,并在水质分析的基础上进行了热水管线腐蚀因素的试验研究,确定腐蚀主要因素为水中的溶解氧含量高,从而造成腐蚀。 相似文献
8.
Ph. D. Candidate:Chen Xue-fengState Key Laboratory of Offshore Coastal Engineering Dalian University of Technology Dalian China e-mail: cxfeng @ student dlut. edu.cn 《水动力学研究与进展(B辑)》2003,15(6)
The reflection coefficient of perforated caissons and the total horizontal forces acting on them were experimentally and numerically analyzed and discussed when wave propagates normally. To consider the viscosity effect of fluid and nonlinear action of waves on structures, the VOF (Volume Of Fluid) method combined with the k-ε turbulence model was used to simulate the interaction between waves and structures. Governing equations were solved with the finite difference method. Through 2D experimental study in the wave flume, the empirical relationship between the reflection coefficient of perforated caissons and the main affecting factors were obtained from the experimental data using the least square method. Also the correlation between the ratio of the total horizontal force acting on perforated caisson and the force acting on solid caisson and the main affecting factors were regressed from the experimental data. 相似文献
9.
水溶液全循环法尿素装置中压分解"三种工艺"的比较 总被引:1,自引:0,他引:1
以生产数据结合理论计算的方法系统地比较、分析了水溶液全循环法尿素装置中中压分解“三种工艺”的热能利用、甲铵分解率、总氨蒸出率、水平衡量、一分加热器生产能力等方面的情况,提出应用和配置预分离-预蒸馏工艺的方法,评论该工艺在水溶液全循环法中的地位和作用。 相似文献
10.
Oleuropein Inhibits LDL Oxidation Induced by Cooking Oil Frying By-products and Platelet Aggregation Induced by Platelet-Activating Factor 总被引:1,自引:0,他引:1
Oleuropein, a polyphenolic glucoside, constituent of olive fruit and oil, has been previously shown to exhibit, in vitro, potent properties as a biological antioxidant. In the present paper, two new properties are demonstrated in vitro as well, concerning its vascular protection activity, against the atheromatic lesion formation and its blood antithrombotic effect. Firstly, it was found that the oxidation of low-density lipoproteins (LDL), induced by different quantities of total polar materials (TPM), was inhibited by 10 μ M (final concentration) of oleuropein, revealing approx. 50% protection. Secondly, platelet-rich human plasma aggregation, induced by either the platelet-activating factor or adenosine diphospate or arachidonic acid, was inhibited by oleuropein. The 10 μ M (final concentration) of oleuropein was proven to be the most effective among the tested concentrations against LDL oxidation, while an IC50=0.41 mM was calculated for its inhibitory activity against platelet aggregation induced by 0.7 μ M platelet-activating factor. 相似文献