全文获取类型
收费全文 | 10190篇 |
免费 | 435篇 |
国内免费 | 144篇 |
专业分类
电工技术 | 282篇 |
技术理论 | 1篇 |
综合类 | 221篇 |
化学工业 | 1970篇 |
金属工艺 | 393篇 |
机械仪表 | 383篇 |
建筑科学 | 369篇 |
矿业工程 | 119篇 |
能源动力 | 339篇 |
轻工业 | 711篇 |
水利工程 | 119篇 |
石油天然气 | 200篇 |
武器工业 | 22篇 |
无线电 | 1148篇 |
一般工业技术 | 2216篇 |
冶金工业 | 1141篇 |
原子能技术 | 115篇 |
自动化技术 | 1020篇 |
出版年
2023年 | 97篇 |
2022年 | 210篇 |
2021年 | 294篇 |
2020年 | 231篇 |
2019年 | 179篇 |
2018年 | 287篇 |
2017年 | 244篇 |
2016年 | 245篇 |
2015年 | 252篇 |
2014年 | 299篇 |
2013年 | 631篇 |
2012年 | 446篇 |
2011年 | 507篇 |
2010年 | 426篇 |
2009年 | 391篇 |
2008年 | 368篇 |
2007年 | 343篇 |
2006年 | 311篇 |
2005年 | 267篇 |
2004年 | 237篇 |
2003年 | 218篇 |
2002年 | 203篇 |
2001年 | 172篇 |
2000年 | 218篇 |
1999年 | 227篇 |
1998年 | 304篇 |
1997年 | 263篇 |
1996年 | 233篇 |
1995年 | 202篇 |
1994年 | 186篇 |
1993年 | 170篇 |
1992年 | 150篇 |
1991年 | 150篇 |
1990年 | 101篇 |
1989年 | 107篇 |
1988年 | 113篇 |
1987年 | 109篇 |
1986年 | 91篇 |
1985年 | 128篇 |
1984年 | 122篇 |
1983年 | 134篇 |
1982年 | 96篇 |
1981年 | 95篇 |
1980年 | 86篇 |
1979年 | 88篇 |
1978年 | 74篇 |
1977年 | 66篇 |
1976年 | 72篇 |
1975年 | 57篇 |
1974年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
Ram Kumar K. Gopalakrishnan Irshad Ahmad C. N. R. Rao 《Advanced functional materials》2015,25(37):5910-5917
Composites of boron nitride (BN) and carboxylated graphene are prepared for the first time using covalent cross‐linking employing the carbodiimide reaction. The BN1–xGx (x ≈ 0.25, 0.5, and 0.75) obtained are characterized using a variety of spectroscopic techniques and thermogravimetric analysis. The composites show composition‐dependent electrical resistivity, the resistivity decreasing with increase in graphene content. The composites exhibit microporosity and the x ≈ 0.75 composite especially exhibits satisfactory performance with high stability as an electrode in supercapacitors. The x ≈ 0.75 composite is also found to be a good electrocatalyst for the oxygen reduction reaction in fuel cells. 相似文献
992.
Red Blood Cell Membrane as a Biomimetic Nanocoating for Prolonged Circulation Time and Reduced Accelerated Blood Clearance 下载免费PDF全文
Lang Rao Lin‐Lin Bu Jun‐Hua Xu Bo Cai Guang‐Tao Yu Xiaolei Yu Zhaobo He Qinqin Huang Andrew Li Shi‐Shang Guo Wen‐Feng Zhang Wei Liu Zhi‐Jun Sun Hao Wang Tza‐Huei Wang Xing‐Zhong Zhao 《Small (Weinheim an der Bergstrasse, Germany)》2015,11(46):6225-6236
For decades, poly(ethylene glycol) (PEG) has been widely incorporated into nanoparticles for evading immune clearance and improving the systematic circulation time. However, recent studies have reported a phenomenon known as “accelerated blood clearance (ABC)” where a second dose of PEGylated nanomaterials is rapidly cleared when given several days after the first dose. Herein, we demonstrate that natural red blood cell (RBC) membrane is a superior alternative to PEG. Biomimetic RBC membrane‐coated Fe3O4 nanoparticles (Fe3O4@RBC NPs) rely on CD47, which is a “don't eat me” marker on the RBC surface, to escape immune clearance through interactions with the signal regulatory protein‐alpha (SIRP‐α) receptor. Fe3O4@RBC NPs exhibit extended circulation time and show little change between the first and second doses, with no ABC suffered. In addition, the administration of Fe3O4@RBC NPs does not elicit immune responses on neither the cellular level (myeloid‐derived suppressor cells (MDSCs)) nor the humoral level (immunoglobulin M and G (IgM and IgG)). Finally, the in vivo toxicity of these cell membrane‐camouflaged nanoparticles is systematically investigated by blood biochemistry, hematology testing, and histology analysis. These findings are significant advancements toward solving the long‐existing clinical challenges of developing biomaterials that are able to resist both immune response and rapid clearance. 相似文献
993.
Jing Hu Kwansoo Chung Xiao-Xing Li Taejoon Park Guo-Feng Zhou Rao Yao 《Metals and Materials International》2011,17(3):527-533
In the present work, a die shape design method to compensate spring-back in the sheet metal forming process is developed based
on a finite element analysis and a genetic algorithm. The proposed method is robust and automated enough for industrial applications.
Using a simple stretch bending process as an example, it was demonstrated that the new method optimizes the die profile effectively.
The good performance of the die profile optimized utilizing the new method was also verified experimentally, confirming that
the new method is likely to be more cost-effective than common design practices in practical applications. 相似文献
994.
995.
Tube-in-tube heat exchangers are widely used in food processing industries and wastewater treatment for both heating and cooling. Enhancement techniques namely active, passive, and compound are developed to reduce the thermal resistance in heat exchangers by improving convective heat transfer with or without increase in surface area. The present experimental study is aimed at analyzing the influence of vibrations on the convective heat transfer of a parallel flow tube-in-tube heat exchanger. The heat exchanger is placed in horizontal position and is subjected to transverse vibrations under turbulent fluid flow conditions. Experiments were performed at four frequencies (20, 40, 60, and 100 Hz), three amplitudes (1, 2, and 3 m/s2), and three vibration generator positions along its length, in the Reynolds number range of 10 710 to 21 420. An enhancement in Nusselt number is found with vibration than without vibration throughout the entire range of Reynolds numbers. A maximum enhancement of 33% at 40 Hz frequency, 3 m/s2 amplitude, and vibration generator position at three-fourth of the tube length was observed. Empirical correlations are developed for Nusselt number to determine the heat transfer coefficient with vibration with an error of 10%. 相似文献
996.
The present paper investigates the effect of fibre content and alkali treatment on tensile, flexural and impact properties of unidirectional Roystonea regia natural-fibre-reinforced epoxy composites which are partially biodegradable. The reinforcement Roystonea regia (royal palm) fibre was collected from the foliage of locally available royal palm tree through the process of water retting and mechanical extraction. The poor adhesion between fibre and matrix is commonly encountered problem in natural-fibre-reinforced composites. To overcome this problem, specific physical and chemical treatments were suggested for surface modification of fibres by investigators. Alkali treatment is one of the simple and effective surface modification techniques which is widely used in natural fibre composites. In the present study both untreated and alkali-treated fibres were used as reinforcement in Roystonea regia epoxy composites and the tensile, flexural and impact properties were determined at different fibre contents. The alkali treatment found to be effective in improving the tensile and flexural properties while the impact strength decreased. 相似文献
997.
The reject water or retentate generated from membrane application for recovery of water from tannery wastewater treatment contains certain refractory organics. These refractory organics are present in substantial quantity in the condensate of reject water also. Hence the treatment of rejects using conventional methods is rather difficult. In this paper, an attempt has been made to treat the reject water from the reverse osmosis (RO) and nano filtration (NF) operation on tannery wastewater using ozonation treatment technique. Ozonation studies on RO and NF rejects indicate that ozone dose of 80 and 100mg/min for 60 and 70 min contact time achieves 59 and 78% chemical oxygen demand (COD) reduction, respectively. The mass balance in ozone indicates the ozone consumption for RO and NF rejects varies from 2.4 to 3.4 and 2.8 to 4.5 g/g of COD removed respectively. The results suggest that ozonation of RO and NF rejects would significantly reduce the refractory organic pollutant loading into the environment from wastewater reuse facility. 相似文献
998.
B.S.S. Chandra Rao K. Mohan KumarV. Kripesh K.Y. Zeng 《Materials Science and Engineering: A》2011,528(12):4166-4172
In this work, tensile deformation of Sn-3.8Ag-0.7Cu (SAC387) solder and composite of SAC387 reinforced with nano-sized Mo particles have been studied with strain rates from 10−5 to 10−1 s−1 and temperatures of 25, 75 and 125 °C. It is found that the yield strength (σY.S) and strain hardening exponent (n) are increased with the strain rate, but the n values decrease with increasing temperatures. The n values of the composite solder are also increased with the percentage of the Mo nano-particles (up to 1 wt.%) and thereafter decrease with further increasing of the Mo particle. The strain rate dependence of the Hollomon parameters is found to be stronger at higher temperatures for SAC387 solder, but it is weaker for the composite solders. Empirical equations for σY.S and Hollomon parameters with strain rate and temperatures have been found for both SAC387 and composite solders. Finally, the fracture surfaces of the solders are examined. 相似文献
999.
Chitara B Panchakarla LS Krupanidhi SB Rao CN 《Advanced materials (Deerfield Beach, Fla.)》2011,23(45):5419-5424
The use of reduced graphene oxide (RGO) and graphene nanoribbons (GNRs) as infrared photodetectors is explored, based on recent results dealing with solar cells, light-emitting devices, photodetectors, and ultrafast lasers. IR detection is demonstrated by both RGO and GNRs in terms of the time-resolved photocurrent and photoresponse. The responsivity of the detectors and their functioning are presented. 相似文献
1000.
GCY-X体膨型堵漏剂的研制与性能评价新方法 总被引:1,自引:0,他引:1
用水溶液聚合法合成了一种具有膨胀可变形性的堵漏剂GCY-X,并对其性能进行了评价.评价结果表明,该堵漏剂在室温下的吸蒸馏水倍数为303倍(m/m),在须五段现场钻井液中的吸液倍数为20倍,抗温可达100℃.通过对现有仪器改造,形成了体膨型堵漏剂产品的封堵性能评价实验方法.封堵评价结果表明,GCY-X与钻井液的配伍性好,配伍钻井液针对宽度为1.2~2.5 mm的岩心模拟裂缝的封堵能力可达100%,承压能力为6MPa.形成的GCY-X产品封堵性能评价实验方法可行有效,弥补了目前针对体膨型堵漏剂封堵性能评价方法存在的不足. 相似文献