全文获取类型
收费全文 | 9673篇 |
免费 | 732篇 |
国内免费 | 309篇 |
专业分类
电工技术 | 364篇 |
综合类 | 421篇 |
化学工业 | 1573篇 |
金属工艺 | 523篇 |
机械仪表 | 632篇 |
建筑科学 | 508篇 |
矿业工程 | 172篇 |
能源动力 | 321篇 |
轻工业 | 471篇 |
水利工程 | 148篇 |
石油天然气 | 300篇 |
武器工业 | 33篇 |
无线电 | 1442篇 |
一般工业技术 | 1574篇 |
冶金工业 | 863篇 |
原子能技术 | 96篇 |
自动化技术 | 1273篇 |
出版年
2024年 | 35篇 |
2023年 | 128篇 |
2022年 | 224篇 |
2021年 | 331篇 |
2020年 | 268篇 |
2019年 | 269篇 |
2018年 | 264篇 |
2017年 | 256篇 |
2016年 | 259篇 |
2015年 | 343篇 |
2014年 | 410篇 |
2013年 | 598篇 |
2012年 | 559篇 |
2011年 | 602篇 |
2010年 | 500篇 |
2009年 | 522篇 |
2008年 | 466篇 |
2007年 | 459篇 |
2006年 | 419篇 |
2005年 | 399篇 |
2004年 | 274篇 |
2003年 | 269篇 |
2002年 | 265篇 |
2001年 | 255篇 |
2000年 | 215篇 |
1999年 | 264篇 |
1998年 | 274篇 |
1997年 | 225篇 |
1996年 | 187篇 |
1995年 | 166篇 |
1994年 | 144篇 |
1993年 | 113篇 |
1992年 | 95篇 |
1991年 | 82篇 |
1990年 | 63篇 |
1989年 | 67篇 |
1988年 | 61篇 |
1987年 | 43篇 |
1986年 | 40篇 |
1985年 | 39篇 |
1984年 | 29篇 |
1983年 | 19篇 |
1982年 | 35篇 |
1981年 | 26篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1977年 | 20篇 |
1976年 | 19篇 |
1974年 | 19篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
针对川东地区高陡构造高地层倾角井井眼轨迹控制难度大,并且上部自流井群泥页岩极易发生垮塌等特点,提出应用VTK(VertiTrak)垂直钻井技术防斜打快,并配合使用活度平衡防塌钻井液,以确保井眼稳定和VTK设备安全.介绍了钻井液体系的选择思路和配方的优选.天东004-X3和板东006-H1两口试验井通过应用该技术,平均机械钻速比邻井相同层位提高了57.1%以上,钻井周期缩短了6.1 d,表明VTK垂直钻井技术在高陡构造高倾角井和易斜地层能有效控制井斜,实现直井段的防斜打快、提高机械钻速,配套的活度平衡防塌钻井液具有“强抑制、平衡滤液活度、超低渗透”特性,能有效解决易塌泥页岩地层的井眼稳定问题,并成功实现化学防塌,较大幅度地降低了钻井液密度. 相似文献
992.
993.
A method was developed to grow ordered silicon nanowire with NiSi(2) tip arrays by reacting nickel thin films on silica-coated ordered Si nanowire (NW) arrays. The coating of thin silica shell on Si NW arrays has the effect of limiting the diffusion of nickel during the silicidation process to achieve the single crystalline NiSi(2) NWs. In the meantime, it relieves the distortion of the NWs caused by the strain associated with formation of NiSi(2) to maintain the straightness of the nanowire and the ordering of the arrays. Other nickel silicide phases such as Ni(2)Si and NiSi were obtained if the silicidation processes were conducted on the ordered Si NWs without a thin silica shell. Excellent field emission properties were found for NiSi(2)/Si NW arrays with a turn on field of 0.82 V μm(-1) and a threshold field of 1.39 V μm(-1). The field enhancement factor was calculated to be about 2440. The stability test showed a fluctuation of about 7% with an applied field of 2.6 V μm(-1) for a period of 24 h. The excellent field emission characteristics are attributed to the well-aligned and highly ordered arrangement of the single crystalline NiSi(2)/Si heterostructure field emitters. In contrast to other growth methods, the present growth of ordered nickel silicide/Si NWs on silicon is compatible with silicon nanoelectronics device processes, and also provides a facile route to grow other well-aligned metal silicide NW arrays. The advantages will facilitate its applications as field emission devices. 相似文献
994.
反相微乳液法制备壳聚糖季铵盐/四氧化三铁复合磁性纳米粒子 总被引:2,自引:0,他引:2
以环氧丙基三甲基氯化铵(ETA)为季铵化试剂,制备了壳聚糖季铵盐(QC)———N-2-羟丙基三甲基氯化铵壳聚糖,采用AgNO3电位滴定法测定了季铵化度。以柠檬酸钠为改性剂,一步法制备了水基Fe3O4磁性纳米粒子。基于静电自组装作用,采用反相微乳液法制备了QC/Fe3O4复合磁性纳米粒子。通过多种手段对所制备的复合磁性纳米粒子的结构进行了表征、对其性能进行了研究。红外光谱(FT-IR)、热重分析(TG)及X射线光电子能谱(XPS)的结果表明,QC主要包覆于Fe3O4的表面。透射电镜(TEM)、X射线衍射(XRD)结果表明,复合磁性纳米粒子磁核为Fe3O4晶体结构,平均粒径大约为50 nm~60 nm。VSM结果表明,所制备的复合磁性纳米粒子仍具有超顺磁性,比饱和磁化强度为19.4emu/g。 相似文献
995.
将液晶单体对苯二甲酸二-(4-羧基苯)酯(M1)与1,10-癸二醇、1,12-十二烷二醇和亮黄(By)合成了一种含有磺酸基的主链液晶离聚物(LCI).将LCI与聚对苯二甲酸丁二醇酯(PBT),聚乙烯(PE)进行熔融共混制备了PBT/PE/LCI共混物.所合成的共混物通过DSC、三维红外图像系统和拉伸试验等方法进行了热性... 相似文献
996.
997.
Polycrystalline bulk samples of CuIn1−xGaxSe2 weregrown with nominal x = 0.15, 0.25 and 0.5. Mobility, conductivity and band gap were measured at room and low temperatures. Mobilities for x = 0.21 were several hundred cm2 V−1s−1 at room temperature and for x = 0.15 were 103 cm2 V−1 s−1, all n type. The band gaps were estimated from the spectra of photoelectrochemical cells at room temperature (with 8.5 K photoluminescence estimates shown in brackets), as 1.10 eV (1.14) for x = 0.21, and 1.07 eV (1.093) for x = 0.15. Crystal mechanical properties as regards cracks were not as good as for CuInSe2, using similar growth techniques. 相似文献
998.
Rong-Biao Zhang Jian-Guang Guo Fu-Huan Chu Ye-Cheng ZhangAuthor vitae 《AEUE-International Journal of Electronics and Communications》2011,65(12):1023-1031
In the received signal strength indicator (RSSI) based indoor wireless sensor networks localization system, RSSI measurements are very susceptible to multipath fading, anisotropy of antenna, low supply voltage of node and so on, which will cause the system failure to achieve a high location accuracy. This paper presents an environmental-adaptive path loss model. In the process of localization, the calibrated coefficient LSV of low supply voltage, which can be determined by monitoring the supply voltage of the sender, is used to calibrate ranging errors caused by its low supply voltage. The blind node utilizes the absolute value of RSSI to generate the phase of the corresponding receiver's location so as to determine the correction coefficient of indoor multipath fading Ri. Furthermore, in order to improve the accuracy of RSSI measurements, we also take full consideration of the effect of antenna to accurately determine the corresponding path loss model of the two communication nodes. The proposed path loss model is suitable for the majority of wireless location systems that are on the basis of RSSI-based ranging techniques. Experiment results show that the estimation accuracy and adaptability of the proposed path loss model are significantly higher than that of the traditional one. 相似文献
999.
Salima Alem Ta-Ya Chu Shing C. Tse Salem Wakim Jianping Lu Raluca Movileanu Ye Tao Francis Bélanger Denis Désilets Serge Beaupré Mario Leclerc Sheila Rodman David Waller Russell Gaudiana 《Organic Electronics》2011,12(11):1788-1793
We investigated the effect of solvents on the morphology, charge transport and device performance of poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) and [6,6]-phenyl C71-butyric acid methyl ester (PC70BM) based solar cells. To carry out this investigation, chloroform and 1,2-dichlorobenzene were chosen as good solvents of the two compounds. Films prepared with chloroform exhibit larger domains than those prepared with 1,2-dichlorobenzene and their size increases with the amount of PC70BM. Fine tuning of the domain size was realized by using a solvent of mixed chloroform and 1,2-dichlorobenzene. At a mixing ratio of 50%:50%, a power conversion efficiency of 6.1% was achieved on PCDTBT:PC70BM (1:3) devices with an active area of 1 cm2, under air mass 1.5 global (AM 1.5 G) irradiation at 100 mW/cm2. 相似文献
1000.
Blaine J. Zern Hunghao Chu Adeboye O. Osunkoya Jin Gao Yadong Wang 《Advanced functional materials》2011,21(3):434-440
Self assembly between cations and anions is ubiquitous throughout nature. Important biological structures such as chromatin often use polyvalent assembly between a polycation and a polyanion. The biomedical importance of synthetic polycations arises from their affinity to polyanions such as nucleic acid and heparan sulfate. However, the limited biocompatibility of synthetic polycations hampers the realization of their immense potential. By examining biocompatible cationic peptides, we hypothesize that a biocompatible polycation should be biodegradable and made from endogenous cations. We design an arginine‐based biodegradable polycation and demonstrate that it is more compatible by several orders of magnitude than conventional polycations in vitro and in vivo. This biocompatibility diminishes when L ‐arginine is substituted with D ‐arginine or when the biodegradable ester linker is changed to a biostable ether linker. We believe that this design can lead to many biocompatible polycations that can significantly advance a wide range of applications including controlled release, tissue engineering, biosensing, and medical devices. 相似文献