首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   46884篇
  免费   4215篇
  国内免费   2017篇
电工技术   2509篇
技术理论   2篇
综合类   2503篇
化学工业   8519篇
金属工艺   2695篇
机械仪表   3092篇
建筑科学   3062篇
矿业工程   1297篇
能源动力   1424篇
轻工业   3194篇
水利工程   649篇
石油天然气   2483篇
武器工业   337篇
无线电   5787篇
一般工业技术   6615篇
冶金工业   2533篇
原子能技术   541篇
自动化技术   5874篇
  2024年   249篇
  2023年   910篇
  2022年   1580篇
  2021年   2283篇
  2020年   1642篇
  2019年   1538篇
  2018年   1630篇
  2017年   1660篇
  2016年   1573篇
  2015年   2021篇
  2014年   2405篇
  2013年   2864篇
  2012年   2992篇
  2011年   3462篇
  2010年   2670篇
  2009年   2618篇
  2008年   2592篇
  2007年   2305篇
  2006年   2396篇
  2005年   1927篇
  2004年   1395篇
  2003年   1277篇
  2002年   1181篇
  2001年   1022篇
  2000年   986篇
  1999年   1031篇
  1998年   876篇
  1997年   739篇
  1996年   653篇
  1995年   548篇
  1994年   425篇
  1993年   287篇
  1992年   239篇
  1991年   210篇
  1990年   179篇
  1989年   162篇
  1988年   106篇
  1987年   92篇
  1986年   60篇
  1985年   57篇
  1984年   41篇
  1983年   39篇
  1982年   30篇
  1981年   23篇
  1980年   26篇
  1979年   18篇
  1978年   16篇
  1976年   19篇
  1973年   13篇
  1971年   10篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
一维驱动二维跟踪太阳自动跟踪系统设计   总被引:8,自引:0,他引:8  
本文从对太阳方位变化规律的分析计算入手,利用天文时间来提供准确可靠的自动跟踪信号,并采用一维驱动实现二维精密跟踪的新技术。依此所设计的新型太阳能聚光器自动跟踪系统与同类产品相比,具有准确可靠、抗干扰能力强、成本低、方便实用等特点;这对于通过聚光方式推动太阳能应用具有重大的现实意义。  相似文献   
132.
薛耀泉  赵涵 《计测技术》1999,(4):3-6,16
研究了利用贝塞尔函数比值来估算得到干涉型光纤水听器光相移的方法,而得到光纤水听器的相移灵敏度。对理论模型进行了模拟,并对一推挽式干涉型零差光纤水听器进行了实际校准。  相似文献   
133.
In the current shift from conventional fossil-fuel-based materials to renewable energy,ecofriendly mate-rials have attracted extensive research interest due to ...  相似文献   
134.
Residual stress fields from cold expansion have been widely used to extend the fatigue life of aircraft structures. However, the spatial statistical character of these residual stress fields has not been established and has not been incorporated in current analysis methods. The objective of this study was to establish a spatial statistical method to quantify the residual stress field around a cold expanded hole. A framework called the Spatial Analysis of Residual Stress (SpARS) was developed utilizing spatial correlation, response surface modelling techniques and statistical resampling methods to characterize the residual stress field. Our results showed that tolerance bounds on residual stress can be quantified using this method. We also demonstrated the SpARS method using recently published round robin case studies. The newly developed model will be useful for aircraft structural fatigue crack growth analyses to incorporate residual stress fields for extending inspection intervals for fatigue and fracture critical structures.  相似文献   
135.
Minoxidil is the most widely used treatment for hair growth, but has been associated with several side effects. In this study, we investigated the effects of heat-killed Enterococcus faecalis EF-2001 on hair loss prevention and regrowth using human dermal papilla cells and male C57BL/6 mice. To examine the effects of EF-2001, we used minoxidil as the positive control. In the in vitro experiments, EF-2001 treatment (75–500 μg/mL) led to the proliferation of human dermal papilla cells in a concentration-dependent manner. In the in vivo experiment, the topical application of 200 µL EF-2001 on the dorsal surface of C57BL/6 male mice led to hair growth. Changes in hair regrowth were examined by visual comparison and hematoxylin and eosin staining of skin sections. We also determined the expression levels of marker genes (Wnt) and growth factors (fibroblast growth factor, insulin growth factor 1, and vascular endothelial growth factor) in the skin tissues of the back of each mouse using a quantitative polymerase chain reaction. EF-2001 accelerated the progression of hair regrowth in mice and promoted hair-follicle conversion from telogen to anagen, likely by increasing the expression levels of growth factors and marker genes.  相似文献   
136.
Three-dimensional (3D) cultures, so-called organoids, have emerged as an attractive tool for disease modeling and therapeutic innovations. Here, we aim to determine if boundary cap neural crest stem cells (BC) can survive and differentiate in gelatin-based 3D bioprinted bioink scaffolds in order to establish an enabling technology for the fabrication of spinal cord organoids on a chip. BC previously demonstrated the ability to support survival and differentiation of co-implanted or co-cultured cells and supported motor neuron survival in excitotoxically challenged spinal cord slice cultures. We tested different combinations of bioink and cross-linked material, analyzed the survival of BC on the surface and inside the scaffolds, and then tested if human iPSC-derived neural cells (motor neuron precursors and astrocytes) can be printed with the same protocol, which was developed for BC. We showed that this protocol is applicable for human cells. Neural differentiation was more prominent in the peripheral compared to central parts of the printed construct, presumably because of easier access to differentiation-promoting factors in the medium. These findings show that the gelatin-based and enzymatically cross-linked hydrogel is a suitable bioink for building a multicellular, bioprinted spinal cord organoid, but that further measures are still required to achieve uniform neural differentiation.  相似文献   
137.
138.
The technological revolution of long-awaited energy-saving and vision-friendly displays represented by bistable display technology is conning.Here we discuss methods,challenges,and opportunities for implementing bistable displays in terms of molecular design,device structure,further expansion,and required criteria,hopefully benefiting the light-related community.  相似文献   
139.
In the past decade, capillary electrophoresis has demonstrated increasing utility for the quantitative analysis of single cells. New applications for the analysis of dynamic cellular properties demand sampling methods with sufficient temporal resolution to accurately measure these processes. In particular, intracellular signaling pathways involving many enzymes can be modulated on subsecond time scales. We have developed a technique to rapidly lyse an adherent mammalian cell using a single electrical pulse followed by efficient loading of the cellular contents into a capillary. Microfabricated electrodes were designed to create a maximum voltage drop across the flattened cell's plasma membrane at a minimum interelectrode voltage. The influence of the interelectrode distance, pulse duration, and pulse strength on the rate of cell lysis was determined. The ability to rapidly lyse a cell and collect and separate the cellular contents was demonstrated by loading cells with Oregon Green and two isomers of carboxyfluorescein. All three fluorophores were detected with a separation efficiency comparable to that of standards. Parallel comparison of electrical lysis to that produced by a laser-based lysis system revealed that the sampling efficiencies of the two techniques were comparable. Rapid cell lysis by an electrical pulse may increase the application of capillary electrophoresis to the study of cellular dynamics requiring fast sampling times.  相似文献   
140.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号