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   22640篇
  免费   2115篇
  国内免费   941篇
电工技术   1235篇
综合类   1037篇
化学工业   3751篇
金属工艺   1471篇
机械仪表   1705篇
建筑科学   1289篇
矿业工程   622篇
能源动力   822篇
轻工业   1533篇
水利工程   317篇
石油天然气   972篇
武器工业   115篇
无线电   3010篇
一般工业技术   3599篇
冶金工业   1516篇
原子能技术   183篇
自动化技术   2519篇
  2024年   178篇
  2023年   498篇
  2022年   794篇
  2021年   1123篇
  2020年   843篇
  2019年   685篇
  2018年   831篇
  2017年   789篇
  2016年   822篇
  2015年   928篇
  2014年   1118篇
  2013年   1352篇
  2012年   1448篇
  2011年   1608篇
  2010年   1380篇
  2009年   1354篇
  2008年   1224篇
  2007年   1016篇
  2006年   976篇
  2005年   852篇
  2004年   651篇
  2003年   634篇
  2002年   590篇
  2001年   498篇
  2000年   466篇
  1999年   486篇
  1998年   538篇
  1997年   403篇
  1996年   360篇
  1995年   276篇
  1994年   229篇
  1993年   155篇
  1992年   113篇
  1991年   83篇
  1990年   79篇
  1989年   65篇
  1988年   46篇
  1987年   37篇
  1986年   33篇
  1985年   23篇
  1984年   17篇
  1983年   10篇
  1982年   9篇
  1981年   16篇
  1980年   11篇
  1979年   5篇
  1978年   6篇
  1977年   9篇
  1976年   16篇
  1973年   2篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
We propose a fast and effective technique to improve sub‐grid visual details of the grid based fluid simulation. Our method procedurally synthesizes the flow fields coming from the incompressible Navier‐Stokes solver and the vorticity fields generated by vortex particle method for sub‐grid turbulence. We are able to efficiently animate smoke which is highly turbulent and swirling with small scale details. Since this technique does not solve the linear system in high‐resolution grids, it can perform fluid simulation more rapidly. We can easily estimate the influence of turbulent and swirling effect to the fluid flow.  相似文献   
52.
In a recent paper (Automatica 49 (2013) 2860–2866), the Wirtinger-based inequality has been introduced to derive tractable stability conditions for time-delay or sampled-data systems. We point out that there exist two errors in Theorem 8 for the stability analysis of sampled-data systems, and the correct theorem is presented.  相似文献   
53.
结合调研测试的实际工程,根据实际工程中地埋管地源热泵系统中水系统的形式及特点,归纳了设计、运行管理、设备故障等几个方面的水系统常见的问题。探讨了地埋管地源热泵水系统的设计问题,指出某些工程水系统存在的问题及解决思路;分析水系统故障的原因及表现,通过对水系统运行状态的观察与测试,从机组COP及系统能效比的角度分析水系统故障的影响:对于运行管理方面,提出相应的水系统形式的运行建议,为优化地埋管地源热泵的设计及运行管理提供了相应参考。  相似文献   
54.
Droplet‐based microfluidics enable the production of emulsions and microparticles with spherical shapes, but the high‐throughput fabrication of nonspherical emulsions and microparticles still remains challenging because interfacial tension plays a dominant role during preparation. Herein, ionic liquids (ILs) containing salts, which possess sufficient osmotic pressure to realize water transport and phase separation, are introduced as inner cores of oil‐in‐oil‐in‐water double emulsions and it is shown that nonspherical emulsions can be constructed by osmosis‐driven arrested coalescence of inner cores. Subsequently, ultraviolet polymerization of the nonspherical emulsions leads to nonspherical microparticles. By tailoring the number, composition, and size of inner cores as well as coalescence time, a variety of nonspherical shapes such as dumbbell, rod, spindle, snowman, tumbler, three‐pointed star, triangle, and scalene triangle are created. Importantly, benefitting from excellent solvency of ILs, this system can serve as a general platform to produce nonspherical microparticles made from different materials. Moreover, by controlling the osmotic pressure, programmed coalescence of inner cores in double emulsions is realizable, which indicates the potential to build microreactors. Thus, a simple and high‐throughput strategy to create nonspherical microparticles with arrested coalescence shapes is developed for the first time and can be further used to construct novel materials and microreactors.  相似文献   
55.
The culture of keratinocytes on flexible membranes has been proposed as a means to simplify, accelerate and improve the efficiency with which proliferating cells are delivered to full thickness or non-healing skin defects. The purpose of this article was to study the ability of chitosan-gelatin manbranes to facilitate the growth of human keratinocytes. The membranes with different chitosan contents were studied. The surface properties of chitosan-gelatin membranes were investigate by SEM, and water contact angle test. The mechanical property of the membranes was tested. Data implied that gelatin could make the membranes more flexible and hydrophilic than chitosan membranes, which may regulate the seeded cells behavior. Loading human keratinocytes on chitosan-gelatin membranes, cells attachment, spread, and growth were investigated by light microscopy, SEM, and MTT test. The results suggested that the adhesion and proliferation of keratinocytes seeded on chitosan-gelatin membranes were same as on tissue culture plate, in which gelatin could modify the interaction between keratinocytes and chitosan membranes. Therefore, chitosan-gelatin membrane is a good candidate for keratinocytes delivery system.  相似文献   
56.
Preparations of PbS-coated titanium dioxide (TiO2) and lead sulfide (PbS) nanoparticles under ultrasonic field at the multibubble sonoluminescence (MBSL) conditions were tested in water solutions. Under the optimal MBSL conditions (20 kHz and 220 W power input), PbS nanoparticles (diameter = 40-50 nm) were prepared by treating lead nitrate and thioacetamide for 20 min in water solutions. The size of PbS nanoparticles was found to be easily increased to about 90 nm in diameter by increasing the reactant concentration twice. A similar sonochemical reaction with TiO2 nanoparticles (about 20-30 nm in diameter) gave rise to PbS-coated TiO2 nanoparticles with a core/shell structure. The PbS thin film coating was quite uniform and the average coating depth of PbS on the TiO2 nanoparticles was about 2-3 nm under the described conditions. It is interesting to note that the coating depth was found to be controlled to 2-10 nm range by increasing the amounts of reactants for Pb and S twice with a sonication time of 30 min.  相似文献   
57.
The presence of protein inclusions, called Lewy bodies (LBs) and Lewy neurites (LNs), in the brain is the main feature of Parkinson’s disease (PD). Recent evidence that the prion-like propagation of α-synuclein (α-syn), as a major component of LBs and LNs, plays an important role in the progression of PD has gained much attention, although the molecular mechanism remains unclear. In this study, we evaluated whether neuronal ApoE regulates the cell-to-cell transmission of α-syn and explored its molecular mechanism using in vitro and in vivo model systems. We demonstrate that neuronal ApoE deficiency attenuates both α-syn uptake and release by downregulating LRP-1 and LDLR expression and enhancing chaperone-mediated autophagy activity, respectively, thereby contributing to α-syn propagation. In addition, we observed that α-syn propagation was attenuated in ApoE knockout mice injected with pre-formed mouse α-syn fibrils. This study will help our understanding of the molecular mechanisms underlying α-syn propagation.  相似文献   
58.
由于多余物的危害及航天产品高精尖的发展需要,多余物防控设计已成为产品设计不可或缺的设计准则.通过对氢氧发动机多余物的特点进行分析,发动机明确了介质精度控制要求并进行了过滤器的设计,可有效对多余物进行防控.针对氢氧发动机的低温特点,还进行了发动机"潮气及未置换干净的空气"的防控设计以防"冰堵".  相似文献   
59.
Prostate cancer (PCa) is the most commonly diagnosed malignancy among men in developed countries. The five-year survival rate for men diagnosed with early-stage PCa is approximately 100%, while it is less than 30% for castration-resistant PCa (CRPC). Currently, the detection of prostate-specific antigens as biomarkers for the prognosis of CRPC is criticized because of its low accuracy, high invasiveness, and high false-positive rate. Therefore, it is important to identify new biomarkers for prediction of CRPC progression. Extracellular vesicles (EVs) derived from tumors have been highlighted as potential markers for cancer diagnosis and prognosis. Specifically, urinary EVs directly reflect changes in the pathophysiological conditions of the urogenital system because it is exposed to prostatic secretions. Thus, detecting biomarkers in urinary EVs provides a promising approach for performing an accurate and non-invasive liquid biopsy for CPRC. In this study, we effectively isolated urinary EVs with low protein impurities using size-exclusion chromatography combined with ultrafiltration. After EV isolation and characterization, we evaluated the miRNAs in urinary EVs from healthy donors and patients with CRPC. The results indicated that miRNAs (miR-21-5p, miR-574-3p, and miR-6880-5p) could be used as potential biomarkers for the prognosis of CRPC. This analysis of urinary EVs contributes to the fast and convenient prognosis of diseases, including CRPC, in the clinical setting.  相似文献   
60.
Cold plate is an important component for a liquid battery thermal management system.In order to study the transient thermal performance of the cold plate under ...  相似文献   
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