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   3655篇
  免费   335篇
  国内免费   6篇
电工技术   29篇
综合类   1篇
化学工业   861篇
金属工艺   86篇
机械仪表   163篇
建筑科学   60篇
能源动力   149篇
轻工业   252篇
水利工程   4篇
石油天然气   1篇
无线电   549篇
一般工业技术   802篇
冶金工业   823篇
原子能技术   25篇
自动化技术   191篇
  2024年   4篇
  2023年   49篇
  2022年   53篇
  2021年   104篇
  2020年   83篇
  2019年   106篇
  2018年   137篇
  2017年   107篇
  2016年   123篇
  2015年   116篇
  2014年   174篇
  2013年   209篇
  2012年   258篇
  2011年   265篇
  2010年   193篇
  2009年   175篇
  2008年   216篇
  2007年   130篇
  2006年   94篇
  2005年   88篇
  2004年   89篇
  2003年   86篇
  2002年   71篇
  2001年   56篇
  2000年   41篇
  1999年   67篇
  1998年   285篇
  1997年   155篇
  1996年   87篇
  1995年   67篇
  1994年   40篇
  1993年   62篇
  1992年   12篇
  1991年   14篇
  1990年   19篇
  1989年   16篇
  1988年   13篇
  1987年   18篇
  1986年   10篇
  1985年   12篇
  1984年   4篇
  1982年   1篇
  1981年   5篇
  1980年   3篇
  1979年   2篇
  1978年   1篇
  1977年   15篇
  1976年   60篇
  1975年   1篇
排序方式: 共有3996条查询结果,搜索用时 0 毫秒
71.
Human joints have respective ranges of motion and joint forces corresponding to each kind of joint; this necessitates considerations of the characteristics of human joints to fabricate wearable strain sensors conformable to the human body, and capable of precisely monitoring complex motions of the human body. In the present study, the “all textile‐based highly stretchable structure” that is capable of precisely sensing motions (folding and rotation) of the human joints (finger, wrist, elbow, spine, and knee) is fabricated by optimizing patterns (straight, blind, and zigzag) of conductive yarns employed as the conductive part of the strain sensor, and several textile substrates (braided elastic fabric, knit fabric, and woven fabric), having preferable elasticity and conformability employed for the fabrication of strain sensors suitable for human joints. In particular, the technology, enabling the prestraining of textile substrate, is exploited to fabricate a strain sensor that is capable of outputting selective signals corresponding to the folding motion of the spinal joint over a predetermined angle of motion, and the gait pattern of the wearer of the sensor, attached to his or her knee joint doing folding and rotational motions, is analyzed.  相似文献   
72.
73.
Hollow carbon–silica nanospheres that exhibit angle‐independent structural color with high saturation and minimal absorption are made. Through scattering calculations, it is shown that the structural color arises from Mie resonances that are tuned precisely by varying the thickness of the shells. Since the color does not depend on the spatial arrangement of the particles, the coloration is angle independent and vibrant in powders and liquid suspensions. These properties make hollow carbon–silica nanospheres ideal for applications, and their potential in making flexible, angle‐independent films and 3D printed films is explored.  相似文献   
74.
75.
76.
We present a straightforward method for simultaneously enhancing the electrical conductivity, environmental stability, and photocatalytic properties of graphene films through one‐step transfer of CVD graphene and integration by introducing TiO2/graphene oxide layer. A highly durable and flexible TiO2 layer is successfully used as a supporting layer for graphene transfer instead of the commonly used PMMA. Transferred graphene/TiO2 film is directly used for measuring the carrier transport and optoelectronic properties without an extra TiO2 removal and following deposition steps for multifunctional integration into devices because the thin TiO2 layer is optically transparent and electrically semiconducting. Moreover, the TiO2 layer induces charge screening by electrostatically interacting with the residual oxygen moieties on graphene, which are charge scattering centers, resulting in a reduced current hysteresis. Adsorption of water and other chemical molecules onto the graphene surface is also prevented by the passivating TiO2 layer, resulting in the long term environmental stability of the graphene under high temperature and humidity. In addition, the graphene/TiO2 film shows effectively enhanced photocatalytic properties because of the increase in the transport efficiency of the photogenerated electrons due to the decrease in the injection barrier formed at the interface between the F‐doped tin oxide and TiO2 layers.  相似文献   
77.
Here we show that the substitution Thr 26-->His in the active site of T4 lysozyme causes the product to change from the alpha- to the beta-anomer. This implies an alteration in the catalytic mechanism of the enzyme. From the change in product, together with inspection of relevant crystal structures, it is inferred that wild-type T4 lysozyme is an anomer-inverting enzyme with a single displacement mechanism in which water attacks from the alpha-side of the substrate. In contrast, the mutant T26H is an anomer-retaining enzyme with an apparently double displacement mechanism in which a water molecule attacks from the opposite side of the substrate. The results also show that the mechanism of wild-type T4 lysozyme differs from that of hen egg-white lysozyme even though both enzymes are presumed to have evolved from a common precursor.  相似文献   
78.
Rapidly growing knowledge about the nature and behaviour of breast cancer has led to many treatment modalities. Consequently, the possibilities of individualizing the treatment of breast cancer increase. The major tool for the determination of an optimal treatment plan is the estimation of the extent of the disease: in other words, staging. As a consequence, together with the expected result of the treatment, the stage of the disease gives information on the prognosis of the patient. Current staging systems insufficiently describe the clinically important features of breast cancer with respect to management and outcome: local and regional extent, invasiveness, aggressiveness, the state of dissemination, and the effectiveness of different treatment modalities. For staging of the local and regional extent, histology plays a prominent role and should be incorporated in future staging systems. Histological workup therefore needs standardisation. Histological parameters as tumour size, grade, nodal status, and vascular invasion are also the most important prognostic factors. Many so-called biological prognostic factors are related to the invasiveness and aggressiveness (metastatic potential) of the tumour, and therefore to the prognosis of the patient. However, these factors do not necessarily predict the effectiveness of certain systemic treatments. Only if the biological foundation of a prognostic factor is completely clarified can treatment be based on this knowledge, and the factor will become a predictor for the treatment effect. Many "biological" prognostic factors do not fulfil this main criterion and are therefore not useful for clinical decision making. A clinically useful staging system covers three primary aims: (1) to guide locoregional treatment, (2) to prognosticate the chance of survival, and (3) to indicate who needs what kind of adjuvant treatment. For the conception of a new staging system the following steps should be taken: standardization of all aspects of histology, identification of regional nodal involvement, and validation of prognostic factors with respect to their predictive value to treatment outcome.  相似文献   
79.
80.
Significant cleavage by hammerhead ribozymes requires activation by divalent metal ions. Several models have been proposed to account for the influence of metal ions on hammerhead activity. A number of recent papers have presented data that have been interpreted as supporting a one-metal-hydroxide-ion mechanism. In addition, a solvent deuterium isotope effect has been taken as evidence against a proton transfer in the rate-limiting step of the cleavage reaction. We propose that these data are more easily explained by a two-metal-ion mechanism that does not involve a metal hydroxide, but does involve a proton transfer in the rate-limiting step.  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