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   701篇
  免费   23篇
  国内免费   1篇
电工技术   44篇
化学工业   193篇
金属工艺   10篇
机械仪表   33篇
建筑科学   17篇
能源动力   32篇
轻工业   67篇
水利工程   4篇
石油天然气   2篇
无线电   39篇
一般工业技术   141篇
冶金工业   58篇
原子能技术   32篇
自动化技术   53篇
  2023年   5篇
  2022年   10篇
  2021年   26篇
  2020年   4篇
  2019年   11篇
  2018年   25篇
  2017年   12篇
  2016年   22篇
  2015年   9篇
  2014年   25篇
  2013年   62篇
  2012年   36篇
  2011年   42篇
  2010年   40篇
  2009年   36篇
  2008年   40篇
  2007年   34篇
  2006年   21篇
  2005年   29篇
  2004年   20篇
  2003年   25篇
  2002年   19篇
  2001年   5篇
  2000年   11篇
  1999年   14篇
  1998年   23篇
  1997年   10篇
  1996年   13篇
  1995年   7篇
  1994年   15篇
  1993年   6篇
  1992年   6篇
  1991年   2篇
  1990年   6篇
  1989年   2篇
  1988年   3篇
  1986年   3篇
  1985年   5篇
  1984年   3篇
  1983年   2篇
  1982年   7篇
  1981年   5篇
  1980年   5篇
  1979年   4篇
  1978年   2篇
  1977年   5篇
  1976年   3篇
  1975年   1篇
  1973年   3篇
  1972年   1篇
排序方式: 共有725条查询结果,搜索用时 578 毫秒
101.
Plants synthesize variable mixtures of herbivore-induced plant volatiles (HIPVs) as part of their evolutionary conserved defense. To elucidate the impact of chewing herbivores with different level of adaptation on HIPV profiles in rice, we measured HIPVs released from rice seedlings challenged by either the generalist herbivore Mythimna loreyi (MYL) or the specialist Parnara guttata (PAG). Both herbivores markedly elicited the emission of HIPVs, mainly on the second and third days after attack compared to control plants. In addition, side-by-side HIPV comparisons using MYL and PAG caterpillars revealed that generalist feeding induced comparably more HIPVs relative to specialist, particularly on day two as highlighted by multivariate analysis (PLS-DA) of emitted HIPVs, and further confirmed in mimicked herbivory experiments. Here, mechanically wounded plants treated with water (WW) released more VOCs than untreated controls, and on top of this, oral secretions (OS) from both herbivores showed differential effects on volatile emissions from the wounded plants. Similar to actual herbivory, MYL OS promoted higher amounts of HIPVs relative to PAG OS, thus supporting disparate induction of rice indirect defenses in response to generalist and specialist herbivores, which could be due to the differential composition of their OS. (196 words).  相似文献   
102.
PEGylated polyplexes (lac-PEGylated polyplexes) composed of poly(L-lysine) and lactosylated poly(ethylene glycol)-small interfering RNA conjugate, which inhibits the RecQL1 gene product, were revealed to show an appreciable growth inhibition of multicellular HuH-7 spheroids (human hepatocarcinoma cell lines) for up to 21 days (IC(50)=6 nM); this system used as an in vitro three-dimensional (3D) model mimicking the in vivo biology of tumors. The PEGylated polyplexes thus prepared had a size of approximately 110 nm with clustered lactose moieties on their periphery as targeting ligands for the asialoglycoprotein-receptor-expressing HuH-7 cells. In contrast, OligofectAMINE/siRNA (cationic lipoplex) was observed to have almost no growth-inhibitory effect against HuH-7 spheroids, even though the lipoplex showed a stronger growth-inhibitory effect than the lac-PEGylated polyplexes on conventional monolayer-cultured HuH-7 cells. The FITC-tagged conjugate in the lac-PEGylated polyplexes showed smooth penetration into the HuH-7 spheroids compared with that in the lipoplexes, as observed by confocal fluorescence-scanning microscopy. This indicates that the small size of approximately 100 nm and the reduced nonspecific interaction due to the nonionic and hydrophilic lactosylated PEG layer contributes to the smooth penetration of the PEGylated polyplexes into the spheroid interior, eventually facilitating their uptake into the cells composing the spheroids. Cellular apoptosis indicating programmed cell death was also observed in the HuH-7 spheroids treated with the PEGylated polyplexes, revealing that the observed growth inhibition was indeed induced by the RNAi of the RecQL1 siRNA. These data suggest that the smart PEGylated polyplexes can indeed penetrate into the multiple cell layers of 3D tumor masses in vivo, exerting therapeutic effects through the RNAi.  相似文献   
103.
A number of photofunctional molecular compounds have been developed recently. Typical examples of these are phototunable valence tautomeric compounds, which are now attracting great attention. When the charge-transfer bands of some Co valence tautomeric compounds are excited at low temperature, metastable redox isomers can be created after irradiation. The lifetimes of the metastable states can be more than several hours. These transformations can involve changes in the magnetic properties of the compounds, as well as their color. Hence, these compounds can be regarded as novel photomagnetic materials. The photoresponsive behaviors of these valence tautomeric compounds are similar to those of spin-crossover complexes (light-induced excited spin-state trapping effects).  相似文献   
104.
Developments in asymmetric hydrogenation from an industrial perspective   总被引:1,自引:0,他引:1  
Examples of developments in asymmetric hydrogenation from various perspectives, in an effort to improve efficiency, are reported. Discussed in this Account are (1) the improved synthesis of BINAP ligands, (2) the design of SEGPHOS ligands for higher enantioselectivity, (3) a new protocol with fewer reaction steps to synthesize beta-aminoesters, and (4) a novel asymmetric hydrogenation mediated by a copper catalyst.  相似文献   
105.
A magnetic vortex is a curling magnetic structure realized in a ferromagnetic disk, which is a promising candidate for a memory cell for future non-volatile data-storage devices. Thus, an understanding of the stability and dynamical behaviour of the magnetic vortex is a major requirement for developing magnetic data-storage technology. Since the publication of experimental proof for the existence of a nanometre-scale core with out-of-plane magnetization in a magnetic vortex, the dynamics of vortices have been investigated intensively. However, a way to electrically control the core magnetization, which is a key for constructing a vortex-core memory, has been lacking. Here, we demonstrate the electrical switching of the core magnetization by using the current-driven resonant dynamics of the vortex; the core switching is triggered by a strong dynamic field that is produced locally by a rotational core motion at a high speed of several hundred metres per second. Efficient switching of the vortex core without magnetic-field application is achieved owing to resonance. This opens up the potentiality of a simple magnetic disk as a building block for spintronic devices such as a memory cell where the bit data is stored as the direction of the nanometre-scale core magnetization.  相似文献   
106.
We performed four-terminal conductivity measurements on a CoSi2 nanowire (NW) at room temperature by using PtIr-coated carbon nanotube (CNT) tips in a four-tip scanning tunneling microscope. The physical stability and high aspect ratio of the CNT tips made it possible to reduce the probe spacing down to ca. 30 nm. The probe-spacing dependence of resistance showed diffusive transport even at 30 nm and no current leakage to the Si substrate.  相似文献   
107.
This paper presents experimental results on polarizers with nonrectangular grooves to be used in high power millimeter wave transmission lines for electron cyclotron heating (ECH) of fusion plasmas. A low-power test at a frequency of 106.4 GHz has been carried out for several polarizers with different groove depths. The polarization characteristics experimentally measured are in good agreement with numerical results in which the actual groove shape functions are taken into account. This confirms the design optimization for future polarizer. Favorable results have also been obtained in a 400 kW-level high-power test for the polarizer installed in an ECH transmission line of the Heliotron-E plasma device.  相似文献   
108.
Neuronal morphological changes in the epidermis are considered to be one of causes of abnormal skin sensations in dry skin-based skin diseases. The present study aimed to develop an in vitro model optimised for human skin to test the external factors that lead to its exacerbation. Human-induced pluripotent stem cell-derived sensory neurons (hiPSC-SNs) were used as a model of human sensory neurons. The effects of chemical substances on these neurons were evaluated by observing the elongation of nerve fibers, incidence of blebs (bead-like swellings), and the expression of nicotinamide mononucleotide adenylyl transferase 2 (NMNAT2). The nerve fiber length increased upon exposure to two common cosmetic preservatives—methylparaben and phenoxyethanol—but not to benzo[a]pyrene, an air pollutant at the estimated concentrations in the epidermis. Furthermore, the incidence of blebs increased upon exposure to benzo[a]pyrene. However, there was a decrease in the expression of NMNAT2 in nerve fibers, suggesting degenerative changes. No such degeneration was found after methylparaben or phenoxyethanol at the estimated concentrations in the epidermis. These findings suggest that methylparaben and phenoxyethanol promote nerve elongation in hiPSC-SNs, whereas benzo[a]pyrene induces nerve degeneration. Such alterations may be at least partly involved in the onset and progression of sensitive skin.  相似文献   
109.
It has been considered that the contribution of the vapor-phase reaction (VPR) to the global three-phase reaction rate may become much lower as the catalyst effectiveness factor approaches unity. In this study, the hydrogenation of 1-methylnaphthalene was performed as an example of slow reactions using a laboratory-scale trickle-bed reactor (TBR) at 583 K, 8.0 MPa. It was qualitatively confirmed that VPR contributed to the product yields in TBR even in this slow reaction system when the liquid velocity was low and the volatility of the liquid was high. Langmuir–Hinshelwood type kinetic equations were established for the vapor-phase reaction. The product yields in TBR neither be explained by liquid- vapor-phase kinetics without external effects, nor the conventional partial wetting model. Therefore, a partial wetting model considering the contribution of VPR was proposed where the catalyst bed composed of externally partial and internally complete wet particles, and completely dry particles was assumed. Using this model, the product yields in TBR were suitably explained.  相似文献   
110.
Spontaneous transition of the plasma confinement mode was observed in the helicalaxis heliotron device “Heliotron J“ for three different plasma heating schemes, i.e. ECHonly, NBI-only and the combination of ECH and NBI. The transition seems to occur above a certain critical density. In addition to the confinement transition, a spontaneous shift of the hitting position of the divertor plasma flux on the wall was observed. This shift could be related with the change of the edge field topology caused by non-inductive toroidal currents.  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