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   4368篇
  免费   261篇
  国内免费   2篇
电工技术   22篇
综合类   5篇
化学工业   1937篇
金属工艺   61篇
机械仪表   74篇
建筑科学   114篇
矿业工程   6篇
能源动力   109篇
轻工业   787篇
水利工程   23篇
石油天然气   18篇
无线电   176篇
一般工业技术   623篇
冶金工业   175篇
原子能技术   11篇
自动化技术   490篇
  2024年   6篇
  2023年   90篇
  2022年   484篇
  2021年   449篇
  2020年   140篇
  2019年   141篇
  2018年   163篇
  2017年   173篇
  2016年   177篇
  2015年   148篇
  2014年   194篇
  2013年   262篇
  2012年   275篇
  2011年   291篇
  2010年   207篇
  2009年   223篇
  2008年   203篇
  2007年   177篇
  2006年   135篇
  2005年   120篇
  2004年   92篇
  2003年   75篇
  2002年   71篇
  2001年   43篇
  2000年   34篇
  1999年   41篇
  1998年   35篇
  1997年   31篇
  1996年   26篇
  1995年   19篇
  1994年   14篇
  1993年   14篇
  1992年   5篇
  1991年   8篇
  1989年   4篇
  1988年   2篇
  1987年   4篇
  1986年   3篇
  1985年   3篇
  1984年   5篇
  1983年   5篇
  1982年   4篇
  1981年   5篇
  1980年   3篇
  1979年   7篇
  1975年   3篇
  1974年   3篇
  1973年   2篇
  1971年   4篇
  1969年   2篇
排序方式: 共有4631条查询结果,搜索用时 15 毫秒
91.
Dendritic cells (DCs) are immune specialized cells playing a critical role in promoting immune response against antigens, and may represent important targets for therapeutic interventions in cancer. DCs can be stimulated ex vivo with pro-inflammatory molecules and loaded with tumor-specific antigen(s). Protocols describing the specific details of DCs vaccination manufacturing vary widely, but regardless of the employed protocol, the DCs vaccination safety and its ability to induce antitumor responses is clearly established. Many years of studies have focused on the ability of DCs to provide overall survival benefits at least for a selection of cancer patients. Lessons learned from early trials lead to the hypothesis that, to improve the efficacy of DCs-based immunotherapy, this should be combined with other treatments. Thus, the vaccine’s ultimate role may lie in the combinatorial approaches of DCs-based immunotherapy with chemotherapy and radiotherapy, more than in monotherapy. In this review, we address some key questions regarding the integration of DCs vaccination with multimodality therapy approaches for cancer treatment paradigms.  相似文献   
92.
Three novel 2,7-substituted acridine derivatives were designed and synthesized to investigate the effect of this functionalization on their interaction with double-stranded and G-quadruplex DNA. Detailed investigations of their ability to bind both forms of DNA were carried out by using spectrophotometric, electrophoretic, and computational approaches. The ligands in this study are characterized by an open-chain (L1) or a macrocyclic (L2, L3) framework. The aliphatic amine groups in the macrocycles are joined by ethylene (L2) or propylene chains (L3). L1 behaved similarly to the lead compound m-AMSA, efficiently intercalating into dsDNA, but stabilizing G-quadruplex structures poorly, probably due to the modest stabilization effect exerted by its protonated polyamine chains. L2 and L3, containing small polyamine macrocyclic frameworks, are known to adopt a rather bent and rigid conformation; thus they are generally expected to be sterically impeded from recognizing dsDNA according to an intercalative binding mode. This was confirmed to be true for L3. Nevertheless, we show that L2 can give rise to efficient π-π and H-bonding interactions with dsDNA. Additionally, stacking interactions allowed L2 to stabilize the G-quadruplex structure: using the human telomeric sequence, we observed the preferential induction of tetrameric G-quadruplex forms. Thus, the presence of short ethylene spacers seems to be essential for obtaining a correct match between the binding sites of L2 and the nucleobases on both DNA forms investigated. Furthermore, current modeling methodologies, including docking and MD simulations and free energy calculations, provide structural evidence of an interaction mode for L2 that is different from that of L3; this could explain the unusual stabilizing ability of the ligands (L2>L3>L1) toward G-quadruplex that was observed in this study.  相似文献   
93.
Eight different calcium phosphate nanoparticles, namely bovine bone bioapatite calcined at 500, 600, and 700°C, Mg-doped brushite, fluorinated calcium phosphate, Ca-deficient hydroxyapatite, hydroxyapatite, and tricalcium phosphate, were characterized employing physico-chemical methods. Their cytocompatibility was evaluated under human osteoblast-like cell line MG-63 culture conditions in elution media and via the direct interaction of cells with calcium phosphate nanoparticles. The main objective was to determine the correlation of the cell indices with the differently determined physical and chemical parameters of the calcium phosphates. Chemical composition, which contributes toward pH changes, and the calcium ion concentration in the medium appear to make up particularly significant factors; moreover, it was proved that the number of material types represents a further important aspect. In the case of a large number of material types, almost no correlation was determined between the analyzed parameters; however, in the case of a small number of apatite types, several positive correlations were found. It can be concluded that it is not possible to identify any monitored parameters that had a major impact on cell behavior or, at least, such an effect which can be generalized. It appears more likely that cell behavior is affected by the interplay of various parameters.  相似文献   
94.
DNA-encoded chemical libraries are often used for the discovery of ligands against protein targets of interest. These large collections of DNA-barcoded chemical compounds are typically screened by using affinity capture methodologies followed by PCR amplification and DNA sequencing procedures. However, the performance of individual steps in the selection procedures has been scarcely investigated, so far. Herein, the quantitative analysis of selection experiments, by using three ligands with different affinity to carbonic anhydrase IX as model compounds, is described. In the first set of experiments, quantitative PCR (qPCR) procedures are used to evaluate the recovery and selectivity for affinity capture procedures performed on different solid-phase supports, which are commonly used for library screening. In the second step, both qPCR and analysis of DNA sequencing results are used to assess the recovery and selectivity of individual carbonic anhydrase IX ligands in a library, containing 360 000 compounds. Collectively, this study reveals that selection procedures can be efficient for ligands with sub-micromolar dissociation constants to the target protein of interest, but also that selection performance dramatically drops if 104 copies per library member are used as the input.  相似文献   
95.
Cold Sintering Process (CSP) was applied on commercial nanopowders to produce nanostructured TiO2 anatase with nano-to-macro porosity. Nanoporous TiO2 based materials were obtained by applying CSP at 150 °C and pressures up to 500 MPa on three TiO2 nanopowders with different specific surface area (s.s.a. = 50, 90 and 370 m2/g), using water as transient aqueous environment. Although TiO2 is insoluble in water, a density of 68% and s.s.a. = 117 m2/g were achieved from the powder with the highest specific surface area. A post annealing process at 500 °C increased the density up to 73% with a s.s.a. = 59 m2/g, and the crystallites dimensions passed from 110 Å in the powder to 130 Å in CSP material and 172 Å after post annealing. Finally, macroporosity was produced by using thermoplastic polymer beads as sacrificial templates within TiO2 nanopowder during CSP, followed by a debonding at 500 °C.  相似文献   
96.
Sinanodonta woodiana (Lea, 1834) is a large Unionid species with a real invasion success. It colonized Europe, Central America, the Indonesian Islands and recently North America. The species life cycle involves a larval parasitic stage on freshwater fish species which contributes to the spread of the mussel. In this paper we describe, for the first time, eight polymorphic microsatellite loci for the species Sinanodonta woodiana. The genetic screening of individuals confirmed that all loci were highly polymorphic. The number of alleles per locus ranged from 7 to 14 and the observed heterozygosity ranged from 0.650 to 0.950. These loci should prove useful to study the species population genetics which could help to infer important aspects of the invasion process.  相似文献   
97.
In this paper, a study on the global gas holdup and hydrodynamic flow regimes developed in a partially aerated bubble column at variable air superficial velocities (UG) in the presence of positive and negative surfactants is presented. According to the results obtained, despite the different liquid phase properties variation caused by the presence of positive (alcohols) and negative (electrolytes) surfactants, both reduce coalescence and the effect in the gas holdup (εG) is equivalent: it increases with the surfactant concentration (C) but only when the (C/Ct) ratio is clearly above 1, being Ct the transition concentration. Contrary to the results obtained for totally aerated bubble columns, for lower values of the (C/Ct) ratio, the holdup remains practically invariable. Considering the crucial role that C and Ct play in the resulting εG, a new prediction equation for εG accounting for the ratio (C/Ct) and UG is presented and its performance for both types of surfactants validated. Additionally, visual and wall pressure fluctuations studies reveal that the vortical flow (VF), characterized by an oscillating bubble plume, prevails in ultrapure water (UPW) but results destabilized in the presence of surfactants. This destabilization results in an evolution to a pseudo-steady flow regime, the double cell turbulent flow regime (DCTF), characterized by a quasi-static bubble jet, located at the column centerline that determines the appearance of two static symmetrical vortices  相似文献   
98.
Poly(vinyl alcohol) (PVA) hydrogels were prepared in the presence/absence of Laponite RD (LRD) by using glutaraldehyde (GL) as chemical crosslinker. The effect of GL concentration (CHO/OH ratio between 0.02 and 0.38) and of clay addition on the PVA hydrogel properties was investigated. The swollen hydrogels showed good transparency and flexibility. LRD incorporation into the PVA hydrogel, revealed by Fourier transform infrared spectroscopy, led to a significant increase of the roughness of the dried hydrogel surface (about two times), as established by atomic force microscopy. The swelling ability was affected in a small extent by the clay addition. The elastic modulus decreased from 4680 to 3340 Pa and from 2195 to 1603 Pa by addition of 0.5% LRD into PVA hydrogels obtained with CHO/OH ratio of 0.02 and 0.06, respectively. The LRD addition reduced the gelation time determined by in situ rheological monitoring of PVA crosslinking reaction. The experimental investigations showed that there is an optimum CHO/OH ratio of 0.02 for which the PVA/LRD hybrid hydrogel presents the properties required by a targeted application, as for example support material for wound dressings. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46661.  相似文献   
99.
Conventional expanded polystyrene can absorb moisture, which significantly degrades its properties. In the present study, it was demonstrated that SiO2 can be deposited on polystyrene beads before pre-expansion and molding steps. Under the applied test conditions, expanded polystyrene with nanocrystalline SiO2 additives had approximately 10% lower moisture adsorption and an 8.4% better resistance to deformation. Expanded polystyrene analysis suggested that the observed improvements were caused by the hydrophobic nature of nanocrystalline SiO2 and, even more importantly, because SiO2 acted as an amalgamation catalyst and significantly increased adhesion between the expanded polystyrene beads during the expanded polystyrene molding process.  相似文献   
100.
The intense development that Metal-Organic Frameworks have experienced along the last two decades, reflects the interest on these compounds as a new generation of multifunctional materials with diverse applications. The first works of Prof. Omar Yaghi devoted to obtain open frameworks by combining rigid aromatic linkers and a variety of metal centers, encouraged the creativity of the scientific community to designcoordination polymers employing aliphatic ligands as multitopic building blocks . Here, a revision of the literature dedicated to rare earth coordination networks mainly based in succinate ligand and derivatives is performed. A structural analysis of 2D and 3D frameworks based on rare earth elements and succinate, was carried out considering their inner connectivities and topologies with focus on those compounds with potential photoluminescent and catalytic technological applications. Thus, a variety of optical behaviours regarding the emission mechanisms, colours, lifetimes, quantum yields as well as chemical/thermal sensing properties are presented and compared with related phases found in literature. The catalytic performance of several rare earth-succinates in three important reactions is discussed in terms of their acidity, dimensionality and available active centers towards the formation of the desired products analysing parameters such as selectivity, yields and TOFs.  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