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   25714篇
  免费   946篇
  国内免费   33篇
电工技术   334篇
综合类   38篇
化学工业   5854篇
金属工艺   450篇
机械仪表   494篇
建筑科学   1337篇
矿业工程   101篇
能源动力   661篇
轻工业   1970篇
水利工程   235篇
石油天然气   73篇
无线电   1892篇
一般工业技术   4657篇
冶金工业   4791篇
原子能技术   209篇
自动化技术   3597篇
  2023年   219篇
  2022年   361篇
  2021年   576篇
  2020年   350篇
  2019年   444篇
  2018年   550篇
  2017年   477篇
  2016年   657篇
  2015年   566篇
  2014年   768篇
  2013年   1461篇
  2012年   1197篇
  2011年   1558篇
  2010年   1106篇
  2009年   1047篇
  2008年   1195篇
  2007年   1114篇
  2006年   965篇
  2005年   777篇
  2004年   774篇
  2003年   678篇
  2002年   583篇
  2001年   446篇
  2000年   383篇
  1999年   429篇
  1998年   843篇
  1997年   598篇
  1996年   467篇
  1995年   445篇
  1994年   403篇
  1993年   382篇
  1992年   278篇
  1991年   203篇
  1990年   282篇
  1989年   269篇
  1988年   224篇
  1987年   238篇
  1986年   236篇
  1985年   280篇
  1984年   230篇
  1983年   231篇
  1982年   215篇
  1981年   200篇
  1980年   174篇
  1979年   205篇
  1978年   170篇
  1977年   192篇
  1976年   245篇
  1975年   162篇
  1974年   126篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Chronic lymphocytic leukemia (CLL) is considered a clonal B cell malignancy. Sporadically, CLL cases with multiple productive heavy and light-chain rearrangements were detected, thus leading to a bi- or oligoclonal CLL disease with leukemic cells originating either from different B cells or otherwise descending from secondary immunoglobulin rearrangement events. This suggests a potential role of clonal hematopoiesis or germline predisposition in these cases. During the screening of 75 CLL cases for kappa and lambda light-chain rearrangements, we could detect a single case with CLL cells expressing two distinct kappa and lambda light chains paired with two separate immunoglobulin heavy-chain variable regions. Furthermore, this patient also developed a prostate carcinoma. Targeted genome sequencing of highly purified light-chain specific CLL clones from this patient and from the prostate carcinoma revealed the presence of a rare germline polymorphism in the POLE gene. Hence, our data suggest that the detected SNP may predispose for cancer, particularly for CLL.  相似文献   
942.
To conduct a well‐planned plant shutdown, so as to reduce flare emissions for the sake of plant profitability and local environmental sustainability, one of the primary tasks is to perform comprehensive and precise accountings for flare emissions. Since the literature is still lacking systematic and quantitative studies, plant‐wide dynamic simulations are employed to simulate an ethylene plant shutdown and characterize its flare emission sources through which dynamic emission profiles of various emission species changing with respect to time are obtained. Plant shutdown emission inventories are enriched with details for point emission sources, and possible technical supports are provided to both industry and environmental agencies on evaluating and developing cost‐effective flare minimization strategies in the future.  相似文献   
943.
A two-step synthesis for methionine-containing hydrophobic and/or aggregation-prone peptides is presented that takes advantage of the reversibility of methionine oxidation. The use of polar methionine sulfoxide as a building block in solid-phase peptide synthesis improves the synthesis quality and yields the crude peptide, with significantly improved solubility compared to the reduced species. This facilitates the otherwise often laborious peptide purification by high-performance liquid chromatography. The subsequent reduction proceeds quantitatively. This approach has been optimised with the methionine-rich Tar-DNA-binding protein 43 (307–347), but is also more generally applicable, as demonstrated by the syntheses of human calcitonin and two aggregation-prone peptides from the human prion protein.  相似文献   
944.
945.
To investigate the effect of leptin in childhood ITP, we measured plasma leptin in 39 children with acute ITP, after treatment and in remission, and in 33 healthy age/BMI-matched controls. We also cultured ITP and control peripheral blood mononuclear cells (PBMCs) with recombinant leptin to assess its direct effect on pro/anti-inflammatory cytokine gene expression. A significant increase in leptin was observed in children with active disease compared to controls. A significant inverse correlation of leptin with platelet count was also observed in children with acute ITP. Leptin remained high after treatment with IVIg, whereas steroid treatment lowered leptin below control levels. In remission, leptin was in the control range. Cytokine gene expression was significantly increased in children with acute ITP compared with controls, with highest expression for IFN-γ and IL-10. IVIg/steroid treatment significantly decreased IFN-γ and IL-10 expression. In remission, IFN-γ and IL-10 expression remained low. Addition of leptin to PBMCs isolated from patients in remission resulted in a significant increase in IL-10 gene expression compared to controls. Further experiments with purified T-cells and monocytes identified monocytes as the source of leptin-induced IL-10. We suggest that leptin acts as an active anti-inflammatory agent in childhood ITP by promoting IL-10 secretion by monocytes.  相似文献   
946.
947.
Polyampholyte latexes can exist within a certain pH range as low‐viscosity aqueous dispersions, while upon a pH shift to the vicinity of the isoelectric point they undergo ionic coacervation. Three classes of coacervation latexes were synthesized and evaluated for their suitability for use in tablet coating applications. Pharmaceutical tablet coatings are commonly based on hydroxypropyl methyl cellulose, poly(vinyl alcohol), and acrylic polymers. Because of the high viscosity of their aqueous solutions, and to the consequent required low concentrations of the tablet coating polymers in the coating solutions to enable sufficiently low viscosity for effective spray application, the current commercial pharmaceutical tablet coating technology requires the removal of large amounts of water during the manufacturing process. In this work, films prepared from high‐solids, low‐viscosity coacervated acrylic latexes showed good hardness, very low tackiness, an excellent combination of optical properties, and very low water vapor permeability. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40049.  相似文献   
948.
949.
Digital Light Processing (DLP) is a powerful technique for the preparation of ceramic parts with high resolution and complex shapes. In the last years, the development of photosensitive slurries for the production of ceramics with good mechanical properties has received much attention. In this work, ZrO2 UV-curable slurries were prepared in two steps for their application in DLP. Firstly, the surface modification of the ZrO2 particles was carried out using a dispersing agent and secondly, the modified powder was dispersed in an acrylate based mixture. Parts with different geometries were printed and a resolution experiment was also carried out in order to determine the limitations of the slurry. Finally, 30 bars were produced to study the mechanical properties of the sintered parts (ρ = 6.00 ± 0.01 g/mL) by 4-point bending tests and Weibull analysis, obtaining a flexural strength σ0 = 741 (718–765) MPa with a Weibull coefficient of 11.4.  相似文献   
950.
In many technical processes gas, multicomponent diffusion takes place in confinements that are rarely uniform in direction of their long axis (e.g., catalysts pores). Here, we show that in conical tubes multicomponent diffusion is hindered. This effect increases with ratio of inlet to outlet cone radius Λ, indifferent of the orientation of the tube. Based on the Maxwell–Stefan equations, predictive analytical solution for ideal multicomponent diffusion in slightly tapered ducts is developed. In two‐bulb diffusion experiments on a uniform tube, the results of Duncan and Toor (1962) were reproduced. Comparison of model and experiment shows that the solution presented here provides a reliable quantitative prediction of the temporal change of H2, N2, and CO2‐concentration for both tube geometries, uniform and slightly conical. In the demonstrated case (Λ = 3.16), mass diffusion is 68% delayed. Thus, for gaseous diffusion in “real,” typically tapered pores the transport limitation is more serious than considered so far. © 2014 American Institute of Chemical Engineers AIChE J, 61: 1404–1412, 2015  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