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   2685篇
  免费   96篇
  国内免费   4篇
电工技术   27篇
综合类   5篇
化学工业   630篇
金属工艺   53篇
机械仪表   62篇
建筑科学   98篇
矿业工程   10篇
能源动力   62篇
轻工业   402篇
水利工程   15篇
石油天然气   6篇
无线电   148篇
一般工业技术   443篇
冶金工业   514篇
原子能技术   10篇
自动化技术   300篇
  2023年   28篇
  2022年   53篇
  2021年   91篇
  2020年   26篇
  2019年   50篇
  2018年   74篇
  2017年   62篇
  2016年   88篇
  2015年   69篇
  2014年   87篇
  2013年   182篇
  2012年   130篇
  2011年   147篇
  2010年   100篇
  2009年   96篇
  2008年   101篇
  2007年   100篇
  2006年   82篇
  2005年   83篇
  2004年   54篇
  2003年   51篇
  2002年   65篇
  2001年   23篇
  2000年   36篇
  1999年   35篇
  1998年   148篇
  1997年   91篇
  1996年   80篇
  1995年   46篇
  1994年   38篇
  1993年   43篇
  1992年   21篇
  1991年   18篇
  1990年   21篇
  1989年   10篇
  1988年   18篇
  1987年   12篇
  1986年   16篇
  1985年   22篇
  1984年   16篇
  1983年   16篇
  1981年   20篇
  1980年   19篇
  1979年   9篇
  1978年   10篇
  1977年   20篇
  1976年   33篇
  1975年   8篇
  1973年   13篇
  1940年   11篇
排序方式: 共有2785条查询结果,搜索用时 11 毫秒
71.
The effect of particle size of whole meal rye bread on the apparent digestibility of macro-nutrients, non-starch polysaccharides (NSP) and energy, the energy value of rye NSP and on faecal weight was studied in balance experiments in seven young women. The whole meal breads were prepared from one single batch of rye milled to two different particle sizes (coarse bread: 50% of particles >2 mm, 90% >1 mm; fine bread: 86% of particles <0·5 mm, 58% <0·2 mm). Two diets containing either coarse (350 g day−1) or fine (377 g day−1) whole meal bread and a low fibre control diet were consumed for 3 weeks each in a 3×3 cross-over design. Relative to the low fibre control diet, digestibility of protein, NSP and energy was significantly lower for the diets containing the whole meal breads. Digestibility of fat was the same for all diets. Partial digestible energy value for each g of NSP from coarse and fine whole meal rye bread was calculated to be −3±7 and 1±5 kJ, respectively. There were no differences between coarse and fine whole meal rye bread in the effects on the parameters measured with the exception on faecal wet weight, which was higher for the coarse bread diet.  相似文献   
72.
The complete sequence of a 40 247 bp DNA segment located on the left arm of chromosome X of Saccharomyces cerevisiae has been determined and analysed. The sequence encodes the 5′ coding region of the URA2 gene and 18 open reading frames of at least 100 amino acids. Ten of these correspond to known genes, whereas eight correspond to new genes. In addition, the sequence contains a tRNA-Ala gene, a tRNA-Asp gene, a Ty4 transposable element and three delta elements. The sequence has been deposited in the EMBL databank under Accession Numbers: Z49405, Z49404, Z49403, Z49402, Z49401, Z49400, Z49399, Z49398, Z49397, Z49396, Z49394, Z49392, Z49391, Z49390, Z49389, Z49387, Z49386, Z49385.  相似文献   
73.
Dielectric and rheological measurements are reported on the effect of cure temperature on the water absorption of tris[(2,3-epoxypropoxy)phenyl] methane cured with a 1 : 1 stoichiometric ratio of 4,4′-diaminodiphenylsulphone. Analysis of the water absorption characteristics of these materials using a combination of dielectric and gravimetric measurements has indicated that water molecules can be found in two distinctly different types of environments. There are water molecules which are strongly interacting with polar groups and water molecules clustered together into sub-micro-scale cavities within the matrix structure. Changes in the final cure temperature have the effect of changing both the extent and distribution of the types of water molecules present in the matrix. Validation of the diffusion coefficients obtained from the dielectric analysis is based on a comparison with gravimetric data and the implications are discussed. Differences observed between these two different types of measurement are related to peculiarity in the dielectric method and its extreme sensitivity to interfacial phenomena.  相似文献   
74.
Rectangular plates were injection molded from two grades of commercial polypropylene (PP) differing in the molar mass distribution. The mold was mechanically sealed when a desired pressure pi,max (up to 1560 bar) was reached. Samples were taken from each plate at different distances from the gate and were investigated by applying various methods. In spatially resolved wide-angle X-ray studies, the cross section of the sample was scanned with a fine X-ray beam (collimated by a Kratky small-angle camera) and the intensity of scattering was registered by a linear detector as a function of position in the cross section. The evaluation of the scattering data delivered profiles of several parameters, describing the distribution of crystallite modification β-PP and γ-PP, the degree of orientation, the size of crystallites, and interplanar spacing, depending on the distance from surface. These results and those from measurements of birefringence and elongation at break, and from polarization microscopy and transmission electron microscopy, provided details of the layered structures in the plates, at different flow lengths, and allowed far-reaching statements about the influence of molecular properties and processing conditions on the development of texture in the plates.  相似文献   
75.
76.
Targeting molecular alterations as an effective treatment for isocitrate dehydrogenase-wildtype glioblastoma (GBM) patients has not yet been established. Sterol-O-Acyl Transferase 1 (SOAT1), a key enzyme in the conversion of endoplasmic reticulum cholesterol to esters for storage in lipid droplets (LD), serves as a target for the orphan drug mitotane to treat adrenocortical carcinoma. Inhibition of SOAT1 also suppresses GBM growth. Here, we refined SOAT1-expression in GBM and IDH-mutant astrocytoma, CNS WHO grade 4 (HGA), and assessed the distribution of LD in these tumors. Twenty-seven GBM and three HGA specimens were evaluated by multiple GFAP, Iba1, IDH1 R132H, and SOAT1 immunofluorescence labeling as well as Oil Red O staining. To a small extent SOAT1 was expressed by tumor cells in both tumor entities. In contrast, strong expression was observed in glioma-associated macrophages. Triple immunofluorescence labeling revealed, for the first time, evidence for SOAT1 colocalization with Iba1 and IDH1 R132H, respectively. Furthermore, a notable difference in the amount of LD between GBM and HGA was observed. Therefore, SOAT1 suppression might be a therapeutic option to target GBM and HGA growth and invasiveness. In addition, the high expression in cells related to neuroinflammation could be beneficial for a concomitant suppression of protumoral microglia/macrophages.  相似文献   
77.
Bacteriological analysis of milk samples from quarters of a dairy cow suffering from subclinical mastitis yielded two isolates of Staphylococcus aureus which gave a negative reaction in the standard coagulase test. Both isolates were also clumping factor and thermonuclease negative, and gave a negative reaction in the Staphaurex? test. The isolates were identified by using commercial biochemical systems, and by PCR analysis of different staphylococcal cell surface protein and exoprotein genes. Further molecular identification of the isolates, which included sequencing of the 16S rRNA gene and RT-PCR of coagulase (coa), clumping-factor (clfA) and thermonuclease (nuc) genes, was consistent with the diagnosis phenotypically 'coagulase-negative variant of Staph. aureus'. The fact that coagulase-negative Staph. aureus variants can occur in the context of intramammary infections in cattle may result in the incorrect diagnosis 'coagulase-negative staphylococci (CNS)' in routine mastitis diagnostic, at least in rare cases. To fully ensure correct species diagnosis, sequencing of the 16S rRNA gene and amplification of specific genes such as coa is necessary in these cases.  相似文献   
78.
Acute transplant rejection is the leading cause of graft loss in the first months after kidney transplantation. Lipoxygenase products mediate pro- and anti-inflammatory actions and thus we aimed to correlate the histological reports of renal transplant biopsies with urinary lipoxygenase products concentrations to evaluate their role as a diagnostic marker. This study included a total of 34 kidney transplant recipients: 17 with an acute transplant rejection and 17 controls. LTE4, LTB4, 12-HETE and 15-HETE concentrations were measured by enzyme immunoassay. Urinary lipoxygenase product concentrations were not significantly changed during an acute allograft rejection. Nevertheless, LTB4 concentrations correlated significantly with the body temperature (P ≤ 0.05) 3 months after transplantation, and 12- and 15-HETE concentrations correlated significantly with renal function (P ≤ 0.05) 2 weeks after transplantation. In conclusion, our data show a correlation for LTB4 with the body temperature 3 months after transplantation and urinary 12- and 15-HETE concentrations correlate positively with elevated serum creatinine concentrations but do not predict acute allograft rejection.  相似文献   
79.
The curing of an epoxy consisting of the solid hardener dicyandiamide (DICY) and the resin diglycidyl ether of bisphenol A (DGEBA) is studied in a system consisting of a tablet of DICY embedded in liquid DGEBA. Dissolution of DICY within the liquid DGEBA in combination with the transport of dissolved DICY from the tablet border into DGEBA and the chemical reaction of both reactants is studied by scanning Brillouin microscopy and infrared spectroscopy. Scanning Brillouin microscopy demonstrates the spatial and temporal evolution of the static and dynamic hypersonic properties in the course of curing in the vicinity of the DICY tablet. Infrared spectroscopy performed on epoxy pieces extracted from the final sample at different distances from the tablet surface give information about the spatial evolution of the curing process. The results achieved by both techniques are finally combined to yield a better understanding of the curing of DICY-based epoxies, which transform upon curing from strongly heterogeneous systems towards increasingly homogeneous systems.  相似文献   
80.
Aerobic treatment of municipal waste water in a membrane bioreactor was studied for 535 d. Apart from sampling, sludge was retained completely by a submerged hollow fibre membrane with a pore-size of 0.2 microm. The pilot plant comprised an anoxic zone to enable denitrification. The maximum liquid hold-up of the plant was 3.9 m3. In this study the reactor performance and the stability of the process and the membrane capacity were investigated. A stable flux of 181 m(-2)h(-1) could be realised with a mean transmembrane pressure difference of 0.3bar with air-bubbling and backflushing the membrane and cleaning it in place every two months for one or two hours. For about 140d, a flux of 271 m(-2)h(-1) was achieved, but cleaning became necessary more often. The hydraulic retention time (HRT) varied between 10.4 and 15.6h. Accordingly the volumetric loading rate was between 1.1 and 1.7kg CODm(-3)d(-1). No inoculum was used. The mixed liquor suspended solids (MLSS) concentration gradually increased to 18-20g MLSSl(-1). The feed to microorganism (F/M) ratio varied according to the operation conditions but decreased against a value of 0.07 kg COD kg(-1) MLSSd(-1). Treatment performance was very stable and on a high level. The COD was reduced by 95%. Nitrification was complete and up to 82% of the total nitrogen could be denitrified.  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