全文获取类型
收费全文 | 8885篇 |
免费 | 604篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 122篇 |
综合类 | 5篇 |
化学工业 | 2303篇 |
金属工艺 | 141篇 |
机械仪表 | 308篇 |
建筑科学 | 345篇 |
矿业工程 | 17篇 |
能源动力 | 370篇 |
轻工业 | 1600篇 |
水利工程 | 131篇 |
石油天然气 | 47篇 |
武器工业 | 2篇 |
无线电 | 471篇 |
一般工业技术 | 1334篇 |
冶金工业 | 852篇 |
原子能技术 | 64篇 |
自动化技术 | 1387篇 |
出版年
2024年 | 31篇 |
2023年 | 97篇 |
2022年 | 306篇 |
2021年 | 407篇 |
2020年 | 257篇 |
2019年 | 276篇 |
2018年 | 364篇 |
2017年 | 383篇 |
2016年 | 408篇 |
2015年 | 281篇 |
2014年 | 352篇 |
2013年 | 699篇 |
2012年 | 576篇 |
2011年 | 697篇 |
2010年 | 472篇 |
2009年 | 500篇 |
2008年 | 443篇 |
2007年 | 357篇 |
2006年 | 303篇 |
2005年 | 212篇 |
2004年 | 181篇 |
2003年 | 168篇 |
2002年 | 152篇 |
2001年 | 111篇 |
2000年 | 114篇 |
1999年 | 104篇 |
1998年 | 310篇 |
1997年 | 228篇 |
1996年 | 147篇 |
1995年 | 97篇 |
1994年 | 61篇 |
1993年 | 59篇 |
1992年 | 28篇 |
1991年 | 23篇 |
1990年 | 22篇 |
1989年 | 23篇 |
1988年 | 18篇 |
1987年 | 13篇 |
1986年 | 15篇 |
1985年 | 18篇 |
1984年 | 25篇 |
1983年 | 26篇 |
1982年 | 14篇 |
1981年 | 17篇 |
1980年 | 14篇 |
1979年 | 11篇 |
1977年 | 16篇 |
1976年 | 24篇 |
1975年 | 7篇 |
1973年 | 7篇 |
排序方式: 共有9499条查询结果,搜索用时 31 毫秒
961.
Endoglin (CD 105) is a cell surface antigen widely expressed on vascular endothelium, syncytiotrophoblast, some tissue macrophages, certain culture cells (including early leukemic B-lineage) and some endothelial cell lines. Though its relation to the transforming growth factor-beta (TGF-beta) receptor system is well documented, its function and detailed pattern of expression still remain to be clarified. We examined the differential tissue distribution of endoglin in human lymphoid organs and placenta with several anti-CD 105 monoclonal antibodies (mAbs) using an indirect immunoperoxidase technique, and performed semi-quantitative measurements using an image-analyzing system for comparison. Arterial, venous and capillary endothelia in these organs were reactive with anti-CD 105 mAbs at varying intensities. Interestingly, a distinctly stronger staining pattern was observed in the high endothelial venules (HEVs) which may indicate a special role for endoglin in lymphocyte trafficking. Syncytiotrophoblast expressed endoglin strongly on their apical cell membrane. Extravillous trophoblasts at certain locations selectively expressed endoglin on their cell membranes, suggesting a special role for this surface antigen during trophoblast differentiation. 相似文献
962.
S Medina M Del Río V Manuel Victor A Hernánz M De la Fuente 《Canadian Metallurgical Quarterly》1998,102(2-3):249-261
The general immunodepression found in ageing organisms may be related to changes in the neuroimmune network. In the present study, the migration capacity of lymphocytes from BALB/c mice of three different ages: young (12 +/- 2 weeks), adult (24 +/- 2 weeks) and old (72 +/- 2 weeks), has been assayed in vitro in response to three neuropeptides: sulfated cholecystokinin octapeptide (CCK-8s), gastrin-releasing peptide (GRP) and neuropeptide Y (NPY) in a physiological range of concentrations (10(-8)-10(-12) M). The capacity of migration to a chemical gradient or chemotaxis was studied by the Boyden's technique using f-met-leu-phe at 10(-8) M as chemoattractant. The results show a different response of lymphocytes to the different neuropeptides, as wells as to age, concentrations and locations studied. However, some similarities were found, for instance the three neuropeptides inhibited chemotaxis in thymus. The stimulatory effects that GRP and NPY exerted in young and adult mice were not observed in old animals. CCK-8s inhibited the chemotaxis in every organ studied, with the effect being more striking in old mice. Our conclusion is that stimulatory effects of the neuropeptides disappear or become inhibitory with ageing. 相似文献
963.
RA Zinn E Alvarez M Mendez M Monta?o E Ramirez Y Shen 《Canadian Metallurgical Quarterly》1997,75(7):1723-1728
Using ammonium sulfate, three levels of dietary S (.15, .20, and .25%, DM basis) were evaluated in a finishing trial with 108 yearling crossbred heifers (384 kg). The basal diet contained (DM basis) 4% alfalfa hay, 6% sudangrass hay, 74% steam-flaked corn, 4% yellow grease, 6% cane molasses, and 6% protein-mineral supplement. Increasing dietary S decreased ADG (quadratic effect, P < .10), DMI (linear effect, P < .10), feed efficiency (quadratic effect, P < .10), diet NE (quadratic effect, P < .10), and longissimus muscle area (linear effect, P < .05). Six Holstein steers (218 kg) with cannulas in the rumen and proximal duodenum were used to evaluate treatment effects on characteristics of digestion. Treatment effects on ruminal and total tract digestion of OM and N were small (P > .10). However, ruminal digestion of ADF and starch was slightly lower (quadratic effect, P < .10), and postruminal digestion of ADF and starch was correspondingly greater (quadratic effect, P < .05) with supplemental S. Dietary S level did not influence (P > .10) ruminal synthesis of microbial N. Increasing dietary S did not influence (P > .10) ruminal pH or lactic acid. Increasing S decreased molar proportions of acetate (quadratic effect, P < .10) and increased molar proportions of propionate (linear effect, P < .10). We conclude that S in excess of .20% of dietary DM may have detrimental effects on growth performance and dietary NE. Excessive dietary S may also compromise carcass merit by decreasing longissimus muscle area. 相似文献
964.
This paper analyses the effect of signal combination techniques in videowatermark detection. A spatial spread spectrum based watermarking techique isused as embedding method, in combination with common error correction codes(BCH, Reed-Solomon with multilevel signaling, binary convolutional codes withViterbi decoding). Besides an analytical evaluation of the bit error rate, theeffectiveness of the channel coding and diversity techniques is also assessedexperimentally under MPEG-2 video compression. 相似文献
965.
The aspects of acute purulent mediastinitis (APM) have been reported on the basis of the analysis of 14 cases treated in the last 5 years. The most frequent causes of APM were the complications after surgery on esophagus ad trachea (10 cases). The other group included patients operated on by sternotomy. Three patients survived. In both of them diagnosis was established within 12 hours from the beginning of APM and early re-thoracotomy was performed. The rest of the patients died because of sepsis and multiply organ failure (MOF). The conclusion is that only early diagnosis as well as aggressive surgical treatment give a chance to save life in such a dangerous severe complication. 相似文献
966.
Margarida Moldão-Martins Gabriela M. Bernardo-Gil Luísa M. da Costa 《European Food Research and Technology》2002,214(3):207-211
The effects of the extraction procedure on the sensory and chemical evaluation of Thymus zygis L. aromatic extracts obtained by hydro distillation and compressed CO2 extraction were studied. Compressed CO2 extractions were performed at a temperature of 313 K and 10 and 15 MPa of pressure for 60 min. Aromatic extracts were analysed by GC and GC-MS. Sensorial analysis of the aromatic extracts incorporated into a sunflower oil was carried out by a panel of 20 trained members. The main compounds of Thymus zygis essential oil obtained by Clevenger distillation are: p-cymene (13.6%), thymol (23.8%), geraniol (18.2%), and geranyl acetate (16.3%). The compositions of supercritical extracts are quite different. The detection threshold of Thymus zygis essential oil was 0.001 mg/kg sunflower oil. The preferred level of essential oil incorporation was 0.02 mg/kg sunflower oil (P<0.05). Sensorial attributes were correlated with chemical compositions and it can be concluded that extracts with higher levels of phenols and geranyl acetate were preferred. 相似文献
967.
968.
Joo Pissarra Sandra Loureno Jos Maria Machado Nuno Mateus David Guimaraens Victor de Freitas 《Journal of the science of food and agriculture》2005,85(7):1091-1097
The commercial wine spirit used for this study revealed that the aldehyde content mainly comprises acetaldehyde but other aldehydes such as propionaldehyde, 2‐methylbutyraldehyde, isovaleraldehyde, methylglyoxal, benzaldehyde and others are also present in significant amounts. A typical grape must was used to assess the influence of wine spirit in the analytical and sensorial characteristics of fortified wines. Decreasing levels of anthocyanins, as well the increase in the red colour and tanning capacity, were observed, and seem to be positively correlated with the increase of the aldehyde content present in the wine spirits used to fortify the must. Using the CIE L*a*b* system, this aldehyde content present in the spirit used seemed to be correlated with the decrease of the wines' lightness (darkening effect), the displacement of the hue angle to higher values (yellowing effect) and the increase of the chromaticity (colour saturation) of the wines. Copyright © 2005 Society of Chemical Industry 相似文献
969.
This article presents the numerical implementation of an elastoplastic behavior model suitable for estimating the damage produced when excavating galleries in deep argilite layers. The main rheological features of the model are related to post-peak behavior, brittle fracture, softening and dilatancy effects. Damage of the rock may increase significantly the hydraulic permeability and vice versa. We focus on numerical difficulties such as suitable calculations for plastic flow at very low confinement levels and those resulting from following the confinement factor in such a way that the algorithms converge until physical collapse. The numerical results obtained with a 2D simulation are in good agreement with generally observed phenomena. Dilatancy produces instantaneous cohesion, which disappears with time. Increasing permeability speeds up this tendency. 相似文献
970.
Tereza Neuma de Castro Dantas Leocadia Terezinha Cordeiro Beltrame Afonso Avelino Dantas Neto Maria Carlenise Paiva de Alencar Moura 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2004,79(6):645-650
One of the major environmental problems in the textile dyeing industry is the removal of color from effluents. The present study deals with color removal from effluents using microemulsions. The wastewater used in this study was the reactive exhausted dye liquor from a dyeing house containing Procion Yellow H‐E4R (CI Reactive Yellow 84), Procion Blue H‐ERD (CI Reactive Blue 160) and Procion Red H‐E3B (CI Reactive Red 120). Color removal was determined by CIE L*a*b* (CIELAB) color space, CIE L*a*b* color difference, ΔE*ab, and absorbance. Color removal greater than 95% was achieved, attaining values lower than the consent requirements established by the Environmental Agency. It was observed that pH is an important parameter in color removal and effluent pH correction from 10.44 to 9 before extraction improved results. The results obtained were modeled using the Scheffé net method and evaluated through the construction of isoresponse diagrams by correlation graphics between experimental values and those obtained through use of model equations, providing an experimental error of less than 2%. The optimized method very efficiently removed all dyes contained in the effluent. The same microemulsion phase recovered after the extraction process can be used at least a further 14 times and all the extractions gave good color removal. Copyright © 2004 Society of Chemical Industry 相似文献