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   7162篇
  免费   594篇
  国内免费   11篇
电工技术   123篇
综合类   4篇
化学工业   1902篇
金属工艺   185篇
机械仪表   235篇
建筑科学   210篇
矿业工程   20篇
能源动力   300篇
轻工业   1474篇
水利工程   75篇
石油天然气   49篇
无线电   424篇
一般工业技术   1195篇
冶金工业   704篇
原子能技术   49篇
自动化技术   818篇
  2024年   27篇
  2023年   80篇
  2022年   200篇
  2021年   409篇
  2020年   254篇
  2019年   326篇
  2018年   341篇
  2017年   355篇
  2016年   312篇
  2015年   229篇
  2014年   317篇
  2013年   597篇
  2012年   474篇
  2011年   516篇
  2010年   349篇
  2009年   379篇
  2008年   336篇
  2007年   293篇
  2006年   243篇
  2005年   147篇
  2004年   148篇
  2003年   141篇
  2002年   119篇
  2001年   84篇
  2000年   84篇
  1999年   88篇
  1998年   203篇
  1997年   151篇
  1996年   125篇
  1995年   70篇
  1994年   61篇
  1993年   53篇
  1992年   29篇
  1991年   16篇
  1990年   29篇
  1989年   17篇
  1988年   28篇
  1987年   11篇
  1986年   14篇
  1985年   13篇
  1984年   8篇
  1982年   7篇
  1981年   8篇
  1980年   7篇
  1978年   6篇
  1977年   6篇
  1976年   20篇
  1975年   7篇
  1974年   7篇
  1973年   6篇
排序方式: 共有7767条查询结果,搜索用时 328 毫秒
941.
942.
Some new commercial methods for the extraction of viral RNA have been introduced recently. In addition to the study published previously (Verhofstede, C., Reniers, S., Van Wanzeele. F., Plum J., 1996. AIDS 8, 1421-1427), seven different methods (four newly developed and three reference methods) for extraction of HIV-1 RNA from plasma have been evaluated. The RNA preparation method that gave the best results (acceptable reproducibility, highest sensitivity, reasonable price, fast and easy to perform), was the QIAamp Viral RNA kit from QIAgen. The High Pure Viral RNA Kit (Boehringer Mannheim) as well as the non-commercialised extraction kits were also very sensitive. The non-commercial tests seem less suitable for routine use and for the processing of large number of samples. Two methods, RNA Insta-Pure LS (Eurogentec) and PANext RNA extraction kit 1 (NTL, PANsystems GmbH) are not adapted for HIV plasma extraction. The single step methods using glass fibre or silica column are rapid (from 60 to 75 min depending on the number of wash steps) and although the price is high they are cheaper than the Boom extraction methods: High Pure Viral RNA Kit (Boehringer Mannheim) ($3.3/sample), QIAamp Viral RNA Kit (Qiagen) ($3.6/sample), Boom extraction ($5/sample). The Qiagen kit is the only kit that combines sensitivity with reproducibility, it is commercialised, rapid and affordable in price and can be automated. For most of the methods evaluated the inter-test variability was acceptable (mean variation coefficient between duplicate extractions varied between 26.4 and 48.6%).  相似文献   
943.
944.
945.
In this work, uniform bicubic B-spline functions are used to represent the surface geometry and interpolation functions in the formulation of boundary-element method (BEM) for three-dimensional problems. This is done as a natural generalization of cubic B-spline curves, introduced by Cabral et al, for two-dimensional problems. Three-dimensional scalar problems, with particular applications to Laplace and Helmholtz equations, are considered.  相似文献   
946.
The author suggests a working classification of dermopertorators from analysis of his own designs and devices described in the literature for forming netlike skin grafts in the treatment of patients with large tissue defects. It is shown that the well-known dermoperforators require essential modernization. The most promising model is a device with plane knives whose simple technology allows their production to be organized in Soviet industry.  相似文献   
947.
A protocol was designed for the rapid and efficient construction of cosmid libraries from cell-associated viral genomes available in very low quantities. Purification of viral DNA from cellular DNA was unnecessary. The vast excess of cellular DNA compensated for the limited amount of available viral DNA, enabling titration of the restriction endonuclease partial digest. A cosmid library of the turkey herpesvirus DNA genome was constructed from 1.5 micrograms of cellular DNA containing approximately 6 nanograms of viral DNA.  相似文献   
948.
949.
A galactomannoglucan (GMG) with an estimated weight–average molar mass of 415,000 g/mol was obtained from an aqueous extract of the mesocarp of fruits of Syagrus oleracea (Mart.) Becc. by fractionation by Sephacryl S-300 HR and Sephadex G-25. Chemical and spectroscopic studies indicated that GMG has a chain of (1 → 4)-linked β-d-mannopyranosyl residues attached to an initial chain of (1 → 3)-linked β-d-galactopyranosyl residues and a terminal chain of (1 → 4)-linked α-d-glucopyranosyl residues which comprised galactose, mannose and glucose in the molar ratio of 30:33:37. Results of the present study indicated that the polysaccharide GMG of S. oleracea significantly inhibited gastric lesions induced by ethanol, showing a gastroprotective property.  相似文献   
950.
This work was aimed at isolating and identifying the microbiota present during the semi-dry method of coffee processing using polyphasic methods and to evaluate microbial diversity with PCR-DGGE. Samples of Coffea arabica L. were collected during different processing stages in southern Minas Gerais, Brazil. The bacterial and fungal isolates were phenotypically characterised and grouped according to the ARDRA technique, in which the 16–23S and ITS1-5.8S regions of the rDNA were sequenced for species identification. The bacterial counts varied from 3.7 to 7 log CFU g−1. The yeast counts ranged from 3.4 to 6.9 log CFU g−1, and the filamentous fungal population varied from 2 to 3.7 log CFU g−1. Bacillus subtilis, Escherichia coli, Enterobacter agglomerans, Bacillus cereus and Klebsiella pneumoniae were the predominant bacteria detected during the processing of the coffee, and Pichia anomala, Torulaspora delbrueckii and Rhodotorula mucilaginosa were the dominant yeasts. All of the yeast and bacterial species detected by PCR-DGGE were isolated using culture-dependent methods, with the exception of one uncultivable bacterial species. Aspergillus was the most common genus among the filamentous fungal isolates. The use of polyphasic methods allowed a better characterization of the microbiota that is naturally present in semi-dry processed coffee.  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