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   470761篇
  免费   5760篇
  国内免费   1832篇
电工技术   9304篇
综合类   582篇
化学工业   68218篇
金属工艺   19609篇
机械仪表   14388篇
建筑科学   11612篇
矿业工程   1512篇
能源动力   11849篇
轻工业   43139篇
水利工程   4099篇
石油天然气   5120篇
武器工业   71篇
无线电   60533篇
一般工业技术   87787篇
冶金工业   92092篇
原子能技术   8577篇
自动化技术   39861篇
  2021年   3393篇
  2019年   3253篇
  2018年   5437篇
  2017年   5434篇
  2016年   5810篇
  2015年   3989篇
  2014年   6760篇
  2013年   20694篇
  2012年   11222篇
  2011年   15502篇
  2010年   12426篇
  2009年   13853篇
  2008年   15011篇
  2007年   15055篇
  2006年   13744篇
  2005年   12574篇
  2004年   12074篇
  2003年   12014篇
  2002年   11726篇
  2001年   11851篇
  2000年   11019篇
  1999年   11772篇
  1998年   29020篇
  1997年   20611篇
  1996年   16028篇
  1995年   12207篇
  1994年   10856篇
  1993年   10625篇
  1992年   7985篇
  1991年   7597篇
  1990年   7098篇
  1989年   6781篇
  1988年   6628篇
  1987年   5667篇
  1986年   5556篇
  1985年   6565篇
  1984年   6028篇
  1983年   5427篇
  1982年   5089篇
  1981年   5164篇
  1980年   4909篇
  1979年   4590篇
  1978年   4472篇
  1977年   5439篇
  1976年   7334篇
  1975年   3945篇
  1974年   3845篇
  1973年   3834篇
  1972年   3121篇
  1971年   2914篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
We report here a series of observations-most of which the reader can experience directly-showing that distinct components of patterned visual stimuli (orthogonal lines of a different hue) vary in perception as sets. Although less frequent and often less complete, these perceptual fluctuations in normal viewing are otherwise similar to the binocular rivalry experienced when incompatible scenes are presented dichoptically.  相似文献   
92.
Prodrugs of mitomycin C (MMC) based on soluble poly-[N-(2-hydroxyethyl)-L-glutamine] (pHEG) polymers have been evaluated as tumour-targeted drugs. These materials are designed to exploit the enhanced permeability of tumour vasculature, combining a passive tumour tropism with decreased systemic liberation of free MMC. A tri- or tetrapeptide linkage (e.g. Gly-Phe-Ala-Leu) between pHEG and the aziridine nitrogen of MMC can combine good hydrolytic stability with rapid cleavage by lysosomal enzymes, releasing free MMC. The conjugates showed decreased systemic toxicity and could be administered to mice at a total MMC dose of 15 mg/kg i.v., compared with just 6 mg/kg for free MMC. Conjugates also showed better activity against animal models of established tumours, achieving up to 77% increased life span (ILS) against solid P388 leukaemia, compared with only 23% for free MMC, and up to 121% ILS against solid C26 colorectal carcinoma, compared with no activity for the free drug. Improving the therapeutic index of anticancer drugs by combining tumour tropism with decreased systemic toxicity is a versatile approach that should produce a new generation of improved anticancer agents.  相似文献   
93.
The impact of crosstalk in an arrayed-waveguide N×N wavelength multiplexer is investigated precisely in relation to its application to wavelength-routing N×N all optical networks. In such systems multiple crosstalk light which has the same wavelength as the signal results in signal-crosstalk beat noise. We confirm that the noise is Gaussian and obtain the relation between crosstalk and power penalty. It is shown that the crosstalk must be less than -38 dB for a 16×16 system to keep the power penalty below 1 dB at a bit error rate of 10-9  相似文献   
94.
In summary, recent literature indicates that the complications of chronic otitis media have been decreasing. However, even with the advent of modern and more powerful antimicrobials and aggressive surgical eradication of disease, the morbidity and mortality are still high. Some complications may initially be quite obvious and some complications may be quite subtle. Therefore, the most important tools in making early diagnosis are careful history and physical examination, and a high index of suspicion for impending complications.  相似文献   
95.
96.
The immunological agglutination reactions of physically absorbed F(ab')2 molecules onto anionic and cationic latex particles have been investigated by means of optical absorbance measurements. These measurements have been conducted under different conditions to determine the most influential factors. Surface F(ab')2 and BSA densities, particle concentration in the reaction medium and polyethylene glycol concentration are some of these factors. Sensitized cationic and anionic latexes differ considerably with respect to their colloidal stability and reactivity. As a general rule, the sensitized cationic latex has a relatively higher colloidal stability and hence, it provides reagents with a better optical response. Less than 0.025 microgram/ml of C-reactive protein has been detected using this particle enhanced optical immunoassay.  相似文献   
97.
98.
BACKGROUND AND DESIGN: Giant aggressive keratoacanthoma is a rare destructive subset of keratoacanthoma that frequently involves the facial region, grows rapidly to a large size, and often recurs after surgical management. The effectiveness of ionizing radiation therapy was examined in a retrospective study involving 16 patients; 14 of the tumors had recurred after surgical therapy. RESULTS: All tumors resolved with satisfactory cosmetic results and without recurrence following a fractionated course of superficial radiation therapy. CONCLUSIONS: Radiation therapy is an effective therapeutic modality for giant aggressive keratoacanthomas.  相似文献   
99.
DNA of plasmid pBR322 irradiated with laser at a wavelength of 193 mm was treated with an extract containing proteins from E.coli K12 AB1157 (wild-type). The enzymes were found to produce single- and double-strand DNA breaks, which was interpreted as a transformation of a portion of cyclobutane pyrimidine dimers and (6-4) photoproducts into nonrepairable single-strand DNA breaks. The products resulted from ionization of DNA, in particular, single-strand breaks, transform to double-strand breaks. A comparison of these data with the data on survival of plasmid upon transformation of E.coli K12 AB1157 enables one to assess the biological significance of single- and double-strand breaks. The inactivation of the plasmid (in AB1157) is mainly determined by the number of directly formed laser-induced single-strand breaks, whereas the contribution of enzymatically produced single- and double-strand breaks is insignificant.  相似文献   
100.
Bone marrow examination revealed a lipid-laden histiocytosis in seven patients undergoing long-term total parenteral nutrition necessitated by extensive short-bowel surgical resection. Clinical abnormalities occurred during this treatment which required bone marrow examination. These included hepatosplenomegaly and peripheral blood cytopenia; the median time to the detection of these abnormalities was 64 months. The most striking change within the bone marrow was the presence of many pigment-laden histiocytes which had the typical morphology of sea-blue histiocytes seen in the so-called idiopathic sea-blue histiocyte syndrome. The occurrence of sea-blue histiocytosis in the bone marrow in association with long-term parenteral nutrition for short-bowel syndrome has not, to our knowledge, been reported previously and should now be considered in the differential diagnosis of bone marrow sea-blue histiocytosis.  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