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   3618篇
  免费   29篇
  国内免费   1篇
电工技术   4篇
综合类   4篇
化学工业   212篇
金属工艺   33篇
机械仪表   28篇
建筑科学   29篇
能源动力   33篇
轻工业   109篇
水利工程   7篇
石油天然气   7篇
无线电   91篇
一般工业技术   256篇
冶金工业   2729篇
原子能技术   9篇
自动化技术   97篇
  2021年   11篇
  2020年   8篇
  2019年   11篇
  2018年   22篇
  2017年   12篇
  2016年   18篇
  2015年   21篇
  2014年   22篇
  2013年   74篇
  2012年   30篇
  2011年   34篇
  2010年   29篇
  2009年   24篇
  2008年   41篇
  2007年   44篇
  2006年   38篇
  2005年   30篇
  2004年   26篇
  2003年   34篇
  2002年   35篇
  2001年   30篇
  2000年   17篇
  1999年   111篇
  1998年   861篇
  1997年   480篇
  1996年   342篇
  1995年   200篇
  1994年   143篇
  1993年   163篇
  1992年   32篇
  1991年   39篇
  1990年   35篇
  1989年   50篇
  1988年   53篇
  1987年   46篇
  1986年   42篇
  1985年   42篇
  1983年   18篇
  1982年   11篇
  1981年   26篇
  1980年   26篇
  1979年   15篇
  1978年   20篇
  1977年   50篇
  1976年   126篇
  1975年   20篇
  1974年   8篇
  1973年   9篇
  1972年   8篇
  1971年   8篇
排序方式: 共有3648条查询结果,搜索用时 31 毫秒
81.
Mann  Z.A. 《Computer》2006,39(7):31-35
Many software developers know the feeling of desperately debugging a program only to discover after a sleepless night that the error stemmed from copy-pasted code segments that had become inconsistent in subsequent editing. The problems arising from copied code are not new, and many researchers have investigated how to automatically find copied code segments. Given the extensive use of copy-paste operations and their tendency to cause inconsistencies, there is clearly a pressing need to rethink current editor programs. One solution is to replace cut, copy, and paste with operations that correspond directly to the intended semantics behind their use. With these operations, the user can specify semantic relationships among copied objects, and the editor program can use that information to help in the long-term support of those relationships. It would thus avoid the inconsistencies that currently arise from the use of cut, copy, and paste.  相似文献   
82.
Green fluorescent protein (GFP) has many applications as a marker in living cells, and has become widely used as a reporter gene in microbial, plant and animal cells. Screening microbial colonies for GFP expression enables various types of assays (e.g. for secretory mutations). However, this is laborious, non-quantitative and potentially hazardous to the operator (due to UV illumination) when performed manually. In order to address this the GloPix robot was developed. The imaging system discriminates between colonies based on the level of fluorescence activity and the picking function automatically transfers cells to microplate wells. Measuring fluorescent activity allows quantitation of fluorescent tag concentration/expression.  相似文献   
83.
84.
In Bacillus transformation, sexual isolation is known to be an exponential function of the sequence divergence between donor and recipient. Here, we have investigated the mechanism under which sequence divergence results in sexual isolation. We tested the effect of mismatch repair by comparing a wild-type strain and an isogenic mismatch-repair mutant for the relationship between sexual isolation and sequence divergence. Mismatch repair was shown to contribute to sexual isolation but was responsible for only a small fraction of the sexual isolation observed. Another possible mechanism of sexual isolation is that more divergent recipient and donor DNA strands have greater difficulty forming a heteroduplex because a region of perfect identity between donor and recipient is required for initiation of the heteroduplex. A mathematical model showed that this heteroduplex-resistance mechanism yields an exponential relationship between sexual isolation and sequence divergence. Moreover, this model yields an estimate of the size of the region of perfect identity that is comparable to independent estimates for Escherichia coli. For these reasons, and because all other mechanisms of sexual isolation may be ruled out, we conclude that resistance to heteroduplex formation is predominantly responsible for the exponential relationship between sexual isolation and sequence divergence in Bacillus transformation.  相似文献   
85.
86.
BACKGROUND: Recent judicial decisions involving informed consent have led to some medical practitioners altering the way they obtain consent. The aim of this study was to determine the degree to which patients understood the risks associated with a surgical procedure after giving routine consent and whether providing additional detailed verbal and/or written information improved their understanding. It was further determined whether the provision of more extensive information altered patients' anxiety levels. METHODS: Patients undergoing femoral popliteal bypass or carotid surgery were randomized to obtain either routine consent only or routine consent with verbal or written or verbal and written consent. Patients undertook a pre-operative risk and complication questionnaire, a pre- and postoperative anxiety and depression evaluation and a follow-up questionnaire 6 weeks after discharge. RESULTS: Thirty-two patients were included in the trial. The comprehension questionnaire resulted in a correct percentage response of 48% for the routine information only, 59% with added verbal information, 59% with added written information and 55% with added written and verbal information. Twenty-five per cent of patients stated that they had a poor understanding of the risks and complications of the procedure. CONCLUSIONS: Additional written or verbal information did not improve a patient's understanding of risks and complications of the procedure. It also did not improve patients' perceived understanding of the operation or its complications. Patients' anxiety levels were unaltered by the increase in the information they were given. The information provided to patients should be simple, easy to understand and list any possible major complications to enable the patient to determine whether to undergo or decline a procedure.  相似文献   
87.
5-HT4 receptors are concentrated in areas of the brain which are rich in dopamine neuronal markers, which may suggest that they influence motor and reward processes. We tested this hypothesis by examining the effects of a 5-HT4 receptor antagonist, 8-amino-7-chloro-(N-butyl-4-piperidyl)methylbenzo-1,4-dioxan-5-car boxylate hydrochloride (SB-204070-A) on amphetamine- and nicotine-induced locomotor stimulation in intact rats. In rats with unilateral 6-hydroxydopamine-induced lesions of the ascending nigrostriatal dopaminergic projection, SB-204070-A was tested for its effects on amphetamine-induced rotation. SB-204070-A was also tested for its effects on rewarded behaviour maintained by intracranial self-stimulation. SB-204070-A did not alter behaviour under any of these conditions, suggesting a lack of involvement of the 5-HT4 receptor in motor and reward processes.  相似文献   
88.
89.
When stimulated through their antigen receptor without requisite costimulation, T cells enter a state of antigen-specific unresponsiveness termed anergy. In this study, signaling through the common gamma chain of the interleukin-2 (IL-2), IL-4, and IL-7 receptors in the presence of antigen was found to be sufficient to prevent the induction of anergy. After culture with IL-2, IL-4, or IL-7, Jak3 kinase was tyrosine-phosphorylated, which correlated with the prevention of anergy. Therefore, a signal through the common gamma chain may regulate the decision of T cells to either clonally expand or enter a state of anergy.  相似文献   
90.
The presence of octoxynol from dried bear-bile was examined. Octoxynol was coextracted when glycolipids by Folch-Suzuki partition method. Octoxynol formed mixed-micelles with glycosphingolipids. The glycolipids were purified by DEAE-Sephadex A-25 column chromatography. The fractions containing mixed micelles were obtained from linear gradient solvent of 0.05M-0.5M ammonium acetate in methanol. HPLC ( Bondapak-NH(2) - linked to a Bondapak-C(18) column) chromatogram showed five peaks. Two possible structures for the fourth peak fraction were proposed as (CH(3))(3)C-CH(2)-C(CH(3))(2)-C(6)H(4)-OR and (CH(3))(3)C-C(CH(3))(2)-CH(2)-C(6)H(4)-OR by NMR spectroscopy. The structure was further confirmed by electrospray tandem mass spectrometry (ESI MS/MS). The spectrum showed a protonated molecule at m/z 559 and three different series of ions with mass difference of 44 were detected in the MS/MS spectrum. Therefore, the structure of the fourth peak fraction from HPLC was confirmed as octoxynol, (CH(3))(3)C-CH(2)-C(CH(3))(2)-C(6)H(4)-(OCH(2)-CH(2))n-OH, based on mass spectrometry and NMR spectroscopy.  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