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   1141篇
  免费   36篇
  国内免费   2篇
电工技术   15篇
化学工业   133篇
金属工艺   8篇
机械仪表   10篇
建筑科学   55篇
能源动力   47篇
轻工业   123篇
水利工程   10篇
石油天然气   3篇
无线电   90篇
一般工业技术   154篇
冶金工业   323篇
原子能技术   8篇
自动化技术   200篇
  2023年   3篇
  2022年   14篇
  2021年   8篇
  2020年   11篇
  2019年   10篇
  2018年   14篇
  2017年   15篇
  2016年   20篇
  2015年   16篇
  2014年   23篇
  2013年   39篇
  2012年   43篇
  2011年   46篇
  2010年   31篇
  2009年   37篇
  2008年   41篇
  2007年   37篇
  2006年   35篇
  2005年   20篇
  2004年   42篇
  2003年   31篇
  2002年   20篇
  2001年   41篇
  2000年   34篇
  1999年   35篇
  1998年   133篇
  1997年   72篇
  1996年   48篇
  1995年   21篇
  1994年   22篇
  1993年   18篇
  1992年   12篇
  1991年   16篇
  1990年   13篇
  1989年   9篇
  1988年   12篇
  1987年   10篇
  1986年   14篇
  1985年   13篇
  1984年   4篇
  1983年   5篇
  1982年   5篇
  1981年   7篇
  1980年   7篇
  1979年   12篇
  1978年   4篇
  1977年   10篇
  1976年   19篇
  1974年   7篇
  1973年   3篇
排序方式: 共有1179条查询结果,搜索用时 31 毫秒
1.
2.
This study explored whether factors related to the work environment could predict changes in body mass index (BMI) and whether the effect of psychosocial factors was dependent on baseline BMI. The sample consisted of 1,980 male employees from the Danish National Work Environment Cohort Study. Changes in BMI between 1995 and 2000 were analyzed, by multiple regression, as a function of background variables and a series of occupational variables obtained in 1995. Age, baseline BMI, job insecurity, and psychological demands predicted changes in BMI. Job insecurity and high or low psychological demands increased the likelihood of weight gain among obese employees, whereas they increased the likelihood of weight loss among employees with a low BMI. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
3.
Indices of fluid balance were evaluated during and after aortic surgery in 16 consecutive patients. Thoracic electrical impedance (TI), heart rate (HR), central venous (CVP), pulmonary artery mean (PAMP), pulmonary wedge (PWP) and mean arterial (MAP) pressures as well as fourteen arterial and venous blood gas variables were followed. Consistent with a reduction of TI during the operation, fluid balance was in excess, and it remained elevated on the first postoperative morning. The HR, MAP and PWP remained stable, while CVP and PAMP decreased. Of the determined variables only TI revealed a meaningful correlation to fluid balance (rho = -0.41; p < 0.01). The results indicate that while central venous and pulmonary artery mean pressures gave the impression of a volume deficit, the positive fluid balance was mirrored by thoracic electrical impedance.  相似文献   
4.
5.
6.
A new sub-class of binding protein-dependent transporter with specificity for a broad range of polar amino acids has been identified by sequence comparison, in Rhizobium leguminosarum, Rhodobacter capsulatus, Escherichia coli and Pseudomonas fluorescens. Southern blotting and PCR analysis has shown that transporters from this new sub-class are widely distributed in Gram-negative bacteria, including, in addition to the above, Citrobacter freundii, Erwinia carotovorum and Rhizobium meliloti. ABC transporters of polar amino acids can be divided into two groups: those with narrow solute specificity and the newly identified sub-class with broad solute specificity. The binding and inner membrane proteins from transporters with a broad solute specificity are larger by approximately 30% than those with a narrow solute specificity. Multiple alignment of the inner membrane proteins from all sequenced polar amino acid transporters indicates there is an N-terminal conserved region that may be involved in solute specificity. A conserved arginine or lysine at residue 30 of this region is changed to glutamate in arginine transporters. Residue 53 also has a strong correlation with the charge on the transported solute, with basic amino acid transporters replacing an aliphatic amino acid at this position with a negatively charged amino acid. The general amino acid permease from R. leguminosarum, which will transport aliphatic as well as basic and acidic amino acids, juxtaposes two prolines at residues 52 and 53 of the N-terminal conserved region.  相似文献   
7.
“We hear about mandatory access to encryption keys by law enforcement but nothing about privacy.” With that statement, Senator John Ashcroft of Missouri, an unannounced candidate for President in 2000, opened Senate Judiciary subcommittee hearings on the Clinton administration's doddering encryption policy. Ashcroft lambasted the administration for asking American citizens to turn over crypto keys to the government after it rifled through 1000 raw FBI files seeking political dirt on opponents.  相似文献   
8.
A polarisation-independent four-port electro-optic tunable filter in the 1530 nm wavelength regime utilising non-polarising relaxed beam splitters and strain-induced polarisation converters on LiNbO3 with 16 nm tuning range and 46 ns tuning speed is reported.  相似文献   
9.
Reverberation chambers can be used to measure the absorption cross section of a dielectric object. The absorption cross section of a dielectric object depends on its size, shape, and electrical material parameters. By comparing with a theoretical model of the absorption cross section, material parameters can be extracted from measurements. A model based on a plane wave approach of incident fields is used here, valid for electrically large material samples in an isotropic environment such as that in a reverberation chamber. Which material parameter can be extracted depends on the properties of the material sample. The presented method combines the accuracy of cavity methods with the flexibility of being able to measure samples of arbitrary size and shape. Because both the reverberation chamber and the material sample are electrically large, the method is particularly useful at millimeter-wave frequencies.  相似文献   
10.
Volatile anaesthetics have historically been considered to act in a nonspecific manner on the central nervous system. More recent studies, however, have revealed that the receptors for inhibitory neurotransmitters such as gamma-aminobutyric acid (GABA) and glycine are sensitive to clinically relevant concentrations of inhaled anaesthetics. The function of GABA(A) and glycine receptors is enhanced by a number of anaesthetics and alcohols, whereas activity of the related GABA rho1 receptor is reduced. We have used this difference in pharmacology to investigate the molecular basis for modulation of these receptors by anaesthetics and alcohols. By using chimaeric receptor constructs, we have identified a region of 45 amino-acid residues that is both necessary and sufficient for the enhancement of receptor function. Within this region, two specific amino-acid residues in transmembrane domains 2 and 3 are critical for allosteric modulation of both GABA(A) and glycine receptors by alcohols and two volatile anaesthetics. These observations support the idea that anaesthetics exert a specific effect on these ion-channel proteins, and allow for the future testing of specific hypotheses of the action of anaesthetics.  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