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   1357篇
  免费   24篇
  国内免费   1篇
电工技术   48篇
综合类   2篇
化学工业   263篇
金属工艺   21篇
机械仪表   20篇
建筑科学   23篇
能源动力   78篇
轻工业   109篇
水利工程   2篇
石油天然气   1篇
无线电   142篇
一般工业技术   270篇
冶金工业   310篇
原子能技术   24篇
自动化技术   69篇
  2022年   8篇
  2021年   18篇
  2020年   11篇
  2019年   8篇
  2018年   17篇
  2017年   24篇
  2016年   21篇
  2015年   17篇
  2014年   28篇
  2013年   55篇
  2012年   50篇
  2011年   57篇
  2010年   33篇
  2009年   40篇
  2008年   53篇
  2007年   59篇
  2006年   51篇
  2005年   46篇
  2004年   44篇
  2003年   54篇
  2002年   43篇
  2001年   30篇
  2000年   19篇
  1999年   39篇
  1998年   123篇
  1997年   85篇
  1996年   47篇
  1995年   35篇
  1994年   32篇
  1993年   37篇
  1992年   16篇
  1991年   15篇
  1990年   13篇
  1989年   7篇
  1988年   11篇
  1987年   18篇
  1986年   16篇
  1985年   7篇
  1984年   16篇
  1983年   7篇
  1982年   10篇
  1981年   9篇
  1980年   13篇
  1979年   3篇
  1976年   13篇
  1975年   3篇
  1972年   5篇
  1971年   2篇
  1969年   2篇
  1968年   3篇
排序方式: 共有1382条查询结果,搜索用时 234 毫秒
81.
Standard soil samples contaminated with various standard cyanocompounds were prepared. Column elution experiments and analyses were conducted. Compounds with an easy capacity for dissociation to ions, such as KCN and potassium hexacyanoferrate(III), were found to be eluted by forming free cyanide even in fresh water. Hexacyanoferrate(II) salts, such as potassium hexacyanoferrate(II) and iron(III) hexacyanoferrate(II), were found not to be dissociated in water, but were dissociated and diffused under alkaline conditions (pH >13). Hexacyanoferrate(II) ion was found to be more easily dissociated in water with a higher pH.Column tests as above were also conducted for soil samples taken from a former paint ink factory using iron(III) hexacyanoferrate(II), cyanogen chloride, potassium cyanate, copper cyanide, as well as potassium cyanide, as raw materials. It was demonstrate that iron(III) hexacyanoferrate(II) was dissociated and eluted under alkaline conditions. The elution rate was reduced when the contaminated soil was sandwiched with standard soil layers.Further, it was found that the Fe(CN)(6)(4-) ion eluted with NaOH from hexacyanoferrate acid in soil, were easily decomposed into cyanic acid or other byproducts by UV with the addition of ozone and H(2)O(2).  相似文献   
82.
'Magic mushrooms' (MMs) are psychoactive fungi containing the hallucinogenic compounds, psilocin (1) and psilocybin (2). Since June 6, 2002, these fungi have been regulated by the Narcotics and Psychotropics Control Law in Japan. Because there are many kinds of MMs and they are sold even as dry powders in local markets, it is very difficult to identify the original species of the MMs by morphological observation. Therefore, we investigated the internal transcribed spacer (ITS) region in the ribosomal RNA gene of MMs obtained in Japanese markets to classify them by a genetic approach. Based on the size and nucleotide sequence of the ITS region amplified by PCR, tested MMs were classified into 6 groups. Furthermore, a comparison of the DNA sequences of the MMs with those of authentic samples or with those found in the databases (GenBank, EMBL and DDBJ) made it possible to identify the species of tested MMs. Analysis by LC revealed that psilocin (1) was contained at the highest level in Panaeolus cyanescens among the MMs, but was absent in the Amanita species.  相似文献   
83.
Tamura H  Kojima R  Usui H 《Applied optics》2003,42(19):4008-4015
A new method for fabricating plastic spherical microlenses was developed, which allowed self-alignment of lenses and self-organized formation of a spherical shape. First a low-surface-energy fluoropolymer thin film was deposited and patterned as a stencil. Then photosensitive phenol resin was patterned on it as the lens material. Finally the resin was annealed in an oil bath to form a sphere. The molten phenol resin spontaneously formed a sphere and positioned itself in the center of the fluoropolymer ring pattern as a result of the difference of surface free energy and the equivalently zero-gravity condition in the oil bath. When a light-emitting-diode printer head was loaded with spherical microlenses, its optical output increased by 1 order of magnitude.  相似文献   
84.
Fourier transform near-infrared (FT-NIR) spectra have been measured for bovine serum albumin (BSA) in an aqueous solution (pH 6.8) with a concentration of 5.0 wt% over a temperature range of 45-85 degrees C. Not only conventional spectral analysis methods, such as second-derivative spectra and difference spectra, but also chemometrics, such as principal component analysis (PCA) and evolving factor analysis (EFA), have been employed to analyze the temperature-dependent NIR spectra in the 7500-5500 and 4900-4200 cm-1 regions of the BSA aqueous solution. Intensity changes of bands in the 7200-6600 cm-1 and 4650-4500 cm-1 regions in the difference spectra indicate variations of the hydration and secondary structure of BSA in the aqueous solution, respectively. The plot of a band intensity at 7080 cm-1 in the different spectra shows a clear turning point at 63 degrees C, revealing that a significant change in the hydration occurs at about 63 degrees C. The forward and backward eigenvalues (EVs) from EFA suggest that marked changes in the hydration and secondary structure of BSA take place in the temperature ranges of 61-65 degrees C and 59-63 degrees C, respectively. In addition, the temperature of 71 degrees C marked in the EFA plots may correspond to the onset temperature of increase in the intermolecular beta-sheet structure.  相似文献   
85.
The applicability of the band-stripping and complementary matching method has been demonstrated by the analysis of temperature-dependent near-infrared (NIR) absorption spectra in the 7500-6500 cm(-1) region of oleic acid (cis-9-octadecenoic acid) in the pure liquid state. This method is based on first derivative-second derivative pair (D1-D2) plots and a new concept called the complementary band, cBDi, created by subtracting all the rest of the bands, exclusive of the ith estimated band, eBDi, from an experimental spectrum. The degree of coincidence of both band shapes provides a suitable measure for the quality of fit for each individual component band. It has been confirmed from the present analysis of the NIR spectra of oleic acid measured over a temperature range of 16-79 degrees C that the change of the peak intensity of the component band at around 6915 cm(-1) due to the first overtone of an O-H stretching vibration of the monomer has two transition points around 35 and 55 degrees C. Moreover, the present study has provided new insight into the analysis of temperature-dependent spectral variations of oleic acid. Among the three temperature ranges, 16-35 degrees C, 35-55 degrees C, and 55-79 degrees C, in the first range the band near 6915 cm(-1) shows a slight increase and in the second range it has a linear intensity change with a slope of 0.002 a.u./degree C. In the third range, a rapid increase of the peak intensity is observed. This band exists even at 15 degrees C (just below the melting point) and shows a shift from 6910 to 6915 cm(-1) and a band narrowing from 85 to 80 cm(-1) (full width at half-height) over a temperature range of 16 to 79 degrees C. Furthermore, it has been found that there are two broad bands at around 6835 and 6778.  相似文献   
86.
Josephson plasma reflectivity edge in YBa2Cu3O6.6 (T c=59 K) was measured in parallel magnetic fields HCuO2 up to 7 T. Upon application of the field, the Josephson plasma edge splits to two reflectivity edges, forming a new peak at finite frequency. Optical conductivity obtained by Kramers–Kronig analysis indicates that a new transverse Josephson plasma mode appears under parallel fields. We propose that the new mode originates from the modulation of the insulating layers with and without Josephson vortices, as has been suggested by free-energy calculations of Josephson vortices with moderate densities.  相似文献   
87.
An electrochemical protein chip was microfabricated. A thin-film three-electrode system, including an array of 36 platinum working electrodes, a set of thin-film Ag/AgCl electrodes, and platinum auxiliary electrodes, was integrated on a glass substrate. Capture antibodies were immobilized in a 4.5-nm-thick double layer of a hexamethyldisiloxane plasma-polymerized film. Because of their highly cross-linked network structure, the capture antibodies could be firmly immobilized. No nonspecific adsorption was observed during a series of procedures to detect target proteins, and electrochemical cross talk between neighboring sites was negligible. The sandwich immunoassay was conducted on a single chip using model proteins, alpha-1-fetoprotein and beta2-microglobulin. A distinct current increase following the oxidation of hydrogen peroxide produced by the enzymatic reaction of glucose oxidase was observed, which indicates that the capture proteins could actually bind the target proteins. Two kinds of protein were detected independently on multiple sites with respective capture antibodies.  相似文献   
88.
Tanaka T  Kojima S  Takeda H  Ino S  Ifukube T 《Ergonomics》2001,44(15):1403-1412
The maintenance of postural balance depends on effective and efficient feedback from various sensory inputs. The importance of auditory inputs in this respect is not, as yet, fully understood. The purpose of this study was to analyse how the moving auditory stimuli could affect the standing balance in healthy adults of different ages. The participants of the study were 12 healthy volunteers, who were divided into two age categories: the young group (mean = 21.9 years) and the elderly group (mean = 68.9 years). The instrument used for evaluation of standing balance was a force plate for measuring body sway parameters. The toe pressure was measured using the F-scan Tactile Sensor System. The moving auditory stimulus produced a white-noise sound and binaural cue using the Beachtron Affordable 3D Audio system. The moving auditory stimulus conditions were employed by having the sound come from the right to left or vice versa at the height of the participant's ears. Participants were asked to stand on the force plate in the Romberg position for 20 s with either eyes opened or eyes closed for analysing the effect of visual input. Simultaneously, all participants tried to remain in the standing position with and without auditory stimulation that the participants heard from the headphone. In addition, the variables of body sway were measured under four conditions for analysing the effect of decreased tactile sensation of toes and feet soles: standing on the normal surface (NS) or soft surface (SS) with and without auditory stimulation. The participants were asked to stand in a total of eight conditions. The results showed that the lateral body sway of the elderly group was more influenced than that of the young group by the lateral moving auditory stimulation. The analysis of toe pressure indicated that all participants used their left feet more than their right feet to maintain balance. Moreover, the elderly had the tendency to be stabilized mainly by use of their heels. The young group were mainly stabilized by the toes of their feet. The results suggest that the elderly may need a more appropriate stimulus of tactile and auditory sense as a feedback system than the young for maintaining and control of their standing postures.  相似文献   
89.
Konno S  Inoue Y  Kojima T  Fujikawa S  Yasui K 《Applied optics》2001,40(24):4341-4343
A 50-mJ green beam was generated at a 1-kHz repetition rate by intracavity frequency doubling of a quasi-cw laser-diode-pumped Nd:YAG laser. The green laser was used for 12-mJ fourth-harmonic beam generation with a CsLiB(6)O(10) crystal.  相似文献   
90.
The aim of this study is to clarify whether sennosides are contained in the leaf of Malva verticillata L., and then to clarify the source of sennosides in health teas including malva leaves. The identification and determination of sennosides were performed with thin layer chromatography and high performance liquid chromatography. The leaf of Malva verticillata L. did not contain sennosides A or B and could be easily distinguished from senna leaf. Our previous report showed that sennosides are contained in weight-reducing herbal teas including malva leaves, and that senna leaf is a herbal component in some teas. Furthermore, in 10 samples of health tea including malva leaves that were bought last year, the smallest amount of sennosides was 6.1 mg/bag, and all health teas including malva leaves contained the leaf and midrib of senna. We suggest that sennosides A and B are not contained in the leaf of Malva verticillata L., and that the sennosides in health teas including malva leaves are not derived from malva leaf but from senna leaf.  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