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   345篇
  免费   0篇
  国内免费   1篇
系统科学   5篇
理论与方法论   2篇
现状及发展   49篇
研究方法   37篇
综合类   241篇
自然研究   12篇
  2019年   2篇
  2017年   1篇
  2016年   2篇
  2015年   2篇
  2013年   1篇
  2012年   16篇
  2011年   24篇
  2010年   4篇
  2009年   2篇
  2008年   11篇
  2007年   20篇
  2006年   13篇
  2005年   14篇
  2004年   10篇
  2003年   4篇
  2002年   8篇
  2001年   7篇
  2000年   13篇
  1999年   2篇
  1997年   1篇
  1996年   1篇
  1994年   1篇
  1992年   11篇
  1991年   5篇
  1990年   12篇
  1989年   8篇
  1988年   4篇
  1987年   8篇
  1986年   12篇
  1985年   9篇
  1984年   3篇
  1983年   5篇
  1982年   6篇
  1981年   4篇
  1980年   1篇
  1979年   7篇
  1978年   3篇
  1977年   9篇
  1976年   3篇
  1975年   6篇
  1974年   10篇
  1973年   5篇
  1972年   7篇
  1971年   11篇
  1970年   7篇
  1969年   3篇
  1968年   9篇
  1967年   8篇
  1966年   4篇
  1965年   6篇
排序方式: 共有346条查询结果,搜索用时 17 毫秒
251.
Zusammenfassung Mit Hilfe von hoch- und niederauflösender Massenspektroskopie sowie Daten eines Gas-chromatograph-Massenspektrometer-Computer-Systems wurden die Droge Darvon3 sowie eine Reihe ihrer Metaboliten im Harn eines Überdosispatienten nachgewiesen.

This publication describes the identification of a drug causing coma in a patient. The drug was identified by analysis of the patient's urine performed at the NIH sponsored Special Research Resource Facility for Mass Spectrometry at M.I.T., under emergency conditions. Most of the experiments, measurements and interpretation reported had to be made within 1 day, thus requiring the simultaneous efforts of many members of M.I.T.'s massspectrometry group.  相似文献   
252.
253.
Résumé Un type d'ascidie peu commun et jusqu'ici non enregistré dans les plantes charnues est décrit. Le point de croissance à l'intérieur du gobelet n'avorta pas, de sorte que le rejeton continua à croître à partir de l'intérieur de l'ascidie pour aboutir à une tête florale.  相似文献   
254.
Separation of bone marrow cells by sedimentation at unit gravity   总被引:7,自引:0,他引:7  
E A Peterson  W H Evans 《Nature》1967,214(5090):824-825
  相似文献   
255.
Evans RL  Hirth G  Baba K  Forsyth D  Chave A  Mackie R 《Nature》2005,437(7056):249-252
Magnetotelluric and seismic data, collected during the MELT experiment at the southern East Pacific Rise, constrain the distribution of melt beneath this mid-ocean-ridge spreading centre and also the evolution of the oceanic lithosphere during its early cooling history. Here we focus on structures imaged at distances approximately 100 to 350 km east of the ridge crest, corresponding to seafloor ages of approximately 1.3 to 4.5 million years (Myr), where the seismic and electrical conductivity structure is nearly constant and independent of age. Beginning at a depth of about 60 km, we image a large increase in electrical conductivity and a change from isotropic to transversely anisotropic electrical structure, with higher conductivity in the direction of fast propagation for seismic waves. Conductive cooling models predict structure that increases in depth with age, extending to about 30 km at 4.5 Myr ago. We infer, however, that the structure of young oceanic plates is instead controlled by a decrease in water content above a depth of 60 km induced by the melting process beneath the spreading centre.  相似文献   
256.
The prompt optical emission that arrives with the gamma-rays from a cosmic gamma-ray burst (GRB) is a signature of the engine powering the burst, the properties of the ultra-relativistic ejecta of the explosion, and the ejecta's interactions with the surroundings. Until now, only GRB 990123 had been detected at optical wavelengths during the burst phase. Its prompt optical emission was variable and uncorrelated with the prompt gamma-ray emission, suggesting that the optical emission was generated by a reverse shock arising from the ejecta's collision with surrounding material. Here we report prompt optical emission from GRB 041219a. It is variable and correlated with the prompt gamma-rays, indicating a common origin for the optical light and the gamma-rays. Within the context of the standard fireball model of GRBs, we attribute this new optical component to internal shocks driven into the burst ejecta by variations of the inner engine. The correlated optical emission is a direct probe of the jet isolated from the medium. The timing of the uncorrelated optical emission is strongly dependent on the nature of the medium.  相似文献   
257.
Evans WE  Relling MV 《Nature》2004,429(6990):464-468
Individuals respond differently to drugs and sometimes the effects are unpredictable. Differences in DNA that alter the expression or function of proteins that are targeted by drugs can contribute significantly to variation in the responses of individuals. Many of the genes examined in early studies were linked to highly penetrant, single-gene traits, but future advances hinge on the more difficult challenge of elucidating multi-gene determinants of drug response. This intersection of genomics and medicine has the potential to yield a new set of molecular diagnostic tools that can be used to individualize and optimize drug therapy.  相似文献   
258.
Evans R 《Nature》2004,429(6990):356-357
  相似文献   
259.
The laboratory rat (Rattus norvegicus) is an indispensable tool in experimental medicine and drug development, having made inestimable contributions to human health. We report here the genome sequence of the Brown Norway (BN) rat strain. The sequence represents a high-quality 'draft' covering over 90% of the genome. The BN rat sequence is the third complete mammalian genome to be deciphered, and three-way comparisons with the human and mouse genomes resolve details of mammalian evolution. This first comprehensive analysis includes genes and proteins and their relation to human disease, repeated sequences, comparative genome-wide studies of mammalian orthologous chromosomal regions and rearrangement breakpoints, reconstruction of ancestral karyotypes and the events leading to existing species, rates of variation, and lineage-specific and lineage-independent evolutionary events such as expansion of gene families, orthology relations and protein evolution.  相似文献   
260.
Nanoscale NiAl-NO3-LDHs with good crystallinity have been synthesized by a method, Separate Nucleation and Aging Steps (SNAS). An NiAl-NO3-LDHs/LDPE composite was prepared by blending NiAl-NO3-LDHs and LDPE in a heated double-roller mixer. The color of this composite changed from olive green to steel gray under UV irradiation. After heating at 80oC for 2 h, the color returned to olive green. The effect of varying the amount of added NiAl-NO3-LDHs and UV exposure time on the photochromic properties of the composite has been investigated. The results showed that the photochromic phenomenon becomes more apparent with increasing amount of NiAl-NO3-LDHs. When the amount reaches 5%, the composite exhibits good photochromic properties and reproducibility. The color change rate of the composite reaches a maximum when the irradiation time exceeds 20 min. The addition of LDPE improves the photochromic cyclability of NiAl-NO3-LDHs significantly. The addition of nanoscale NiAl-NO3-LDHs also improves the mechanical properties of LDPE to some extent.  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