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   5247篇
  免费   478篇
  国内免费   4篇
  2022年   37篇
  2021年   85篇
  2020年   42篇
  2019年   55篇
  2018年   59篇
  2017年   63篇
  2016年   93篇
  2015年   159篇
  2014年   210篇
  2013年   259篇
  2012年   364篇
  2011年   309篇
  2010年   216篇
  2009年   195篇
  2008年   290篇
  2007年   271篇
  2006年   289篇
  2005年   229篇
  2004年   279篇
  2003年   225篇
  2002年   225篇
  2001年   97篇
  2000年   100篇
  1999年   93篇
  1998年   73篇
  1997年   60篇
  1996年   50篇
  1995年   44篇
  1994年   37篇
  1993年   59篇
  1992年   80篇
  1991年   81篇
  1990年   69篇
  1989年   72篇
  1988年   54篇
  1987年   71篇
  1986年   69篇
  1985年   58篇
  1984年   42篇
  1983年   47篇
  1982年   46篇
  1981年   23篇
  1980年   21篇
  1979年   40篇
  1978年   32篇
  1977年   25篇
  1976年   22篇
  1974年   21篇
  1973年   29篇
  1970年   24篇
排序方式: 共有5729条查询结果,搜索用时 15 毫秒
1.
2.
3.
A total dosage up to 1 mg PGF2a as i.v. infusions of 10–40 μg/min. was investigated on patients with arrhythmias of several kinds. We found therapeutic effects in 5 of 6 patients with constant extrasystoles and in one patient with digitalis - induced partial AV-block respectively. In 3 of 4 patients with acute tachyarrhythmias the results were not convincing, probably due to a dosage not high enough. An increase of the diastolic stimulation threshold usually seen with other antiarrhythmics was not to be observed in 3 patients. The mechanism of action of PGF2a has not yet been clarified.  相似文献   
4.
5.
Fort Greely, Alaska has an extensive complex of weapon training and testing areas located on lands withdrawn from the public domain under the Military Lands Withdrawal Act (PL106-65). The Army has pledged to implement a program to identify possible munitions contamination. Because of the large size (344,165,000 m2) of the high hazard impact areas, characterization of these constituents will be difficult. We used an authoritative sampling design to find locations most likely to contain explosives-residues on three impact areas. We focused our sampling on surface soils and collected multi-increment and discrete samples at locations of known firing events and from areas on the range that had craters, pieces of munitions, targets, or a designation as a firing point. In the two impact areas used primarily by the Army, RDX was the most frequently detected explosive. In the impact area that was also used by the Air Force, TNT was the most frequently detected explosive. Where detected, the explosives concentrations generally were low (<0.05 mg/kg) except in soils near low-order detonations, where the explosive-filler was in contact with the soil surface. These low-order detonations potentially can serve as localized sources for groundwater contamination if positioned in recharge areas.  相似文献   
6.
A strain of Methylomonas albus BG8WM, a type 1 obligate methanotroph, which had been maintained for 2 ycars by serial passage on solid medium containing methanol as a carbon source was found to mutate at a frequency of 10-5-10-6 to resistance to dichloromethane (DCMR), the parental strain BG8 did not give rise to DCMR colonies. DCMR strains were no longer capable of growth on methane as a carbon cource and exhibited greatly reduced or undetectable methane mono-oxygenase activity. The mutants fell into three groups on the basis of SDS-PAGE analysis of the polypeptide profiles of the particulate fraction of cell extracts. One or more of four polypeptides of Mr 70,000, 50,000, 25,000 and 23,000 were implicated as being components of the methane mono-oxygenase. Spontaneous reversion to growth on methane and sensitivity to dichloromethane occurred at a frequency of about 10-8. The loss of methane mono-oxygenase activity was not associated with loss of the resident 55 kb plasmid.Abbreviations DCMR dichloromethane-resistant - SDS-PAGE sodium dodecyl sulphate polyacrylamide gel electrophoresis - NMS nitrate minimal salts medium  相似文献   
7.

Background  

Populations of the Oriental White-backed Vulture (Gyps bengalensis) have declined by over 95% within the past decade. This decline is largely due to incidental consumption of the non-steroidal anti-inflammatory veterinary pharmaceutical diclofenac, commonly used to treat domestic livestock. The conservation status of other Gyps vultures in southern Asia is also of immediate concern, given the lack of knowledge regarding status of their populations and the continuing existence of taxonomic uncertainties. In this study, we assess phylogenetic relationships for all recognized species and the majority of subspecies within the genus Gyps. The continuing veterinary use of diclofenac is an unknown but potential risk to related species with similar feeding habits to Gyps bengalensis. Therefore, an accurate assessment of the phylogenetic relationships among Gyps vultures should aid in their conservation by clarifying taxonomic uncertainties, and enabling inference of their respective relatedness to susceptible G. bengalensis.  相似文献   
8.
9.
  1. Download : Download high-res image (63KB)
  2. Download : Download full-size image
Highlights
  • •MS-based clinical assay that accurately determines phospho Rab10 occupancy.
  • •Stable isotope labeled phosphopeptide injected as a standard with endogenous tryptic phospho Rab peptide for accurate ratio determination.
  • •Determination of pRab levels in neutrophils of Parkinson disease patients.
  • •Relevance of pRab levels as marker of PD.
  相似文献   
10.
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