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   276030篇
  免费   30236篇
  国内免费   258篇
  306524篇
  2016年   3083篇
  2015年   4297篇
  2014年   4850篇
  2013年   7378篇
  2012年   7938篇
  2011年   8190篇
  2010年   5427篇
  2009年   5005篇
  2008年   7415篇
  2007年   7527篇
  2006年   7163篇
  2005年   6907篇
  2004年   6817篇
  2003年   6599篇
  2002年   6390篇
  2001年   11748篇
  2000年   11791篇
  1999年   9326篇
  1998年   3387篇
  1997年   3621篇
  1996年   3518篇
  1995年   3126篇
  1994年   3108篇
  1993年   3103篇
  1992年   7867篇
  1991年   7852篇
  1990年   7514篇
  1989年   7474篇
  1988年   6852篇
  1987年   6602篇
  1986年   6020篇
  1985年   6208篇
  1984年   5147篇
  1983年   4338篇
  1982年   3373篇
  1981年   3144篇
  1980年   2944篇
  1979年   4951篇
  1978年   3811篇
  1977年   3724篇
  1976年   3432篇
  1975年   3785篇
  1974年   4175篇
  1973年   4092篇
  1972年   3666篇
  1971年   3435篇
  1970年   3086篇
  1969年   2995篇
  1968年   2745篇
  1967年   2370篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
OBJECTIVES--To document the number of children aged less than 15 years who developed diabetes and were managed within one large health district, and to evaluate the outcome of those children managed without hospital admission at diagnosis. DESIGN--A retrospective study over 1979-88, when a paediatrician and a physician with special interests in childhood diabetes initiated joint clinics. Data collected from the district diabetes register and files of consultants and health visitors specialising in diabetes. SETTING--Referral of children to consultants in Leicestershire (total population 863,000). MAIN OUTCOME MEASURES--The proportion of children managed without hospital admission, comparison of readmission rates and glycated haemoglobin concentrations between children admitted and those not admitted. RESULTS--Over 10 years 236 children aged 10-14 years developed diabetes (annual incidence rate 12.8/100,000 child population (95% confidence interval 11.3 to 14.7)). In total 138 were not admitted to hospital but received supervised management based at home. Admitted children were younger or acidotic or their family doctors did not contact the diabetes team. Duration of admission declined from seven days in 1979-80 to three days in 1987-8. Ninety two were not admitted to hospital during the 10 years for any reason. Significantly fewer children who received management at home were readmitted for reasons related to diabetes than the group treated in hospital (30 (22%) v 40 (41%); p = 0.004). Concentrations of glycated haemoglobin were no different between the two groups. CONCLUSIONS--Children with newly diagnosed diabetes may be safely and effectively managed out of hospital. Domiciliary or community based management depends on the commitment of consultants specialising in diabetes working in close cooperation with general practitioners, specialist nurses in diabetes, and dietitians.  相似文献   
922.
Spherical porous microcarriers (PMCs) made from collagen-glycosaminoglycan crosslinked copolymers have exhibited considerable promise as growth surfaces for the proliferation of anchorage-dependent mammalian cell lines and have demonstrated the ability to entrap anchorage-independent cells. However, quantification of cell growth on PMCs has proved difficult. A method of measuring the proliferation of PMCs, based on image analysis, is presented. Using CV1 and CHO cell lines, samples of PMCs were removed from culture at various times, fixed, embedded and sectioned. The 2 microns sections were stained, photographed and digitized in three colors. A computer program was developed to evaluate digitized PMC cross-sections and to classify pixels as conforming to either background, cytoplasmic, matrix or nuclear parameters, based on a set of classification rules determined by statistical analysis. Growth curves were generated by relating the number of pixels occupied by cellular material to the total number of pixels in the PMC cross-section. The PMCs were found to foster cell proliferation, with cell densities approaching 100% occupancy.  相似文献   
923.
924.
A multiple chemostat system has been developed in which metal specimens can be exposed to a consortium of bacteria. The system comprises a single test chemostat containing the test specimen operated at a high dilution rate to facilitate the wash out of planktonic bacteria, selecting for attached or biofilm growth. This chemostat is fed at a steady low rate by a number of separate chemostats each of which contains a pure axenic culture of one member of the consortium being tested. This system has the advantage of providing a continual inoculum of the test species to the test specimen allowing both aerobic and anaerobic bacteria to be grown in the same system. Constant levels of three bacterial types were maintained in the system: Pseudomonas aeruginosa, Thiobacillus ferrooxidans and Desulfovibrio vulgaris. Exposure of 316L stainless steel electrodes to this system resulted in increased corrosion of coupons exposed biotically, as compared to those exposed abiotically. A current monitoring technique and electrochemical impedance spectroscopy were used to evaluate effects of bacteria on metallic corrosion.  相似文献   
925.
Osmium-ammine (OA)/SO2 selectively contrasted RNA- and DNA-containing structures in thin sections from Lowicryl-embedded samples. No cell structures were stained after Epon embedding. RNAse and DNAse digestion experiments demonstrated that only RNA and DNA were stained in Lowicryl thin sections. Protease digestion did not modify the staining reaction. The very fine end-reaction produced a very high resolution of the stained structures. The staining reaction was not due to the presence of SO2 but to the low pH of the solution (ranging from 1.5-2.2). OA in glycine buffer, pH 1.5, selectively contrasted nucleic acids. Electrostatic bonds between nucleic acids and OA complex were probably involved in the staining reaction. Increasing the pH value of the staining medium resulted in loss of OA specificity for nucleic acids. The high electrolyte concentration of the staining medium hindered the staining reaction.  相似文献   
926.
Rapid purification of high-activity Taq DNA polymerase.   总被引:3,自引:1,他引:2       下载免费PDF全文
  相似文献   
927.
928.
The Spanish ``Asturiana' cattle breed is characterized by the segregation of a genetically determined muscular hypertrophy referred to as double-muscling or ``culones'. We demonstrate by linkage analysis that this muscular hypertrophy involves the mh locus previously shown to cause double-muscling in the Belgian Blue cattle breed, pointing towards locus homogeneity of this trait across both breeds. Moreover, using a twopoint and multipoint maximum likelihood approach, we show that flanking microsatellite markers are in linkage disequilibrium with the mh locus in both breeds albeit with different alleles. Finally, we discuss how allelic homogeneity across breeds might be exploited to achieve efficient genetic fine-mapping of the mh locus. Received: 13 September 1996 / Accepted: 20 January 1997  相似文献   
929.
930.
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