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   918篇
  免费   41篇
  国内免费   16篇
  2023年   13篇
  2022年   8篇
  2021年   12篇
  2020年   14篇
  2019年   15篇
  2018年   13篇
  2017年   12篇
  2016年   19篇
  2015年   23篇
  2014年   34篇
  2013年   45篇
  2012年   28篇
  2011年   32篇
  2010年   25篇
  2009年   42篇
  2008年   39篇
  2007年   53篇
  2006年   38篇
  2005年   36篇
  2004年   34篇
  2003年   32篇
  2002年   36篇
  2001年   29篇
  2000年   27篇
  1999年   21篇
  1998年   15篇
  1997年   22篇
  1996年   13篇
  1995年   12篇
  1994年   13篇
  1993年   10篇
  1992年   16篇
  1991年   10篇
  1990年   11篇
  1989年   23篇
  1988年   8篇
  1987年   15篇
  1986年   8篇
  1985年   13篇
  1984年   8篇
  1983年   9篇
  1982年   7篇
  1981年   11篇
  1980年   7篇
  1979年   5篇
  1975年   7篇
  1974年   5篇
  1973年   9篇
  1972年   15篇
  1971年   15篇
排序方式: 共有975条查询结果,搜索用时 15 毫秒
11.
3-Phosphoglycerate kinase (ATP:3-phospho-d-glycerate 1-phosphotransferase, EC 2.7.2.3) has been covalently immobilized on a polyacrylamide-type support containing carboxylic groups activated by water-soluble carbodiimide. The activity was 88 units g?1 xerogel. The activity versus pH profile showed a sharper maximum at pH 6.5 in the case of the immobilized enzyme. The immobilized enzyme had a broad apparent optimum temperature range between 40 and 50°C. The apparent Km values of the immobilized 3-phosphoglycerate kinase were lower for both 3-phosphoglycerate and ATP than those of the soluble enzyme. In the case of the immobilized enzyme stabilities were enhanced.  相似文献   
12.
Some optimal multivariate tests   总被引:1,自引:0,他引:1  
JOHN  S. 《Biometrika》1971,58(1):123-127
  相似文献   
13.
14.
Host specificity tests of the moth,Microthrix inconspicuella Ragonot in Australia, indicated that larvae could feed and develop on young apple leaves. Additional tests in South Africa on leaves and fruit of the 4 apple varieties, Jonathan, Starking (Red Delicious), Granny Smith and Golden Delicious, showed that apples were not a preferred food. Little feeding occurred and pupation happened infrequently. No 2nd generation resulted whenM. inconspicuella colonies were confined on apple fruit or leaves.   相似文献   
15.
Polyporus admirabilis, P. dictyopus, P. guianensis, P. pseudobetulinus, P. tubaeformis andP. udus are reported for Japan for the first time.Polyporus tubaeformis had been confused withP. melanopus, but the Japanese collections were conspecific with Norwegian isolates ofP. tubaeformis. A key to allPolyporus species in Japan is provided.Polyporus hartmanni is reported for the first time outside the Australian continent. As the species has a bipolar heterothallism and produces brown rot, its taxonomic relationship withPolyporus s. str. is discussed.The Japanese Science and Technology Agency (STA) is thanked by the authors for financial support.  相似文献   
16.
Field tests of running and laboratory tests were performed in La Paz [high altitude (HA), 3700 m] and in Clermont-Ferrand [low altitude (LA), 300 m] to investigate their validity at HA. Prepubertal boys of mean ages 10.6 years (HA1,n = 16; LA1,n = 28) and pubertal boys of 13.7 years (HA2,n = 12; LA2,n = 41) took part in the study. All the boys performed a 30-m sprint (v 30m), a 30-s shuttle run (v 3os) and a progressive shuttle run test until their maximal aerobic velocity (v maxsRT). Maximal oxygen consumption was extrapolated from the last test. . In the laboratory, the boys performed a force-velocity test (P max), a Wingate test (P Wing) and a graded test to measure maximal oxygen consumption ; direct method) on a cycle ergometer. At similar ages, there was no significant difference between HA and LA boys forv 30m andP max. Thev 30s of HA boys was 3%–4% lower than those of LA boys (P<0.05); there was no significant difference forP Wing. Significant relationships were observed at both altitudes betweenP max (watts per kilogram) andv 30m (HA:r=0.76; LA:r=0.84) and betweenP Wing andv 30s (HA:r=0.67; LA:r = 0.77); the slopes and the origins were the same at HA and LA. The ,v maxSRT and were lower by 9%, 12% and 20%, respectively, at HA than at LA (P<0.05). However, the relationships between and (litres per minute) at HA (r=0.88) and at LA (r=0.93) were identical. In conclusion, chronic hypoxia did not modify performance in very short dash exercises. The influence of HA appeared when the exercise duration increased and, during a maximal shuttle run test, performance was reduced by 10% at HA. Moreover, it was possible to assessP max,P Wing and at HA as well as at LA from field tests.  相似文献   
17.
Jeffries et al. (2018) investigated testing for a treatment difference in the setting of a randomized clinical trial with a single outcome measured longitudinally over a series of common follow-up times while adjusting for covariates. That paper examined the null hypothesis of no difference at any follow-up time versus the alternative of a difference for at least one follow-up time. We extend those results here by considering multivariate outcome measurements, where each individual outcome is examined at common follow-up times. We consider the case where there is interest in first testing for a treatment difference in a global function of the outcomes (e.g., weighted average or sum) with subsequent interest in examining the individual outcomes, should the global function show a treatment difference. Testing is conducted for each follow-up time and may be performed in the setting of a group sequential trial. Testing procedures are developed to determine follow-up times for which a global treatment difference exists and which individual combinations of outcome and follow-up time show evidence of a difference while controlling for multiplicity in outcomes, follow-up, and interim analyses. These approaches are examined in a study evaluating the effects of tissue plasminogen activator on longitudinally obtained stroke severity measurements.  相似文献   
18.
Plots of P-values to evaluate many tests simultaneously   总被引:3,自引:0,他引:3  
SCHWEDER  T.; SPJ?TVOLL  E. 《Biometrika》1982,69(3):493-502
  相似文献   
19.
Determination of window size for analyzing DNA sequences   总被引:4,自引:0,他引:4  
Summary DNA sequences are generally not random sequences. To show such nonrandomness visually, DNA sequence data are often plotted as moving averages for a certain length of window slid along a sequence. Here a simple algorithm is presented for determining the window size and for finding a nonrandom region of sequence.  相似文献   
20.
Iodination and immunoprecipitation techniques together with indirect fluorescent antibody tests identified two polypeptides (SP) of molecular weights 88,000–92,000 and 66,000–70,000 in the surface coat of bloodstream forms of the mouse trypanosome, Trypanosoma musculi. As parasites multiply and enter the early plateau phase of infection the 88,000–92,000 SP is present while the 66,000–70,000 SP is only detectable after the mid-plateau phase. Western blotting of parasite extracts showed that the 88,000–92,000 SP was present throughout the course of infection, but it appears to become masked by the 66,000–70,000 SP or possibly immunoglobulin from about 16 days after infection. Based on results when Western blots of parasite extracts were probed with antibodies affinity purified against the 88,000–92,000 SP, the two SP appear to be immunologically related and the smaller may be a cleavage product of the larger. This would explain why affinity purified antibodies to each SP bound to trypanosomes collected 8 days after infection, when only the 88,000–92,000 is detectable in parasite extracts. However, the failure of antibodies affinity purified against the 66,000–70,000 SP to bind to the 88,000–92,000 SP in Western blots suggests that the smaller SP has some epitopes that are immunologically distinct from those of the larger SP.  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