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   6001篇
  免费   499篇
  国内免费   7篇
  2023年   30篇
  2022年   62篇
  2021年   126篇
  2020年   90篇
  2019年   135篇
  2018年   144篇
  2017年   136篇
  2016年   176篇
  2015年   274篇
  2014年   275篇
  2013年   432篇
  2012年   475篇
  2011年   464篇
  2010年   238篇
  2009年   239篇
  2008年   347篇
  2007年   291篇
  2006年   288篇
  2005年   261篇
  2004年   246篇
  2003年   227篇
  2002年   221篇
  2001年   118篇
  2000年   106篇
  1999年   108篇
  1998年   64篇
  1997年   48篇
  1996年   57篇
  1995年   34篇
  1994年   46篇
  1993年   35篇
  1992年   57篇
  1991年   52篇
  1990年   65篇
  1989年   35篇
  1988年   49篇
  1987年   37篇
  1986年   34篇
  1985年   29篇
  1984年   25篇
  1983年   27篇
  1982年   32篇
  1981年   28篇
  1980年   24篇
  1979年   31篇
  1977年   17篇
  1976年   19篇
  1975年   15篇
  1974年   28篇
  1972年   16篇
排序方式: 共有6507条查询结果,搜索用时 489 毫秒
91.
Energy costs and energy sources in karate (wado style) were studied in eight male practitioners (age 23.8 years, mass. 72.3 kg, maximal oxygen consumption (VO2max) 36.8 ml · min–1 · kg–1) performing six katas (formal, organized movement sequences) of increasing duration (from approximately. 10 s to approximately 80 s). Oxygen consumption (VO2) was determined during pre-exercise rest, the exercise period and the first 270 s of recovery in five consecutive expired gas collections. A blood sample for lactate (la) analysis was taken 5 min after the end of exercise. The overall amount of O2 consumed during the exercise and in the following recovery increased linearly with the duration of exercise (t) from approximately 1.51 (for t equal to 10.5 s (SD 1.6)) to approximately 5.81, for t equal to 81.5 s (SD 1.0). The energy release from la production (VO21a ) calculated assuming that an increase of 1 mmol · l–1 la corresponded to a VO2 of 3 mlO2 · kg–1 was negligible for t equal to or less than 20 s and increased to 17.3 ml · kg–1 (la = 5.8 mmol · l–1 above resting values) for t equal approximately to 80 s. The overall energy requirement (VO2eq) as given by the sum of VO2 and VO2la was described by VO2eq = 0.87 + 0.071 · t (n = 64; r 2 = 0.91), where VO2eq is in litres and t in seconds. This equation shows that the metabolic power (VO2eq · t –1) for this karate style is very high: from approximately 9.51 · min–1 for t equal to 10 s to approximately 4.91 · min–1 for t equal to 80 s, i.e. from 3.5 to 1.8 times the subjects' VO2max. The fraction of VO2eq derived from the amount of O2 consumed during the exercise increased from 11% for t equal to 10 s to 41 % for t equal to 80 s whereas VO21a was negligible far t equal to or less than 20 s and increased to 13 % o for t equal to 80 s. The remaining fraction (from 90% for t equal to 10 s to 46% for t equal to 80 s), corresponding to the amount of O2 consumed in the recovery after exercise, is derived from anaerobic alactic sources, i.e. from net splitting of high energy phosphates during the exercise.  相似文献   
92.
We have isolated nine yeast artificial chromosomes (YACs) containing the gene that encodes the human gonadotropin-releasing hormone receptor (GnRH-R) gene by screening the YAC library of the Centre d'Etude du Polymorphisme Humain (Hôpital Saint-Louis, Paris, France) by the use of the polymerase chain reaction. We defined the location of the GnRH-R gene relative to 4q microsatellite markers D4S392 and D4S409. The genetic positions of these markers on chromosome 4 are 76 and 77 cM, respectively. This location was further established by chromosomal in situ hybridization.  相似文献   
93.
The aim of the present study was to compare serum levels of soluble forms of interleukin-2 receptor, CD4 and CD8, released by lymphocytes during activation of the immune system, in patients with allergic bronchial asthma, with those in healthy subjects. Significantly higher levels of soluble IL-2R and soluble CD4 were found in patients with asthma compared with the control group. In contrast, lower levels of soluble CD8 values were found in patients with asthma compared to the control group. Significant correlations were found for both sIL-2R and sCD4 and these two molecules, with lung function measured as bronchial responsiveness to inhaled methacholine. These results strengthen previous suggestions that in allergic bronchial asthma, activation of T cells plays a significant role in the disease pathogenesis.  相似文献   
94.
Simultaneous measurements of the transmural potential difference (PD) and the short-circuit current intensity (Isc) in the posterior intestine of the fish Blennius parvicornis were made in normal Ringer and in solutions of different ionic composition. The ouabain effects on these two parameters were also tested in normal Ringer solution. The absence of K+ from the Ringer solution on both the mucosal and serosal sides has no apparent effect on the PD and Isc within the first 15 min, but it makes them null after 30 min. When Na+ is substituted in both compartments, using Tris as substitute, a serosal negativity increase is initially observed, but it gradually decreases to zero after 30 min of experimentation. Similarly the PD and Isc drop to zero in the absence of Cl- (sulfate as substitute). Ouabain diminishes the serosa negative potential difference to zero after 30 min presenting a lineal relation to the Isc. A likely transport mechanism for Cl- dependent on the Na+ - K+ pump, is discussed.  相似文献   
95.
96.
The release of [3H]GABA induced by elevated extracellular potassium (K)o, from thin rat brain cortex slices, has been compared with that of [3H]noradrenaline ([3H]NA), released by the same procedures, both from normal slices, and from slices pre-treated with reserpine and nialamide, [3H]NA being predominantly a vesicular component in the former situation, and a soluble substance in the latter one. 46 mM-(K)o released considerably more [3H]NA from normal than from drug-treated slices, while the release of GABA was about two thirds of the latter. When 4min ‘pulses’ of increasing concentrations of potassium were applied, it was observed that the release of GABA and of [3H]NA from drug-treated slices increased in proportion to (K)o, up to 36-46 mM and then declined considerably with higher (K)o. The dependency of potassium-induced release on the concentration of calcium in the medium, indicated that release of [3H]NA from normal slices was proportional to calcium up to 1.5-2 mM, while that of [3H]NA from drug-treated slices increased up to 0.5 mM-Calcium, and then declined with higher concentrations. GABA release also increased up to 0.5 mM-calcium, but no further changes were observed at higher concentrations. The calcium antagonist D-600 inhibited high (K)o-induced release of [3H]NA from normal slices to a greater extent than that of [3H]GABA or of [3H]NA from drug-treated slices. These results, in which elevated (K)o-induced release of [3H]GABA resembles considerably that of soluble NA, but differs from that of NA present in synaptic vesicles, suggest that release of [3H]GABA also occurs from the soluble cytoplasmic compartment, and that the partial calcium requirement that is found is unrelated to that of transmitter secretion. These findings are also a further indication of the lack of specificity of elevated (K)o as a stimulus for inducing transmitter secretions.  相似文献   
97.
98.
A total of 51 restriction sites were recognized within the BK virus genome by the combination of 10 different restriction endonucleases. These sites were mapped and oriented relative to one another as well as to the five fragments generated by the digestion of BK virus DNA with HindIII and EcoRI. The result was a comprehensive physical map suitable for in-depth characterization of the functions of BK virus at the molecular level.  相似文献   
99.
Metabolic rate of obese patients is reported, recorded to cellular active mass. The metabolic rate is higher in obese patients and the value is diucthy related to individual actual weight. The dinamic-specific action of proteins is normal.  相似文献   
100.
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