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   1082191篇
  免费   113700篇
  国内免费   594篇
  1196485篇
  2018年   9674篇
  2016年   13031篇
  2015年   17107篇
  2014年   20405篇
  2013年   29403篇
  2012年   32810篇
  2011年   33695篇
  2010年   23078篇
  2009年   21342篇
  2008年   30189篇
  2007年   31518篇
  2006年   29533篇
  2005年   28502篇
  2004年   28220篇
  2003年   27151篇
  2002年   26660篇
  2001年   46263篇
  2000年   46354篇
  1999年   37256篇
  1998年   13603篇
  1997年   13815篇
  1996年   13072篇
  1995年   12168篇
  1994年   11810篇
  1993年   11883篇
  1992年   30535篇
  1991年   29938篇
  1990年   29218篇
  1989年   28546篇
  1988年   26394篇
  1987年   25238篇
  1986年   23736篇
  1985年   23814篇
  1984年   19580篇
  1983年   17083篇
  1982年   13138篇
  1981年   12059篇
  1980年   11119篇
  1979年   18702篇
  1978年   14919篇
  1977年   13557篇
  1976年   12959篇
  1975年   14485篇
  1974年   15678篇
  1973年   15524篇
  1972年   14250篇
  1971年   12845篇
  1970年   11197篇
  1969年   11054篇
  1968年   9835篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
In a multicentre, randomised, prospective trial 89 patients (67 children and 22 adults) with the minimal change nephrotic syndrome were treated with three intravenous pulses of methylprednisolone followed by low dose oral prednisone for six months (group given methylprednisolone) or with high dose oral prednisone for four weeks followed by low dose oral prednisone for five months (control group). Five patients in the group given methylprednisolone and one in the control group did not respond initially. The time to response was shorter in children treated with methylprednisolone. No significant differences between the two groups were observed in the number of patients who relapsed or number of relapses per patient per year. Patients given methylprednisolone tended to relapse earlier than patients in the control group. Side effects related to treatment were significantly fewer in the group given methylprednisolone than in the control group. These data suggest that a short course of methylprednisolone pulses followed by low dose oral prednisone is only marginally less effective than a regimen of high dose oral steroids but can improve the ratio of risk to benefit associated with treatment of the minimal change nephrotic syndrome.  相似文献   
153.
Monosomy 21: a new case confirmed by in situ hybridization   总被引:4,自引:0,他引:4  
Summary A new case of total monosomy 21 in a newborn is described. The diagnosis was first made using the cytogenetic data; it was then confirmed by the dosage of copper-superoxide dismutase (SOD-1) which showed a 50% decrease. In situ hybridization with a probe previously assigned to chromosome 21 was used to rule out the possibility of a partial monosomy with an unbalanced reciprocal translocation.  相似文献   
154.
A series of measurements of blood pressure in normotensive and hypertensive subjects showed that measurements made with a sphygmomanometer with the arm dependent by the side were consistently higher than those made with the arm horizontal at heart level. The mean difference in a group of 90 hypertensive outpatients was 11/12 mm Hg. Failure to appreciate the importance of arm position may lead to erroneous measurements of blood pressure. This has important implications for clinical practice and research.  相似文献   
155.
1. Because L-asparagine augments insulin release evoked by L-leucine, the metabolism of these two amino acids was investigated in rat pancreatic islets. 2. L-Leucine inhibited the uptake and deamidation of L-asparagine, but failed to exert any obvious primary effect upon the further catabolism of aspartate derived from exogenous asparagine. 3. L-Asparagine augmented the oxidation of L-leucine, and effect possibly attributable to activaion of 2-ketoisocaproate dehydrogenase. 4. The association of L-asparagine and L-leucine exerted a sparing action on the utilization of endogenous amino acids, so that the integrated rate of nutrients oxidation was virtually identical in the sole presence of L-leucine and simultaneous presence of L-asparagine and L-leucine, respectively. 5. It is proposed that the enhancing action of L-asparagine upon insulin release evoked by L-leucine is attributable to an increased generation rate of cytosolic NADPH rather than any increase in nutrients oxidation.  相似文献   
156.
157.
Temperature-sensitive (ts) mutations of the G101 phage were isolated after mutagenesis with hydroxylamine. A complementation analysis of 61ts mutants showed that these mutants may be divided into at least 12 complementation groups. Twots mutants probably originated in genes which control lytic functions of the G101 phage. It was shown by three factor crosses that all of the 12ts mutations tested are localized on that side of the “c” region where the probablecI repressor gene is positioned. Sevents mutations is closely linked to thecI 26 clear marker, three exhibit a closer linkage and two do not exhibit any linkage withcI. All mutations isolated until now can be arrange linearly. According to the present knowledge the preliminary genetic map of the G101 phage is linear.  相似文献   
158.
The design and characteristics of inexpensive and simply constructed equal-energy response photosynthetic irradiance sensors is described for use particularly where several cells are required in comparative ecological studies either above or below water. The dimensions of the sensors can be changed proportionally to suit different applications or components. The response of the sensor to irradiance at varying angles corresponds very closely to that required by the cosine law. The sensor is comparatively insensitive to other environmental variables in field use and gave a stable output; the long term drift was proportional to electrical output but in continuous use, drift is regular and could reach -0.08 year-1 of the total. The spectral range and cosine response is discussed in comparison to other more expensive (x 5–10) commercially available, sensors and to local standards.  相似文献   
159.
160.
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