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   1581篇
  免费   132篇
  国内免费   1篇
  2023年   11篇
  2022年   16篇
  2021年   46篇
  2020年   10篇
  2019年   23篇
  2018年   38篇
  2017年   29篇
  2016年   34篇
  2015年   64篇
  2014年   77篇
  2013年   106篇
  2012年   137篇
  2011年   120篇
  2010年   68篇
  2009年   61篇
  2008年   92篇
  2007年   89篇
  2006年   92篇
  2005年   59篇
  2004年   57篇
  2003年   38篇
  2002年   42篇
  2001年   25篇
  2000年   29篇
  1999年   30篇
  1998年   15篇
  1997年   15篇
  1996年   14篇
  1995年   13篇
  1994年   17篇
  1993年   12篇
  1992年   25篇
  1991年   16篇
  1990年   18篇
  1989年   15篇
  1988年   11篇
  1985年   8篇
  1983年   11篇
  1979年   6篇
  1977年   8篇
  1976年   6篇
  1975年   8篇
  1974年   7篇
  1973年   7篇
  1972年   11篇
  1971年   9篇
  1970年   6篇
  1969年   7篇
  1967年   6篇
  1966年   9篇
排序方式: 共有1714条查询结果,搜索用时 15 毫秒
1.
2.
BackgroundA soluble form of CD26/dipeptidyl peptidase-IV (sCD26/DPP-IV) induces DPP-IV enzymatic activity that degrades incretin. We investigated fasting serum levels of sCD26/DPP-IV and active glucagon-like peptide-1 (GLP-1) in Malaysian patients with type 2 diabetes mellitus (T2DM) with and without metabolic syndrome (MetS), as well as the associations between sCD26/DPP-IV levels, MetS, and antidiabetic therapy.MethodsWe assessed sCD26/DPP-IV levels, active GLP-1 levels, body mass index (BMI), glucose, insulin, A1c, glucose homeostasis indices, and lipid profiles in 549 Malaysian subjects (including 257 T2DM patients with MetS, 57 T2DM patients without MetS, 71 non-diabetics with MetS, and 164 control subjects without diabetes or metabolic syndrome).ResultsFasting serum levels of sCD26/DPP-IV were significantly higher in T2DM patients with and without MetS than in normal subjects. Likewise, sCD26/DPP-IV levels were significantly higher in patients with T2DM and MetS than in non-diabetic patients with MetS. However, active GLP-1 levels were significantly lower in T2DM patients both with and without MetS than in normal subjects. In T2DM subjects, sCD26/DPP-IV levels were associated with significantly higher A1c levels, but were significantly lower in patients using monotherapy with metformin. In addition, no significant differences in sCD26/DPP-IV levels were found between diabetic subjects with and without MetS. Furthermore, sCD26/DPP-IV levels were negatively correlated with active GLP-1 levels in T2DM patients both with and without MetS. In normal subjects, sCD26/DPP-IV levels were associated with increased BMI, cholesterol, and LDL-cholesterol (LDL-c) levels.ConclusionSerum sCD26/DPP-IV levels increased in T2DM subjects with and without MetS. Active GLP-1 levels decreased in T2DM patients both with and without MetS. In addition, sCD26/DPP-IV levels were associated with Alc levels and negatively correlated with active GLP-1 levels. Moreover, metformin monotherapy was associated with reduced sCD26/DPP-IV levels. In normal subjects, sCD26/DPP-IV levels were associated with increased BMI, cholesterol, and LDL-c.  相似文献   
3.
A palaeocommunity of large Conichnus conicus, a conical, cone-in-cone shaped burrow, created by sea anemones, occurs in medium-grained, crossbedded, well-sorted sandstone in the middle part of the Cretaceous Guneri Member of the Bhuj Formation in India. The trace fossil Conichnus is considered to be a common element of the Skolithos ichnofacies and is interpreted to reflect equilibrium movement in response to substrate aggradation. In the present study, three different varieties of Conichnus conicus are distinguished based on morphology and internal fabric. Community dynamics and burrowing behavior are revealed by inter-burrow relationships, burrow initiation levels and sedimentology. Three types of behavior are envisaged: retrusive equilibrium, protrusive equilibrium response, and escape behavior. Palaeocommunity dynamics show that the tracemakers consisted of only adult organisms that initiated burrows during neap tides and are adapted to feed effectively during weak flow conditions. The occurrence of Conichnus palaeocommunity in the Guneri Member indicates the tidal conditions in a fully marine setting. Results presented herein may aid in the understanding of palaeocommunity dynamics in other shallow marine sequences.  相似文献   
4.
Summary To investigate the use of RFLP analysis in the Triticeae, a set of low copy number probes has been isolated from a wheat cDNA library. The probes identify each of the 14 homoeologous chromosome arms of wheat as determined by analysis of DNA fragments hybridizing to the probes in aneuploid lines of Chinese Spring. These probes can be used in RFLP analyses both for the assignment of homoeology of alien chromosomes or arms added to wheat, and for the determination of chromosome dosage in wheat aneuploids. Different chromosomes from various Triticeae species can therefore be followed in a wheat genetic background using a single technique. The potential uses of the set in facilitating the transfer of alien segments into wheat are outlined.  相似文献   
5.
PACAP, a VIP-like peptide, in neurons of the esophagus.   总被引:1,自引:0,他引:1  
The lower esophagus of guinea-pig, cat, sheep and man was analyzed for pituitary adenylate cyclase activating peptide (PACAP), a novel vasoactive intestinal peptide (VIP)-like peptide, using immunocytochemistry and radioimmunoassay. PACAP-immunoreactive nerve fibers were numerous in the longitudinal and circular muscle layers of sheep and man, moderate in numbers in cat, while being few in the esophagus of guinea-pig. A few PACAP-immunoreactive nerve cell bodies and numerous nerve fibers were seen in the myenteric ganglia of the esophagus of cat, sheep and man. In the lower esophagus of cat, sheep and man all PACAP-containing nerve cell bodies and nerve fibers stored VIP. The results of radioimmunoassay of PACAP in extracts of specimens from man were in good agreement with the immunocytochemical findings. High performance liquid chromatography revealed one major peak of PACAP-like immunoreactivity in extracts of human esophagus. We suggest that neuronal PACAP may serve to modulate motor activity and secretion in the lower esophageal sphincter region.  相似文献   
6.
7.
A reduction in the viability of cowpea rhizobia was observed when Rhizobium trifolii IARI and cowpea Rhizobium strain 3824 were inoculated together in soil. The reduction in number of cowpea rhizobia in soil was found to be associated with the reduction in number of nodules per plant and retardation in plant growth. An antimicrobial substance was isolated from R. trifolii which, on electron microscopic investigation, demonstrated the presence of several phage-like structures.  相似文献   
8.
Means of increasing the very low activity of a reconstituted protein synthesising system from rabbit reticulocytes were investigated. Increasing the concentration of labelled amino acid, addition of polyamines, use of Sepharose-filtered as opposed to centrifuged ribosomes, use of untreated as opposed to gel-filtered cytosol and an increase in ratio of cytosol to ribosomes all contributed to the increase in activity of the system to the point where activity was clearly consistent with initiation taking place. Similar activities could not be attained with rat liver cytosol though rat liver ribosomes incorporated well in reticulocyte cytosol. Incorporation by lysates was also found to be dependent on the concentration of the labelled amino acid added.  相似文献   
9.
Following illumination with wavelengths longer than 700 nm, the intensity of light emission from Pothos aurea leaf falls for 1 min and then increases to a maximum after 2 min in the dark. The spectrum of this minute-range liminescence matches that of prompt fluorescence excited at the same wavelength, but differs from that of prompt or minute-range delayed emission excited by wavelengths shorter than 700 nm. This emission is less sensitive to heat damage than millisecond delayed emission, and may originate from photosystem I.  相似文献   
10.
Simultaneous reduction in alkaloid yield and level of phosphatases by high concentrations of phosphate was observed inClaviceps sp. SD-58. Tryptophan-induced culture showed an increase in alkaloid yield and the level of phosphatases. Phosphate caused repression of both acid phosphatase (isoenzyme I) and alkaline phosphatase (isoenzymes III and V).  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