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   181212篇
  免费   14328篇
  国内免费   49篇
  2018年   1807篇
  2017年   1756篇
  2016年   2248篇
  2015年   2137篇
  2014年   2934篇
  2013年   4186篇
  2012年   4798篇
  2011年   5306篇
  2010年   3715篇
  2009年   3352篇
  2008年   4853篇
  2007年   5122篇
  2006年   4818篇
  2005年   4539篇
  2004年   4689篇
  2003年   4590篇
  2002年   4572篇
  2001年   8383篇
  2000年   8577篇
  1999年   6311篇
  1998年   1989篇
  1997年   2035篇
  1996年   1801篇
  1995年   1674篇
  1992年   5197篇
  1991年   5362篇
  1990年   5138篇
  1989年   5117篇
  1988年   4732篇
  1987年   4485篇
  1986年   4076篇
  1985年   4234篇
  1984年   3408篇
  1983年   2911篇
  1982年   1929篇
  1981年   1728篇
  1980年   1718篇
  1979年   3211篇
  1978年   2545篇
  1977年   2278篇
  1976年   2081篇
  1975年   2547篇
  1974年   2884篇
  1973年   2802篇
  1972年   2651篇
  1971年   2415篇
  1970年   2116篇
  1969年   2022篇
  1968年   1906篇
  1967年   1743篇
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
411.
Product of polymerase chain reaction designated as PKPIJ-B was isolated after amplification from genomic DNA of potato (Solarium tuberosum L., Zhukov Jubilee cultivar) using the designed primers. Nucleotide sequence of PKPIJ-B was determined and amino acid sequence of protein was restored. Analysis of this sequence has allowed us to suggest that isolated gene fragment encodes chymotrypsin and trypsin inhibitor protein (PKCI-23 potato Kunitz-type chymotrypsin inhibitor) of potato tubers.  相似文献   
412.
The synthesis of some monocyclic beta-lactams (monobactams) by the Staudinger reaction using D-glucosamine propanedithioacetal as chiral auxiliary is reported. The influence of several radicals at C3, C4, and C1' (sugar moiety) as well as other structural aspects are considered in relation to the antielastase activity.  相似文献   
413.
414.
415.
Lactic acid produced from the cells is a potential cause of extra- and intracellular acidification. Due to scarce technical tools, lactic acid that leads to acidification could not be reduced and direct evidence of the relationship between metabolic lactate and apoptosis has not yet been elucidated. In this study, we designed a cellular pH regulation system in CHO cells by a reduction of lactate dehydrogenase (LDH) activity through LDH antisense mRNA expression. This inhibited lactate production and, therefore, acidification of the cytosol. Under HCO3(-)-buffered growth conditions, both the parent CHO cells and the engineered CHO cells maintained their extracellular pH and intracellular pH fairly well. However, upon acidification of the cytosol, only the parent CHO cells underwent apoptosis under HCO3(-)-free conditions. In fact, we observed a number of apoptosis-related events only in control cells, including mitochondrial dysfunction, cytochrome c release, and an increase in caspase-3 enzymatic activity.  相似文献   
416.
A new method is proposed to analyse dependencies in point processes, which takes into account specific character of neuronal activity. Simulation modelling of neuronal network revealed that the estimated weight of connection depends monotonically on the value of the model synaptic strength. In contrast to the crosscorrelation, the method allows for nonlinear interconnections and does not require point processes to be stationary and samples to be large. Examples are presented of the method's application to neurophysiological data analysis.  相似文献   
417.
The amide content of total proteins and protein fractions (alpha-, beta-, gamma-cristallins and albuminoid) from cortex and nuclear lens zones of cattle has been investigated. The amide content in proteins of cortex and nuclear lens of young animals (1,5-2 years old) is the same. The decrease of the amide content in the proteins of nuclear lenz zone of old animals (6-12 years old) is due to fraction of readily hydrolysed amides. The data obtained prove the posttranslational desamidation of lens proteins at ageing. beta-Cristallines--the proteins with the highest amides content is exposed to posttranslational desamidation most of all.  相似文献   
418.
Results are presented from experimental investigations of the angular distributions and energy spectra of fast ions produced in deuterium polyethylene targets under irradiation by picosecond laser pulses with intensities of up to 2 × 1018 W/cm2 in the SOKOL-P facility. The parameters of ion fluxes were measured by time-of-flight spectrometers based on semiconductor detectors.  相似文献   
419.
420.
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