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   2735篇
  免费   278篇
  国内免费   244篇
  3257篇
  2024年   10篇
  2023年   53篇
  2022年   65篇
  2021年   115篇
  2020年   113篇
  2019年   135篇
  2018年   125篇
  2017年   95篇
  2016年   125篇
  2015年   81篇
  2014年   158篇
  2013年   199篇
  2012年   96篇
  2011年   104篇
  2010年   138篇
  2009年   149篇
  2008年   171篇
  2007年   165篇
  2006年   160篇
  2005年   126篇
  2004年   98篇
  2003年   96篇
  2002年   80篇
  2001年   54篇
  2000年   50篇
  1999年   38篇
  1998年   42篇
  1997年   34篇
  1996年   27篇
  1995年   25篇
  1994年   30篇
  1993年   22篇
  1992年   30篇
  1991年   27篇
  1990年   17篇
  1989年   14篇
  1988年   14篇
  1987年   12篇
  1986年   14篇
  1985年   21篇
  1984年   30篇
  1983年   13篇
  1982年   22篇
  1981年   17篇
  1980年   19篇
  1979年   13篇
  1978年   3篇
  1977年   5篇
  1975年   2篇
  1974年   2篇
排序方式: 共有3257条查询结果,搜索用时 0 毫秒
11.
Lemna paucicostata Hegelm. T-101, a short-day plant, flowers when plants preirradiated with red light (R) for 24 h are subjected to inductive darkness for 72 h followed by two short-day cycles (6 h R+ 18 h dark). However, flowering is inhibited by blue-or far-red-light pulses applied at the beginning of the inductive dark period. These inhibitory light effects are fully reversible by a R pulse. The action spectra for the inhibitory light effect and for its reversal show that the light pulses act exclusively through phytochrome. It is concluded that a low level of Pfr at the beginning of the inductive dark period prevents flowering.Abbreviations R red (light) - B blue (light) - FR far-red (light)  相似文献   
12.
The C-D stretching regions of the infrared and Raman spectra of 14 different palmitic and stearic acids containing isolated CD2 groups are reported. Anomalous behaviour is observed when substitution occurs near the terminal methyl group, which behaviour can not be explained in terms of crystal field effects.  相似文献   
13.
Copper(II) N-salicylidene-(S)-alaninate trihydrate reacting as the S-enantiomeric parent compound with KOCN in hot diluted methanol yielded by slow crystallisation from the cooled reaction mixture (in the course of 1 day) the racemic product K[Cu{sal-(RS)-ala}(NCO)]. The parameters of the axial type EPR spectrum in X-band region and the LF band position in the electronic spectrum are typical of an axially distorted square pyramidal coordination of the Cu(II) atom in this complex. The spectral properties of the complex cuprate prepared and its basal crystallographic data are consistent with those of the earlier studied15 K2[Cu2{sal-(RS)-ala}2(μ-NCO)2] synthetized by using [Cu{sal-(RS)-ala}(H2O)].H2O as the racemic parent complex in the reaction mixture with KOCN.  相似文献   
14.
Summary A new system of dispersal units has been elaborated, based on weight and morphological features functional in dispersal. Weight was divided into eight classes and the functional morphological features were selected in such a way that their effectiveness could be tested by experiments.The spectra of weight and dispersal adaptations of dispersal units sampled in Euphorbio-Pinetum nigrae and Fumano-Stipetum habitats south of Vienna are calculated with this system and then compared.The results show that both communities can be characterized with such spectra. It is also possible with these spectra to make statements about the ecological and social position of the association in a succession.Nomenclature follows Ehrendorfer (1973).  相似文献   
15.
We have examined the 5-exo-hydroxylation of camphor by cytochrome P450 in [18O] water/buffer solution. In the NADHO2-dependent reaction of the reconstituted multienzyme system, no 18O-label is observed in the product alcohol. Similarly, in the m-chloroperbenzoic acid or cumene hydroperoxide supported reactions with ferric P450, solvent oxygen is not incorporated into hydroxycamphor. When the analagous reaction is carried out using iodosobenzene as the exogenous oxidant, however, the alcoholic oxygen of the product is derived entirely from the solvent. These results cannot be explained by equilibration of the iodosobenzene oxygen with solvent water before reacting with P450, and suggest a unique mechanism for iodosobenzene-supported P450 oxygenations. We propose two distinct mechanistic activities for cytochrome P450: a hydroxylase, and an oxene transferase, with the former encompassing the classic oxygenase as well as “peroxygenase” reactions.  相似文献   
16.
Rhodospirillum rubrum strain F24.1 is a spontaneous revertant of nonphototrophic mutant F24 derived from wild-type strain S1. Strain F24 shows no detectable photochemical activity and contains, at most, traces of the photoreaction center polypeptides. Strain F24.1 has a phototrophic growth rate close to that of the wild-type strain (Picorel, R., del Valle-Tascón, S. and Ramírez, J.M. (1977) Arch. Biophys. Biochem. 181, 665–670) but shows little photochemical activity. Light-induced absorbance changes in the near-infrared, photoinduced EPR signals and ferricyanide-elicited absorbance changes indicate that strain F24.1 has a photoreaction center content of 7–8% as compared to strain S1. Polyacrylamide gel electrophoresis of isolated F24.1 chromatophores shows the photoreaction center polypeptides to be present in amounts compatible with this value. Photoreaction center was prepared from strain F24.1 and showed no detectable difference with that of strain S1. It is concluded that strain F24.1 photosynthesis is due entirely to its residual 7–8% of typical photoreaction center.  相似文献   
17.
王燕  高友鹤 《生命科学》2010,(2):119-123
长期以来,肾脏病的治疗进展一直十分缓慢,这是因为目前一些肾脏病在诊断分型上存在很多缺陷,分型通常只能依靠细微的组织病理学差异,这使早期诊断、预后追踪以及疗效观察都十分困难。如果能发现像肌钙蛋白一样特异的生物学标志物,将有助于提高肾脏病的诊疗水平。由于尿液与泌尿系统之间存在着天然的联系,这使得尿液在反映泌尿系统功能方面具备"地理"优势。因此,尿蛋白质组学的兴起和发展为肾脏病及其他泌尿系统疾病的研究开启了一扇新的大门。该文综述了尿蛋白质组学技术的发展及其在各种泌尿系统疾病研究中的应用。  相似文献   
18.
朝鲜毛球蚧蜡泌物的超微形态与红外光谱特征   总被引:4,自引:3,他引:4  
谢映平  郑乐怡 《昆虫学报》2002,45(3):329-335
采用扫描电镜和红外光谱技术研究了朝鲜毛球蚧Didesmococcus koreanus在不同发育阶段蜡泌物的超微形态和化学成分。结果发现:该虫在低龄期的蜡泌物的形态是长丝状,到3龄和成虫期是由湿蜡凝结成不同大小的颗粒,块状和片状。雄虫蜡壳是薄蜡片构成,表面呈鱼鳞状凹凸。低龄期若虫蜡泌物的红外光谱特征与雌成虫的十分相似,说明二者所含的主要化学成分是相同的,雄虫和低龄若虫及雌成虫蜡壳萃取物的红外光谱的吸收峰型基本一致,但在1 240.7 cm-1处出现一个中等强度的特征峰,这充分说明3种蜡泌物的有机化合物种类和结构一致,只是雄虫分泌物与另二者比较具有特征官能团,从而,利用该吸收峰可以区别出雄虫。此外,根据红外光谱特征分析,可以知道该虫蜡泌物的化学成分主要为长链脂肪酸、脂肪醇和一些带芳香环的化合物。  相似文献   
19.
We herein report the joint occurrence of an autistic disorder (AD) and X-linked hypophosphatemia. X-linked hypophosphatemia (XLH), an X-linked dominant disorder, is the most common of the inherited renal phosphate wasting disorders. Autism is a pervasive developmental disorder that occurs mainly due to genetic causes. In approximately 6-15% of cases, the autistic phenotype is a part of a broader genetic condition called syndromic autism.Therefore, reports of cases with the joint occurrence of a known genetic syndrome and a diagnosis of ASD by a child psychiatrist are relevant. A joint occurrence does not, however, mean that there is always a causal link between the genetic syndrome and the autistic behavioural phenotype. In this case, there are a number of arguments countering a causal link.  相似文献   
20.
Transmissible spongiform encephalopathies (prion diseases) in animals may be associated with a zoonotic risk potential for humans as shown by the occurrence of variant Creutzfeldt-Jakob disease in the wake of the bovine spongiform encephalopathy epidemic. Thus, the increasing exposure of humans in North America to cervid prions of chronic wasting disease (CWD) in elk and deer has prompted comprehensive risk assessments. The susceptibility of humans to CWD infections is currently under investigation in different studies using macaques as primate models. The necessity for such studies was recently reinforced when disease-associated prion protein and its seeding activity were detected in muscles of clinically inconspicuous CWD-infected white-tailed deer (WTD). Increasing evidence points to the existence of different CWD strains and CWD prions may also change or newly emerge over time. Therefore, CWD isolates examined in macaques should be characterized as precisely as possible for their molecular identity. On this basis other CWD field samples collected in the past, present or future could be systematically compared with macaque-tested inocula in order to assess whether they are covered by the ongoing risk assessments in primates. CWD typing by Fourier transform-infrared spectroscopy of pathological prion protein may provide a method of choice for this purpose.  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