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   4446篇
  免费   334篇
  2022年   32篇
  2021年   85篇
  2020年   48篇
  2019年   53篇
  2018年   86篇
  2017年   73篇
  2016年   126篇
  2015年   137篇
  2014年   231篇
  2013年   251篇
  2012年   299篇
  2011年   289篇
  2010年   183篇
  2009年   155篇
  2008年   233篇
  2007年   198篇
  2006年   213篇
  2005年   187篇
  2004年   176篇
  2003年   154篇
  2002年   125篇
  2001年   122篇
  2000年   83篇
  1999年   84篇
  1998年   42篇
  1997年   35篇
  1996年   31篇
  1995年   36篇
  1994年   38篇
  1993年   39篇
  1992年   67篇
  1991年   61篇
  1990年   61篇
  1989年   47篇
  1988年   41篇
  1987年   52篇
  1986年   41篇
  1985年   50篇
  1984年   45篇
  1983年   34篇
  1982年   33篇
  1981年   23篇
  1979年   31篇
  1978年   22篇
  1977年   32篇
  1975年   24篇
  1973年   24篇
  1972年   22篇
  1969年   30篇
  1967年   19篇
排序方式: 共有4780条查询结果,搜索用时 31 毫秒
971.
Effect of some pollutants like heavy metals, non-metals and pesticides on the circulating level of C-reactive protein (CRP) which is an acute phase plasma protein was studied in a freshwater murrel C. punctatus. Fish was exposed to nonlethal doses of these xenobiotics which were apparently safe. But the level of CRP detected by sensitive single radial immunodiffusion (SRID) technique showed that within 12 hr of exposure the nonlethal doses of xenobiotics could initiate the acute phase response in terms of elevated CRP titre. Heavy metals caused the acute phase within 24 hr, nonmetals and Metacid-50 within 48 hr exposure. The carbamate compound, carbaryl demonstrated a biphasic response to CRP level which may be correlated with the reversible type of anticholinesterase property of this compound while Metacid-50 is an irreversible type of anticholinesterase agent. The assessment of the CRP level in the serum of fish may be utilized as a primary bioindicator of a contaminated environment toxic enough to mount an acute phase response.  相似文献   
972.
C R Meyer  P Ghosh  E Remy    J Preiss 《Journal of bacteriology》1992,174(13):4509-4512
A mutant glgC gene contained in a 10.9-kb PstI fragment was cloned from the Escherichia coli B strain SG5 via colony hybridization by using a wild-type glgC probe. The altered allosteric properties of the expressed ADPglucose synthetase were found to result from the conversion of proline to serine at amino acid residue 295.  相似文献   
973.
B. CHATTERJEE, A. GHOSH AND A. DAS. 1992. A mutant strain of Emericella nidulans MNU 82 was isolated by multistep mutation. The β-amylase produced by the mutant was able to digest raw starch. It was readily and strongly adsorbed onto raw starch at pH 5.0. The enzyme to starch ratio was 1950 U/g starch. The enzyme showed no correlation between the capacity of raw starch digestion and adsorption of the enzyme.  相似文献   
974.
Zirconium     
Summary The action of Zirconium (Zr) on biological systems presents an enigma. It is ubiquitous, being present in nature in amounts higher than most trace elements. It is taken up by plants from soil and water and accumulated in certain tissues. The entry into animal systems in vivo is related to the mode of exposure and the concentration in the surrounding environment. Retention is initially in soft tissues and then slowly in the bone. The metal is able to cross the blood brain-barrier and is deposited in the brain and the placental barrier to enter milk. The daily human uptake has been known to be as high as 125 mg. The level of toxicity has been found to be moderately low, both in histological and cytological studies. The toxic effects induced by very high concentrations are nonspecific in nature. Despite the presence and retention in relatively high quantities in biological systems, Zr has not yet been associated with any specific metabolic function. Very little information is available about its interaction with the compounds of the genetical systems, such as nucleic acids. Apparently, the metal is neither an essential nor toxic element in the conventional sense. However, the increasing exposure to this element through its increasing use in new materials and following radioactive fallout, has increased the importance of the study of its effects on living organisms. The tetravalent nature of the ionic state and the high stability of the compounds formed are important factors that need to be considered, as also the accumulation of this element in the brain, reminiscent of the relationship between Al3+ and Alzheimer's disease.  相似文献   
975.
Low molecular mass serine proteinase inhibitors isolated from human articular cartilage, intervertebral disc, meniscus, and costal cartilage were compared chromatographically. Similar charge and size properties were exhibited when these inhibitors were examined by gel permeation and cation exchange chromatography. The individual proteinase inhibitory species separated by these procedures all cross-reacted with a polyclonal antibody raised against the mucous proteinase inhibitors (MPIs) obtained from human bronchial secretions, however the distribution of these MPI-like species varied with the origin of the connective tissue. The major inhibitory species present in human articular cartilage and intervertebral disc were purified to homogeneity using gel filtration, cation exchange, trypsin affinity and high performance reverse phase chromatography. The amino-terminal sequences of the purified cartilage intervertebral disc inhibitors was found to be identical to the published sequence of MPIs isolated from parotid and seminal secretions. These findings indicate that the endogenous small molecular mass cationic serine proteinase inhibitory proteins present in human cartilaginous connective tissues are members of the MPI family of proteinase inhibitors.  相似文献   
976.
977.
Crop production for human food and nutritional security is largely dependent on pollination process especially by insects. We assessed the role of pollination in connection with micronutrient supply from edible crops to the Korean population. The study included 42 predominant crop types of varying pollinator dependence. A higher pollinator dependency than present global average was noted in connection with all minerals deemed nutritionally important and vitamins. Pollinator-dependent (PD) crops provide a substantial share of micronutrients to the population, especially with regard to vitamins C and E and elements iron. A positive trend was found in the PD supply of all micronutrients over the last 30?years in Korea, but the rate of increment was somewhat lower for vitamins C and K as well as folate. The results demonstrated the importance of pollination for human nutritional security and conservation of insect pollination system for the sustained ecosystem service.  相似文献   
978.
Plasmonics - Ag nanoparticles (NPs) were deposited on the sol-gel-processed Erbium-doped Indium Oxide (In2O3:Er) thin films (TFs) using thermal evaporation cum glancing angle deposition technique...  相似文献   
979.
Bioprocess and Biosystems Engineering - Direct measurement of cell biomass is difficult in a solid-state fermentation (SSF) process involving filamentous fungi since the mycelium and the solid...  相似文献   
980.
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