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   4986篇
  免费   286篇
  国内免费   1篇
  2022年   47篇
  2021年   102篇
  2020年   64篇
  2019年   81篇
  2018年   109篇
  2017年   99篇
  2016年   138篇
  2015年   184篇
  2014年   214篇
  2013年   272篇
  2012年   352篇
  2011年   323篇
  2010年   201篇
  2009年   165篇
  2008年   250篇
  2007年   223篇
  2006年   203篇
  2005年   185篇
  2004年   174篇
  2003年   133篇
  2002年   146篇
  2001年   107篇
  2000年   78篇
  1999年   83篇
  1998年   47篇
  1997年   30篇
  1996年   39篇
  1995年   31篇
  1994年   28篇
  1992年   56篇
  1991年   65篇
  1990年   53篇
  1989年   62篇
  1988年   49篇
  1987年   54篇
  1986年   38篇
  1985年   77篇
  1984年   51篇
  1983年   57篇
  1981年   35篇
  1980年   44篇
  1979年   54篇
  1978年   35篇
  1976年   27篇
  1975年   27篇
  1974年   34篇
  1973年   31篇
  1971年   35篇
  1970年   29篇
  1969年   35篇
排序方式: 共有5273条查询结果,搜索用时 15 毫秒
91.
The major cuticular components of Indian tasar silkworm,Antheraea mylitta Drury, were sequentially extracted and estimated to ascertain preferential utilization of these components for growth by the entomopathogenic fungusPenicillium citrinum Thom. Proteins which constituted 61.64% dry weight of cuticule were found to play a key role in the growth ofP. citrinum whereas lipids (7.15%) and chitin (30.02%) were least involved. Also, this study suggests absence of any mycocidal substance in the cuticle ofA. mylitta.  相似文献   
92.
An objective of the CSR sugarcane breeding programme in Australia was to assess the scope for broadening the genetic base of the commercial sugarcane germ plasm through interspecific hybridization with Saccharum spontaneum clones. The contribution of both selection history and S. spontaneum to sugar yield and its components was investigated in the germ plasm pool assembled. The analysis was conducted on a data-set of 256 clones, consisting of parents and full-sib families generated from 32 biparental crosses, tested in six environments. The minimum number of generations back to S. spontaneum ancestor in the clone's pedigree was used as a germ plasm score. The geographical origin and selection history of each parent and their use in the biparental crosses were used to develop a selection history score for parents and offspring. The variation for seven attributes, cane yield, commercial cane sugar %, sugar yield, stalk number per stool, stalk weight, fibre % and ash % juice was partitioned according to the germ plasm and selection history scores. Significant (P<0.05) clone variation and clone x environment interaction for all attributes was present. The germ plasm scores accounted for a significant (P<0.05) component of the clone variation for all of the attributes except cane yield. There was an increase in sugar yield with an increase in the minimum number of generations back to a S. spontaneum clone. The selection history groups accounted for a high proportion of the variation among parental clones for all of the attributes except cane yield. This suggested that parents were the outcome of strong selection pressure for the commercial cane attributes. However, the selection history groups for the offspring produced by random mating of parents did not account for a high proportion of the variation for the attributes. Using the mixture method of classification we partitioned the 256 clones into five groups for patterns of performance for the seven attributes across the six environments. The five groups emphasized major differences in the patterns of performance for the seven attributes across environments. The distribution of germ plasm and selection history scores in each of the five groups indicated that their patterns of performance were associated with selection history and minimum generations to S. spontaneum. Therefore, both the analysis on selection history and germ plasm scores (extrinsic classification) and the analysis on the mixture method of classification (intrinsic classification) emphasized the influence of selection history on the sugar yield of sugarcane.  相似文献   
93.
94.
We studied grooming among adults of a one-male multifemale troop of free-ranging Hanuman langurs (Presbytis entellus)living near Jodhpur, India, for 9 years. The 11–13 females devoted about 6% of their day to allogrooming. Adult males, whose tenures averaged 2.2 years, were transient figures in the troop's history, as reflected by their rather peripheral role in the grooming network. Females groomed males 4–40 times more frequently (1006 episodes) than vice versa- (176 episodes). Adult females received 97% of all grooming from other adult females (6655 episodes). Although females exhibited an age- inversed dominance hierarchy, they did not compete for grooming access to particular troop mates. Dyads of all possible rank differences occurred as frequently as expected: 51% of grooming was directed up the hierarchy and 49% down it. Young, high- ranking individuals gave and received significantly more grooming than the oldest, low- ranking females did. The pattern seemed to be influenced by kin selection because of the presumably high degree of female relatedness. They invested most in troopmates with the highest reproductive value, i.e., the youngest individuals. This trend was coupled with a preference of closest kin (mothers and daughters). Reciprocity was the outstanding feature since all adult females groomed and were groomed by all others. Such a tight social net might establish the necessary cohesion during frequent territorial disputes with neighboring troops.  相似文献   
95.
Biological, serological and coat protein properties of a potyvirus (Poty-Rape) causing a mosaic disease of Brassica campestris and B. juncea in India were investigated. The virus readily infected 4 of the 5 plant species in the family Brassicaceae in which it induced severe systemic mosaic symptoms; it also induced chlorotic and necrotic local lesions in Chenopodium amaranticolor , but failed to infect 4 other species of Chenopodiaceae or 20 species of Amaranthaceae, Apiaceae, Canabinaceae, Compositae, Cucurbitaceae, Euphorbiaceae, Leguminosae and Solanaceae. The virus was transmitted in a non-persistant manner by Myzus persicae, Brevicoryne brassicae and Aphis gossypii. The Average size, of the virus particles in a purified preparation was 740 nm × 12 nm. SDS-PAGE analysis of the viral coat protein showed two major bands of approximately 37 kDa and 31 kDa, a pattern very similar to that of a reference isolate of turnip mosaic virus (TuMV) from the U.S. In Western-blot immunoassay, an antiserum to TuMV reacted with both the coat protein bands of the Poty-Rape islate and the reference TuMV, but not with the coat proteins of four other potyviruses. The high performance liquid chromatographic profile of tryptic peptides from the coat protein of Poty-Rape was found to be very similar to that of the reference TuMV, but differed substantially from those of four other potyviruses. The Poty-Rape isolate is considered to be a distinct strain of, TuMV.  相似文献   
96.
When Chlorella vulgaris 11h, Chlorella vulgaris C-l, Chlamydomonasreinhardtii, Chlamydomonas moewusii, Scenedesmus obliquus, orDunaliella tertiolecta were illuminated in with 0.5 mM NaHCO3,the pH of the medium increased in a few minutes from 6 to about9 or 10. The alkalization, which was accompanied by O2 evolution,was dependent on light, external dissolved inorganic carbon(DIC) as HCO-3, and algae grown or adapted to a low, air-levelCO2 in order to develop a DIC concentrating mechanism. Therewas little pH increase by algae without a DIC concentratingprocess from growth on 3% CO2 in air. Photosynthetic O2 evolutionwithout alkalization occurred using either internal DIC or externalCO2 at acidic pH. The PH increase stopped between pH 9 to 10,but the alkalization would restart upon re-acidification betweenpH 6 and 8. Alkalization was suppressed by the carbonic anhydraseinhibitors, acetazolamide, ethoxyzolamide or carbon oxysulfide.The pH increase appeared to be the consequence of the externalconversion of HCO3 into CO2 plus OH during photosynthesisby cells with a high affinity for CO2 uptake. Cells grown onhigh CO2 to suppress the DIC pump, when given low levels ofHCO3 in the light, acidified the medium from pH 10 to7. Air adapted Scenedesmus cells with a HCO3 pump, aswell as a CO2 pump, alkalized the medium very rapidly in thelight to a pH of over 10, as well as slower in the dark or inthe light with DCMU or without external DIC and O2 evolution.Alkalization of the medium during photosynthetic DIC uptakeby algae has been considered to be part of the global carboncycle for converting H2CO3 to HCO3 and for the formationof carbonate salts by calcareous algae from the alkaline conversionof bicarbonate to carbonate. These processes seem to be a consequenceof the algal CO2 concentrating process. 1Present address: Department of Biology, Faculty of Science,Niigata University, Niigata, 950-21 Japan.  相似文献   
97.
Cell Biochemistry and Biophysics - Despite attempts to maintain asepsis, good manufacturing practices, and the use of terminal sterilization by millipore filtration, the nuclear practitioner is...  相似文献   
98.
The effect of nicotinamide-adenine dinucleotides (NAD+ and NADP+) on Ca2+ transport in rat liver nuclei was investigated. Ca2+ uptake and release were determined with a Ca2+ electrode. Ca2+ uptake was dependent on adenosine triphosphate (ATP; 2mM). The presence of NAD+ (2mM) or NADP+ (1 and 2mM) caused a significant inhibition of Ca2+ uptake following addition of 2mM ATP. Ca2+, which accumulated in the nuclei during 6 min after ATP addition, was significantly released by the addition of NAD+ (0.5–2mM) or NADP+ (0.1–2mM). However, the effect of NADH (2mM) or NADPH (2mM) on Ca2+ uptake and release clearly weakened in comparison with the effects of NAD+ and NADP+. Meanwhile, ryanodine (10M), thapsigargin (10M) or oxalate (0.5mM) had no effect on Ca2+ uptake and release in rat liver nuclei. These reagents did not significantly alter the effects of 2mM NAD+ on Ca2+ uptake and release. Thus, NAD+ and NADP+ had a potent effect on Ca2+ transport in rat liver nuclei. The present findings suggest that the liver cytosolic NAD+ (NADP+) is a factor in the regulation of the nuclear Ca2+ concentration. (Mol Cell Biochem121: 127–133, 1993)  相似文献   
99.
This paper describes and then analyzes the decision-making arrangements that prevail among the Raikas—nomadic shepherds from Western India. The paper suggests, using a simple analytical framework, that the existing distribution of decision-making during migration helps the Raikasto utilize available economies of scale, represent the different interest groups in their collectives, and control their decision-makers. At the same time, the ordinary shepherds in the camp are able to extract a comfortable subsistence from a complex and harsh environment by delegating much of their decision-making responsibilities to the leaders in the camp. To the extent shepherds in other parts of the world migrate over long distances and must confront similar issues of delegation of responsibilities and control over decision-makers, the analysis holds general relevance.  相似文献   
100.
Rare earth metals play a conspicuous role in magnetic resonance imaging (MRI) for detecting cancerous cells. The alkali metal potassium is a neurotransmitter in the sodium–potassium pump in biomedical sciences. This unique property of rare earth metals and potassium drew our attention to carry forward this study. Therefore, in this work, previously synthesized potassium (K) complexes formed by the reflux of 4-N,N-dimethylaminobenzoic acid (DBA) and potassium hydroxide in methanol, and named [(μ2–4-N,N-dimethylaminobenzoate-κO)(μ2–4-N,N-dimethylaminobenzoic acid-κO)(4-N,N-dimethylaminobenzoic acid-κO) potassium(I) coordination polymer)] were treated hydrothermally with La2O3 nanomaterials to obtain a nanohybrid La2O3/K-complex. After that, the K-complex was analyzed using single-crystal X-ray diffraction and 1H and 13C NMR spectroscopy. In addition, the structural and morphological properties of the as-prepared nanostructured La2O3/K-complex were also characterized, which involved an investigation using X-ray diffraction (XRD)spectroscopy, Fourier transform infrared (FTIR) spectroscopy, atomic force spectroscopy (AFM), transmission electron microscopy (TEM), and energy dispersive X-ray (EDX) analysis. After this, the electrochemical redox behaviour of the synthesized nanohybrid material was studied using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Therefore, the results from these studies revealed that the as-prepared material was a La2O3/K-complex that has a promising future role in sensing various analytes, as it showed effective electrocatalytic behaviour.  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