全文获取类型
收费全文 | 1920篇 |
免费 | 101篇 |
国内免费 | 1篇 |
专业分类
2022篇 |
出版年
2023年 | 19篇 |
2022年 | 24篇 |
2021年 | 23篇 |
2020年 | 31篇 |
2019年 | 32篇 |
2018年 | 61篇 |
2017年 | 41篇 |
2016年 | 54篇 |
2015年 | 76篇 |
2014年 | 83篇 |
2013年 | 116篇 |
2012年 | 137篇 |
2011年 | 106篇 |
2010年 | 84篇 |
2009年 | 66篇 |
2008年 | 87篇 |
2007年 | 73篇 |
2006年 | 72篇 |
2005年 | 51篇 |
2004年 | 42篇 |
2003年 | 58篇 |
2002年 | 36篇 |
2001年 | 43篇 |
2000年 | 34篇 |
1999年 | 28篇 |
1998年 | 17篇 |
1997年 | 16篇 |
1996年 | 19篇 |
1995年 | 16篇 |
1994年 | 11篇 |
1993年 | 16篇 |
1992年 | 17篇 |
1991年 | 18篇 |
1990年 | 18篇 |
1989年 | 22篇 |
1988年 | 22篇 |
1987年 | 15篇 |
1986年 | 15篇 |
1985年 | 28篇 |
1984年 | 20篇 |
1983年 | 21篇 |
1982年 | 17篇 |
1980年 | 11篇 |
1979年 | 20篇 |
1978年 | 20篇 |
1975年 | 13篇 |
1973年 | 16篇 |
1972年 | 11篇 |
1971年 | 13篇 |
1967年 | 10篇 |
排序方式: 共有2022条查询结果,搜索用时 0 毫秒
71.
Eliška Zapomělová Jitka Jezberová Pavel Hrouzek Daniel Hisem Klára Řeháková Jaroslava Komárková 《Journal of phycology》2009,45(6):1363-1373
Occurrences of rare cyanobacteria Anabaena reniformis Lemmerm. and Aphanizomenon aphanizomenoides (Forti) Horecká et Komárek were recently detected at several localities in the Czech Republic. Two monoclonal strains of An. reniformis and one strain of Aph. aphanizomenoides were isolated from distant localities and different sampling years. They were characterized by a combination of morphological, genetic, and biochemical approaches. For the first time, partial 16S rRNA gene sequences were obtained for these morphospecies. Based on this gene, all of these strains clustered separately from other planktonic Anabaena and Aphanizomenon strains. They appeared in a cluster with Cylindrospermopsis Seenaya et Subba Raju and Raphidiopsis F. E. Fritsch et M. F. Rich, clustered closely together with two An. kisseleviana Elenkin strains available from GenBank. A new generic entity was defined (Sphaerospermum gen. nov., with the type species S. reniforme, based on the traditional species An. reniformis). These results contribute significantly to the knowledge base about genetic heterogeneity among planktonic Anabaena–like and Aphanizomenon–like morphospecies. Accordingly, the subgenus Dolichospermum, previously proposed for the group of planktonic Anabaena, should be revaluated. Secondary metabolite profiles of the An. reniformis and Aph. aphanizomenoides strains differed considerably from 17 other planktonic Anabaena strains of eight morphospecies isolated from Czech water bodies. Production of puwainaphycin A was found in both of the An. reniformis strains. Despite the relatively short phylogenetic distance from Cylidrospermopsis, the production of cylindrospermopsin was not detected in any of our strains. 相似文献
72.
Tomá? Sieger Cecilia Bonnet Tereza Serranová Ji?í Wild Daniel Novák Filip R??i?ka Du?an Urgo?ík Ev?en R??i?ka Bertrand Gaymard Robert Jech 《PloS one》2013,8(11)
The oculomotor role of the basal ganglia has been supported by extensive evidence, although their role in scanning eye movements is poorly understood. Nineteen Parkinsońs disease patients, which underwent implantation of deep brain stimulation electrodes, were investigated with simultaneous intraoperative microelectrode recordings and single channel electrooculography in a scanning eye movement task by viewing a series of colored pictures selected from the International Affective Picture System. Four patients additionally underwent a visually guided saccade task. Microelectrode recordings were analyzed selectively from the subthalamic nucleus, substantia nigra pars reticulata and from the globus pallidus by the WaveClus program which allowed for detection and sorting of individual neurons. The relationship between neuronal firing rate and eye movements was studied by crosscorrelation analysis. Out of 183 neurons that were detected, 130 were found in the subthalamic nucleus, 30 in the substantia nigra and 23 in the globus pallidus. Twenty percent of the neurons in each of these structures showed eye movement-related activity. Neurons related to scanning eye movements were mostly unrelated to the visually guided saccades. We conclude that a relatively large number of basal ganglia neurons are involved in eye motion control. Surprisingly, neurons related to scanning eye movements differed from neurons activated during saccades suggesting functional specialization and segregation of both systems for eye movement control. 相似文献
73.
74.
Agents known to influence Ca2+ homeostasis affected significantly the vegetative growth and starvation-induced conidiation ofTrichoderma viride. Ca2+ in millimolar concentrations stimulated both growth and conidiation; a Ca2+ deprivation of the fungus by the chelation of extracellular Ca2+ (not Mg2+ or divalent trace metals) with EGTA (ethyleneglycolbis(2-aminoethylether)-N,N,N′,N′-tetraacetic acid) restricted both the
vegetative growth rate and starvation-induced conidiation. Both processes were affected by either Ca2+ or EGTA with different efficiencies. Divalent cations (Sr2+, Ba2+, Co2+, Ni2+, Mg2+, Cd2+, Cu2+, Mn2+) and La3+ (inorganic Ca2+ blockers) in millimolar concentrations exerted complex (stimulatory, inhibitory, or biphasic) effects on growth and conidiation.
In general, their effects on the two processes were mutually different either qualitatively, or quantitatively, or both. Organic
Ca2+ antagonists (verapamil and dihydropyridines) inhibited the vegetative growth. The results show that Ca2+ is required for vegetative growth and conidiation, and that different Ca2+-dependent mechanisms may be involved in the two processes. Divalent cations could serve as a tool for investigating the relationship
between growth and conidiation. 相似文献
75.
Percutaneous cryoablation of colorectal liver metastases: potentiated by two consecutive freeze-thaw cycles 总被引:12,自引:0,他引:12
Cryoablation may be beneficial for selected patients with liver tumours. Two freeze-thaw cycles at the same location have been recommended during treatment as this potentiate the effect of ablation in experimental studies. However, single freeze ablations are used by some as double freeze procedures are time-consuming and have been associated with increased risk of complications. Estimation of ice-ball volume is difficult using regularly used monitoring techniques. Magnetic resonance imaging, however, allows excellent and multiplanar visualisation of the frozen region during ablation. We comment on the effect of double freeze cycles in regard to ice-ball volume as estimated from magnetic resonance imaging during percutaneous cryoablation of colorectal liver metastases. The ice-ball volume at the end of the second freeze cycle was median 42% larger than the volume at the end of the first freeze. Double freeze cycles may thus facilitate tumour destruction. 相似文献
76.
D. Holá M. Benešová J. Honnerová F. Hnilička O. Rothová M. Kočová H. Hniličková 《Photosynthetica》2010,48(4):545-558
The response of selected photosynthetic and morphological parameters of plants to drought was examined in 5 inbred lines of
maize (Zea mays L.) and their 10 F1 hybrids. The aim of the study was to establish whether the photosynthetic performance of parental genotypes
under drought conditions correlates with the performance of their progeny and whether the net photosynthetic rate, the chlorophyll
fluorescence parameters or the content of photosynthetic pigments could be used as reliable physiological markers for early
breeding generations. The relative importance of the additive and the nonadditive (dominance, maternal) genetic effects in
the inheritance of these parameters was also assessed by means of the quantitative genetics analysis. The results showed that
the nonadditive genetic effects associated with a particular combination of genotypes or a particular direction of crossing
are at least equally and often even more important as the additivity and that these genetic effects almost totally change
with the exposure of plants to drought conditions. This was reflected in the inability to predict the response of F1 hybrids
to drought on the basis of the photosynthetic performance of their parents, which indicates that the practical usability of
such parameters in maize breeding programs is rather limited. 相似文献
77.
Forward genetic analysis of the circadian clock separates the multiple functions of ZEITLUPE 下载免费PDF全文
Kevei E Gyula P Hall A Kozma-Bognár L Kim WY Eriksson ME Tóth R Hanano S Fehér B Southern MM Bastow RM Viczián A Hibberd V Davis SJ Somers DE Nagy F Millar AJ 《Plant physiology》2006,140(3):933-945
The circadian system of Arabidopsis (Arabidopsis thaliana) includes feedback loops of gene regulation that generate 24-h oscillations. Components of these loops remain to be identified; none of the known components is completely understood, including ZEITLUPE (ZTL), a gene implicated in regulated protein degradation. ztl mutations affect both circadian and developmental responses to red light, possibly through ZTL interaction with PHYTOCHROME B (PHYB). We conducted a large-scale genetic screen that identified additional clock-affecting loci. Other mutants recovered include 11 new ztl alleles encompassing mutations in each of the ZTL protein domains. Each mutation lengthened the circadian period, even in dark-grown seedlings entrained to temperature cycles. A mutation of the LIGHT, OXYGEN, VOLTAGE (LOV)/Period-ARNT-Sim (PAS) domain was unique in retaining wild-type responses to red light both for the circadian period and for control of hypocotyl elongation. This uncoupling of ztl phenotypes indicates that interactions of ZTL protein with multiple factors must be disrupted to generate the full ztl mutant phenotype. Protein interaction assays showed that the ztl mutant phenotypes were not fully explained by impaired interactions with previously described partner proteins Arabidopsis S-phase kinase-related protein 1, TIMING OF CAB EXPRESSION 1, and PHYB. Interaction with PHYB was unaffected by mutation of any ZTL domain. Mutation of the kelch repeat domain affected protein binding at both the LOV/PAS and the F-box domains, indicating that interaction among ZTL domains leads to the strong phenotypes of kelch mutations. Forward genetics continues to provide insight regarding both known and newly discovered components of the circadian system, although current approaches have saturated mutations at some loci. 相似文献
78.
Boelo Schuur Marek Blahušiak Caecilia R. Vitasari Michal Gramblička André B. De Haan Ton J. Visser 《Chirality》2015,27(2):123-130
Enantioseparation through liquid extraction technology is an emerging field, e.g., enantioseparations of amino acids (and derivatives thereof), amino alcohols, amines, and carboxylic acids have been reported. Often, when a new selector is developed, the versatility of substrate scope is investigated. From an industrial point of view, the problem is typically approached the other way around, and for a target racemate, a selector needs to be found in order to accomplish the desired enantioseparation. This study presents such a screening approach for the separation of the enantiomers of dl ‐α‐methyl phenylglycine amide (dl ‐α‐MPGA), a model amide racemate with high industrial relevance. Chiral selectors that were reported for other classes of racemates were investigated, i.e., several macrocyclic selectors and Pd‐BINAP complexes. It appeared very challenging to obtain both high extraction yields and good enantioselectivity for most selectors, but Pd‐BINAP‐based selectors performed well, with enantioselectivities up to 7.4 with an extraction yield of the desired enantiomer of 95.8%. These high enantioselectivities were obtained using dichloromethane as solvent. Using less volatile chlorobenzene or 1‐chloropentane, reasonable selectivities of up to 1.7 were measured, making these the best alternative solvents for dichloromethane. Chirality 27:123–130, 2015. © 2014 Wiley Periodicals, Inc. 相似文献
79.
A complete cellulase from Penicillium pinophilum was evaluated for the hydrolysis of α-cellulose derived from steam exploded sugarcane bagasse and other cellulosic substrates. α-Cellulose at 1% substrate concentration was completely hydrolyzed by Penicillium cellulase within 3 h wherein at 10% the hydrolysis was 100% within 24 h with an enzyme loading of 10 FPU/g. The hydrolysate yielded glucose as major end product as analyzed by HPLC. Under similar conditions, hydrolysis of Sigmacell (microcrystalline cellulose), CP-123 (pulverized cellulose powder) and ball milled Solka Floc were 42%, 56% and 52%, respectively. Further the hydrolysis performance of Penicillium sp. cellulase is compared with Trichoderma reesei cellulase (AccelleraseTM 1000) from Genencore. The kinetics of hydrolysis with respect to enzyme and substrate concentration will be presented. 相似文献
80.
Cyanobacterial mats (CBM) are important components of wetland ecosystems in limestone-based regions of the Caribbean. During two sampling periods (July 1999 and January 2000) we measured N2-fixation in samples from 23 different marshes simultaneously with measurements of relevant environmental factors. Samples were evaluated for abundance of five groups of cyanobacteria: (1) Leptolyngbya, (2) Oscillatoria, (3) Chroococcales, (4) Nostoc-& Stigonematales, and (5) dead sheaths. Differences in nitrogen fixation, expressed as nitrogenase activity in nmol C2H4 cm–2 h–1, were best explained by the proportion of heterocyst-forming cyanobacteria. The samples were analyzed for the natural abundance of 15N. 15N values ranged from –1.99 to 11.44 and were strongly negatively correlated with N2-fixation. With all data included, 15N was also strongly correlated with nitrates in water. With the samples from Little Belize (high nitrate content marshes) excluded, the effect of nitrate became insignificant. N2-fixation predicted from 15N measured on an independent data set from September 2000 was moderately accurate (r2 = 0.68, 0.52 and 0.54 for predictions based on July 1999, January 2000 and combined data sets, respectively). When individual sample sets were divided into two groups with 15N < 2 and 15N > 2, the two groups were always highly significantly different in terms of their N2-fixation. The presented evidence suggests that 15N can be used as a reliable indicator of N2-fixation by CBM. 相似文献