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31.
Soil acidity, ecological stoichiometry and allometric scaling in grassland food webs 总被引:1,自引:0,他引:1
The factors regulating the structure of food webs are a central focus of community and ecosystem ecology, as trophic interactions among species have important impacts on nutrient storage and cycling in many ecosystems. For soil invertebrates in grassland ecosystems in the Netherlands, the site-specific slopes of the faunal biomass to organism body mass relationships reflected basic biochemical and biogeochemical processes associated with soil acidity and soil C : N : P stoichiometry. That is, the higher the phosphorus availability in the soil, the higher, on average, the slope of the faunal biomass size spectrum (i.e., the higher the biomass of large-bodied invertebrates relative to the biomass of small invertebrates). While other factors may also be involved, these results are consistent with the growth rate hypothesis from biological stoichiometry that relates phosphorus demands to ribosomal RNA and protein production. Thus our data represent the first time that ecosystem phosphorus availability has been associated with allometry in soil food webs (supporting information available online). Our results have broad implications, as soil invertebrates of different size have different effects on soil processes. 相似文献
32.
Igor N. Stadnichuk Evgeny P. Lukashev Irina V. Elanskaya 《Photosynthesis research》2009,99(3):227-241
The features of the two types of short-term light-adaptations of photosynthetic apparatus, State 1/State 2 transitions, and
non-photochemical fluorescence quenching of phycobilisomes (PBS) by orange carotene-protein (OCP) were compared in the cyanobacterium
Synechocystis sp. PCC 6803 wild type, CK pigment mutant lacking phycocyanin, and PAL mutant totally devoid of phycobiliproteins. The permanent
presence of PBS-specific peaks in the in situ action spectra of photosystem I (PSI) and photosystem II (PSII), as well as
in the 77 K fluorescence excitation spectra for chlorophyll emission at 690 nm (PSII) and 725 nm (PSI) showed that PBS are
constitutive antenna complexes of both photosystems. The mutant strains compensated the lack of phycobiliproteins by higher
PSII content and by intensification of photosynthetic linear electron transfer. The detectable changes of energy migration
from PBS to the PSI and PSII in the Synechocystis wild type and the CK mutant in State 1 and State 2 according to the fluorescence excitation spectra measurements were not
registered. The constant level of fluorescence emission of PSI during State 1/State 2 transitions and simultaneous increase
of chlorophyll fluorescence emission of PSII in State 1 in Synechocystis PAL mutant allowed to propose that spillover is an unlikely mechanism of state transitions. Blue–green light absorbed by
OCP diminished the rout of energy from PBS to PSI while energy migration from PBS to PSII was less influenced. Therefore,
the main role of OCP-induced quenching of PBS is the limitation of PSI activity and cyclic electron transport under relatively
high light conditions. 相似文献
33.
Viscoelastic properties of waxy maize starch and selected non-starch hydrocolloids gels 总被引:3,自引:0,他引:3
A. Ptaszek W. Berski P. Ptaszek T. Witczak U. Repelewicz M. Grzesik 《Carbohydrate polymers》2009,76(4):567-577
Polysaccharides play a significant role in food systems as texture forming agent. Their solutions posses some peculiar rheological behaviors. Some information about structure of these biopolymers and relaxation processes occurring in their solutions may be obtained by investigation of linear viscoelasticity properties. The aim of this research was to investigate viscoelastic properties of systems consisting of waxy maize starch–hydrocolloid–water. To achieve this aim two techniques were applied: rheological measurements in frequency domain and structural studies by means of AFM method. The results were interpreted on basis of time–temperature superposition principle and phenomenological theory of viscoelasticity. Thermal stability of analyzed systems allowed applying time-temperature superposition principle. Calculation of aT parameter enabled to obtaine the master curves. Continuous Maxwell model was applied to analyze phase separation in examined systems. Relaxations spectra obtained by Tikhonov regularization method were heterogeneous, indicating on non-homogenous structure of system. 相似文献
34.
The aim of the present study is to explore whether membrane targeting of K+ channel-interacting protein 1 (KChIP1) is associated with its EF-hand motifs and varies with specific phospholipids. Truncated
KChIP1, in which the EFhands 3 and 4 were deleted, retained the α-helix structure, indicating that the N-terminal half of KChIP1 could fold appropriately. Compared with wild-type KChIP1,
truncated KChIP1 exhibited lower lipid-binding capability. Compared with wild-type KChIP1, increasing membrane permeability
by the use of digitonin caused a marked loss of truncated KChIP1, suggesting that intact EF-hands 3 and 4 were crucial for
the anchorage of KChIP1 on membrane. KChIP1 showed a higher binding capability with phosphatidylserine (PS) than truncated
KChIP1. Unlike that of truncated KChIP1, the binding of wild-type KChIP1 with membrane was enhanced by increasing the PS content.
Moreover, the binding of KChIP1 with phospholipid vesicles induced a change in the structure of KChIP1 in the presence of
PS. Taken together, our data suggest that EF-hands 3 and 4 of KChIP1 are functionally involved in a specific association with
PS on the membrane. 相似文献
35.
Ferenc Faigl Bernadett Vas‐Feldhoffer Veronika Kudar Mátyás Czugler Krisztina Pál Miklós Kubinyi 《Chirality》2009,21(10):905-910
Site selective mono‐ and dimetalation methods have been developed for the functionalization of 1‐[(1,1′‐biphenyl)‐2‐yl]‐1H‐pyrrole. Optical resolution of the prepared 1‐[(3‐carboxy‐1,1′‐biphenyl)‐2‐yl]pyrrole‐2‐carboxylic acid provided new atropisomeric 1‐arylpyrrole derivatives. The absolute configuration of the pure dicarboxylic acid enantiomers was determined by single crystal X‐ray diffraction and CD spectroscopy. Chirality 2009. © 2009 Wiley‐Liss, Inc. 相似文献
36.
The stability of brain networks with randomly connected excitatory and inhibitory neural populations is investigated using
a simplified physiological model of brain electrical activity. Neural populations are randomly assigned to be excitatory or
inhibitory and the stability of a brain network is determined by the spectrum of the network’s matrix of connection strengths.
The probability that a network is stable is determined from its spectral density which is numerically determined and is approximated
by a spectral distribution recently derived by Rajan and Abbott. The probability that a brain network is stable is maximum
when the total connection strength into a population is approximately zero and is shown to depend on the arrangement of the
excitatory and inhibitory connections and the parameters of the network. The maximum excitatory and inhibitory input into
a structure allowed by stability occurs when the net input equals zero and, in contrast to networks with randomly distributed
excitatory and inhibitory connections, substantially increases as the number of connections increases. Networks with the largest
excitatory and inhibitory input allowed by stability have multiple marginally stable modes, are highly responsive and adaptable
to external stimuli, have the same total input into each structure with minimal variance in the excitatory and inhibitory
connection strengths, and have a wide range of flexible, adaptable, and complex behavior. 相似文献
37.
辣根过氧化物酶的热稳定剂 总被引:2,自引:1,他引:1
保持酶的天然状态和高催化特性具有重要的意义。本研究筛选了辣根过氧化物酶(HRP)的稳定剂并研究了其作用机制。结果发现硫酸镁和明胶能够显著提高HRP的热稳定性,并且两者具有协同作用。在硫酸镁和明胶组成的酶稳定剂存在的条件下,HRP在50oC保温80h后仍能保持89%的活性,常温下存放90d后可保持57%的活性,而未加稳定剂的对照样品中HRP的残留活性分别为6%和小于1%。通过对HRP的Soret带吸收光谱,色氨酸内源荧光,ANS荧光进行分析,揭示酶稳定剂可以明显降低在加热条件下HRP的变性程度,从而维持较为稳定的天然构象。 相似文献
38.
Scott R. Kronewitter Hyun Joo An Maria Lorna de Leoz Carlito B. Lebrilla Suzanne Miyamoto Gary S. Leiserowitz 《Proteomics》2009,9(11):2986-2994
Annotation of the human serum N‐linked glycome is a formidable challenge but is necessary for disease marker discovery. A new theoretical glycan library was constructed and proposed to provide all possible glycan compositions in serum. It was developed based on established glycobiology and retrosynthetic state‐transition networks. We find that at least 331 compositions are possible in the serum N‐linked glycome. By pairing the theoretical glycan mass library with a high mass accuracy and high‐resolution MS, human serum glycans were effectively profiled. Correct isotopic envelope deconvolution to monoisotopic masses and the high mass accuracy instruments drastically reduced the amount of false composition assignments. The high throughput capacity enabled by this library permitted the rapid glycan profiling of large control populations. With the use of the library, a human serum glycan mass profile was developed from 46 healthy individuals. This paper presents a theoretical N‐linked glycan mass library that was used for accurate high‐throughput human serum glycan profiling. Rapid methods for evaluating a patient's glycome are instrumental for studying glycan‐based markers. 相似文献
39.
Absorption spectra at ca 100 K from 400 to 750 nm and fluorescence emission spectra at 77 K from 600 to 750 nm were obtained from: 1) etiolated leaves of the H-ordeum vulgare L. (barley) mutant albozonata 2 and SAN 9789-treated Avena sativa L. (oat) with low levels of carotenoids, and 2) preparations of protochlorophyllide holo-chrome from Phaseolus vulgaris L. cv. Commodore (bean).
This allowed clear resolution for the first time of the Soret bands of the green pigments before and after light-induced accumulation of intermediate(s) in protochlorophyllide to chlorophyllide photoreduction and after conversion of the intermediate(s) to chlorophyllide by warming the samples to 233 K in darkness. Although the intermediate(s) differ(s) in absorption and fluorescence in the red wavelength region from both protochlorophyllide and chlorophyllide, the extinction in the Soret band is not distinguishable from that of chlorophyllide. These observations indicate that the C7-C8 double bond in ring IV of protochlorophyllide has been altered in intermediate(s) accumulated at low temperature in intense light, such that the transition state exhibits the character of a π complex. 相似文献
This allowed clear resolution for the first time of the Soret bands of the green pigments before and after light-induced accumulation of intermediate(s) in protochlorophyllide to chlorophyllide photoreduction and after conversion of the intermediate(s) to chlorophyllide by warming the samples to 233 K in darkness. Although the intermediate(s) differ(s) in absorption and fluorescence in the red wavelength region from both protochlorophyllide and chlorophyllide, the extinction in the Soret band is not distinguishable from that of chlorophyllide. These observations indicate that the C7-C8 double bond in ring IV of protochlorophyllide has been altered in intermediate(s) accumulated at low temperature in intense light, such that the transition state exhibits the character of a π complex. 相似文献
40.
啤酒废酵母制备碱不溶性葡聚糖 总被引:3,自引:0,他引:3
以啤酒废酵母为原料,采用碱提法确定了碱不溶性葡聚糖的制备条件,使用1.0 mol.L-1的NaOH溶液,以固液比为1:5进行提取,45℃处理6 h。此条件下碱不溶性葡聚糖得率可达10.94%,其多糖质量分数可达91.57%。红外光谱分析显示产品为β-(1-3)键的葡聚糖,其中不含甘露聚糖。 相似文献