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91.
92.
Local polarity and hydrogen bonding inside the Sec14p phospholipid-binding cavity: high-field multi-frequency electron paramagnetic resonance studies 下载免费PDF全文
Smirnova TI Chadwick TG Voinov MA Poluektov O van Tol J Ozarowski A Schaaf G Ryan MM Bankaitis VA 《Biophysical journal》2007,92(10):3686-3695
Sec14p promotes the energy-independent transfer of either phosphatidylinositol (PtdIns) or phosphatidylcholine (PtdCho) between lipid bilayers in vitro and represents the major PtdIns/PtdCho transfer protein in the budding yeast Saccharomyces cerevisiae. Herein, we employ multi-frequency high-field electron paramagnetic resonance (EPR) to analyze the electrostatic and hydrogen-bonding microenvironments for series of doxyl-labeled PtdCho molecules bound by Sec14p in a soluble protein-PtdCho complex. A structurally similar compound, 5-doxyl stearic acid dissolved in a series of solvents, was used for experimental calibration. The experiments yielded two-component rigid limit 130- and 220-GHz EPR spectra with excellent resolution in the gx region. Those components were assigned to hydrogen-bonded and nonhydrogen-bonded nitroxide species. Partially resolved 130-GHz EPR spectra from n-doxyl-PtdCho bound to Sec14p were analyzed using this two-component model and allowed quantification of two parameters. First, the fraction of hydrogen-bonded nitroxide species for each n-doxyl-PtdCho was calculated. Second, the proticity profile along the phospholipid-binding cavity of Sec14p was characterized. The data suggest the polarity gradient inside the Sec14p cavity is a significant contributor to the driving molecular forces for extracting a phospholipid from the bilayer. Finally, the enhanced g-factor resolution of EPR at 130 and 220 GHz provides researchers with a spectroscopic tool to deconvolute two major contributions to the x-component of the nitroxide g-matrix: hydrogen-bond formation and local electrostatic effects. 相似文献
93.
The aim ofthe study was to assess laying traits, the weight of eggs and characters ofthe laying rhythm of pheasants in the first and second years of reproduction. Pheasants (10 cockerels and 50 hens) were kept in aviaries. Daily, individual control of laying was performed beginning with the day of the first laying and ending with the last egg. The following parameters were evaluated: age at first laying, length of the laying period, number of laid eggs and the average weight of the egg in the 8th week of laying. The laying rhythm was also assessed and comprised: the number of egg clutches, the number of eggs in a clutch, the number of eggs in the longest clutch, the number of intervals, the length of intervals and the longest interval between clutches. During the first period of reproduction, in comparison with the second, pheasants laid slightly more eggs of similar average weight. The first laying period was longer than the second and was characterised by a greater number of egg clutches and greater number of intervals between clutches. The greatest number of eggs was laid in 10-egg and longer clutches, although the l-egg clutches were the most numerous. A positive correlation was found between the number of eggs and the number of clutches, the greatest number of eggs in a clutch and the number of intervals between clutches. The similar values of the reproductive characters of one- and two-year old pheasants point to the possibility of longer utilization of these birds than only for one laying period. On the other hand, the considerable variability between the experimental hens with regard to the number and the length of egg clutches, as well as the intervals between them, indicate the possibility to carry out selection taking into account traits characterising the laying rhythm. 相似文献
94.
95.
Dyguda-Kazimierowicz E Sokalski WA Leszczyński J 《Journal of molecular modeling》2007,13(6-7):839-849
The subject of this study was an analysis of the role of active site residues in the phosphoryl transfer reaction catalyzed
by 4-methyl-5-β-hydroxyethylthiazole kinase (ThiK). The ThiK-catalyzed reaction is of special interest due to the lack of
a highly conserved aspartate residue serving as a catalytic base. ONIOM(B3LYP:PM3) models of stationary points along the reaction
pathway consisted of reactants, two magnesium ions and several highly conserved ThiK active site residues. The results indicate
that an SN2-like mechanism of ThiK, with γ-phosphate acting as an alcohol-activating base is reasonable. Geometries of substrates, transition
state and products were utilized in the non-empirical analysis of the physical nature of catalytic interactions taking place
in the ThiK active site. The role of particular residues was investigated in terms of their ability to preferentially stabilize
the transition state relative to substrates (differential transition state stabilization, DTSS) or products (differential
product stabilization, DPS). It seems that Mg2, Glu126 and Cys198 play a major catalytic role, whereas Mg1 and the same Cys198
are responsible for product release. It is remarkable that no dominant role of an electrostatic term in the interactions involved
in catalytic activity is observed for product release. Determination of catalytic fields expressing differential electrostatic
potential of the transition state with respect to substrates revealed the optimal electrostatic features of an ideal catalyst
for the studied reaction. The predicted catalytic environment is in agreement with experimental data showing increased catalytic
activity of ThiK upon mutation of Cys198 to aspartate.
Figure Catalytic fields for ThiK-catalyzed reaction juxtaposed with the positions of active site residues of a model system. Magnesium
ions are considered part of the transition state/reactants. The surface of constant electronic density is colored according
to differential electrostatic potential of transition state with respect to reactants. The sign of the differential potential
reflects the electrostatic properties of a complementary molecular environment. Red (green) color denotes regions where a negative (positive) charge would be optimal for catalytic activity 相似文献
96.
Bytnerowicz A Arbaugh M Schilling S Fraczek W Alexander D Dawson P 《TheScientificWorldJournal》2007,7(Z1):98-109
Since the mid-1950s, native pines in the San Bernardino Mountains (SBM) in southern California have shown symptoms of decline. Initial studies in 1963 showed that ozone (O3) generated in the upwind Los Angeles Basin was responsible for the injury and decline of sensitive trees. Ambient O3 decreased significantly by the mid-1990s, resulting in decreased O3 injury and improved tree growth. Increased growth of trees may also be attributed to elevated atmospheric nitrogen (N) deposition. Since most of the N deposition to mixed conifer forest stands in the SBM results from dry deposition of nitric acid vapor (HNO3) and ammonia (NH3), characterization of spatial and temporal distribution of these two pollutants has become essential. Although maximum daytime O3 concentrations over last 40 years have significantly decreased (approximately 3-fold), seasonal means have been reduced much less (approximately 1.5-fold), with 2-week long means occasionally exceeding 100 ppb in the western part of the range. In the same area, significantly elevated concentrations of HNO3 and NH3, up to 17.5 and 18.5 microg/m3 as 2-week averages, respectively, have been determined. Elevated levels of O3 and increased N deposition together with long-term drought predispose the SBM forests to massive bark beetle attacks making them susceptible to catastrophic fires. 相似文献
97.
Dong A Xu X Edwards AM;Midwest Center for Structural Genomics;Structural Genomics Consortium Chang C Chruszcz M Cuff M Cymborowski M Di Leo R Egorova O Evdokimova E Filippova E Gu J Guthrie J Ignatchenko A Joachimiak A Klostermann N Kim Y Korniyenko Y Minor W Que Q Savchenko A Skarina T Tan K Yakunin A Yee A Yim V Zhang R Zheng H Akutsu M Arrowsmith C Avvakumov GV Bochkarev A Dahlgren LG Dhe-Paganon S Dimov S Dombrovski L Finerty P Flodin S Flores A Gräslund S Hammerström M Herman MD Hong BS 《Nature methods》2007,4(12):1019-1021
We tested the general applicability of in situ proteolysis to form protein crystals suitable for structure determination by adding a protease (chymotrypsin or trypsin) digestion step to crystallization trials of 55 bacterial and 14 human proteins that had proven recalcitrant to our best efforts at crystallization or structure determination. This is a work in progress; so far we determined structures of 9 bacterial proteins and the human aminoimidazole ribonucleotide synthetase (AIRS) domain. 相似文献
98.
Bartke A 《Cell metabolism》2007,6(3):153-154
Global reduction in insulin signaling has been linked to extended life span in a range of organisms. New work on mice with brain-specific or whole-body reductions in insulin receptor substrate 2 (IRS2) (Taguchi et al., 2007) points to a role for insulin/IGF-1 signaling in the central control of mammalian aging. 相似文献
99.
100.
Marcin Brzeziski Joanna Pyrlik Marcin Churski Ewa Komar Andrzej Zalewski 《Ethology : formerly Zeitschrift fur Tierpsychologie》2019,125(11):791-801
The perception and assessment of predation risk often cause changes in the activities of animals and induce behavioural responses that may in turn affect their movements and distribution. To simulate high predation risk in a midfield pond riparian habitat, we used fresh faeces from ranch American mink Neovison vison and recorded behavioural responses of water voles Arvicola amphibius. In areas where mink odour was deployed, the numbers of captured vole individuals and their trappability were significantly lower than in control areas. Several voles migrated from the zones with deployed mink faeces to the areas without faeces, thus proving that increased predation risk affects the distribution of individuals in a population. The response to mink odour was much more pronounced in females than in males; in areas with deployed mink faeces, not a single female was trapped. We conclude that although American mink is a non‐native, invasive predator, water voles respond to mink odour by reducing their activity and/or by avoiding places with higher predation risk. 相似文献