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991.
In this study, we used a random approach to determine which amino acid pairs in human coagulation factor IX precursor are more sensitive to its 99 variants. The results show that the randomly unpredictable amino acid pairs are more sensitive to variants. 相似文献
992.
993.
994.
Cell cycle-dependent expression of volume-activated chloride currents in nasopharyngeal carcinoma cells 总被引:25,自引:0,他引:25
Chen L Wang L Zhu L Nie S Zhang J Zhong P Cai B Luo H Jacob TJ 《American journal of physiology. Cell physiology》2002,283(4):C1313-C1323
Patch-clamping and cell imageanalysis techniques were used to study the expression of thevolume-activated Cl current,ICl(vol), and regulatory volume decrease (RVD)capacity in the cell cycle in nasopharyngeal carcinoma cells (CNE-2Z). Hypotonic challenge caused CNE-2Z cells to swell and activated aCl current with a linear conductance, negligibletime-dependent inactivation, and a reversal potential close to theCl equilibrium potential. The sequence of anionpermeability was I > Br > Cl > gluconate. The Cl channelblockers tamoxifen, 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB),and ATP inhibited ICl(vol). Synchronous cultures of cells were obtained by the mitotic shake-off technique and by adouble chemical-block (thymidine and hydroxyurea) technique. Theexpression of ICl(vol) was cell cycle dependent,being high in G1 phase, downregulated in S phase, butincreasing again in M phase. Hypotonic solution activated RVD, whichwas cell cycle dependent and inhibited by the Cl channelblockers NPPB, tamoxifen, and ATP. The expression of ICl(vol) was closely correlated with the RVDcapacity in the cell cycle, suggesting a functional relationship.Inhibition of ICl(vol) by NPPB (100 µM)arrested cells in G0/G1. The data also suggest that expression of ICl(vol) and RVD capacity areactively modulated during the cell cycle. The volume-activatedCl current associated with RVD may therefore play animportant role during the cell cycle progress. 相似文献
995.
In this study, a new method is proposed to estimate the torque-vector directions of each shoulder muscle. The method is based on a multiple regression model that reconstructs shoulder torque, which is calculated from the hand force and posture, from the surface EMG of many muscles recorded simultaneously. The torque-vector directions of eleven shoulder muscles of four subjects were obtained at up to 30 different arm postures with this method. The mean confidence interval (p < 0.05) of the estimated torque-vector direction of each subject was 7.7-10.6 degrees. The correlation coefficient between the measured shoulder torque and reconstructed shoulder torque was between 0.76-0.84. The results for majority of the muscles were in accordance with previous studies, and reasonable from the viewpoint of anatomy. The torque-vector directions of a muscle, which are estimated with this method, have more of a functional meaning than a pure anatomical or mechanical one. These indicate the direction of the shoulder torque accompanying the muscle activation for a normal shoulder action that involves the cooperative contraction of many muscles. 相似文献
996.
Ribonucleotide reduction is the only known biological means for de novo production of deoxyribonucleotides, the building blocks of DNA. These are produced from ribonucleotides, the building blocks
of RNA, and the direction of this reaction has been taken to support the idea that, in evolution, RNA preceded DNA as genetic
material. However, an understanding of the evolutionary relationships among the three modern-day classes of ribonucleotide
reductase and how the first reductase arose early in evolution is still far off. We propose that the diversification of this
class of enzymes is inherently tied to microbial colonization of aerobic and anaerobic niches. The work is of broader interest,
as it also sheds light on the process of adaptation to oxygenic environments consequent to the evolution of atmospheric oxygen. 相似文献
997.
Dragoi V 《Biological cybernetics》2002,86(6):419-426
Simple exposure to repeatitive stimulation is known to induce short-term learning effects across a wide range of species.
These effects can be both suppressive and facilitatory depending on stimulus conditions: repeatitive presentation of a weak
stimulus decreases the strength of the response (habituation), whereas presentation of a tonic stimulus following a series
of weak stimuli transiently increases the response strength (dishabituation). Although these phenomena have been comprehensively
characterized at both behavioral and cellular levels, most existing models of nonassociative learning focus exclusively on
the suppressive or facilitatory changes in response, and do not attempt to relate cellular events to behavior. I propose here
a feedforward model of habituation effects that explains both suppressive and facilitatory changes in response relying on
the interaction between excitatory and inhibitory processes that develop in parallel on two different timescales. The model's
properties are used to explain the rate sensitivity property of habituation and recovery and stimulus dishabituation.
Received: 1 June 2001 / Accepted in revised form: 4 December 2001 相似文献
998.
999.
Ethanol production from corn cob hydrolysates by <Emphasis Type="Italic">Escherichia coli</Emphasis> KO11 总被引:2,自引:0,他引:2
de Carvalho Lima KG Takahashi CM Alterthum F 《Journal of industrial microbiology & biotechnology》2002,29(3):124-128
Corn cob hydrolysates, with xylose as the dominant sugar, were fermented to ethanol by recombinant Escherichia coli KO11. When inoculum was grown on LB medium containing glucose, fermentation of the hydrolysate was completed in 163 h and
ethanol yield was 0.50 g ethanol/g sugar. When inoculum was grown on xylose, ethanol yield dropped, but fermentation was faster
(113 h). Hydrolysate containing 72.0 g/l xylose and supplemented with 20.0 g/l rice bran was readily fermented, producing
36.0 g/l ethanol within 70 h. Maximum ethanol concentrations were not higher for fermentations using higher cellular concentration
inocula. A simulation of an industrial process integrating pentose fermentation by E. coli and hexose fermentation by yeast was carried out. At the first step, E. coli fermented the hydrolysate containing 85.0 g/l xylose, producing 40.0 g/l ethanol in 94 h. Baker's yeast and sucrose (150.0
g/l) were then added to the spent fermentation broth. After 8 h of yeast fermentation, the ethanol concentration reached 104.0
g/l. This two-stage fermentation can render the bioconversion of lignocellulose to ethanol more attractive due to increased
final alcohol concentration. Journal of Industrial Microbiology & Biotechnology (2002) 29, 124–128 doi:10.1038/sj.jim.7000287
Received 20 February 2002/ Accepted in revised form 04 June 2002 相似文献
1000.