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981.
Genetic analysis of superoxide dismutase, the 23 kilodalton antigen of Mycobacterium tuberculosis 总被引:28,自引:1,他引:27
The gene encoding a 23 kilodalton protein antigen has been cloned from Mycobacterium tuberculosis by screening of a recombinant DNA library with monoclonal antibodies. The product of the gene has been identified as the superoxide dismutase (SOD) of M. tuberculosis on the basis of sequence comparison and by expression of the recombinant protein in a functionally active form. The derived amino acid sequence of M. tuberculosis SOD reveals a close similarity to manganese-containing SODs from other organisms, in spite of the fact that previous studies using the purified enzyme have identified iron as the preferred metal ion ligand. SOD is present in the extracellular fluid of logarithmic-phase cultures of M. tuberculosis, but the structural gene is not preceded by a signal peptide sequence. Insertion of the M. tuberculosis SOD gene into a novel shuttle vector demonstrated the mycobacteria but is ineffective in Escherichia coli. 相似文献
982.
Biodegradation of toxic and environmental pollutants. 总被引:1,自引:0,他引:1
Organic chemicals that are toxic to humans and to the environment can be transformed and metabolized by a variety of microorganisms. Such chemicals include trichloroethylene, chloroform, carbon tetrachloride, toluene, phenols, chlorinated phenols, polychlorinated biphenyls and polyaromatic hydrocarbons. This review focuses on some of the most important recent developments in the biodegradation of these toxic chemicals. Depending on the compound and the organism, the extent of our understanding ranges from the molecular level to the conceptual. 相似文献
983.
Kim B. Saunders Patricia A. D’Amore 《In vitro cellular & developmental biology. Animal》1992,28(7-8):521-528
Summary Heterotypic cell-cell interactions appear to be involved in the control of development and function in a wide variety of tissues.
In the vasculature, endothelial cells and mural cells (smooth muscle cells or pericytes) make frequent contacts, suggesting
a role for intercellular interactions in the regulation of vascular growth and function. We have previously grown endothelial
cells and mural cells together in mixed cultures and found that heterocellular contact led to endothelial growth inhibition.
However, this mixed culture system does not lend itself to the examination of the effects of contact on the phenotype of the
individual cell types. We have therefore developed a co-culture system in which cells can be co-cultured across a porous membrane,
permitting intercellular contact while maintaining pure cell populations. Co-culture of endothelial cells and smooth muscle
cells across membranes with pore sizes of 0.02, 0.4, 0.6, and 0.8μm maintained the two cell types as homogeneous populations, whereas smooth muscle cells migrated across the membrane through
pores of 2.0μm. Vascular cell co-culture across membranes with 0.8-μm pores resulted the inhibition of endothelial cell proliferation and the generation of conditioned media which inhibited
endothelial cell growth. The arrangement of the cells in this co-culture system mimics thein vivo orientation of vascular cells in which mural cells are separated from the abluminal surface of the endothelium by a fenestrated
internal elastic lamina or basement membrane. Because this co-culture system maintains separable populations of cells in contact
or close proximity allowing for biochemical and molecular analyses of pure populations, it should prove useful for the study
of cell-cell interactions in a variety of systems. 相似文献
984.
985.
We have earlier identified and purified two protein-lysine N-methyltransferases (Protein methylase III) fromEuglena gracilis [J. Biol. Chem.,260, 7114 (1985)]. The enzymes were highly specific toward histone H1 (lysine-rich), and the enzymatic products were identified as ε-N-mono-, di- and trimethyllysines. These earlier studies, however, were carried out with rat liver histone H1 as thein vitro substrate. Presently, histone H1 has been purified fromEuglena gracilis through Bio-Rex 70 and Bio-Gel P-100 column chromatography. TheEuglena histone H1 showed a single band on SDS-polyacrylamide gel electrophoresis and behaved like other histone H1 of higher animals, whereas it had a much higherR f value than the other histones H1 in acid/urea gel electrophoresis. When theEuglena histone H1 was [methyl-3H]-labeledin vitro by a homologous enzyme (one of the twoEuglena protein methylase III) and analyzed on two-dimensional gel electrophoresis, three distinctive subtypes of histone H1 were shown to be radiolabeled, whereas five subtypes of rat liver histone H1 were found to be labeled. Finally, by the combined use of a strong cation exchange and reversed-phase Resolve C18 columns on HPLC, we demonstrated thatEuglena histone H1 contains approximately 9 mol% of ε-N-methyllysines (1.40, 1.66, and 5.62 mol% for ε-N-mono-, di- and trimethyllysines, respectively). This is the first demonstration of the natural occurrence of ε-N-methyllysines in histone H1. 相似文献
986.
Taek-Jae Kim Jong-Sei Park Ho-Sang Shin 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1992,575(2)
The metabolites of trimeprazine were identified in urine of rats by gas chromatography—mass spectrometry. After the oral administration of trimeprazine, the urinary metabolites were extracted with diethyl ether before or after hydrolysis with β-glucuronidase. The identified metabolites were N-demethyltrimeprazine, 3-hydroxytrimeprazine, N-demethyl-3-hydroxytrimeprazine and trimeprazine sulphoxide. 相似文献
987.
Operation Everest II: metabolic and hormonal responses to incremental exercise to exhaustion. 总被引:5,自引:0,他引:5
P M Young J R Sutton H J Green J T Reeves P B Rock C S Houston A Cymerman 《Journal of applied physiology》1992,73(6):2574-2579
The reasons for the reduced exercise capacities observed at high altitudes are not completely known. Substrate availability or accumulations of lactate and ammonium could have significant roles. As part of Operation Everest II, peak oxygen uptakes were determined in five normal male volunteers with use of progressively increasing cycling work loads at ambient barometric pressures of 760, 380, and 282 Torr. Decrements from sea level (SL) to 380 and 282 Torr occurred in peak power output (19 and 47%), time to exhaustion (19 and 48%), and oxygen uptake (41 and 61%), respectively. Arterial saturations after exhaustive exercise were decreased to 63% at 380 Torr and 39% at 282 Torr. At 380 and 282 Torr, postexercise plasma concentrations of glucose and free fatty acids were not increased, whereas plasma glycerol concentrations were decreased relative to SL (145 +/- 24 microM at 380 Torr and 77 +/- 10 microM at 282 Torr vs. 213 +/- 24 microM at SL). Preexercise plasma insulin concentrations were elevated at both 380 and 282 Torr (87 +/- 16 pM at 380 Torr and 85 +/- 18 pM at 282 Torr vs. 41 +/- 30 pM at SL). In general, postexercise concentrations of plasma catecholamines were decreased at altitude compared with SL. Preexercise lactate and ammonium concentrations were not different at any simulated altitude. From these data neither substrate availability nor metabolic product accumulation limited exercise capacity at extreme simulated altitude. 相似文献
988.
K Nakayama K Hatsuzawa W S Kim K Hashiba T Yoshino H Hori K Murakami 《European journal of biochemistry》1990,191(2):281-285
It has been recently reported that, in Xenopus oocytes injected with the mRNA for human renin, this secretory renal glycoprotein acquires phosphomannosyl residues on its asparagine-linked oligosaccharide chains, remains intracellular and undergoes a proteolytic cleavage which removes the prosegment. To understand the influence of glycosylation on the fate of renin in Xenopus oocytes and whether it is specific for human renin, we have expressed human renin and mouse Ren1 renin, which are glycosylated at two and three selected asparagine residues, respectively, and mouse Ren2 renin, which is not glycosylated, in Xenopus oocytes. The majority of human and Ren1 renins remained intracellular and underwent proteolytic cleavage, whereas mouse Ren2 renin was secreted efficiently. When human and Ren1 renins were expressed in oocytes treated with tunicamycin, both were secreted efficiently. A mutant of human renin, which had amino-acid substitutions at both glycosylation sites, was also secreted efficiently, whereas that mutated at one of the two sites was not. These results indicate that the majority of all of the glycosylated renin molecules remain intracellular and undergo proteolytic cleavage, probably due to the acquisition of phosphomannosyl residues, and the human renin remains intracellular if it is only glycosylated at one of the two sites. 相似文献
989.
McQueen Donald J. Johannes Mark R. S. Lafontaine Nathalie R. Young Andrew S. Longbotham Eric Lean David R. S. 《Hydrobiologia》1990,(1):337-341
We used two analyses to test the hypothesis that planktivore abundances contribute to the residual variations of Secchi depth
or chlorophyll-a plotted with respect to mean summer epilimnetic total phosphorus. The first analysis involved 15 lake years of data from
six lakes. The data set comprised mark-recapture assessments of piscivore and planktivore numbers and estimates of mean summer
chlorophyll-a, total phosphorus and Secchi depth. We found that residual chlorophyll-a variation was not significantly (p>0.05) correlated with planktivore densities, but that planktivore densities did contribute (p<0.02) to the residual variation of Secchi depth on mean total phosphorus. The second analysis included all of the data used
in the first plus an additional 13 lake years of data from the literature. These data showed that the percentage of the total
fish community comprising planktivores did not significantly (p>0.05) contribute to the residual variation in chlorophyll-a with respect to mean summer total phosphorus. Together, our results suggest that planktivore abundance has a significant
cascading impact on water clarity, but no long term statistically significant impact on mean summer chlorophyll-a concentration. 相似文献
990.
The lambda S lysis gene was cloned into a Saccharomyces cerevisiae expression vector under GAL1 control. Induction with galactose in S. cerevisiae terminated cell growth and prevented colony formation. Several membrane proteins immunoreactive with anti-S antibody accumulated in the membranes, indicating that sodium dodecyl sulfate-resistant oligomers of S are formed, similar to those observed in the membranes of Escherichia coli cells killed by expression of the S gene. These observations suggest that the S gene product functions as a cytotoxic protein in the yeast cytoplasmic membrane as it does in the bacterial membrane. 相似文献